The hardness and surface material of some metal material will change because the heat, internal stress or special processing during crushing process of cutting machine, and finally affect polishing effect. Such as stainless steel, titanium alloy and so on.
After electrical discharge machining makes the metal surface harder to grind than ordinary machining and heat treatment.
Before the end of electrical discharge machining should use a precision EDM spark to repair the metal surface, to avoid the formation of hardened layer. The hardness of this hardening thin layer is higher than the metal itself, it must be removed.
In order to provide a good basis to the follow-up of polishing, it is better to increase a rough grinding step before polishing, completely remove the damaged surface layer, and become a average roughness for the metal surface.