Evaluation of the Effect of Contact Resistance on the Resistance Welding

A Study on the Phenomena of Spot Welding

Abstract

There are various methods of evaluating the effect of contact resistance. Some people say that just by contact resistance, welding is possible. The others regard it of little importance.
The former illustrate their theory by the fact that while two lapped plates can produce weld nugget, a single plate can not produce nugget under the same welding current.
However, in the case of a single plate, by the ffinging phenomena of current distribution the current path spreads wider than in two lapped plates, so the effect of lowered current density cannot be overlooked. Whether the nugget is produced or cannot be directly associated with the effect of contact resistance.
We devised special test pieces as shown in Fig. 10, with which we succeeded in eliminating the influences of fringing of current distribution and contact resistance between electrode tip and plate. With these test pieces we made equivarent experiments on two lapped plates and a single plate. From the oscillogram we could get the change of resistance, and evaluate the effect of contact resistance only.
After the experiments, we could know that, of contact resistances, film resistance was almost useless, but that contact resistance made the current density of contact surface higher, at the same time making the heat generation effective, so the contact resistance proved to be apparently effective.
But it is also an undeniable fact that contact resistance is not so essential that without it nugget cannot be formed.