Hydra-lock chucking

[tripleZ]

Hydra-lock Conform-A chucks...does anybody have any experience with them?

I'm working on a problem part right now. Ø105.3 mm flange OD, Ø96.015 mm minor OD, and a thru hole of Ø78.7 approximately. The part is roughly 16.5 mm long with a 6.35 mm thick flange. The material is 303 stainless.

Coming to my machining center, I've got pre-molded parts that are out of round up to about 0.008" (0.203 mm), and the out-of-roundness varies across all three diameters. Since I turn every surface on the part, the operation is done in two steps in a twin spindle lathe. My problem is the Ø96 feature. I have a total tolerance of 0.03 mm and a total roundness spec of 0.03 mm.

I've used various combinations of pie jaws and pressures, both ID and OD, to try and get the parts round, but I'm still intermittently running into tri-lobe forms and egg-shapes that take me out of spec. I can make parts to print, but with 100% inspection end up with about 40% fallout. I can add a third operation that clamps just the faces of the part and trues up the flange Ø 1st. Then my normal machining process takes over. I end up with a round part but have an added operation.

I've gotten mixed reviews on the Hydra-lock Conform-A chucks that say they can conform to the part ID or OD without rounding it up (up to 70% that is). Based on their calculations, two of these chucks in sequence will solve my issue. Has anybody on the boards used these chucks in production machining? Pros? Cons? Have you used any other workholding styles for a similar issue?

My added 3rd step makes the parts to print, but needless to say mgmt doesn't like the added cost. I've thought also about an expanding collet with a high number of "fingers", but I think the pressure may still be enough to deform the part.

Thanks in advance!

 

[PeterStock]

If you are making a number of these could you make a part with a slight interference fit with the ID? You could machine the ID first, place the part on this holder and machine the OD features with the ID supported.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

 

[MikeHalloran]

I'm thinking a nail-shaped mandrel that doesn't touch the ID, but chucking on it clamps the workpiece between the chuck face on the mandrel's flange. You cut the flange OD like that, in the twin spindle lathe, then clamp the flange with the other spindle...

.... then you somehow magically spit the mandrel out through the hole in the spindle that's just gripped it, recovering the mandrel for later use ...

... and proceed with the rest of the operations as now.


It's the 'magically' part that I'm not real certain of..



Mike Halloran
Pembroke Pines, FL, USA

 

[tripleZ]

I hear you Mike. I've found a few companies (Northfield for instance) that make pull down chucks, but I'd have to pull down on the OD flange (similar concept to what you're proposing). I could bore the ID, ID chamfers, and top face in op #1, then flip the part to my second spindle and machine all the other features with a left handed cutter. I'm nervous with the toolholder & part clearances but might be able to make it work. I'll have to see what they come back at me with and see if I have the real estate in the machine bed.

I did rig up a manual C-clamp operation as an initial op. I've got my roundness now down to 0.0007" on average which is good. Now I just need that way to keep it a two-operation rather than a three-operation process.

Peter, the idea is sound. My part however deforms just about every time I touch it with pie jaws. I can correct the out-of-roundness to a point, but once it gets beyond a certain level all I do is exacerbate the issue. We've tried what you've suggested, but can't improve the fallout beyond 40%.