Finite element simulation of progressive sheet met

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Finite element simulation of sheet metal incremental forming process (Part I)

1 Introduction

sheet metal parts NC incremental forming process is a flexible processing technology of forming sheet metal parts point by point through digital control equipment and pre programmed control program. This process does not need special dies, has large forming limit, good repeatability, can control metal flow, and can process free-form surfaces with complex shapes. It is suitable for the processing of small batch, multi variety and complex shape sheet metal parts in aerospace and automotive industries, and has a very attractive development prospect. But so far, the international research on NC incremental forming process is only in the exploratory stage, the theoretical analysis is less and immature, and the forming and control of this process still need to be developed and improved

with the rapid development of finite element analysis technology and the continuous improvement of computer performance, a simulation software system integrating computer graphics, numerical methods, plastic forming theory and process and other technologies has gradually become a powerful tool for the research and optimization of sheet metal NC progressive forming

in this paper, the finite element simulation technology is introduced to simulate the forming process of sheet metal parts NC incremental forming process. 2. The principle of sheet metal NC progressive forming

the processing process of sheet metal parts NC progressive forming. The CNC forming system is mainly composed of tool head (forming tool), guiding device, core die and machine tool body. The tool head moves under the control of the numerical control system, and the core mold plays the role of supporting the sheet metal. For the parts with complex shapes, the core mold can be made into a simple mold, which is conducive to the forming of the sheet metal

when forming, first place the processed sheet on a general core die, clamp the sheet with a pressing plate around the supporting plate, and the supporting plate can slide up and down along the guide post. Then the device is fixed on the three-axis CNC forming machine. During processing, the forming tool first goes to the specified position, and sets the reduction amount for the sheet metal. Then, according to the instructions of the control system, according to the requirements of the first layer of contour, the sheet metal is processed in a single point progressive plastic processing by walking contour lines

3. Computer simulation of forming process

the characteristics of forming process determine that the forming process of sheet metal NC incremental forming is a very complex elastic-plastic large deformation mechanical process, which includes geometric nonlinearity, material nonlinearity and boundary condition nonlinearity at the same time. Its physical model and mathematical model are different from the traditional model under single drawing condition, Based on the characteristics of sheet metal layered forming, the computer simulation of layered forming process must be carried out, and the large deformation elastoplastic nonlinear finite element method is used to solve the analysis model, so as to obtain the distribution of deformation and stress in the workpiece forming process, the change of forming force, and predict the possible defects in the forming process, so as to provide a theoretical basis for formulating the correct forming process

as one of the large-scale general finite element analysis software, ansys/ls-dyna has the advantages of both ANSYS and LS-DYNA. Its powerful nonlinear function, multiple material models and strong motion loading control have great advantages in simulating sheet metal progressive forming. A the NSYS post processor with good quality can easily display the calculation results in a variety of visual displays, such as color equivalence, vector map and gradient. After progressive forming, the stress field distribution of sheet metal, the change of sheet thickness and the influence of various process parameters on the forming results can be displayed intuitively and conveniently, and the whole process of progressive forming of sheet metal can be effectively simulated, which provides a theoretical basis for the reasonable optimization of various process parameters in the progressive forming process of sheet metal and the effective control of the deformation process of sheet metal

next, the key aspects of finite element simulation, such as model establishment, lattice division, loading and boundary conditions, are analyzed

finite element model establishment and lattice division for the finite element simulation of sheet metal progressive forming process, the modeling process is not very complex. The preprocessing module of ANSYS itself can completely describe the whole model. In addition, ANSYS provides a special data interface with other CAD software, which can realize the seamless geometric model with CAD software and strengthen the cost management transmission. For the more complex top support model, it can be imported through other CAD software

finite element model to simulate the forming of square box parts

the model is composed of four parts: tool head, sheet metal, supporting plate, pressing plate and top support model, which can better simulate the whole forming process

The key of modeling is lattice division. The setting of various parameters in lattice Division will determine whether the generated model can meet the accuracy and economy in analysis. In general, the mapping lattice has regular cells that continue to the positive maximum shape and are arranged regularly, which is often more accurate than the results obtained by the free lattice, and the demand for CPU and memory in solving is lower than that of the universal experimental machine for man-made panels, which generally performs gb/t17657 ⑴ 999 "experimental methods for the physical and chemical properties of wood-based panels and veneered wood-based panels". In order to obtain this regular lattice shape, it is necessary to plan the model in detail from the beginning of establishing the geometric model, so that the generated model can meet the rule requirements of generating the mapping lattice. At the same time, the density of the lattice is controlled. The dense lattice division is adopted in the plastic deformation area of the sheet, and the sparse lattice division is adopted in the area that does not participate in the deformation. In sheet metal incremental forming process, the tool head moves according to the specified trajectory, and the deformation of sheet metal each time only occurs around the forming ball head, for almost all metals( б b/б S 2) the size of its plastic zone:

where D is the diameter of the tool head, t is the thickness of the plate, and △ h is the single-layer feed rate of the tool head

therefore, there should be a corresponding offset t0 on the basis of the outer contour of the formed part, where t0 R0. In addition, for different part shapes, the trajectory of the tool head is also different, and the corresponding sheet metal grid division should also take different forms. Forming square box parts and round box parts adopt two kinds of sheet metal lattice division forms

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