Maufacturing Term Paper

TERM PAPER

MANUFACTURING SCIENCE

MEC-104

TOPIC: WELDING TECHNIQUES

USED IN

AUTOMOBILE

INDUSTRY

Submitted to: Submitted by:

Mr Achitanand Dubey Mr Prarit Patyal

Roll. No.:- B 44

Reg.No:- 11003359

DOS:-23-10-2010 Class:-G4001

ACKNOWLEDGEMENT

I am very much indebted to my respected teacher, Mr Achitanand Dubey who helped me and guided me throughout the completion of this topic “WELDING TECHNIQUES USED IN AUTOMOBILE INDUSTRY”.

I even my regards to my dear friends who helped me a lot in gathering the data for this term paper. They also encouraged me to complete my term paper with full determination and dedication.

Last but not the least, I would like to thank my parents, whose blessings are always with me and have inspired me to work harder.

Thanks to everyone related with this piece of work.

INDEX

Introduction

Advantages of welding

Disadvantages of welding

Applications of welding

Welding as a commercial operation

Types of welding processes

1. Fusion welding

2. Solid state welding

Various welding processes used in automobile industry

1. Resistance welding processes

2. Gas metal arc welding

3. Gas tungsten arc welding

4. Electron beam welding

5. Laser beam welding

6. Stud welding

7. Ultrasonic welding

Bibliography

Conclusion

INTRODUCTION

Welding is a process used to join materials, in which two or more parts of a work material are coalesced at their contacting surfaces by a suitable application of heat and/or pressure.

Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the work pieces and then adding a filler material to form a pool of molten material (i.e. the weld pool) that cools to become a strong joint, with pressure or sometimes used in conjunction with heat, or by itself, to produce the weld. The assemblage of parts that are joined by welding is called a weldment.

Many different forms of energy sources can be used for welding like:-

a gas flame an electric arc a laser an electron beam friction ultrasound

Welding can be done in many different environments, including open air, under water and in outer space.

Regardless of location where it is done, welding always remains dangerous, and precautions are taken to avoid

Burns electric shock eye damage poisonous fumes overexposure to ultraviolet light

Although welding is considered a new process, its origins can be traced to ancient times. Around 1000 B.C. the Egyptians and others in the eastern Mediterranean area learned to accomplish forge welding. It was a natural extension of hot forging, which they used to make weapons, tools, and other implements. It was until the 1800s that the technological foundations of modern welding were established and two important discoveries were made, the electric arc and the acetylene gas. By the end of the 18th century, new welding methods were developed like arc welding and resistance welding. And in the 19th century, oxyfuel gas welding method was developed.

ADVANTAGES OF WELDING

Welding provides a permanent joint.

The welded parts become a single entity.

The welding joint can be stronger than the parent materials, if filler material used has strength properties superior to those of the parents, and if proper welding techniques are used.

Welding is usually the most economical way to join components in terms of material usage and fabrication costs.

Welding is not restricted to the factory environment. It can be accomplished “in the field.”

DISADVANTAGES OF WELDING

Most welding operations are performed manually and are expensive in terms of labour cost.

Many welding operations are considered skilled trades and the labour performing these operations may be scarce.

Most of the welding processes are inherently dangerous as they involve the use of high energy.

As welding accomplishes a permanent bond between the components, it does not allow for convenient disassembly.

The welded joint can suffer from certain quality defects. The defects can reduce the strength of the joint.

APPLICATIONS OF WELDING

The principal applications of welding are:-

Construction, such as buildings and bridges

Piping, pressure vessels, boilers and storage tanks

Shipbuilding

Aircraft and aerospace

Automotive and railroad

WELDING AS A COMMERCIAL OPERATION

Owing to its versatility as an assembly technique for commercial products, many welding operations are performed in factories. However, several of the traditional processes, such as arc welding and oxyfuel gas welding, use equipment that can be very easily moved to the work place, so these operations are not only limited to the factories.

