Highly conductive materials like aluminum require very high power to form quality spot welds. However aluminum alloys are routinely spot welded (see Table I for weldability). Here, cleanliness is much more of a concern than with low-carbon steels because of aluminum’s rapid surface oxidation characteristics. For optimum quality and weld performance, expensive cleaning procedures to remove surface oxide are required. For demanding applications, equipment to monitor surface resistivity from lot to lot is necessary to assure consistency of quality. This leads to a related consideration. If aluminum has been chosen for an important reason, such as lightweight or high strength-to-weight ratio, the added expense of ensuring a high-quality weld should be justified. If it has not, re-evaluation of the original material selection is in order or, perhaps, another assembling method should be considered.
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.
Spot welding is a resistance welding process that is used primarily for welding two or more metal sheets together by applying pressure and heat to the weld area. It works by contacting copper alloy electrodes to the sheet surfaces, whereby pressure and electric current are applied and heat is generated by the passage of current through resistive materials such as low carbon steels. See more info at https://www.weldingsuppliesdirect.co.uk/welding-equipment/spot-welding.html.
Portable spot welders are compact, lightweight and handy for difficult-to-access joints. As such, they are most commonly used in coachbuilding. They have an average welding capacity of 2 + 2mm and are relatively inefficient due to the fact that the electrodes aren’t cooled between cycles. Automatic adjustment makes it easier to adjust the spot parameters according to the thickness of sheet and welding head used.