Improving the formability limts of lightweight metal alloy sheet using advanced processes -finite element modeling and experimental validation-
Weight reduction is one of the major goals in the automotive, appliance and electronics industries. One way of achieving this is to use lightweight alloys such as aluminum and magnesium. However, due to their limited formability at room temperature, advanced testing methods and forming processes are needed. Room and elevated temperature hydraulic bulge tests (using a submerged tool) were conducted for Al 5754-O and Mg AZ31-O to determine their mechanical properties. Experiments were conducted between room temperature and 225 C, at various approximate true strain rates. Strain values up to 0.7 were obtained under equi-biaxial state of stress at elevated temperatures. Deep drawability of these alloys is investigated experimentally using a servo motor driven mechanical press and computational modeling [at room temperature (using solid dies), against liquid pressure (hydroforming) and at elevated temperatures (warm forming)]. Limiting Draw Ratio (LDR) of Al 5754-O is increased from 2.1 (room temperature) to 2.4 when hydroforming is used. This value is increased to 2.9 when warm forming is used. Formability of Mg AZ31-O is found to be limited at room temperature while LDR up to 3.2 is obtained at elevated temperatures. The in-die dwelling concept is developed by using the flexibility of the servo press and blanks were heated in the tool set prior to forming. Several lubricants for elevated temperature forming were evaluated using the deep draw test and a PTFE based film performed satisfactorily. Deep drawing tests were conducted to determine the process window (max. punch velocity as functions of blank size and temperature) for Al 5754-O and Mg AZ31-O. Maximum punch velocities of 35 mm/s and 300 mm/s were obtained for the Al and Mg alloys, respectively. Differences in formability were found for the same Mg alloy sheets from two different suppliers. Additional experiments were conducted in order to understand the effect of constant and variable punch velocity and the temperature on the mechanics of deformation. Variable punch velocity is found to improve the thickness distribution of the formed part and provide 60 % reduction in the drawing time. Good agreement between the computational models and experiments are obtained.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:formability drawability elevated temperature hydraulic bulge test deep drawing warm forming servo press
Date of Publication:01/01/2008