Processing Foundation And Experiments In Micro-Milling

Nowadays, the requirements of miniature and microparts have a high growth in the academic and industrial fields. With the variety of microcomponents demands, the conventional micromanufacturing technology, Micro-Electro-Mechanical System (MEMS), has limitations in the fabrication of workpieces with different materials and complex shapes. The microcutting technology can fabricate microcomponents with 3D free form surfaces and various engineering materials, and fill the gap between micro/nano and macro domain. Based on systemically summarizing the micromachining equipments and processing mechanism, the key technologies about micromachining, such as measuring the residual stress in the micro milled elastic alloy film, predicting the surface roughness, modeling the 3D microcutting force and analyzing the wear mechanism of ultra-fine grain carbide microcutter, have been investigated.Any micro deformation caused by the residual stress will damage the performance of the micro parts. There are difficulties to measure the residual stress for the micro/nano characteristic dimension of the micro components. In this paper, the microgroove in 3J21 elastic alloy thin film was fabricated using the developed 3-axis precision micromilling machine tool, with the TiAlN coated carbide micro-end-milling cutter. The cutting diameter of the micromilling tool is 0.15mm, the minimum thickness of the film in the microgroove bottom is 8μm, and the yield is greater than 80%. Nanoindentation is used to measure the relationship between the load and deformation, using the Nano Indenter XP system, MTS. Based on the deep measurement theory and the data of load-deformation, the Young's modulus of the thin film in the microgroove bottom is 56.05±3.96GPa. The microbridge testing theory, using in the manufacturing of silicon materials with MEMS, is introduced to the metal micromachining field. The mechanical model is developed based on the microbridge testing and the plate theory. The residual tension stress is 189.4±3.61MPa using the developed mechanical model. This method has solved the problem that the residual stress in the micro milled elastic alloy thin film couldn't be measured.The surface roughness is an important parameter for the evaluation of the surface quality. The mathematical model was developed for the surface roughness prediction using RSM. Analysis of variance was performed to evaluate the significance of regression. The fitting degree of the model is 97.5%. The SQP was used to optimize the processing parameters. The error between the theoretical optimum solution and the measuring value is 8.1%. The results show that the optimum solution is authentic. The influence of cutting parameter's main and interactive effects on the surface finish was analyzed by factorial design. The results show that: L and D take more effects on surface roughness than fz and ap. This is the major difference from the conventional end milling. The surface finish will go to bad with the decrease of fz for the size effect of edge radius when fz is less than the minimum cutting thickness.The cutting force is important to understand the micromilling mechanism, plan appropriate cutting conditions, optimize the micro tool geometry, and monitor the process state. A 3D mechanical cutting force model was developed based on the shear and slip-line field method. The size effects of tool edge radius, minimum chip thickness and elastic restitution in the ploughing field were included in the cutting force model. A new instantaneous undeformed chip thickness was used to represent the real trajectory of the tool tip. The simulated cutting force profile of the proposed model has good agreement with the experimental data, compared to the conventional cutting force model with the assumption that the tool tip is sharp. The influence of cutting conditions on the cutting force was analyzed based on the experiments.The investigation of microcutter's wear type and mechanism is helpful to understand the microcutter's wear reason, improve machinability, and prolong the cutter life. Series of cutter wear experiments were conducted to research the main wear type and its mechanisms of the TiAlN coated and uncoated carbide microcutter. The results show that the notable feature in the wear of microcutter, different from the traditional milling technique, is that the wear of microcutter mainly occurs in the mini field of the micro tool nose. And tool nose breakage is serious than conventional milling.