A spot welding machine works by using electrical resistance to generate heat and join overlapping metal pieces together under pressure.
Understanding Spot Welding
Spot welding, also known as Resistance Spot Welding (RSW), is a process used to join two or more sheets of metal without using filler material. It is a form of resistance welding, meaning it utilizes the resistance of the materials themselves to create the necessary heat.
The Core Mechanism
The process centers around two electrodes, typically made of copper alloy, which clamp down on the overlapping metal sheets.
Here’s how the fundamental principle works, incorporating information from the reference:
- Pressure Application: The machine applies pressure by squeezing the workpieces between the electrodes. This ensures good contact between the metal sheets and the electrodes, and also between the sheets themselves.
- Current Passage: A high-amperage electric current is passed through the electrodes and consequently through the stacked metal sheets.
- Heat Generation: As the reference states, heat is generated by the passage of welding current through the resistive metals. The resistance is highest at the interface between the two metal sheets.
- Melting and Fusion: The intense heat generated at the point of highest resistance quickly melts a small area of the metal at the interface.
- Weld Formation: While still under pressure and after the current is switched off, the molten metal cools and solidifies, forming a single, strong bond – a "spot" weld.
This creates a nugget of fused metal connecting the two sheets at that specific spot.
Key Steps in the Spot Welding Process
Spot welding typically follows these basic steps:
- Positioning: The metal workpieces are placed overlapping each other between the electrodes.
- Squeeze Time: The electrodes close and apply pressure, holding the pieces firmly together.
- Weld Time: The welding current is turned on for a precisely controlled duration. Heat is generated, and a molten nugget forms.
- Hold Time: The current is switched off, but the pressure is maintained, allowing the molten nugget to cool and solidify under compression.
- Off Time: The electrodes open, and the welded workpieces are removed.
Practical Applications
Spot welding is widely used in various industries due to its speed, efficiency, and suitability for automating. A prime example is the automotive industry, where it is used extensively to assemble car bodies from numerous stamped metal panels.
