How do "ARC Welders" work? --- David, Farnham, Surrey, United Kingdom
The "arc" in "arc welder" is an electric arc. It is the same arc seen in an "arc light" and it creates tremendous heat. There is enough heat to melt steel, so it makes a good welding system.
To weld with an arc welder you connect one clamp (the ground clamp) from the machine to the pieces of metal you are welding together. The other clamp connects to the welding rod. With the arc welder on, you touch the welding rod to the metal and pull it away a few millimeters to create the arc. Moving this arc over the seam in a zigzag pattern will melt the metal and fuse the two pieces together.
The welding machine itself is basically a big transformer. It is producing a relatively low voltage and a high current (e.g. 40 volts at 100 amps). For more info see: How Welding Works