Development and Simulation of low melting point tr

2022-08-16
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Development and Simulation of low melting point trial production mold for automobile panels

trial production mold for automobile panels is an important link in the process of automobile development. Only body panels that are proved to be qualified by tests can be put into production. Based on a lot of practice, this paper introduces the development process of a low melting point alloy trial mold, and expounds in detail the mold design, mold pouring and trial mold based on AutoForm, and prospects the development of trial mold

trial production characteristics of body panels

the development of body panels involves many fields and disciplines, such as automobile structure, body strength, mass production technology, manufacturing cost and so on. Therefore, for the designed panels, we must make samples as required and do a lot of tests. Only the body panels that are proved to be qualified by the tests can be put into production and manufacturing

at present, the trial moulds mainly solve the problems of drawing and shaping of body panels. Blanking, trimming and hole opening are generally completed by laser cutting or manual work. Flanging, folding and other works with low requirements for R fillet are generally positioned by relevant fixtures and completed manually. For flanging with high requirements, press assistance or special flanging equipment can be used. Therefore, the forming and drawing die of body panels is the key to the trial production of the whole body

the characteristics of trial production of body panels are: (1) the number of production pieces is small, generally from a few to dozens; (2) The cycle is short, for example, the whole sample production cycle of a pair of door inner panel is only one to one and a half months; (3) The quality is close to the quality of mass-produced parts. For example, the reference point (RPS point), batch inspection point (PMP point) and matching surface size point (CP point) of trial produced parts must be qualified, and the size over tolerance (BK point) generally cannot exceed 2 in a single part. The experimental force that the sample can bear is as small as a few 10cn (such as spandex yarn for textile)

nowadays, major automobile design units generally adopt the method of rapid molding to manufacture body covering samples. The main methods are: low melting point alloy mold, polyurethane mold, metal spraying mold, die-free stamping based on discrete surface, etc. Among them, the low melting point alloy mold is a mold that uses polyurethane material master mold and uses low melting point alloy to directly cast concave mold and blank holder ring. The main process is shown in Figure 1

Figure 1 mold development process

trial mold design technology based on AutoForm

the body development and mold manufacturing of the world's major automotive groups should rely on one or more sheet metal forming simulation software to improve its success rate and ensure the mold manufacturing cycle. The internationally popular software mainly includes DYNAFORM of American ETA company, PAM series software of French ESI group, AutoForm of German AutoForm Engineering Co., Ltd., KMAS software of Jilin Jinge mold engineering research center, sheetform of Beihang, vform of Huazhong University of science and technology, etc. Among them, AutoForm is characterized by:

1) providing a complete solution from the conceptual design of products to the mold design after polyethylene and polypropylene, which are most common in daily life. Its main modules include user interface, automesher, onestep, diedesigner, incremental solution, trim Hydro (hydroforming), supporting windows and UNIX operating systems

2) it is suitable for the design of complex deep drawing and drawing forming dies, the verification of stamping process and die surface design, the optimization of forming parameters, the minimization of material and lubricant consumption, and the evaluation and optimization of new sheets (such as tailor welded blanks and clad plates)

3) it is fast, effective and reliable in algorithm. The latest implicit incremental finite element iterative solution technology does not need to accelerate the simulation process manually, and can get the results in a shorter time than the explicit algorithm; Its incremental algorithm has more accurate results than the reverse algorithm, and makes the nonlinear strain path, which is very important in FLC failure analysis, feasible. Even large and complex parts are proved to be feasible and reliable by industrial practice

4) it has fast solution speed, friendly interface, easy to use, and reliable results for complex engineering applications. AutoForm can be simulated directly by designers without large hardware investment and senior simulation and analysis experts. Its high-quality results can also be quickly used for evaluation. It has a significant effect in shortening the development and verification time of products and molds, reducing the cost of product development and molds, and improving product quality. It provides a quantitative concept for the evaluation of stamping forming, and brings obvious competitive advantages and market opportunities to enterprises

simulation of trial production mold based on AutoForm

mold surface design

the process supplementary surface of the mold can be realized according to the steps in Figure 2

Figure 2 is based on the AutoForm mold design process

onestep verification: after the latest halogen-free brand (the expansion of its heat-conducting resin series), the new polymer series with good electrical properties, and the innovative rubber for the manufacturer of wire and cable mixture check whether the parts have negative stamping angle, check the draft angle of the parts, which is generally not less than 5 ~ 7 °. In onestep function, first fill the holes and gaps, round the edges, and then calculate according to the product data, or product + pressing surface, or product + pressing surface + process supplementary surface, so as to obtain the minimum blank, wrinkle, crack and other defects, FLD, material elongation and thickness thinning rate and other parameters, so as to judge whether further mold design is needed

taking autoform4.0 as an example, the most important thing is to set the value of processor/constraint, which represents the deformation resistance of the material in the forming process. Generally speaking, the strength of the pressing bar of the panel mold can be known indirectly through the restraint value. If the safety area can cover 2/3 of the surface of the part, the OP20 process of the part can be achieved by adjusting the size of the process supplementary surface and the lacing rib in the future mold design process

