Page 38 - MetalForming March 2017

36 MetalForming/March 2017
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Resistance Spot-Welding
Since most RSW machines do not display the critical process variables, fabricators should use an external amperage meter and force gauge during machine setup.
At the same time, we can control current passing through the weld joint by adjusting the transformer’s tap switch (if equipped) and the percent-current setting on the machine’s electronic control. Electrical current, passing through the resistance of the weld-zone interface, creates the required heat; application of the electrode pressure on the weld joint forges the molten material. As a result, the molecules fuse ˆtogether to form the weld nugget.
The Rest of the Story
Getting back to our customer who believed that an extremely long weld time was the answer to producing strong spot welds, we proved through destructive testing that only eight cycles of weld time would produce a much stronger weld joint than the 73 cycles of weld time being used prior to our arrival.
In fact, while the “over-baked” assembly broke apart easily when hammered, our properly welded part never did break despite the operator’s best efforts to prove us wrong. We left the customer happy and confident in the RSW process, optimized with a shorter weld time that increased his pro- duction rate; produced consistently high-quality welds; and improved welding-electrode life. MF