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.
European preparations for the ITER VV sectors manufacture
Abstract For the benefit of the bidders for the Call-for-Tender for the 7 sectors of the ITER Vacuum Vessel, launched in early 2010, a large amount of relevant technical information was included to ensure a rapid start to successful manufacture programme, without the need for a full-scale prototype, which would cause an unacceptable delay to the ITER schedule. The methodology of the logical structures of the specification and the additional planned mock-ups are described and the results from nearly a decade of R&D and manufacturing studies carried out inside the EU under the auspices of EFDA and F4E are also summarised. The work covers the evolution of novel manufacturing schemes and technologies, including a modular special local machining centre for making holes in the shell of the vessel with weld preparation included. New results from the combined studies by three parties, and using a round-robin trial system on the UT inspection of single-sided welds, including the successful control of the root side are described. A full-scale, partial prototype has demonstrated the successful construction segments using jigs to control the distortion from conventional welding, from the inner shell to the outer shell, and then the joining of the segments to form a part sector. The paper also summarises the results from the prototype segment, manufactured without jigs and using only EB welds. In order to be able to achieve the required as-welded tight tolerances, two specialised computational techniques have been developed, using SYSWELD and ANSYS codes and calibrated with the mock-ups in order to efficiently predict welding distortions. Based on this successful practical and theoretical work, computer models of the complete poloidal segments or sectors, including jigs, were can now generated and used to investigate many welding sequences in order to optimise the construction and achieve all the tolerances.