| The sheet metal forming technology is closely related to the manufacturing fields of automobiles,ships,aerospace and so on,and its forming quality directly affects the appearance and performance of the product.The traditional mold forming technology requires relatively high experience.The mold design and manufacturing cycle is long.A set of molds can only produce a corresponding part.With the development of society,sheet metal forming has the characteristics of small-batch production,diverse appearance and rapid update.At the same time,with the appearance of new materials,the forming process of new materials also needs to be solved.Multi-point forming is a digitally intelligent sheet forming technique.The multi-point die disperses the overall shape of the traditional die into discrete height-adjustable basic body punches,which relies on the envelope surface formed by the basic body punch for forming.Thanks to the reconfigurability of multi-point molds,a set of multi-point molds can be used to form parts of different specifications according to the requirements.The mold surface can be quickly corrected during the forming process for error compensation.a set of molds can be used for the multi-step and segment forming of the material,which is a fast and efficient sheet metal forming technique.According to the relative motion of the basic body in the multi-point forming process,multi-point forming can be divided into multi-point mold forming and multi-point press forming.The multi-point mold forming is pre-shaped before the sheet forming,and there is no relative movement of the basic bodies during the forming process.However,each basic body is instantaneously adjusted during the forming of the sheet material in the multi-point press forming process.The multi-point forming punch is divided into a fixed punch and an swing punch.The swing punch can be self-adaptively shaped according to the deformation of the sheet during the forming process.Swing head unit multi-point press forming combines the advantages of multi-point presses and swing punches.Since the sheet material is more constrained during forming,wrinkle defects can be effectively suppressed,and high-quality non-defective shaped parts can be finally obtained.With the development of computer technology and finite element theory,the use of sheet metal forming numerical simulation technology has been widely used in the development of product.The simulation analysis of the forming process of the sheet metal can predict the forming defects and optimize the process parameters through numerical simulation to understand the distribution on the stress and strain of the formed parts,which have guiding significance for the actual production of the sheet metal.In this paper,numerical simulation method was used to study the multi-point forming of new materials,optimize the process parameters,and use multi-step multi-point forming process to obtain high-quality qualified workpieces.Combining the multi-point press and the swing head unit,swing head unit multi-point press forming is proposed to verify the good effect of suppressing wrinkling in sheet metal forming,broadens the application area of multi-point forming.The influence of the change of the parameters of the polyurethane elastic cushion on the multi-form forming quality of the sheet material was analyzed.The main research contents and conclusions of this article are as follows:1.Establishment of multi-point forming finite element modelThe multi-point forming principle and process of sheet metal have been explored.The difference between multi-point forming and traditional die forming was analyzed.The advantages and development trends of multi-point forming methods for sheet metal are illustrated.Based on the multi-point forming principle and finite element theory of sheet metal,a finite element model of sheet metal forming was established.A detailed discussion of the establishment of geometric models,material models,boundary conditions,element types,and mesh divisions involved in the establishment of finite element models was established,which laid the foundation for the numerical simulation of sheet metal forming.2.Research on Multi-pass multi-point forming process of sheetsThe principle of multi-step multi-point forming was discussed.The method of multipoint forming surface compensation and the cause of wrinkle defects in sheet metal forming were explored.Using a combination of numerical simulation and multi-point forming test to perform springback compensation on the 1561 aluminum alloy marine outer plate to determine the multi-pass forming process.One-step forming and multi-step forming simulation was performed.The forming effect was analyzed from the stress distribution and strain distribution of the formed parts.The simulation results were verified by a multi-point forming test.The results show that the multi-step forming process not only can increase the material forming limit,but also can effectively suppress the occurrence of wrinkle defects and reduce the stress and strain value of the formed parts compared with the one-step forming process.The stress,strain distribution and thickness distribution of the formed parts obtained by the multi-step forming method are evenly distributed,and at the same time,the error is reduced and the quality is improved.3.Study on the forming method of swing head unit multi-point press formingThe force state of the ball element in the multi-point forming process is analyzed,and the cause and area of the wrinkle defect of the ball element are discussed.Combining the advantages of the swing punch and the multi-point press forming,the finite element model of swing head unit multi-point press forming was established with the spherical workpiece as the research object.The stress,strain and thickness distributions of formed part in the multipoint mold forming,Swing head unit multi-point press forming,and the multi-point press forming are compared to verify the advantages of multi-point press forming with a swing head unit in suppressing wrinkle defects.The results show that the stress,strain,and thickness distributions of the formed parts are the most uniform,and the wrinkle defects can be effectively suppressed to obtain high quality forming,which due to the uniform deformation and full restraint of the sheet material in swing head unit multi-point press forming.4.Research on the effect of polyurethane elastic cushion parameters on the quality of sheet metal formingTaking the Spherical workpiece as the research object,the effect of the number,hardness and thickness of the elastic cushion on the quality of the formed part were analyzed by the finite element numerical simulation method.The following analysis results were obtained: The elastic cushion can effectively inhibit the indentation defects in multi-point forming.The layered elastic cushion can improve the stress-strain distribution of the formed part,and obtain a continuous and uniform stress and strain forming part.The layered elastic cushion can improve the stress-strain distribution of the formed part and obtain a continuous uniform stress and strain forming part.As the number of elastic cushion increasing,the residual stress of the formed part decreases,but the springback increases.The ability to inhibit wrinkle defects on the sheet material enhanced with the increase of the hardness of the elastic cushion with the same thickness of the elastic cushion.Compared with the forming quality of the sheet material under the conditions of the polyurethane elastic cushion and the 65 Mn spring steel elastic cushion,Since the 65 Mn spring steel is equivalent to the overall mold shaping as an elastic cushion,it can effectively suppress wrinkling compared to the polyurethane elastic cushion and obtain a high-quality formed part.As the thickness of the elastic cushion increasing,the wrinkle defects of the multi-point formed part of the sheet decrease,but the local bending effect is obvious.Therefore,the selection of the elastic cushion in the multi-point forming needs to be comprehensively considered according to actual needs. |
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