A new method for determination of friction coefficient in sheet metal forming of Mg alloy AZ31B is presented in this paper. The method is based on the bulging test of sheet metal in which the specimen is processed with a hole at the center. The diameter of the hole will increase along the stroke of the punch and the dimensional change of the hole has a certain relationship with the friction coefficient at the punch/specimen interface. Thus, the friction coefficient can be determined indirectly according to the dimension of the hole in the bulging process. The bulging process of the sheet is simulated using FE code DEFORM-2D. The analysis model is set up according to the experiment of the bulging and the friction calibration curves are generated from the simulations of the bulging by setting different coefficients of friction. The friction coefficient can be determined by measuring the hole dimension during the bulging process and comparing it with the friction calibration curves.

The true stress-strain curves of AZ31B magnesium alloy sheet were obtained by using the uniaxial tensile tests at the temperature ranging from 50°Cto 300°C and the initial strain rate ranging from 0.001/s to 0.1/s. The influence of temperature and strain rate on the flow stress was analyzed. The results show that the flow stress decreases and the elongation in fracture increases with increasing temperature and decreasing strain rate，and the plastic performance is improved obviously. Through the analysis of the true stress-strain curves，a mathematical model of the flow stress was established based on an exponential form whose power is a quadratic function. All the coefficients in the model were fitted as functions of temperature and strain rate. The comparison of the calculated results with experimental data shows that the model established in this study can accurately reflect work hardening and strain softening effect of AZ31B magnesium alloys during the hot deformation. It can be used for the prediction of flow stress for AZ31B magnesium alloys under hot work conditions and numerical simulation of forming processes.

This paper deals with problems in the coining process for manufacturing surgical slit knife using two-dimensional (2D) and three-dimensional (3D) finite element (FE) simulations. The FE simulations are performed to investigate the material flow, and especially stress distribution on the coining dies. The main objective of this paper is to study the feasibility of a coining process for manufacturing a given geometry of surgical slit knife without forming defects and die failure. Very high stress distribution on the coining dies is found by 2D simulations of the coining process that exceeds the strength limit of the die material. The optimum preform and preforming die geometry are determined by FE simulations in order to reduce the die stress. 3D simulations of the preforming and coining processes are conducted with the optimal design to show that the geometry of the product can be achieved without defects by the coining process.