一般自由曲面應用五軸加工可令刀具軸的方向保持在曲面被切削點的法線方向或採取某特定的姿態來提高加工的品質及效率,因此五軸加工之應用逐漸普遍化,特別是若干有特殊品質需求的模具之加工或具複雜曲面之元件如葉輪曲面加工。 傳統五軸同動NC加工程式之獲得係由CAD/CAM(Computer Aided Design and Computer Aided Manufacturing)軟體將平滑的刀具移動路徑軌跡及刀軸方位的變化轉換成以有限個短直線及刀軸角度變化的線性切削指令(G01)來近似,因此產生的NC程式指令相當龐大,增加控制器讀取程式的負擔及執行加工時的速度延遲,造成加工品質不佳問題。本文主要是研究將原始CAD/CAM軟體輸出的五軸切削刀具路徑的各離散點及刀具軸方位資料擬合成五軸同動的B-spline切削指令(例如應用Siemens 840D之ORICURVE指令)來取代龐大的G01指令,如此可大為簡化加工程式長度,並提高加工品質及效率。本文將原本以線性插值進行五軸切削的刀具路徑資料(Cutter Location data,CL-data)直接轉化為用五軸B-spline曲線取代的切削指令並將該曲線的控制點數降低以壓縮NC程式長度。由本文方法所建構的五軸B-spline切削指令程式經實際在搭配Siemens 840D控制器的五軸加工機上切削自由曲面驗證結果顯示本文方法確實可行。
Some NC controllers can handle NC data written in NURBS (Non Uniform Rational B-spline) interpolated curve equation such as B-SPLINE command and G06.2 command. The use of NURBS expression enables us to decrease the amount of NC data, to eliminate the error due to the linear interpolation and to get rid of rapid acceleration and deceleration. In this paper, we use Matlab to compute and create CNC five-axis B-spline cutting commands for free form surface machining according to five-axis tool path CL-data calculated from CAD/CAM systems. For verification, some free form surface machining experiments have been performed using five-axis B-spline NC commands on a five-axis CNC machine tool with Siemens-840D controller. The results show the proposed algorithm for constructing five-axis B-spline cutting commands is doable and effectively.