Dr. N. RAMACHANDRAN, NITC1 2 METAL JOINING Even the simplest object is an assembly of components Complex ones - greater number of parts- subassemblies.

Dr. N. RAMACHANDRAN, NITC 1


METAL JOINING• Even the simplest object is an assembly of

components• Complex ones - greater number of parts-

subassemblies joined to perform the function• METHODS-

WELDING, BRAZING, SOLDERING, ADHESIVE BONDING, MECHANICAL JOINING

NITC


WHY JOINING?

• IMPOSSIBLE TO MAKE AS ONE PIECE• EASINESS AND ECONOMY IN

MANUFACTURE• EASY IN REPAIRS AND MAINTENANCE• FUNCTIONAL PROPERTIES DIFFER- e.g.: Carbide tips of tools,corrosion resistant

parts, tungsten carbide tip of pens, brake shoes to metal backing etc…

• TRANSPORTING SITE/ CUSTOMER

NITC


CLASSIFICATION

• According to the STATE of the materials being joined

• Extent of external heating- PRESSURE• Use of FILLER materials

NITC


Joining Processes

RESISTANCE

MECH. JOINING

ARCCUTTINGCHEMICAL

CONSUMABLE NON CONSUMABLE

Oxy-fuelThermit

LIQUID

SOLID

LIQUID-SOLID

SpotSeam

ProjectionFlashStud

percussion

GTAWPAWEBWLBW

SMAWSAW

GMAWFCAWEGWESW

ForgeCold

UltrasonicFriction

ExplosionDiffusion

BrazingSolderingAdhesive Bonding

FasteningCrimpingSeamingStitching

NITC


History of welding

And

American Welding Society


Vulcan – The Roman Fire God


Welding Heat Exchanger


Dr. N. RAMACHANDRAN, NITC 10• Thermite Welding Patent 729573


• 1800-1850s• Scientists are using the oxy-hydrogen blowpipe as a laboratory tool to

examine refractory metals to the extreme temperature of 4468°F. • 1800• Alessandra Volta discovers that two dissimilar metals connected by a

substance became a conductor when moistened, forming a 'Voltaic Cell'. • 1801 • Sir Humphrey Davy (1778-1829) of London England, experimented and

demonstrated the arc between two carbon electrodes using a battery. This was the forerunner to electric-arc lighting.

• Vanadium was discovered in Mexico and was thought to be a form of chromium for the next three decades. In 1830, it was rediscovered by N.C. Sefstrom, and in 1887, H.E. Rosco isolated the element from its compounds, mainly vanadite and carnotite. It was named for the Scandinavian love goddess Vanadis.

• 1808 • Magnesium is discovered as a chemical element by Sir Humphrey Davy. • Sir Humphrey Davy proved the existence of aluminum.


• 1818 • Robert Hare, a professor of Chemistry at the University of

Pennsylvania invents the hydrogen blowpipe. • 1820• Hans Christian Oersted established connection between electricity

and magnetism. • Andre-Marie Ampere pioneered the field of electromagnetism. • 1823• Charles Macintosh opens a rubber factory in Glasgow Scotland. • 1827 • Friedrich Wholer discovers aluminum in 1827 • 1828• Wallaston produced sponge platinum and welded it together by

cold-pressing, sintering and then hammering while the metal was hot.

• 1831• Michael Faraday invents the Dynamo creating electricity from

magnets


• 1835-1836 • English chemist Edmund Davy (1785-1857), a cousin of Sir Humphrey Davy described the

properties of acetylene, but was unable to give correct formula. • Frenchman Sainte Claire Deville invents the oxygen-hydrogen blowpipe. Used mainly as

laboratory equipment for melting platinum and producing enamel. • 1838• Charles Goodyear discovers the vulcanization of rubber, giving rise to the development of

rubber hoses for welding gases. • Eugene Desbassayrs de Richemont patents a process of fusion welding • 1839 • Michael Faraday discovers the homopolar device that generates voltage. • 1840 • Frenchman E. Desbassayns de Richemont invents the first air-hydrogen blowpipe. • de Richemont coins the phrase "soudure autogène", improperly translated into English as

"autogenous welding". Welding implies solid state whereas fusion welding implies a liquid state.

• 1841 • German H. Rossier used the air-hydrogen blowpipe for soldering lead. • 1846 • James Nasmyth, while investigating the proving of ship chain for the British Admiralty,

discovered and gave the reason for the convex forge welding "scarf". By preparing the surfaces to be welded with a slightly convex surface the flux and swarf are squeezed out of the joint. Otherwise they are trapped in the joint weakening it. This was the first improvement in the forge welding process in 3000 years. Prior to this time the shape of the joint was randomly flat concave or convex.


• 1856 • James Joule, an Englishman, first experimented with a bundle of wire in

charcoal and welded the wires by heating with an electric current. This was the first example of heating by internal resistance to produce a weld. Years later, Elihu Thomson perfected the process into what will then be known as resistance welding.

• 1860s • An Englishman named Wilde successfully used the theories of Volta and Davy

and the primitive electric sources of the time to make "Joins" and received a patent for the earliest form of the art now known as "electric welding".

• 1860 • French chemist Berthelot (1827-1907) accurately gave the correct formula of

C2H2 to acetylene. Also found it to be unstable (1863) under certain pressure and temperature.

• 1862 • A German, Friedrich Wohler (Woehler), produces acetylene gas from calcium

carbide. • 1863• The first successful oil pipeline was built by Samuel Van Sickel at Titusville,

Pennsylvania where 2-1/2 miles of 2 inch diameter cast Pipeline was laid for the transfer of 800 barrels of crude oil. The pipe was screw coupled and hammered since welding was not yet invented for pipe joining. The Dresser coupling, invented in 1891 was the first time a mechanical joint could be assembled without excessive leaking. This method was the standard for pipelining until the mid-1930s, when welding overtook the assembly process.


• 1865• John Motley Morehead, a graduate of North Carolina State

University in 1891, was working as a chemist for Willson Aluminum Company determined that when heating slacked lime mixed with coal tar and immersed in water would produce acetylene gas. Acetylene is formed when bicarburet of H2 and ground carbon produces a solid of calcium carbide when immersed in water. This was originally discovered 56 years earlier by Edmund Davy.

• 1876• Otto Bernz of Newark New Jersey founded the Otto Bernz Company

selling plumber's tools and the gasoline torch "Alway's Reliable". • 1877-1903 • Development of gas welding and cutting, carbon arc and metal arc

welding. • Elihu Thomson invents a low-pressure resistance welding machine

which was accomplished by causing internal resistance enough to reach the plastic stage of a metal. Later, it was referred to as Incandescent Welding.

• 1877• During a lecture at the Franklin Institute (Philia), E. Thomson

reversed the process of (...)


• 1881 • Auguste DeMeritens working at an associated laboratory founded by the periodical

"l'Electricien" - Cabot Laboratory (Cabat), France was using arc heat to join lead plates for storage battery. French Patent Number 146010 was issued.

• 1885 • Nikolai N. Benardos (Bernados) and Stanislav Olszewaski (Olszewaski) secured a

British patent with carbon arc welding. Both men were working under the direction of A. DeMeritens with the arc lighting industry at the Cabot Laboratory (Cabat) in France. Carbon was oxidized at the carbon tip and created CO2 at the arc for shielding. Both men had to generate their electricity using a steam-engine (prime-mover) to turn the generator and produce electricity. The alternative was to use batteries which did not last long because of the short-circuiting involved. Patents applied for and received besides Britain: Belgium, Germany, Sweden, and France.

• 1886 • N. N. Benardos obtained Russian Patent (No. 11982) electric arc welding with carbon

electrode called ""Elecktrogefest" or "Electrohephaestus". The methods of cutting and welding metals by the arc was termed "Electrohefest" in memory(sic) of Hephaestus, the ancient Greek god of Fire and Blacksmith work. (The Romans renamed Hephaestus to Vulcan and which is shown on the title page, giving instruction to the craftsmen forging metal.)

• Benardos receives permission from the Russian Government to organize production in 1885 for "The production of this plant is based on welding and brazing by electricity and also producing devices for electrical illumination" (Note: emphasis mine)

• Electric furnace installed for production of aluminum alloys. An important step in early development of the Aluminum industry.


• 1887 • N.N. Benardos and S. Olszewaski secured an American Patent for

the welding apparatus. (U.S. Patent No. 363320, May 17) • The "blowpipe" or "torch", using the gases acetylene and liquefied

air or oxygen, was developed. • Thomas Fletcher develops blowpipe that could be used with either

hydrogen or coal gas and oxygen • An English shop began making tanks, casks, and iron garden

furniture with the electric arc process. • 1888• Benardos/Olczewski granted patent 12984 for Carbon Arc Welding. • 1889 • Hans Zerner is issued German Patent 53502.3.12.1889 for the Twin

Carbon Arc welding process?. • C. Coffin is issued patent 395878, 'Process of Electric Welding'. • The US Commissioner to the 1889 Paris Universal Exposition upon

seeing the arc welding process demonstrated wrote in a report "...As the metal is burnt and brittle where it is welded, the process is not a success."



• 1890 • C. L. Coffin in Detroit Michigan awarded first U.S. Patent (No. 419032, Jan

1) for metal electrodes. This was the first record of metal melted from an electrode and actually carried across the arc to deposit filler metal in the joint to make the weld. One electrode was carbon and the other electrode was filler material.

• Coffin also described the GTAW beginnings when a weld was made in non-oxidizing atmospheres.

• A bank robber in Great Britain used the newly developed "blowtorch" to gain access to bank vaults.

• 1892 • Canadien Thomas 'Carbide' Willson and American James Turner Moorhead

begin to commercially produce acetylene as a product from calcium carbide in Spray, North Carolina.

• Slavianoff suggests that a bare metallic electrode could be substituted for the carbon electrodes of the Benardos process.

• Concurrently, C. L. Coffin is also credited with introducing the bare metallic electrode in the US

• Baldwin Locomotive Works was using Carbon Arc Welding (CAW) for locomotive maintenance. The weld joints were hard and brittle because of the carbon flaking off into the weld puddle.

• 1886-1898 • Elihu Thompson of the Thompson Welding Co. invented Resistance

Welding (RW).


• 1895 • The combustion of Oxygen and Acetylene was

discovered by Henri LeChatelier in his home country of France. Describes combustion of acetylene with equal volume of oxygen proceeds in two stages:

• Step 1: 4 CO + 2O2 = 4CO2

• Step 2: 2 H2 + O2 = 2H2O• Machine for liquid air generation placed in operation • Lord Reyleigh and Sir William Ramsey discover Argon

(Ar). • Konrad Roentgen (Bavaria) observed the effects of x-

radiation while passing electric current through a vacuum tube.


• 1895-1905 • During a 10 year period in the U.S. and at a rate of one

accident per day, boilers were exploding with the loss of life from the accidents at twice that rate.

• 1900• E. Fouch and F. Picard develops oxyacetylene torch in

France. • 1901 • Menne invented the Oxygen Lance in Germany. • Soon after Charles Picards invention of the oxyacetylene

blowpipe in Paris France, this invention was called upon to repair a cast iron part on an acetylene pump. Quite by accident, the filler metal had enough silicon present to prevent the formation of the excessively hard white iron.

• 1902 • President Teddy Roosevelt took over the Panama Canal

project from the French.


• 1903 • Hans Goldschmidt of Essen, Germany invented Thermit Welding (TW), an exothermic

reaction between aluminum powder and a metal oxide.. Used to weld railroad rails together.

• Oxyacetylene is applied commercially. • 1904 • Concentrated Acetylene Company invents the portable cylinder for the auto

headlights. • 1905 • L. W. Chubb of Westinghouse Electric & Manufacturing, East Pittsburg, PA,

experiments with electrolytic condensers and rectifiers and found that wires could be connected to aluminum plates. Also found that copper could be joined in a like manner. When the cells discharged, sparks were formed.

• 1907 • Two German welders came to the U.S. and formed Siemund-Wienzell Electric

Welding Co. and patented a metal arc welding method. Another German formed company, Enderlein Electric Welding Co. also started up. This was the beginning of the arc welding industry in the U.S.

• Lincoln Electric Company of Cleveland Ohio began by manufacturing electric motors in 1895. By 1907, Lincoln Electric were manufacturing the first variable voltage DC welding machine.

• 1907-1914 • Oscar Kjellberg (pronounced 'Shellberg') of Sweden and the ESAB (Elektriska

Svetsnings-AtkieBolaget) Company invented the covered or coated electrode by dipping bare iron wire in thick mixtures of carbonates and silicates. The purpose of the coating was to protect the molten metal from oxygen and nitrogen. His pioneering of covered electrode development paved the road during the next twenty years in the research of reliable flux coated electrodes.


• 1908 • Oscar Kjellberg received Patent No. 231733 for the coated welding

electrode. • N. N. Benardos develops electroslag welding process. • 1909 • Strohmenger developed the Quasi-arc electrode which was wrapped in

asbestos yarn. • The keel of the H.M.S. TITANIC was laid on March 31 at Harland and

Wolff shipyard. • Schonner, a physicist with BASF (Badischen Anilen und SodaFabrik)

invents the plasma arc system using a gas vortex stabilized arc. • First industrial application of plasma at BASF (Badische Anilin und

Sodafabrik) by a physicist manufacturing nitrogen dioxide (NO2). • 1910• Charles Hyde of Great Britain is issued a patent for brazing steel tubes. By

clamping two pieces into position, copper is placed in the joints as metallic strips, plating or powder mixed in a paste. Heated in a hydrogen furnace (oxygen-free atmosphere) and by capillary attraction flows copper into the joint

• 1911 • H.M.S. TITANIC is launched on May 31. • First attempt to lay 11 miles of pipeline using oxy-acetylene welding near

Philadelphia, Pennsylvania. • American physicist (Matters) developed a plasma arc torch for heating a

metal fusing furnace.


• 1912 • Lincoln Electric Co. introduced the first welding machines after

experimentation started in 1907. • E. G. Budd Spot Welds (SW) the first automobile body in Philadelphia,

Pennsylvania. • Langmuir gives the "plasma" to a gas or gas mixture brought to such a

high temperature that all diatomic molecules are dissociated and the atoms partially ionized and where all monotomic gases are fully ionized.

• Firecracker welding technique, a version of shielded metal arc welding is patented in Germany.

• Strohmenger introduced coated metal electrodes in Great Britain. The electrodes had a thin wash coating of lime or clay resulting in a stable arc.

• Strohmenger obtained US patent covering an electrode coated with a blue asbestos with a binder of Sodium Silicate (NAXX). This was the first electrode which produced weld metal free of impurities.

• 1913 • Avery and Fisher develop the acetylene cylinder in Indianapolis, Indiana. • 1914 • A 34 mile pipeline was laid near Enid, Oklahoma using oxy-aceylene

welding for the oil industry.


• 1915-1916• Underwater cutting was carried out but interest did not come about until 1926. • 1916• Companies licensed resistance welding equipment, mostly spot welding was the

intended use. • 1917 • Because of a gas shortage in England during World War I, the use electric arc

welding to manufacture bombs, mines, and torpedoes became the primary fabrication method.

• 1918 • Admiralty testing of metal-arc welding on Barge Ac 1320 leads Lloyd's Register to

permit metal-arc welding in main structures on an experimental basis. • 1917-1920 • During World War I, a Dutchman, Anthony Fokker, began using welding in the

production of Fuselages in German fighter planes. • HMS Fulagar (Fullagar) was first all welded hull vessel - Great Britain. • The repair of sabotaged German ships in New York Harbor highlighted the first

important use welding because the German merchant marines tried to destroy the ships boilers on 109 ships. A team of engineers from a railroad company (possibly the Rock Island Line) was tasked to the repair. Later, 500,000 troops were delivered to the European War in France using these repaired ships. The success of the weld repairs catapulted welding to the arena for manufacturing and repair and dashed it sordid past as a controversial operation.


• 1919 • President Woodrow Wilson established The United States Wartime Welding

Committee of the Emergency Fleet Corporation under the leadership of Dr. Comfort Avery Adams.

• Dr. Comfort Avery Adams, held a meeting on January 3rd to form the "American Welding Society ". The Constitution of this meeting was approved on March 27.

• C. J. Holslag used Alternating Current (AC) for welding, but this was not popular until 1930.

• The AWS Constitution of the January meeting was approved on March 27. • Reuben Smith developed and patented the paper-coated electrode. The weld did not

leave a slag and produced an acceptable weld. • 1920s • Various welding electrodes were developed:

– Mild steels electrodes for welding steels of less than 0.20% carbon; – Higher carbon and alloy electrodes; and – Copper alloy rods.

• Researchers found that Oxygen (O2) and Nitrogen (N2) when in contact with molten metal caused brittle and porous welds.

• Alexandre and Langmuir, from General Electric Co., used Hydrogen in chambers to weld. Began with two carbon electrodes and later switched to Tungsten.

• Bundy-Weld of Bundy Company, Detroit Michigan uses sheetmetal coated with a copper paste and is rolled tightly around itself and placed in a furnace. The brazed joint is formed into one piece tubing.

• The automotive industry began using Automatic Welding with a bare wire fed to the workpiece to the production of differential housings.

• Poughkeepsie Socony (1235 tons), the first all-welded tanker was launched in the USA.


• 1920 • P.O. Nobel of General Electric Company developed automatic welding,

using Direct Current (DC) using the arc voltage to regulate feed rate. Primary use was to repair worn motor shafts and crane wheels.

• The British ship "Fulagar" was constructed by the Cammell-Lairds and launched. In 1924, the ship grounded. A report in the British "Journal of Commerce" (July 17, 1924) reported that she held steadfast and if rivets were used in the construction, the ship would surely have opened up and not be able to get off the bank.

• After WW I, the Treaty of Versailles limited the Germans from designing and building ships in excess of 10, 000 tons for armored ships and cruisers not to exceed 6,000 tons. Welding was an experimental production option before WW I but the Germans used it to develop the next stage of warships by saving weight whereby the ship could then carry more armament or armor plating in selected areas.

• Torch brazing is in full swing using silver and gold filler metals and mineral fluxes as protective cover.

• Electrification of Russia begins utilizing hydroelectric power sources. • 1921• Leslie Hancock pioneered flame cutting machine where the burner followed

the path of a magnetized stylus tracking around the contour of a metal template. The stylus is propelled by a gramophone motor.


• 1922 • "No longer in the tones of a Walt Whitmanesque muscular America, the

skyscraper celebrated the technology that was bringing the world together." • The first issue of the "Proceedings of the American Welding Society" was

published in January (Vol. 1, No. 1). The name was changed in February, the next month, to "Journal of American Welding Society ".

• The Prairie Pipeline Company weld an 8 inch diameter pipeline 140 miles long to carry crude oil from Mexico to Jacksboro, Texas. The advantage of welding over fittings saved the project 35 percent and the cost of weld, labor and material was $2.00 per welded joint.

• 1923 • Institute of Welding Engineers was formed and headquartered in New York

City. • Naval Research Laboratory (NRL) was formed by the US Government

which was motivated by Thomas Edison's belief that history demonstrates a relationship between technological innovation and national security.

• 1924 • 1st all-welded steel buildings constructed in U.S. by General Boiler Co. "to

the exclusion of rivets". • Resistance, gas and metallic arc welding in the manufacturing of all steel

automobile bodies at the E.G. Budd Manufacturing Company. • Mechanical flash welder used for joining rails together. • First recognition of welding design was presented in papers written by: J. C.

Lincoln, S. W. Miller, C. J. Holslag, H. A. Woofter, and J. H. Deppler.


• 1925 • ASME Boiler Code Construction Code Section VIII is issued for unfired pressure

vessels. • AWS Board of Directors approves "Standardization of Hose Connections for Welding,

and Cutting Torches and Regulators" • AWS held First Welding Show with the National Fall Meeting, 21-23 October, in Boston. • A.O. Smith fabricates a single-piece heavy walled pressure vessel entirely by welding

and was PUBLICLY tested then placed in an oil cracking service. • 1926 • H.M. Hobart and P.K. Devers used atmospheres of Helium and Argon for welding with a

bare rod inside the atmosphere. Due to the impurities of the inert gases and the corresponding high cost along with a lack of knowledge about current density, commercial applications were not realized at this time.

• UNA-METHOD - Trade name for the rail joint welding process, arc welding apparatus, electrodes and supplies. UNA Welding & Bonding Co. Cleveland Ohio.

• FUSARC - (need info)...? • Irving Langmuir, a noted chemist with General Electric Co. developed the Atomic

Hydrogen Welding (AHW) Process. Co-authored with R. A. Weinman the paper was "Atomic Hydrogen Arc Welding"

• Naval Research Laboratory (NRL) employee, P. W. Swain authored a paper "X-ray tests of weld " which was to have an impact with the welding industry much longer than the introduction of Atomic Hydrogen Arc Welding. The technique used a gamma-ray radiation as a shadow method to detect flaws in cast or welded steels. The techniques was used to detect flaws on the US Navy 9000 tonne heavy cruisers. The process was later identified as a Nondestructive test method and contributed to the success of developing improved steel castings for the U.S. Navy.

• Landstroth and Wunder of A. O. Smith Co. solid extruded heavy coatings for metal-arc welding electrodes.


• 1927 • Lindberg's Ryan monoplane fuselage was manufactured with welded steel

alloy tubing. • Soviet Union production of Resistance Welding machines at Elektrik Works

called the "AT-8" and the "ATN-8: apparatus's for spot-welding and the "AS-1" and the "AS-25-1" for buttwelding.

• John J. Chyle of A. O. Smith Corp. invented and patented the first extruded, all-position, cellulosic, titanium dioxide later classified as E6010 type welding electrode.

• 1928 • In East Pittsburgh, Pennsylvania, on the Turtle Creek, America's First All-

Welded Railroad Bridge was erected by Westinghouse Electric and Manufacturing Company. Westinghouse used the bridge to transport the large generators from facilities to the rest of the country by way of the railways. Weighing in at 20,000 pounds and at 62 foot long, the bridge was manufactured without the use of rivets, a common method of bridge construction of those days. The testing of the bridge was completed by driving a locomotive on the bridge. (Information Courtesy of Mr. LaFave)

• Code for Fusion Welding and Gas Cutting in Building Construction (predecessor of AWS D1.1) was issued by the American Welding Society.


• 1929 • Lincoln Electric Co. started production of heavy coated electrodes

(Fleetweld 5) and sold the electrodes to the public. Sues A.O. Smith and wins.

• 1st European All-Welded bridge in Lowicza, Poland. Designed in 1927 by Professor Stefana Bryly and spanning the Sludwie River this bridge was still in use as late as 1977, whereby it was being replaced with a newer highway and bridge which is designed for wider traffic. The Polish Government planned to move the bridge 80 meters up stream and establish the bridge as a historical monument. In 1995, AWS President ED Bohnart presented to the Government of Poland, the AWS Historic Welded Structure Award.

• Welding symbols are established by the American Welding Society

• General Electric experiments with "Controlled-Atmosphere brazing", using hydrogen gas for copper to steel brazes.

• Welding conferences are held on the campuses of Lehigh and Syracuse


• 1930-1940s • Atomic hydrogen arc welding process developed. Found that hydrogen

was liberated releasing heat, which was 1/2 of the BTU of acetylene. Used primarily for tools steels. Development included an automatic version of the process.

• 1930 • Specifications for welding electrodes were beginning to be written. • H. M. Hobart issued Patent Number 1746081, for "Arc Welding" and P. K.

Devers was issued Patent Number 1746191 for "Arc Welding" on Feb 4 for using a concentric nozzle with a wire feed. This became known later as Gas Metal Arc Welding (GMAW). Work was based on various atmospheres in 1926.

• Germany started development work to find a suitable substitute for their dwindling supply of critical alloys. Experiments in the U.S. and Germany found that Thermoplastics when heated could be pressed together and obtain a permanent bond. In 1938 this principle was incorporated into "Hot Gas" welding technique. Thermoplastic rod and sheet were heated simultaneously by a stream of hot air while the rod was pressed into the sheet causing a bond. World War II forced Germany to further develop and use welded Thermoplastic as a corrosion resistant structural material.


• 1930 continued….• Stud Welding (SW) was developed by the New

York Navy Yard to fasten wood to steel. • Submerged arc welding developed by National

Tube Co. in McKeesport, PA by Robinoff. Later sold rights to Linde Air Products and renamed UNION-MELT. Used in late 30s and early 40s in shipyards and ordnance factories.

• 1st all-welded merchant ship was built in Charleston, South Carolina.

• Advancements in protective atmospheres that dissociate chromium oxide from the surface of stainless steel are performed in furnaces without the mineral flux and were found in laboratories with no commercial equivalence


• 1931 • E. G. Budd Manufacturing Company of Philadelphia spot welded stainless steel

(18-8) and built the Privateer. The spot-welding was a process called "shotwelding" a proprietary process developed by E.G. Budd.

