Grinding closes the pores of all grades of this porous steel. Milling will close the pores of 7 micron and reduce the pore size of the 20-micron material down to about 7 microns (when done correctly) by partially closing the pore opening at the surface. Stoning, using a back and forth/side to side method, will re-establish permeability by removing the metal that is crushed over the pores. Stoning and polishing, up to about a number 800 - 1000 stone/paper finish, is possible. During the stoning and polishing process, it is important to occasionally flush the pores at the surface to prevent packing the pores with debris.
Electric Discharge Machining is the best way to re-establish permeability. This method will burn away the metal fragments that are crushed over the pores by milling and/or grinding.
Note: When using wire EDM machining methods, Porcerax II is porous and generates waste particles that can create "arcing" conditions between the wire and the work-piece. This arcing can cut the wire. As a countermeasure, increase wire winding speed.
Note: When using an electrode for EDM, it is important to program a peak-to-valley burn rate that exceeds the pore size; i.e. < 7 micron depth for 7 micron pore size is desirable.
The illustrations above show how particles created by the wire EDM process carry the electrical current across to the work-piece, creating the potential for a discharge that can break the wire. Increasing the wire winding speed not only greatly reduces the potential for wire breakage but also increases machining times.
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