Finite Element Analysis of Stamping of Automobile Beam

Transcription

1 Journal of Networking and Telecomunications Original Research Article Finite Element Analysis of Stamping of Automobile Beam Xiaoli Fu,Yuedong Qiu,Mingtu Zhao School of Automotive Engineering, Chengde University of Technology, Hebei, China ABSTRACT With the development of numerical simulation and analysis technology, plastic forming theory, stamping technology and computer technology, DynaForm technology with a finite element as the core has been developed rapidly. DynaForm technology for sheet metal stamping can simulate the entire process of sheet metal stamping. In this paper, the metal beam is used as the research object, and the finite element analysis is carried out by DynaForm software. The causes and control methods of the typical defects in the forming process are analyzed. The radius, punching speed, Coefficient, blank holder force, drawbead and other parameters on the quality of the impact of automotive beams. Combined with the actual production of a reasonable forming process and improve the way. The simulation used to guide the practice, can shorten the mold development time, reduce the cost of molds, improve business income; the production practice has a certain guiding significance. KEYWORDS: numerical simulation; stamping; beam; DynaForm 1. Introduction 1.1. Introduction According to statistics, in the automotive industry, 60 to 70% of the workpiece is the use of stamping to get. The car cover mainly refers to the parts that make up the cab and body surface of the car, including some surface parts of the engine and chassis, the extra cover, and the inner cover. Compared with the general sheet metal stamping parts, the automobile cover has the characteristics of large size, complicated shape and small relative thickness of the sheet. The forming process is prone to defects such as cracking, thinning, wrinkling and forming. Therefore, the manufacture of the cover is a key part of the automobile body manufacturing Introduction to stamping technology Stamping is the press and dies on the plate, strip, pipe and profiles, such as the application of external force, resulting in plastic deformation or separation, so as to obtain the required shape and size of the workpiece processing methods. The world's steel, there are 60 to 70% of the plate, most of which after stamping into finished products. Stamping has many unique advantages regarding both technical and economic aspects. The main performance is as follows: (1) Stamping forming high efficiency, easy to operate, easy to achieve mechanization and automation. (2) Stamping due to mold to ensure that the stamping parts of the size and shape accuracy, and do not destroy the surface quality of stamping parts. So it is possible to manufacture parts of the general dimensional tolerance grade and shape and to manufacture precision (tolerances at micron level) and complex shapes. (3) Stamping can be processed into a larger size, the shape of more complex parts. (4) Stamping is generally no chip scrap production, the material consumption less, and do not need other heating equipment, which is a kind of material, energy-saving processing methods, the cost is low. As the stamping has so much superiority, stamping in the national economy in a wide range of applications. Stamping in the motor, automobile manufacturing, instrumentation, aerospace, weapons manufacturing, have a very important position. Copyright This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License ( permitting all non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 24

