Optimal Parameter Design of High-speed CNC Milling Process Using Taguchi Methods

[[abstract]]高速、高品質、與短交期，已成為模具製造業的發展趨勢，而以往針對特定產品所開發的最佳加工參數，對其它模具加工而言，未必適用。高速CNC銑削加工本質上為一種轉寫性的加工，以田口方法的觀點，若程式輸入之尺寸、或幾何形狀，能夠在沒有任何因素之干擾下，完全的轉寫在加工件上，則稱高速CNC銑削加工系統達到理想機能。但是，在銑削過程中，難免因為控制因素之參數設計不完美、或受到誤差因素之干擾，使得加工件之尺寸、或幾何形狀之精確度產生變異。為此，本研究使用田口方法動態特性理論，提出「程式輸入尺寸vs.輸出加工件尺寸」、「程式輸入幾何形狀vs.輸出加工件幾何形狀」、與「雙輸入vs.雙輸出理想機能模型」三種理想機能模式，滿足模具製造業對於高速、高品質、與短交期之需求。實驗結果顯示，藉由田口方法動態特性理論、與理想能模型之建立，可增進模具銑削加工之尺寸、與幾何形狀精確度，並可同時滿足高速、高品質、與短交期之需求。 其次，在實際工業應用裡，常遭遇多種品質特性同時尋求最佳化的問題，以高速CNC銑削加工為例，工件尺寸精確度、表面粗糙度、與刀具壽命，往往是重要的品質特性指標，由於最佳製程參數設計常依品質特性而異，以至常發生不同品質特性間之最佳參數設計常會發生矛盾之現象。為解決此困擾，本研究應用田口品質損失函數的理念，以總品質損失最小化之觀點，來開發高速CNC銑削加工多重品質特性之最佳製程參數。由實驗結果得知，經由多重品質特性所獲得之最佳加工參數，其總品質損失皆會低於任何單一品質特性所造成之品質損失。[[abstract]]The mold & die industry is developing with the characteristics of high speed, high quality and short lead time. However, the optimal processing parameters that are developed for specific products are not applicable to other mold processing applications. The high-speed CNC milling process is a transformable writing process in inature. According to Taguchi Method, the CNC milling process system demonstrate its ideal function when the programmed dimensions or geometries can be applied to products without any interference in the transformable writing process. However, the dimension or geometry of a product may vary in accuracy due to incomplete parameter design of control factors or the interference of noise factors that might occur in the CNC milling process. In the circumstances, the Study provides three ideal functional models — Programmed Dimension vs. Product Dimension, Programmed Geometry vs. Product Geometry, and Double Input vs. Double Output — based on the dynamic characteristic theory of Taguchi Method to meet the requirements for high speed, high quality and short lead time of the mold & die industry. Relevant research show that the accuracy of dimensions and geometries of the CNC milling process can be improved and, thus, the requirements for high speed, high quality and short lead time are met by implementing the dynamic characteristic theory of Taguchi Method and creating ideal function models. In actual industrial applications, on the other hand, optimization is usually requested simultaneously for multiple quality characteristics. The dimensional accuracy, surface roughness and tool life of a product, for example, are the most important indicators of quality characteristics in the high-speed CNC milling process. However, since the design of optimal processing parameters varies depending on quality characteristics, conflict may occur between optimal parameter designs of different quality characteristics. To solve this problem, the Study provides optimal processing parameters for multiple quality characteristics of the CNC milling process based on Taguchi quality loss functions and from the viewpoint of minimizing total quality losses. The result of the experiment shows that the total quality loss of the optimal processing parameters designed for multiple quality characteristics is lower than the quality loss brought by any single quality characteristic