Modeling, Simulation and Optimization of Superplastic Forming of Lightweight Alloys

  • Mohammad Al Bakri

Student thesis: Master's Thesis

Abstract

Eco-design regulations have been driving transportation industry, the automotive in particular, to cut down fuel consumption and exhaust gas emissions. Among the different proposed means to achieve such cuts, weight reduction is one of the most effective and least costly solutions. Lightweight materials, such as titanium, aluminum and magnesium alloys have great weight saving potentials as they are 40-75% lighter than conventional steels. However, special forming technologies, such as Superplastic Forming (SPF), are required to overcome the limited formability of such alloys. SPF is a near net shape forming process that offers many advantages over conventional forming operations including design flexibility, weight reduction and the ability to form light weight materials into complex shapes. However, low production rates and the non-uniformity of the formed parts are hindering the widespread use of this technology. Although numerous analytical and numerical studies on SPF can be found in literature, several aspects and parameters affecting the process have not yet been thoroughly addressed. Frictional forces acting at the die-sheet interface is one example. This research aims to advance the state of SPF by proposing new solutions that help optimizing the process and overcoming its limitations. The effects of interfacial friction distribution on the forming process are studied in detail. Both homogeneous and variable friction distributions have been addressed and optimized. The effects of frictional forces on deformation stability has also been investigated, and the results are utilized to devise variable strain rate forming paths that are able to reduce forming time while maintaining the integrity of the formed parts. Moreover, forming limit diagrams for magnesium alloys formed at elevated temperatures have been thoroughly studied. A novel speed control algorithm for constant strain rate mechanical stretching formability tests has been developed. The algorithm actively controls the speed of the punch so as to maintain a constant effective strain rate in the sheet, or any region of interest, following a user-defined control scheme. All of these issues have been investigated in a cost-effective manner using the finite element method along with advanced constitutive material models.
Date of AwardDec 2011
Original languageAmerican English
SupervisorMarwan Khraisheh (Supervisor)

Keywords

  • Light Metals

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