Investigation of micro shearing & micro hole-flanging processes customized for progressive forming via experiment & FE simulation

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Investigation of micro shearing & micro hole-flanging processes customized for progressive forming via experiment & FE simulation

 

Author: Fu, Changmeng
Title: Investigation of micro shearing & micro hole-flanging processes customized for progressive forming via experiment & FE simulation
Degree: M.Sc.
Year: 2015
Subject: Microfabrication
Microtechnology
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Mechanical Engineering
Pages: xii, 114 pages : illustrations (some color)
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2825398
URI: http://theses.lib.polyu.edu.hk/handle/200/8185
Abstract: As an ancient and also modern art, forming plays a more important role than anywhere in the automotive manufacturing industry, where almost all metal parts from the body structure of the vehicle to the smallest lug nut on the wheels are able to be fabricated by industrial metal forming processes. Currently, there appears an obvious and rapidly-developing trend in automotive industry, which is miniaturization. This trend would result in considerate benefits due to the potential of lighter weight, less volume, reduced cost and improved efficiency. Also this kind of trend of miniaturization is occurring in other industry areas, such as electronics, automobiles, biomedicine, aerospace and so on. For meeting this kind of demands, different micromanufacturing technologies has been prompted and developed during last decades. Among all micro manufacturing technologies, microforming process provides a promising way to produce final parts with near-net shape, excellent mechanical properties and low production cost. 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, influence of size effect over flow stress, deformation properties and ductile fracture criteria on the sheet metal is studied, via conducting standard uniaxial tensile tests with different thicknesses and grain sizes. And the flow stress curves are analysis from different angles to find out the influence of size effects. Finally FE simulations on tensile tests are conducted to obtain the ductile fracture values under different fracture criteria, for the purpose of simulation of specific micro forming processes.
Then, two scenarios for shearing process are designed and investigated. The two sets of tooling of the shearing processes are designed based on a micro progressive forming system. Load-stroke curves, forming quality of formed billets and material flow behaviors are all discussed for two scenarios by implementing experiments and FEM simulation. Materials used in experiments are heat treated in different conditions for distinctive grain sizes, in order to research the influence of grain size effect on micro shearing processes. All material data required in the FEM simulations are obtained by uniaxial tensile tests and simulations In addition, a series of micro-hardness tests are performed for scenario 1, for investigating the grain size effects over relationship between hardness and the distance to the hole. Finally, a specific micro hole-flanging process customized for a micro progressive forming process is investigated. Before this research, the flanging process has never been considered under micro scale. The tailor-made hole-flanging process is designed to perform with ironing, as a low clearance-thickness ratio is adopted and the metal is squeezed between the punch and the die, leading to a thinner thickness. In order to investigate the grain size effects on the micro hole-flanging with ironing, materials used in experiments are annealed in different conditions to obtain different average diameters of grains. Load-stroke relationships, inhomogeneous deformation phenomena of final parts, dimensional accuracy and material flow behaviors are all discussed based on the results of experiments and FEM simulation.

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