Resistance Welding & its Types

Resistance Welding & its Types (Spot Welding, Seam Welding, Projection Welding) with Advantages, Disadvantages & Applications

 Resistance Welding 

            A welding process that utilizes a combination of heat and pressure to accomplish coalescence, the heat being generated by electrical resistance to current flow at the junction to be welded. In resistance welding coalescence is produced by the heat obtained from resistance of work to the flow of electric current in a circuit. Work piece is a part of electric circuit. Application of pressure is necessary. No filler metal is needed.

Advantages, Disadvantages & Applications of Resistance Welding

Advantages of resistance welding:

• Fast rate of production.

• No filler rod is needed.

• Semi automatic equipments.

• Less skilled workers can do the job.

• Both similar and dissimilar metals can be welded

• High reliability and reproducibility are obtained.

Disadvantages of resistance welding:

• The initial cost of equipment is high.

• Skilled persons are needed for the maintenance of equipment and its controls

• In some materials special surface preparation is required.

• Bigger jobs [more thickness] cannot be welded.

Applications of resistance welding:

• Used for joining sheets, bars, rods and tubes

• Making metal furniture.

• Welding aircraft and automobile parts.

• Making cutting tools, fuel tanks of cars etc.

Types of resistance welding:

1.Spot welding

2.Seam welding

3.Projection welding

4.Upset butt welding

5.Flash butt welding.

Here we will discuss about first three types of resistance welding.

 Spot Welding 

            It is a resistance welding process. Over lapping sheets are joined by local fusion at one or more spots. Heat is generated by resistance to the flow of electric current through work pieces. Work pieces are held together under force by two electrodes one above and other below the two overlapping sheets.

Procedure Spot Welding:

            Electrodes are brought together against the over lapping work pieces and pressure is applied so that the surface of the work pieces under the electrodes come in physical contact. As the current is switched on of the order of 3000-100000 A depending upon the metal thickness, the small area where the work pieces are in contact is heated to 815-930°C. Then welding current is cut off and extra electrode force is applied. The electrode pressure is released to get the spot weld. This brings the various interfaces into intimate contact and thus affects the contact resistance between the two work pieces. It ensures the completion of the electric circuit. It permits the weld to be made at low temperatures. It provides a forging action and thus reduces the deposit. Neither it should be too low which may cause high contact resistance resulting in pits of electrode, nor should be too high which decreases the contact resistance.

Applications of Spot Welding:

• Spot welding of two 12.5 mm thickness plates of steel has been done satisfactorily as a replacement of riveting.

• Many assemblies that do not require gas tight or liquid tight can be economically welded.

• In automobile and aircraft industries.

 Seam Welding 

            Resistance seam welding is a group of welding process where in coalescence is produced by the heat obtained from the resistance of the work to the flow of electric current in a circuit. Work piece is a part of electric circuit. Application of pressure is necessary. No filler metal is needed. The resulting welding is a series of overlapping resistance spot welds made progressively along a job by rotating the circular electrodes.

Principle of Seam Welding:

            It is similar to spot welding. Except that circular rolling electrodes are used to produce a continuous air-tight seam of overlapping welds. Overlapping welds are produced by the rotating electrodes and a regularly interrupted current. The current applied to welding electrodes is intermittent. It is on for definite length of time and off for another definite and short period. If the current is put off and on quickly, a continuous fusion zone made of overlapping nuggets is obtained and the process is known as stitch welding. If individual spot welds are obtained by constant and regularly timed interruptions of the welding current, the process is known as roll spot welding.

Advantages, Disadvantages & Applications of Seam Welding

Advantages of Seam Welding:

• It can produce gas tight or liquid tight joints.

• Overlap can be less than for spot or projection welds.

• A single seam weld or several parallel seams may be produced simultaneously.

Disadvantages of Seam Welding:

• Welding can be done only along a straight or uniformly curved line.

• It is difficult to weld thickness greater than 3 mm.

• A change in the design of electrode wheels is required to avoid obstructions along the path of the wheels during welding.

Applications of Seam Welding:

• Girth welds can be made in round, square or rectangular parts.

• Except for copper and high copper alloys, most of other metals of common industrial use can be seam welded.

• Besides lap welds, seam welding can be used for making butt-seam welds too.

• Used in containers, radiators and heat exchangers, pressure vessels, tanks, water floats, nuclear components, appliance drums, brewery tanks, motor shells etc.

 Projection Welding 

            It is one type of resistance welding process where in coalescence is produced by the heat obtained from resistance to electric current flow through work parts held together under pressure by electrodes. Resulting welds are localized at predetermined points by projections embossments or intersections. The projections serve to concentrate the welding at these areas and to facilitate fusion without the necessity of applying a large current.

Advantages, Disadvantages & Applications of Projection Welding

Advantages of Projection Welding:

• A number of welds [projections] can be made simultaneously.

• It can be applied for metals that are too thick to be spot welded.

• Projection welding electrodes process longer life than spot welding ones because of less wear and maintenance resulting from fusion and overlapping.

Disadvantages of Projection Welding:

• It is limited to combinations of metal thickness and composition which can be embossed.

• Metals that are not strong enough to support projections [example. some brasses and copper] cannot be projection welded satisfactorily.

• Forming of projection on one of the work piece is an extra operation.

Applications of Projection Welding:

• Automobiles have many areas that are projection welded.

• Small fasteners, nuts etc., can be welded to larger components.

• It is particularly applicable to mass production work i.e., welding of refrigerator condensers, crosset wire welding etc.

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