Study On Microcutting Mechanism Based On Minimum Uncut Chip Thickness

With the development in fields of aerospace, national defense industry, modern medicine and biological engineering technology, the demands of tiny device function, the complexity of the structure and the reliability have become increasingly. The requirements of precision 3D micro parts with feature size in micrometer level to millimeter level, using a variety of materials, a certain shape precision and surface quality have increased urgently. As the micro-machining process can achieve a high degree of automation, fit to a variety of materials,3D arbitrarily shaped parts, it has become to be of a new technology in micro-scale mechanical manufacturing.In micromachining, because the cutting parameters are in the same order of cutting tool edge radius, the processing unit is small enough which in turn makes the cutting process happened within inside of material grain. Hence, the cutting process is equivalent to a discontinuous one. The effect of cutting tool micro geometry, which is ignored in traditional cutting process, has to be considered seriously in micromachining. In micromachining research, the minimum uncut chip thickness and its impact on surface integrity and chip morphology, as well as the finite element simulation in micromachining, are the key technical problems.Because of the existence of minimum uncut chip thickness, the micromachining process consists of two mechanisms:plowing and chip remove. In different cutting process, the minimum uncut chip thickness corresponds to different parameters’critical value. By giving definition of minimum uncut chip thickness in different cutting process, considering the effects of cutting tool geometry and workpiece properties, an analytical model for predicting the minimum uncut chip thickness is built. Through finite element simulation, analytical model and the AE signals produced in micro milling process, the minimum uncut chip thickness for OFHC Copper, Al 7050, Ti-6A1-4V and Inconel 718 are decided. Results show that processing technology, cutting tool geometry, workpiece mechanical and thermal physical properties influence the minimum uncut chip thickness together.By using mathematical analysis and coordinate translation, transformation, etc. methods, the actual geometry of cutting tool involved into workpiece for turning inserts and milling inserts can be get. Results show that for turning inserts, S-shaped inserts both with cylindrical control and with conical control involved in machining is sphere. Non-S-shaped inserts with cylindrical control involved in machining is ellipsoid. Non-S-shaped inserts with conical control involved in machining is paraboloid. For micro-milling inserts, the actual geometry of the four different milling insets involved in machining is sphere with different sphere radius. By using DEFORM simulation software and cutting experiments, the cutting tool geometry effect on cutting force and minimum uncut chip thickness are analysed. The simulation and experiments results can be used as theoretical and experimental basis for analyzing the tool geometry on research of mechanism of minimum uncut chip thickness.Surface integrity is the surface texture or surface state for parts after processing or treatment. The evaluation index include surface roughness, workpiece harden and microstructure, etc. Workpiece material properties, cutting tool geometry and cutting parameters are the primary reasons of affecting surface integrity. Micro-milling experiments are conducted by using four different micro-milling inserts. The workpiece are OFHC Copper, Al 7050, Ti-6A1-4V and Inconel 718. The machined surfaces in different cutting conditions are analyzed in terms of surface roughness and geometric morphology. Results show that in micromachining, there exist a critical value of feed-rate-per-tooth makes the surface roughness lowest. The critical value is close to the minimum uncut chip thickness. When the sphere radius of the cutting tool involved into workpiece is smaller, the geometric morphology texture of the machined surface distributed uniformly; when the sphere radius of the cutting tool involved into workpiece is larger, the geometric morphology texture of the machined surface presents high density in middle part and low density in edge portion. Considering cutting tool geometry and workpiece material properties, a theoretical model for predicting surface roughness is proposed. It can be used for reasonable selection of cutting parameters and cutting tools.Understanding of chip formation mechanism is the foundation of chip morphology control in micromaching. On the base of micromachining experiments, the effects of cutting tool geometry and cutting parameters on chip formation and chip morphology are studied. According to the minimum uncut chip thickness and geometric model of chip formation, an analytical model for predicting chip curve radius is developed. By using finite element simulation and experiments results, the prediction model is verified. The prediction model can be used for tool life prediction and milling parameters optimization.