2 Xiaoli Fu, et al According to the China Mold Association released statistics show that in 2008 China's total output of stamping dies about 61 billion yuan, of which exports about 1.72 billion yuan. According to China's customs statistics, in 2004 China's imports of stamping die about 46.6 billion yuan. From the above figures can be seen: 2004 China's stamping die total market size of about billion yuan. Among them, the domestic market demand for billion yuan, the total supply of about billion yuan, the market supply rate of 82%. In the overall situation of supply and demand, there are two specific circumstances: First, most of the imported molds are large and complex precision molds, and export molds are mostly small and medium-sized low-grade stamping die; the second is due to China's mold prices lower than the international market prices Many, with a certain degree of competitiveness, so its prospects in the international market Finite Element Numerical Simulation of Sheet Metal Forming The research of numerical simulation of sheet metal forming began in the 1960s [1] [2]. In the early 1970s, the finite element method began to be applied to the numerical simulation of sheet metal forming. In the early 1980s, Ford Motor Company's SCTang and GM's MSWang, who have been exploring for a long time, successfully carried out a numerical simulation of the stamping process of the car's trunk lid and the car's fender [3] [4] ], Created a car cover stamping forming numerical simulation technology applications [5]. With the development of numerical simulation analysis technology, plastic forming theory, stamping technology and computer technology, DynaForm technology with a finite element as the core has been developed rapidly. The DynaForm technology for sheet metal stamping can be used to simulate the whole process of sheet metal stamping. The forming results such as forming limit, thinning rate, strain amount and rebound amount can be obtained by observing the flow of material., Wrinkling, rebound and other defects to predict, so as to understand the material parameters, friction, mechanical parameters, mold parameters on the impact of sheet metal forming performance. The application of numerical simulation technology in the forming process of automobile panel is of great significance to improve the mold research and development ability, which is mainly reflected in shortening the mold production cycle, improving the quality of the cover and reducing the cost [6]. Foreign, sheet metal forming finite element analysis technology has become a number of mold manufacturing companies and car manufacturers to improve product competitiveness means, in addition to CAE simulation analysis as product design and manufacturing processes insurmountable process specifications. Today, many automotive industries are beginning to use DynaForm to simulate sheet forming processes [7]. In the United States, DynaForm technology has been widely used; advanced computer simulation has been gradually combined with the test, and has replaced the traditional experimental means of development trends. France's Renault Motor Company not only has its technical staff specializing in numerical simulation research work, and with the Beijing University of Aeronautics and Astronautics, light metal sheet metal parts of the stamping technology for numerical simulation analysis [8]. In addition, Japan's Ogihara company has also established for a variety of models based on finite element technology sheet metal forming database, at present, the company can develop 30% to 50% of the stamping parts for sheet metal forming simulation analysis The China started in the numerical simulation of stamping, started in the late 1980s [9] [10], and mainly concentrated in colleges and universities, such as Shanghai Jiaotong University, Huazhong University of Science and Technology, Jilin University. Jilin University, He Jinbao [11] and others use DynaForm software on the cylindrical parts of the finite element analysis, a complete discussion of the method to prevent wrinkling of parts and parts of the fracture when the blank holder and blank holder force to determine the method. In the Phoenix [12] and others using the DynaForm software on the car cover the stamping process of numerical simulation, analysis of the factors affecting its forming [13]. In short, improving the forming process and mold design of automobile panel is the key to improve the product quality and enhance the market competitiveness, and the sheet metal forming finite element numerical simulation technology will play an important role in the mold design and process optimization process of the cover, as an effective means of forming process analysis The source and meaning of the subject As shown in Figure 1-1, the vehicle beam is a typical type of internal cover, which is a typical bearing part. In the vehicle impact, the shock plays a significant role. Therefore, the shape of the car beam is directly related to the quality of the car's quality and the safety of the use of cars. The four short sides of the beam on both sides of the use of followup flanging to complete the beam body with a drawing forming. 25

3 Finite Element Analysis of Stamping of Automobile Beam Figure 1-1 Beam model In the design process of the automobile drawing die mold surface design, the design of the binder surface and the process surface is an important part of the design of the drawing section of the automobile panel. The rationality of the design is to determine whether the drawing can proceed smoothly and the key to getting qualified workpieces [14]. In the traditional stamping process analysis, the mold design stage is mainly based on the experience of the mold engineer, must be repeated trial mode and repair mode [15] [16]. This method of mold design greatly extended the mold development time, which led to increased cost of the mold. In this paper, the forming process of automobile beam is numerically simulated by means of sheet forming analysis and numerical simulation special software DynaForm developed by LSTC and ETA. The causes and control methods of typical defects in the forming process are analyzed, Combined with the actual production of a reasonable forming process and improve the way [17] [18]. Using simulation results to guide the production practice, this method greatly shortens the mold development time, reduces the mold cost and improves the enterprise income [19]. 2. Finite Element Analysis of Stamping Forming of Beam 2.1. The establishment of beam geometry model Import the workpiece 3D model The three-dimensional model of the vehicle beam studied in this paper is shown in Figure 1-1. It has the following characteristics: the drawing depth is large, and the distribution is uneven, the sidewall and the bottom surface, the side wall and the flange have a small rounded transition. Conducive to full shape. Meshing The success of finite element analysis depends largely on the quality of the mesh. Grid overlap will cause the calculation to enter the loop, which is not allowed. Using Dynaform's self-adaptive meshing feature, you can quickly model the grid. And then use the pre-processing in the mold face check function to find unreasonable units to be corrected so that you can get high-quality grid model. Product model to process model transformation The process of transformation from the automotive cover product model to the process model is the process of designing the corresponding mold from the shape of the cover according to the designed stamping process. The specific process is as follows: 1) Determine the stamping direction Choose the right and reasonable direction of the stamping can not only decide whether to pull out the qualified parts, but also affect the surface of the material and the surface of the surface. Reasonable stamping direction should meet the following four requirements: (1) No negative angle When the stamping direction is set, no punching negative angle (red for the negative area and green as a reasonable area) as shown in Figure 2-1 (a) is not allowed; Figure 2-1 (b) Stamping negative angle, more reasonable. 26

