| Summary: | 碩士 === 國立虎尾科技大學 === 機械與電腦輔助工程系碩士班 === 104 === The modern cutting technique coupled with the science/technology developments are flourishing day by day. It has resulted in the increased demand for precision and excellent products more stringently. The needs for high quality cutting-tool and machine-tool have also correspondingly increased. The machine-tool industry is in a pursuit of making high performance, high production efficiency and low cost machine tools. In addition, the functions of high speed machining and light weight structure are also usually set as a development goal. However, there is a conflict between machining precision and structure vibration. In order to get the good grinding quality for cutting-tool and better precision for machining, more analyses regarding rigidity and dynamic characteristic of the machine-tool structure itself should be performed in advance. And it would be helpful in designing and manufacturing of a better machine-tool as well as structure strengthening, which the occurrence of structure resonance may be avoided. Machine-tool manufacturers often face the problems of stiffness improvements for structure and how to find out what part should be modified exactly is the major concern. Furthermore, how to create a design rule that will minimize the development costs has also been a matter of great importance to the manufacturers.
A cutting-tool grinding machine and a simultaneous turning lathe with multiple cutting-tool were used as the analysis objects in this study. First of all, the numerical modal analyses were performed for these objects by finite element method, and the natural frequency, damping ratio and mode shape of the structures are obtained consequently. Next, the experimental modal analyses were conducted to investigate the modal characteristics of these machine-tool structures and to verify the results obtained from the numerical modal analyses. The structure modal parameters of the major sub-system and whole system of these machine tools can all be obtained from the above modal analyses. The weaker zones within the structures may be pointed out and located also from the investigations both on the results of mode shape and maximum deformation due to resonant vibration of the structure. These insufficient stiffness locations in the structures are the improvement reference for structure strengthening. By increasing the number of reinforcement ribs, changing the geometrical dimensions in the parts and changing the locations of some holes distributed in the machine-tool structure design, the stiffness on those weaker zones may be improved accordingly. Finally, the numerical analysis models are modified based on these design changes and the numerical modal analyses are performed repeatedly once again, and the stiffness improvement results of the structure can be further identified from the comparison between the modified results at that time and original prototype results. Through these two case studies it was concluded that the numerical and experimental modal analyses applied crossly on the improvement processes of the structure modal parameters for those new development machine tools is feasible.
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