Abstract
The measured resistance between skin sheets was compared with the calculational results of steel substrate resistance, particle resistance and contact resistance. It was found that the resistance between skin sheets was mainly composed of contact resistance because contact area between particles and skin sheet was very small.
From the calculational results of the distribution of welding current and voltage in the skin sheet, it was considered that their distribution spread widely outside of the contact area between electrode and skin sheet comparing to ordinary steel sheet. Maximum value of voltage and current was observed at the edge of contact area.
It seems reasonable to suppose that welding current and voltage are directly related to the time to exclusion of resin and the occurrence of pin-hole defects respectively. Therefore the effective factors to both current and voltage were investigated in detail.
In the case of high resistance between skin sheets, the distribution of welding voltage spread widely within the skin sheet and welding current becomes lower. This fact was confirmed to cause the harmful effect to the weldability. Also the size of work piece affected weld quality. In paticular, the smaller the size of work piece became, the higher welding voltage loaded and the pin-hole defects occurred. Futhermore, since 90% of current flows outside of contact area, it was considered that these materials were seemed to have many shunting points.
