ELECTRIC WELDING PART – 02 – WELDING PROCESSES

There are two methods of Electric Welding.

(a) Non-fusion or pressure welding

This process involves heating of work-pieces to the temperature range in which the base metal of the work-pieces becomes plastic state and the work-pieces joined together by applying pressure them. Filler metal is not used in pressure welding.

(b) Fusion or non-pressure welding                      

In this process heating of work-pieces to be joined to a temperature above the melting point of the metal of the work-pieces and the work-pieces are joined together without the application of any pressure. This process requires additional filler metal through an electrode.

There are about 35 different welding and brazing process and several soldering methods, in use by the industry today.

CLASSIFICATION OF WELDING PROCESSES

(1) RESISTANCE WELDING

(a) Spot welding                (b) Seam welding

(c) Projection welding       (d) Resistance butt welding

(e) Flash butt welding       (f) Percussion welding

(2) ARC WELDING

(a) Carbon Arc welding             (b) Plasma Arc welding

(c) Shield Metal Arc Welding     (d) T.I.G. Welding

(e): M.I.G. Welding

(3) GAS WELDING

(a) Air Acetylene               (b) Oxy Acetylene

(c) Oxy Hydrogen Welding

(4) THERMO CHEMICAL WELDING

(a) Thermit welding           (b) Atomic welding

(5)  RADIANT ENERGY WELDING

(a) Electric Beam Welding        (b) Laser Beam Welding

(6) SOLID STATE WELDING

(a) Cold welding                (b) Diffusion welding

(c) Forge welding              (d) Fabrication welding

(e) Hot pressure welding   (f) Roll welding

RESISTANC WELDING

PRINCIPLE OF ARC WELDING

Resistance welding is a fairly simple heat generation process. The passage of current through a resistance generates heat.

The general heat generation formula for resistance welding is: Heat = I² x R x t x K

where, “I” is the weld current through the work-pieces, “R” is the electrical resistance in ohms of the work-pieces and “t” is the weld time, and “K” is a thermal constant.

The weld current (I) and duration of current (t) are controlled by the resistance welding power supply.

The resistance of the work-pieces (R) is a function of the weld force and the materials used. 

The thermal constant “K” can be affected by part geometry, fixturing and weld force.

ADVANTAGES OF RESISTANCE WELDING

1. Very short process time.

2. No consumables, such as brazing materials, solder, or welding rods.

3. Operator safety because of low voltage.

4. Clean and environmentally friendly.

5. A reliable electro-mechanical joint is formed.

6. Parent metal is not harmed.

7. Both similar and dissimilar metals can be welded.

8. Heat is localized when required.

9. Lesser skill is required.

10. Difficult shapes and sections can be welded.

DISADVANTAGES OF RESISTANCE WELDING

1. High initial cost

2. High maintenance cost

IMPORTANT TERMS IN WELDING

1. Amperage - The strength of an electrical current measured in amperes or the magnitude of an electric current measured in amperes, especially the rated current of an electrical component or device

2. Arc voltage – The voltage across the welding arc. Arc voltage has an important effect on the weld bead shape and the depth of penetration; the precise effect being dependent on the joint preparation. 

3. Arc Current – The current that flows through a circuit while a weld is being made.

4. Arc Length – The distance from the tip of the electrode or wire to the work piece.

5. Arc Blow – The deflection of an electric arc from its normal path because of magnetic forces.

6. Duty cycle – The percentage of time during a time period that a power source can be operated at rated output without overheating.

7. Squeeze time – It is the time that elapses between the initial application of the electrode pressure on the work and the first application of current.

8. Arc Time – The time during which an arc is maintained.

9. Weld time – The time for which the welding current flows through the parts being welded. It is usually expressed in cycles of supply.

10. Hold time – The time during which pressure is applied at the point of welding after the welding current has created to flow.