Cryogenic machining of porous tungsten for enhanced surface integrity

Cryogenic machining of porous tungsten is being developed as an alternative sustainable process to current industry practice of machining plastic infiltrated workpieces. Eliminating the use of plastic infiltrant is contingent on the ability to control as-machined surface properties of porous tungsten. To this end, the influence of various machining parameters and cooling conditions on machining mechanisms, particularly as a function of cutting temperature, is explored. By employing modified polycrystalline diamond cutting tools, high speed cryogenic machining of porous tungsten by ductile shear was achieved. Cutting speeds of up to 400 m/min are possible with this novel approach, and very low surface roughness of Ra ≈ 0.4 μm is realized, at the expense of surface porosity. At low cutting speeds, rake angle has a key impact on surface morphology, with more negative rake angles increasing the amount of brittle fracture occurring on the machined surface and thereby increasing surface porosity. An excellent mix of open surface porosity and low surface roughness may be achieved at low cutting speeds of 20 m/min when a sharp edged cutting tool with a rake angle of −5° is used. Using a separate set of machining parameters for rough and finish machining may offer an optimum approach to realize economical cryogenic machining of porous tungsten.