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Multi-point thermoforming is a new flexible technique for manufacturing three-dimensional polymer sheet parts. The fixed die utilized in conventional thermoforming process is replaced by a multi-point die, which can be reconfigured rapidly and nearly cost-free. In the present study, the effects of the elastic conditions on the surface quality and shape accuracy of the formed workpiece have been investigated through experiments and numerical simulations. The results show that an elastic cushion with proper thickness and hardness can significantly improve the surface quality of the workpiece. It has also been found that the application of lubrication can improve the shape accuracy of the formed workpiece. [ABSTRACT FROM AUTHOR]

Multi-point forming is an advanced flexible manufacture technology, which has been used in many fields successfully. In order to provide a flexible method for forming a polymer, multi-point forming is applied to the manufacture of polycarbonate sheet. An optimized DSGZ constitutive model is established to describe the stress–strain relation of polycarbonate sheet, and its parameters are determined according to experimental data. The multi-point forming process of polycarbonate sheet is introduced briefly, and a simple calculating scheme of punch height is developed. Numerical simulations of spherical and saddle-shaped parts are carried out by dynamic explicit finite element analysis, and the effects of punch number and punch radius on the surface accuracy and shape accuracy are studied. The multi-point forming experiments of polycarbonate sheet are done, and the comparisons of shape error between experimental parts and objective parts are conducted, which show that the polycarbonate products have good surface accuracy and shape accuracy. [ABSTRACT FROM PUBLISHER]

The precise characterisation of hot flow behavior of titanium alloys is of vital importance for practical hot forming processes. To precisely determine the hot flow behavior of titanium alloys under the forming conditions, Gleeble hot tensile tests are usually performed to simulate the forming processes by accurately controlling the deformation temperatures and strain rates under designed conditions. However, there exists a non-uniform temperature distribution during the Gleeble tests, which leads to inaccuracies in the determined hot flow behavior. To overcome such an issue, this paper proposed a new strain-based correction method for Gleeble hot tensile tests, enabling the mitigation of the non-uniform temperature-induced stress-strain curve inaccuracies. The non-uniform temperature zones have been successfully excluded in the calculation of the true strain levels. A series of hot uniaxial tensile tests of TA32 at temperatures, ranging from 750 °C to 900 °C, and strain rates, 0.01/s~1/s, were carried out. The obtained stress-strain correlations for a large gauge zone were characterized using the new correction method, which was further used to evaluate the hardening behavior of titanium alloys. The results have shown that the ductility, strain hardening component (i.e., n), strain rate hardening component (i.e., m) and uniform strain value (i.e., ε u ) are over-estimated, compared to conventional method. Higher strain rates and lower temperature leads to enhanced hardening behavior. This research provides an alternative correction method and may achieve more accurate stress-strain curves for better guidance of the hot forming process for titanium alloys. [ABSTRACT FROM AUTHOR]