Joining and Cutting Processes. Engr 241-R11 Fusion Welding Processes Fusion Welding involves heating two materials above their melting temperatures (electrically.

Joining and Cutting Processes

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Fusion Welding Processes• Fusion Welding involves heating two

materials above their melting temperatures (electrically or chemically).

• Filler (rods) metals are added to the weld area during the welding of a joint (supply additional material to weld zone).

Processes

Oxyfuel Gas

ArcConsumed Electrode

Non-Consumed Electrode

Resistance

Solid State

Other – “High Energy”

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Oxyfuel Gas Welding• Process that uses a fuel gas combined

with oxygen to produce a flame• Typically used for structural sheet-metal

fabrication, automotive bodies, and various repair tasks

• Most common fuels used - acetylene (oxyacetylene).

• Manual operation, portable & flexible.Low equipment cost.

Torch

• allows for controlling and mixing gases

Oxygen and fuel gas cylinders

Cylinder Safety

• Caps on when moving

• Secure to truck or wall

• Keep upright (Acetylene) (1/7 Rule)

• Hand over regulator when opening

• Read labels – don’t rely on colors

• Dangers of compressed oxygen

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• Neutral Flame: 1:1 ratio (oxygen vs. fuel).

• Oxidizing Flame: greater oxygen supply (not for steels).

• Reducing (Carburizing) Flame: lower oxygen supply (lower temperature)- brazing.

Oxyfuel Gas Welding- Flame Types

• Neutral - the oxygen and fuel gases combine• oxygen burns up the carbon and the

hydrogen in the fuel gas then releases only heat and harmless gases

• flame temp is 5589 deg F.

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Oxyfuel Gas Welding- Flux

• Retard oxidation of surfaces of the parts being welded

• Dissolves/Removes oxides or other substances

• Stronger joints

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Arc Welding Processes (Consumable Electrode)

• Developed in the mid-1800s

• Heat obtained through electrical energy

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Shielded Metal Arc Welding (SMAW)• Stick welding• 50% of all large-scale industrial

welding operations- portable process.

• Electric arc generated between tip of

coated electrode and the workpiece.

• Electrode coating produces a

shielding gas to protect from oxygen.

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Electric arc between flux covered electrode and base metal

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SMAW (Cont.)• (DCEN) electrode negative

• Workpiece positive, electrode negative.• Sheet metals - shallow penetration, gap

joints.

• (DCEP) electrode positive• Electrode positive, workpiece negative.• Deeper penetration.

• (AC) Alternating current

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• Thick sections, large electrodes at max current.

• Manual, portable, and flexible. AC-DC machines, low cost equipment

SMAW (Cont.)

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Submerged Arc Welding • Weld arc is shielded by a granular flux.• Flux is fed to weld zone by gravity.• Flux covers molten metal which

prevents spatter, sparks, UV radiation, or fumes.

• Flux is recovered.• 4-10 times productivity of SMAW,

automatic, horizontal, low skill,

Submerged Arc

Underwater SMAW• use well insulated electrode holder

and special water proof covered electrodes

• because of rapid cooling - use stringer beads not weaving

• short arc length and DCEN

• poor visibility - use #4 or #8 lens

• communication system

• normally have 80% of the tensile strength and 50 of the ductility of normal welds

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Gas Metal Arc Welding (GMAW)

• Formerly MIG (Metal Inert Gas).

• Argon, helium, carbon dioxide, or mix

(Shield the arc to prevent oxidation).

• Wire fed automatically through nozzle

into arc.

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• Rapid, economical, twice SMAW productivity.

• Most production done today

• Can be automated (robots), low skill, DC, medium cost equipment.

GMAW (Cont.)

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• Same as GMAW but electrode is tubular and filled with flux.

• Automatic feeding of wire (like GMAW).• Uses no external gas source• Fast growing• Thin to thick sections.• Can be automated (robotics), DC, medium

cost.

Flux Cored Arc Welding (FCAW)

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• For welding butt joint edges vertically in one pass.

• Metal deposited between two pieces joined – space enclosed by copper shoes sliding upward with weld

• Also around pipe

• 1/2” to 3” thickness.

• Usually automated, High equipment cost.