the basis for judging wrinkling and fracture in the simulation is: in sheet metal stamping, compression instability is the main form of wrinkling, and wrinkling is judged by the unit thickening rate; Local necking caused by tensile instability is the main form of fracture, and the fracture is judged by forming limit diagram (FLD)

determine the stamping direction: the die takes no negative stamping angle as the first priority principle, and determines the stamping direction according to the principle of average normal direction, minimum stretching and minimum stamping quality difference. The choice of stamping direction is also related to the equilibrium deformation of the material. In addition to automatically rotating the data according to the requirements of the stamping direction definition, AutoForm can also automatically indicate the dangerous area of the stamping of the profile

determine the pressing surface: the determination of the pressing surface (binder) is based on the principle of smoothness. Considering the principles of drawing depth, smoothness of the pressing surface contour, regularity of the surface contour and so on, AutoForm will automatically generate the pressing surface. The formation of the pressing surface is controlled by the contour spline curve, so the adjustment of the contour spline curve to determine the fitting degree between the pressing surface and the workpiece is the key. In the trial mold, in order to improve the processing speed, the pressing surface is best made into a plane or a single curvature surface. For AutoForm, in addition to automatically generating the pressing surface by defining parameters, you can also manually generate control curves to form the pressing surface

determine the process supplementary surface: after the forming of the pressing surface, consider the forming of the sheet and the processibility of the subsequent work, and make the process supplementary surface from the original data surface to the pressing surface. In AutoForm, the process supplementary surface is determined by several pairs of related parameters. Changing one parameter may affect other parameters, so it is a very tedious work to supplement the ideal process supplementary surface in AutoForm

autoform has the following advantages in the generation of pressing surface and process supplementary surface: strong sense of geometry, easy for intuitive evaluation; Fully parameterized, easy to modify; Fully integrated with onestep and incremental solution; Through 2D simulation, the optimization of process supplementary contour is completed, and the process supplementary surface is completed automatically and interactively

determine the draw bead: the layout of draw bead not only needs to consider adjusting the local flow speed of the sheet in the forming process, but also needs to consider the possible problems during subsequent trimming and drawing. In the mold process design, AutoForm provides the concept of equivalent drawbead, but in the mold structure design, the specific geometric dimensions of drawbead, such as the corner radius of concave rib, the height of convex rib, the corner radius of convex rib, and the gap between convex and concave ribs, are provided by AutoForm special modules

calculation based on AutoForm and validation

stamping simulation should be carried out after the die design. AutoForm uses the incremental module. According to the principle of incremental method, it carries out repeated optimization simulation or selective simulation for the mold process plan, and comprehensively discusses the mold process design

it uses many modern simulation techniques, such as applying a new implicit finite element algorithm to ensure the iterative convergence of the solution; The consideration of bending effect is conducive to the solution of springback; Adaptive lattice, time order control, powerful contact algorithm for complex tool description, automatic determination of numerical control parameters and accurate full Lagrange theory are used to ensure fast and accurate solution; New cutting algorithm to increase accuracy

it also integrates many engineering application technologies. For example, the equivalent drawbead resistance model can consider the bending and anti bending effects when the sheet passes through the drawbead, and the geometric model of the drawbead will produce different friction coefficients for different materials. The material parameter library of the software is highly open. In addition to hundreds of widely used material databases in the United States, Japan and Europe, it can establish a parameter library to meet the needs of users

autoform incremental has many advantages in the simulation process, such as: high speed, and the simulation time for a pair of front cover molds is only 2-3 hours; Accurate. According to practical experience, the similarity of simulation can reach about 70%; It can represent relevant analog quantities in detail, such as fracture, thinning, elongation, wrinkling, forming limit diagram FLD, material inflow, slip and impact line, forming force, etc; It can completely simulate the whole process of stamping, such as gravity sliding, blank holder, drawing, trimming, shaping, etc

Figure 3 is a state diagram of stamping parts after mold simulation. In the figure, the area with sufficient deformation (green), the area with insufficient deformation (gray), the material tearing area (red), and the material wrinkling area (purple) can be seen. According to these conditions, we can modify the size of the die process surface or sheet, the number and location of holes, and the strength and location of the pressing bar

Figure 3 simulation deformation state diagram

design of trial production die for automobile panel

due to the low accuracy of AutoForm, most of the process supplementary surfaces generated by AutoForm need to be reconstructed by CAD software according to its characteristics. The design of the trial production mold only designs the punch in the drawing stage. At the same time, in order to improve the manufacturing speed, the trial production mold generally only designs the mold core, there is no mold base, and the mold generally does not contain the oblique cutting mechanism

the trial mold design is also a process of data collation. Adopt unified and standardized CAD data, including almost all information from design to mold processing, which can be used as a reference for people in all links of mold manufacturing in the future

manufacturing technology of concave die and blank holder of trial mold

low melting point alloy mold refers to the use of mother mold, using low melting point alloy directly

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