Most welding operations are labour intensive. For example, arc welding is usually performed by a skilled worker, called a welder, who manually controls the path or placement of the weld to join individual parts into larger units. In factories, the welder generally works with fitter, who arranges the individual components for the welder.

Because of the hazards of manual welding, and in efforts to increase productivity and improve product quality, various forms of mechanization and automation have been developed. The categories include machine, automatic and robotic welding.

Machine welding can be defined as mechanized welding with equipment that performs the operation under the continuous supervision of the operator.

Automatic welding is capable of performing the operation without adjustment of the controls by a human operator.

In robotic welding, an industrial robot or programmable manipulator is used to automatically control the movement of the welding head relative to the work.

TYPES OF WELDING PROCESSES

Some 50 different types of welding operations have been catalogued by the American welding society. They use various types or combinations of energy to provide the required power. We can divide the welding processes into two major groups:

1. Fusion welding

2. Solid state welding

1. Fusion welding: - Fusion welding processes use heat to melt the base metals. In many fusion welding operations, a filler metal is added to the molten pool to facilitate the process and provide bulk and strength to the welded joint. A fusion welding operation in which no filler material is added is called autogenous weld. This category of welding includes the most widely used welding processes which are given below:-

i. Arc welding

ii. Resistance welding

iii. Oxyfuel gas welding

iv. Electron beam welding

v. Laser beam welding

2. Solid state welding: - It refers to joining process in which coalescence results from application of pressure alone or a combination of heat and pressure. If heat is used, then the temperature is kept below the melting point of the metals being welded. No filler metal is utilized. Some welding processes in this group are as follows:-

i. Diffusion welding

ii. Friction welding

iii. Ultrasonic welding

VARIOUS WELDING PROCESSES USED IN AUTOMOBILE INDUSTRY

1. RESISTANCE WELDING PROCESSES:-

Resistance welding is a technology widely used in manufacturing industry for joining metal sheets and components. The weld is made by conducting a strong current through the metal combination to heat up and finally melt the metals at localized point(s) predetermined by the design of the electrodes and/or the work pieces to be welded. A force is always applied before, during and after the application of current to confine the contact area at the weld interfaces and, in some applications, to forge the work pieces.

Depending on the shape of the work pieces and the form of the electrodes, resistance welding processes can be classified into various processes as described below:-

i. Resistance Spot Welding

Spot welding is a resistance welding process for joining metal sheets by directly applying opposing forces with electrodes with pointed tips. The current and the heat generation are localized by the form of the electrodes. The weld nugget size is usually defined by the electrode tip contact area.

Spot welding is the predominant joining process in automotive industry for assembling the automobile bodies and large components. It is also widely used for manufacturing of furniture and domestic equipment etc.

Rechargeable Spot Welding Machine

Rechargeable spot welding machine is capable of storing energy in the condenser and then flow into the transformer generating a strong current. Short duration of welding produces a better welding effect on low-resistant welding materials such as stainless steel, copper, bronze and aluminium. Rechargeable spot welding machine produces excellent welding outcomes.

Rechargeable spot welding machine

Perhaps the most common application of spot welding is in the automobile manufacturing industry, where it is used almost universally to weld the sheet metal to form a car. Spot welders can also be completely automated, and many of the industrial robots found on assembly lines are spot welders (the other major use for robots being painting).

ii. Resistance Projection Welding

Projection welding is a resistance welding process for joining metal components or sheets with embossments by directly applying opposing forces with electrodes specially designed to fit the shapes of the work pieces. The current and the heat generation are localized by the shape of the work pieces either with their natural shape or with specially designed projection. Large deformation or collapse will occur in the projection part of the work pieces implying high process/machine dynamics.

