Investigation On Cutting Force Modeling And Tool Wear Factor In Micromilling

With the rapid development of aerospace, medical equipment and electronic communication device, et al, people have an increasing demand for miniature components, which have more and more complex structure, higher reliability and higher precision. In the past decades, micro electro mechanical system (MEMS) technology has been widely used in the manufacture of various miniature components. However, the micro electro mechanical system technology has some obstacles, such as the poor 3D processing ability, the relatively low processing efficiency, the relatively high processing cost and mainly confined to the processing of silicon based materials etc, thus it has been unable to meet the needs of the growing demand for miniature components and reduce the cost in industry. The micromilling technology overcomes the obstacles of micro electro mechanical system technology. Micromilling process, one of micro machining methods, has wide applications in micro and ultra-precision devices for its prominent capabilities in versatile material processing and complex 3D surface machining. In addition, it can process high aspect ratios of parts, and has more excellent economic efficiency, and rapid process compared to micro electro mechanical systems method. Thus, micromilling technology has been one of the main machining technologies for complex micro parts.In general, micromilling means the machining of the characteristic dimensions between 1μm and 1 mm, and the milling cutters with the diameter below 1 mm. However, due to sharp decreases of the machining scale and parameters, micromilling process shows many differences from traditional milling, such as size effect, minimum chip thickness, effective rake angle, microstructure of workpiece material and tool runout, etc. At present, the processing mechanism of micromilling is still not clear, so the processing technic of traditional milling technology is usually used in micromilling process. Micromilling cutting force is the basis of process control, parameter optimization and understanding the machining mechanism in micromilling, and tool wear is one of the most important factors that affect the machining accuracy and production efficiency of miniature components. This paper takes the machining mechanism of micromilling as the breakthrough, and the research on the precise modeling and simplification of micromilling cutting force model and tool wear factor as the concrete object, so as to lay a theoretical foundation for the process control, process optimization and understanding the machining mechanism in micromilling, and finally to provide scientific guidance for improving the machining quality, production efficiency and reduce processing cost of micro components. The main research contents and innovation points in this paper are summarized as follows:(1) The progress of cutting force modelling and tool wear in micromillingThe cutting force modeling and tool wear of micromilling is thoroughly discussed and summarized, by combining the latest research progress of the micromilling technology at home and abroad, and starting from the different mechanics between micromilling and traditional milling. The effects of cutting edge radius, tool runout and deflection on cutting force modeling and tool wear are surveyed. Explore the problems in cutting force modeling and tool wear that still need to pay attention to, and look ahead its development direction.(2) A generic instantaneous undeformed chip thickness model in micromillingWith the insufficiency of celebrated instantaneous undeformed chip thickness model as the breakthrough, the actual cutting area in micromilling is derived, and then a generic instantaneous undeformed chip thickness model is proposed by considering the trochoidal trajectory of the tool tip, the tool runout and the cutting trajectory of all passing teeth in one cycle. The accuracy of the model is verified by the real experimental data and the result are shown superior to known models.(3) Identification of dual-mechanism cutting force coefficients for micromilling cutting force modelWith the least identification experiment, more accurate micromilling cutting force prediction effect and a larger serviceable range as the goals, this study presents a new approach to identify the dual-mechanism cutting force coefficients based on the characteristic of instantaneous undeformed chip thickness which has considered the tool runout. Simulations and experiments are conducted to validate the proposed approach, and the results show good agreement between them.(4) A micromilling cutting force simplified modelWith the contradiction between computational efficiency and prediction accuracy of micromilling cutting force model as the breakthrough, a micromilling cutting force simplified model is proposed based on the analysis of the actual entry angle and exit angle which consider the influence of tool runout. The model only needs one calculation of the average cutting thickness, which can realize the simulation of micromilling cutting force. The validity of the simplified model is verified by comparing the simulation results with the micromilling force model which adopt the traditional discrete method.(5) Micro tool wear factorAt present there is still no versatile tool wear evaluation criteria and wear factor in micromilling. Based on the experiment of micromilling AISI4340 workpiece, two commonly wear evaluation criteria (the flank wear and diameter wear) are compared, then the influence factor of micromilling cutting parameters on tool wear and the optimal cutting parameters are discussed.