• For welding bridges, pipes, tanks, ships

Electrogas Welding

Electrogas - use shielding gas - flux cored wire fed in joint

• arc maintained between electrode and weld

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Electro-slag Welding • Similar to EGW.

• Weld begins at part bottom, molten slag

extinguishes arc.

• Heat then produced continuously by elect.

Resist. of molten slag

• Very thick sections - 2” to 36”.

• High cost of equipment.

Vertical joint - arc started between electrode & bottom

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Electrodes

• Strength of deposited metal.

• Type of coating.

• Size (1/16 to 5/16 in diameter).

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Electrode Classifications

• E6011-A1

• E - arc welding electrode

• 60 – 60,000 psi min. tensile strength

• 1 – next to last digit – position

• 11 – last two digits together, type of covering and

current to be used

• A1 – alloying elements

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• Clay like material.

• Silica binders and powdered materials (Oxides, carbonates, fluorides, metal alloys, cellulose)

Electrode Coatings

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1. Stabilize the arc.

2. Generate a gas shield.

3. Control rate at which the electrode melts.

4. Act as a flux to protect weld (from oxidation).

5. Add alloying elements to joint ie. Protect from becoming brittle).

Electrode Coatings (Cont.)

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Arc Welding (Non-Consumable Electrode)

• Gas Tungsten-Arc Welding (GTAW)

• Plasma Arc Welding (PAW)

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Gas Tungsten-Arc Welding (GTAW)

• Formerly TIG (Tungsten Inert Gas).

• Shielding gas is supplied from an

external source. Argon or helium (high

cost).

• Filler metal is supplied from filler wire.

• Tungsten electrode is not consumed.

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GTAW-NCE (Cont.)

• Good for thin parts, high quality welds. Used for welding aluminum, magnesium, titanium, and refractory metals.

• all positions, AC-DC, medium distortion, portable equipment, medium cost of equipment.

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Plasma Arc Welding

• Argon and helium.

• Arc is hot ionized gas (60,000 degrees °F).

• Transferred- workpiece is part of circuit.

• Non-transferred- Arc between tungsten

electrode and nozzle.• High energy, deep penetration, stable arc,

less thermal distortion, high speed, > ¼” thick material, high skill, medium cost of equipment.

Separate shielding gas protects the welding or cutting process

Resistance Welding Processes

• Spot

• Seam

• Projection

• Stud

• Flash

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1.) Resistance Spot Welding

• Uses pressure and resistivity of parts to form nugget.

• Must be clean but not oxide free

• Used for sheet metal parts

Spot - most common

Two pieces fused with small nugget

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2.) Resistance Seam Welding

• Like spot welding but with rollers.

• Continuous or “roll spot welding”.

two wheeled electrodes travel over metal - current passes through them

can produce intermittent seam of overlapping spots for leak proofing

Seam welding I-Beams

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3.) Resistance Projection Welding

• High elect resistance developed at joint by embossing projections on surfaces to be welded

form projections with dies

current passes through two pieces and is concentrated at bumps

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4.) Resistance Stud welding

• Similar to flash welding

• Threaded rod or hanger welded to flat plate

Stud • no drilling or punching holes in

structure

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5.) Resistance Flash welding

• Also Called “Upset Welding”

• Heat generated from arc as ends of two bars or sheets begin to make contact and develop an electrical resistance at the joint

• After heating occurs and metal softens, an axial force is applied.

generally used to weld the butt ends of two pieces

parts are held in two clamps with ends together

high current passed between them

• high resistance causes small arcs to occur between uneven surfaces

adv: fast and no pre -cleaning of surfaces

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Solid State Welding• Processes in which joining takes place

without fusion of the workpiece, thus no liquid (molten) phase is present in the joint.

• Clean surfaces in atomic contact under pressure and maybe heat (increases diffusion) form bonds and produce a strong joint.

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Solid State Welding

• Cold Welding

• Ultrasonic Welding

• Friction Welding

• Explosion Welding

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1.) Cold Welding

• Surfaces degrease, wire brush, or wiped to remove oxide smudge.

• Roll bonding or hot roll bonding (cladding).

