Question

In which type of welding is heavy, current (50,000 A) passed through the joint and welding is done under external pressure?
1. Arc welding
2. Spot welding
3. Gas welding
4. Forge welding

Answer 1

Correct Answer - Option 2 : Spot welding

Explanation:

Spot welding:

• It is the joining of two metal sheets and fusing them together between copper electrode tips at suitably spaced intervals by means of heavy electric current passed through the electrodes
• The joint formed by spot welding provides high mechanical strength and it is not air or watertight, for such welding it is necessary to localize the welding current and to apply enough pressure on the sheet to be welded
• The electrodes are made up of copper or copper alloy or water-cooled
• The welding current varies widely depending upon the thickness and composition of the plates
• The period of the flow of current varies widely depending upon the thickness of the sheets to be joined
• A step-down transformer is used to reduce a high voltage and low current supply to required low voltage and high current supply
• The current varies from 1000 A to 10,000 A and the voltage between the electrodes is usually less than 2 V.
• In this welding, maximum resistance is at the interface between two sheets

Arc welding 

• Arc welding involves either a consumable or non-consumable electrode.
• An arc is produced between the tip of the electrode and the workpiece to be welded, using an AC or DC power supply.
• There are following types of Arc welding
  • Flux-cored welding
  • Submerged arc welding
  • Shielded gas welding
    • TIG welding
    • MIG welding
    • PAW welding

Gas welding

• In gas welding Heat source is the flame produced by the combustion of fuel gas and oxygen.
• Acetylene (C₂H₂) is the principal fuel gas employed in this welding.
• No pressure is involved in this welding.
• Filler metal can be added in the form of a wire or rod.

Forge welding 

• Forge welding is solid-state welding.
• The ends to be joined are then overlapped on the anvil and hammered to the degree necessary to produce an acceptable weld.
• There is no application of current only pressure is there.