Post Machining on Heat Treated 420SS 2

[whiv]

Hello....We have a Ø.800 420SS metal injected molded part that is heat treated to RC48-52. It has a hub with a cast hole on each side of the part and that needs to be reamed to the final size. We press fit a Torlon journal. We brought the post machining in house and our machine shop is having fits. They are using solid carbide reamers but are not having much success. Is there another reamer material they should be using? Is there a specific machine speed they should be using? Should we first ream the part, then heat treat? I'm worried the heat treating will shrink the hub IDs and we'll have to machine again. Thanks.

 

[TVP]

Powder metallurgy 420 stainless steel quenched & tempered to 48-52 HRC will be exceptionally difficult to ream, due to the extreme hardness of the microstructure (essentially untempered martensite). Machining before heat treatment may be one option, depending on how tight the dimensional control for the hole needs to be. If you have to ream after heat treat, then likely you will need a high performance system, e.g. Mapal HPR with PCBN blades. Here is a link to their catalog:

http://www.mapal.com/fileadmin/00_PDF-Dateien/Kataloge/englisch/Reiben_Feinbohren_V1.0.0_e.pdf

 

[Duwe6]

Agree to the probability of HT shrinking the hole. If it was me, I would try one piece reamed to size and then HT'd. The remaining reaming should be very small. Might not even be needed.

When in doube, ask the parts.

 

[whiv]

Thank you TVP & Duwe6.

 

[Duwe6]

You are very welcome.