• Combustion Engineering shipped the first commercial land boiler fabricated by ASME welding code to Fisher Body Div. of General Motors Corporation.

• 1932 • Submerged Arc Welding (SAW) developed by National Tube Co. in McKeesport,

PA by Robinoff. Later sold rights to Linde Air Products and renamed UNION-MELT. Used in late 30s and early 40s in shipyards and ordnance factories.

• British Corporation Register and Lloyd's introduce revised rules and approvals for the use of welding on ships.

• 1933 • Lincoln Electric Co. published 1st edition of "Procedure Handbook of Arc Welding

Design and Fabrication" with the purpose to have its customers use arc welding efficiently. As a full service company, this book provided the customers a knowledge of welding education and training.

• English Antiquarian, H. A. P. Littledale patents the "Littledale Process (British Patent No. 415,181)", following the same approach that Pliny and Theophilus wrote about from the past two millenniums. Mixing copper salts with seccotine glue ultimately would produce the following reaction {CuO+C -> Cu + CO} which is where brazing would theoretically be reached. The temperature the reaction takes place: 850C.


• 1934 • 1st All-welded Excavator - HARNISCHFAGER Corp. • 1st All-welded British bridge - Middlesborough, England • Lloyd's Rules for pressure vessels permits inspection

using X-Ray technology. In Scotland, welding was beginning to be recognized as a separate crafts trade and the Trade Unions were opposed to this recognition. The General Secretary of the Boilermaker's Union argued that it was unfair to condemn any young man to a lifetime of welding. (Scotland). The Shipbuilding Employers insisted on the separate recognition.

• Westinghouse introduces the "Ignitron" which would become the basis for resistance welding timing controllers.

• American Welding Society presents John C. Lincoln the Samuel Wylie Miller Medal for "Meritorious Achievement". The award cited him for his work on the variable voltage machine, the ductility and strength of welds, the carbon arc automation process, and his efforts to expand the use of welding in many industries.


• 1935 • Granulated flux developed in 1932 and a continuous bare wire feed became

known as "Submerged Arc Welding (SAW)" and saw major applications in shipbuilding and pipe fabrication (see 1932 for a different account).

• Solid extruded electrodes are introduce in Britain and subsequently the first British welding electrode standard written.

• Welding has "Arrived" when London, England hosts 900 attendees at the "Great Symposium" on the "Welding of Iron and Steel"

• Solar Aircraft Company of San Diego California develops a flux to combat welding problems with stainless steel manifolds for the U.S. Navy and was regarded as a closely-guarded military secret. Where flux is applied to the front of the weld, this was placed on the backside of weld, protecting from oxide formation. Later, the product was developed further to accommodate the Heliarc process.

• 1936 • 1st All-welded Box Girder Crane by HARNISCHFAGER Corp., Milwaukee WI. • 1st All-welded Gear were fabricated by HARNISCHFAGER Corp. Milwaukee WI. • First Specification for Design, Construction, Alteration and Repair of Highway

and Railway Bridges by Fusion Welding was issued by the American Welding Society.

• Tentative Rules for the Qualification of Welding Processes and Testing of Welding Operators was submitted by AWS.

• The Soviet Union at the Electrik Works started using the electronic control gears as the first valve timer with a thyristor contactor (RVE-1) for resistance welding.

• Japan Welding Society stipulates the rules of qualification testing in "The Standard of Qualification for Arc Welding Operator".


• 1937 • BS 538: Metal arc welding in mild steel, was issued, legitimizing arc

welding structural applications. • Norman Cole and Walter Edmonds, metallurgists from California are

granted a patent for their product named "Colmonoy". Derived from COLe and edMONds and allOY.

• 1938 • The Welding Handbook, First Edition was printed and edited by

William Sparagen and D. S. Jacobus. • Pressure vessel industry began implementing the high production

value of Automatic Welding. • The German Shipbuilding Industry uses welding extensively to

reduce the weight of warships and increase the overall size of the ship. This restriction was put in place after World War I.

• K. K. Madsen of Denmark describes Gravity Welding as a specialized electrode holder and the mechanism which will maintain a covered electrode in contact with the workpiece.

• A.F. Wall purchases Colmonoy and renames to Wall-Colmonoy (Detroit).


• 1939 • Floyd C. Kelly of General Electric publishes "Properties of Brazed 12% Chrome Steel" as an

early investigation of the strength of brazed joints.4Aluminum Spot Welding saw application in the Aviation Industry. He describes:

– Single lap tensile specimens – 45 degree vee-type tensile specimen – Butt brazed tensile specimens.

• Aluminum Spot Welding saw application in the Aviation Industry. • Ultrasonic Fluxless soldering patented in Germany. Process is conceived in 1936. • Air Arc Gouging is developed (USA). • Stud Welding (Nelson Stud Welding Co.) used by the US Navy to reduce time installing studs

during fabrication of ships and aircraft carriers. • 1940s • With World War II GTAW was found to be useful for welding magnesium in fighter planes, and

later found it could weld stainless steel and aluminum. • Canadian Welding Society (CWS) formed. • Exchequer, first all-welded ship built at Ingalls Shipyard in Mississippi. • J. Dearden and H. O'Neill (UK) discuss "Weldability" in terms of carbon equivalencies. • Sun Shipbuilding Company builds the world's largest ocean-going tanker, I. Van Dyck (11650

DWT). This was the first large scale use of automatic welding applied in shipyard work. • First mass soldering technique, Dip Soldering, is used for Printed Wiring Boards (PWB) to

keep up with the development of electronic equipment such as, Television, radios, etc. • Little advancement was made in brazing and there were no dry-hydrogen facilities, except for

laboratories, for brazing Stainless steel and there were no vacuum furnaces. • Germany was using 85Ag-15Mn brazing alloys as the best high temperature filler metal

available. Used for brazing hollow sheet metal blades used in the turbine engines and stators.


• 1940• Gas shielded metal arc welding developed by Hobart

and Devers at Battelle Memorial Institute. • 1941 • Engineers at Northrup Aircraft Co. and Dow Chemical

Co. developed the GMAW process for welding magnesium, and later licensed it to Linde Co. with a water cooled, small diameter electrode wires using CV power. Because of the high cost of inert gas, the cost savings were not recognized until much later.

• PLUTO - PipeLine Under The Ocean was created using the Flash Weld (FW) process for 1000 miles of 3 inch diameter pipe, to assist in the invasion of Normandy Beach, France. Once in place, the pipeline began pumping 1 million gallons of petrol per day directly to depots deep in the French country side.

• Friction Surfacing. H. Klopstock and A. R. Neelands "An Improved Method of Joining and Welding Metals" British Patent 572789, October 1941.


• 1942 • Chief of Research, V. H. Pavlecka, and engineer Russ Meredith of Northrup Aircraft Inc.

designed the Gas Tungsten Arc Welding (GTAW) process to weld magnesium and stainless steel. Alternate names are TIG (tungsten inert gas) and Argonarc and Heliarc. Heliarc is the term originally applied to the GTAW process. (Patent Number 2274631, 24 February 1942).

• The invention of GTAW was probably the most significant welding process developed specifically for the aircraft industry and remained so until recently, with the Friction Sir Weld process of the 1990's. Mr. Northrup of Northrup Aircraft Inc. was a visionary who wanted an all-welded aircraft (i.e., manufacturing costs, and lightweightness of the aircraft). Meredith was working from research of Devers and Hobart at General Electric (1920s) who had experimented with tungsten arcs in non-oxidizing atmospheres. The high reactivity of magnesium (Northrup's dream metal) would cause problems with more conventional processes, so, Meredith to began developing a torch with better handling characteristics and would use inert gas enshrouding tungsten. Thus, the Heli-arc process.

• From the Dec 1942 Welding Journal: "The full importance of arc welding on the future of magnesium alloys cannot be fully appreciated at this time but the fabrication of these strong light alloys has opened the possibilities that were not considered even a year ago. For the man in industry, this method of joining offers simplicity of structure, ease and speed of fabrication and over-all economy."

• US Patent 2269369, Jan 6, 1942 issued to George Hafergut for Firecracker Welding. • Traveling 285 miles north of Edmonton Canada and barging 1100 miles north to the

Norman Well refinery a base camp was setup to build the Canadian Oil (CANOL) project. Working for 20 months, 1800 miles of pipeline was laid along side of 2000 miles of road. The last weld was laid on 1 February 1944. On 1 April 1945 the wells were shut down.

• Second Edition of the Welding Handbook was printed and issued. • SAW proves it worthiness during World War II with the building of the Liberty Ships. • G.L. Hopkins of Woolrich Arsenal defines the problem of cracking in alloy steels and

hydrogen in welding electrodes.


• 1943 • Union-Melt is now commonly referred to as Submerged Arc Welding

(SAW). The process used rods rather than wire filler metal and could weld work pieces up to 2 -1/2 inches thick.

• Sciaky (USA) markets the three-phase resistance welder. • 1944 • 1st Low-hydrogen electrodes used in fabrication of alloy armor tanks

vehicles by the Heil Corp in response to the chrome and nickel shortages from World War II for the U.S. Army.

• The Bureau of Navy Aeronautics designed and E. G. Budd Mfg. built the "Conestoga", a stainless steel aircraft. Despite the success of the aircraft, aluminum and rivets became the influencing factor in aircraft design.

• 1945• After World War II, the Allies brought from Germany the alloy

combination, 85Ag-15Mn which has a 1760°F brazing temperature. • ElectoBrazing is used for manufacturing shafts to gears.


• 1946 • Sprayweld Process (US Patent 2361962) issued to Wall-Colmonoy uses

an alloy powder spray which produces a smooth, welded deposits. • General Electric Co. Ltd (UK) invents the Cold Pressure Welding

Process. • High Frequency (HF) stabilized AC tungsten-arc welding is used for

aluminum alloys. • 1947 • The Final Report of a Board of Investigation, ordered by the Secretary of

the Navy, "To Inquire Into The Design and Methods of Construction of Welded Steel Merchant Vessels, 15 July 1946" was issued.

• Canadian Welding Bureau was created as a division of the Canadian Standards Association

• The Austrian Welding Society is formed and publishes a monthly magazine "Scheisstechnik"

• Nicrobraz, developed by Robert Peaslee of Wall-Colmonoy, is a 2500°F nickel alloy braze filler metal used in hydrogen furnaces. Used for stainless steel fuel supply connecting injectors to injector pumps for 18 cylinder reciprocating engines. The fledgling aircraft engine industry needed something else for engines to experience a hot shutdown without blowing the silver braze filler metal out from the brazed joints. Typical alloy was 85Ag-15Mn (BAg-23).


• 1948 The Ohio State University Board of Trustees established the

Department of Welding Engineering on January 1 as the first of its kind for a Welding Engineering cirriculum at a University. OSU pioneered the Welding Engineering through an emphasis in the Industrial Engineering Department the previous nine years. The advantages of this engineering degree is 1) Enable satisfactory administration of problems relating to education and research in the welding field. 2) Recognition is given to the Welding Engineer as an entity among applied sciences. 3) A degree is authorized which is descriptive of a particular discipline imposed in training for professional work in the field.

Air Reduction Company develops the Inert-Gas Metal-Arc (MIG) process.


SIGMA Welding (Shielded Inert Gas Metal Arc) was developed to weld plate greater than1/8 inch instead of the "Heli-Arc" welding process. The arc is maintained in a shield of argon gas between the filler metal electrode and the workpiece. No flux is used. Licensed by Linde Air Products Co.

•1948-1949

Curtiss-Wright Corporation looks at brazing as a strong, lightweight process for durable assemblies.

•1949

American Westinghouse introduces and markets welding machines using Selenium Rectifiers.

US Navy uses inert-gas metal arc welding for aluminum hulls of 100 feet in length.

•1950

The Kurpflaz Bridge in Germany was built as the first welded orthotropic deck.


•1950s

Electron Beam (EB) welding process developed in France by J. A. Stohr of the French Atomic Energy Commission. First Public disclosure was 1957.

Wave soldering is introduced to keep up with the demand of Printed Wiring Boards used in the electronics age.

Research on testing of brazed joint begins as serious endeavor for the next ten years.

•1950

Electroslag Welding (ESW) is developed at the E. O. Paton Welding Institute, Ukraine USSR.

Third Edition of the Welding Handbook is printed by AWS.

Flash Butt Welding is the standard for welding rail line construction.


•1951

Russia use Electroslag Welding (ESW) process in production.

The Philip Roden Co. of Milwaukee Wisconsin announces the DryRod electrode oven. This oven is intended to provide a controlled moisture environment of 0.2% moisture standard set forth by the government. This oven provides adjustable temperature control of 200-550 F, vented and holding 350 pounds of electrodes.

•1953

Modifying the Gas Metal Arc Welding (GMAW) process, Lyubavskii and Novoshilov used CO2 with consumable electrodes. Resulted in hotter arc, uses higher current, and larger diameter electrodes.

The Ohio State University established a Welding Engineering College curriculum out of the Industrial Engineering Department.

•

http://www.weldinghistory.org/htmlhistory/link_osu_we.html


•1957 Flux Cored-Arc Welding (FCAW) patented and reintroduced by National Cylinder Gas Co. Plasma Arc Welding (PAW) Process developed by Robert M. Gage Russia, Britain, and USA independently develop a short-circuiting transfer for low-current low-voltage welding in a carbon dioxide atmosphere. Braze repair process for cracks in jet engine combustion chambers and transition ducts. 1958 The Soviet Union introduced the Electroslag Welding (ESW) Process at the Brussels World Fair in Belgium. This welding process had been used since 1951 in the USSR which was based on the concept and work of an American, R. K. Hopkins. Perfected at the Paton Institute Laboratory in Kiev, Ukraine, USSR and the Welding Research Laboratory in Braitislava, Czechoslovakia. AWS Committee on Brazing and Soldering is formed to develop a test for evaluating strength of brazed joints. Robert Peaslee proposes a test in the Welding Journal.


• 1959

Electroslag welding process was first used at the Electromotive Division of General Motors in Chicago and was called the "Electro-Molding Process".

Development of Inside-Outside Electrode which did not require an external gas shielding - Innershield from Lincoln Electric Co.

• 1958-1959

Short Arc (Micro-wire Short Arc) developed from refined power supplies and smaller diameter wires.

• 1960s

Pulsed Arc Welding...(more to follow)

Space Program is underway...(more to follow)

Difficult to stabilize GTAW at below 15 amps, Microplasma is developed to overcome the limitation.


1960 Development of a cold wall vacuum furnace. First laser beam produced using a ruby crystal for the Light Amplification Stimulated Emission Radiation (LASER). Explosive welding is developed in USA. Hughes Aircraft Company (Mainar) develops the first ruby laser (springtime). Bell Telephone Laboratories (Ali Javan) developed and presented the first gas laser using neon and helium (fall time) 1962 The Mercury Space Capsule is formed using inner and outer titanium shell, seam welded together using a three-phase resistance welder by Sciaky. 1963 U.S.S. Thresher sinks off the coast of New Hampshire and by December, the U.S. Navy charters the Submarine Safety Program (SUBSAFE) to control the fabrication, inspection and quality control of submarine construction. The presumed failure was with a silver-brazed piping joint, but after the investigation, the whole welding and brazing program was suspect. Included was the material properties of the welding and brazing filler metals.


• 1965-1967

CO2 lasers are developed for cutting and welding.

• 1967

H. J. Clarke makes the following Predictions during the AWS Plummer Lecture in Houston as he ties the current state of technology of welding to the future of progress:

World's Population would be greater than 5 Billion.

Large scale farming of the ocean and fabrication of synthetic protein.

Controlled thermonuclear power as a source of energy.

General immunization against bacteria and virile infections, perfected and available.

Primitive forms of life will created in the lab.

Automation will have advance for performance of menial chores and complicated functions.

Housewives would be ordering groceries and everyday items from central stores linked to the home electronically. (!!!)


• Children will be receiving education at home - "either by television or with personal teaching machines and programmed instructions"

Moon - mining and manufacture of propellant and on Mars, permanent unmanned research stations.

Weather manipulation by the military.

Effective anti-ballistic missile defense in the form of air-launched missiles and directed energy beams.

Libraries will be "computer-run"

Gravity welding is introduced in Britain after its initial discovery by Japan.

• 1969

The Russian Welding Program in Space began by producing Electron Beam welds on SOYUZ-6. Welding an AMG6 and DM-20 aluminum alloys with the Vulkan process. Sponsored by the E. O. Paton Welding Institute Academy of Science.


• 1970

As miniaturization developed from the pressure to increase component densities, Surface Mount Technology is developed. This required new ways to make soldered joints, including the development of vapor phase, infrared, hot gas and other re-flow technologies.

First AWS International Brazing Conference including 24 papers presented created much interest in the brazing process.

BP discovers oil off the coast of Scotland.

• 1971

British Welding Institute (Houldcroft) adds oxidizing gas jet around laser beam to develop laser cutting.


• 1973

The American Astronauts used Electron Beam welding process in June 1973 welding Aluminum Alloy 2219-T87, Stainless 304 and Pure Tantalum.

Welding equipment manufacturers concentrate on equipment refinement instead of new processes.

Two Supertankers, Globtik Tokyo and Globtik London (476025 DWT) were built for carrying 153 million gallons (3 million barrels) of crude oil


• 1976

First automotive production application of lasers weld begins with General Motors Corporation, Dayton Ohio using two 1.25 kW CO2 lasers. for welding valve assemblies for emission control systems.

• 1977

The US Federal Highway Administration issues a moratorium of Electroslag Welding (ESW) when cracks are discovered during an inspection of a bridge in Pittsburgh, Pennsylvania on an interstate highway. Failure analysis was conducted by Lehigh University on Interstate 79.

• 1980

The Fort McHenry tunnel contract, for 750 Million Dollars, is awarded to begin construction, completing Intestate 95 through Baltimore, Maryland. This is the largest tunnel of its kind, 180 feet at the bottom with two separate four lane immersed tunnels removing 3.5 million cubic yards of dredge.


• 1983

Homopolar pulse welding variation of the upset welding process research begins at the University of Texas at Austin at the Center for Electromechanics.

• 1987

Laser research begins a unique method for depositing complex metal alloys (Laser Powder Fusion).

• 1991

TWI of Cambridge England develops the Friction Stir Weld (FSW) process in its laboratory. This process differs from conventional rotary technology whereby a hard, non consumable, cylindrical tool causes friction, plasticizing two metals into a Solid-State Bond. No shielding gas or filler metal is required. Metals joined successfully include, the 2XXX, 6XXX and 7XXX series aluminum. NASA is the first US venture which welded the massive fuel tank for the Space Shuttle.

Brazing Handbook (Fourth Edition) shows the data of the filler metal/base metal failure transitions between 1T and 2T overlap and is the key for the design data (factor of safety).


1996 Over 7,00,000 brazements are produced for the aircraft industry in the US and Canada. Over 132,010,00 units of brazed automotive parts are produce. 1999 The Edison Welding Institute develops a solution to obtaining deeper penetration of a GTA weld by introducing FLUX onto the surface of the weld. This FLUX helps drive the welding arc heat deeper into the weld joint and permits 300 percent more penetration. 2000 Magnetic Pulse Welding (MPW) is introduced by Pulsar Ltd. of Israel using capacitive power as a solid state welding process. Discharging 2 Million amps in less than 100 microseconds this process can create a metallurgical, a non-metallurgical or a mechanical lock, depending on the substrate involved. No heat affected zone (HAZ) is created since only a rise of 30oC occurs. Tailored welded blanks of aluminum are used where spot welding was once performed.


2000Researchers from Argonne National Laboratory use the energy of the x-ray to weld metal-matrix composite (Ti or Al / Al2O3 or SiC) materials. Diode laser welding, once limited to compact disks, laser printers, and laser pointers, are now making their way to the manufacturing floor. Welding Type 304 Stainless steel (0.024 inch), Titanium foil (0.005 inch thick) and laser brazing with a silicon-bronze brazing wire. Conductive heat resistance seam welding (CHRSEW) is developed. The process uses steel cover sheets placed on top of aluminum butted together. Using conventional seam welding, the heat generated from the steel forms a molten interface on the aluminum and fusion is made at the butt joint. The steel covers are then removed.


• 2001 AWS D17.1, "Specification for Fusion Welding for Aerospace Applications" is published in March. The efforts of approximately 50 individuals from a cross-section of the Aviation Industry and government produces the first commercial aviation welding specification. Flame brazing 5XXX aluminum alloys using non-corrosive flux. Sulzar Elbar introduces laser powder welding technology. Permits rebuilding of substrate material (High Creep Resistance) and reproduction of the single crystal structure.

• 2002 From Linde Gas in Germany, a Diode laser using process gases and "active-gas components" is investigated to enhance the "key-holing" effects for laser welding. The process gas, Argon-CO2, increases the welding speed and in the case of a diode laser, will support the transition of heat conductivity welding to a deep welding, i.e., 'key-holing'. Adding active gas changes the direction of the metal flow within a weld pool and produces narrower, high-quality weld. CO2 Lasers are used to weld polymers. The Edison Welding Institute is using through-transmission lasers in the 230-980 nm range to readily form welded joints. Using silicon carbides embedded in the surfaces of the polymer, the laser is capable of melting the material leaving a near invisible joint line. 2003 2004 2005 Future developments.


ABOUT AWS The American Welding Society (AWS) was founded in 1919 as a multifaceted, nonprofit organization with a goal to advance the

science, technology and application of welding and related joining disciplines

• The Engineering Societies Building (left) in New York City was the home of AWS until 1961 when the Society moved to the United Engineering Center, also in New York City.


From factory floor to high-rise construction, from military weaponry to home products, AWS continues to lead the way in supporting welding education and technology development to ensure a strong, competitive and exciting way of life for all Americans.

• The Society moved its headquarters to Miami in 1971 (left).


• The American Welding Society, in conjunction with the Department of Energy, has put together a vision that will carry the welding industry through 2020.


• Technical Publications

• AWS offers over 300 books, charts, videos, replicas, proceedings, and software. 160 AWS-developed codes, recommended practices, and guides are produced under strict American National Standards Institute (ANSI) procedures, including one of the most consulted codes in the world, D1.1 Structural Welding Code - Steel.


Foundation

• Founded in 1989, to support research and education in welding and related technologies. It is committed to annually awarding fellowships to deserving graduate students for important research in areas important to the requirements of industry. Accordingly, each year the AWS Foundation administers six $20,000 grants - matched in kind by the participating universities. The award of scholarships to vocational and undergraduate college students is also a high priority and a student loan program has also been developed to prepare students for welding related careers.

http://www.aws.org/foundation/


• The Professional Program

The AWS Professional Program offers a broad spectrum of Technical Papers describing the latest findings in welding research, processes and applications. Special sessions and gatherings exploring the boundaries of industry issues are also significant features of the convention. Subjects cover an entire range of industry concerns from the joining of space age materials to production management techniques, testing, quality assurance and more.


Which welding process(es) will see an increase in use and which will see a decrease in use during the next decade?

• There was much speculation, but almost unanimously the process chosen for decline was shielded metal arc welding (SMAW). A very few speculated a decline in the use of gas metal arc (GMAW) and gas tungsten arc welding (GTAW). A significant group felt the continuous wire processes (FCAW, GMAW) would experience the most use. The GTAW process was the next most mentioned. One of the reasons stated for its increase was "the need for high-quality work on thin materials."


Welding Forges into the Future

Where do you see the use of welding automation heading in your industry?


• In what areas of welding do we need more knowledge? • Safety and Health. The industry needs more knowledge and

awareness regarding the hazards of welding, according to the respondents.

Welding of the newer grades of high-strength steels, high- alloy steels and heat treatable steels.

• We need to "keep up the 'how to weld' information with the increase in 'new' alloys, which are becoming more difficult to weld."

Automation. A variety of topics relating to automation. These included training in computerization and automation; information on short-run automation; and the need to create standard platforms for welding equipment, robot controllers, sensing devices and other automation peripherals.

The basics While universities and institutions are doing basic research, they cannot tell you the best process and fastest speed for a 1Ž4-in. fillet weld."


• What are the strengths of the welding industry? What are its weaknesses?

• What business improvements during the next ten years would be in your company's best interests?

• What has to be done in the future to keep the welding industry healthy?

More than 50% of the respondents believe improving the image of welding so top students

will be drawn to the industry and bettering training methods for welders and welding engineers are the

keys to welding's future.


• Are you optimistic or pessimistic about the future of your particular industry?

92% of respondents indicated they are at least optimistic about the future.

One respondent summed up his reasons this way:

Metallics will be around for a long time and they will need to be joined.


