The Forming Die Design and Experimental Research of CFETR Vacuum Vessel Shells
Vacuum vessel (VV) is the main component of the China fusion engineering test reactor. Shell forming is relatively in the earliest phase, one of the most important processes during VV manufacturing. The profile errors caused by spring back of shells at room temperature will directly influence the subsequent manufacturing and experimental studies, so a set of dies, whose profiles can be easily revised, has been designed based on the spring-back theory. The empirical formula has been used to calculate the theoretic die profile value, which is mostly determined by the mechanical properties of 316LN stainless steel. Then, choosing four relevant values to simulate the forming process in which the optimal profile errors of shell must be controlled within 1.5 mm. The optimal dimensional value of the dies has been confirmed to guide the forming experimental study. After the experiment, the actual profile errors, thickness reduction, maximum spring back, maximum deformation rate, and the surface residual stress have been measured, and those data are an accurate indicator from the finite element analysis, also verifying the reasonability of the manufacturing process in turn.
Spring-back simulation of sheet metal forming for the HT-7U vacuum vessel
Abstract The HT-7U vacuum vessel is an all-metal welded double wall toroidal structure, which has characteristics of ultra-high vacuum and thin shell. Some of the forming tools will be fabricated according to its outline dimensions. In order to design a optimal shape for the forming tools and avoid an undesirable local deformation at the head of sheet, the software package ansys/ls-dyna and dynaform were utilized to simulate the process of the deep drawing in sheet metal forming and develop a parameter optimization system for the design of the die and punch. During the numerical simulation the updated LaGrange formulation and elastic–plastic constitutive equation were adopted to solve the problem of large strain and large deformation in sheet forming process. According to the simulation analysis results the optimum shape of the die and punch surface was finally determined.
Section analysis of industrial sheet-metal stamping processes
Abstract A finite element modeling program, KMAS-2D, was developed using plane-strain and axisymmetric curve element models for the section analysis of sheet forming with arbitrary draw-in and irregular tool shapes. A quasi-flow corner theory of elastic–plastic finite deformation and a normally anisotropic yield criterion are introduced. The modified Coulomb law is used to model the interfacial friction, and the tool geometry is described by the line segment scheme. The computer program was used successfully for simulation of several typical forming processes. An application is also made to an industry-scale problem with complex tool geometry. Comparisons of the calculated results with experimental data are given.