Key Words: Automotive Cover Parts Drawing Die Stamping Die Design Adjustment

The automobile cover is a thin plate stamping part that constitutes the automobile body, and has the characteristics of thin material, complicated shape, large structural size and high surface quality requirements. Stamping parts with more complicated shapes can be completed through multiple steps of stamping, but the quality of the covering parts is largely controlled by the quality of the drawing molds. The stretching molds are the key to punching out high-quality appearance parts. The design and manufacture of large-scale stretched tensile molds is a difficult problem that automobile manufacturers and stamping dies manufacturers must overcome.

1 Design of large-size cover drawing die

1.1 Determination of stamping process plan for drawing stamping parts

The technicality of the tensile part is the first problem to be considered in the preparation of the stamping process of the cover. Only a reasonable and technically stretchable design is designed.In order to ensure no wrinkles, no cracking, less wrinkles and less cracking during the stretching process. The processing of the cover stretching process is not only the stretching process establish good deformation conditions and provide convenience for future processes. Therefore, when designing the tensile member, not only the punching direction but also the pressing surface should be considered.

The shape, the shape and position of the drawing ribs, the rationality of the process addition and the relationship with the next process.

(1) Determination of the punching direction.

Correctly determining the direction of stretching is not only a guarantee for obtaining an ideal tensile member, but also has a large influence on the arrangement of subsequent processes, so the stretching direction is the first element for determining the tensile member. The main consideration when determining the direction of stretching is to ensure that the punch can smoothly enter the die and enter all corners of the tensile member; the punch and the blank should be as large as possible when starting the stretching, and the contact surface should be located in the center of the die as much as possible. The feed resistance of the binder surface should be uniform.

(2) Reasonably increase the process supplement.

There are many types of automobile covers, some of which are complex in shape, asymmetrical in structure, and difficult to form directly. The necessary process supplements are provided to improve the processability of the tensile members and improve the quality of the tensile members. The process replenishing part is an indispensable part of the stretching part, and it needs to be cut off after the stretching is completed. Therefore, it is determined that the replenishing part of the stretching part should follow the following principles: make the stretching depth as shallow as possible; The process supplement should be as small as possible.

(3) Determination of the shape of the binder surface.

The pressing surface is part of the process replenishment. When increasing the process replenishment, the shape of the pressing surface must be correctly determined so that the feeding resistance of each part of the pressing surface is uniform. To do this, it must be ensured that the stretching depth is uniform in all directions, because only the drawn blank is pressed against the die at the bead ring.

No wrinkles or creases are formed on the material surface to ensure that the tensile members are not wrinkled or cracked. When determining the shape of the pressing surface, the stretching depth should be reduced as much as possible to make the forming surface gentle. Since the convex mold has a certain stretching effect on the tensile hair, it is necessary to ensure that the unfolding length of the pressing surface is shorter than the protruding length of the convex mold. The material can be stretched. If the unrolled surface is longer than the punch, it may form ripples or wrinkles during stretching.

Even if some of the tensile members do this, there is no guarantee that no corrugations or wrinkles will be produced at the end, because the pressing material is pressed at each moment in the whole process from the contact of the punch to the blank and the end of the stretching. The unfolding length is longer and shorter than the unfolding length of the surface of the punch. The short punch has a tensile force on the blank and a long time to form a corrugation or wrinkle. When determining the shape of the pressing surface, special attention must be paid to the angle between the pressing surface and the angle of the surface of the punch to avoid ripples or wrinkles. At the same time, it should be stated that the angle must be less than 180°. If the pressing surface is the flange part of the cover itself, the radius R of the die should be determined according to the specific conditions, because the radius of the fillet of the cover is generally small, directly As the die radius of the die is not conducive to stretching, it must be increased to not cause wrinkles or cracks during stretching. The enlarged rounded corners can be used to meet the product requirements through subsequent shaping operations.

(4) Process cut and process hole settings.

Process cuts and process holes are mainly used for some parts with severe local deformation or reversed stretched workpieces. They must be distributed in the process replenishment and can be removed in the subsequent trimming and punching process. The process cuts and process holes are permanently located at the corners where the tensile stress is greatest, and are adapted to the shape of the local raised edges for proper material flow. The position, size, number and shape need to be determined during the trial of the tensile die. The general process incision is punched out during the working process of the mold, and sometimes it is also punched out on the blanking or blanking material to change the stress state during forming, so that the local deformation can be alleviated.

2 Structural design of the working part of the stamping dies of the cover parts

2.1 Determination of the radius of the convex and concave corners

The size of the fillet radius of the convex and concave molds plays a large role in obtaining the ideal tensile member. Common defects in the stretching of the cover are cracking and wrinkling. When the radius of the punch is too small, the bending deformation of the transition between the straight wall portion and the bottom portion of the drawn blank is increased, so that the strength of the dangerous section is weakened. When the fillet radius of the die is small, the tensile stress of the sidewall of the blank increases correspondingly. In both cases, the tensile coefficient increases, and the deformation resistance of the sheet increases, thereby causing an increase in the total tensile force. And the life of the mold is reduced. If the fillet radius of the punch and the die is too large, the deformation resistance of the sheet is small, and the fluidity of the metal is good, but the effective area of the presser is also reduced, so that the article is easily wrinkled. So determine the convex,

The radius of the die must be considered in combination with the deformation characteristics of the workpiece, the drawing ribs, and the radius of the fillet radius of the convex and concave molds.

2.2 Determination of the position and quantity of the drawing ribs

In the design of automobile cover stamping dies, the direction of stretching, the replenishment part of the process and the shape of the binder surface are the prerequisites for determining whether or not the satisfactory part can be stretched, and the setting of the drawing ribs is a necessary condition, and the drawing ribs is The main function is to increase the deformation resistance of the material around the whole week or local to control the inflow of the material and improve the rigidity of the workpiece, and it is also the most effective method for preventing wrinkling and cracking of the cover. The number and position of the drawing ribss are mainly determined according to the shape of the cover and the depth of the stretch. For the parts with large tensile depth, 1 to 3 drawing ribss are generally arranged in the straight part, and no pull is provided on the arc. Yanjin; when the tensile depth of each part of the same part is large, there is no drawing ribs in the deep part, and the drawing ribs is needed in the shallow part; the drawing ribs is set in the part with small feed resistance; The drawing ribs is set in a small part; the drawing ribs is set in the part which is easy to wrinkle. The direction of the drawing ribs must be perpendicular to the direction of flow of the material of the drawn blank. The drawing ribs is installed on the pressing surface of the presser ring, or it is installed on the die pressing surface, which does not affect the action of the drawing ribs. However, when the die is adjusted on the press, the drawing ribs is generally not polished, so the drawing ribs is required. It is mounted on the pressing surface of the upper pressing ring, and the drawing rib groove is arranged on the lower die pressing surface for sanding and grinding. If the pressing surface is the flange of the cover itself, the drawing rib groove on the concave mold is often polished, and the loss of the pressing surface of the concave mold is larger, which may affect the stretching depth. When the loss reaches a certain level, it needs to be repaired. At this time, the layout of the drawing ribs should take into consideration the convenience of maintenance. If the maintenance is convenient, the drawing ribs can be placed on the pressing surface of the presser ring. If the maintenance is difficult, Then, the drawing ribs should be mounted on the lower die pressing surface, so that the loss of the die blank surface can be reduced.