Question

Describe spot welding and projection welding with neat sketches.

Answer 1

### Spot Welding

Spot welding is a type of resistance welding used to join two or more metal sheets by applying heat and pressure to a small, localized area. It works by using electrical resistance and pressure to create a molten "spot" at the interface between the two sheets, which then solidifies to form a strong bond.

How it works:

1. Electrodes are placed on both sides of the metal sheets.
   

1. A high electric current is passed through the sheets, which generates heat due to the electrical resistance of the material.
   

1. The heat melts the metal at the point of contact, creating a small molten pool.
   

1. Pressure is applied to the molten area by the electrodes, which forces the molten metal to solidify, creating a weld nugget.
   

Applications:

1. Commonly used in automotive manufacturing, electronics, and sheet metal fabrication.
   

Here’s a simplified diagram for spot welding:

`
  |-----------------------|
  |       Electrodes       |
  |-----------------------|
        |         |
  Metal Sheet   Metal Sheet
   (Upper)       (Lower)
`

The electrodes apply pressure to the sheets while current passes through, heating the area where they meet.

---

Projection Welding

Projection welding is a variation of spot welding, where instead of a flat surface, projections (small raised points or bumps) are formed on one of the workpieces. The projections help localize the weld area and concentrate the heat into specific spots.

How it works:

1. Projections are made on one of the workpieces (typically the upper sheet).
   

1. The parts are positioned together, and pressure is applied.
   

1. An electric current is passed through the workpieces, which creates heat at the projection points.
   

1. The projections melt and form localized welds between the sheets.
   

Applications:

1. Used in applications requiring multiple welds, such as joining small parts to a base metal or for sheet metal assemblies.
   

Here’s a simplified diagram for projection welding:

`
  |-----------------------|
  |       Electrodes       |
  |-----------------------|
        |         |
  Metal Sheet   Metal Sheet
    (Upper)      (Lower)
     w/ Projections
`

The projections concentrate heat and form multiple welds, rather than just one spot.

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Both of these welding processes are efficient for mass production and can be automated, especially in industries like automotive manufacturing.