Papers by Author: Zhen Yu Shi

Abstract: This paper presents an experimental study on precision milling of high volume fraction SiC_P/Al composites with single flute polycrystalline diamond (PCD) end mills. Based on a series of tests, the present study is focused on surface roughness of machined surface and tool wear of single flute PCD end mills. The effect of cutting parameters such as feed per tooth (f_z) and depth of cut (a_p) on the machined surface roughness (Ra) was investigated. Tool wear was also inspected and analyzed by Scanning Electron Microscope (SEM). According to the results of experiment, there is a layer of aluminum covered on the machined surface. This layer of aluminum can improve the machined surface quality. Through the comparsion of surface roughness in different cutting parameters, it can decrease surface roughness (Ra) by means of using very small cutting parameters. Flank wear and chipping are two main kinds of tool wear. The observed wear mechanism of PCD tools is abrasive wear and adhesive wear. The purpose of this study is to provide an experimental result for further investigation on milling of high volume fraction SiC_P/Al composites.

Abstract: The effect of cutting tool geometry has long been an issue in understanding mechanics of cutting process. Tool geometry has significant influence on chip formation, heat generation, tool wear, surface finish and surface integrity during cutting process. This paper presents the actually geometry of milling tool involved in cutting process based on mathematics analytical methods including matrix translation and rotation. Results show that according to the different helix angle and tool fluted, the geometry of cutting tool involved in cutting is different. For two or three-fluted mirco-milling tools, no mater helix angle is 30 or 45, the actually geometry involved in cutting is sphere. Different cutting tool corresponds to different sphere radius. Experiments were set up to validate the effect of cutting tool geometry on cutting forces. Results show that the smaller of the sphere radius of cutting tool, the lower of the cutting force; the larger of the sphere radius, the higher of the cutting force.

Abstract: As the deformation of chip increases with cutting speed, the morphology of chip changes from continuous to serrated type. It is supposed that serrated chips generate due to adiabatic shear instability in the primary deformation zone. A new analytical model for predicting adiabatic shear critical condition in orthogonal cutting is proposed by considering cutting conditions and properties of workpiece material. It is found that the influence of shear strain on the onset of adiabatic shear could be neglected. The shear strain rate and temperature, however, play a leading role on the onset of adiabatic shear. At lower cutting speed the shear strain rate plays a dominant role while at higher cutting speed the situation is just the reverse. With the increase of cutting speed, the yield stress, material characteristic constant and uncut chip thickness will facilitate adiabatic shear instability, while the coefficient of strain rate hardening, coefficient of strain hardening, coefficient of thermal softening, thermal diffusivity and tool rake angle have negative effect on adiabatic shear instability.