Investigation of micro extrusion & deep drawing processes via experiment & FE simulation

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Investigation of micro extrusion & deep drawing processes via experiment & FE simulation


Author: Yang, Bo
Title: Investigation of micro extrusion & deep drawing processes via experiment & FE simulation
Degree: M.Sc.
Year: 2011
Subject: Hong Kong Polytechnic University -- Dissertations
Metals -- Microstructure.
Microelectromechanical systems -- Materials.
Department: Dept. of Mechanical Engineering
Pages: xiii, 121 leaves : ill. (some col.) ; 31 cm.
Abstract: Due to the trend of product miniaturization in commercial market, micro-parts are highly demanded in the last decade, which are widely used in laptops, cell phones, IC industry and micro sensors. It is estimated that the whole industry brought by the micro products will reach billions of dollars annually. Some special manufacturing techniques such as corrosion, EDM, LIGA is possible to fabricate micro-parts, but they are all time consumer with high cost, which may not meet the basic requirement of commercial market, the mass production. Metal forming process, due to its high productivity, high material usage and the good mechanical properties of the formed parts, presents a promising manufacturing process for mass production of micro-parts. However, when dimensions of parts are scaled down to micro/meso range, traditional theory is no longer adequate in that condition, the so called size effect occurs in microforming. The relative forming process theory and technology in this field are still not mature. Hence, it is necessary to establish a systematical theory about the material behavior under microforming and the operation procedures in microforming. In this thesis, size effect is studied systematically and experimentally, using both sheet metals and bulk material. Copper sheet with the thinnest down to 0.1mm and cylinder billets with the three dimensions down to 1mm are prepared. Specimens are carefully divided into several groups, specific heat treatment conditions are designed for each group of samples, in order to get different grain size. The size effect in material flow stress is investigated in uniaxial tension test of sheets. The results show strongly size effect for different groups of specimens. Besides, two microforming process, micro-deepdrawing and micro extrusion are investigated in this thesis. Due to the difficulty of positioning tiny circular samples in micro-deepdrawing, a new blanking-deepdrawing multi mold is designed for this experiment, which combined blanking and deepdrawing together. The influence of process-determining factors, e.g. drawing clearance C, die radius Rd and the punch radius Rp, are studied. In the micro extrusion process, 4 different types of extrusion are investigated, which are forward extrusion, forward-rod & backward-can compound extrusion, backward extrusion and double cup extrusion. FE-Simulation using commercial software Abaqus is implemented for these two microforming processes. The experimental data of material flow stress is involved in the simulation, and the results are compared with experiment. The influence of friction, which is hard to investigate in real experiment, is simulated in Abaqus.

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