The surface of the materials must be clean and metallically bright.
The electrical conductivity must be given attention in particular at the contact points - stud / work piece and ground connection / work piece.
Paint, rust, scale, grease or oil or other coatings unsuitable for welding (e.g. anodised) must be removed from the weld area (mechanically or chemically).
In particular, galvanized component surfaces must be checked for weldability.
With very short welding times of < 50 ms, the surface must be cleaned particularly carefully.
In the case of aluminium, existing oxide layers should be removed.
Rear side markings
Even with such short welding times, deformations or markings on stainless steel or aluminium up to a sheet thickness of 4 mm often cannot be avoided. Visibility is strongly dependent on the structure of the reverse side, especially on highly polished or lacquered sheets. In the sheet thickness range of 0.6 mm, the shrinkage of the weld pool always results in a thermally induced indentation.
Thermal rear side markings, such as tarnish points, do not usually occur in capacitor discharge ignition, but only in drawn arc ignition, where welding times are significantly longer. Characteristics and visibility depend, among other things, on the material thickness, the time energy input / stud diameter and the material.