| Summary: | 碩士 === 國立高雄應用科技大學 === 機械與精密工程研究所 === 103 === Factors that influence the precision of conventional milling include machine rigidity and spindle run-out in addition to tool wear, chatter, and tool deflection. In particular, tool deflection exerts greater effects on surface error in micro-end-milling process than in conventional milling process; therefore, this topic should be investigated. In this study, emphasis was placed on micro-end-milling, and an underformed chip thickness model involving radial cutter run-out as well as an analytical prediction model of micro milling force were applied to predict the cyclic cutting forces, which were applied as the external forces for tool vibration in micro-end-milling process. Moreover, according to the cutting tool geometry, a graphics software program was used to visualize a three-dimensional solid modelling for a helical micro-end-mill developed by the OSG Corporation, Japan. Subsequently, the ANSYS finite element analysis software was used to analyze the natural vibration frequency of the milling cutter. To simplify the cutter geometry, the cone and flute parts were separately replaced by an equivalent cylinder with the same mass moment of inertia and deflection, simplifying the two parts to a two-segment elastic cylindrical cantilever beams. Regarding the deflection equations for the cutting tool, a dynamic deflection analytic expression for the helical micro-end-mill (equivalent to three-segment beam) was derived from the principle of linear superposition. Specifically, the elastic beam theory and quasi-static cutting load were used to generate the deflection equation for the tool-holder (the first segment) of the micro-end-mill; the Euler-Bernoulli elastic cantilever beam theory was adopted to generate the dynamic deflection analytic expression for the cone and flute parts (equivalent to a two-segment beam). The linear superposition of the two deflection equations produce the dynamic deflection analytical expression for the micro-end-mill in micro-end-milling process, which could be used to analytically calculate the dynamic deflection of the micro milling cutter in micro-end-milling process with radial cutter run-out. Subsequently, the aforementioned theories were used to predict the surface errors on the sidewalls of workpieces of material AL6061-T651, S420 stainless steel and OFC (Oxygen Free Copper) in micro-end-milling process. Several micro-end-milling experiments were then conducted, and in these experiments, the BMT-WLI white light interferometer was employed to measure the surface topography errors on the sidewalls of the workpieces. Both the simulation and experiments demonstrated that the dynamic deflection model of the micro milling cutter proposed in this study achieved superior accuracy and predicted the surface errors on the sidewalls of the workpiece in micro-end-milling effectively and accurately. Therefore, the model can be applied to process parameters planning in the early stage of micro-end-milling to improve the precision and quality of machining and to enhance the additional value of products.
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