K.F. Zhang

3-D FEM analysis of the temperature field and the thermal stress for plastics thermalforming

Abstract The FEM software ARVIP-3D is developed to simulate the deformation, temperature field, thermal stress and warpage of 3-D plastics thermalforming and blow molding. Temperature has a great effect on plastics forming behavior by influencing the material performance parameters, the fluid viscosity and the fluid behavior exponent. Combined with the rigid–visco-plastic FEM equation for forming computation, the Arrhenius and Williams equation for viscosity computation, the Calerkin FEM equation for the temperature field, the FEM software is developed. Whilst simulating the 3-D temperature field, the dynamic heat-conduction boundary condition is adopted, latent heat and deformation heat being treated as dynamic internal heat source in FEM equation. The computational results of adopting the analytical method and the FEM program developed by the authors indicate that the program of analyzing the temperature field is accurate. The simulation result of the temperature distribution corresponding to the thickness distribution agrees well with the experimental results of other researchers. This provides the theoretical basis and a guide for acquiring the thickness distribution of a part by a simple, convenient and non-destructive temperature measurement in practical production, and provides a useful tool to optimize the technique to secure an even distribution of thickness in the part. The warpage and thermal-stress analysis can predict defects and optimize the cooling system to secure an even temperature distribution within the part to assure the parts final shape, practical performance and strength.

Superplasticity and Diffusion Bonding of IN718 Superalloy

The superplasticity and diffusion bonding of IN718 superalloy were studied in this article. The strain rate sensitivity index m was obtained at different temperatures and various initial strain rates using the tensile speed mutation method; m readied its maximum value 0.53 at an inititil strain rate of 1×10−4s−1 at 1253K. The diffusion bonding parameters, including the bonding temperature T, pressure p, and time t, affected the mechanism of joints. When the bonded specimen with 25μm thick nickel foil interlayer was tensile at room temperature, the shear fracture of the joints with nickel foil interlayer took place at the IN718 part. Microstructure study was carried out with the bonded samples. The microstructure shows an excellent bonding at the interfaces. The optimum parameters for the diffusion bonding are: T=1273-1323K, p=20-30MPa, t=45-60min.