Stress relieving question. Getting distortion during machining.

Ukraine Train · Aug 4, 2016

I'm working with some mild steel DOM tube and after milling a groove on the inside it's springing out into an oval shape. I'm looking at maybe stress relieving these. What temperature would that be done at? The inside surface is honed smooth and I'm concerned about scale building up during the process. Should I expect to see that? Or distortion to the size or straightness? Parts are 5.125" dia. x 5/16" wall x 23.375" long.

Clive603 · Aug 4, 2016

What condition is the supplied material in? As drawn, stress relieved annealed or full annealed. If you can its far better to buy in stress relieved or fully annealed condition instead of trying ad-hoc processing with limited facilities. Theoretically DOM carries simple symmetric hoop stresses so it should stay round after machining. In practice, as you have found out, basic stress condition is often assymetric so it shifts after cutting. Ideally the factory understands their process so buying annealed should get you material with the necessary process adjustments to shift any asymmetry.

Alice

Milland · Aug 4, 2016

Can you change your process first? Perhaps trying a smaller grooving tool, making sure it's very sharp to minimize stress input, and making multiple cuts for width and depth.

You can try "re rounding" a bad part on a press with some plastic or wood support blocks, what's your roundness tolerance? How far down the tube does the out of round travel?

dgfoster · Aug 4, 2016

Ukraine Train said:
I'm working with some mild steel DOM tube and after milling a groove on the inside it's springing out into an oval shape. I'm looking at maybe stress relieving these. What temperature would that be done at? The inside surface is honed smooth and I'm concerned about scale building up during the process. Should I expect to see that? Or distortion to the size or straightness? Parts are 5.125" dia. x 5/16" wall x 23.375" long.

The groove must be circumferential like an oil-ring groove? Or is it longitudinal and if so what length and, in either event, location from the end? Depth? Width? In use the tube is eventually part of a weldment, a liner sleeve, ends pressed into another part and functions in what way? It could be restrained by hoops? It is low number or high volume part? The tolerance for cylindricity is? The oval shape is seen as a hump when laying a straight edge on the outside and along the length of the part? Or looking at the end of the part, it is egg-shaped?

Answers to these questions (and probably others) may help refine answers (which I won't have but others may) and suggestions.

Denis

Ukraine Train · Aug 4, 2016

I think maybe groove wasn't the right word; it's more of a slot so it's not spread evenly around the part. One on each side of the ID. Pictures speak a thousand words so here it is. The part will not be welded after.

Porschefix · Aug 4, 2016

To answer your question you can anneal the steel. Here is an approximate chart. You did not mention the alloy you're using so the final analysis is up to you. Will this affect other characteristics your customer needs? Was the matl. spec'd for the application?
Yes you may have scaling issues, but I would wrap it in stainless foil and charge the tubing with argon or nitrogen. That should eliminate scaling.
That said the better solution is to buy the matl. in annealed condition as prev. mentioned.

Milland · Aug 4, 2016

The other issue is that stress relieving may itself give you warped parts, SR is best when there's still material to be removed as a finish cut so that you can cut away the remaining distortions. Unless there's good reason not to do it, I would try to get a process in places where a press is used to "re round" the part. If you can't get satisfactory results that way, then trying to get your supplier to have the material SR'd, then honed before you do the slotting is the way to go.

Milland · Aug 4, 2016

Here's some more comprehensive information on SR: http://www.heat-treat-doctor.com/documents/Stress Relief.pdf Keep in mind that if the part has be heat treated for hardness prior to you getting if for machining that some loss of hardness may occur from SR if you run it too hot.

Heavey Metal · Aug 4, 2016

What you have is skived and roller burnished.

Your print calls for honed.

You sr and it will jump naked.

Ukraine Train · Aug 4, 2016

Well, my tubing supplier just told me that the material is stress relieved in the mill after processing. Material is ST52 DOM tube. They're trying to get me the exact process that's used at the mill. For the moment the plan is to press these back into shape.

Milland · Aug 4, 2016

Ukraine Train said:
Well, my tubing supplier just told me that the material is stress relieved in the mill after processing. Material is ST52 DOM tube. They're trying to get me the exact process that's used at the mill. For the moment the plan is to press these back into shape.

If this is a significant job, could be worth setting up some indicators on dedicated fixturing to give you quick references for displacement and springback. I think there's some posts on PM from someone who made a pretty sweet straightening bench, might be worth looking there for ideas.

Heavey Metal · Aug 4, 2016

You need to buy honed material like the print says

dgfoster · Aug 4, 2016

Besides the post-machining straightening, I would be tempted to test machine some scrap that was compressed egg-shaped while machining it to varying degrees opposite the distortion you have experienced post-machining. Probably would not work, but....surfaces stresses relieved and induced by machining are complex.

Denis

Search

Largest Manufacturing Technology Community on the Web

Search

Stress relieving question. Getting distortion during machining.

Ukraine Train

Cast Iron

Clive603

Titanium

Milland

Diamond

dgfoster

Diamond

Ukraine Train

Cast Iron

Porschefix

Hot Rolled

Milland

Diamond

Milland

Diamond

Heavey Metal

Banned

Ukraine Train

Cast Iron

Milland

Diamond

Heavey Metal

Banned

dgfoster

Diamond

Similar threads