Projection welding is widely used in electrical, electronics, automotive and construction industries, and manufacturing of sensors, valves and pumps etc.

iii. Resistance Seam Welding

Seam welding is a resistance welding process for joining metal sheets in continuous, often leak tight, seam joints by directly applying opposing forces with electrodes consisting of rotary wheels. The current and the heat generation are localized by the peripheral shapes of the electrode wheels.

Seam welding is mostly applied in manufacturing of containers, radiators and heat exchangers etc.

2. GAS METAL ARC WELDING

Gas metal arc welding (GMAW), sometimes referred to by its subtypes metal inert gas (MIG) welding or metal active gas (MAG) welding, is a semi-automatic or automatic arc welding process in which a continuous and consumable wire electrode and a shielding gas are fed through a welding gun. A constant voltage, direct current power source is most commonly used with GMAW, but constant current systems, as well as alternating current, can be used. There are four primary methods of metal transfer in GMAW, called globular,

short-circuiting, spray, and pulsed-spray, each of which has distinct properties and corresponding advantages and limitations.

Equipment:-

To perform gas metal arc welding, the basic necessary equipment is a welding gun, a wire feed unit, a welding power supply, an electrode wire, and a shielding gas supply.

Welding gun and wire feed unit:-

GMAW torch nozzle cutaway image.

(1) Torch handle, (2) Molded phenolic dielectric (shown in white) and threaded metal nut insert (yellow), (3) Shielding gas diffuser, (4) Contact tip, (5) Nozzle output face

Circuit diagram:-

GMAW Circuit diagram

(1) Welding torch, (2) Work piece, (3) Power source, (4) Wire feed unit, (5) Electrode source, (6) Shielding gas supply.

Operation

GMAW weld area.

(1) Direction of travel, (2) Contact tube, (3) Electrode, (4) Shielding gas, (5) Molten weld metal, (6) Solidified weld metal, (7) Workpiece.

The electrode is fed automatically through the torch. A consistent contact tip-to-work distance (the stick out distance) is important, because a long stickout distance can cause the electrode to overheat and will also waste shielding gas. Stickout distance varies for different GMAW weld processes and applications. For short-circuit transfer, the stickout is generally 1/4 inch to 1/2 inch, for spray transfer the stickout is generally 1/2 inch. The orientation of the gun is also important—it should be held so as to bisect the angle between the workpieces; that is, at 45 degrees for a fillet weld and 90 degrees for welding a flat surface. The travel angle, or lead angle, is the angle of the torch with respect to the direction of travel, and it should generally remain approximately vertical.

3. GAS TUNGSTEN ARC WELDING

Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is an arc welding process that uses a non-consumable 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 plasma.

Operation:-

GTAW weld area

Manual gas tungsten arc welding is often considered the most difficult of all the welding processes commonly used in industry. Because the welder must maintain a short arc length, great care and skill are required to prevent contact between the electrode and the workpiece.

To strike the welding arc, a high frequency generator (similar to a Tesla coil) provides a spark; this spark is a conductive path for the welding current through the shielding gas and allows the arc to be initiated while the electrode and the workpiece are separated, typically about 1.5–3 mm (0.06–0.12 in) apart. This high voltage, high frequency burst can be damaging to some vehicle electrical systems and electronics, because induced voltages on vehicle wiring can also cause small conductive sparks in the vehicle wiring or within semiconductor packaging. Vehicle 12V power may conduct across these ionized paths, driven by the high-current 12V vehicle battery. These currents can be sufficiently destructive as to disable the vehicle; thus the warning to disconnect the vehicle battery power from both +12 and ground before using welding equipment on vehicles.

An alternate way to initiate the arc is the "scratch start". However, scratch starting can cause contamination of the weld and electrode. Some GTAW equipment is capable of a mode called "touch start" or "lift arc"; here the equipment reduces the voltage on the electrode to only a few volts, with a current limit of one or two amps (well below the limit that causes metal to transfer and contamination of the weld or electrode). When the GTAW equipment detects that the electrode has left the surface and a spark is present, it immediately (within microseconds) increases power, converting the spark to a full arc.

