Material deformation 2

[gersen]

Hello
at work we had a problem with some pieces.
We made 4 pieces like the picture below using a oxycutted plate th. 650 mm material 1.0577.
We machined a hole Ø500 +0.1, but after few weeks the hole has an eccentricity of 1 mm.
Can the cause of this be residual stresses inside the material? Should we have made a stress relieving tratment beforehand?

I gladly read your opinions on this.

 

[3DDave]

Yes, though there would be changes in the crystal structure that was left from the cutting as well. You may recall the difference between face centered cubic and body centered cubic crystals? They have different sizes and (I never memorized it) one of those two can end up unstable and capable of changing due to even room temperature energy levels.

You may wish to consult with a metallurgist on the specific alloy, cutting, any welding material, any weld schedule, and post-cutting and post-weld heat treating to stabilize the part before machining it.

As an aside, I talked with a casting house and they would dial in the dimensions of parts by altering the heat-treat while keeping within the desired material property range by changing the relative amounts.

 

[rothers]

We manufacture similar parts (bearing chocks for rolling mills) from normalised EN 10083-2 C 60 flame cut from a ultrasonically tested forged billet. Stress relieved after flame cutting, proof machined leaving a machining allowance, further stress relief heat treatment, stabilisation by resting for 3 months and only then final machining.

 

[robyengIT]

oxycut 650 mm ???? that's why !

BTW, we had similar problems with big bronze bushes due to difference of the ambient temperature (temperature of manufacture and temperature of installation)

 

[EdStainless]

rohters is on the money with this one.
It doesn't really matter how you cut them, though the higher heat input from oxy is a bit worse.
but in any case multiple stress relief cycles are needed if you want tight stable tolerance.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Tmoose]

Can you see (measure and record, actually) similar changes in the 640 and 690 dimensions ?

Was the 500 mm bore the last machining operation ?

 

[gersen]

They just inform me of the process they use:
- first milling of the outside dimension 643x743x1210
- turning of bore to Ø500-0.3 (simmetrical part)
- finishing of the outside with milling and drilling
- finishing of bore to Ø500+0.1

I think the removing of a lot of material on the outside after the internal turning produce an inbalance in the internal stresses.