Those big welding robots look like they’re dancing, swinging in and out of position like ballet dancers – but these ballet dancers have really hot hands!

Each robot carries a big,copper-welding gun that looks like a claw. The points of the welding gun are called tips. Using 3D mathematical modeling, engineers plan out exactly where the robot needs to make the welds and how many welds are needed.

At the right time, the robot swings the gun into place and begins firing. The tips squeeze together the two pieces of metal that need to be welded. They press with between 480 and 1,900 pounds of pressure. Then, an electrical current is zapped through the tips into the metal. That creates a temperature of 1,540 degrees Celsius or 2,804 degrees Fahrenheit. The steel melts. When it cools, the two pieces of metal are fused together. Each vehicle has thousands of these spot welds holding it together.

GM is also looking into a new type of welding robot that uses laser beams to melt the metal and form the weld. In the near future, you may see these laser-welding robots on the assembly line.