Once the arc is struck, the welder moves the torch in a small circle to create a welding pool, the size of which depends on the size of the electrode and the amount of current. While maintaining a constant separation between the electrode and the workpiece, the operator then moves the torch back slightly and tilts it backward about 10–15 degrees from vertical. Filler metal is added manually to the front end of the weld pool as it is needed.

GTAW system setup

4. ELECTRON BEAM WELDING (EBW):-

The qualities of speed and precision make EBW a favoured joining process in a number of automotive applications. Both vacuum and non-vacuum process derivatives have been widely industrially employed. It has helped to develop a large number of automotive applications. In many ways EB welding is well-suited to mass production as it is a non-contact joining technology, with little in the way of moving or wearing parts to worry about. Although the equipment is rarely inexpensive, consumables costs are typically low, making the process extremely cost-effective. Some examples of typical automotive applications are given below;

Gear welding

Both continuous and intermittently loaded gear components are welded via EBW. Of the latter variety, synchromesh rings are welded to gears in their millions. EB machines that perform this task usually have small chambers with rapid pump-downs. They may also employ a pre-evacuation strategy so that unwelded parts are made ready to be welded, and the electron gun is more effectively utilised.

EB welding is often used to make gears that are difficult or impossible to make via normal mass-production machining techniques. This can result in smaller, lighter gears, or it may simply reduce costs. Auto-gearboxes frequently utilise EB welding for the manufacture of gears, planetary gear hubs, and other parts.

Turbochargers

Modern high specific output diesel engines invariably utilise turbocharging as a means of improving power output and fuel consumption figures. At one end of a shaft, a compressor wheel forces the air into the engine; this is driven by a turbine wheel spinning at up to ~200000rpm, propelled by the exhaust gases. This sounds like some form of perpetual motion, but it isn't- it is just one method of achieving forced induction, by which means the overall efficiency of an engine may be increased. The compressor wheel operates at relatively low temperatures, so is normally made of an aluminium alloy. But the turbine wheel sees very high temperatures, and must be made from a heat resistant alloy. Typically this is a Ni base alloy, of a type that until recently would only be found inside a jet engine.

These alloys are inherently expensive, and materials costs are saved here if the wheel can be welded to an inexpensive steel shaft. EB welding is a favoured process here, providing welding speed, integrity, and very low distortion. The narrow angle EB is able to weld in relatively inaccessible locations, even on the largest diameter impellers, unlike competing technologies, e.g. laser welding techniques. EB welding has an excellent track record, having made millions of sound, cost-effective welds in this application.

Typical turbocharger wheel and shaft welding installation Courtesy of CVE

Other applications

Non-Vacuum (NVEB) welding has been used for over thirty years to make a variety of welds at extremely high production rates, typically in thinner section parts. Power outputs of 30kW are readily attained, giving extremely high joint completion rates. In total it is estimated that several billion automotive components have now been NVEB welded.

NVEB is also favoured for high speed welding of automotive structural components.

EB systems have also been deployed for many other automotive applications, including leather perforation, camshaft hardening, etc. There is surely a multitude of other future developments.

5. LASER BEAM WELDING

A robot performs remote fibre laser welding.

Laser beam welding (LBW) is a welding technique used to join multiple pieces of metal through the use of a laser. The beam provides a concentrated heat source, allowing for narrow, deep welds and high welding rates. The process is frequently used in high volume applications, such as in the automotive industry.

LBW is a versatile process, capable of welding carbon steels, HSLA steels, stainless steel, aluminum, and titanium. Due to high cooling rates, cracking is a concern when welding high-carbon steels. The weld quality is high, similar to that of electron beam welding. The speed of welding is proportional to the amount of power supplied but also depends on the type and thickness of the workpieces. The high power capability of gas lasers make them especially suitable for high volume applications. LBW is particularly dominant in the automotive industry.

