Manufacturing Process for 17-7 PH Stainless Valve Plates

[hycpres]

We have a need to make some very flat plates from hardened 17-7 PH stainless. The problem we're having is that the plates are ported and ground flat and parallel within 0.001", and we must have a final hardness of around 42Rc. We've already failed on one batch, where we ended up with the plates warped about 0.010". Does anyone have a suggestion for order of processes, figuring they need to be ported out, ground flat, and heat treated?

 

[israelkk]

Grind after heat treatment. Or use a jig (two thick plates)
to squeeze and keep the 17-7 flat during heat treatment.

 

[hycpres]

Start in Cond A or C, do you think? Also, the ones that ended up not flat were lasered to give us the porting. There's some thought here that perhaps the heat from the laser cutting caused some warping, so we thought maybe water jet next time.

 

[TVP]

I think > 6 mm when I see the word plate so I seriously doubt that the laser cutting had much of an influence on part warpage unless the thickness is quite small. One sequence would be to rough cut everything in the solution annealed condition, then age to the desired strength/hardness, followed by finish milling or grinding. Unless you need to make large quantities of these parts, then I would not worry about the reduced machinability of 17-7 PH in the aged condition. With today's tool technology, hard milling can be quite effective, likewise with grinding.

 

[hycpres]

By solution annealed, you mean Cond A, correct? Sorry I forgot to mention, starting thickness is .075", finish thickness is 0.055"

 

[EdStainless]

I would suggest the same as TVP.
rough machine, then age, then finish machine. Unless you have to make hundreds of these, and even then you will have better luck. You might want to even machine the ports and before you go to final flatness re-age. As I recall if you stay at a slightly lower temp for a shorter period of time you won't screw up the properties and you may get a bit of stress relief.

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Plymouth Tube

 

[TVP]

Yes, condition A is the solution annealed condition.

 

[tripleZ]

0.055"? What are the outer plate dimensions? I'd guess that heat and/or clamping forces from machining or grinding could throw you out by a few thousandths. What method are you using for grinding? Double disc? Single side grinding via blocking in?

If the plates are simply flat plates, you may want to try a fine grinding operation that uses opposing horizontal wheels. I've had excellent flatness results utilizing this technology. Note that this grinding process is the final operation after hardening.