CMM與CAD/CAM系統在模具整合製造上的應用

隨著精密模具幾何形狀與機能的日益複雜，逆向工程製造觀念的興起，三次元量測儀與 CAD/CAM系統在整個模具的電腦整合製造中，有著日趨重要的地位。本文整合了三次元量測儀與PC級CAD/CAM軟體，以量測所得的點群數據資料為基礎，從自由曲面的取樣量測、曲面重建、加工、檢驗到誤差的評估與原因的分析，進行逆向快速造模技術與自由曲面誤差驗證的研究。首先，以CMM作為曲面量測資料數位化的工具，透過自行發展的轉檔程式，將量測資料點轉入SmartCAM中，建立舉昇曲面，以重建出工件的曲面模型，並產生加工程式，最後再利用CNC加工機加工出仿雕成品。在產生刀具路徑的過程中，為減少電腦處理的點群數量，我們利用SmartCAM作了曲線模型資料點的簡化；同時，為了減少資料點簡化後所新增的誤差，又利用Spline曲線進行曲面模型的修正；最後，並以實際的加工成品，進行誤差的驗證。為了驗證仿雕曲面的精度，並了解逆向工程中的各項製程誤差，我們利用自行發展的程式，將幾何模型資料庫中的點群資料轉成 CMM的自動量測程式，量出加工成品的實際尺寸。並且利用量測所得的實際結果與原來CAD Model中的資料，計算出Z值的誤差。再利用這些檢測點在Z方向的誤差，畫出誤差的Z-map圖形，觀察誤差分佈的狀況；或者將檢測結果轉入SmartCAM中，繪成檢測還原圖，與原來CAD Model 中的圖形作比較，藉以分析誤差產生的原因，改善製程中的各項疏失。我們發現來自量測與工件座標定位上的誤差必需加以注意，而來自幾何模型與資料點簡化的誤差，如果以是Cubic Spline作為曲線擬合的幾何模型，幾何偏差並不嚴重。

關鍵字

三次元量測儀；電腦輔助設計製造；逆向工程

並列摘要

With the increasing product geometry complexity, product functional requirements， and the arise of reverse engineering technology，the integration of CMM(Coordinate Measuring Machine) and CAD/CAM in mold/die design and manufacturing has taken its role. The successful implementation of reverse engineering technology starts from the digization of the procut' s geometry. First, the problem is how to perform path planning so that the surface geometry can best be preserved. Then, the next question is how to interface these digitized point data into the commercial CAD/CAM systems most efficiently and accurately.When the point data were translated into the CAD/CAM systems, the choose of proper surface building procedure is very important. The machining scheduling and cutting process parameters may contribute to the accuracy of the final reverse- manufactured die. In the thesis, the rapid prototyping of die by reverse engineering technology was investigated. The part was digitized by CMM in section line format. The point data set was reformatted and translated into the SmartCAM package. The part surface geometry was rebuilt from section lines into lofted surface.In order to speed up tool path generation, data reduction capability inside SmartCAM was utilized to build the model. An experiment was designed to evaluate various error sources such as digitization, model building and surface model selection.A CAD model of complex free-form surface was built. From the CAD model, one hundred thousand projection points was created and were used as error checking points. After the part was machined, coordinates of fifteen hundred points of these check points was measured by CMM.It was found that the inconsistancy in coordinate orientation of machining and measurement systems was the major error sources. Sharp edges or boundaries may be lost in the digization process. Surface model built by the data reduction set with cubic spline curve fitting will only contribute minor error.

並列關鍵字

CMM ； CAD/CAM ； Reverse Engineering

國際替代計量

CMM與CAD/CAM系統在模具整合製造上的應用

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