• Since time machines still exist only in the stories of H. G. Wells and other works of science fiction, no one can tell us exactly how welding will fare in the 21st century. However, the people who responded to the Welding Journal survey represent a cross section of fabricators of welded products and producers of welding equipment and related products. Together they offer a wide range of experience and knowledge. Answering the questions separately, in their respective cities, they still formed a consensus. They agree the future looks promising for welding. It remains and will continue to be a productive, cost-effective manufacturing method. However, steps must be taken to bring more skilled personnel into the industry, or changes must be made to accommodate for the lack of skilled personnel (e.g., welding automation). They also indicated the welding industry must embrace all of the modern-day technological tools to keep pace with the rest of the world. .


LIQUID STATE PROCESSES

• Partial melting and fusion of joint• Physical and mechanical changes taking place• Can be with application of pressure or by addition

of filler material

• Prior to joining, PREPARATION TO BE DONE

STANDARDS- AWS; ASTM-

TYPES OF GROOVES, JOINTS

NITC


Types of welds and symbols

• FILLET, SQUARE BUTT, SINGLE V, • DOUBLE V, SINGLE U, DOUBLE U, • SINGLE BEVEL BUTT, DOUBLE BEVEL BUTT, • SINGLE J BUTT, DOUBLE J BUTT, • STUD, BEAD(EDGE OR SEAL), PLUG, • SPOT, SEAM, MASHED SEAM, • STITCH, PROJECTION, • FLASH, UPSET etc. (REFER sketches supplied)

NITC


Standard location of elements of weld symbol

L PS

Specification process.

No tail- SMAW

Other side of arrow

Near side of Arrow

Field weld

Weld all around

Size

Length of weldUnwelded length

G- Grind C- Chip

F-File M-Machine

R- Rolling

Reference line

Finish symbol

Arrow connecting reference line to arrow side of joint /to edge prepared /member or both

NITC


ROOT

GROOVE ANGLE

Joint angle

Root Face

Groove face

NITC


WELD POSITIONS WELD MOVEMENTS

• FLAT

• HORIZONTAL

• VERTICAL

• OVERHEAD

• H

• O

• C

• J

• U

• ZIGZAG

NITC

Slide 2 of 18

WELDING TERMINOLOGY


WELDING TECHNIQUES

FOREHAND BACKHAND

THIN

Same direction torch

Heat concentrated away from bead

Even flow, rippled design

THICK

Opposite direction torch

Heat concentrated on bead

Broad bead


WELD POSITIONS

• FLAT HORIZONTAL VERTICAL OVERHEAD

NITC


WELD MOVEMENTS

O ZIGZAGL

I STRAIGHT

Z


ASME P Material Numbers Explained

ASME has adopted their own designation for welding processes, which are very different from the ISO definitions adopted by EN24063.

DesignationDescription

OFW Oxyfuel Gas Welding

SMAW Shielded Metal Arc Welding (MMA)

SAW Submerged Arc Welding

GMAW Gas Metal Arc Welding (MIG/MAG)

FCAW Flux Cored Wire

GTAW Gas Tungsten Arc Welding (TIG)

PAW Plasma Arc Welding

Straight polarity = Electrode -ve Reverse polarity = Electrode +ve

http://www.gowelding.com/wp/pnumbers.htm


F Number General Description

1 Heavy rutile coated iron powder electrodes :- A5.1 : E7024

2 Most Rutile consumables such as :- A5.1 : E6013

3 Cellulosic electrodes such as :- A5.1 : E6011

4 Basic coated electrodes such as : A5.1 : E7016 and E7018

5 High alloy austenitic stainless steel and duplex :- A5.4 : E316L-16

6 Any steel solid or cored wire (with flux or metal)

2X Aluminium and its alloys

3X Copper and its alloys

4X Nickel alloys

5X Titanium

6X Zirconium

7X Hard Facing Overlay

ASME F Numbers

Note:- X represents any number 0 to 9


ASME A Numbers

These refer to the chemical analysis of the deposited weld and not the parent material. They only apply to welding procedures in steel materials.

A1Plain unalloyed carbon manganese steels.

A2 to A4 Low alloy steels containing Moly and Chrome Moly

A8 Austenitic stainless steels such as type 316.


ASME Welding Positions Note the welding progression, (vertically upwards or downwards),

must always be stated and it is an essential variable for both procedures and performance qualifications.

Welding Positions For Groove welds:-

Welding PositionTest Position ISO and EN

Flat 1G PA

Horizontal 2G PC

Vertical Upwards Progression 3G PF

Vertical Downwards Progression 3G PG

Overhead 4G PE

Pipe Fixed Horizontal 5G PF

Pipe Fixed @ 45 degrees Upwards 6G HL045

Pipe Fixed @ 45 degrees Downwards 6G JL045


G

for Groove Welds

F

for Fillet Welds


G

for Groove Welds

F

for Fillet Welds



Welding Positions For Fillet welds:-

Welding PositionTest Position ISO and EN

Flat (Weld flat joint at 45 degrees)

1F PA

Horizontal 2F PB

Horizontal Rotated 2FR PB

Vertical Upwards Progression

3F PF

Vertical Downwards Progression

3F PG

Overhead 4F PD

Pipe Fixed Horizontal 5F PF





Multiple-pass layers. Weld layer sequence


Welding Positions QW431.1 and QW461.2

Basically there are three inclinations involved. Flat, which includes from 0 to 15 degrees inclination 15 - 80 degrees inclination Vertical, 80 - 90 degrees For each of these inclinations the weld can be rotated from the flat position to Horizontal to overhead.


Effects of expansion and contraction


CONTROLLING DISTORTION


HEAT AFFECTED ZONE



LIQUID STATE PROCESSES

• Partial melting and fusion of joint• Physical and mechanical changes taking place• Can be with application of pressure or by addition

of filler material

• Prior to joining, PREPARATION TO BE DONE

STANDARDS- AWS; ASTM-

TYPES OF GROOVES, JOINTS

NITC


OXY ACETYLENE WELDING (OAW)

Oxyacetylene Welding (OAW)

The oxyacetylene welding process uses a combination of oxygen and

acetylene gas to provide a high temperature flame.


Oxyacetylene Welding (OAW)

• OAW is a manual process in which the welder must personally control the the torch movement and filler rod application

• The term oxyfuel gas welding outfit refers to all the equipment needed to weld.

• Cylinders contain oxygen and acetylene gas at extremely high pressure.


Typical Oxyacetylene Welding (OAW) Station


STEPS for OAW1. PREPARE THE EDGES AND MAINTAIN

PROPER POSITION- ………………………….(USE OF FIXTURES, CLAMPS)

2. OPEN ACETYLENE AND IGNITE

3. OPEN OXYGEN AND ADJUST FLAME

4. HOLD TORCH AT ABOUT 45O AND FILLER METAL AT 30 TO 40 O

5. TOUCH FILLER ROD TO JOINT AND CONTROL MOVEMENT

6. SINGLE BEAD MADE


• FOR DEEP JOINTS, MULTIPLE PASSES

• CLEANING EACH WELD BEAD IS IMPORTANT

• EQUIPMENT- WELDING TORCH- VARIOUS SIZES AND SHAPES

• CYLINDERS DIFFERENT THREADS, ANCHORED AND NOT DROPPED


CAPABILITIES• LOW COST. MANUAL AND HENCE SLOW

• PORTABLE, VERSATILE AND ECONOMICAL FOR LOW QUANTITY AND REPAIR WORKS

• FOR ALL FERROUS AND NONFERROUS METALS

LIMITATIONS THICKNESS < 6 MM

• SKILL ESSENTIAL---FOR PIPE, PRESSURE VESSELS, LOAD BEARING STRUCTURAL MEMBERS


Oxygen Cylinders

• Oxygen is stored within cylinders of various sizes and pressures ranging from 2000- 2640 PSI. (Pounds Per square inch)

• Oxygen cylinders are forged from solid armor plate steel. No part of the cylinder may be less than 1/4” thick.

• Cylinders are then tested to over 3,300 PSI using a (NDE) hydrostatic pressure test.


Oxygen Cylinders

• Cylinders are regularly re-tested using hydrostatic (NDE) while in service

• Cylinders are regularly chemically cleaned and annealed to relieve “jobsite” stresses created by handling .


Cylinder Transportation

• Never transport cylinders without the safety caps in place

• Never transport with the regulators in place

• Never allow bottles to stand freely. Always chain them to a secure cart or some other object that cannot be toppled easily.


Oxygen Cylinders

• Oxygen cylinders incorporate a thin metal “pressure safety disk” made from stainless steel and are designed to rupture prior to the cylinder becoming damaged by pressure.

• The cylinder valve should always be handled carefully


Pressure Regulators for Cylinders

• Reduce high storage cylinder pressure to lower working pressure.

• Most regulators have a gauge for cylinder pressure and working pressure.


Pressure Regulators for Cylinders

• Regulators are shut off when the adjusting screw is turn out completely.

• Regulators maintain a constant torch pressure although cylinder pressure may vary

• Regulator diaphragms are made of stainless steel


Pressure Regulators Gauges Using a “Bourdon” movement

• Gas entering the gauge fills a Bourdon tube

• As pressure in the semicircular end increases it causes the free end of the tube to move outward.

• This movement is transmitted through to a curved rack which engages a pinion gear on the pointer shaft ultimately showing pressure.


Regulator Hoses

• Hoses are are fabricated from rubber

• Oxygen hoses are green in color and have right hand thread.

• Acetylene hoses are red in color with left hand thread.

• Left hand threads can be identified by a groove in the body of the nut and it may have “ACET” stamped on it


Check Valves &Flashback Arrestors

• Check valves allow gas flow in one direction only

• Flashback arrestors are designed to eliminate the possibility of an explosion at the cylinder.

• Combination Check/ Flashback Valves can be placed at the torch or regulator.


Acetylene Gas

• Virtually all the acetylene distributed for welding and cutting use is created by allowing calcium carbide (a man made product) to react with water.

• The nice thing about the calcium carbide method of producing acetylene is that it can be done on almost any scale desired. Placed in tightly-sealed cans, calcium carbide keeps indefinitely. For years, miners’ lamps produced acetylene by adding water, a drop at a time, to lumps of carbide.

• Before acetylene in cylinders became available in almost every community of appreciable size produced their own gas from calcium carbide.


Acetylene Cylinders

• Acetylene is stored in cylinders specially designed for this purpose only.

• Acetylene is extremely unstable in its pure form at pressure above 15 PSI (Pounds per Square Inch)

• Acetone is also present within the cylinder to stabilize the acetylene.

• Acetylene cylinders should always be stored in the upright position to prevent the acetone form escaping thus causing the acetylene to become unstable.


Acetylene Cylinders

• Cylinders are filled with a very porous substance “monolithic filler” to help prevent from large pockets of pure acetylene forming

• Cylinders have safety (Fuse) plugs in the top and bottom designed to melt at 212° F (100 °C)


Acetylene Valves

• Acetylene cylinder shut off valves should only be opened 1/4 to 1/2 turn

• This will allow the cylinder to be closed quickly in case of fire.

• Cylinder valve wrenches should be left in place on cylinders that do not have a hand wheel.


Oxygen and Acetylene Regulator Pressure Settings

• Regulator pressure may vary with different torch styles and tip sizes.

• PSI (pounds per square inch) is sometimes shown as PSIG (pounds per square inch -gauge)

• Common gauge settings for cutting– 1/4” material Oxy 30-35psi Acet 3-9 psi

– 1/2” material Oxy 55-85psi Acet 6-12 psi

– 1” material Oxy 110-160psi Acet 7-15 psi

• Check the torch manufactures data for optimum pressure settings


Regulator Pressure Settings

• The maximum safe working pressure for acetylene is 15 PSI !


Typical torch styles

• A small welding torch, with throttle valves located at the front end of the handle. Ideally suited to sheet metal welding. Can be fitted with cutting

• attachment in place of the welding head shown. Welding torches of this general design are by far the most widely used. They will handle any oxyacetylene welding job, can be fitted with multiflame (Rosebud) heads for heating applications, and accommodate cutting attachments that will cut steel 6 in. thick.

• A full-size oxygen cutting torch which has all valves located in its rear body. Another style of cutting torch, with oxygen valves located at the front end of its handle.


Typical startup procedures

• Verify that equipment visually appears safe IE: Hose condition, visibility of gauges

• Clean torch orifices with a “tip cleaners” (a small wire gauge file set used to clean slag and dirt form the torch tip)

• Crack (or open) cylinder valves slightly allowing pressure to enter the regulators slowly

• Opening the cylinder valve quickly will “Slam” the regulator and will cause failure.



• Never stand directly in the path of a regulator when opening the cylinder

• Check for leaks using by listening for “Hissing” or by using a soapy “Bubble” solution

• Adjust the regulators to the correct operating pressure

• Slightly open and close the Oxygen and Acetylene valves at the torch head to purge any atmosphere from the system.



• Always use a flint and steel spark lighter to light the oxygen acetylene flame.

• Never use a butane lighter to light the flame


Flame Settings

• There are three distinct types of oxy-acetylene flames, usually termed:– Neutral– Carburizing (or “excess acetylene”)– Oxidizing (or “excess oxygen” )

• The type of flame produced depends upon the ratio of oxygen to acetylene in the gas mixture which leaves the torch tip.


TYPES of FLAMES• Neutral- with inner cone(30400C-33000C), outer envelope,

(21000C near inner cone, 12600C at tip)- high heating

• Reducing- Bright luminous inner cone, acetylene feather, blue envelope– Low temperature, good for brazing, soldering, flame

hardening

Hydrogen, methyl acetylene, propadiene also used as fuel.

• Oxidising- pointed inner cone, small and narrow outer envelope– Harmful for steels, good for Cu- Cu based alloys

NITC


OXY ACETYLENE WELDING (OAW)

Types of Flames

Neutral Reducing Oxidising

high heating low temperature good for Cu- Cu alloys


Pure Acetylene and Carburizing Flame profiles


Neutral and Oxidizing Flame Profiles


Flame definition

• The neutral flame is produced when the ratio of oxygen to acetylene, in the mixture leaving the torch, is almost exactly one-to-one. It’s termed ”neutral” because it will usually have no chemical effect on the metal being welded. It will not oxidize the weld metal; it will not cause an increase in the carbon content of the weld metal.

• The excess acetylene flame as its name implies, is created when the proportion of acetylene in the mixture is higher than that required to produce the neutral flame. Used on steel, it will cause an increase in the carbon content of the weld metal.

• The oxidizing flame results from burning a mixture which contains more oxygen than required for a neutral flame. It will oxidize or ”burn” some of the metal being welded.


Quiz time

• The regulator diaphragm is often made from _______?

A: reinforced rubber

B: malleable iron

C: tempered aluminum

D: stainless steel


Quiz time

• The hose nuts for oxygen and acetylene differ greatly, because the acetylene hose nut has.

A: a left hand thread.

B: has a groove cut around it. C: may have ACET stamped on it.

D: All of the above.


Quiz time

• An oxygen cylinder must be able to withstand a ________ pressure of 3300 psi (22753 kPa) to be qualified for service.

A: atmospheric

B: hydrostatic

C: hydroscopic

D: vapor


Quiz time

• Why is the area above 15 psig often marked with a red band on a acetylene low pressure regulator ?

• Answer – Acetylene pressure above 15 psig is unstable

and should not be used


Quiz time

• True or False ?– A flint and steel spark lighter is the generally

used to light the oxyacetylene flame.

• Answer: True


Quiz time

• Acetylene cylinder fuse plugs melt at a temperature of ________° F or 100°C

• Answer – 212°F


Quiz time

• What is the maximum safe working gauge pressure for acetylene gas?

A: 8 psig (55 kPa)

B: 15 psig (103 kPa)

C: 22 psig (152 kPa)

D: 30 psig (207 kPa)


Quiz time

• The colour of and oxygen hose on a oxyacetylene welding outfit is ______?

• Answer – Green/Blue


Quiz time

• The type of safety device is used on a oxygen cylinder.

A: A fusible plug

B: A check valve

C: A pressure safety disk

D: A spring loaded plug


Quiz time

• True or False ?– The regulator is closed when the adjusting

screw is turned out.

• Answer: True


Quiz time

• The colour of acetylene hose on a oxyacetylene welding outfit is ______?

• Answer – Red


Quiz time

• No part of an oxygen cylinder walls may be thinner than _______?

A: 1/4”in (6.4 mm)

B: 3/8”in (9.5 mm)

C: 3/16”in (4.8 mm)

D: 7/32”in (5.6 mm)


Quiz time

• To prevent the occurrence of flashbacks, a ________ should be installed between either the torch and hoses or regulators and hoses.

A: a two way check valve.

B: flame screen.

C: flashback arrestor.

D: three way check valve.


Quiz time

• What type of safety device is used on a acetylene cylinder.

A: A spring loaded plug

B: A pressure safety disk

C: A fusible plug

D: A check valve


Quiz time

• Mixing _______ and water will produce acetylene gas.

A: calcium carbide

B: potassium carbonate

C: carbon dioxide

D: acetylene carbide


LIQUID STATE PROCESSPARTIAL MELTING

BY STRIKING AN ARC

AFTER THE INVENTION OF ELECTRICITY

HOW ARC STRUCK?

ARC COLUMN THEORY


ARC WELDING


• ARC WELDING ELECTRIC ARC

WITHOUT ADDITIONAL EXTERNAL SOURCE

AUTOGENEOUS NONCONSUMABLE- CONSUMABLE

CARBON ARC WELDING (CAW) - OLDEST

METALLIC ARC WELDING (MAW)

COATING MATERIALS

ARC TO BE CREATED BY ELECTRICITY

WHEN? WITH THE INVENTION OF AC DYNAMO IN 1877


BEGINNING IN 1881- TO CONNECT PLATES OF STORAGE BATTERY

1886- BUTT WELDING TECHNIQUE WAS DEVELOPED

BUTTED, CLAMPED HIGH CURRENT PASSED

AT THE JOINT, RESISTANCE OF METAL TO ELECTRIC CURRENT PRODUCES HIGH HEAT- PIECES FUSED


ARC WELDING- MELTING AND FUSING OF METAL BY ELECTRODES

1ST BY N.V. BERNADO USING CARBON ELECTRODES

CONSISTANTLY IMPROVED

1895 N.G. SLAVIANOFF USED METALLIC ELECTRODES

1905 BARE ELECTRODES COATED—SHIELDING--- (SAW)

PORTABLE AND AUTOMATIC WELDING MACHINES


ARC WELDING PROCESSES

USE OF CONSUMABLE ELECTRODES SHIELDED METAL ARC WELDING

(SMAW)• SIMPLEST AND MOST VERSATILE• ABOUT 50% OF INDUSTRIAL WELDING

BY THIS PROCESS• CURRENT- 50 TO 300 A, < 10 KW• AC/DC USED• FOR THICKNESSES UPTO 19 –20 MM

SHIELDED METAL ARC WELDING (SMAW)


•Shielded metal arc welding (SMAW), •Also known as Manual Metal Arc (MMA) welding • Informally as stick welding

is a manual arc welding process that uses a consumable electrode coated in flux to lay the weld.

•An electric current, in the form of either alternating current or direct current from a welding power supply, is used to form an electric arc between the electrode and the metals to be joined.

http://en.wikipedia.org/wiki/Arc_welding

http://en.wikipedia.org/wiki/Electrode

http://en.wikipedia.org/wiki/Flux_%28metallurgy%29

http://en.wikipedia.org/wiki/Current_%28electricity%29

http://en.wikipedia.org/wiki/Alternating_current

http://en.wikipedia.org/wiki/Direct_current

http://en.wikipedia.org/wiki/Welding_power_supply

http://en.wikipedia.org/wiki/Electric_arc

http://en.wikipedia.org/wiki/Metal

ANODE +

CATHODE -

ELECTRICAL / IONIC THEORY

IONS FROM ANODE TO CATHODE,AS METAL IONS ARE +VE CHARGED

DC

ARC COLUMN THEORY

•TOUCH AND THEN ESTABLISH A GAP TO BALANCE THE ATOMIC STRUCTURE

•IONS COLLIDE WITH GAS MOLECULES

•PRODUCES A THERMAL IONISATION LAYER

•IONISED GAS COLUMN – AS HIGH RESISTANCE CONDUCTOR

•ON STRIKING CATHODE, HEAT GENERATED•TERMED AS IONIC THEORY

•NOT COMPLETE IN EXPLAINING ARC COLUMN THEORY•THUS, ELECTRON THEORY


ANODE +

CATHODE -

ELECTRON THEORY

IONS FROM ANODE TO CATHODEAS METAL IONS ARE +VE CHARGED

-VELY CHARGED ELECTRONS DISSOCIATED FROM CATHODE MOVE OPPOSITE WITH HIGH VELOCITY

DC(MASS- 9.1x 10-28 gm)

CAUSES HEAT IN ARC COLUMNRELEASES HEAT ENERGY IN

STRIKING THE ANODE

CALLED ELECTRON IMPINGEMENT

AND IONIC BOMBARDMENT

ARC COLUMN THEORY


HIGH HEAT

MEDIUM HEAT

LOW HEAT

ANODE+

CATHODE -

ELECTRON IMPINGEMENT

IONIC BOMBARDMENT


MAGNETIC FLUX THEORY

• THE COLUMN NOT FLAIRING

DUE TO THE FLUX LINES AROUND THE ARC COLUMN.

(Right hand Thumb Rule)

THIS COMPLETES THE ARC COLUMN THEORY


POLARITYAC

1. Currents higher than those of DCRP can be employed (400 A to 500 Afor 6 mm electrode)

2. Arc cleaning of the base metal

3. Normal penetration4. Equal heat distribution

at electrode and job5. Electrode tip is colder as

compared to that in DCRP

6. Average arc voltage in argon atmosphere is 16V


DCRP 1. Currents generally less than 125 amps (upto 6 mm dia electrodes) to avoid overheating

2. 2/3rd heat at electrode and 1/3rd at the job

3. Least penetration4. Average arc voltage on

argon atmosphere is 19V

5. Chances of electrode overheating, melting and losses

6. Better arc cleaning action


DCSP1. Welding currents upto

1000 amps can be employed for 6 mm electrodes

2. 33.33% heat is generated at the electrode and 66.66% at the job.

3. Deep penetration

4. Average arc voltage in an argon atmsphere is 12 V

5. Electrode runs colder as compared to AC or DCRP

6. No arc cleaning of base metal

METALLURGY OF WELDING

During joining, localized heating occurs.

This leads to metallurgical and physical changes in materials welded.

Hence, study of:

1. Nature of welded joint2. Quality and property of welded joint3. Weldability of metals4. Methods of testing welds5. Welding design6. Process selection- important

.


(2) Fusion Zone

(1) Base Metal

Structures: (1) SMALL (2) MEDIUM (3) LARGE

Properties of (2) and (3) important

(3) Heat Affected Zone (HAZ)


• Cooling of Bead- similar to a casting in mould, which is metallic here.

Cooling is slow Hence the structure is coarse and Strength toughness and ductility low.

But use of proper electrodes improves these.

• The purpose of coating the electrode is to achieve the improved properties. If without, nitrides and oxides of base metal form and these result in weak and brittle nature.

• With coating, properties comparable with base metal achieved.


Arc column makes CRATER on striking the surface- Temperature above 1500 C

Gas shield

Flux + impurities- less dense. Floats as SLAG

Slag prevents heat loss- makes an evenly distribution of heat radiation.

Preheating to receive the molten metal at an elevated temperature and modify the structure. Not for M.S.

Locked in stresses due to heating and cooling- to be relieved by PEENING, or other heat treatment processes.


MAGNETIC ARC BLOW -- FOR AC SUPPLY.

Current through conductor- magnetic Flux lines perpendicular to current flow- apply Right hand Thumb Rule.

Three areas of magnetic field

1. Arc; 2. Electrode; 3. Work piece, when ground.

Forward pull of Arc column results, called as Magnetic Arc Blow.


EQUIPMENT



PURPOSE OF COATING• Gives out inert or protective gas- shields• Stabilizes the arc- by chemicals• Low rate consumption of electrode- directs arc and

molten metal• Removes impurities and oxides as slag• Coatings act as insulators- so narrow grooves welded• Provide means to introduce alloying elements

Bare electrodes - carbon- more conductive- slow consumption in welding


ELECTRODE COATING INGREDIENTS• Slag forming ingredients- silicates of sodium, potassium, Mg,

Al, iron oxide, China clay, mica etc.• Gas shielding- cellulose, wood, starch, calcium carbonate• De-oxidising elements- ferro manganese, ferro silicon- to

refine molten metal• Arc stabilizing – calcium carbonate, potassium silicate,

titanates, Mg silicate etc.• Alloying elements- ferro alloys, Mn, Mo., to impart special

properties• Iron powder- to improve arc behaviour, bead appearance• Other elements - to improve penetration, limit spatter,

improve metal deposition rates,


• As the weld is laid, the flux coating of the electrode disintegrates, giving off vapors that serve as a shielding gas and providing a layer of slag, both of which protect the weld area from atmospheric contamination.

