Micro-cutting Mechanism And Research On Surface Integrity Based On Specific Cutting Energy

With the development of micro-electromechanical systems,the demand on micro-parts is increasing.Micro-cutting is one of the most effective methods in micro-machining and it shows its superiority in the manufacturing of miniature parts.3J33 maraging steel used in the manufacturing of the key parts of gyroscopes was studied in this dissertation.The deformation and ductile fracture of workpiece material in the deformation zone of micro-cutting were studied,and the effect of cutting-edge radius on material deformation and ductile fracture were revealed.A new method to determine the minimum uncut chip thickness in micro-cutting was proposed,and the influence of the minimum uncut chip thickness on the surface residual stress field was analyzed.The energy consumption model of micro-cutting was proposed considering the cutting-edge radius effect and the high-speed cutting condition.Orthogonal micro-cutting experiments were carried out to validate the established model.The relationship between specific cutting energy and surface generation was studied by micro-milling experiments.The cutting mechanism of micro-cutting was investigated from an energy perspective in order to lay a theoretical foundation for the popularization of micro-cutting.The material deformation and the ductile fracture in the deformation zone of micro-cutting were investigated.The distributions of stress,strain and temperature in the deformation zone of micro-cutting were analyzed by FEM.It was found that the material with greater stress,strain and temperature in the deformation zone extended to the position of tool cutting-edge.Micro scratching tests were carried out to analyze the material deformation in micro-scale machining.The plastic uplift,scratching hardness and elastic recovery rate of the material were studied.It was found that the scratching hardness and the elastic recovery rate of the material exhibited larger values when the scratching depth was relatively smaller.Chip roots experiments were carried out to investigate the chip deformation and ductile fracture in micro-cutting of maraging steel.The results showed that the chip deformation coefficient was greater with smaller uncut chip thickness.Dimples were found at the chip-workpiece separation zone,which proved the occurence of ductile fracture of the material ahead of the tool-tip.Ploughing affected the difficulty level of the occurrence of ductile fracture.It was found that ductile fracture was more likely to occur when the ploughing effect was decreased.A new method was proposed to determine the minimum uncut chip thickness in micro-cutting.The height of the stagnation zone was computed by FEM to verify the minimum uncut chip thickness obtained through the new method.The influence of the minimum uncut chip thickness on the surface residual stress field of the machined surface was investigated.In addition,the power conversion process of the machined surface in micro-cutting was analyzed.The results showed that the minimum uncut chip thickness in micro-cutting of 3J33 maraging steel was 0.25 times of cutting-edge radius.The residual stress and its influence depth were increased with the minimum uncut chip thickness.The surface stored energy was increased with the work applied to the machined surface.The energy consumption model of micro-cutting was established considering the cutting-edge radius effect and the high-speed cutting condition.The energy was divided into three portions which were shearing energy,friction energy and new surface generation energy.Orthogonal micro-cutting experiments were carried out to validate the established model.It was found that the shearing energy accounted for the largest proportion,followed by the friction energy and the new surface generation energy.The friction energy along the tool flank face was close to the friction energy along the tool rake face when the uncut chip thickness was relatively smaller.The specific cutting energy was increased with a decrease in the uncut chip thickness.In addition,the proportions of the friction energy along the tool flank face and the new surface generation energy were also increased with a decrease in the uncut chip thickness.As a result,the friction along the tool flank face and ductile fracture of the workpiece material were responsible for the size effect of specific cutting energy.Micro-milling experiments were carried out to study the relationship between specific cutting energy and surface generation.The specific cutting energy index was used to analyze the cutting mechanism,chip morphology,surface roughness and burr formation in micro-end milling.The results showed that the ploughing effect got intense with larger top burrs and smaller chips in the case of relatively greater specific cutting energy index._The specific cutting energy was divided into specific shearing energy and specific ploughing energy in micro-side milling.The chip morphology and surface integrity were analyzed based on the two portions of specific cutting energy.It was found that the length of the chips and the width of the lamellar units were increased with the proportion of the specific shearing energy.With the increase of the proportion of the specific ploughing energy,the surface roughness was decreased at first and then increased.The energy-based efficiency factor was defined as the proportion of the specific shearing energy to evaluate the efficiency of material removal in micro-cutting,and it was used to select the cutting parameters according to the specific cutting energy index and the surface roughness.It was found that small surface roughness could be obtained with a low energy consumption and a high energy efficiency when fz/re was in the range of 0.25?1.