| With the fast development of modern industry, the variety of the sheet metal forming part is manufacturing at an incredible speed, and its requirement is increasing urgently. Therefore, the research and development of the sheet metal plasticity forming process technology is an important component of the national economy sustainable development. The sheet metal plasticity forming technology with the advantages of its high production efficiency, the finer product quality and the raw materials low consumption is widely used in the industrial field such as automobile, ship, aerospace and electron.In order to meet the requirement of the sheet metal plasticity forming of the modern industry, such as multi-variety, small batch, flexible and digital processing, the multi-point forming technology is combined with the incremental forming technology each other, which will give the reins to the high efficiency advantage of the multi-point forming technology and the high-precision advantage of the incremental forming technology, so the combined forming technology will overcome their lack of ability to improve the forming capability, the forming precision and the forming efficiency for the sheet metal. The combined forming new technology is the development and supplement of the digital shaping method and will provides an effective means for the high efficiency, high accuracy and digital manufacturing of the complicated sheet metal part. The multi-point and incremental complex digital forming equipment for the sheet metal can achieve the product-line testing and carry out the product closed-loop forming. Its processing capacity and its product quality have a qualitative leap and the manufacturing cost is far lower than the manufacturing cost of the multi-point forming press with the same forming accuracy. This equipment is applicable to the production of the complicated three-dimensional curved surface part of the sheet metal and the use of the manufacturing industry that can produce a batch of smaller car and aircraft, at the same time it can implement the flexible and digital manufacturing for the sheet-type parts.The main contents and conclusions are as follows:1. Study on the combined forming technology and the mechanical calculation method.In this paper, the combined forming method based on multi-point forming and incremental forming of sheet metal is putted forward. The technology makes use of the high efficiency features of the multi-point forming technology and the high-precision features of the incremental forming technology, which can achieve the high efficiency and high-accuracy digital forming for a complicated three-dimensional curved surface shape part. According to the characteristics of multi-point forming and incremental forming, two kinds of combined forming way are given: the multi point performing-incremental postforming way and the incremental forming way based on multi point die. By comparing the combined forming technology of sheet metal with the multi-point forming and incremental forming method, the advantages of the forming efficiency and the forming accuracy are pointed out. Combining with their own characteristics of two kinds of forming method, their respective scope of application is pointed out. Through the theoretical analysis of the stress and strain of sheet metal in the combined forming process, the basic mechanical calculation method of the combined forming of sheet metal is given. By studying the parameter such as the stress, strain, thickness thinning and the forming force in the combined forming process of sheet metal, the theoretical calculation formula of the parameter is given, which will provide an important basis for the power choice and the parameter settings of the experimental equipment and the equipment, at the same time, a theoretical basis is provided for the parameter choice of the numerical simulation and the result demonstration in the combined forming process.2. Study on the combined forming experimental installationThis paper introduces the structure of the combined forming system. This system is mainly composed of several sub-systems such as mechanical hydraulic pressure system, electrical control system, computer software system and so on. In order to realize the online checking of the product and the closed-loop forming, the combined forming system should also include the online checking and information feedback of product. Several key institutions composing the combined forming system is studied such as the forming tool head, its driving mechanism, the blank clamping device, the structure the fundamental element with multi-point die, the shape adjusting way of the fundamental element and so on, also the structure chart the element-group model and the calculation method of element height are given. The control system structure of combined forming system is illuminated. These studies provide a good protection for carrying out the forming experiment of the system and a useful exploration for developing the practical forming equipment.3. Study on the surface measurement method and the combined forming experimentThis paper introduces the part information acquiring technology such as the self-adaptation digital measuring method of the free crooked surface laser scanning, CT image edge information extraction method. The author discusses the de-noising method of the measurement data based on wavelet transform and the testing data treatment method of the located measurement data justification by three fiducial points. On this basis, the key question of the reconstruction of crooked surface based on NURBS is studied, which will establish the foundation for realizing the digital testing and the closed-loop forming. Through the Tensile test, the testing data for the physical performance of experiment material such as 08Al steel plate and L2Y2 aluminum is given, which will provide a strong basis for the combined forming experiment and the numerical simulation of material performance. Based on the research on the combined forming experiment of the typical shape part such as the face profile forming part and the spherical-shaped part, the author directly illustrates the combined forming process of two kinds of forming way and their own forming characteristics, at the same time, the author analyses the defect appearance and its suppression method in the combined forming process of the sheet metal, which will carry out a preliminary exploration for improving the forming performance of sheet metal. The author studies the combined forming experiment of the sphere-shaped sheet metal holding, which will establish a good foundation for the practical application of the combined forming technology in the cranial prosthesis forming. These studies will establish some practical foundations for the theoretical analysis and numerical simulation of the combined forming of sheet metal. The successful application of the combined forming technology in the cranial prosthesis forming is a useful attempt of the practical application the combined forming technology of sheet metal.4. Study on the numerical simulation of the combined forming processThis paper describes the relevant theory of the numerical simulation of sheet metal plasticity forming and gives the basic equation of continuum mechanics and illustrates the material constitutive relation. In order to make the numerical simulation results closer to the real situation, the elastic-plastic material model submitting Hill normal anisotropy yield criteria should be adopted well and truly in the process of the numerical simulation. This paper introduces the finite element equation of the dynamic explicit analysis and the related issues. Therefore, using the dynamic explicit finite element method has some advantages such as a short calculation time, the process stabilization, a high vectorization, a high parallelization and so on in the numerical simulation of the plasticity forming of sheet metal. In the combined forming process of sheet metal, the study of some issues such as the element selection, contact, and friction will establish a theoretical foundation for the numerical simulation analysis of the combined forming process. This paper introduces the flow of the numerical simulation of the combined forming process and gives the establishment method and the application example such as the material model, solid model element selection, meshing and the boundary conditions in the numerical simulation of the combined forming process. The finite element model of the combined forming process is established.5. Analysis of the numerical simulation resultThis paper performs the numerical simulation of the combined forming process of sheet metal by applying dynamic explicit finite element method, such typical shapes part as the spherical-shaped, box-shaped, round shape parts. And so this paper also analyzes the sheet metal formability such as distortion rule, the equivalent stress distribution and the thickness change in the combined forming process. The numerical simulation result of spherical-shaped part forming process shows that a reasonable choice of elastic cushion can't only effectively inhibit the indentation flaw which the combined forming process will bring, but also guarantee the forming quality of the part. The numerical simulation result of forming sheet metal holding spherical-shaped part shows that if the multipoint die applies the punch as far as possible in the combined forming process of the holding sheet metal, the shaped parts will be more precise. Their simulation results of the box-shaped part and round box-shaped part show the tool head should be used to go the helix way in the combined forming process. a reasonable choice of the tool head feed rate can improve the forming capability the and forming quality of shaped part. By comparing the numerical simulation result and the experiment data, the author proves the accuracy and validity of numerical simulation.
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