Forming characteristics and main forming barriers of automobile covers
MO Jian\|hua LIU Jie HUANG Shu\|huai (State Key Lab of Plastic Forming Simulation and Die & Mould Technology Huazhong University of Science and Technology 430074)
《Journal of Plasticity Engineering》2001-02
1 forming characteristics and main forming obstacles of automobile panel
1. Characteristics of the vehicle cover
The general forming process of automobile panel is shown in Fig. 6. 39. The forming process includes: (a) billet, and the billet has a certain degree of downward bending of; (b) through the edge-holding device because of its self-weight, and at the same time pressing deep-drawing bars; The (c) punch decreases and the sheet metal contacts with the punch. With the expansion of the contact area, the sheet metal gradually fits with the punch and the; (d) punch continues to move downward, and the material is drawn into the mold cavity continuously, and the side wall is formed. (e) convex, concave die, the material is pressed into the die cavity shape; (f) continues to press to make the workpiece set, the punch reaches the dead point; (g) unloading.
As the automobile covering part has the characteristics of complex shape, high surface quality requirement and the like, the automobile covering part has the following characteristics of:
(1) there are many forming processes.
(2) the forming of automobile panel is the compound forming of drawing, bulging, bending, etc. No matter how complex the shape is, one-time forming is often used.
(3) since most of the automobile panels are non-axisymmetric and non-rotating complex curved-shaped parts, which are not uniform, the main deformation obstacles in deep drawing are wrinkling and tensile cracking. For this reason, it is often used to control the deformation by adding the supplementary surface and drawing bar.
(4) for the forming of large automobile panel, a large and stable blank holder force is needed, so the double power press is widely used in deep drawing.
(5) for the sake of easy drawing and forming, the steel sheet with good stamping performance such as 08 steel is used, and the surface quality of the steel plate is good and the dimension precision is high.
(6) the forming process and die design of automobile panel should be based on automobile panel drawing and main model. The main model is a model of the shape of the car, which is made on the basis of the final master drawing plate, the main template and the automobile cover drawing according to the size scale of 1:1. Often made of wood and fiberglass. The main model is a necessary supplement to the automobile panel diagram. Only the main model can truly represent the information of the automobile panel. Due to the popularization and application of CAD/CAM technology, the main model is being replaced by computer virtual entity model. The traditional oil sludge model to the main model of the automotive design process, is being conceptual design, Instead of modern design methods such as parametric design, the design and manufacturing cycle is greatly shortened and the manufacturing precision is improved.
1.2 main forming obstacles to automotive panels
Because the shape of automobile panel is complex, many positions are non-axisymmetric and non-rotating complex curved shape parts, so the deformation of deep drawing is not uniform, so the wrinkling and cracking during forming are the main obstacles to forming.
1. Wrinkle forming and Anti-wrinkle measures of Automobile Panel
In the drawing process of the automobile panel shown in Fig. 6 / 39, compressive stress occurs in the panel when the sheet is in contact with the punch at the beginning of the drawing. As the drawing goes on, when the compressive stress exceeds the allowable value, the sheet will lose stability and wrinkle.
Fig. 6 / 40 shows the relationship between in-plane stress and wrinkling direction. According to the relationship between the stress and the wrinkle direction, the stress and deformation in the sheet surface can be qualitatively judged when the automobile panel is drawn up and wrinkled, and the corresponding measures to reduce the wrinkle and prevent the wrinkle can be worked out.
In production practice, the corresponding anti-wrinkle measures are taken from the structure, forming technology and die design of automobile panel.
For parts that are simpler in shape and easier to deform, or where the relative thickness of the part is larger (because the critical wrinkling stress of the sheet is approximately proportional to the square of the thickness), The wrinkle can be prevented by using a flat edge holder (or without the use of a side holder).
For the parts with complex shape and difficult deformation, the wrinkle can be prevented only by setting up a reasonable process to replenish the surface and drawing the deep reinforcement.