I have machined a bushing made of 45 steel with a heat treatment hardness of 219-250HB, a bore size of Φ44_(+0.02)~(+0.08)mm, and an outer diameter of Φ50_(-0.10)~(-0.02)mm. , length 390mm. The surface roughness of the inner hole is required to reach R_(?)0+4. Such low surface roughness is difficult to guarantee. We analyzed that reducing the surface roughness of the bore before rolling is a key. When finishing the inner hole of the car, the surface roughness is R_(?)1.6, then
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