If there is 112 V present on the frame, between operations when the machine is in a sense idle. The first thought would be improper grounding. On an AC welder one pad of the transformer (usually the negative) is tied to ground. This could be the machine frame, which should be tied to the ground of the weld control, which should be tied to the ground of the supply feeding the machine. The input feed will include L1, L2 and a ground conductor. The ground from the input conductor should be tied to the common ground point that is bonded to the machine frame, AC transformer pad and weld control ground.
In some circumstances a floating ground or ground loop may be present and can cause an issue. Ground loops can be introduced by multiple ground paths. If this is the case and the issue cannot be resolved then a “Ground Reactor” might be the solution to provide safety for personnel.
See:
The ground reactor is designed to trip the feed breaker anytime a threshold voltage limit is experienced.
GROUND REACTOR
Reference: RWMA Resistance Welding Manual 4th Edition