Collet Manufacturing Question

[nickjk]

Collet Manufacture Question

I have a single slot collet design that I need to release for build but have questions related to the manufacturing procedure.
The collet will be made from 440C stainless and heat treated to 59-61 Rock “C”.
After heat treat the collet taper and I.D. will be ground to size.
My thoughts on manufacturing were to turn the collet leaving grind stock on important diameters.
At the end of the turning operation the collet would be slotted for the single slot leaving a small amount of material holding the collet together at both ends for stability during heat treat and grind.
The collet would then be hardened in a vacuum furnace AMS 2759/5 with a gas quench. After heat treat the collet would be ground as required then the web at the end of each side of the slot would be removed by grinding.

My source for turning the collet feels because it is a single slot it would be best not to slot the collet before heat treat but to slot it after heat treat and grind ( as a last operation).

What would be best for minimizing distortion and burr removal?

Any suggestions would greatly be appreciated.

Thanks

 

[tomwalz]

Any reason not to trust the heat treater?

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[MiketheEngineer]

No reason to not trust the heat treater - it's just that parts distort after treating and need to be checked/reground - whatever...

 

[mfgenggear]

nick

I agree with the turn source, except it will not be feasible to grind the diameter after slotting, it needs to be in the restrained condition during grinding, unless it can be tooled as such. in other words held in the restrained condition while grinding. I would grind then slot.

reason: the dia will distort after slotting.

you should check with your grinding source.

yes 440C will distort badly during heat treat if not process correctly.

Mfgenggear

 

[nickjk]

mfgenggear

The turn source believes the slot should be done with an abrasive wheel after grind is complete.

Just met with the grind source and they would like to receive the part with a partial slot, webs at the end to cut away after finish grind.
He said because of the wall thickness, cutting the full slot after grind would be slow and introduce a great deal of heat.

See attached sketch.

Thanks,

Nickjk

Thank you,

 

[mfgenggear]

Nick

how many of these are to be made?

my experience 440 can distort bad. so it's important to discuss it with your local heat treater, and that someone is looking out for it.
I personally would not slot them before heat treat.
tell the grinders to use plenty of coolant & to use the minimum of pressure during grinding of the slot. It's never fun slotting with thin grinding wheel, but it is done offten in grinding shops with a surface grinder.

the slot will cause your sleeves to distort more during heat treat.
but for a low quantity just add more stock for the grinders to true up the diameters. for example instead of let's say .003 stk/surf leave approx .006 stk per surf. the object is to allow for out of roundness & runout of the outer taper to the inner taper. thus expect this collet to go egg shape during heat treating.

can the slot be machined by wire EDM then there would be no distortion or heat. I do this for small quantities.

an other suggestion is to use A-2 tool steel, it does not distort at all.

Cheers

Mfgenggear

 

[nickjk]

mfgenggear,

Thanks for the reply

In your experience, after grind, is the slot hard to deburr at the bore?

The heat treat source did not feel the part would distort greatly.
He feels the greater the change in cross section, the more distortion there would be, because the part is uniform, distortion may be low. One thing I noticed is they really do not want to predict the outcome, standard response, all parts distort differently, which is true.

I currently have .005-.007 stk. per side for the prototype.
If after machining the prototypes we can reduce the stock the grinder will let me know.

when I get the quote from the grind source I will talk to him in more detail about his ability to slot completely through after grinding. I have read the same thing, it can be done with an abrasive wheel mounted to a surface grinder.

Prototype quantities are low, but producton quantities are high. I would rather start learning now then later.

Nickjk

 

[mfgenggear]

Nick

"In your experience, after grind, is the slot hard to deburr at the bore?"

if slotted then deburr, then heat teat, use a generous edge break like .005-.025". yes it is harder to deburr after heat treat.
but the edge can be deburr easily. if it is a low quantity then just hand deburr, if it's high volume it will have to be machined.



"The heat treat source did not feel the part would distort greatly.
He feels the greater the change in cross section, the more distortion there would be, because the part is uniform, distortion may be low. One thing I noticed is they really do not want to predict the outcome, standard response, all parts distort differently, which is true."

I have had good & bad results with heat treating 440, yes I agree if the cross section is uniform that helps. however depending on the procedure used, how it is racked, and this case quench.
I have had good success with my vendors vacuum heat treat with gas high & low pressure quench.

make sure the parts are racked standing up or hung in free state.
I like using graphite heat treat fixtures. it works great.

Good Luck


Cheers

Mfgenggear