非軸對稱複合包芯材擠製加工之研究

Abstract

複合包芯材之異形擠製加工是指由兩種或兩種以上不同材料所組成之複合材料，並在擠製前後具有不同斷面形狀的一種加工方法。此複合材料因其優異的機械特性，已經廣泛地應用在工業界如電極、導線和化學設備等。如超導線材在製造過程中為了增加芯材的疊積密度，往往將其做成六角形斷面，被覆於純銅之常導體內部。 本論文從單一材料之異形擠製出發，進一步擴展至針對複合包芯材之異形擠製加工，並做材料於加工過程之變形模式分析。研究中使用極限解析（Limit Analysis）中的上界法（Upper-Bound Method），利用滿足塑性邊界流動、材料不可壓縮等條件，建構在擠製方向速度分量可以為凸狀分佈的運動可容許速度場，並藉著簡單形搜尋（Simplex Method）最佳化方法改變可變參數，求出使塑性變形所消耗總功率為最小者之運動可容許速度場，從中可求得材料各點的速度分佈、加工所需之能量及其他的物理量。接著探討在不同的加工條件（模具半模角、斷面減縮率、模具面摩擦因數、材料組合情形與擠製產品外形）組合下，各組成材料間的變形行為與彼此間的影響，進而提供健全擠製的加工範圍。最後並以實驗來印證理論解析所提出之結論是正確與可靠的。

Composite clad rods which are composed of two or more different materials are often extruded to product which have the different non-axisymmetric cross sectional areas from the billets. Owing to their excellent mechanical characteristics, composite clad rods are being used extensively in the industry as electrodes, conductors and chemical devices. For instance, in the processing of superconductor wire, in order to increase the packing density, it is usually packing superconductor rods which have a hexagonal cross sectional area next to each other inside the high purity copper tube. In this study, we started from the extrusion of monometallic clads with non-axisymmetric cross sectional areas, then extended to the extrusion of composite clad rods. We present a numerical simulation model based on the upper-bound theorem to analyze the composite clad rods under extrusion. A three-dimensional admissible velocity fields in with the component in the extrusion axis has a convex distribution is derived under the condition of incompressibility of materials or the constant volume flow. The SIMPLEX optimum method was adopted to minimize the total extrusion power by varying the value of many optimal parameters. Then, we discuss the simulated numerical results for various process variables such as semi-die angle, reduction of area, friction between die and billet, strength ratio of constituent materials and product shape complexity. Conditions for which the billet can be safely extruded is also discussed. Finally, an extrusion experiment is conducted and it is found both the analytical and the experimental results are very closed.