Research on the Formation Mechanism and Distribution Characteristics of Surface Roughness in End Milling

The cutting variables of end milling are positively correlated with the machined surface roughness, but their mechanism of action remains unclear. Since the cutting tool used in end milling is a three-dimensional solid, under the action of horizontal cutting force, there exist both axial tensile strain and axial compressive strain in the cutting tool at the same time, thus putting forward an assumption about the formation mechanism of machined surface roughness: cutting variables affect the axial tensile strain of the cutting edge through the horizontal cutting force, and cause the cutting-edge tip to vertically wedge into the machined surface, thereby influencing the unevenness of the processed surface. Based on the cutting-tool deflection model of a two-segment cantilever beam and the horizontal cutting force formula, the mathematical expression for the axial strain at the sharp tip of the cutting edge was derived. Groove milling and half-groove milling experiments were done, and the experimental results show that the roughness Ra value in the central area is significantly higher than that in the cut-in area, with its maximum average value being 1.32 times that of the cut-in area. The surface roughness rises following the rise in depth of machining and feed per cutting tooth, but this relationship is significant. The laboratory findings are consistent with the theoretical analysis results, indicating that the assumption about the formation mechanism of surface roughness should be reasonable, and the surface roughness in the central area is greater than that in the cutting tool cut-in area. The research results provide a kind of new insight into the formation mechanism of machined surface roughness, which can serve as a reference for relevant research and cutting practices.