Short Answer:
Resistance welding is a metal joining process where heat is generated by passing an electric current through the contact area of the two metal pieces. The resistance to current flow at the joint creates enough heat to melt the metal and form a solid weld after cooling. No filler material is needed in this process.
This type of welding is widely used in mass production industries, especially in making automobile bodies, metal furniture, and electrical components. It is fast, clean, and automatic, making it ideal for spot welding, seam welding, and projection welding tasks.
Detailed Explanation:
Resistance Welding
Resistance welding is a fusion welding technique in which metals are joined by applying heat generated from electrical resistance at the joint. The process does not involve any external flame, arc, or filler metal. Instead, it uses electric current and pressure to join metal surfaces.
This method is mostly used where high production speed and consistent weld quality are needed. The welding happens in a very short time—usually within a few seconds—and the entire process can be automated, which is why resistance welding is popular in manufacturing and assembly lines.
How Resistance Welding Works
The working principle of resistance welding is based on Joule’s Law of heating, which states that heat produced (H) is proportional to the square of current (I), resistance (R), and time (t):
H = I² × R × t
Here’s how it works:
- Workpiece Placement
Two metal sheets or parts are placed between electrodes made of copper or other conductive materials. - Application of Pressure
Electrodes press the metal parts together tightly to ensure proper contact. - Electric Current Flow
A large amount of current is passed through the joint for a short time. - Heat Generation at Joint
Due to the resistance at the contact area, heat is produced, melting the metal locally. - Formation of Weld Nugget
The melted area forms a small weld nugget, which solidifies into a strong joint once the current stops and pressure is maintained.
Types of Resistance Welding
- Spot Welding
- Most common type
- Used to join overlapping metal sheets at single points
- Seen in car body panels and steel cabinets
- Seam Welding
- Like spot welding but continuous
- Electrodes are rotating wheels
- Used for leak-proof joints in tanks and pipes
- Projection Welding
- Uses small raised projections on one workpiece
- Heat is concentrated at projections
- Common in nut/bolt welding
- Flash Welding
- Used for joining parts with uneven ends
- Arcing and resistance heat used to melt edges before pressing them together
Advantages of Resistance Welding
- No filler material or flux required
- Very fast process (welding in seconds)
- Clean and smokeless, no sparks or fumes
- Easily automated for mass production
- Produces strong and consistent joints
Limitations
- Only suitable for thin sheet metals
- High initial cost of equipment
- Requires good surface contact between metals
- Not suitable for non-conductive materials
Applications of Resistance Welding
- Automobile Industry – Car body spot welding
- Electrical Equipment – Switches, relays, connectors
- Metal Furniture – Chairs, tables, racks
- Battery and Electronics – Terminal and tab welding
- Household Appliances – Washing machine, refrigerator frames
Conclusion
Resistance welding is a fast, efficient, and clean method of joining metals using electrical resistance and pressure. It is widely used in industries where high-speed and large-volume production is required. The process does not need any filler metal and is mostly automated, which makes it cost-effective in the long run. Spot welding and seam welding are the most common types used in day-to-day manufacturing applications.