Low-damage ductile removal of silicon carbide based on distributed undeformed chip thicknesses in composite ultrasonic vibration-assisted grinding (CUVAG)
摘要
Silicon carbide (SiC) faces the machining problems of severe surface/subsurface damage owing to its inherent brittleness and extreme hardness. With the aim of achieving low-damage ductile removal of SiC, a calculating model of equivalent undeformed chip thickness (EUCT) in composite ultrasonic vibration-assisted grinding (CUVAG) is established. Then, the distributed EUCTs are accurately calculated and statistically analyzed, as well as their effects on the resultant grinding forces, ground surface morphology and roughness, and subsurface damage. The results show that the elliptic vibration can significantly increase EUCT at the maximum probability density (apmax), with an enhancement effect twice of the axial vibration. As the wheel speed rises from 2.6 m/s to 9.1 m/s, apmax first decreases from 3.12 μm to 2.51 μm and then increases again, exhibiting periodic fluctuations and displaying a double-peak feature at 3.6 m/s and 6.3 m/s, while the influence of workpiece infeed speed is relatively minor. As apmax increases from 0.5 μm to 4.3 μm, the concentration of the skewedly distributed EUCTs first decreases and then increases, with the normalized entropy first rising from 0.73 to 0.875 and then falling to 0.63. The material removal process undergoes three sequential stages: Ductile-dominated removal, hybrid ductile-brittle removal, and brittle-dominated removal. By adjusting apmax close to the critical value of 0.35 μm, the proportion of ductile-dominated removal can be obviously raised up to more than 30%, with the propagation of cracks effectively suppressed and the ground surface roughness smaller than 0.05 μm. The research outcomes will provide theoretical foundations and methodological support for realizing low-damage ductile-dominated machining of hard and brittle materials.