• Because of the versatility of the process and the simplicity of its equipment and operation, shielded metal arc welding is one of the world's most popular welding processes.

http://en.wikipedia.org/wiki/Shielding_gas


• It dominates other welding processes in the maintenance and repair industry, used extensively in the construction of steel structures and in industrial fabrication.

• The process is used primarily to weld iron and steels (including stainless steel) but aluminum, nickel and copper alloys can also be welded with this method.

• Flux-Cored Arc Welding (FCAW) , a modification to SMAW is growing in popularity

http://en.wikipedia.org/wiki/Iron

http://en.wikipedia.org/wiki/Steel

http://en.wikipedia.org/wiki/Stainless_steel

http://en.wikipedia.org/wiki/Aluminum

http://en.wikipedia.org/wiki/Nickel

http://en.wikipedia.org/wiki/Copper

http://en.wikipedia.org/wiki/Alloy

http://en.wikipedia.org/wiki/Flux-cored_arc_welding

Dr. N. RAMACHANDRAN, NITC 172Various welding electrodes and an electrode holder


SAFETY PRECAUTIONS• Uses an open electric arc, so risk of burns – to be prevented by protective clothing in the form of heavy leather gloves and long sleeve jackets.

•The brightness of the weld area can lead arc eye, in which ultraviolet light causes the inflammation of the cornea and can burn the retinas of the eyes. •Welding helmets with dark face plates to be worn to prevent this exposure

http://en.wikipedia.org/wiki/Protective_clothing

http://en.wikipedia.org/wiki/Leather

http://en.wikipedia.org/wiki/Glove

http://en.wikipedia.org/wiki/Arc_eye

http://en.wikipedia.org/wiki/Ultraviolet_light

http://en.wikipedia.org/wiki/Cornea

http://en.wikipedia.org/wiki/Retina

http://en.wikipedia.org/wiki/Helmet


• New helmet models have been produced that feature a face plate that self-darkens upon exposure to high amounts of UV light

• To protect bystanders, especially in industrial environments, transparent welding curtains often surround the welding area.

• These are made of a polyvinyl chloride plastic film, shield nearby workers from exposure to the UV light from the electric arc, but should not be used to replace the filter glass used in helmets.

http://en.wikipedia.org/wiki/Polyvinyl_chloride


Arc eye, also known as arc flash or welder's flash or corneal flash burns, is a painful condition sometimes experienced by welders who have failed to use adequate eye protection. It can also occur due to light from sunbeds, light reflected from snow (known as snow blindness), water or sand. The intense ultraviolet light emitted by the arc causes a superficial and painful keratitis.

Symptoms tend to occur a number of hours after exposure and typically resolve spontaneously within 36 hours. It has been described as having sand poured into the eyes.

ARC EYE

http://en.wikipedia.org/wiki/Welder

http://en.wikipedia.org/wiki/Eye

http://en.wikipedia.org/wiki/Sunbed

http://en.wikipedia.org/wiki/Snow

http://en.wikipedia.org/wiki/Snow_blindness

http://en.wikipedia.org/wiki/Water

http://en.wikipedia.org/wiki/Sand

http://en.wikipedia.org/wiki/Ultraviolet

http://en.wikipedia.org/wiki/Keratitis


SignsIntense lacrimation Blepharospasm Photophobia Fluorescein dye staining will reveal corneal ulcers

under blue light

Management• Instill topical anaesthesia • Inspect the cornea for any foreign body • Patch the worse of the two eyes and prescribe analgesia • Topical antibiotics in the form of eye drops or eye

ointment or both should be prescribed for prophylaxis against infection

http://en.wikipedia.org/wiki/Lacrimation

http://en.wikipedia.org/wiki/Blepharospasm

http://en.wikipedia.org/wiki/Photophobia

http://en.wikipedia.org/wiki/Fluorescein

http://en.wikipedia.org/wiki/Anaesthesia

http://en.wikipedia.org/wiki/Cornea

http://en.wikipedia.org/wiki/Analgesia


SUBMERGED ARC WELDING (SAW)

http://en.wikipedia.org/wiki/Image:Submerged_arc_welder.lincoln.triddle.jpg


CONTROL PANEL

http://en.wikipedia.org/wiki/Image:Submerged_arc_welder_control_panel.lincoln.triddle.jpg


SUBMERGED ARC WELDING


DC-:

DC+ = Optimum Penetration

DC - = Optimum deposition rate


Submerged Arc Welding (SAW)

• Is a common arc welding process. • A continuously fed consumable solid or tubular

(metal cored) electrode used.• The molten weld and the arc zone are protected

from atmospheric contamination by being “submerged” under a blanket of granular fusible flux.

• When molten, the flux becomes conductive, and provides a current path between the electrode and the work

http://en.wikipedia.org/wiki/Welding

http://en.wikipedia.org/wiki/Flux_%28metallurgy%29


• Normally operated in the automatic or mechanized mode.

• Semi-automatic (hand-held) SAW guns with pressurized or gravity flux feed delivery are available.

• The process is normally limited to the 1F, 1G, or the 2F positions (although 2G position welds have been done with a special arrangement to support the flux). Deposition rates approaching 45 kg/h have been reported — this compares to ~5 kg/h (max) for shielded metal arc welding.

• Currents ranging from 200 to 1500 A are commonly used; currents of up to 5000 A have been used (multiple arcs).

http://en.wikipedia.org/wiki/Shielded_metal_arc_welding

http://en.wikipedia.org/wiki/Electrical_current


• Single or multiple (2 to 5) electrode wire variations of the process exist

• SAW strip-cladding utilizes a flat strip electrode (e.g. 60 mm wide x 0.5 mm thick).

• DC or AC power can be utilized, and combinations of DC and AC are common on multiple electrode systems.

• Constant Voltage welding power supplies are most commonly used, however Constant Current systems in combination with a voltage sensing wire-feeder are available.


SAW• Fusion Welding Process

• Automatic / Semi Automatic

• Arc Between Consumable Electrode And Work

• Arc Covered Under granular Flux

• Wire / Electrode Continuously Fed To Weld Pool

• Wire / Arc Under Flux Moves Along The Groove

• Wire, BM & Flux Close to Arc Melt Under Flux

• On Cooling Weld Metal Solidifies

• Molten Flux Forms Thick Slag Coating On Weld

SAW

•••••••••••••••••••

+ –Wire

Flux

SlagWeld

Base Metal

Hopper

Power SourceFlux

+

Arc

Flux For SAW

• Sodium Chloride

• Potassium Chloride

• Titanium Dioxide

• Sodium Silicate

• Deoxidizing Agents

Types Of Flux

• Fused Flux

• Agglomerated Flux» Neutral Flux» Active Flux

Types Of Flux

• Neutral Flux-Wire compatible to base metal

- Single flux suitable for several material

• Active Flux- Single flux suitable for specific application- Wire may be different from basemetal- To be welded within the recommended parameters

Function Of Flux In SAW• Stabilizes Arc• Prevents contamination of weld metal• Cleans the weld from unwanted impurities• Increases Fluidity of molten metal• Generates inert gas shielding while metal transfers• Forms slag after melting & covers weld• Allows deposited metal to cool slowly• Compensates alloying elements Within the weld• Eliminates spatter generation• Helps in even & uniform bead finish

Baking Requirements For Flux

• Spread the loose Flux in a Tray Of baking Oven

• Identify The Tray With The Quality/Grade Of Flux

• Bake Tray in an Oven Between 300° C to 350° C

• Baking Time 2 Hrs to 3 Hrs

• Reduce the temperature to 100 ° C to 150 ° C

• Hold the Flux at this temperature till use

Why Baking Flux?

• To remove the moisture (H2O)

• To avoid possible cracking of weld due to H2

How Does Moist Flux Generate Crack Within Weld?

• Moist Flux introduce atomic hydrogen at high temperature in weld

• On cooling, atomic hydrogen try to form molecules

• The reaction results in stresses and fine cracks • Cracks occur within hardened metal - HAZ • Known as “Hydrogen Embrittlement” or “Under

Bead Crack” or Delayed Crack

Reuse Of Flux

• Flux May Be Reused Provided

- Weld Not Highly Critical In Impact / Chemistry

- Reuse Limited To Maximum Twice

- All Slag Particles Are sieved & Removed

- Rebaked If not Remained In Hot

- Minimum 50% Fresh Flux Well Mixed

- Customer Spec. Doesn't Prohibit The Same

Types Of Power Source

• Thyrester – DC

• Rectifier – DC

• Motor Generator – DC

• Transformer - AC

Characteristic Of Power Source

Machine weldingDrooping – Cons. A Linear – Cons. V

V V

A A

V1

V2V2V1

A2A1 A2A1

SAW Wire - Electrode

• Consumable Electrode / Wire • Layer Wound On Spool / Coil• CS & LAS Wires Coated with Cu • Conducts Current and generates Arc• Chemistry Compatible To Base Metal• Grade Of Flux Can Be Same For CS & LAS• Wire melts & deposited as filler in joint

Typical Welding Parameter

Sr no

Wire Ø mm

Current AVoltage

VSpeed

mm/minDep. Rate Per Arc Hr

Wire & Flux

1 1.6 200-300 22-26 750-1500 3 – 4 kgs CS wire

+

Neutral Flux

2 2 250-350 24-26 750-1250 3- 4.5 kgs

4 2.5 300-350 25-27 750-1250 4 –4.5 kgs

5 3 400-500 28-30 500-100 5 – 5.5 kgs

6 4 550-650 30-32 400-750 5.5 - 7 kgs

7 5 600-800 30-34 350-700 6 - 8 kgs


Important parameters

Current

Wave Offset

Wave Balance

Frequency


•Wave Offset Variation

time

Cur

rent

, Vol

tage

, Pow

er

* Wave offset refers to the shift in the amplitude direction. Equal amplitude in positive and negative side is referred as zero offset whereas an increase in wave offset implies that the positive amplitude is increased from its equilibrium position of 50% and proportionate decrease in negative amplitude from its equilibrium position of 50% and decrease in wave offset implies that the positive amplitude is decreased from its equilibrium position of 50% and proportionate increase in negative amplitude from its equilibrium position of 50%

Level 150%,50%

Level 2+75%,-25%

Level 3+25%,-75%


time

Cur

rent

, Vol

tage

, Pow

er

•Wave Balance Variation

Wave balance refers to the amount of time the waveform spends in DC+ part of cycle but the amplitude will be same.

Level 1+50, -50

Level 2+75, -25

Level 3+25, -75


•Effect of Frequency

time

Cur

rent

, Vol

tage

, Pow

er

Frequency refers to shift of peak current with respect to the zero crossing. Here we observe that at lower frequency shift of peak current with respect to the zero crossing is less than in comparison to higher frequency. So Penetration & deposition will be more at lower frequency.

Level 1Low

Level 2medium

Level 3High

Important Terminology used in Critical SAW

• Preheating

• Post Heating or Dehydrogenation

• Intermediate Stress leaving

• Inter pass Temperature• Post Weld Heat Treatment

What Is Preheating?

• Heating the base metal along the weld joint to a predetermined minimum temperature immediately before starting the weld.

• Heating by Oxy fuel flame or electric resistant coil

• Heating from opposite side of welding wherever possible

• Temperature to be verified by thermo chalks prior to starting the weld

Why Preheating?

• Preheating eliminates possible cracking of weld and HAZ

• Applicable to

-Hardenable low alloy steels of all thickness

-Carbon steels of thickness above 25 mm.

-Restrained welds of all thickness• Preheating temperature vary from 75°C to 200°C

depending on hardenability of material, thickness & joint restrain

How does Preheating Eliminate Crack?

• Preheating promotes slow cooling of weld and HAZ

• Slow cooling softens or prevents hardening of weld and HAZ

• Soft material not prone to crack even in restrained condition

What Is Post Heating?

• Raising the pre heating temperature of the weld joint to a predetermined temperature range (250° C to 350° C) for a minimum period of time (3 Hrs) before the weld cools down to room temperature.

• Post heating performed when welding is completed or terminated any time in between.

• Heating by Oxy fuel flame or electric resistant coil• Heating from opposite side of welding wherever

possible• Temperature verified by thermo chalks during the period

Why Post Heating?

• Post heating eliminates possible delayed cracking of weld and HAZ

• Applicable to

-Thicker hardenable low alloy steels

-Restrained hardenable welds of all thickness

• Post heating temperature and duration depends on hardenability of material, thickness & joint restrain

How does Post Heating Eliminate Crack?

• SAW introduces hydrogen in weld metal

• Entrapped hydrogen in weld metal induces delayed cracks unless removed before cooling to room temperature

• Retaining the weld at a higher temperature for a longer duration allows the hydrogen to come out of weld

What Is Intermediate Stress Relieving?

• Heat treating a subassembly in a furnace to a predetermined cycle immediately on completion of critical restrained weld joint / joints without allowing the welds to go down the pre heat temperature. Rate of heating, Soaking temperature, Soaking time and rate of cooling depends on material quality and thickness

• Applicable toHighly restrained air hardenable material

Why Intermediate Stress Relieving?

• Restrained welds in air hardenable steel highly prone to crack on cooling to room temperature.

• Cracks due to entrapped hydrogen and built in stress

• Intermediate stress relieving relieves built in stresses and entrapped hydrogen making the joint free from crack prone

What Is Inter- Pass Temperature?• The temperature of a previously layed weld bead

immediately before depositing the next bead over it

• Temperature to be verified by thermo chalk prior to starting next bead

• Applicable to

Stainless Steel

Carbon Steel & LAS with minimum impact

Why Inter Pass Temperature?

• Control on inter pass temperature avoids over heating, there by

-Refines the weld metal with fine grains

-Improves the notch toughness properties

-Minimize the loss of alloying elements in welds

-Reduces the distortion

What Is Post Weld Heat Treatment?

• Heat treating an assembly on completion of all applicable welding, in an enclosed furnace with controlled heating/cooling rate and soaking at a specific temperature for a specific time.

• Rate of heating, Soaking temperature, Soaking time and rate of cooling depends on material quality and thickness

• Applicable to-All type of CS & LAS


Material applications

• Carbon steels (structural and vessel construction);

• Low alloy steels;

• Stainless Steels;

• Nickel-based alloys;

• Surfacing applications (wearfacing, build-up, and corrosion resistant overlay of steels).


Advantages of SAW

• High deposition rates (over45 kg/h) have been reported;

• High operating factors in mechanized applications;

• Deep weld penetration; • Sound welds are readily made (with good

process design and control); • High speed welding of thin sheet steels at over

2.5 m/min is possible; • Minimal welding fume or arc light is emitted.


Limitations of SAW

• Limited to ferrous (steel or stainless steels) and some nickel based alloys;

• Normally limited to the 1F, 1G, and 2F positions; • Normally limited to long straight seams or

rotated pipes or vessels; • Requires relatively troublesome flux handling

systems; • Flux and slag residue can present a health &

safety issue; • Requires inter-pass and post weld slag removal.


Key SAW process variables

• Wire Feed Speed (main factor in welding current control); • Arc Voltage; • Travel Speed; • Electrical Stick-Out (ESO) or Contact Tip to Work (CTTW); • Polarity and Current Type (AC or DC).

Other factors

• Flux depth/width; • Flux and electrode classification and type; • Electrode wire diameter; • Multiple electrode configurations.



FCAW

GAS TUNGSTEN ARC WELDING (GTAW)


GTAW

http://en.wikipedia.org/wiki/Image:GTAW.png

http://en.wikipedia.org/wiki/Image:GTAW_welding.jpg


GTAW• Fusion Welding Process• Arc Between Non-Consumable

Tungsten Rod And Work• Arc & Weld Pool Shielded By Argon/Gas• Filler Wire Separately Added To Weld

Pool• Welding Torch & Tungsten Rod Cooled

by Flow OF Argon / Cooling Water


GAS TUNGSTEN ARC WELDING (GTAW)

• ELECTRODE NOT CONSUMED

• TUNGSTEN ELECTRODES USED

• ARGON- HEAVIER FOR NARROW AND LIMITED EXPANSION,WIDER, DEEPER PUDDLE

• HELIUM FOR EVEN EXPANSIONLIMITED STRESS BUILDUP

• MORE He, MORE HEAT IN ARC

• Ar-He MIX FOR AUTOMATIC GTAW

• Ar- CO2 FOR CARBON STEELS, ECONIMICAL, INCREASES WETTING ACTION

• GTAW TORCH- WATER OR AIR COOLED

CONSTANT CURRENT SOURCE.(IIIr TO SMAW)


GTAW Equipment & Accessories

• Power Source – Inverter, Thyrister, Rectifier, Generator

• High Frequency Unit• Water Cooling System• Welding Torch- (Ceramic Cup, Tungsten Rod, Collet,

Gas-lens) • Pedal Switch• Argon Gas Cylinder • Pressure Gauge, Regulator, Flow Meter • Earthing Cable With Clamp


Equipment & Accessories

– +

Argon Gas In

Flow Meter

Welding Cable & Cooling Water In Tube

HF Unit & Water Cooling

System

Argon Cylinder

Pressure Regulator

Cooling Water In

Cooling Water OutArgon Shielding

Tungsten Rod

Power Source

Work

Arc

+High Frequency

Connection

Solenoid Valve

Ceramic Cup

Pedal Switch

Gas Lens


Equipment

GTAW torch, disassembledGTAW torch with various electrodes, cups, collets and gas diffusers

http://en.wikipedia.org/wiki/Image:TIG_torch-accs..JPG

http://en.wikipedia.org/wiki/Image:TIG_torch_breakdown.JPG


Gas tungsten arc welding (GTAW), commonly known as Tungsten Inert Gas (TIG) welding• Is an arc welding process that uses a

nonconsumable tungsten electrode to produce the weld.

• The weld area is protected from atmospheric contamination by a shielding gas (usually an inert gas such as argon), and a filler metal is normally used, though some welds, known as autogenous welds, do not require it.

• A constant current welding power supply produces energy which is conducted across the arc through a column of highly ionized gas and metal vapors known as a plasma.


http://en.wikipedia.org/wiki/Tungsten



http://en.wikipedia.org/wiki/Argon


http://en.wikipedia.org/wiki/Plasma


• Most commonly used to weld thin sections of stainless steel and light metals such as aluminum, magnesium, and copper alloys.

• The process grants the operator greater control over the weld than competing procedures such as shielded metal arc welding and gas metal arc welding, allowing for stronger, higher quality welds.

• GTAW is comparatively more complex and difficult to master, and furthermore, it is significantly slower than most other welding techniques.

• A related process, plasma arc welding, uses a slightly different welding torch to create a more focused welding arc and as a result is often automated.


http://en.wikipedia.org/wiki/Aluminium

http://en.wikipedia.org/wiki/Magnesium



http://en.wikipedia.org/wiki/Gas_metal_arc_welding

http://en.wikipedia.org/wiki/Plasma_arc_welding


GTAW system setup

http://en.wikipedia.org/wiki/Image:GTAW_setup.png


Applications

• Aerospace industry is one of the primary users of gas tungsten arc welding. The process is used in a number of other areas.

• Many industries use GTAW for welding thin workpieces, especially nonferrous metals.

• It is used extensively in the manufacture of space vehicles, and is also frequently employed to weld small-diameter, thin-wall tubing.

• Is often used to make root or first pass welds for piping of various sizes.

• In maintenance and repair work, the process is commonly used to repair tools and dies, especially components made of aluminum and magnesium.

• Because the welds it produces are highly resistant to corrosion and cracking over long time periods, GTAW is the welding procedure of choice for critical welding operations like sealing spent nuclear fuel canisters before burial.

http://en.wikipedia.org/wiki/Nuclear_fuel


QualityGTAW ranks the highest in terms of the quality of weld produced.Operation must be with free from oil, moisture, dirt and other impurities, as these cause weld porosity and consequently a decrease in weld strength and quality. To remove oil & grease, alcohol or similar commercial solvents used, while a stainless steel wire brush or chemical process remove oxides from the surfaces of metals like aluminum. Rust on steels removed by first grit blasting the surface and then using a wire brush to remove imbedded grit. These steps important when DCEN used, because this provides no cleaning during the welding process, unlike DCEPor AC.

To maintain a clean weld pool during welding, the shielding gas flow should be sufficient and consistent so that the gas covers the weld and blocks impurities in the atmosphere. GTA welding in windy or drafty environments increases the amount of shielding gas necessary to protect the weld, increasing the cost and making the process unpopular outdoors.


http://en.wikipedia.org/wiki/Grit_blasting

http://en.wikipedia.org/wiki/Image:08-TIG-weld.jpg


• Because of GTAW's relative difficulty and the importance of proper technique, skilled operators are employed for important applications.

• Low heat input, caused by low welding current or high welding speed, can limit penetration and cause the weld bead to lift away from the surface being welded.

• If there is too much heat input, the weld bead grows in width while the likelihood of excessive penetration and spatter increase.

• If the welder holds the welding torch too far from the workpiece, shielding gas is wasted and the appearance of the weld worsens.


• If the amount of current used exceeds the capability of the electrode, tungsten inclusions in the weld may result. Known as tungsten spitting, it can be identified with radiography and prevented by changing the type of electrode or increasing the electrode diameter.

• If the electrode is not well protected by the gas shield or the operator accidentally allows it to contact the molten metal, it can become dirty or contaminated. This often causes the welding arc to become unstable, requiring that electrode be ground with a diamond abrasive to remove the impurity.

http://en.wikipedia.org/wiki/Radiography


• GTAW welding torches designed for either automatic or manual operation and are equipped with cooling systems using air or water. The automatic and manual torches are similar in construction, but the manual torch has a handle while the automatic torch normally comes with a mounting rack.

• The angle between the centerline of the handle and the centerline of the tungsten electrode, known as the head angle, can be varied on some manual torches according to the preference of the operator.

• Air cooling systems are most often used for low-current operations (up to about 200 A), while water cooling is required for high-current welding (up to about 600 A).

• The torches are connected with cables to the power supply and with hoses to the shielding gas source and where used, the water supply.

http://en.wikipedia.org/wiki/Ampere


• The internal metal parts of a torch are made of hard alloys of copper or brass in order to transmit current and heat effectively.

• The tungsten electrode must be held firmly in the center of the torch with an appropriately sized collet, and ports around the electrode provide a constant flow of shielding gas.

• The body of the torch is made of heat-resistant, insulating plastics covering the metal components, providing insulation from heat and electricity to protect the welder.


http://en.wikipedia.org/wiki/Brass

http://en.wikipedia.org/wiki/Collet

http://en.wikipedia.org/wiki/Image:TIG_torch_breakdown.JPG


GTAW TORCH

Tungsten Rod

Ceramic Cup

Arc

Argon Gas Inlet

Cooling Water Outlet

Cooling Water Inlet Tube with cable

Base Metal

Torch HandleCap with collet For Holding Tungsten

Argon Shielding Gas

Earthing Cable


• The size of the welding torch nozzle depends on the size of the desired welding arc, and the inside diameter of the nozzle is normally at least three times the diameter of the electrode.

• The nozzle must be heat resistant and thus is normally made of alumina or a ceramic material, but fused quartz, a glass-like substance, offers greater visibility.

• Devices can be inserted into the nozzle for special applications, such as gas lenses or valves to control shielding gas flow and switches to control welding current.

http://en.wikipedia.org/wiki/Alumina


Power supply• GTAW uses a constant

current power source, meaning that the current (and thus the heat) remains relatively constant, even if the arc distance and voltage change.

• This is important because most applications of GTAW are manual or semiautomatic, requiring that an operator hold the torch.

• Maintaining a suitably steady arc distance is difficult if a constant voltage power source is used instead, since it can cause dramatic heat variations and make welding more difficult.

http://en.wikipedia.org/wiki/Image:Welding_power_supply-Miller-Syncrowave350LX-front-triddle.jpg


• The preferred polarity of the GTAW system depends largely on the type of metal being welded.

• DCEN is often employed when welding steels, nickel, titanium, and other metals. It can also be used in automatic GTA welding of aluminum or magnesium when helium is used as a shielding gas. The negatively charged electrode generates heat by emitting electrons which travel across the arc, causing thermal ionization of the shielding gas and increasing the temperature of the base material. The ionized shielding gas flows toward the electrode, not the base material, and this can allow oxides to build on the surface of the weld.

• DCEP is less common, and is used primarily for shallow welds since less heat is generated in the base material. Instead of flowing from the electrode to the base material, as in DCEN, electrons go the other direction, causing the electrode to reach very high temperatures. To help it maintain its shape and prevent softening, a larger electrode is often used. As the electrons flow toward the electrode, ionized shielding gas flows back toward the base material, cleaning the weld by removing oxides and other impurities and thereby improving its quality and appearance.



http://en.wikipedia.org/wiki/Titanium


• AC commonly used when welding aluminum and magnesium manually or semi-automatically, combines the two direct currents by making the electrode and base material alternate between positive and negative charge. This causes the electron flow to switch directions constantly, preventing the tungsten electrode from overheating while maintaining the heat in the base material. This makes the ionized shielding gas constantly switch its direction of flow, causing impurities to be removed during a portion of the cycle.

