Spot welding is a process that joins metal surfaces by applying heat generated from resistance to electric current flowing between two metal sheets clamped together by electrodes. When a large current passes through the joint, it generates heat due to resistance and melts the metals, fusing them together. The basic steps are to squeeze the sheets together with electrodes, apply an alternating current to generate heat and melt the metals, hold the heat, forge the weld by continuing pressure, then remove pressure to cool. Spot welding is commonly used in automotive manufacturing and other industries due to its speed, not requiring filler metals, and ability to simultaneously weld multiple sheets.

1. Asif Hussain
M14-351
Metallurgy and Materials Engineering
College of Engineering and Emerging
Technologies University of the Punjab Lahore

2. Introduction
Spot welding is the process in which the adjoining metal
surfaces are joint together by the heat obtained from resistant
to current flow, thus forming welding Nugget between them.

3. Working Principle:
 At Low voltage, high current flowing through the joint generates large amount
of heat due to High Contact Resistance, which causes Melting of Joint and
further Fusion of Metals.
 Mathematically, the heat generated is given by the formula:
 H = I2Rt

4. How Does it Work?
 Let us consider two plates and try to join them

5. Five basic steps:
 Squeeze
 Weld
 Hold
 Forge
 Pressure off

6. 1. Squeeze:
1. Lap Joint 1. Clamping Between Electrodes
1. Connect the electrodes with the step
down transformer.

7. 2. Weld:
1. Switch on the AC Source 2. Large amount of Heat generation

8. 3. Hold:
4. Forge

9. 5. Pressure Off step
 Removal of the electrodes from the join area and further the joint is allowed
to cool.
So the technique in which metals are joint with each
other by resistance heating at a single point is called
Resistance spot welding

10. Equipment:
 Electrodes
 Water Supply
 Heat regulator
 Pressure Gauge
 Foot switch
 Hydraulic or Air Cylinder
 Knee

11.  Advantages:
Limitations:
 Quick and Easy
 No need of Flux and Filler metals
 Multiple sheets joined together at the same time
 No dangerous open flames
 Saves production cost
 Difficulty for maintenance or repair
 Generally have higher cost than most arc welding equipment
 Low tensile and fatigue strength
 The full strength of the sheet cannot prevail across a spot welded joint

12.  Applications:
 Automobile industry
 Dental Prosthesis
 Batteries
 Nuts and Bolts