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Numerical and Experimental Study on Direct-reverse Quick Gas Blow Forming of Magnesium Alloy Sheet

Author: ZhangZhiPeng
Tutor: WangGang
School: Harbin Institute of Technology
Course: Materials Processing Engineering
Keywords: direct-reverse bulging pre-forming die design thickness distribution AZ31magnesium alloy
CLC: TG146.22
Type: Master's thesis
Year: 2012
Downloads: 11
Quote: 0
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Abstract


Uneven thickness distribution is inevitable in traditional sheet metal quick gasblow forming. Direct-reverse quick gas blow forming (DR-QGBF) can improve boththe thickness distribution and the formability effectively. The key point inDR-QGBF is the pre-forming die design. Numerical simulation and experimentalstudy on DR-QGBF of magnesium alloy was investigated in this thesis.Finite element analysis software MARC was used for the pre-forming diedesign in direct-reverse QGBF of cylinder parts. It was found that wall thicknesswas improved significantly with inner straight line and outer curve outline in thepre-forming die. The feeding circular area in flange played a role of feeding inDR-QGBF. The larger the circular area width, the better the feeding effect. But toolarge width would cause the waste to increase.A reverse calculation pre-forming die design method was proposed based onsub-regional forming assumption. With this method, most dimensions of thepre-forming die can be calculated. The dimension that cannot be calculated can bedetermined by finite element analysis. It was proved that this method was feasible inpre-forming die design.DR-QGBF experiments of hemisphere and cylindrical parts were conducted. Itwas shown that bulging formability of magnesium alloy sheet and thicknessdistribution of the as-formed parts could be improved with reasonable pre-formingdie. When the outline of the pre-forming die is simple and of small curvature, thepre-forming can be completed in a short time with high gas pressure. Compared tosingle direction quick gas blow forming, the total forming time was not prolongedbut shortened. Experimental results were in good agreement with the numericalresults, which verified the accuracy of finite element analysis.No obvious tissue damage in microstructure of magnesium alloy sheet appearedafter the repeat bending deformation in DR-QGBF. A small amount of cavities werefound in the junctions of large grains and small grains at the bottom and sidewall ofthe cylindrical part. Grains at the bottom corner area were refined and becameuniform in size due to dynamic recrystallization. There was hardly any cavity at thebottom corner. It proved that number of cavities might be reduced and thesuperplastic forming limit might be improved by improving the uniformity in grainsize of magnesium alloy sheet.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallic materials > Non - ferrous metals and their alloys > Light non-ferrous metals and their alloys > Magnesium
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