Spot Welding Machine

Welding is a process to join two pieces of metal firmly together, effectively bonding them into a single piece by using molten metal at the joint – either melting the pieces themselves so that their metal literally flows into the metal of the other piece, or using a molten filler metal to effect the join. It is one of the most secure methods of joining two pieces of metal together, and many welding methods create a weld along the whole length of the join.

In many cases, however, only a light connection is required between two thin pieces of metal. In this case, spot welding may be used to fasten the metal pieces together. Spot welding involves, as its name suggests, welding the metal only at specific spots. The spot welding machine used for this process is very different from other welders such as arc welders – it is based around a pair of electrodes rather than using a welding gun as the means for creating the weld. The principle is fairly simple, but the adjustments must be precisely calibrated to get a proper weld for the type and thickness of metal being spot welded. On the other hand, the simplicity of the idea behind spot welding makes it possible for some enterprising tinkerers to build their own, home-made spot welding machines.

What a Spot welding machine is and how it works

The basic mechanism through which a spot welding machine operates is with a pair of copper alloy electrode clamps. These clamps are used to clamp the two sheets of metal to be joined together, placed side by side. A powerful current is then fired through the electrodes, strong enough to melt the metal at the point where the electrodes are bracketing it. The molten metal from both pieces of metal mixes together, then cools and hardens into a single metal continuum, effectively fusing the two pieces together at the points where the spot welding has been carried out.

Spot welding is most effective with thin pieces of metal, where the current passes directly between the upper and lower parts of the electrode. The thicker the pieces of metal, the more of the electricity disperses sideways into the metal rather than traveling through it to complete the circuit. Thus, greater and greater amounts of electrical power are needed to spot weld thicker pieces of metal. The practical limit on the thickness of metal that can be fused in this way is 1.25” for steel plate, with other types of metal have thinner limits. Beyond these limits, spot welding is ineffective or impossible.

The best thickness of metal for spot welding is very thin – from between half a millimeter to 3 millimeters. The time during which the metal is exposed to the electrical current must be carefully controlled if the spot welding is to produce good, solid results. Depending on the thickness and the type of metal, anywhere from 0.01 to 0.63 seconds of current may be necessary. Too little or too much can crack the metal, so precise adjustment is usually necessary for anything beyond hit-or-miss results to be attained. Voltage used is very low – generally no more than 10 volts for the thickest piece of aluminum, and considerably less than that for other kinds of metals. High amperage is needed for the process, however, with 90,000 to 100,000 amperes being needed to fuse aluminum.

Portable Spot welding machines

Portable spot welding machines can rarely muster the amperage necessary to weld aluminum sheets together, but are quite adequate for welding thin mild, galvanized, or stainless steel sheets. Little more than a foot long, featuring a heavy-duty power cord and a pair of tongs at the front which contain the electrodes, these hand-held devices allow anyone to carry out spot welding on metal up to 1/8” thick. This is enough for most home and light professional users, and the well-designed controls allow these welders to get the weld they need quickly, easily, and safely. Technology continues to advance and spot welding is now practical on both the large and small scale.