Through the analysis of the process and die design practice of the oil tank, the process analysis method of forming special-shaped parts and the principles that should be considered in die design are summarized. Key words: special-shaped parts, process analysis, structural design and die design drawing 1 is a sketch of an air-cooled diesel fuel tank. In this paper, the best parting surface will be determined from the production process, and its stress and strain will be qualitatively analyzed, so as to take corresponding control measures in die design, and thus explore the process analysis method of drawing special-shaped parts and the principles that should be considered in die design. I. Process analysis 1. The oil tank shown in the determination drawing of parting surface 1 belongs to rectangular box-shaped parts. When in use, its placement state is the same as that shown in Figure 1. The upper plane is riveted with an oil tank port, as shown in figure 1, and the lower plane is provided with an oil outlet nut, as shown in figure 1. The fuel tank port and outlet nut must be assembled before the fuel tank seam welding. The selection principle of parting surface of box-shaped parts is: to meet the requirements of workpiece use, to concentrate the process, to invest less tooling and to consume less labor. Through the analysis of the box structure, it is concluded that the oil tank should be composed of two parts, which are welded by seam welder in the workshop. If the upper and lower bodies have different structures, the upper and lower bodies need two sets of forming dies, shaping dies and trimming dies. To meet the above principles, the two parts should be exactly the same, so as to reduce the investment in the mold. In view of this, the box-shaped part has three parting schemes. The following three schemes are compared and analyzed from three aspects: the use of fuel tank, molding technology and economic technology, and the best parting scheme is determined. Scheme ① is classified in section A, which is convenient for the assembly and riveting of oil tank port and oil outlet nut. However, due to the existence of the oil tank port, the periphery of the parting surface can not be completely welded, which increases the welding process cost. In addition, because the upper and lower parts of the oil tank are high rectangular boxes, both of them need to be drawn twice and formed once, so the die investment is high, there are many processes and the process is difficult. In addition, high rectangular box drawing requires high drawing performance, which will increase the cost of raw materials. Scheme ② is classified in longitudinal section B. The upper and lower bodies are drawn with ordinary rectangular boxes, which is easy to form, centralized in process, less in tooling investment and labor consumption. However, the fuel tank port must be offset, and the periphery of the parting surface cannot be completely welded, which increases the welding process cost, and the fuel tank port is offset, which is not conducive to practical use. Scheme (3) classifies C. The upper and lower bodies are special-shaped parts, which is convenient for the assembly and riveting of the oil tank mouth and the oil outlet nut. The periphery of the parting surface can be fully seam welded, which completely conforms to the selection principle of the parting surface of the box-shaped part and meets the use requirements of the workpiece, and has the advantages of centralized technology, less tooling investment and less labor consumption. The comprehensive cost is the lowest. However, the drawing of special-shaped parts is more difficult than that of ordinary box-shaped parts. To sum up, the product quality of scheme ① is guaranteed, but there are many processes, large labor consumption and large investment in tooling and equipment. Scheme 2: Too much labor and poor product quality affect the appearance quality of the whole machine. Scheme ③ has the advantages of centralized process, less tooling investment, less labor consumption and the lowest comprehensive cost, but the die structure is complex, and measures to eliminate defects must be taken to ensure product quality. We determined that Scheme ③ was the best scheme, so we suggested that the product structure should be classified as inclined section. 2. Deep drawing process analysis of parts. After parting, the upper and lower valve bodies are asymmetric planar flange parts as shown in Figure 2. In the process of sheet metal drawing, the stress in the thickness direction is relatively small and can be ignored, so it is generally considered as a plane stress state. Take a unit at the corner a of the flange. According to the basic drawing principle, its stress state is plane stress state. As shown in Figure 3, the radial tensile stress σ 1 and the tangential compressive stress σ3. The radial tensile stress σ 1 is unevenly distributed along the periphery of the box, with the largest value in the middle of the fillet and the smallest value in the middle of the straight edge. The distribution of tangential compressive stress σ3 is the same as that of radial tensile stress σ 1, which is the largest in the middle of the fillet and gradually decreases with the distance from the fillet. Taking a element at B can be approximately simplified to an axisymmetric stress state, as shown in Figure 4, σr is the tensile stress, σ θ is the compressive stress, and σr and σ θ reach the maximum in the middle of the fillet. In the process of drawing, the resistance of fillet is greater than that of straight edge, so the material flow speed of fillet is slower than that of straight edge. Because the compressive stress at the fillet is relatively large, the residual material at the fillet cannot flow to the straight edge smoothly, so the bulge defect will appear at the corner, the fillet (point A) of the flange will wrinkle, and the concave surface, distortion, relaxation, ripple and other defects will appear at the straight edge. The solution is to set the drawbead in an appropriate position. The function of drawbead is: 1. Increase the feeding resistance and avoid the defects such as sag, distortion, relaxation and ripple in the drawn part; 2. Adjust the flow rate of materials to make the flow resistance of all parts in the drawing process uniform, or make the amount of materials flowing into the die cavity meet the needs of all parts of the workpiece to prevent the phenomenon of "more wrinkles and less cracks". The principle of bead arrangement is: the sequence number requires the arrangement principle 1 to increase the feeding resistance and improve the deformation degree of the material, and the bead is placed in a whole circle or intermittently 1 or 1-3.