Material Stretch in Bump Forming??

Yes.

We often suffer from the lack of QC on steel and other materials.

The incidence is especially high when the material is manufactured or provided from a foreign country that is Metric measurement based and they have to convert from one system to the other.

I have a relative that is a QC supervisor in a US factory that manufactures close tolerance aircraft components including jet engine parts.

He more than once has admitted that he "passes" components that are out of tolerance to avoid getting any of his "old buddies" on the floor in trouble and in some cases to avoid budget overruns.

If the SS plate grew 3/16" during forming I would be suspect of the thickness of the plate as the growth had to come from somewhere and it might be there was too much pressure applied during forming.

UMMMM!!!!!

I think I will be driving instead of flying now!! Which airline does he pass Good / Bad parts to? Remember the Challenger. That exact Q.C. practice is what killed our astronauts! That is a Federal offense!

What was the temperature of the plate when measured? Yes a plate can grow during forming as the added length comes from the compression of the material. Factor in the heat growth as well as the reduction of gage(thickness) when formed Also if there are any waves in the plate when received the length will be shorter, when you form it the waves are removed and the plate will measure longer. This happens a great deal when we re-level a plate.

3/16 over 2,816/16 isn't very much.

I think it grew.

Now you owe them $5.37 for the extra material!

Thanks All, It was a beautiful bump form job - darn near perfect on the radius, it lined up with our etch marks for fit almost perfectly...it was just too long.

Thanks for your insights.

I find it hard to believe that 1/2 thick SS can grow in length while being formed. The part came in at 176.1875".

yes it can,

just like it can shrink when welded.

I could have ground the excess off in the time it took to read this thread. Have they no Boilermakers or Pipefitters?

You must have a big grinder with a lot of beef leaning on it. It would take a little while to grind off 40" x .50" x .1875" 316L SS. Fixing it was not an issue with a hand held plasma torch ... and a grinder after that.

I'd say, that's a lot of material to remove.

I can see the next question in this forum will be:

"How can I remove 3/16" of an inch on 176" length on a 1/2" plate of 316 stainless."

It grue some. As usual the conversation involves the ignomious "they". If "they" who supplied the steel had measured after the forming, they should have known they were off by a few parts per thousand, and if the specs were tighter than that, then it should have been rejected or corrected. The other "they" in this story must have been your people who rolled it up into a pipe shape?

The first 'they' was us, we cut 3/16" off the finished part that arrived from the second 'they', the vendor.

I ordered the part from an outside vendor because our press brake could not form this part as ours is only 12' long and not enough power to do a good bump form on 1/2" SS with this radius.

I supplied the print to form to and a flat .dxf pattern for burning. We did no forming on this part, the first 'they' discovered it was too long as it would not fit in the weldment they were building.

The vendor asked me what I wanted as a resolution to a fix and I told her it was fixed already. Depending on how the other 37 long form parts turn out will determine if I decide to get a credit for the time we spent fixing the part.

I am so impressed with the fine form job that I am hesitant back charge for our fix time.

it doesn't pay, as long as they did a good job, and you can work with it.

Agreed. Good vendors are hard to find.

That sounds like "they" have it under control!