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?