Question concerning projection welding

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We have an automated projection welding machine which joins two brackets to a frame, 6 projection welds per bracket. After the frame is welded it is then sent through a furnace where porcelin (sp) is baked on. During this process sections of the porcelin "fall off". The theory is that stored energy from the weld process is released from the heat of the oven and "pops" off the porcelin. Just wondering if anyone has seen a similar problem and could make some suggestions.

Thanks

-- Clay Brown (clayb@peoplepc.com), November 27, 2001

Answers

05/12/2001

Dear Clay Brown,

This is a rather funny problem.The only answer I can find is that there must be lot of stresses generated in the job due to the projection welding on the bracket.These stresses must be getting released when you pass the frame through the furnace causing some porcelain to fall off.But I have never come across such a problem earlier.

Regards,

Subhash

-- Subhash Patwardhan (artech1@vsnl.com), December 05, 2001.


Thanks for your reply, this is also our theory, although there is some disagreement as to whether it is electrical energy or mechanical energy that is being stored and released.

-- Clay Brown (clayb@peoplepc.com), December 05, 2001.

Clay- I believe the stored energy theory is more of a situation where as the parts are put into a tension state from the welding process (poor tooling alignment, incorrect weld schedules for materials, welding process not correct for application, etc.). When the metal is put into the oven and heated, this may cause the "normalizing" of the frame and brackets. This reminds me of the old porcelain coated cookware - when the metal was dented, the coating would pop off. This was due to the stress created by the deforming metal underneath a brittle, hard coating. I would take a very careful look at your tooling and welding setup for stresses to be induced into your application. As a test, weld a component and pass it through your furnace (don't porcelain coat it) let it cool, then pass it through the coating process. This will help determine if the popping coating was stress related or other problems. I have never heard of an electrical or magnetic field on the part that would cause the coating to pop off, I would think if this was the problem, the coating would not adhere to the entire part.Try passing some of the unwelded components through the porcelain process to see if the popping coating could be from surface contamination. Let me know if I can be of further assistance, sometimes an outside eye can see things missed by familiarization. Happy Holidays Ray Michelena 423.308.3250

-- Ray Michelena (raymichelena@tjsnow.com), December 17, 2001.

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