Research On Basis Of Size Effect Inmicro Milling

Micro milling has been one of the most effective technologies for micro-machining due to its controllable machining accuracy, relatively high machining efficiency, capability to fabricate complex structures and curved face and low processing cost. However, the application of micro milling in the machining of micro products is mainly limited to the size effect, which could lead to serious burr formation and bad surface roughness. So aiming at decreasing the burr formation and the surface roughness, the influence of the size effect which is mainly caused by the similarity between chip thickness and the cutting edge radius or the workpiece material’s grain size is researched; the machining parameters chosen criteria is proposed to optimize the cutting parameters in this paper. The main research work is as follows:(1) The influence of cutting edge radius and undeformed chip thickness on specific cutting energy is revealed by modeling of the micro cutting process, FEM simulation and MD simulation. In order to calculate the specific cutting energy caused by theoretical sharp cutting edge, an experiment research method which could separate the specific cutting energy caused by the cutting edge from the total specific cutting energy is proposed. This method could be used to decouple the cutting edge size effect and the materials size effect.(2) The influence of cutting edge radius on specific cutting energy, burr formation, surface roughness and chip formation is researched by FEM simulation and cutting experiments. When the ratio of undeformed chip thickness to cutting edge radius(a0/rn)<1, the energy spent in chip formation decreases but the energy which is consumed due to materials’ extrusion deformation caused by the cutting edge increases as the a0/rn decreases, which leads to the rapid increase of the specific cutting energy. The specific cutting energy under different a0/rn could quantify the influence of cutting edge radius size effect on micro cutting.(3) The influence of material’s grain size on specific cutting energy and burr formation is researched by different grain size oxygen free copper cutting experiments. The result shows that the amount of the crystal boundary which is machined and the crystal which is likely to form the burr in tool’s per unit cutting distance will lead to the variation of the specific cutting energy. The influence of material’s grain size on specific cutting energy in micro cutting is less significant than the influence of a0/rn on specific cutting energy.(4) According to the influence of a0/rn on specific cutting energy, the influence area of micro milling size effect which is featured by strong, transitional and weak size effect area is proposed and the selection principle of the machining parameters of micro milling is established using the influence area of micro milling size effect. The oxyacid free copper, 6061 aluminium alloy, and pure tungsten machined by the self-made PCD micro milling tool verify the feasibility of the selection principle. Typical miniature structures are fabricated to show the machining quality of desirable burr formation and surface roughness.