A Study on the Influence of the Fluctuation of Source Voltage during Spot Welding on the Strength of Weld

Abstract

It is well known that even a-slight fluctuation of the welding current reflects upon the quality of the spot weld.
The fluctuation of the welding current is frequently caused by the fluctuation of the source voltage during the spot welding, so it is most important to keep the source voltage constant to improve the consistency of spot weld.
The purpose of this report is to discass a few problems concerning with the influence of fluctuation of the source voltage during welding on the strength of weld. The following results were obtained.
(1) The influence of the drop of the source voltage on the strength of weld depended upon the material to be welded and the welding conditions, and was more sensitive in aluminum alloy than steel.
(2) The influence of fluctuation of the source voltage in the beginning of welding cycle on the strength of weld was greater than in the rear period in aluminum alloy, but in steel it was reversible.
(3) The strength of weld decreased slowly with the drop of the source voltage in steel, but in aluminum alloy gave the Vee curve property having the minimum strength at critical conditions, and about 10 percentage drop of the source voltage in the beginning of welding cycle produced the worst result in aluminum alloy.
(4) It was found to be wrong to correlate the strength of weld only with the effective current equivalent to modified welding current.