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Zinc plating causing cracks in a hardened sheetmetal part

October 24, 2009

I am experiencing crack problem in a component.

component is sheet metal punched part by progressive tool
this undergoes hardening process to achieve 330 to 380 HV
we have taken care to introduce hydrogen embrittlement 8 hours of degaussing after plating
but still the some of the parts in the batch fail by cracking during torque test.

any body could suggest what care we need to take for eliminate this problem

thanks & best regards

Hareesh S
engineer with product company - India

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You bake a part to reduce embrittlement, not to induce it. It could be loosely looked at as a degassing step, not a degaussing step which reduces magnetism.

I think that you are working on the outer limits of the metal's capability. If I understand your post, you are doing multiple "press" steps which will induce stresses into the metal. Normally a bake step will reduce this, but you are on the edge of that working. You may have to harden after the "press steps" which will take care of the induced stress.

Other than that, you might be able to use the bake step as a PARTIAL annealing step which will unfortunately lower the hardness. Too high a temp will seriously affect the plate.

James Watts
- Navarre, Florida
October 27, 2009