Projection welding

Advantages,disadvantages & applications

Advantages of Projection Welding:•   More than one spot weld can be made in a single operation.• Welding current and pressure required is less.• Suitable for automation.• Filler metals are not used. Hence, clean weld joints are obtained.

Disadvantages of Projection Welding:• Projections cannot be made in thin work pieces.• Thin work pieces cannot withstand the electrode pressure.• Equipment is costlier.

Applications of Projection Welding:• A very common use of projection welding is the use of special nuts that have

projections on the portion of the part to be welded to the assembly. Also, used for welding parts of refrigerator, condensers, refrigerator racks, grills etc

Upset welding

• Upset welding is a form of resistance welding in which coalescence occurs simultaneously across the entirety of the abutting surface area, or progressively along a joint, using heat from the base metals’ resistance to the current passing through them.

OR • In upset welding(UW), the w/p to be joined are brought together to

mate with each other in a butt joint compared to lap joint that has been used so far. The two w/p are held tightly together & current is applied, so that the heat is generated through the contact area bet’n the two plates. Because of the joint being under pressure, the ends of the two pieces get slightly upset & hence its name upset.

• This is useful for joining the two ends of rods or similar pieces.

Advantages,disadvantages&applications

Advantages:• suitable for joining many alloys that are difficult to weld using fusion

processes.• Since no melting takes place, the weld metal retains many of the

characteristics of the base metal.• Resulting welds have a hot worked structure, and thereby have higher

strength than fusion welds in the same mate.• Since the material being joined is not melted, compositional gradients are

not introduced, second phase materials are minimally disrupted.

Disadvantages:

Applications:• upset welding has been adapted for fabrication of structures considered

very large compared to typical resistance welding applications. The process has been used for closure of capsules, small vessels, and large containers.

Flash welding

Conti……

• Flash Welding is a Resistance Welding (RW) process, in which ends of rods (tubes, sheets) are heated and fused by an arc struck between them and then forged (brought into a contact under a pressure) producing a weld.

• The welded parts are held in electrode clamps, one of which is stationary and the second is movable. Flash Welding method permits fast (about 1 min.) joining of large and complex parts.

• Welded part are often annealed for improvement of toughness of the weld.

• Steels, Aluminum alloys, Copper alloys, Magnesium alloys, Copper alloys and Nickel alloys may be welded by Flash Welding.

Advantages,disadvantages&applications

Applications:• Thick pipes, ends of band saws, frames, aircraft landing gears are

produced by Flash Welding.

Resistance seam welding

Conti……

• Seam Welding is a Resistance Welding (RW) process of continuous joining of overlapping sheets by passing them between two rotating electrode wheels. Heat generated by the electric current flowing through the contact area and pressure provided by the wheels are sufficient to produce a leak-tight weld.

Gas metal-arc welding(GMAW)

or (MIG)

Conti…..

• Metal Inert Gas Welding (Gas Metal Arc Welding) is a arc

Welding process, in which the weld is shielded by an external gas (Argon, helium, CO2, argon + Oxygen or other gas mixtures).

• Consumable electrode wire, having chemical composition similar to that of the parent material, is continuously fed from a spool to the arc zone. The arc heats and melts both the work pieces edges and the electrode wire. The fused electrode material is supplied to the surfaces of the work pieces, fills the weld pool and forms joint.

• Due to automatic feeding of the filling wire (electrode) the process is referred to as a semi-automatic. The operator controls only the torch positioning and speed.

Advantages,disadvantages

Advantages of Metal Inert Gas Welding (MIG, GMAW):• Continuous weld may be produced (no interruptions);• High level of operators skill is not required;• Slag removal is not required (no slag);

Disadvantages of Metal Inert Gas Welding (MIG, GMAW): • Expensive and non-portable equipment is required;• Outdoor application are limited because of effect of wind,

dispersing the shielding gas.

Flux-cored arc welding

Conti….

• The flux-cored arc welding(FCAW) process is a modification of the GMAW, where the solid electrode wire is replaced by tubular electrode containing a flux at center of the electrode throughout its length.

• Since the electrode is not a solid wire, the feeding units should be properly designed so as not to put excess on the electrode resulting in its flattening.

• flux availability to remove the oxide and other contaminations in the form of slag, which covers the weld bead during solidification and cooling, and protects it for longer periods.

Advantages,disadvantages& applications

Applications: FCAW is normally used for the welding of structural steels and alloy steels etc.