Research On Numerical Simulation Of Micro Copper Cylinder Upseptting Deformation Process

The existing means of finite-element method is based on the classic forming theory, so it needs to be improved to simulate the micro forming. In the thesis, the similarities and differences between the processes of macro and micro upsetting are analysed by experiments and metal plasticity deformation theories. Then transitional surface layer model are established to simulate the process of micro upsetting.Using the precision micro-forming apparatus, the constant-strain rate compression experiments are performed with the pure copper cylinder. The differences between micro forming and macro forming are analysed through observing and observing the topography and microstructure of the deformed specimens. And the effects of specimen size, grain size and strain rate on the flow stress have been investigated with the upsetting tests. The experiment results show that the micro forming follows the plasticity forming theories and Hall-Petch relations. However, it has also demonstrated its features: flow stress of specimen is not only the function of grain size but also decreases with the decreasing of the specimen size. When the specimens have the same diameter, the proportion of the surface layer increases with the decreasing of the specimen height, which leads to the more obvious size effect flow stress. The grains located at the surface of the specimen are less restricted than grains inside the material. In micro scale, the deformation of the surface grain likes the deformation of monocrystal, and inhomogeneous flow of material is obviously emerged.The transitional surface layer model is established based on the character-ristics of the micro forminging. The specimen is divided into three parts: surface layer, transitional layer and interior portion. The deformation of surface grains tends to that of monocrystal deformation, and the inhomogeneous properties of the grains are adopted by considering the difference of grain orientation. The deformation of transitional grain is influenced with the neighbouring grains. The deformation of internal grain is considered as the polycrystal deformation.The finite element simulation software is used to analyze the micro...