thermal vs. vibratory stress relieve

[Cedarman1978]

Would it be beneficial to blanchard grind the scale from A-36 HRS before stress relieving and then finish machining? I have 1 1/4" x 24" x 45" plate that will be N/C machined to finish thickness of approx. .90". The backside will be cored out to leave approx .38 face thickness. It must end up flat w/in .005" and parallel to bottom w/in .010". We have a vibratory machine in house. I was planning on B/G to full clean up, then stress relieve, then finish machine. How does this sound to all you experienced guys?

 

[bklauba]

Cedarman1978,

This sounds feasable. I have VSR Processed mild steel and 300-series stainless discs, 80 - 100 inches in diameter, ~ 2" thick, that were then BG'd to w/i 0.005" flat. (They started out moving 0.020" when 0.030" was removed, prior to VSR Treatment.)

But I would only used a resonance-based vibration system with servo-control, automatic scanning and recording of the amplitude vs. vibrator frequency data. Otherwise, the possibilities of getting erratic data, or (worse) false positives would worry me.

BK

 

[bklauba]

I checked my files on the job I described. It was done for a job shop outside Detroit that specializes in Blanchard and VTL work.

Two VSR Treatments were done, due to the area beneath and near the vibrator being stiffened. Vibratory stress relief works by utilizing flexure; vibration is merely a means to cause such flexure, resonance being the most efficient means of achieving sufficient flexure levels.

After one of the first stainless disks was treated, it was quite flat after BG'ing, except for where the vibrator was mounted: There was a high spot there. An additional treatment with the vibrator moved resulted in a stable part. The remaining disks all were treated twice, moving the vibrator 'tween treatments, and all of them were stable.

If you are planning on using a fixture, I would still do two treatments. The workpiece should have three shims between it and the fixture, located far from the corners of the workpiece, so as to minimize damping. A three point arrangement (center of one long side; two points on opposing side spaced ~ 1/4 of length apart, centered) will allow both the bend and torsional resonance modes to be excited, as long as the vibrator has the speed range and speed regulation to reach and detect these.

BK

 

[BTIGUY]

Cedarman

YES, your proposed approach is exactly my recommendation too, not because the scale would represent a problem but it is always a good idea to get the part as stress free as possible before finish machining.

BTIGuy