• Some power supplies enable operators to use an unbalanced alternating current wave by modifying the exact percentage of time that the current spends in each state of polarity, giving them more control over the amount of heat and cleaning action supplied by the power source.

• In addition, operators must be wary of rectification, in which the arc fails to reignite as it passes from straight polarity (negative electrode) to reverse polarity (positive electrode).

• To remedy the problem, a square wave power supply can be used, as can high frequency voltage to encourage ignition.



http://en.wikipedia.org/wiki/Rectification_%28electricity%29

http://en.wikipedia.org/wiki/Square_wave


Tungsten Rod

• Non Consumable Electrode.

• Maintains Stable Arc

• Tip to be Ground to a cone Shape of 60º to 30º angle

• Thoriated Tungsten for General Application, Zerconiated Tungsten for Aluminium Welding

• Sizes :- 2, 2.4 & 3 mm Ø

Tungsten Rod

Ground to 300-60º angle

ISO Colour Code


ISO Class

ISO Color AWS ClassAWS Color

Alloy [18]

WP Green EWP Green None

WC20 Gray EWCe-2 Orange ~2% CeO2

WL10 Black EWLa-1 Black ~1% LaO2

WL15 Gold EWLa-1.5 Gold ~1.5% LaO2

WL20 Sky-blue EWLa-2 Blue ~2% LaO2

WT10 Yellow EWTh-1 Yellow ~1% ThO2

WT20 Red EWTh-2 Red ~2% ThO2

WT30 Violet ~3% ThO2

WT40 Orange ~4% ThO2

WY20 Blue ~2% Y2O3

WZ3 Brown EWZr-1 Brown ~0.3% ZrO2

WZ8 White ~0.8% ZrO2

•The electrode used in GTAW is made of tungsten or a tungsten alloy, because tungsten has the highest melting temperature among metals, at 3422 °C.• The electrode is not consumed during welding, though some erosion (called burn-off) can occur. •Electrodes can have either a clean finish or a ground finish—clean finish electrodes have been chemically cleaned, while ground finish electrodes have been ground to a uniform size and have a polished surface, making them optimal for heat conduction. •The diameter of the electrode can vary between 0.5 mm and 6.4 mm, and their length can range from 75 to 610 mm .

http://en.wikipedia.org/wiki/Gas_tungsten_arc_welding#_note-17%23_note-17

http://en.wikipedia.org/wiki/Ceria


http://en.wikipedia.org/wiki/Lanthanum%28III%29_oxide


http://en.wikipedia.org/wiki/Thoria


http://en.wikipedia.org/wiki/Yttrium%28III%29_oxide




http://en.wikipedia.org/wiki/Zirconia



http://en.wikipedia.org/wiki/Tungsten

http://en.wikipedia.org/wiki/Celsius


• A number of tungsten alloys have been standardized by the International Organization for Standardization and the American Welding Society in ISO 6848 and AWS A5.12, respectively, for use in GTAW electrodes- refer table

• Pure tungsten electrodes (classified as WP or EWP) are general purpose and low cost electrodes. Cerium oxide (or ceria) as an alloying element improves arc stability and ease of starting while decreasing burn-off. Using an alloy of lanthanum oxide (or lanthana) has a similar effect. Thorium oxide (or thoria) alloy electrodes were designed for DC applications and can withstand somewhat higher temperatures while providing many of the benefits of other alloys.

• However, it is somewhat radioactive, and as a replacement, electrodes with larger concentrations of lanthanum oxide can be used. Electrodes containing zirconium oxide (or zirconia) increase the current capacity while improving arc stability and starting and increasing electrode life.

• Electrode manufacturers may create alternative tungsten alloys with specified metal additions, and these are designated with the classification EWG under the AWS system.

• Filler metals are also used in nearly all applications of GTAW, the major exception being the welding of thin materials. Filler metals are available with different diameters and are made of a variety of materials. In most cases, the filler metal in the form of a rod is added to the weld pool manually, but some applications call for an automatically fed filler metal, which is fed from rolls.

http://en.wikipedia.org/wiki/International_Organization_for_Standardization

http://en.wikipedia.org/w/index.php?title=American_Welding_Society&action=edit

http://en.wikipedia.org/wiki/Cerium


http://en.wikipedia.org/wiki/Lanthanum


http://en.wikipedia.org/wiki/Thorium


http://en.wikipedia.org/wiki/Radioactive_contamination

http://en.wikipedia.org/wiki/Zirconium



shielding gases• Necessary in GTAW to protect the welding area from atmospheric

gases such as nitrogen and oxygen, which can cause fusion defects, porosity, and weld metal embrittlement if they come in contact with the electrode, the arc, or the welding metal. The gas also transfers heat from the tungsten electrode to the metal, and it helps start and maintain a stable arc.

• The selection of a shielding gas depends on several factors, including the type of material being welded, joint design, and desired final weld appearance.

• Argon is the most commonly used shielding gas for GTAW, since it helps prevent defects due to a varying arc length. When used with alternating current, the use of argon results in high weld quality and good appearance.

• Another common shielding gas, helium, is most often used to increase the weld penetration in a joint, to increase the welding speed, and to weld conductive metals like copper and aluminum.

• A significant disadvantage is the difficulty of striking an arc with helium gas, and the decreased weld quality associated with a varying arc length.


http://en.wikipedia.org/wiki/Nitrogen

http://en.wikipedia.org/wiki/Oxygen

http://en.wikipedia.org/wiki/Argon

http://en.wikipedia.org/wiki/Helium




Shielding Gas• Inert Gas - Argon , Helium• Common Shielding Gas – Argon• When Helium Is Used – Called Heli – Arc Welding• When Argon Is Used – Called Argon Arc Welding• Inert Gas Prevents Contamination Of Molten Metal• It Prevents Oxidation Of Tungsten Rod• It Ionizes Air Gap and Stabilizes Arc• It Cools Welding Torch & Tungsten Rod


Shielding Gas• Argon - Purity 99.95%

• Impure Argon Results In Porosities

• Purity Verified by Fusing BQ CS plate

• Leakage of Argon in Torch Results in Porosity.

• Check Leakage by Closing the Ceramic Cup With Thump


Argon Gas Cylinder• Light Blue In Colour

• Full Cylinder Pressure: 1800 psi ( 130 Kgs / Cm2 )

• Volume Of Argon In Full Cylinder: 7.3 M3

• Commercial Argon (99.99%) Cost: Rs 70/- Per M3

• High Purity Argon (99.999) Cost: Rs 87/- Per M3


Back Purging

Purging Gas Commercial Argon or Nitrogen

• Applicable to Single Sided full penetration

• Prevents oxidation of root pass from opposite side of weld

• Essential for high alloy steels, nonferrous metals and alloys

• Desirable For All Material

Welding Torch

Root Pass

Purging Gas InPurging Gas Out

Purging chamber

Filler Wire


• Argon-helium mixtures are also frequently utilized in GTAW, since they can increase control of the heat input while maintaining the benefits of using argon. Normally, the mixtures are made with primarily helium (often about 75% or higher) and a balance of argon. These mixtures increase the speed and quality of the AC welding of aluminum, and also make it easier to strike an arc.

• Argon-hydrogen, is used in the mechanized welding of light gauge stainless steel, but because hydrogen can cause porosity, its uses are limited.

• Nitrogen can sometimes be added to argon to help stabilize the austenite in austentitic stainless steels and increase penetration when welding copper. Due to porosity problems in ferritic steels and limited benefits, however, it is not a popular shielding gas additive.

http://en.wikipedia.org/wiki/Hydrogen


http://en.wikipedia.org/wiki/Austenite


Materials• Most commonly used to weld stainless steel

and nonferrous materials, such as aluminum and magnesium, but it can be applied to nearly all metals, with notable exceptions being lead and zinc.

• Its applications involving carbon steels are limited not because of process restrictions, but because of the existence of more economical steel welding techniques, such as gas metal arc welding and shielded metal arc welding.

• GTAW can be performed in a variety of other-than-flat positions, depending on the skill of the welder and the materials being welded.

http://en.wikipedia.org/wiki/Lead

http://en.wikipedia.org/wiki/Zinc




A TIG weld showing an accentuated AC etched zone

Closeup view of an aluminium TIG weld AC etch zone

http://en.wikipedia.org/wiki/Image:TIG_Weld_low_magnification.jpg

http://en.wikipedia.org/wiki/Image:TIG_weld_etch_zone_closeup.jpg


• Aluminum and magnesium are most often welded using alternating current, but the use of direct current is also possible, depending on the properties desired. Before welding, the work area should be cleaned and may be preheated to 175-200 °C for aluminum or to a maximum of 150 °C for thick magnesium workpieces to improve penetration and increase travel speed.

• AC current can provide a self-cleaning effect, removing the thin, refractory aluminium oxide (sapphire) layer that forms on aluminium metal within minutes of exposure to air. This oxide layer must be removed for welding to occur. When alternating current is used, pure tungsten electrodes or zirconiated tungsten electrodes are preferred over thoriated electrodes, as the latter are more likely to "spit" electrode particles across the welding arc into the weld.

• Blunt electrode tips are preferred, and pure argon shielding gas should be employed for thin workpieces. Introducing helium allows for greater penetration in thicker workpieces, but can make arc starting difficult.

http://en.wikipedia.org/wiki/Aluminum


http://en.wikipedia.org/wiki/Alternating_current

http://en.wikipedia.org/wiki/Direct_current

http://en.wikipedia.org/wiki/Sapphire


• Direct current of either polarity, positive or negative, can be used to weld aluminum and magnesium as well.

• DCEN allows for high penetration, and is most commonly used on joints with butting surfaces, such as square groove joints. Short arc length (generally less than 2 mm or 0.07 in) gives the best results, making the process better suited for automatic operation than manual operation. Shielding gases with high helium contents are most commonly used with DCEN, and thoriated electrodes are suitable.

• DCEP is used primarily for shallow welds, especially those with a joint thickness of less than 1.6 mm. While still important, cleaning is less essential for DCEP than DCEN, since the electron flow from the workpiece to the electrode helps maintain a clean weld. A large, thoriated tungsten electrode is commonly used, along with a pure argon shielding gas.


Steels• For GTA welding of carbon and stainless steels, the

selection of a filler material is important to prevent excessive porosity. Oxides on the filler material and workpieces must be removed before welding to prevent contamination, and immediately prior to welding, alcohol or acetone should be used to clean the surface.

• Preheating is generally not necessary for mild steels less than one inch thick, but low alloy steels may require preheating to slow the cooling process and prevent the formation of martensite in the heat-affected zone.

• Tool steels should also be preheated to prevent cracking in the heat-affected zone. Austenitic stainless steels do not require preheating, but martensitic and ferritic chromium stainless steels do. A DCEN power source is normally used, and thoriated electrodes, tapered to a sharp point, are recommended. Pure argon is used for thin workpieces, but helium can be introduced as thickness increases.

http://en.wikipedia.org/wiki/Carbon_steel


http://en.wikipedia.org/wiki/Martensite

http://en.wikipedia.org/wiki/Heat-affected_zone

http://en.wikipedia.org/wiki/Tool_steel


Dissimilar metals

• Welding dissimilar metals often introduces new difficulties to GTA welding, because most materials do not easily fuse to form a strong bond. Welds of dissimilar materials have numerous applications in manufacturing, repair work, and the prevention of corrosion and oxidation. In some joints, a compatible filler metal is chosen to help form the bond, and this filler metal can be the same as one of the base materials (eg:, using a stainless steel filler metal stainless steel and carbon steel as base materials), or a different metal (such as the use of a nickel filler metal for joining steel and cast iron). Very different materials may be coated or "buttered" with a material compatible with a particular filler metal, and then welded. In addition, GTAW can be used in cladding or overlaying dissimilar materials.

• When welding dissimilar metals, the joint must have an accurate fit, with proper gap dimensions and bevel angles. Care should be taken to avoid melting excessive base material. Pulsed current is particularly useful for these applications, as it helps limit the heat input. The filler metal should be added quickly, and a large weld pool should be avoided to prevent dilution of the base materials.

http://en.wikipedia.org/wiki/Corrosion

http://en.wikipedia.org/wiki/Oxidation


http://en.wikipedia.org/wiki/Cast_iron

http://en.wikipedia.org/wiki/Cladding

http://en.wikipedia.org/wiki/Overlaying


Process variationsPulsed-current• In the pulsed-current mode, the welding current rapidly

alternates between two levels. • The higher current state is known as the pulse current,

while the lower current level is called the background current.

• During the period of pulse current, the weld area is heated and fusion occurs. Upon dropping to the background current, the weld area is allowed to cool and solidify.

• Pulsed-current GTAW has a number of advantages, including lower heat input and consequently a reduction in distortion and warpage in thin workpieces. In addition, it allows for greater control of the weld pool, and can increase weld penetration, welding speed, and quality. A similar method, manual programmed GTAW, allows the operator to program a specific rate and magnitude of current variations, making it useful for specialized applications.


Dabber• The Dabber variation is used to precisely place

weld metal on thin edges. The automatic process replicates the motions of manual welding by feeding a cold filler wire into the weld area and dabbing (or oscillating) it into the welding arc. It can be used in conjunction with pulsed current, and is used to weld a variety of alloys, including titanium, nickel, and tool steels. Common applications include rebuilding seals in jet engines and building up saw blades, milling cutters, drill bits, and mower blades

http://en.wikipedia.org/wiki/Jet_engines

http://en.wikipedia.org/wiki/Milling_cutter

http://en.wikipedia.org/wiki/Drill_bit


Heat-affected zone

The cross-section of a welded butt joint, with the darkest gray representing the weld or fusion zone, the medium gray the heat affected zone, and the lightest gray the base material.

http://en.wikipedia.org/wiki/Image:Welded_butt_joint_x-section.png


• The heat-affected zone (HAZ) is the area of base material, either a metal or a thermoplastic, which has had its microstructure and properties altered by welding. The heat from the welding process and subsequent re-cooling causes this change in the area surrounding the weld. The extent and magnitude of property change depends primarily on the base material, the weld filler metal, and the amount and concentration of heat input by the welding process.

• The thermal diffusivity of the base material plays a large role – if the diffusivity is high, the material cooling rate is high and the HAZ is relatively small. Alternatively, a low diffusivity leads to slower cooling and a larger HAZ. The amount of heat inputted by the welding process plays an important role as well, as processes like oxyfuel welding use high heat input and increase the size of the HAZ. Processes like laser beam welding give a highly concentrated, limited amount of heat, resulting in a small HAZ. Arc welding falls between these two extremes, with the individual processes varying somewhat in heat input

http://en.wikipedia.org/wiki/Metal

http://en.wikipedia.org/wiki/Thermoplastic


http://en.wikipedia.org/wiki/Thermal_diffusivity

http://en.wikipedia.org/wiki/Oxyfuel_welding

http://en.wikipedia.org/wiki/Laser_beam_welding


• To calculate the heat input for arc welding procedures, the formula used is:

where Q = heat input (kJ/mm), V = voltage (V), I = current (A), and S = welding speed (mm/min). The efficiency is dependent on the welding process used, with shielded metal arc welding having a value of 0.75, gas metal arc welding and submerged arc welding, 0.9, and gas tungsten arc welding, 0.8.

http://en.wikipedia.org/wiki/Kilojoule

http://en.wikipedia.org/wiki/Millimetre

http://en.wikipedia.org/wiki/Volt

http://en.wikipedia.org/wiki/Amp



http://en.wikipedia.org/wiki/Submerged_arc_welding

http://en.wikipedia.org/wiki/Gas_tungsten_arc_welding


Types Of GTAW Power Source

• Inverter- DC

• Thyrister – DC



• Transformer – AC (For Aluminium Welding Only)


Power Source

• Provides Electric Energy – Arc – Heat

• Drooping Characteristic

• OCV – Appx. 90V,

• Current Range 40 A to 300 A ( Capacity Of M/s)

• Arc Voltage 18V to 26V


Characteristic Of GTAW Power Source

A

Vertical Curve

V1

V2

A1 A2

Drooping – Constant Current

V


High Frequency Unit

• Provides High Voltage Electric Energy With Very high Frequency – 10000 Cycles / Sec.

• Initiates low energy Arc / Spark & Ionize Air Gap.

• Electrically charges Air Gap For welding Current to Jump Across the Tungsten Tip & BM to Form An Arc.

• HF Gets Cut Off, Once Welding Arc Struck.


Water Cooling System

• Provides Cooling Water To Welding Torch.

• Cools Tungsten Rod, Torch handle & Welding Cable.

• Cooling Water Returns through Flexible Tube Which Carries welding cable within.


Pedal Switch

Switches system on And off in sequence

When Pedal Pressed• Solenoid valve opens, Argon gas flows• High Frequency current jumps from

tungsten rod generating sparks• Welding current flows generating an

arc across tungsten rod and work. • High frequency gets cut off from the

system & welding continues. When Pedal Released1 Current gets cut off, Arc extinguishes 2 Gas flow remains for few more

seconds before it stops.


Argon Gas Cylinder- Pressure Regulator + Flow Meter

• Cylinder Stores Argon At High Pressure

• Regulator Regulates Cylinder Pressure to Working Pressure

• Flow Meter Controls Flow Rate

Argon Cylinder

Flow Meter

Pressure Regulator

Flow Regulator

Pressure gauges

Cylinder Valve

Connection To Torch


Tools For GTAW

• Head Screen

• Hand gloves

• Chipping Hammer

• Wire Brush

• Spanner Set


Filler Wire

• Added Separately to the weld pool.

• Compatible to base metal

• Used in cut length for manual welding.

• Used from layer wound spool for automatic welding.

• Sizes :- 0.8, 1, 1.2, 1.6, 2, 2.4 & 3 mm


ASME Classification Of Filler Wire

SS Filler Wire:

SFA-5.9, ER 308, 308L, 316, 316L, 347, 309

LAS Filler Wire:

SFA 5.28, ER 70S A1, ER 80S B2, ER90S D2,

ER 80S Ni2

CS Filler Wire:

SFA- 5.18 , ER 70S2 C = 0.07%, Mn = 0.9% – 1.4%, Si = 0.4 – 0.7%, P = 0.025%, S = 0.035%


Dos & Don'ts In GTAW

• Always Connect Electrode – Ve

• Keep Always Flow Meter Vertical

• Check & Confirm Argon Purity

• Clean Groove & Filler wire With Acetone

• Grind Tungsten Tip to Point

• Don’t Strike Arc With Electrode + Ve

• Don’t strike Arc Without Argon Flow

• Don’t Strike Arc By touching Tungsten Rod

• Don’t Touch Weld Pool With Tungsten Rod

• Don’t Lift and break Arc

Dos Don’ts



• Break The Arc Only By Pedal Switch

• Lift The Torch only After 5 Sec Of Arc Break.

• Ensure Pre Purging & Post Purging of 5Sec

• Ensure Argon Flow & Water Circulation To Torch

• When Arc is Stopped Don’t Lift Torch immediately.

• Don’t Weld With Blend Tungsten Rod

• Don’t Weld With Argon Leaking Torch

• Don’t Weld Without Water Circulation

Dos Don’ts



• Provide Back Purging For Single Sided Full Penetration Welds

• Use N2 or Argon as Back Purging Gas For CS & LAS

• Use Argon As Back Purging Gas For SS & Non Ferrous Alloys

• Don’t Weld Single Sided Full Penetration Welds Without Back Purging

• Don’t Use N2 As Back Purging Gas For Non Ferrous Alloys

• Don’t Empty Ag Cylinders Fully.

Dos Don’ts


Defects In GTAW

1. Cracks 2. Lack Of Fusion

3. Porosity 4. Undercut

5.Lack Of Penetration 6. Excess Penetration

7.Overlap 8. Suck Back

9. Under Flush 10. Burn Through

11. Tungsten Inclusion 11.Stray Arcing


Crack

Cause Remedy

1) Wrong Consumable

2) Wrong Procedure

3) Improper Preheat

4) Inadequate Thickness In Root Pass

1) Use Right Filler Wire

2) Qualify Procedure

3) Preheat Uniformly

4) Add More Filler Wire in root Pass

crack


Lack Of Fusion

Cause Remedy

1) Inadequate Current

2) Wrong Torch angle

3) Improper bead placement

1) Use Right Current

2) Train /Qualify welder

3) Train/Qualify Welder

Lack Of Fusion


PorosityCause Remedy

1) Impure Argon Gas

2) Argon Leak Within Torch

3) Defective Filler Wire

4) Wet surface of BM

5) Rusted / Pitted Filler wire

6) Improper Flow Of Argon

1) Replace Argon Cylinder

2) Replace Leaking Torch

3) Replace Filler Wire

4) Clean & Warm BM

5) Clean Filler Wire

6) Provide Gas lens

Porosity . .


Undercut

Cause Remedy

1) Excess Current

2) Excess Voltage

3) Improper Torch angle

1) Reduce the Current

2) Reduce Arc length

3) Train & Qualify the Welder

Under cut


Lack Of Penetration*Cause Remedy

1) Excess Root Face

2) Inadequate Root opening

3) Over size Filler Wire

4) Wrong Direction of Arc


6) Improper weaving technique

1) Reduce Root Face

2) Increase Root Opening

3) Reduce Filler Wire size

4) Train / Qualify Welder


6) Train & Qualify Welder

LOP

* Applicable to SSFPW


Excess Penetration*Cause Remedy

1)Excess root opening

2) Excess Current

3) Inadequate root face

4) Excess Weaving

5) Wrong Direction Of Arc

1) Reduce root gap

2) Reduce Current

3) Increase Root face

4) Train Welder

5) Train Welder

Excess Penetration



Overlap

Cause Remedy

1) Wrong Direction Of Arc


3) Excess Filler Wire

1) Train & Qualify Welder

2) Increase Current

3) Reduce Filler Metal

Overlap


Suck Back*Cause Remedy

1) Excess weaving in root

2) Excess Current

3) Inadequate root face

4) Wrong Electrode angle

1) Reduce weaving

2) Reduce Current

3) Increase root face


Suck Back

* Applicable to SSFPW in 4G, 3G & 2G


Under flushCause Remedy

1) Inadequate weld beads in

final layer

2) Inadequate understanding on

weld reinforcement

3) Wrong selection of filler wire

size

1) Weld some more beads

in final layer

2) Train / Qualify welder


Under flush


Burn through*Cause Remedy

1) Excess Current

2) Excess Root opening

3) Inadequate Root face

4) Improper weaving


2) Reduce root opening



Burn trough

*Applicable to root pass


Tungsten InclusionCause Remedy

1) Ineffective HF

2) Improper Starting of Arc

3) Tungsten Tip Comes in

Contact With Weld

1) Rectify HF Unit

2) Never Touch Weld

With Tungsten Rod


Tungsten Inclusion


Stray Arcing

Cause Remedy

1) HF Not In Operation

2) Inadequate Skill of Welder

1) Rectify HF Unit

2) Train the Welder

Arc Strikes

What Is GMAW ?• A Fusion Welding Process – Semi Automatic• Arc Between Consumable Electrode &Work• Arc Generated by Electric Energy From a Rectifier

/ Thyrester / Inverter• Filler Metal As Electrode Continuously fed From

Layer Wound Spool. • Filler Wire Driven to Arc By Wire Feeder through

Welding Torch• Arc & Molten Pool Shielded by Inert Gas through

Torch / Nozzle

Gas Metal Arc Welding• MIG – Shielding Gas Ar / Ar + O2 / Ar + Co2

• MAG – Shielding Gas Co2

• FCAW – Shielding Gas Co2 With Flux cored Wire

Note:- Addition of 1 – 5% of O2 or 5 – 10% of Co2 in Ar. increases wetting action of molten metal

Power Source For MIG / MAG

• Inverter- DC

• Thyrister – DC



Characteristic Of GMAW Power Source

Constant V / Linear Characteristic

Appx. Horizontal Curve

V1V2

A1 A2A

V

Current & Polarity

DC- Electrode +Ve

Stable Arc

Smooth Metal TransferRelatively Low SpatterGood Weld Bead Characteristics

DC- Electrode – ve, Seldom UsedAC- Commercially Not In use

Accessories Of GMAW

• Power Source• Wire Feed Unit• Shielding Gas Cylinder, Pressure gauges/

Regulator, Flow meter (Heater For Co2 )

• Welding Torch • Water Cooling System (For Water cooled Torch)• Earthing Cable With Clamp

Tools For GMAW • Head Screen With DIN 13 / 14 Dark Glass• Hand Wire Brush / Grinder With Wire Wheel • Cutting Pliers• Hand Gloves • Chipping Hammer / Chisel & hammer • Spanner Set• Cylinder Key• Anti-spatter Spray• Earthing Cable With Clamp

GMAW Torch

Torch HandleSpring Conduit

JobArc

Gas Cup

Shielding Gas

Filler Wire - ElectrodeNozzle Tip

On / Off Switch

Equipment & Accessories

+ –

Wire Inside Spring Lining

Flow Meter

Welding Torch Wire Feeder

Shielding Gas Cylinder

Pressure Regulator

Argon / Co2 Shielding

Power Source

With Inductance

Work

Arc–

Solenoid Valve

Copper Cup

Wire Spool

Electrode / Wire

Shielding GasHeater

(Only For Co2)

Contact Tip

Switch

Torch With Cable Max. 3Mtr


GAS METAL ARC WELDING (GMAW)ALMOST REPLACING SMAW, FASTER, INTRODUCED IN 1940’S, DCRP GENERALLY EMPLOYED, CONTINUOUS WIRE FEEDING MODES OF METAL TRANSFER1

SPRAY

2

SHORT CIRCUIT

3

GLOBULAR

4

BURIED ARC

5

PULSED ARC

HIGH VOLTAGE

HIGH AMPERAGE

(WIRE FEED)

VERY LOW VOLTAGE

MODERATE

WIRE FEED

BETWEEN 1&2

UNIQUE IN GMAW,

HIGHER WIRE FEED

PULSING BETWEEN

MODES

DROPLETS-

DEEP Penet.

