| Summary: | 碩士 === 國立中央大學 === 機械工程學系 === 107 === Manufacturing accuracy of a pair of screw rotors greatly affects the performance of a twin-screw vacuum pump. In the practical application, form milling with the finger-shaped cutting tools is one of the commonly used ways to manufacture the screw rotors. Nevertheless, how to reduce and control the rotor profile error, caused by the tool abrasion, by means of the adjustment of cutting tool offsets on the CNC milling machine has not been studied by now. Therefore, the mathematical model is presented to generate the finger-shaped cutting tool profile based on the discrete rotor profile points with clearance. Next, the relative motion relationship between the cutting tool and the screw rotor on a traditional milling machine with the tool offsets is established to pursue the cutting simulation and study the manufactured rotor profile deviation with respect to different milling tool offsets, including three linear and two angular offsets. In addition, the sensitivity matrix method combined with the singular value decomposition (SVD) is applied to obtain a feasible combination of tool offsets to achieve the desired rotor profile accuracy. As the results shown in the numerical examples, it has been validated that the manufacturing accuracy of rotor profile can be reduced by applying the proposed method.
Keywords: form milling, tool offset, sensitivity matrix, SVD, vacuum pump, manufacturing accuracy
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