Improvements in Resistance Welding of Aluminium for Automobile Manufacture 810359
Work has been carried out to determine the influence of electrode configuration, electrode material and the use of dual pressure welding schedules on the number of welds which can be made with a pair of electrodes when resistance welding 1mm 2117 aluminium alloy.
It was found that 4.8mm tip diameter 1% Cr-Cu truncated cone electrodes gave an average life of 1380 welds compared to 400 welds with 75mm radius domed 1% Cr-Cu electrodes. Consistent results could not be obtained with pimple electrodes. For the welding conditions employed, electrode life was found to be dependent on the mechanical properties of the electrode material and independent of softening temperature. The best results were obtained with Class 3, 2.5% Co - 0.42% Be-Cu electrodes (average 1700 welds) and the shortest lives with the high conductivity Class 1 materials usually recommended for resistance welding of aluminium.
The effect of dual pressure was investigated for pedestal and gun stations. Using 4.8mm tip diameter 1% Cr-Cu truncated cone electrodes on a pedestal machine it was found that lives could be extended from an average of 1300 welds, the lives ending as a result of solidification cracking, to more than 3000 by increasing the forge force from 3.1 to 7.8kN. In the latter case the lives ended due to electrode sticking. With conventional dual pressure schedules electrode life increases with increased forge level but the timing of the forge initiation must be precisely controlled so that it occurs at the end of the last current cycle. The extension in life is lost if the initiation is delayed by 1 cycle. A similar trend in results was obtained when using a welding gun fitted with 3.2mm tip diameter electrodes. The electrode life was increased from an average of 500 welds to an average of 1650 welds when a forge force of 5.7kN was employed.
As some welding guns, designed for use with mild steel, are not capable of withstanding the high forge forces normally recommended, equipment was developed so-as to give a modified dual pressure schedule. This system gave low forge forces whilst retaining a high rate of application. The results obtained with this system when using a forge force of 2.9kN achieved within 0.4 cycles after initiation were the same as those obtained when using a conventional forge force of 5.7kN.