FOR THICK

COOLEST MODE, LEAST Penetration.

FOR CARBON STEELS, 6 TO 12 MM

HIGH SPPED, LOW SPATTER, DEEP Penet., FOR MS AND SS

NO GUN OSCILLATION

ARGON ST.

(FOR NARROW)

75 % Ar + 25% CO2

90%Ar + 7.5% CO2 +2.5% He

FOR THICK TO THIN, DISSIMILAR


Metal Transfer In GMAW

Dip/Short Circuiting Globular Spray

CS Solid Wire 1.2 mm Φ

Above230A

24 – 35 V

120 to 250A

16 – 24 V

Up to 120A

14 – 22V

Co2 or Ar Co2 or Ar Only Ar / Ar+O2

Function Of Shielding Gas In GMAW

• Prevents Air contamination of weld Pool• Prevents Contamination During Metal

Transfer• Increases fluidity of molten metal• Minimizes the spatter generation• Helps in even & uniform bead finish


Gas Metal Arc WeldingEffects of Shielding gas

1. Filler Metal Deposition Rate and Efficiency

2. Spatter Control and Post weld Cleaning

3. Bead Profile and Overwelding

4. Bead Penetration, Potential for Burn-through

5. Out-of-position Weldability

6. Welding Fume Generation Rates

7. Weld Metal Mechanical Properties


GASES• PUROPOSE- 1.TO SHIELD MOLTEN PUDDLE FROM CONTAMINATION 2.CREATE A SMOOTH ELECTRICAL CONDUCTION PATH FOR ELECTRONS IN ARC• SOME GASES (ARGON)MAKE SMOOTH PATH, BUT SOME

RESISTS (CO2) PATH.• STRAIGHT ARGON FOR NARROW BEADS• 98% Ar+ 2 OXYGEN FOR SPRAY, • He FOR COPPER, THICK Al (WITH Ar).• 75 % Ar + 25% CO2 FOR SHORT CIRCUIT., • STRAIGHT CO2 ECONOMICAL, BUT SPATTERING.

• 90%Ar + 7.5% CO2 +2.5% He FOR BURIED ARC, SS.• 90% Ar + 10% He FOR AUTOMATIC V, WIRE FEED SYSTEMS

• A CONSTANT VOLTAGE POWER SOURCE USED.

Shielding Gases For GMAW

• MIG: Argon Or Helium For SS, CS, LAS & Non-ferrous Mt & Al

• MIG: Ar + 1 to 2 % O2, Wire With Add. Mn & Si For SS, CS, LAS & Non-ferrous Mt & Al

• MIG: Ar + 5 to 20 % Co2 Wire With Add. Mn & Si For SS, CS, LAS & Non-ferrous Mt & Al

• MAG: Co2 With Solid Wire For CS & LAS

• FCAW: Co2 With Flux Cored Wire For CS, LAS & SS Overlay


Different types of shielding gases

Pure Gases

• Argon

• Helium

• Carbon Dioxide


Argon.

Argon is a monatomic (single-atom) gas commonly used for GTAW on all materials and GMAW on nonferrous metals.

Argon is chemically inert, making it suitable for welding on reactive or refractory metals.

Low thermal conductivity and ionization potential, properties that result in a low transfer of heat to the outer areas of the arc.

Helium.

• Helium also is a monatomic, inert gas, most commonly used for GTAW on nonferrous materials.

• In contrast to argon, helium has a high conductivity and ionization potential, which gives the opposite effects.

• Helium provides a wide profile ,good wetting on the edges of the bead, and higher heat input than pure argon.

• The high ionization potential can create difficulty in arc starting unless high-frequency or capacitive arc starting is used for GTAW


Carbon dioxide

CO2 usually is used for GMAW short-circuit transfer and FCAW.

The CO2 will disassociate into CO and O2 at the temperatures encountered in the arc. This creates

the potential for oxidizing of the base metal

Recombination of the CO/O2 gives wide penetration profile at the surface of the weld, while the low ionization potential and thermal conductivity create a hot area at the center of the arc column.

For GMAW applications, pure CO2 is unable to produce spray transfer, and it promotes globular

transfer, which causes spatter.


The traditional pure argon penetration profile is deep and narrow.

The helium penetration profile is wider than argon’s

The CO2 penetration profile is marked by good width and depth


Other Gases Used in Mixtures

•Oxygen• Oxygen creates a very wide and shallow penetration profile, with high heat input at the surface of the work.

• Spray transfer is facilitated, as well as wetting at the toe of the weld.

• Oxygen/argon mixes exhibit a characteristic "nailhead" penetration profile with GMAW carbon steel, Oxygen also is used in trimixes with CO2 and argon,

•Hydrogen• Active shielding gas -at concentrations of less than 10 %

• Hydrogen is primarily used with austenitic stainless steels

• Hydrogen is not suitable for ferritic or martensitic steels because of cracking issues.

• Hydrogen also may be used in higher percentages (30 percent to 40 percent) in plasma cutting operations on stainless steel to increase capacity and reduce slag.


Gas Mixtures

Different combinations of welding processes and materials require different combinations of welding gases.

The graphic on the left shows good shielding gas coverage. The graphic on the right shows what happens when air is allowed to seep into and contaminate the

gas.


ARGON/CO2

•CO2 content varies from 5 percent to 25 percent.

•Used for spray transfer on heavy materials or when low heat input and shallow penetration are desired for thin materials.

•High CO2 content promotes short-circuit transfer and can provide additional cleaning action and deep penetration in heavy materials

ARGON/O2

•Oxygen percentage usually is between 2 and 5.

•Typically used in spray transfer on fairly clean materials

ARGON/O2/CO2

•Work well in both spray transfer and short-circuit mode and may be used on many material thickness.

•Oxygen tends to promote spray transfer at low voltages, while the CO2 aids penetration.


The argon/CO2 penetration profile can be adjusted by the amount of CO2 contained in the gas mixture

The argon/O2 penetration profile is deeper and not as wide as that of the argon/CO2 profile.


+ POINTS OF GMAW• HIGH WELDING SPEED• NO NEED TO CHANGE ELECTRODES (ONLY WIRE SPOOL

IN GMAW)• HAZ SMALL• VERY LITTLE SMOKE AND VERY LIGHT SiO2 SLAG(CALLED

GLASS SLAG)• LEAST DISTORTION• EASE OF OPERATION (QUICK LEARNING)• GUN MANIPULATION EASIER• MOST FLEXIBLE PROCESS- VERSATILE• VERY FEW MACHINE ADJUSTMENTS FOR THICK TO THIN

CHANGE• MS, MCS, TOOL STEEL GRADES, SS, COPPER, Al, Mg

WELDED• FCAW, SAW, ESW- OTER FORMS OF GMAW


ABOUT THE POWER SOURCE

• DCRP, DCSP, ACHF USED

• ELECTRODES OF 0.25 mm TO 6.4 mm FOR DIFFERENT APPLICATIONS

• ELECTRODES CODED, WITH COLOR STRIPS

• BEST FOR ALUMINIUM, SINCE OXIDE FILM BREAKS BY PENETRATION

Frequent cleaning and shaping of electrode tip to be done


WELDING TECHNIQUE

GMAW

SHIELDING GAS Argon (95%) +O2(5%)

PLATE THICKNESS (mm)

7

TRAILING SHIELD Argon (99.99%)

GROOVE GEOMETRY SINGLE ‘V’ 45 ANGLE

ROOT GAP (mm) 2

ROOT FACE (mm) 1

CURRENT (A) 300-310

VOLTAGE (V) 30-31

SPEED (mm/sec) 5.8

HEAT INPUT (KJ/mm) 1.5-1.6

NO. OF PASSES 1

o

45 1 . 0 mm

2 mm


Welding Hull of Ships


For increasing productivity in Fabrication by GMAW Process different shielding

gases used


Typical Welding Parameters used Typical Welding Parameters used

Gases Used Code Current (Amp)

Voltage (Volt)

Welding Speed (Meter/Min)

Heat Input

(KJ/mm)

95%Ar-5%O2 A 200-210 29 0.374 0.95

B 250-260 30 0.375 1.22

C 300-310 30 0.37 1.5

80%Ar-20%CO2 D 200-210 29 0.374 1.0

E 250-260 29 0.374 1.2

F 300-310 30 0.375 1.5

Pure CO2 G 200-220 30 0.374 1.01

H 250-260 30 0.375 1.28

I 300-320 31 0.375 1.6

Gas Flow Rate : 18-20 lpm

Electrode Stick Out : 15mm

Polarity : DCEP


Sample code Heat Input

(KJ/mm)

Yield Strehgth

(N/mm2)

% Elongation Avg. Impact

Toughness (J)

NG-A-5O2 1.0 604 23 48

NG-B-5O2 1.22 666 21 38

NG-C-5O2 1.5 775 20 33

NG-D-20CO2 1.0 716 15 30

NG-E-20CO2 1.2 627 18 33

NG-F-20CO2 1.5 663 14 14

Experimental results of a typical study:Experimental results of a typical study:


Weld Bead MorphologyWeld Bead Morphology

95%Ar-5%O2

Deep

Penetration *

80%Ar-20%CO2

PureCO2

Narrow Penetration

Bead in V Groove Weld Bead on Plate Weld

Bead in V Groove Weld Bead on Plate Weld

*When used for single pass welding of plates of thickness 6-7 mm


2

3

4

5

6

7

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6

Heat Input (KJ/mm)

Pene

tratio

n (m

m)

80 Ar / 20 CO2

Pure CO2

95 Ar / 5 O2

Effect of shielding gas on weld penetration Effect of shielding gas on weld penetration


60

65

70

75

80

85

90

95

100

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6

Heat Input (KJ/mm)

Dep

ositi

on E

ffici

ency

(%)

80 Ar / 20 CO2

Pure CO2

95 Ar / 5 O2

Effect of shielding gas on deposition efficiencyEffect of shielding gas on deposition efficiency


2

3

4

5

6

7

8

9

10

0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6

Heat Input (KJ/mm)

Dep

ositi

on R

ate

(Kg/

hr)

80 Ar / 20 CO2

Pure CO2

95 Ar / 5 O2

Effect of shielding gas on Deposition rateEffect of shielding gas on Deposition rate

Types Of Wire Feeding In GMAW

• Push Type– Wire fed in to The torch by Pushing through Flexible

Conduit From A Remote Spool

• Pull Type– Feed Rollers Mounted on The Torch Handle Pulls the

Wire From A Remote spool

• Self Contained– Wire Feeder & The Spool On the Torch

ASME Classification For CS GMAW Wire

• SFA 5.18 : - CS Solid Wire

ER 70 S – 2, ER 70 S – 3

ER 70 S – 6, ER 70 S – 7

• SFA 5.20 :- CS Flux Cored Wire

E 71 T-1, E 71 T-2 ( Co2 Gas )

E 71 T-1M, E 71 T-2M ( Ar + Co2 Mix)

GMAW CS Wire

• Generally Copper Coated– Prevents Oxidation / rusting in Storage– Promotes Electric Conductivity in Arcing

• Available In Solid & Flux Cored– Size in mm 0.8, 1, 1.2, 1.6, 2, 2.4, 3

• Manganese & Silicon ( Mn 1 – 2 %, Si Max 1%)– Act As Deoxidizing Agents– Eliminate Porosity– Increase Wetting Of Molten Pool

Metal Transfer In MIG

• Short-Circuiting / Dip Transfer

• Globular Transfer

• Spray Transfer

Metal Transfer In MIG

Dip/Short Circuiting Globular Spray

CS Solid Wire 1.2 mm Φ

Above230A

24 – 35 V

120 to 250A

16 – 24 V

Up to 120A

14 – 22V

Co2 or Ar Co2 or Ar Only Ar / Ar+O2

Short-Circuiting / Dip Transfer• Wire In Contact With Molten Pool 20 to 200 times per Second• Operates in Low Amps & Volts – Less Deposition• Best Suitable for Out of Position Welding• Suitable for Welding Thin Sheets• Relatively Large opening of Root Can be Welded• Less Distortion• Best Suitable for Tacking in Set up • Prone to Get Lack of Fusion in Between Beads

Globular Transfer

• Metal transferred in droplets of Size grater than wire diameter

• Operates in Moderate Amps & Volts – Better Deposition

• Common in Co2 Flux Cored and Solid Wire

• Suitable for General purpose Welding

Spray Transfer• Metal transferred in multiples of small droplets• 100 to 1000 Droplets per Second• Metal Spray Axially Directed• Electrode Tip Remains pointed• Applicable Only With Inert Gas Shielding –

Not With Co2

• Operates in Higher Amps & Volts – Higher Deposition Rate

• Not Suitable for Welding in Out of Position.• Suitable for Welding Deep Grooves

Pulsed Spray Welding

• Power Source Provides Two different Current Levels“Background” and “Peak”at regular interval

• “Background” & “Peak” are above and below the Average Current

• Best Suitable for Full Penetration Open Root Pass Welding

• Good Control on Bead Shape and Finish

Synergic Pulse GMAW

• Parameters of Pulsed Current (Frequency, Amplitude, Duration, Background Current) Related to Wire feed Rate

• One Droplet detaches with each pulse• An Electronic Control unit synchronizes wire feed

Rate with Pulse Parameters • Best Suitable for Most Critical Full Penetration

Open Root Pass Welding• Good Control on Open Root penetration, Bead

Shape and Finish

GMAW Process Variables• Current• Voltage• Travel Speed• Stick Out / Electrode Extension • Electrode Inclination • Electrode Size• Shielding Gas & Flow Rate• Welding Position

Parameter For 1.2 ф FC Wire• Current – 200 to 240 A

• Voltage – 22-24

• Travel Speed 150 to 250 mm / min

• Stick Out / Electrode Extension – 15 to 20 mm

• Electrode Inclination – Back Hand Technique

• Shielding Gas – Co2, 12 L/Min

Parameter For 1.2 ф Solid Wire• Current – 180 to 220 A

• Voltage – 20-22

• Travel Speed 150 to 200 mm / min

• Stick Out / Electrode Extension – 10 to 20 mm

• Electrode Inclination – Back Hand Technique

• Shielding Gas – Co2 – 12 L/Min

Results In Change Of Parameters• Increase In Current

– More deposition, More Penetration, More BM Fusion• Increase In Voltage

– More Weld Bead Width, Less Penetration, Less Reinforcement, Excess Spatter

• Increase In Travel Speed– Decrease in Penetration, Decrease in Bead Width,

• Decrease In Gas Flow rate– Results In porosity

• Long Stick Out / Electrode Extension– Excess Weld Deposit With Less Arc intensity, Poor Bead Finish,

Shallow Penetration

Common Defects In GMAW

1. Porosity 2. Spatters

3. Lack Of Fusion 4. Under Cut

5. Over Lap 6. Slag

7. Crack 8. Lack Of Penetration

9. Burn Through 10. Convex Bead

11. Unstable Arc 12. Wire Stubbing

Porosity

Cause Remedy1) Less Mn & Si In Wire

2) Rusted / Unclean BM / Groove

3) Rusted wire

4) Inadequate Shielding Gas

1) Use High Mn & Si Wire

2) Clean & warm the BM

3) Replace the Wire

4) Check & Correct Flow Rate

Porosity . .

SpattersCause Remedy

1) Low Voltage

2) Inadequate Inductance

3) Rusted BM surface

4) Rusted Core wire

5) Quality Of Gas

1) Increase Voltage

2) Increase Inductance

3) Clean BM surface

4) Replace By Rust Free wire

5) Change Over To Ar + Co2

Spatters• • •

Lack Of FusionCause Remedy


2) Inadequate Voltage

3) Wrong Polarity

4) Slow Travel Speed

5) Excessive Oxide On Joint


2) Use Right Voltage

3) Connect Ele. + Ve

4) Increase Travel speed

5) Clean Weld Joint

Lack Of Fusion

Undercut

Cause Remedy

1) Excess Voltage

2) Excess Current

3) Improper Torch angle

4) Excess Travel Speed

1) Reduce Voltage

2) Reduce Current

3) Train & Qualify the Welder

4) Reduce Travel Speed

Under cut

Overlap

Cause Remedy

1) Too Long Stick Out

2) Inadequate Voltage

1) Reduce Stick Out

2) Increase the Voltage

Overlap

SlagCause Remedy

1) Inadequate Cleaning




1) Clean each bead




Slag

Crack

Cause Remedy

1) Incorrect Wire Chemistry 2) Too Small Weld Bead

3) Improper Preheat

4) Excessive Restrain

1) Use Right Wire

2) Increase wire Feed

3) Preheat Uniformly

4) Post heating or ISR

crack

Lack Of Penetration*Cause Remedy

1) Too Narrow Groove Angle

2) Inadequate Root opening

3) Too Low Welding current


5) Puddle Roll In Front Of Arc

6) Long Stick Out

1) Widen The Groove

2) Increase Root Opening

3) Increase Current


5) Correct Torch Angle

6) Reduce Stick Out

LOP


Burn through*Cause Remedy

1) Excess Current

2) Excess Root opening

3) Inadequate Root face

4) Too Low Travel Speed

5) Quality Of Gas


2) Reduce root opening


4) Increase Speed

5) Use Ar + Co2

Burn trough*Applicable to root pass

Convex Bead FinishCause Remedy

1) Low Current

2) Low Voltage

3) Low Travel Speed

4) Low Inductance

5) Too Narrow Groove

1) Increase Current

2) Increase Voltage

3) Increase Travel Speed

4) Increase Inductance

5) Increase Groove Width

Uneven bead finish

Unstable arc

Cause Remedy

1) Improper Wire Feed

2) Improper Gas Flow

3) Twisted Torch Conduit

1) Check Wire Feeder

2) Check Flow Meter

3) Straighten Torch Cab

Wire Stubbing

Cause Remedy

1) Too Low Voltage

2) Too High Inductance

3) Excess Slope

4) Too Long Stick Out

1) Increase Voltage

2) Reduce Inductance

3) Adjust Slope

4) Reduce Stick Out

Important Terminology used in Critical Welding

• Preheating

• Post Heating or Dehydrogenation

• Intermediate Stress leaving

• Inter pass Temperature

• Post Weld Heat Treatment

What Is Preheating?

• Heating the base metal along the weld joint to a predetermined minimum temperature immediately before starting the weld.

• Heating by Oxy fuel flame or electric resistant coil• Heating from opposite side of welding wherever

possible• Temperature to be verified by thermo chalks prior to

starting the weld

Why Preheating?

• Preheating eliminates possible cracking of weld and HAZ• Applicable to

Hardenable low alloy steels of all thickness

Carbon steels of thickness above 25 mm.

Restrained welds of all thickness

• Preheating temperature vary from 75°C to 200°C depending on hardenability of material, thickness & joint restrain

How does Preheating Eliminate Crack?

• Preheating promotes slow cooling of weld and HAZ

• Slow cooling softens or prevents hardening of weld and HAZ

• Soft material not prone to crack even in restrained condition

What Is Post Heating?

• Raising the pre heating temperature of the weld joint to a predetermined temperature range (250° C to 350° C) for a minimum period of time (3 Hrs) before the weld cools down to room temperature.

• Post heating performed when welding is completed or terminated any time in between.

• Heating by Oxy fuel flame or electric resistant coil• Heating from opposite side of welding wherever possible• Temperature verified by thermo chalks during the period

Why Post Heating?

• Post heating eliminates possible delayed cracking of weld and HAZ

• Applicable to

Thicker hardenable low alloy steels

Restrained hardenable welds of all thickness• Post heating temperature and duration depends on

hardenability of material, thickness & joint restrain

How does Post Heating Eliminate Crack?

• SMAW introduces hydrogen in weld metal• Entrapped hydrogen in weld metal induces

delayed cracks unless removed before cooling to room temperature

• Retaining the weld at a higher temperature for a longer duration allows the hydrogen to come out of weld

What Is Intermediate Stress Relieving? • Heat treating a subassembly in a furnace to a

predetermined cycle immediately on completion of critical restrained weld joint / joints without allowing the welds to go down the pre heat temperature. Rate of heating, Soaking temperature, Soaking time and rate of cooling depends on material quality and thickness

• Applicable to

Highly restrained air hardenable material

Why Intermediate Stress Relieving?

• Restrained welds in air hardenable steel highly prone to crack on cooling to room temperature.

• Cracks due to entrapped hydrogen and built in stress

• Intermediate stress relieving relieves built in stresses and entrapped hydrogen making the joint free from crack prone

What Is Inter- Pass Temperature?

• The temperature of a previously layed weld bead immediately before depositing the next bead over it

• Temperature to be verified by thermo chalk prior to starting next bead

• Applicable to

Stainless Steel

Carbon Steel & LAS with minimum impact

Why Inter Pass Temperature?

• Control on inter pass temperature avoids over heating, there by

Refines the weld metal with fine grains

Improves the notch toughness properties

Minimize the loss of alloying elements in welds

Reduces the distortion

What Is Post Weld Heat Treatment?

• Heat treating an assembly on completion of all applicable welding, in an enclosed furnace with controlled heating/cooling rate and soaking at a specific temperature for a specific time.

• Rate of heating, Soaking temperature, Soaking time and rate of cooling depends on material quality and thickness

• Applicable to

All type of CS & LAS

Why Post Weld Heat Treatment?

• Welded joints retain internal stresses within the structure

• HAZ of welds remains invariably hardened

• Post Weld Heat Treatment relieves internal stresses and softens HAZ. This reduces the cracking tendency of the equipment in service


Weldability

• The weldability of a material refers to its ability to be welded. Many metals and thermoplastics can be welded, but some are easier to weld than others. It greatly influences weld quality and is an important factor in choosing which welding process to use.



• Steels• The weldability of steels is inversely

proportional to a property known as the hardenability of the steel, which measures the ease of forming martensite during heat treatment. The hardenability of steel depends on its chemical composition, with greater quantities of carbon and other alloying elements resulting in a higher hardenability and thus a lower weldability. In order to be able to judge alloys made up of many distinct materials, a measure known as the equivalent carbon content is used to compare the relative weldabilities of different alloys by comparing their properties to a plain carbon steel.


http://en.wikipedia.org/wiki/Hardenability


http://en.wikipedia.org/wiki/Alloy

http://en.wikipedia.org/wiki/Equivalent_carbon_content

http://en.wikipedia.org/wiki/Carbon_steel


• The effect on weldability of elements like chromium and vanadium, while not as great as carbon, is more significant than that of copper and nickel, for example. As the equivalent carbon content rises, the weldability of the alloy decreases. The disadvantage to using plain carbon and low-alloy steels is their lower strength—there is a trade-off between material strength and weldability. High strength, low-alloy steels were developed especially for welding applications during the 1970s, and these generally easy to weld materials have good strength, making them ideal for many welding applications.

http://en.wikipedia.org/wiki/Chromium

http://en.wikipedia.org/wiki/Vanadium

http://en.wikipedia.org/wiki/Carbon



http://en.wikipedia.org/wiki/HSLA_Steel

http://en.wikipedia.org/wiki/1970s


• Stainless steels, because of their high chromium content, tend to behave differently with respect to weldability than other steels. Austenitic grades of stainless steels tend to be the most weldable, but they are especially susceptible to distortion due to their high coefficient of thermal expansion. Some alloys of this type are prone to cracking and reduced corrosion resistance as well. Hot cracking is possible if the amount of ferrite in the weld is not controlled—to alleviate the problem, an electrode is used that deposits a weld metal containing a small amount of ferrite. Other types of stainless steels, such as ferritic and martensitic stainless steels, are not as easily welded, and must often be preheated and welded with special electrodes.


http://en.wikipedia.org/wiki/Ferrite


• Aluminum• The weldability of aluminum alloys varies significantly,

depending on the chemical composition of the alloy used. Aluminum alloys are susceptible to hot cracking, and to combat the problem, welders increase the welding speed to lower the heat input. Preheating reduces the temperature gradient across the weld zone and thus helps reduce hot cracking, but it can reduce the mechanical properties of the base material and should not be used when the base material is restrained. The design of the joint can be changed as well, and a more compatible filler alloy can be selected to decrease the likelihood of hot cracking. Aluminum alloys should also be cleaned prior to welding, with the goal of removing all oxides, oils, and loose particles from the surface to be welded. This is especially important because of an aluminum weld's susceptibility to porosity due to hydrogen and dross due to oxygen.


http://en.wikipedia.org/wiki/Oxide

http://en.wikipedia.org/wiki/Oil

http://en.wikipedia.org/wiki/Porosity

http://en.wikipedia.org/wiki/Hydrogen

http://en.wikipedia.org/wiki/Dross

http://en.wikipedia.org/wiki/Oxygen


• References• Lincoln Electric (1994). The Procedure Handbook

of Arc Welding. Cleveland: Lincoln Electric. ISBN 9994925822.

