三軸工具機銑削路徑之精加工表面研究

Abstract

加工產品的表面品質不僅決定產品的外觀，更決定了產品的受力特性等重要因素。現代三軸切削中心機已具有高效率，高自由度，高剛性和高尺寸精度等優勢，如果可提高加工表面品質便可進一步提升加工效益。因此本研究將利用三軸切削中心機，針對工件常見的斜面和曲面進行精加工表面的分析和研究，考慮等高路徑的分層切深（stepdown），平行路徑的路徑間隔（stepover）並讓刀具路徑平行輪廓，殘料高度（height of scallop），主軸轉速（spindle speed），線速度（cutting speed），進給量（feed rate），刀具半徑，斜面斜率，曲面之曲率半徑，平銑刀和球銑刀對加工表面的影響。 由實驗結果發現，進給方向的表面粗糙度主要受到進給量和主軸轉速的影響；垂直於進給方向的表面粗糙度，則受到路徑和刀具所產生的殘料影響。斜面加工時，平銑刀加工的表面粗糙度不如球銑刀，球銑刀和工件相切的接觸寬度較短，不會有波紋產生且較容易得到良好的表面粗糙度；使用等高路徑加工斜面，進給方向的粗糙度較平行路徑優良，垂直於進給方向之粗糙度則是平行路徑較為優良。曲面加工時，使用球銑刀搭配等高路徑之加工表面不會有波紋產生，但是搭配平行路徑於含有Z軸的座標平面加工曲面時，容易因為刀具和工件接觸點的變化，複製刀具表面的微小誤差至加工表面形成波紋，其波紋度和曲面的曲率半徑相關，較小的曲率半徑波紋度較明顯。可利用不同刀具的表面特性進行波紋干涉，也可利用不同路徑進行互補，減少加工表面之波紋度。

Surface quality of machined products do not only determines the appearance of the products, but also determines the features of products. Novel three-axis milling CNC machines have advantages of high efficiency, high flexibility, high rigidity and high accuracy. Therefore, improving the efficiency and quality of the surface finishing by using three-axis CNC milling machine is a essential issue. This study will use a three-axis CNC milling machine to research the finishing oblique surface and curved surface. Considering the toolpath stepover, stepdown, height of scallop, spindle speed, cutting speed, feed rate, tool radius, slope gradient, radius of curvature, end mills and ball end mills effect on the machined surface. The experimental results show that feed rate and spindle speed effect surface roughness in the feed direction. The scallop is caused by toolpath and tool radius, and effect surface roughness in cross feed direction. Ball end mills is easier than end mills to get low surface roughness in oblique surface finishing. Furthermore, the surface roughness of oblique in feed direction made by contour toolpath is better than parallel toolpath. For curved surface finishing, using ball end mills with parallel toolpath will produce surface waviness caused by small shape errors of tool. Surface waviness is related to radius of curvature, and can be removed by second processing.