EDM of NiHard prts
EDM of NiHard prts
(OP)
A shop has declined to machine the bore of an 82 inch diameter part made of A532 Class II Type D abrasion resistant cast iron. Not quite the same as any of the "nihards" but Rc 56.
Their suggestion was we would need to have the parts EDMed.
My experience with NiHard and similar alloys is it takes very little localized heating (and especially subsequent cooling) to cause spontaneous cracking. I expect that the EDM process may pre-crack the surfaces it creates.
There was a time when EDM was related with unavoidable surface damage and reduced materila propeties which for some applications meant the EDMed surface to some depth had to be removed if the part was to perform well. Knife blades, forging dies and suspension parts come to mind.
These parts will be installed on a hub with 0.006" - 0.014" interference, so the material of the bore may already be in tension.
Is there now a gentle EDM that will not compromise or pre-damage sensitive ferrous materials?
Their suggestion was we would need to have the parts EDMed.
My experience with NiHard and similar alloys is it takes very little localized heating (and especially subsequent cooling) to cause spontaneous cracking. I expect that the EDM process may pre-crack the surfaces it creates.
There was a time when EDM was related with unavoidable surface damage and reduced materila propeties which for some applications meant the EDMed surface to some depth had to be removed if the part was to perform well. Knife blades, forging dies and suspension parts come to mind.
These parts will be installed on a hub with 0.006" - 0.014" interference, so the material of the bore may already be in tension.
Is there now a gentle EDM that will not compromise or pre-damage sensitive ferrous materials?
RE: EDM of NiHard prts
RE: EDM of NiHard prts
You need to locate a shop with NiHard experience. The place I witnessed the machining is out of business.
Bill
RE: EDM of NiHard prts
I would agree with the posts above, finding someone with a boring mill would be preferable.
Comprehension is not understanding. Understanding is not wisdom. And it is wisdom that gives us the ability to apply what we know, to our real world situations
RE: EDM of NiHard prts
Old and rigid machines with slow speed attachment and Cobalt based tool bits are preferred. At times, if the casting is not properly supported or clamped, it can crack.