Process After machining before harding or else after 1

[Sumit10]

Hello

I am bit confused between process of machining is to be done after hardening or before? ,I have RFQ for pin which has thread rolling,hardening supplier is suggest me for machining is after hardening & machining supplier is suggest me machining process before hardening ,I have attached drawing pl suggest me the process & effect of hardening on part after hardening & before hardening.

 

[handleman]

The print says, "If in doubt, ask". It probably means to ask your customer, not some random bunch of folks on the internet.
"Case harden" seems a bit non-specific. There are a few methods available for case hardening.
Is your customer OK with you posting their prints on the internet?

 

[IFRs]

Given that case hardening changes the surface hardness and machining removes material at the surface, I'd think you would machine before hardening.

 

[BrianPetersen]

There are no tight tolerances on this drawing and this is a small part. Machine first, harden after.

It gets trickier when tight tolerances and fine surface finishes are involved. Then it usually becomes rough machine first, harden second, grind to final surface finish and tolerance last.

 

[chez311]

Sumit10,

As with most things the answer is not necessarily a yes or no answer. There are many ways to skin this cat.

Your heat treat vendor probably suggested machining after hardening because heat treating can impart varying levels of distortion into your part, depending on a combination of size, shape, material, heat treat process (esp. temperature/time at temperature and quenching), and target hardness. Your machining vendor probably wants to machine before heat treat because obviously its easier (and usually less expensive) to do so before it is hardened.

As to which way you go - it depends on the tolerances involved. There really isn't much mention of them on the print and there is no straightness or other form tolerance shown. If you can accept whatever distortion is expected post-heat treat in both the body of the part and threads by machining prior to heat treat then thats probably the most cost effective method. If not then you'll have to work out with your suppliers the best method - sometimes thats fully machining after heat treat, sometimes it involves partial machining, then heat treat, then final machine/grinding. Thats something for you to work out with your suppliers and design team/customer.

Also something to keep in mind is the "HEAT TREATMENT SPECIFICATION APPLIES TO THIS AREA ONLY" note. Does that mean the part need ONLY be hardened in that zone, or is some level of hardening acceptable throughout the part? Most methods of case hardening except induction hardening will apply to the entire part. As handleman said, ask your customer (and/or whoever made the print) - we can't answer all these questions for you.

Given that case hardening changes the surface hardness and machining removes material at the surface, I'd think you would machine before hardening.

Its not unheard of to machine/grind/turn post case hardening - all you need to do is ensure the surface hardness/min case depth is within spec. That just means the initial case depth (pre-machining) will have to be a bit deeper to account for material removal.

 

[racookpe1978]

There are no tight tolerances on this drawing and this is a small part. Machine first, harden after.

Yes, that is the best way for large tolerance small parts. Else your machining is removing the hardened outer surface, and making machining much more difficult.

 

[Tmoose]

I think that drawing is missing some tolerances.

Maybe there is a reference to ISO DIN 2768 that was "cut off" by the screen shot, but I don't think even 2768fH would be appropriate for some of the features I "envision" (WAG - bearing journals/seats, seal surfaces,etc).

 

[drawoh]

Sumit10,

If I send you that drawing, I am telling you that I want the part to be hard. I will test for this. I have no way of knowing if you hardened it before or after machining.

--
JHG

 

[Pud]

I have never come across threads which are case hardened not being annealed after hardening. Usually by induction heating.
I have also seen hardened shafts being thread ground to remove the case. It cannot be thread rolled after hardening.




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