Ideally, equal thicknesses of two sheet metal parts to be joined produces an evenly distributed weld nugget within the two layers. When this is not practical, materials of different thicknesses can also be joined and produce a centered weld nugget by using a larger electrode on the thicker member. At a ratio above about 3-to-1 (thickest to thinnest member), spot welding becomes difficult. At this point, another joining method should be considered–for example, projection welding. Note that weld deformation is always greater on the thinner member. For this reason, stiffeners and brackets spot welded to cosmetic parts should be thinner than or equal in thickness to the exposed surface material.
Start off by drilling 7.5mm holes in the front sheet of metal at a spacing of normally 25mm to 40mm (or whatever the original spot weld spacing was). Then clamp this sheet onto the back sheet. 7.5mm is a reasonably good hole size for 0.8 or 1.0mm sheet. Thicker sheet might require a slightly larger hole size. Try a little test piece out like this one before welding a whole sill onto a car and check the weld has penetrated through both sheets.
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 details on Tecna Spot Welder Price.
Stationary spot welders are mounted on a column with a jack and mobile arms. The frame is heavy and bulky and the machine has a welding capacity of 0.5–10mm. The body of the machine often equipped with a 380V generator and two arms with a mechanical, pneumatic or hydraulic jack to adjust operating height, as well as heat-resistant electrodes made of copper or copper-chromium alloy. No electric arc is produced, and the arms are water-cooled in closed circuit. The arms and electrodes are interchangeable to vary spot size and form across different types of weld.