In addition, higher strength steels may require special techniques or treatments like tempering after welding. Spot weldability of HSLA (high-strength low-alloy) steels is directly related to composition and type of microalloying elements. It is advisable to check with the supplier before specifying spot welding here. Stainless steels are spot weldable, some grades more readily than others. Austenitic grades of the 300 series are the most commonly welded types, followed by ferritic. Martensitic stainlesses are the least common because welded joints are always much more brittle. All stainless steels require careful adjustment of welding parameters and/or special methods to obtain optimum quality welds.
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.
Where is Spot Welding Used? Spot welding has applications in a number of industries, including automotive, aerospace, rail, white goods, metal furniture, electronics, medical building and construction. Given the ease with which spot welding can be automated when combined with robots and manipulation systems, it is the most common joining process in high volume manufacturing lines and has in particular been the main joining process in the construction of steel cars for over 100 years. See more details at Tecna Spot Welder Parts.
As is often the case with machine tools, there are two types: portable (for ease of use but with limited performance); and stationary (better suited to intensive work and thicker metal sheet).