Year

2014

Degree Name

Doctor of Philosophy

Department

School of Mechanical, Materials and Mechatronic Engineering, Faculty of Engineering and Information Sciences

Abstract

The rapid development of product miniaturization has promoted significant research in the field of micro-forming. However wrinkles and folds in the flange and cup wall, tear in the corner radius, and earing on the cup edge were often observed in a micro deep drawing process. Results of a deep drawing process have indicated that a reduction of the cup wall thickness always appears at the cup corner radius, and the cup edge thickenning compared to the initial blank thickness made it difficult to eject a cup. Generally tear began to occur at the cup corner radius.

This thesis aims to investigate the micro deep drawing of Aluminium AA1235 of thicknesses 130 to 300 μm. The above issues of cup drawing discussed above have been considered in the experiments which are supported by a three-dimensional (3D) FEM simulation. The mechanical properties and microstructure of AA1235 have been characterized by tensile tests, EBSD/SEM and TEM for a number of processes such as fully annealed, four and six cycles accumulative roll bonding (ARB), combined asymmetric rolling (AR) with ARB and heat treatment after ARB and AR process. Under these conditions, the effects of anisotropy and grain size have been considered. Tensile tests have been carried out for annealed AA1235 as well as ARB processed sample with thicknesses from 16 to 300 microns to account for the size effect in the forming operation.

The investigation specifically focus on the issues that affect the product quality such as: wrinkling, tearing, earing, size effect, heat treatment, anisotropy, grain size, die and punch corner radii, blank thickness, and clearance.

Another focus of investigation is on the deep drawing of materials processed by conditions such as: fully annealed, four-cycle ARB process and subsequent stress relieved, combined six cycles ARB process and AR. A safe region for micro deep drawing has been mapped out, based on the forming limit diagram (FLD).

A 3D FEM simulation model, fully validated by experiment, has been set up to quantify the effects of different deep drawing variables on the quality of the products such as wrinkles. Simulation results without wrinkles have already been obtained with blank thickness of 300 μm and diameter of 14 and 15 mm. Wrinkles began to appear at the cup edge to the blank thickness of 150 μm, and the more wrinkles to the blank thickness of 70 μm.

Results from the experiment and simulation have shown that the use of a bulged punch for the first time with a profiled shape between two diameters offers advantages such as; (1) prevent the formation of wrinkles, (2) reduce the occurrence of earing, (3) increase the cup wall thickness in the area of the cup corner radius and hence less tear, and (4) reduce the cup edge thickness.

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