Some of the advantages of LBW (laser beam welding) in comparison to EBW (electron beam welding) are as follows:

the laser beam can be transmitted through air rather than requiring a vacuum

the process is easily automated with robotic machinery

x-rays are not generated

LBW result in higher quality welds.

A derivative of LBW, laser-hybrid welding, combines the laser of LBW with an arc welding method such as gas metal arc welding. This combination allows for greater positioning flexibility, since GMAW supplies molten metal to fill the joint, and due to the use of a laser, increases the welding speed over what is normally possible with GMAW. Weld quality tends to be higher as well, since the potential for undercutting is reduced.

6. STUD WELDING

Slab base weld nuts

Stud welding is a form of spot welding where a bolt or specially formed nut is welded onto another metal part. The bolts may be automatically fed into the spot welder. Weld nuts generally have a flange with small nubs that melt to form the weld. Studs have a necked down, un-threaded area for the same purpose. Weld studs are used in stud welding systems. The tip on the weld end of the stud serves a two-fold purpose:

1. It acts as a timing device to keep the stud off of the base material

2. It disintegrates when the trigger is pulled on the gun.

When the tip disintegrates, it melts and helps solidify the weld to the base material.

Stud welding, also known as stud arc welding, joins a stud and another piece of metal together. The stud is usually joined to a flat plate by using the stud as one of the electrodes. The polarity used in stud welding depends on the type of metal being used. Welding aluminum, for example, would usually require direct-current electrode positive (DCEP). Welding steel would require direct-current electrode negative (DCEN).Stud welding is very versatile. Typical applications include

automobile bodies

electrical panels

shipbuilding

building construction

7. ULTRASONIC WELDING

Ultrasonic welding of thin metallic foils

Ultrasonic welding is an industrial technique whereby high-frequency ultrasonic acoustic vibrations are locally applied to workpieces being held together under pressure to create a solid-state weld. It is commonly used for plastics, and especially for joining dissimilar materials. In ultrasonic welding, there are no connective bolts, nails, soldering materials, or adhesives necessary to bind the materials together.

When welding plastics, the interface of the two parts is specially designed to concentrate the melting process. One of the materials usually has traditionally a spiked energy director which contacts the second plastic part. The ultrasonic energy melts the point contact between the parts, creating a joint. This process is a good automated alternative to glue, screws or snap-fit designs. It is typically used with small parts (e.g. cell phones, consumer electronics, disposable medical tools, toys, etc.) but it can be used on parts as large as a small automotive instrument cluster. Ultrasonic can also be used to weld metals, but are typically limited to small welds of thin, malleable metals, e.g. aluminum, copper, nickel. Ultrasonic would not be used in welding the chassis of an automobile or in welding pieces of a bicycle together, due to the power levels required.

For automobiles, ultrasonic welding tends to be utilized in the assembly of large plastic components and electrical components such as

instrument panels

door panels

lamps

air ducts

steering wheels

upholstery

engine components

As plastics have continued to replace other materials in the design and manufacture of automobiles, the assembly and joining of plastic components has increasingly become a critical issue. Some of the advantages of ultrasonic welding are

low cycle times

automation

low capital costs

flexibility

does not damage surface finish, which is a crucial consideration for many car manufacturers, because the high-frequency vibrations prevent marks from being generated

BIBLIOGRAPHY

I have taken reference from the following sources:-

Fundamentals of modern manufacturing by Mikell P. Groover

Manufacturing engineering and technology by Serope Kakpakjian and Steven Schmid

Google.com

Wikipedia.com

CONCLUSION

This is the final submission of my study and research on the topic i.e. “welding techniques used in automobile industry.” I have completed my work with full dedication and determination and now, I have almost complete and thorough knowledge of this topic.

So, I conclude by thanking my respected sir, Mr. Achitanand Dubey and everybody else who helped me throughout my work.