| Author: | Liu, Hui |
| Title: | Study on the size effect affected the deformation behaviour and quality of the microgear fabricated by progressive microforming |
| Advisors: | Fu, Mingwang (ME) |
| Degree: | M.Sc. |
| Year: | 2021 |
| Subject: | Gearing Microtechnology Micromachining Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Mechanical Engineering |
| Pages: | xiii, 101 pages : color illustrations |
| Language: | English |
| Abstract: | In the recent years, there is a growing need for micro parts in many industrial products of automobile, medical, telecommunications and many other industries. To satisfy the needs of miniaturization, different microforming technologies have been promoted and developed in the past years. Among these technologies, microforming technology stands out due to its low production cost, high forming speed and easy processing of original materials. In all microforming processes, the direct use of sheet metal to produce microfabricated products is one of the effective methods for mass production. However, the size effect has an extremely important influence on the forming effect of microforming parts. Depth understanding of the size effect on the forming effect of microparts will contribute to the development of designing and manufacturing industrial microparts. With the development of Micro-Electro-Mechanical Systems (MEMS), the demand of microgears is increasing. It is necessary to pay more attention to the manufacturing of the microgear with shaft. In this paper, H75 brass with excellent mechanical properties and large-scale application is selected as the manufacturing material of microgears. Firstly, the forming process of micro gear is simulated by DEFORM software to verify the formability of the microgear. To obtain the mechanical properties of the original materials, the brass sheets were annealed at different conditions, the dog-bone-shape specimen with different grain size was tensile tested, the results were calculated and fitted, and then the fitting results were input into the simulation to study the effect of the different grain size on forming microgear. Then, the microforming system was designed and produced and two kinds of microgears with different grain size were formed by this forming system. The forming results of microgears with different grain size are analyzed. The results show that the quality of the die including surface roughness, dimensional accuracy and die clearance, has important effect on the forming results of microgears. When the grain size of the original material is larger, the anisotropy of single grain has an obvious effect on the forming effect. With the increase of grain size, the undesirable geometries and surface quality worsen, but the deformation load are smaller, which indicates that it need less manufacturing power. These findings facilitate the production of microgears in the aspects of process monitoring and product qualities control and enrich the understanding of sheet-metal bulk forming in the progressive microforming. At last, the reasons of forming problems are analyzed, aiming at the problems, the microforming system is improved and the dies are redesigned. |
| Rights: | All rights reserved |
| Access: | restricted access |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| 5934.pdf | For All Users (off-campus access for PolyU Staff & Students only) | 7.53 MB | Adobe PDF | View/Open |
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