Good design practices attempt to limit spot welding on appearance or cosmetic surfaces. While textured paints can be used to hide small electrode marks on finished surfaces, grinding, or filling and grinding, is often required and can double the cost of the welding operation. Often, structural elements such as stiffeners are required to reinforce large cosmetic surfaces. For these applications, designers should select material which is thinner than the material from which the appearance part is fabricated. This assures that weld shrinkage will occur on the noncosmetic part which helps to control the cost of filling and abrasive finishing.
Position the welding torch with the wire in the center of the hole contacting the back sheet of metal. It is important to arc against this back sheet rather than on the edge of the hole, otherwise the weld might not penetrate into the back sheet. The torch should ideally be pointing directly into the hole rather than at the angle in the photograph. Start welding in this position and don’t move the welder until the hole is almost full of weld. Then move the welder outwards in ever increasing circles until the weld is completed.
Although aluminium has a thermal conductivity and electrical resistance close to that of copper, the melting point for aluminium is lower, which means welding is possible. However, due to its low resistance, very high levels of current need to be used when welding aluminium (in the order of two to three times higher than for steel of equivalent thickness). In addition, aluminium degrades the surface of copper electrodes within a very small number of welds, meaning that stable high quality welding is very hard to achieve. For this reason, only specialist applications of aluminium spot welding are currently found in industry. Various new technology developments are emerging to help enable stable high quality spot welding in aluminium. Read more details at Auto Body Spot Welder.
Electric welding relies on the Joule Effect. This is the thermal result of the electrical resistance, occurring when an electric current passes through a conductive metal – in this case metal sheets for assembly. If that last sentence went over your head, here’s how it works: to weld two or more sheets together without adding a filler metal, they are tightly compressed between two heat-resistant electrodes (i.e. non-melting), generally made of copper, and a high-intensity current is applied to melt the plates together at that point. The result is a small merging of metal which constitutes a welding point. The welding time is very short, between one and two seconds, and the shape of the resulting welding spot depends on your choice of electrodes.