• Processes takes advantage of materials solubility (soft, ductile materials)

Tool can be hand, pneumatic, or hydraulic

• dies must be designed to impose proper pressure for different metals

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2.) Ultrasonic Welding

• Sonotrode oscillates 10-75 kHz• Contact causes plastic deformation.• Temperature is 1/3 to 1/2 of melting

temperature (except in plastics).• Suited for metallic dissimilar metals

and non-metallic materials (thin parts).• Can use roll transducer for seams.

UT spot welds

UT seam welds with lateral drive rollers

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3.) Friction welding• One component rotates at high speed while

other is stationary. Pressure contact causes heating. Part must be stopped fast to avoid shearing weld.

• Wide variety of materials, good joint strength

• Solid bars up to 3” & tubes up to 10”.

• Surface speed 3000ft/min.

• Automated, low skill, high machine cost.

Friction welding

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4.)Explosion Welding • Pressure generated by detonating a

layer of explosive placed over one of the components.

• Causes wavy interface and cold

pressure welding by plastic

deformation.

• Good bond strength.

• Clad dissimilar metals.

“Other” High Energy Welding Processes

• involves concentrating a lot of energy on a small spot

• produces deep narrow welds

• two processes include:

• Electron beam

• LASER beam

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Electron beam welding (EBW)

• Electrons-focused, Vacuum required.

• High quality welds, very expensive

equipment

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Laser Beam Welding (LBW)• Focused laser

• Good quality, little distortion, good strength, ductile, non-porous.

• Automated,

• high equipment cost.

Cutting

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Oxyfuel Gas Cutting

• Cuts mostly by oxidation

• For ferrous metals

• Rough surface, high distortion, can cut underwater.

Cutting

Alignment of torch tip orifices with the kerf

• one orifice should proceed and one should follow the cut

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Plasma Arc Cutting (PAC)

• Highest temperatures

• Rapid cutting, good surface, narrow kerf, popular with Robotics/Flexible automation

Separate shielding gas protects the welding or cutting process

Transferred vs. Non Transferred Arc

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Lasers & Electron Beam Cutting• Accurate

• Wide variety of material

• Good surface, narrow kerf.

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Brazing, Soldering,

Adhesive Bonding, and

Mechanical Fastening

Processes

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Brazing• Characteristics

• filler metal is placed at or between the faying surfaces to be joined.

• temperature is raised to melt the filler metal but not the work piece.

• Above 840 deg F.• surface should be cleaned.

• Flux• prevents oxidation.• removes films from work piece surfaces.

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Soldering Characteristics

• solder fills joint by capillary action.• use of soldering irons, torches, ovens.• lower temperature than brazing. (below

840)• Copper, Silver and Gold are easy to

solder while• Aluminum and stainless steels are not.

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Flux

• Inorganic acids or salts• Zinc ammonium chloride solution-

cleaning.• Remove afterward to avoid corrosion.

• Non-corrosive resin based fluxes• Electrical application.

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Adhesive Classifications• Chemically reactive

• Pressure sensitive

• Hot Melt

• Evaporative or diffusion

• Film and tape

• Delayed tack

• Electrically and thermally conductive

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Adhesives Advantages• Interface gives strength, sealing,

insulation, electrochemical corrosion from dissimilar metals, reduces vibration and noise.

• Distributes load, gives structural integrity (no holes), improved appearance.

• Good for thin, fragile, and porous parts.• Limited distortion because of low

temperature.

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• Service temperatures.• Possibly long bonding time.• Great care in surface preparation.• Difficulty in testing bonded joints

nondestructively.• Limited reliability of adhesively

bonded structures during service life.

Adhesives Limitations

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Mechanical Fastening Characteristics• Ease of manufacture.• Ease of assembly and transportation.• Ease of disassembly, maintenance,

replacement or repair.• Ease on creating designs for movable

joints (hinges, sliding mechanisms, adjustable components, fixtures).

• Lower over all cost of manufacture of the product.

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Mechanical Fastening Methods

• Threaded fastener.

• Rivets.

• Metal stitching or stapling.

• Seaming.

• Crimping.

• Snap-in fasteners.

• Shrink & Press fit.

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Thermoplastic Joining• External heat sources

• Hot air, gasses, elect resist, lasers

• Internal heat sources• Ultrasonic, Friction

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Thermoset Welding

• Threaded or molded inserts

• Mechanical fasteners (self tapping

screws)

• Solvent bonding