Author: Zheng, Junyuan
Title: Study on size effect affected progressive and compound microforming of conical flanged parts directly using sheet metals
Advisors: Fu, Mingwang (ME)
Degree: M.Sc.
Year: 2018
Subject: Hong Kong Polytechnic University -- Dissertations
Sheet-metal work
Sheet-metal -- Formability
Sheet-metal work -- Mathematical models
Sheet-metal -- Formability -- Mathematical models
Department: Faculty of Engineering
Pages: xi, 89 pages : color illustrations
Language: English
Abstract: Forming plays an important role in modern industries to fabricate metal parts. Currently, an obvious trend of miniaturization has been rapidly developed, which would result in considerate benefits due to the potential of lighter weight, reduced cost, and less volume. To meet the demand for miniaturization, different micromanufacturing technologies has been promoted and developed in the last decades. In these technologies, the microforming process is a promising method to fabricate parts with excellent mechanical properties and low production cost. Among all the microforming processes, manufacturing of microparts directly using sheet metals is one of the efficient ways for mass production. However, in the manufacturing of microparts via micro-deformation of materials, the course-grained billet material consists of only a few grains, where the mechanical response and deformation of material behave significantly different from those in macroscale due to the size effect. To explore the size effect on deformation behavior and product quality of microparts, progressive forming systems including punching, extrusion, and blanking with three scales were developed to fabricate conical flanged parts by directly using copper sheets with different grain sizes and the related deformation behaviors were extensively studied. In addition, uniaxial tensile tests with different thicknesses and grain sizes were conducted, and FE simulations based on the fracture criteria values and the flow stress curves obtained from uniaxial tensile tests were conducted for further investigating on the deformation behavior and material flow. The numerical simulation results were compared with the experimental results. Through physical experiments and measurements and analysis of deformation related variables, the load-stroke curves are divided into several stages. For the microformed parts, the division of microstructural evolution was found and the undesirable geometries were generated, which comply with the simulation analysis of effective strain. A worse forming quality appeared on the conical surface, where the defects including microcracks, micro-bulges, micro-fissure, and micro-pits were observed. In addition, the origin of undesirable geometries and the deterioration of surface regularity were studied. From the experimental results, it is found that the properly coarse-grained microparts can reduce undesirable geometries, but at a slight cost of deteriorating the conical surface quality. This investigation thus provides an in-depth understanding and for fabricating conical flanged microparts directly using sheet metal from the aspects of deformation behaviors and product quality control and enriching the knowledge of this unique microforming process.
Rights: All rights reserved
Access: restricted access

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