What causes 10 - 15 % of my weld nuts to have damaged threads after projection welding?

Nut welding is a very common operation in manufacturing. Hundreds of thousands of nuts are welded every day. Most are loaded and welded on automated lines. The tooling and fixtures include locating equipment to ensure the nut is positioned properly each time. In many cases a “Pin” is used to locate the hole in the nut and hold it in place. This pin frequently must be insulated to prevent current flow into the threads of the nut. If there is flow it will probably be an arc which will damage the threads.

 Nut Welding System 002



This is the likely source for the damaged threads. It could also be grit and grime that gets into the hole from the surface of the pin. In general it is wear and tear on the locator pin. If the pin was insulated, its insulation is failing and current is beginning to flow. It should be replaced.

Another article in this blog discusses this topic:

What Materials are Used for Nut Welding Pins?

Discussion of options for pins and their pro’s and con’s are discussed.

Reference: RWMA – Resistance Welding Manual 4th Edition

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