hot straightening 17-4PH investment castings 2

[foundrydude]

I am having a problem with 17-4 PH investment castings that are distorting during machining. My customer wants to machine in the fully HTR condition, Homo + Solution + H925.
They are 6 inch diameter, thin-wall collars that are used to strap an A to A missile to a fighter wing.
We hot size at 1900 F, soak time 30 minutes, after annealing, but prior to age harden. The castings are perfectly to dimension when delivered, however when un-clamped after machining the inside diameter, they spring closed some. Improper heat treat? Cold work stress imparted during hot sizing? Does not happen all the time. Any suggestions are welcomed.
Thanks,
Foundrydude

 

[TVP]

Can you provide a little more detail on the hot sizing operation? How are the parts cooled? How is the mandrel/sizing tool removed?

 

[gariartola]

Have you checked whether the deformation concentrates on the free gaps that the lathe's chuck leaves? If it is a positioned defect like that, the deformation might have been produced by the clamping in the lathe. A quick check could be clamping a part without machining it and increasing the chuck load to see if the deformation you find occours.
I so, I would use soft chucks and make sure that the hydraulic circuitry of the clamping system is working properly and gives no peak loads.
I hope this is helpful.