Welding adjustment values
The most important parameters in resistance pressure welding are the welding current, the time and the force. In addition, of course, there are the non-productive times that have already been described.
These 3 main parameters are set according to the material, the process and the requirements of the welded joint. Based on experience, there are recommended values for this from DVS, car manufacturers and machine builders. For resistance spot welding, simple rules of thumb can be used for these parameters for sheet steel. It then applies:
- For the welding current: I » 9.5 * Eh in kA
- For the welding time: ts » 8 * h in periods (20 ms )
- For the electrode force: F » 2000 * h in Newton
Where h represents the sheet thickness of the thinnest single sheet.
These parameters are necessary to achieve a required welding lens diameter, which is also specified in DVS leaflets and in manufacturers’ guidelines. There is a simple rule for this too, the minimum diameter dL » 5 * Öh in mm. As with many things in life, there is a lot of leeway. The values given are intended to be indicative only. In the specific case, of course, the corresponding factory standard or DVS specification applies. Under this condition, the following parameter recommendations are also to be understood as rough guide values. They are intended to give the user a point of reference and serve as a basis for further optimisation.
When using materials of different thicknesses, the lens diameter and thus the basic parameters are selected according to the thinnest individual sheet. Important in this context is the fact that the possible welding lens diameter can only reach about 80 % of the electrode diameter. These given guide values refer to a medium time welding as it is often used in practice. The best welding qualities can be achieved with short-time welds. For this, the parameters must then be adjusted, the welding current and the force upwards and the welding time, as the name suggests, downwards. Short-time welding is unfortunately not always feasible in reality due to poor fits and pressure conditions.
These parameter reference values apply to alternating current 50 Hz and can also be used for medium frequency. Due to the direct current characteristic, however, it is possible to work with shorter times or lower currents at medium frequency, which has a positive effect on electrode life and energy consumption.
When using aluminium or higher-strength or coated steel types, the parameters must also be adapted to the conditions of the material such as thermal and current conductivity or resistance. You can find more information on this in the DVS leaflets, the reference value tables of the machine manufacturers or, of course, from your Harms & Wende partner.