• Residual stresses are stresses that remain after the original cause of the stresses has been removed. Residual stresses occur for a variety of reasons, including inelastic deformations and heat treatment. Heat from welding may cause localized expansion, which is taken up during welding by either the molten metal or the placement of parts being welded. When the finished weldment cools, some areas cool and contract more than others, leaving residual stresses. Castings may also have large residual stresses due to uneven cooling.

http://en.wikipedia.org/wiki/1994

http://en.wikipedia.org/wiki/Cleveland

http://en.wikipedia.org/w/index.php?title=Special:Booksources&isbn=9994925822

http://en.wikipedia.org/wiki/Stress_%28physics%29



• While un-controlled residual stresses are undesirable, many designs rely on them. For example, toughened glass and pre-stressed concrete depend on them to prevent brittle failure. Similarly, a gradient in martensite formation leaves residual stress in some swords with particularly hard edges (notably the katana), which can prevent the opening of edge cracks. In certain types of gun barrels made with two tubes forced together, the inner tube is compressed while the outer tube stretches, preventing cracks from opening in the rifling when the gun is fired. Parts are often heated or dunked in liquid nitrogen to aid assembly.

• Press fits are the most common intentional use of residual stress. Automotive wheel studs, for example are pressed into holes on the wheel hub. The holes are smaller than the studs, requiring force to drive the studs into place. The residual stresses fasten the parts together. Nails are another example.

http://en.wikipedia.org/wiki/Glass#Toughened_glass

http://en.wikipedia.org/wiki/Pre-stressed_concrete

http://en.wikipedia.org/wiki/Brittle


http://en.wikipedia.org/wiki/Hardness

http://en.wikipedia.org/wiki/Katana

http://en.wikipedia.org/wiki/Nitrogen

http://en.wikipedia.org/wiki/Nail



Resistance WeldingCommonly used resistance welding processes:• Resistance Spot Welding (RSW), • Resistance Seam Welding (RSEW),&• Resistance Projection Welding (PW) or

(RPW)• Resistance welding uses the application of

electric current and mechanical pressure to create a weld between two pieces of metal. Weld electrodes conduct the electric current to the two pieces of metal as they are forged together.


• The welding cycle must first develop sufficient heat to raise a small volume of metal to the molten state. This metal then cools while under pressure until it has adequate strength to hold the parts together. The current density and pressure must be sufficient to produce a weld nugget, but not so high as to expel molten metal from the weld zone.

• High Frequency Resistance Welding (HFRW) Percussion Welding (PEW) and Stud Welding (SW), too.


Resistance Welding Benefits

• High speed welding • Easily automated • Suitable for high rate

production

• Economical

Weld Nugget

Electrode

Electrode

HAZ

H = I2 R t K

K- energy losses through radiation & conduction

•resistances of the electrodes

•electrode- w/p contact resistance

•resistance of the individual parts to be welded

•w/p-w/p contact resistance (maintained high)


• Resistance Welding Limitations

• Initial equipment costs

• Lower tensile and fatigue strengths

• Lap joints add weight and material

Common Resistance Welding Concerns

•Optimize welding process variables.

•Evaluate current welding parameters and techniques.

•And thus eliminate common welding problems and discontinuities - such as


Resistance Welding Problems and Discontinuities

• Cracks • Electrode deposit on work • Porosity or cavities • Pin holes • Deep electrode indentation • Improper weld penetration • Surface appearance • Weld size • Irregular shaped welds


RESISTANCE SPOT WELDING

• AIR OPERATED ROCKER ARM SPOT WELDING MACHINE


RESISTANCE SPOT WELDING

ELECTRODE DESIGNS FOR EASY ACCESS INTO COMPONENTS


RESISTANCE SEAM WELDING


RESISTANCE PROJECTION WELDING


HIGH FREQUENCY BUTT WELDING OF TUBES


FLASH WELDING

FOR SOLID RODS & TUBES DESIGN GUIDELINES

GOODPOOR


RESISTANCE STUD WELDING




UNDERWATER WELDING





DISTORTION• Welding involves highly localized heating of the

metal being joined together. • The temperature distribution in the weldment is

nonuniform. • Normally, the weld metal and the heat affected zone

(HAZ) are at temperatures substantially above that of the unaffected base metal.

• Upon cooling, the weld pool solidifies and shrinks, exerting stresses on the surrounding weld metal and HAZ.

• If the stresses produced from thermal expansion and contraction exceed the yield strength of the parent metal, localized plastic deformation of the metal occurs.

• Plastic deformation results in lasting change in the component dimensions and distorts the structure. This causes distortion of weldments.


Types of distortion

• Longitudinal shrinkage • Transverse shrinkage • Angular distortion • Bowing • Buckling • Twisting


Effects of expansion and contraction


CONTROLLING DISTORTION


HEAT AFFECTED ZONE


Factors affecting distortion

• If a component were uniformly heated and cooled distortion would be minimized. However, welding locally heats a component and the adjacent cold metal restrains the heated material. This generates stresses greater than yield stress causing permanent distortion of the component. Some of the factors affecting the distortion are:

1. Amount of restraint 2. Welding procedure 3. Parent metal properties 4. Weld joint design 5. Part fit up


• Restraint - to minimize distortion. Components welded without any external restraint are free to move or distort in response to stresses from welding. It is not unusual for many shops to clamp or restrain components to be welded in some manner to prevent movement and distortion. This restraint does result in higher residual stresses in the components.

• Welding procedure impacts the amount of distortion primarily due to the amount of the heat input produced. The welder has little control on the heat input specified in a welding procedure. This does not prevent the welder from trying to minimize distortion. While the welder needs to provide adequate weld metal, the welder should not needlessly increase the total weld metal volume added to a weldment.


• Parent metal properties, which have an effect on distortion, are coefficient of thermal expansion and specific heat of the material. The coefficient of thermal expansion of the metal affects the degree of thermal expansion and contraction and the associated stresses that result from the welding process. This in turn determines the amount of distortion in a component.

• Weld joint design will effect the amount of distortion in a weldment. Both butt and fillet joints may experience distortion. However, distortion is easier to minimize in butt joints.

• Part fit up should be consistent to fabricate foreseeable and uniform shrinkage. Weld joints should be adequately and consistently tacked to minimize movement between the parts being joined by welding.


Welding Discontinuities

Some examples of welding discontinuities are shown below. Evaluation of the discontinuity will determine if the

discontinuity is a defect or an acceptable condition

Incomplete Fusion - A weld discontinuity in which fusion did not occur between weld metal and fusion faces or adjoining weld beads.


Undercut - A groove melted into the base metal adjacent to the weld toe or weld root and left unfilled by weld metal.

Overlap - The protrusion of weld metal beyond the weld toe or weld root.


Underfill - A condition in which the weld face or root surface extends below the adjacent surface of the base metal.

Incomplete Joint Penetration - A joint root condition in a groove weld in which weld metal does not extend through the joint thickness

•Partial joint penetration groove welds are commonly specified in lowly loaded structures. However, incomplete joint penetration when a full penetration joint is required, as depicted above, would be cause for rejection. A fix for an incomplete penetration joint would be to back gouge and weld from the other side. Another acceptable partial penetration joint is shown below.


Partial penetration joint on the left without discontinuities is an acceptable condition.

Appropriate engineering decisions need to be applied to determine what type of joint should be specified for a given application.


Several different representations of weld Cracking


Representation of a convex fillet weld without discontinuities


SOLID STATE PROCESSES• Joining without fusion of work pieces• No liquid (molten ) phase present in joint• Principle: If two clean surfaces are brought into

atomic contact with each other - made with sufficient pressure -(in the absence of oxide film and other contaminents) they form bonds and produce strong joint

• To improve strength, heat and some movement of mating surfaces by plastic deformation employed.

Eg: USW, Friction Welding (FRW)


FORGE WELDING (FOW)

• Both elevated temperature and pressure applied to form strong bond between members

• Components heated and pressed/ hammered with tools, dies or rollers

• Local plastic deformation at interface breaks up the oxide films – improves bond strength.

• Not for high load bearing applications.


COLD WELDING (CW)• Pressure applied to work pieces either through dies

or rolls• One (or both) of the mating parts must be ductile• Interface cleaned prior to welding- brushing etc.

Roll

Rolling metal

Bare metal


Explosive welding• Solid state bonding process• Joining by the cohesive force between atoms of two intimate

contact surfaces High pressure waves- thousands of MPa created-• To weld dissimilar metals, thick to thin, high difference in

Melting Point metals.• Not a costly process• Extremely large surfaces can be joined (2m X 10 m)• Welding of heat treated metals without affecting the process• No HAZ• Incompatible metals joined(thin foils to heavy plates)

severe deformation needed for joining.


• Principle: Explosive Impulse used to produce

extremely high normal pressure and a slight shear or sliding pressure ( uses a detonator for this)

Two properly laid metal surfaces brought together with high relative velocity at high pressure and with proper orientation

Large amount of plastic interaction between surfaces results. TWO WAYS


(1)Contact technique

(2) Impact technique

• (1). Plastic interaction by positioning explosive charge to deliver shock waves at an oblique angle to parts to be welded- Less frequently used.

• (2). Two pieces explosively projected towards each other.

• Impact with high velocity (200 – 400 m/s)


•Plastic interaction by positioning explosive charge to deliver shock waves at an oblique angle to parts to be welded- Less frequently

used.

(1)Contact technique


(2) Impact technique

Two pieces explosively projected towards each other. Impact with high velocity (200 – 400 m/s)


• Detonation velocity approx. 7000 m/s in the detonation front.

• Produces pressure at interface 7000 to 70,000 atms. Parts driven at an angle Velocity of impact and angle of collapse selected. Joining as s result of intense plastic flow at the surface called “surface jetting”

• For good joint, surface to be free from contaminants

• Pressure sufficient to bring surfaces within interatomic distances of each other [ In a range of speed and angle of impact, a high velocity metal jet forms. Removes surface contamination. Speed, angle(10 to 100) of detonation important]


• Bond as strong as the weaker of the two obtained. 100 % efficient joint, (eg. In sheet forming in aerospace industries)

• At the interface, microhardness slightly increased. (because of plastic deformation and strain hardening- a very thin hardness zone)


• Titanium cladding common• Others- Ni, SS(50 mm), tantalum, carbon steels,

for heat exchangers, tubes, pressure vessels, etc.• No change in chemical and physical properties

of parent metal• But, not for brittle alloys. Metal must possess

some ductility. • [Quantity of charge, detonation velocity, and

deformation characteristics of flyer plate decide the weld]

• Also spot welding by small charge. Handy explosive spot welding sets available (for 10mm to 12 mm spots)


• Minus points: Severe deformation needed for joining (minimum 40 to 60%), as welding is by pressure.


THERMIT WELDING • THERMITE- based on Therm, meaning heat• Involves exothermic reactions between metal oxides and metallic reducing agents• Heat of reaction used for welding.•

• Fine particles of iron oxide, aluminium oxide, iron & aluminium

• Reactions are:

(3/4) Fe3 O4 + 2 Al --- (9/4) Fe + Al2O3 + Heat

3 FeO + 2 Al --- 3 Fe + Al2O3 + Heat

Fe2O3 + 2Al --- 2Fe + Al2O3+ Heat

THERMIT WELDING


Thermit Welding


Slide 13 of 18

THERMIT WELDING


• Mixture is non explosive. Produces temperature of 32000 C within a minute

• Practically about 22000- 24000 C. Other materials to impart special properties added. Applying a Mg fuse of special compounds of peroxides, chlorates/ chromates.

• Welding copper, brasses, bronzes and copper alloys to steel using oxides of copper, nickel, aluminium, manganese – temperatures of 50000 C obtained


THERMIT WELDING OF RAILS

PLASMA WELDING


• Plasma is commonly known as fourth state of matter after solid, liquid and gas. This is an extremely hot substance which consists of free electrons, positive ions, atoms and molecules. It conducts electricity.How it works:By positioning the electrode within the body of the torch, the plasma arc can be separated from the shielding gas envelope. Plasma is then forced through a fine-bore copper nozzle which constricts the arc. There are three operating modes which can be produced by varying bore diameter and plasma gas flow rate:•Microplasma: 0.1 to 15A.•Medium current: 15 to 200A.•Keyhole plasma: over 100A.The plasma arc is usually operated with a DC, drooping characteristic power source. Because its unique operating features are results of the special torch arrangement and separate plasma and shielding gas flows, a plasma control console can be added on to a normal TIG power source. Full plasma systems are also available. The plasma arc is not stabilised with sine wave AC. Arc reignition is difficult when there is a long electrode to workpiece distance and the plasma is constricted, extreme heating of the electrode during the positive half-cycle causes balling of the tip which can disturb arc stability. Special-purpose switched DC power sources are available. By misbalancing the waveform to reduce the duration of electrode positive polarity, the electrode is kept passably cool to maintain a pointed tip and achieve arc stability.





• ElectrodeThe electrode used for the plasma process is tungsten-2%thoria and the plasma nozzle is copper. The electrode tip diameter is not as critical as for TIG and should be maintained at around 30-60 degrees. The plasma nozzle bore diameter is critical and too small a bore diameter for the current level and plasma gas flow rate will lead to excessive nozzle erosion or even melting. Large bore diameter should be carefully used for the operating current level.Because too large a bore diameter, may give problems with arc stability and maintaining a keyhole.Plasma and shielding gasesThe normal combination of gases is argon for the plasma gas, with argon plus 2 to 5% hydrogen for the shielding gas. Helium can be used for plasma gas but because it is hotter this reduces the current rating of the nozzle. Helium's lower mass can also make the keyhole mode more difficult.


http://www.airproducts.com/sitemap.htm

http://www.airproducts.com/search/search.asp

http://www.airproducts.com/tmm/tellmemore.asp


• Applications:Microplasma welding:Microplasma was traditionally used for welding thin sheets (down to 0.1 mm thickness), and wire and mesh sections. The needle-like stiff arc minimises arc wander and distortion. Although the alike TIG arc is widely used, the newer transistorised (TIG) power sources can produce a very stable arc at low current levels.Medium current welding:When used in the melt mode this is a substitute to normal TIG.The advantages are:1-Deeper penetration (from higher plasma gas flow).2-Greater tolerance to surface contamination including coatings (the electrode is within the body of the torch).The major disadvantage lies in the bulkiness of the torch, making manual welding more difficult. In mechanised welding, greater attention must be paid to maintenance of the torch to ensure consistent performance.


• Keyhole welding:This has several advantages which can be exploited: deep penetration and high welding speeds. Compared with the TIG arc, it can penetrate plate thicknesses up to l0mm, but when welding using a single pass technique, it is more usual to limit the thickness to 6mm. The normal methods is to use the keyhole mode with filler to ensure smooth weld bead profile (with no undercut). For thicknesses up to 15mm, a vee joint preparation is used with a 6mm root face. A two-pass technique is employed and here, the first pass is autogenous with the second pass being made in melt mode with filler wire addition.


• As the welding parameters, plasma gas flow rate and filler wire addition (into the keyhole) must be carefully balanced to maintain the keyhole and weld pool stability, this technique is only suitable for mechanised welding. Although it can be used for positional welding, usually with current pulsing, it is normally applied in high speed welding of thicker sheet material (over 3 mm) in the flat position. When pipe welding, the slope-out of current and plasma gas flow must be carefully controlled to close the keyhole without leaving a hole.


Gas

MIG/TIGWelding

Plasma ArcWelding

LaserWelding

LaserCutting

PlasmaCutting

Oxy-FuelCutting

ThermalSpraying

Acetylene X X

Air X X X

Alumaxx Plus X

Argon X X X X X X

Argon/hydrogen TIG X X

Carbon dioxide MAG X X Cooling

Carbon monoxide X

Ferromaxx Plus MAG

Ferromax 15 MAG

Ferromaxx 7 MAG

Helium TIG X X X

Hydrogen X

Inomaxx Plus MAG

Inomaxx 2 MAG

Inomaxx TIG TIG X

Nitrogen X X X

Nitrogen/hydrogen mixes

X

Oxygen X X X

Propane X X

Propylene X X


The process is simple to operate- Can be used manually or in an automated manner.

Possible to spray a wide range of metals, alloys and metal matrix composites (MMCs) in wire form. A limited range of cermet coatings (with tungsten carbide) can also be sprayed in cored wire form, where the hard ceramic phase is packed into a metal sheath as a fine powder.The combination of high arc temperature (6000 K) and particle velocities in excess of 100 m.sec-1 gives arc sprayed coatings superior bond strengths and lower porosity levels when compared with flame sprayed coatings. However, the use of compressed air for droplet atomization and propulsion gives rise to high coating oxide content.

Arc SprayingArc spraying is the highest productivity thermal spraying process. A DC electric arc is struck between two continuous consumable wire electrodes which form the spray material. Compressed gas (usually air) atomises the molten spray material into fine droplets and propels them towards the substrate


• Because of the high temperature and high thermal energy of the plasma jet, materials with high melting points can be sprayed.

• Plasma spraying produces a high quality coating by a combination of a high temperature, high energy heat source, a relatively inert spraying medium and high particle velocities,

typically 200–300 m.sec-1. • However, inevitably some air

becomes entrained in the spray stream and some oxidation of the spray material may occur. The surrounding atmosphere also cools and slows the spray stream.

•Uses a DC electric arc to generate a stream of high temperature ionised plasma gas, which acts as the spraying heat source. •The arc is struck between two non-consumable electrodes, a tungsten cathode and a copper anode within the torch. •The torch is fed with a continuous flow of inert gas, which is ionised by the DC arc, and is compressed and accelerated by the torch nozzle so that it issues from the torch as a high velocity (in excess of 2000 m/sec), high temperature (12000–16000 K) plasma jet. •The coating material, in powder form, is carried in an inert gas stream into the plasma jet where it is heated and propelled towards the substrate.

PLASMA SPRAYING PROCESS


Applications

• Plasma spraying is widely applied in the production of high quality sprayed coatings.

• Spraying of seal ring grooves in the compressor area of aeroengine turbines with tungsten carbide/cobalt to resist fretting wear.

• Spraying of zirconia-based thermal barrier coatings (TBCs) onto turbine combustion chambers.

• Spraying of wear resistant alumina and chromium oxide ceramic onto printing rolls for subsequent laser and diamond engraving/etching.

• Spraying of molybdenum alloys onto diesel engine piston rings.


HIGH VELOCITY OXYFUEL SPRAYING

This differs from conventional flame spraying in that the combustion process is internal, and the gas flow fates and delivery pressures are much higher than those in the atmospheric burning flame spraying processes. The combination of high fuel gas and oxygen flow rates and high pressure in the combustion chamber leads to the generation of a supersonic flame with characteristic shock diamonds. Flame speeds of 2000ms-1 and particle velocities of 600–800ms-1 are claimed by HVOF equipment suppliers. A range of gaseous fuels is currently used, including propylene, propane, hydrogen and acetylene.

The most recent addition to the thermal spraying family, high velocity oxyfuel spraying (HVOF SPRAYING) has become established as an alternative to the proprietary, detonation (D-GUN) flame spraying and the lower velocity, air plasma spraying processes for depositing wear resistant tungsten carbide-cobalt coatings.


• Although similar in principle, potentially significant details, such as powder feed position, gas flow rates and oxygen to fuel ratio, are apparent between each system.

• The HVOF process produces exceptionally high quality cermet coatings (e.g., WC-Co), but it is now also used to produce coatings of metals, alloys and ceramics. Not all HVOF systems are capable of producing coatings from higher melting point materials, e.g., refractory metals and ceramics. The capability of the gun is dependent upon the range of fuel gases used and the combustion chamber design.

• A liquid fuel (kerosene) HVOF system, has just been launched, which is capable of much higher deposition rates than the conventional gas-fuelled units.


HVOF spraying is a very recent process development, yet the high quality of the coatings produced at competitive cost has already seen its introduction in a number of very significant industries. Potential applications overlap with plasma and D-gun spraying, particularly for WC-Co coatings.

Tungsten carbide-cobalt coatings for fretting wear resistance on aeroengine turbine components.

Wear resistant cobalt alloys onto fluid control valve seating areas.

Tungsten carbide-cobalt coatings on gate valves.

Various coatings for printing rolls, including copper, alumina, chromia.

NiCrBSi coatings (unfused) for glass plungers.

NiCr coatings for high temperature oxidation/corrosion resistance.

Alumina and alumina-titania dielectric coatings.

Biocompatible hydroxylapatite coatings for prostheses.

Applications


Schematic of High Velocity Oxyfuel (HVOF) Spraying System

Process

Particle Velocity

(m/s) Adhesion (MPa)Oxide Content

(%) Porosity (%)Deposition Rate

(kg/hr)

Typical Deposit Thickness (mm)

Flame 40 <8 10–15 10–15 1–10 0.2–10

Arc 100 10–30 10–20 5–10 6–60 0.2–10

Plasma 200–300 20–70 1–3 1–8 1–5 0.2–2

HVOF 600–800 >70 1–2 1–2 1–5


Comparison of Thermal Spraying Processes and Coating Characteristics

Process Particle Velocity (m/s) Adhesion (MPa) Oxide Content (%) Porosity (%)Deposition Rate

(kg/hr)

Typical Deposit Thickness

(mm)

Flame 40 <8 10–15 10–15 1–10 0.2–10

Arc 100 10–30 10–20 5–10 6–60 0.2–10

Plasma 200–300 20–70 1–3 1–8 1–5 0.2–2

HVOF 600–800 >70 1–2 1–2 1–5


Thermal Spraying Gases

Process Fuels that can be used Other gases

HVOF Acetylene, hydrogen, propylene, propane, or liquid kerosene depending on material type

Oxygen and argon

Arc spraying Normally compressed air but can use nitrogen or argon

Flame spraying Mainly acetylene, but sometimes propane depending on material

Oxygen

Plasma spraying Argon and hydrogen


Electro Slag Welding


Slide 14 of 18

ELECTROGAS WELDING

ELECTRON BEAM WELDING •The electron beam gun has a tungsten filament which is heated, freeing electrons.

•The electrons are accelerated from the source with high voltage potential between a cathode and anode.

•The stream of electrons then pass through a hole in the anode. The beam is directed by magnetic forces of focusing and deflecting coils. This beam is directed out of the gun column and strikes the workpiece.

•The potential energy of the electrons is transferred to heat upon impact of the workpiece and cuts a perfect hole at the weld joint. Molten metal fills in behind the beam, creating a deep finished weld.


• Electron Beam Welding (EBW) is a unique way of delivering large amounts of concentrated thermal energy to materials being welded. It became viable, as a production process, in the late 1950's. At that time, it was used mainly in the aerospace and nuclear industries. Since then, it has become the welding technique with the widest range of applications. This has resulted from the ability to use the very high energy density of the beam to weld parts ranging in sizes from very delicate small components using just a few watts of power, to welding steel at a thickness of 10 to 12 inches with 100 Kilowatts or more. However, even today most of the applications are less than 1/2" in thickness, and cover a wide variety of metals and even dissimilar metal joints


Slide 16 of 18

ELECTRON BEAM WELDING

http://www.staff.ncl.ac.uk/s.j.bull/mmm373/WELD/sld001.htm




http://www.staff.ncl.ac.uk/s.j.bull/mmm373/WELD/index.htm

http://www.staff.ncl.ac.uk/s.j.bull

http://www.staff.ncl.ac.uk/s.j.bull/mmm373/WELD/tsld016.htm









• The electron beam stream and workpiece are manipulated by means of precise, computer driven controls, within a vacuum welding chamber, therefore eliminating oxidation, contamination.


