Speeds for circular grinding Ni Hard castings

[sacem1]

We cast some saucer type disks called "Suction Liners" for the minning industry between 40" and 68" in diameter, weight from 800 lbs to 1800 lbs each in a cast iron with Ni added that gives an end RHN of 450.

This pieces have to be heat treated to soften the pieces in order to machine them, average metal removed about 1/4".

After this premachining the pieces are heat treated to 450-500 BHN and returned to the shop for final rectifiyin with solid carbide (HB 05) to final tolerances wich are in the +0 -0.008" range.

This is costly and time consuming so we have thought about casting the piece, heat treating it to final hardness and just grind the piece from as cast to final dimension in a vertical grinding machine.

Does someone out there do a similar operation?, what turning and grinding SFM might I have to use and with what grade of grinding wheel? Has anyone stumbled and abandoned this process because of unsurmountable problems?

Buying this equipment is not cheap and we would like to have some feed back before jumping into the process, thanks for any help you can give.

By the way production rate should be about 2 or 3 pieces per day.

SACEM1

 

[BillPSU]

I've heard they have good success machining ni-hard with borazon tools. You might give a tool rep a call.

 

[sacem1]

Thanks BillPSU:

Really the problem is not with what tool we can machine it but to be able to forget the heat treatment to soften the material for the premachining, if we try to work with the tools we use to give it the final cut, the as-cast surface simply breaks any tool that is hard enough to be able to cut the Ni-Hard with out tempering and you have to machine first in a softer state to leave a smooth enough surface so that after hardening the cutters don't shatter.

SACEM1

 

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