Effects of electrode spacing, plate width, plate thickness, electrode force and back up stool materials on shunting currents in the plates and their effects on tensile shear strength were investigated. And theoretical analysis was also given.
1. For wider plate width, shunting current increases. However, for width greater than 240 mm, no remarkable increase of the current is observed.
2. In 2 mm thick plate, flashing between upper plate and upper electrode occurres because of large shunting current in upper plate. Accordingly, series spot welding seems to be difficult for the steel sheet thicker than 2 mm.
3. Shunting current is affected by back up stool materials (resistivity of stool) and tensile shear strength is affected by the shunting current and thermal conductivity of the stool. (See Fig. 14, Fig. 15).
4. Shunting current in upper plate is available to increase tensile shear strength, depending on current level as shown in Fig. 17. Lower plate shunting current can be divided to effective part and ineffective part for tensile shear strength as shown in Fig. 18.
5. Basic equation of current in plate of series spot welding is given in equation (7). Calculated value from the equation agrees with measured value within 5% error.