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Machining Nihard castings

Yogesh

Plastic
Joined
Aug 1, 2006
Location
India
Does anybody of you have a experience machining Nihard casting at 550BHN hardness. I have a pump casing weight 32Kgs, 14" in dia and 6" long. My customer whants the seal area dia of 3.250" to be machined within +/-0.003" and a 12" dia within +/-0.005". I have never done this on a direct Nihard castings,but with machinable metal inserts.
 
Wow Yogesh, you have a tough one there. I have no help to offer, mainly consolation! I don't know what Nihard is but at 550Bhn that has got to be a metal removal challenge!
Good luck with it.
 
550 Brinell is equal to about 55HRc. Some of the Ni-Hard alloys are over 700BHn, so yours is machinable with the correct tooling.

Ceramic or Cermet inserts would be the least expensive choice.

Superabrasives are the next step up. These include Cubic boron nitride (CBN), Polycrystalline diamond (PCD), and a combination of the two called Polycrystalline cubic boron nitride (PCBN). PCBN inserts are designed for machining Ni-hard cast iron, hardened cast iron, high chrome alloy steels, and pearlitic gray cast iron.

Check with your insert supplier. They should be able to recommend an insert for this material.
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Barry Milton
 
Thanks Barry, I have tried with some ceramic and CBN, but the problem is the casting has a step out on the face. This gives a intermittent cut and hammered on the tool, so inserts are breaking rather then wear.

I have been suggested by another expert on this forum for spindle grinding, maybe with a tool post grinding attachment :confused:
 
Try PCBN500 or 600 it’s for tough for interrupted applications, around 380 SFM at .100-.075 radial DOC and .011-.009 Per rev.
However, you need to be careful of blowholes, and grind any high spots as they may be sand spots.
 








 
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