4 Xiaoli Fu, et al (A) Stamping negative angle (b) No punching negative angle Figure 1. Schematic diagram of stamping (2) No slip correct and reasonable direction of the stamping to ensure that the start of the punch and punch contact with the rough state of good, flat, multi-point contact, balance force, the material does not occur. The larger the contact area, the smaller the angle between the contact surface and the horizontal plane, and the less difficult the blank is to cause the workpiece to break due to the local stress overload. The higher the moldability of the material in the drawing, the easier it is to obtain the complete punch shape, the more conducive to improving the deformation of the workpiece quality. Set the depth of formation to be as shallow as possible. (3) No lateral force correct and reasonable stamping direction to ensure that the feed resistance balance, drawing depth uniform. Because the depth of the drawing to ensure uniform pressure to ensure that the feed surface of the material evenly, and the pressure of the material part of the material evenly to ensure that the drawing pieces do not crack, no wrinkles, it should be as much as possible to reduce product tilt. (4) No impact line car plate shall not be left in the workpiece surface traces of the impact line. 2) The design of the process complement surface In order to successfully achieve the extension, we must first construct a closed surface. In order to construct a closed surface, it is necessary to add a processed supplement to both ends of the workpiece model. The process replenishment is an integral part of the complete drawing, which refers to the part of the workpiece itself, which has a critical effect on the success of the drawing and is one of the signs of measuring the level of the stamping process design. Figure 2-2 in the blue part of the car beam drawing die for the process to add the surface. Figure 2. adds the workpiece after the process Reasonable to add the process to meet the surface should meet the following four requirements: (1) Must be added after the completion of a complete extension, that is, to generate a complete shell, in order to facilitate the drawing; (2) To balance the forming resistance, control the inflow of materials, drawing depth to ensure uniform, can make full use of the material forming limit, but also to avoid cracking and wrinkling; (3) Must meet the design requirements of the binder surface; (4) Must meet the requirements of the trimming, flanging process after drawing. 27

5 Finite Element Analysis of Stamping of Automobile Beam Design the process of filling the surface should be based on the location of the trimming line to reasonably determine the size of the filling surface, in particular, die corner. Because the die fillet on the material feed resistance is very large, directly related to the drawing of the forming effect, so the value should be reasonable. In the ability to pull out the qualified workpiece under the premise of the process as much as possible to reduce the part. 3) Determine the binder surface The binder surface is part of the process. Before adding the process, it must first determine the shape of the binder surface to ensure that the feed resistance of each part of the sheet is relatively uniform. To do this, we must first ensure that the depth of the drawing as much as possible, only when the blank holder can be flat on the flat surface of the pressure in the case of rolling, drawing pieces cannot appear wrinkling, cracking and other defects. In determining the binder surface to note the following five aspects: (1) Press the surface as much as possible to choose the plane; (2) If the binder surface must be a direction of the curve, then the other direction to keep a straight line; (3) Pressure surface as far as possible to avoid a sharp change; (4) Pressure surface should try to reduce the depth of drawing; (5) The expansion length of the binder surface is close to the length of the punch, or the length of the bobbin is longer than that of the punching length. If the length of the bobbin is longer than that of the punch, May produce wrinkles or even ripples. Figure 2-3 shows the size of the punch in this paper, and Figure 2-4 shows the dimensions of the binder surface. Figure 2-3 Punches Expanded dimensions Figure 2-4 Bushing surface expansion dimensions 4) The formation of convex and concave die and its meshing In the process of finite element analysis of automobile panel stamping, the mold is treated as a rigid body. The calculation process does not need to calculate the stress and strain in the mold, which does not affect the critical time step of the system. Therefore, the grid of the mold surface For the contact treatment between the billets, even the quality of the unit is very bad, but also can easily carry out contact treatment, so the mold grid shape and density of the stamping process of the finite element analysis process and the results will not produce significant The division of the molded mesh as long as it can be adapted to simulate the shape of the mold surface can be. The meshing is shown in Figure