• How an Electron Beam Machine WorksThe EB system is composed of an electron beam gun, a power supply, control system, motion equipment and vacuum welding chamber. Fusion of base metals eliminates the need for filler metals. The vacuum requirement for operation of the electron beam equipment eliminates the need for shielding gases and fluxes.


Slide 15 of 18

ELECTRON BEAM WELDING

















• Two welding modes are used in the (EBW):1-Conductance mode:Mainly applicable to thin materials, heating of the weld joint to melting temperature is quickly generated at or below the materials surface followed by thermal conductance throughout the joint for complete or partial penetration. The resulting weld is very narrow for two reasons:a- It is produced by a focused beam spot with energy densities concentrated into a .010 to.030 area.b- The high energy density allows for quick travel speeds allowing the weld to occur so fast that the adjacent base metal does not absorb the excess heat therefore giving the E.B. process it's distinct minimal heat affected zone.2-Keyhole mode:It is employed when deep penetration is a requirement. This is possible since the concentrated energy and velocity of the electrons of the focused beam are capable of subsurface penetration. The subsurface penetration causes the rapid vaporization of the material thus causing a hole to be drilled through the material. In the hole cavity the rapid vaporization and sputtering causes a pressure to develop thereby suspending the liquidus material against the cavity walls. As the hole is advanced along the weld joint by motion of the workpiece the molten layer flows around the beam energy to fill the hole and coalesce to produce a fusion weld. The hole and trailing solidifying metal resemble the shape of an old fashion keyhole.Both the conductance and keyhole welding modes share physical features such as narrow welds and minimal heat affected zone .The basic difference is that a keyhole weld is a full penetration weld and a conductance weld usually carries a molten puddle and penetrates by virtue of conduction of thermal energy.


Electron Beam Welding

• Electron Beam Welding joins ferrous metals, light metals, precious metals, and alloys, to themselves or each other.• Multi-axis EB control• High ratio of depth-to-width• Maximum penetration with minimal distortion• Exceptional weld strength• Ability to weld components up to 10 feet in diameter• High precision and repeatability with virtually 0% scrap• Versatility from .002" depth to 3.00" depth of penetration


Electron Beam Welding Facts

• Electron Beam Welding Advantages• Maximum amount of weld penetration with the least amount of heat input reduces distortion• Electron beam welding often reduces the need for secondary operations• Repeatability is achieved through electrical control systems• A cleaner, stronger and homogeneous weld is produced in a vacuum• The electron beam machine's vacuum environment eliminates atmospheric contaminates in the weld• Exotic alloys and dissimilar materials can be welded• Extreme precision due to CNC programming and magnification of operator viewing• Electron beam welding frequently yields a 0% scrap rate• The electron beam process can be used for salvage and repair of new and used components


Electron Beam Welding Speeds/Depth of Penetration


• Electron Beam Welding Limitations• The necessity of an electron beam welding vacuum chamber limits the size of the workpiece — EBTEC's maximum chamber size is 11' 4" wide x 9' 2" high x 12' deep

Electron Beam Welding Speeds/Depth of Penetration


LASER BEAM WELDING(LBW)

• LASER- Light Amplification by Stimulated Emission of Radiation

• Focusing of narrow monochromatic light into extremely concentrated beams (0.001 mm even)

• Used to weld difficult to weld materials, hard to access areas, extremely small components, In medical field to weld detached retinas back into place

• Laser Beam- coherent Laser production- complex process.


The LASER, an acronym for "Light

Amplification by Stimulated Emission

of Radiation," is a device that produces

a concentrated, coherent beam of

light by stimulating molecular or

electronic transitions to lower energy

levels, causing the emission of photons.


Al2O3 + 0.05% Chromium • solid state RubyLaser- Neon flash tube emits light into

specially cut ruby crystals- absorbs light -electrons of chromium atoms get stimulated-

• Increase in stimulation ---- electrons increase from normal(ground) orbit to an exited orbit. More energy input- energy absorbed exceeds thermal energy- no longer to heat energy.

• Electrons drop back to intermediate orbit- emits PHOTONS (light) called spontaneous emission

• With continued emission, released photons stimulate other exited electrons to release photons- called stimulated emission

• Causes exited electrons to emit photons of same wave length.


• Power intensities > 10 kw/cm2

• No physical contact between work and welding equipment

• 2 mirrors- coherent light reflected back and forth, becomes dense, penetrates partially reflective mirror, focused to the exact point

• Very little loss of beam energy• Solid state, liquid, semiconductor and gas lasers used.• Solid state uses light energy to stimulate electrons

Ruby, Neodymium, YAG• Gas lasers use electrical charge to stimulate electrons

Gas lasers- higher wattage outputs. Used for thicker sections - CO2, N2, He

• Liquid- nitrobenzene; Gas- based on gallium arsenide


Laser Welding Facts• Laser Welding Advantages

• Processes high alloy metals without difficulty• Can be used in open air• Can be transmitted over long distances with a minimal loss of power• Narrow heat affected zone• Low total thermal input• Welds dissimilar metals• No filler metals necessary• No secondary finishing necessary• Extremely accurate• Welds high alloy metals without difficulty

• CO2 Laser Welding Speeds


• The solid-state laser utilizes a single crystal rod with parallel, flat ends. Both ends have reflective surfaces. A high-intensity light source, or flash tube surrounds the crystal. When power is supplied by the PFN (pulse-forming network), an intense pulse of light (photons) will be released through one end of the crystal rod. The light being released is of single wavelength, thus allowing for minimum divergence


• One hundred percent of the laser light will be reflected off the rear mirror and thirty to fifty percent will pass through the front mirror, continuing on through the shutter assembly to the angled mirror and down through the focusing lens to the workpiece.

• The laser light beam is coherent and has a high energy content. When focused on a surface, laser light creates the heat used for welding, cutting and drilling.

• The workpiece and the laser beam are manipulated by means of robotics. The laser beam can be adjusted to varying sizes and heat intensity from .004 to .040 inches. The smaller size is used for cutting, drilling and welding and the larger, for heat treating


Laser Welding Limitations• Rapid cooling rate may cause cracking in certain metals• High capital cost• Optical surfaces easily damaged• High maintenance cost


Slide 17 of 18

LASER WELDING


Slide 18 of 18

LASER WELDING


Laser beam cutting• Along with beam, oxygen used to help

cutting. Ar, He, N, CO2 also for steel, alloys etc.

Two ways to weld1. Work piece rotated or moved past beam2. Many pulses of laser (10 times/sec)used.

Narrow HAZ., speeds of 40 mm/sec to 1.5 m/sec Cooling system to remove the heat- gas and liquid cooling used


• Klyston tubes (glass to metal sealing), capacitor bank, triggering device, flash tube, focusing lens, etc. in the setup.

• Cathode of molybdenum, tantalum or titanium used.


1987Laser research begins a unique method for depositing complex metal alloys (Laser Powder Fusion).

2002

From Linde Gas in Germany, a Diode laser using process gases and "active-gas components" is investigated to enhance the "key-holing" effects for laser welding. The process gas, Argon-CO2, increases the welding speed and in the case of a diode laser, will support the transition of heat conductivity welding to a deep welding, i.e., 'key-holing'. Adding active gas changes the direction of the metal flow within a weld pool and produces narrower, high-quality weld. CO2 Lasers are used to weld polymers. The Edison Welding Institute is using through-transmission lasers in the 230-980 nm range to readily form welded joints. Using silicon carbides embedded in the surfaces of the polymer, the laser is capable of melting the material leaving a near invisible joint line.

Soldering and Brazing•Soldering and Brazing are joining

processes where parts are joined without melting the base

metals.

•Soldering filler metals melt below 450 °C.

•Brazing filler metals melt above 450 °C. (De)soldering a contact from a wire

•Soldering is commonly used for electrical connection or mechanical joints, but brazing is only used for mechanical joints due to the high temperatures involved


Soldering

• A method of joining metal parts using an alloy of low melting point (solder) below 450 °C (800 °F).

• Heat is applied to the metal parts, and the alloy metal is pressed against the joint, melts, and is drawn into the joint by capillary action and around the materials to be joined by 'wetting action'.

• After the metal cools, the resulting joints are not as strong as the base metal, but have adequate strength, electrical conductivity, and water-tightness for many uses.


Soldering and Brazing Benefits

• Economical for complex assemblies

• Joints require little or no finishing

• Excellent for joining dissimilar metals

• Little distortion, low residual stresses

• Metallurgical bond is formed

• Sound electrical component connections


Soldering can be done in a number of ways

Including passing parts over a bulk container of melted solder, using an infrared lamp, or by using a point source such as an electric soldering iron, a brazing torch, or a hot-air soldering tool.

A flux is usually used to assist in the joining process. Flux can be manufactured as part of the solder in single or multi-

core solder, in which case it is contained inside a hollow tube or multiple tubes that are contained inside the strand of solder.

Flux can also be applied separately from the solder, often in the form of a paste.

In some fluxless soldering, a forming gas that is a reducing atmosphere rich in hydrogen can also serve much the same purpose as traditional flux, and provide the benefits of traditional flux in re-flow ovens through which electronic parts placed on a circuit card are transported for a carefully timed period of time.


• One application of soldering is making connections between electronic parts and printed circuit boards.

• Another is in plumbing. Joints in sheet-metal objects such as cans for food, roof flashing, and drain gutters were also traditionally soldered.

• Jewelry and small mechanical parts are often assembled by soldering.

Soldering can also be used as a repair technique to patch a leak in a container or cooking vessel.


• Soldering is distinct from welding in that the base materials to be joined are not melted, though the base metal is dissolved somewhat into the liquid solder much as a sugar cube into coffee - this dissolution process results in the soldered joint's mechanical and electrical strengths.

• A "cold solder joint" with poor properties will result if the base metal is not warm enough to melt the solder and cause this dissolution process to occur.


• Due to the dissolution of the base metals into the solder, solder should never be reused

• Once the solder's capacity to dissolve base metal has been achieved, the solder will not properly bond with the base metal and a cold solder joint with a hard and brittle crystalline appearance will usually be the result.

• It is good practice to remove solder from a joint prior to resoldering - desoldering wicks or vacuum desoldering equipment can be used.

• Desoldering wicks contain plenty of flux that will lift the contamination from the copper trace and any device leads that are present. This will leave a bright, shiny, clean junction to be resoldered.


• The lower melting point of solder means it can be melted away from the base metal, leaving it mostly intact through the outer layer.

• It will be "tinned" with solder.

• Flux will remain which can easily be removed by abrasive or chemical processes.

• This tinned layer will allow solder to flow into a new joint, resulting in a new joint, as well as making the new solder flow very quickly and easily.


Common joining problems and discontinuities:

• No wetting

• Excessive wetting

• Flux entrapment

• Lack of fill (voids, porosity)

• Unsatisfactory surface appearance

• Base metal erosion


• Basic electronic soldering techniques

All solder pads and device terminals must be clean for good wetting and heat transfer.

The soldering iron or gun must be clean, otherwise components may heat up excessively due to poor heat transfer.

The devices must then be mounted on the circuit board properly.

One technique is to elevate the components from the board surface (a few millimeters) to prevent heating of the circuit board during circuit operation.

After device insertion, the excess leads can be cut leaving only a length equal to the radius of the pad.

Plastic mounting clips or holders are used for large devices to reduce mounting stresses.


• Heat sink the leads of sensitive devices to prevent heat damage.

• Apply soldering iron or gun to both terminal lead and copper pad to equally heat both.

• Apply solder to both lead and pad but never directly to the tip of soldering iron or gun.

• Direct contact will cause the molten solder to flow over the gun and not over the joint.

• The moment the solder melts and begins to flow, remove the solder supply immediately.

• Do not remove the iron yet. The remaining solder will then flow over the junction of the lead and pad, assuming both are free of dirt.

• Let the iron heat the junction until the solder flows and then remove the iron tip. This will ensure a good solid junction.

• Remove the iron from the junction and let the junction cool. Solder flux will remain and should be removed.


• Be sure not to move the joint while it is cooling. Doing so will result in a fractured joint.

• Do not blow air onto the joint while it is cooling; Instead, let it cool naturally, which will occur fairly rapidly.

• A good solder joint is smooth and shiny. The lead outline should be clearly visible. Clean the soldering iron tip before you begin on a new joint. It is absolutely important that the iron tip be free of residual flux.

• Excess solder should be removed from the tip. This solder on the tip is known as keeping the tip tinned. It aids in heat transfer to the joint.

• After finishing all of the joints, remove excess flux residue from the board using alcohol, acetone, or other organic solvents.

• Individual joints can be cleaned mechanically. • The flux film fractures easily with a small pick and can

be blown away with canned air. • In solder formulations with water-soluble fluxes,

sometimes pressurized carbon dioxide or distilled water are used to remove flux.


• Traditional solder for electronic joints is a 60/40 Tin/Lead mixture with a rosin based flux that requires solvents to clean the boards of flux.

• Environmental legislation in many countries, and the whole of the European Community area, have led to a change in formulation.

• Water soluble non-rosin based fluxes have been increasingly used since the 1980's so that soldered boards can be cleaned with water or water based cleaners. This eliminates hazardous solvents from the production environment, and effluent.


Lead-free electronic soldering

• More recently environmental legislation has specifically targeted the wide use of lead in the electronics industry. The directives in Europe require many new electronic circuit boards to be lead free by 1st July 2006, mostly in the consumer goods industry, but in some others as well.

• Many new technical challenges have arisen, with this endeavour.


• For instance, traditional lead free solders have a significantly higher melting point than lead based solders, which renders them unsuitable for use with heat sensitive electronic components and their plastic packaging. To overcome this problem solder alloys with a high silver content and no lead have been developed with a melting point slightly lower than traditional solders.

• Not using lead is also extended to components pins and connectors. Most of those pins were using copper frames, and either lead, tin, gold or other finishes. Tin-finishes is the most popular of lead-free finishes. However, this poses nevertheless the question of tin-whiskers. Somehow, the current movement brings the electronic industry backs to the problems solved 40 years ago by adding lead.

• A new classification to help lead-free electronic manufacturers decide what kind of provisions they want to take against whiskers, depending upon their application criticity.


Stained glass soldering• Historically soldering tips were copper, placed in

braziers. One tip was used; when the heat had transferred from the tip to the solder (and depleted the heat reserve) it was placed back in the brazier of charcoal and the next tip was used.

• Currently, electric soldering irons are used; they consist of coil or ceramic heating elements, which retain heat differently, and warm up the mass differently, internal or external rheostats, and different power ratings - which change how long a bead can be run.

• Common solders for stained glass are mixtures of tin and lead, respectively:

• 60/40: melts between 361°-376°F • 50/50: melts between 368°-421°F • 63/37: melts between 355°-365°F • lead-free solder (useful in jewelry, eating containers, and

other environmental uses): melts around 490°F


Pipe/Mechanical soldering

• Sometimes it is necessary to use solders of different melting points in complex jobs, to avoid melting an existing joint while a new joint is made.

• Copper pipes used for drinking water should be soldered with a lead-free solder, which often contains silver. Leaded solder is not allowed for most new construction, though it is easier to create a solid joint with that type of solder. The immediate risks of leaded solder are minimal, since minerals in municipal or well water supplies almost immediately coat the inside of the pipe, but lead will eventually find its way into the environment.

• Tools required for pipe soldering include a blowtorch (typically propane), wire brushes, a suitable solder alloy and an acid paste flux, typically based on zinc chloride. Such fluxes should never be used on electronics or with electronics tools, since they will cause corrosion of the delicate electronic part.


Soldering defects• Soldering defects are solder joints that are not soldered correctly. • These defects may arise when solder temperature is too low. • When the base metals are too cold, the solder will not flow and will "ball

up", without creating the metallurgial bond. • An incorrect solder type (for eg. electronics solder for mechanical

joints or vice versa) will lead to a weak joint. • An incorrect or missing flux can corrode the metals in the joint. Without

flux the joint may not be clean. • A dirty or contaminated joint leads to a weak bond. A lack of solder on a

joint will make the joint fail. • An excess of solder can create a "solder bridge" which is a short

circuit. Movement of metals being soldered before the solder has cooled will make the solder appear grainy and may cause a weakened joint.

• Soldering defects in electronics can lead to short circuits, high resistance in the joint, intermittent connections, components overheating, and damaged circuit boards. Flux left around integrated circuits' leads will lead to inter-lead leakage.

• It is a big issue on surface mount components and causes improper device operation as moisture absorption rises. In mechanical joints defects lead to joint failure and corrosion


Soldering processes

• Wave soldering • Reflow soldering • Infrared soldering • Induction soldering • Ultrasonic soldering • Dip soldering • Furnace soldering • Iron soldering • Resistance soldering • Torch soldering Silver soldering/Brazing


Brazing

• Is similar to soldering but uses higher melting temperature alloys, based on copper, as the filler metal.

• "Hard soldering", or "silver soldering" (performed with high-temperature solder containing up to 40% silver) is also a form of brazing, and involves solders with melting points above 450 C. Even though the term "silver soldering" is more often used than silver brazing, it is technically incorrect.

• Since lead used in traditional solder alloys is toxic, much effort in industry has been directed to adapting soldering techniques to use lead-free alloys for assembly of electronic devices and for potable water supply piping.


Brazing• Brazing is a joining process whereby a non-ferrous filler

metal and an alloy are heated to melting temperature (above 450°C;) and distributed between two or more close-fitting parts by capillary action.

• At its liquid temperature, the molten filler metal interacts with a thin layer of the base metal, cooling to form an exceptionally strong, sealed joint due to grain structure interaction. T

• he brazed joint becomes a sandwich of different layers, each metallurgically linked to each other.

• Common brazements are about 1/3 as strong as the materials they join, because the metals partially dissolve each other at the interface, and usually the grain structure and joint alloy is uncontrolled.

• To create high-strength brazes, sometimes a brazement can be annealed, or cooled at a controlled rate, so that the joint's grain structure and alloying is controlled.


• In Braze Welding or Fillet Brazing, a bead of filler material reinforces the joint. A braze-welded tee joint is shown here.

• In another common specific similar usage, brazing is the use of a bronze or brass filler rod coated with flux, together with an oxyacetylene torch, to join pieces of steel. The American Welding Society prefers to use the term Braze Welding for this process, as capillary attraction is not involved, unlike the prior silver brazing example.

• Braze welding takes place at the melting temperature of the filler (e.g., 870 °C to 980 °C for bronze alloys) which is often considerably lower than the melting point of the base material (e.g., 1600 °C for mild steel).


• A variety of alloys of metals, including silver, tin, zinc, copper and others are used as filler for brazing processes.

• There are specific brazing alloys and fluxes recommended, depending on which metals are to be joined. Metals such as aluminum can be brazed though aluminum requires more skill and special fluxes. It conducts heat much better than steel and is more prone to oxidation.

• Some metals, such as titanium cannot be brazed because they are insoluble with other metals, or have an oxide layer that forms too quickly at intersoluble temperatures.


• Although there is a popular belief that brazing is an inferior substitute for welding, this is false.

• For example, brazing brass has a strength and hardness near that of mild steel, and is much more corrosion-resistant.

• In some applications, brazing is indisputably superior. For example, silver brazing is the customary method of joining high-reliability, controlled-strength corrosion-resistant piping such as a nuclear submarine's seawater coolant pipes.

• Silver brazed parts can also be precisely machined after joining, to hide the presence of the joint to all but the most discerning observers, whereas it is nearly impossible to machine welds having any residual slag present and still hide joints.


• In order to work properly, parts must be closely fitted and the base metals must be exceptionally clean and free of oxides for achieving the highest strengths for brazed joints.

• For capillary action to be effective, joint clearances of 0.002 to 0.006 inch (50 to 150 µm) are recommended. In braze-welding, where a thick bead is deposited, tolerances may be relaxed to 0.5 mm.

• Cleaning of surfaces can be done in several ways. Whichever way is selected, it is vitally important to remove all grease, oils, and paint. For custom jobs and part work, this can often be done with fine sand paper or steel wool.

• In pure brazing (not braze welding), it is vitally important to use sufficiently fine abrasive. Coarse abrasive can lead to deep scoring that interferes with capillary action and final bond strength. Residual particulates from sanding should be thoroughly cleaned from pieces.

• In assembly line work, a "pickling bath" is often used to dissolve oxides chemically. Dilute sulfuric acid is often used. Pickling is also often employed on metals like aluminum that are particularly prone to oxidation.


• In most cases, flux is required to prevent oxides from forming while the metal is heated. The most common fluxes for bronze brazing are borax-based. T

• he flux can be applied in a number of ways. It can be applied as a paste with a brush directly to the parts to be brazed. Commercial pastes can be purchased or made up from powder combined with water (or in some cases, alcohol). Alternatively, brazing rods can be heated and then dipped into dry flux powder to coat them in flux.

• Brazing rods can also be purchased with a coating of flux. In either case, the flux flows into the joint when the rod is applied to the heated joint. Using a special torch head, special flux powders can be blown onto the workpiece using the torch flame itself.

• Excess flux should be removed when the joint is completed. Flux left in the joint can lead to corrosion.

• During the brazing process, flux may char and adhere to the work piece. Often this is removed by quenching the still-hot workpiece in water (to loosen the flux scale), followed by wire brushing the remainder.


• Brazing is different from welding, where even higher temperatures are used, the base material melts and the filler material (if used at all) has the same composition as the base material.

• Given two joints with the same geometry, brazed joints are generally not as strong as welded joints. Careful matching of joint geometry to the forces acting on the joint, however, can often lead to very strong brazed joints.

• The butt joint is the weakest geometry for tensile forces. The lap joint is much stronger, as it resists through shearing action rather than tensile pull and its surface area is much larger. To get joints roughly equivalent to a weld, a general rule of thumb is to make the overlap equal to 3 times the thickness of the pieces of metal being joined.

• The "welding" of cast iron is usually a brazing operation, with a filler rod made chiefly of nickel being used although true welding with cast iron rods is also available.


• Vacuum brazing is another materials joining technique, one that offers extremely clean, superior, flux free braze joints while providing high integrity and strength.

• The process can be expensive because it is performed inside a vacuum chamber vessel however, the advantages are significant. For example, furnace operating temperatures, when using specialized vacuum vessels, can reach temperatures of 2400 °C. Other high temperature vacuum furnaces are available ranging from 1500 °C and up at a much lesser cost.

• Temperature uniformity is maintained on the work piece when heating in a vacuum, greatly reducing residual stresses because of slow heating and cooling cycles.

• This, in turn, can have a significant impact on the thermal and mechanical properties of the material, thus providing unique heat treatment capabilities.

• One such capability is heat treating or age hardening the work piece while performing a metal-joining process, all in a single furnace thermal cycle.

Reference: M.J.Fletcher, “Vacuum Brazing”. Mills and Boon Limited: London, 1971.


Advantages over welding• The lower temperature of brazing and brass-welding is less

likely to distort the work piece or induce thermal stresses. For example, when large iron castings crack, it is almost always impractical to repair them with welding. In order to weld cast-iron without recracking it from thermal stress, the work piece must be hot-soaked to 1600 °F. When a large (more than fifty kilograms (100 lb)) casting cracks in an industrial setting, heat-soaking it for welding is almost always impractical. Often the casting only needs to be watertight, or take mild mechanical stress. Brazing is the premium, preferred repair method in these cases.

• The lower temperature associated with brazing vs. welding can increase joining speed and reduce fuel gas consumption.

• Brazing can be easier for beginners to learn than welding.• For thin workpieces (e.g., sheet metal or thin-walled pipe)

brazing is less likely to result in burn-through.


• Brazing can also be a cheap and effective technique for mass production. Components can be assembled with preformed plugs of filler material positioned at joints and then heated in a furnace or passed through heating stations on an assembly line. The heated filler then flows into the joints by capillary action.

• Braze-welded joints generally have smooth attractive beads that do not require additional grinding or finishing.

• The most common filler materials are gold in colour, but fillers that more closely match the color of the base materials can be used if appearance is important.


Possible problems• A brazing operation may cause defects in the

base metal, especially if it is in stress. This can be due either to the material not being properly annealed before brazing, or to thermal expansion stress during heating.

• An example of this is the silver brazing of copper-nickel alloys, where even moderate stress in the base material causes intergranular penetration by molten filler material during brazing, resulting in cracking at the joint.

• Any flux residues left after brazing must be thoroughly removed; otherwise, severe corrosion may eventually occur.


Brazing processes

• Block Brazing • Diffusion Brazing • Dip Brazing • Exothermic Brazing • Flow Brazing • Furnace Brazing • Induction Brazing • Infrared Brazing • Resistance Brazing • Torch Brazing • Twin Carbon Arc Brazing • Vacuum Brazing

Dr. N. RAMACHANDRAN, NITC1 2 METAL JOINING Even the simplest object is an assembly of components Complex ones - greater number of parts- subassemblies.

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