Annual Report 2002–03

傑出研究計劃 Outstanding R e s e a r c h P r o j e c t Faculty of Engineering 工程學院 從熱能分布解讀金屬沖壓過程 金屬沖壓加工在現代製造業中非常重要，也是香 港和珠江三角洲逾萬家工廠的生計。在茂森精藝 金屬製造有限公司和香港創新及科技基金的資助 下，自動化與計算機輔助工程學系杜如虛敎授和 徐揚生敎授領導開發了一個金屬沖壓加工過程的 診斷系統。由於金屬板料在沖壓過程中需要吸收 能量才能變形，這種能量會進而轉化為熱量，所 以只要分析熱能的分布，就可以判斷是否有過度 的殘餘應力和異常的應變分布等，從而找到沖壓 過程中的潛在問題的根源。 這種嶄新技術結合了紅外熱像技術與有限元分 析。為解決二維圖像中部分資訊會被掩蓋的缺 陷，他們利用計算機視覺技術，將紅外圖像作三 維重建，以大幅提高判斷的準確性；而有限元分 析則可快速預測金屬板件的張力和溫度，並輔助 模具設計。他們又提出另一個基於相似性理論的 新方法，利用金屬零件的幾何形狀，以及理論上 這些形狀在沖壓過程中與應變分布及溫度分布的 密切關係，來比較零件沖壓時的實隙溫度分布， 從中找到沖壓過程中的各種問題。這技術協助廠 家將複雜的診斷和調試工作，從過去的數星期減 至現在的數天，甚至數小時。 Diagnosing Sheet Metal Stamping Processes Based on Thermal Energy Distribution Sheet metal stamping, the business of some 10,000 factories in H o ng K o ng and the Pearl River Delta, plays an important role in modern manufacturing. W i t h the support o f Mansfield Manufacturing Co. Ltd. and the Innovation and Technology Fund, Prof. R. D u and Prof. Y.S. X u o f the Department o f A u t o m a t i on and C omp u t e r - A i d ed Engineering led a team to develop an innovative system for diagnosing sheet metal stamping processes. The basic idea o f the research is based on the fact that sheet metal absorbs energy to deform during the stamping process. This energy is converted to heat and, hence, by analysing the heat distribution, one can diagnose f o r ma b i l i ty problems such as wrinkling, tearing, and large residue stress. The system has two key technologies: infrared thermal imaging and Finite Element Analysis ( F E A ). To solve the occlusion problem in 2 D infrared images, the researchers made use of computer vision techniques to reconstruct the 3 D thermal distribution model f r om several infrared images. To predict the thermal distribution, they developed a F E A model that w o u ld help the die design. They also devised a new method based on similarity measure to diagnose the stamping process, as the geometrical shape o f the parts has a close relationship w i t h the temperature distribution o f the part. The n ew system can quickly uncover the hidden problems in the stamping process and cut d o wn the d o wn time and tryout time f r om days to hours. 56 香 港 中 文 大 學 年 報 CUHK Annual Report 2002-2003