As a result of the remarkable demands on electronic and other portable compact devices, the need to produce various miniaturized parts, particularly those made from metallic sheet is growing. In other words, in order for manufacturing companies to stay in competition, they are required to develop new and innovative fabricating processes to produce micro components with more complex features and a high standard of quality and functionality. Microforming is a micro fabrication process that can be employed efficiently for mass production with the advantages of greatly minimizing material waste and producing highly accurate product geometry. However, since the clearance between the rigid tools, i.e. punch and die, utilized in microforming techniques is relatively very small, there is a high risk of damaging the tools during the forming operations. Therefore, the use of forming tools made of flexible materials in sheet metal forming processes at micro scale has powerful potential advantages. The main advantages include a reduction in the production cost, eliminating the alignment and mismatch difficulties, and also the creation of parts with different geometrical shapes using the same flexible tool. As the workpiece is in contact with a flexible surface, this process can significantly improve the quality of the obtained products. Despite these clear advantages, micro flexible forming techniques are currently only utilized in very limited industrial applications. One reason for this is that the deformation behaviour and failure mode of sheet metals formed at micro scale are not yet well understood. Additionally, the experience-based knowledge of the micro-forming process parameters is not sufficient, particularly when flexible tools are used. Hence, to advance this technology and to improve the production quality of formed micro parts, more investigation of the key process parameters related to the material deformation are needed. The main contribution of this work is the development of a novel technique for achieving micro deep drawing of stainless steel 304 sheets using a flexible die and where an initial gap (positive or negative) is adopted between the blank holder plate and an adjustment ring utilized in the size-scaled forming systems developed for this purpose. The interesting point here is that this study presents the first attempt of employing flexible material as a forming die tool in the micro deep drawing technology to produce micro metallic cups at different scaling levels. Polyurethane rubber materials are employed in this study for the forming flexible die with various Shore A hardness. Also, the stainless steel 304 sheets utilized for the workpieces have different initial thicknesses. Various parameters that have a significant influence on the sheet formability at micro scale are carefully considered, these include initial gap value, rubber material properties, initial blank thickness, initial blank diameter, friction coefficients at various contact interfaces, diameter and height of the rubber die and process scaling factor. The size effect category of process dimension was also taken into account using similarity theory. Three size-scaled micro deep drawing systems were developed correspondingly to three different scaling factors. In each case, finite element simulations for the intended micro drawing systems are performed with the aim of identifying optimum conditions for the novel forming methodology presented in this thesis. The numerical models are built using the known commercial code Abaqus/Standard. To verify the microforming methodology adopted for the proposal technique as well as to validate the predictions obtained from simulations, an appropriate number of micro deep drawing experiments are conducted. This is achieved using a special experimental set up, designed and manufactured to fulfil the various requirements of the micro-forming process design procedure. The new knowledge provided by this work provides, for the first time, a predictive capability for micro deep drawing using flexible tools that in turn could lead to a commercially viable production scale process.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:622013 |
| Date | January 2014 |
| Creators | Irthiea, Ihsan Khalaf |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/4807/ |
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