6 Xiaoli Fu, et al (A) Blanking grid meshing Estimate the blank size and divide the grid (B) Die meshing Figure 3. Meshing Figure 2-3 can also be seen as the workpiece to expand the contour line, its external bias 10mm as a blank contour line, select 10mm as the offset amount to ensure the reliability of the material and save the material. In order to obtain the desired results, a smaller unit grid is used, and a decrease in the cell size may reduce the critical time integration step, thereby increasing the computational cost. Figure 2-6 Blank size 2.3. To determine the molding process parameters Setting of control parameters The molding process parameters mainly refer to the relative position, contact type, friction coefficient, and blank holder force, stamping speed, drawing bar parameters and material performance parameters between the convex and concave mold, the blank holder and the sheet metal. The main forming parameters of the subject are as follows: using anti-drawing forming, the mold gap is 1.65mm; the initial friction coefficient is taken as the default value of 0.125, that is, the friction coefficient under the non-lubricating condition, Side way. Tool positioning Automotive cross-stamping presses for the single presses, single presses are generally based on the punch, the punch in the next, the die in the above, in this case the deep drawing is also known as 'anti-deep drawing' The In this paper, the initial design of the punch, die, sheet, blank holder position from high to low are: die, sheet metal, blank holder, punch, the specific location shown in Figure 2-7: 29

7 Finite Element Analysis of Stamping of Automobile Beam Process settings Figure 2-7 Tool positioning Single-action press work has two movements, first press and the edge of the die and the die of the material movement, that is, die down movement, so that it has with the sheet metal, press edge ring contact, thus pressing the sheet. And then die stamping action, that die continues to move down, the sheet metal to be stretched, to be convex and concave mold contact, die movement to stop, get the final shape of the sheet. (1) Stamping speed setting In the actual stamping process, the molding speed is slow. However, if the actual stamping speed is used during the simulation process, the calculation time will be too long. Therefore, it is necessary to manually increase the die punching speed to reduce the solution time. On the other hand, the movement speed of the mold is too fast to the molding quality, so it is necessary to choose the punching speed reasonably so that the calculation time can be reduced and the pressing speed can be controlled within the allowable range of the workpiece forming. In the simulation of finite element simulation, the stamping speed of the mold should be kept within the range of 2000 mm / s to 5000 mm / s, and the other velocity curve should start at zero at zero. (2) The setting of the blank holder force The method of estimating the blank holder force F [20] is as follows: F = qa Where A - crimping area (blank area minus the convex cavity opening area) Q - The blank holder force per unit area Q empirical formula [21] is: Q = 48 (z-1.1) Where z - the reciprocal of the drawing coefficient of each process - Tensile strength of blank material T - Material thickness D - Rough diameter 2.4. Finite element analysis After the completion of the pre-processing can be carried out finite element analysis, Dynaform introduced Lsdyna to calculate the operation, and generate a d3plot file. The simulation results of the vehicle beam in this paper are shown in Figure

8 Xiaoli Fu, et al (B) Material flow (C) Thinning rate chart Figure 2-8 Simulation results It can be seen from the forming limit diagram, this drawing is a certain forming margin, so this simulation is partial safety, and there will be no cracking phenomenon. The top plate of the beam has a maximum thickness of mm, a thickening rate of 9.4%, and a permissible thickening rate of 10%. The thinnest point is mm; the thinning rate is 31.85%, exceeding the allowable reduction rate of 30%, so that both ends of the beam sidewall have the risk of rupture. From the material flow can be seen: the material at both ends of the material is too slow, easy to form a rupture, the middle of the middle of the sheet easily faster wrinkles. From the analysis of the shape of the product, the depth of the middle and the end structure of the workpiece is significantly different, the radius of the fillet is too small, resulting in a large difference in deformation, very easy to lead to non-uniform flow of the sheet, resulting in forming The thickness of the side wall is thin and the edge of the side wall is likely to be broken, and the forming is difficult in the middle part due to the insufficient plastic deformation Summary of this chapter This chapter uses the BSE module in the DynaForm software to complete the blank size estimation and the process supplement to the beam workpiece. The unit lattice in the pre-processing was completed and the parameters were set. The dynamic simulation was carried out with DynaForm software. The simulation results were obtained and the defects in the results were analyzed. Optimization of Process Parameters of Automobile Beam During the press forming process of the vehicle beam, the mold parameters (die fillet, blank holder, drawbead, etc.) and process parameters (blank holder force, punching speed, friction coefficient, etc.) are decisive to the forming degree and forming quality of the workpiece The impact of [22] [23]. In the actual stamping production process, once the 31

