離心式葉輪葉片之精加工製程規劃

Tool Path Planning for Finish Milling the Blade of Centrifugal Impeller

葉世煒(Shih-Wei Yeh)

指導教授 ： 蔡哲雄

國立臺北科技大學/機電學院/製造科技研究所/碩士(2006年)

https://doi.org/10.6841/NTUT.2006.00285

摘要

離心式葉輪葉片其外型幾何複雜，兩葉片間在三維空間中會有Z方向的重疊，由於葉片的兩個側面係屬直紋曲面（Ruled surface）設計，因此該曲面的精切削通常利用五軸加工機以五軸同動側銑的方式來加工，使刀具與工件避免發生碰撞，提高精切削效率，且加工後表面光平度較佳。但葉片面是扭曲的不可展（Indevelopable）直紋曲面，若以一個道次直接側銑，將會對葉片面造成過切或讓切（Overcut or Undercut）的加工誤差。誤差值相對於薄的葉片厚度而言，比例相當的大，本文即是提出修正的精切削方法。
本文首先探討使用不同直徑的端銑刀側銑、不同扭曲情形的曲面及不同側銑高度等之側銑面尺寸誤差的情形，建立數據並歸納三者關係。本文精密規劃刀具側銑葉片面，沿著葉片高度方向分成三或四個道次，刀側皆非緊貼葉片面，係以計算的傾角進行。本文以葉輪葉片面及輪轂面的曲面參數方程式為基礎，並以前述側銑直紋曲面誤差分析之迴歸方程式為輔，來精密計算每個刀具路徑點的刀尖座標及刀軸方位。本文選擇以Matlab程式來執行上述的刀具路徑計算，獲得的資料再輸入Unigraphics CAD/CAM軟體，進行模擬比較加工誤差情形，並輸出五軸NC程式進行實作驗證。本文方法雖增加精切削時間，但細薄的葉片精度可大大的提升，增加葉輪使用壽命及效率。

關鍵字

五軸加工 ； 離心式葉輪 ； 葉片精加工 ； 不可展直紋曲面

並列摘要

The blade of centrifugal impeller is complicated in geometry, there is overlap of Z-direction in three-dimensional space between two blades. Because two sides of the blade are designed for the ruled surface, so the finish cutting of this surface usually uses 5-axis machines to be processed with moving 5-axis simultaneously during the flank milling operation. The blade is a twist indevelopable ruled surface, if finish cutting the blade surface by flank milling with only one pass, then it will cause serious dimensional error of the machined surface with respect to the very thin blade thickness. This paper puts forward a modificatory finish milling method.
At first this paper investigates on dimensional error for using different diameter of end mill cutter, flank milling different twisty ruled surface, and flank milling different height in order to establish the data and sum up the relations between these three situation. This paper plans accurately flank milling of the blade, it plans three or four milling processes along high direction of the blade. The side of end mill cutter is not contacted the blade surface for each milling process, in which milling with a calculated inclined angle away from blade surface. This paper based on the surface parametric equations of blade and hub and the fitted empirical equations of dimensional error to calculate accurately end mill position and its axis orientation among the milling process. This paper uses Matlab to compute all the finish milling tool location data, and then the data input Unigraphics CAD/CAM software for tool path verification and output 5-axis NC codes. Although the method of this paper increases time of finish milling, but the precision of thin blade is improved much, the impeller is increased life-span and efficiency.

並列關鍵字

5-axis machining ； Centrifugal impeller ； Blade finish machining ； Indevelopable ruled surface

參考文獻

[1] E. L. J. Bohez, S. D. R. Senadhera, K. Pole, J. R. Duflou and T. Tar, "A Geometric Modeling and Five-Axis Machining Algorithm for Centrifugal Impellers", Journal of Manufacturing Systems, Vol. 16 No. 6, 1997, pp. 422-436.

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[8] C. Menzel, S. Bedi, and S. Mann, “Triple Tangent Flank Milling of Ruled Surfaces,” Computer-Aided Design, Vol. 35, 2004, pp. 289-296.

[11] C. Y. Wu, “Arbitrary Surface Flank Milling of Fan, Compressor, and Impeller Blades,” Asme Joural of Engineering for Gas Turbines and Power, Vol. 177, 1995, pp. 534-539.