9 Finite Element Analysis of Stamping of Automobile Beam mold parameters are determined, only the process parameters can be adjusted [24]. There are many uncertainties in the impact of stamping process parameters on the quality of automobile panel stamping. This is one of the difficulties in the process optimization and quality control of the forming process [25]. Through the finite element technology can make qualitative guidance on the adjustment of the stamping process, the test design method can reduce the blindness of the repeated mold repair to a certain extent, and can get the reasonable process combination within the test range with fewer test times and reduce the production cost. In the future simulation, the problems such as cracking and wrinkling in the process of finite element analysis of automobile beams by Dynaform can be avoided by the following methods: (1) Convex and concave die radius is moderate The fillet radius is closely related to the flow of the material. In a certain range, the larger the corners of the die, the more conducive to the material at both ends of the sheet to the top of the workpiece flow; the workpiece is not easy to flow through the lack of material and rupture. However, if the die fillet is too large, it will lead to flow resistance is too small, with a large area of blank in the molding process in a floating state, easy to produce wrinkles in the fillet, resulting in cracking. So the die fillet is too large or too small are not conducive to the beam forming, it exists an optimal value. (2) The appropriate blank holder force The greater the blanket force, the more the material on the edge of the sheet easier to inflow, the more serious the tendency of sheet metal cracking; the other hand, the lower the blank holder force, the easier the material into the edge of the sheet, The more serious the tendency to wrinkle. The actual production process should be combined with drawing resistance and friction coefficient, considering the size of blank holder force. Taking into account the high cost of high presses, can be molded under the premise of the workpiece should try to use a small blank holder force. (3) Moderate friction coefficient The greater the coefficient of friction, the smaller the coefficient of friction, the easier the penetration of the material on the edge of the sheet, the smaller the tendency of the sheet to crack, wrinkle The more serious the tendency. The actual production process should be combined with stamping parts forming effect, the friction coefficient to make an appropriate local adjustment. The adjustment of the friction coefficient can be adjusted by changing the mold surface finish, plus lubricating oil and other methods to adjust. (4) Reasonable punching speed The greater the stamping speed, the material at the edge of the sheet is too late to have the end of the punching, the tendency of the sheet to crack is more serious; on the other hand, the smaller the stamping speed, the material at the edge of the sheet is full, The tendency to crack is reduced. (5) Pull resistance is moderate Pull the bar to play a role in blocking the flow of sheet metal, the greater the resistance of the drawing, wrinkling phenomenon reduced, and cracking phenomenon increased. 3. Conclusions In this paper, DynaForm software is used to simulate the process of punching the automobile beam, which provides a basis for the design of the actual automobile crossbar stamping die. The design of the actual stamping molding parameters provides theoretical guidance. A finite element analysis model was established and analyzed by DynaForm software. Through the analysis of forming limit diagram, material flow chart and thinning rate graph, it can be seen that the radius, blank holder force, friction coefficient, punching speed and drawing resistance of convex and concave die have great influence on the forming process. In the actual production, should be based on simulation, select a reasonable value. References 1... D.M. Woo. On the complete solution of the deep drawing problem. Int. J. Mech. Sci, 1986, 10: N.M. Wang. Large plastic deformation of a circular sheet caused by punch stretching. J. Appl. Mech. ASME, 1970, 37: N.M. Wang, S.C. Tang. Analysis of bending effect in sheeting forming operation. In: Proceeding of NUMIFORM'86, Rotterdam, 1986: S. C. Tang. Finite element prediction of the deformed shape of automobile trunk deck-lid during the binder-wrap stage. IN: C. C. Chen, ed, Experimental Verification of Process Models, ASM Metals Park, OH, 1981:

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