【Abstract】 The design points and main debugging experience of the automobile cover drawing die are introduced, and the wrinkles and cracking phenomena which are easy to occur in the stretching process of the automobile cover are analyzed. From the process analysis and the die structure design and Several aspects such as debugging explain the importance of design and debugging of tensile die.

Key Words Automotive Cover Parts Drawing 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 dies. The drawing dies are the key to punching out high-quality appearance parts. The design and manufacture of large-scale stretched tensile dies is a difficult problem that automobile manufacturers and stamping dies manufacturers must overcome.

Adjustment of cover part drawing die

The adjustment of the automobile cover parts drawing die plays a vital role in the quality of the parts. The debugging is good, which not only improves the quality of the stamping parts, but also shortens the manufacturing cycle of the dies. The purpose of die debugging is to improve the die designer's intentions and make up for the defects in die design and manufacturing. Since the cracking and wrinkling are the main defects of the tensile die, the key to the trial is to control the flow of the material during the stretching process. Because the material flows easily, it is easy to cause wrinkles, and the difficulty of material flow will cause the workpiece to crack, so a balance point must be found between the two. The size of the die gap, the size of the blanking force, the number and position of the drawbeads, etc. also restrict the cracking and wrinkling.

The production, the following only talk about a little experience accumulated in the die debugging process.

(1)Adjustment of the clearance between the convex and concave dies.

In the adjustment process of the drawing die, the reliability of the convex and concave die gap directly affects the quality of the drawing parts. If improperly adjusted, the side wall of the drawing parts is likely to wrinkle on the side with a large gap, and even a wave-shaped defect may appear at the periphery; and the side with a small gap may cause partial sheeting due to excessive extrusion. Thin, increasing the tensile force, causing the workpiece to crack. In addition, uneven gaps may also cause streaks on the sidewalls of the drawing partss.

For symmetrical or closed tensile dies, the correct way to avoid the above phenomenon during production is to fix the upper die to the press slider with a set screw when installing the die on the press table. The lower die is simply fixed on the press table pad (do not tighten the lower die plate bolt), and the bottom dead center position of the press slider is adjusted upwards to avoid the die die when the die is closed, and then the press is started. The slider is idle for several times. Finally, the slider is lowered to the bottom dead center to stop, and the lower die fixing bolt is re-tightened, and then the trial mode is started to ensure uniform gap around the convex and concave die.

(2)Adjustment of the pressing force

The adjustment of the blank holder force mainly refers to the case where the double-action press is used for stretching. The larger blank holder force can prevent wrinkles and increase the rigidity of the tensile member, and the smaller the blank holder force causes the workpiece to wrinkle. Due to the asymmetry of some complicated tensile members, the deformation is uneven everywhere. If the same blanking force is used, the peripheral resistance of the material is the same, which is bound to wrinkle in the small deformation of the workpiece, and pull in the severely deformed part. Crack phenomenon.

The outer slide of the double-action stretching press is connected with the link mechanism at four suspension points, and each point can be mechanically adjusted to adjust the blanking force at each point to form a deformation condition favorable to the metal flow. If the working principle and structural principle of the double-action stretching press are mastered, the blanking force is adjusted according to the degree of deformation of the stretching member, so that the feeding resistance which is adapted to the deformation is maintained everywhere, and the wrinkling and pulling are effectively suppressed. The occurrence of cracking.

(3) Adjustment of material pressing gap

In the case that the pressing force is difficult to control, the method of adjusting the stretching gap can eliminate the adverse effect of the change of the pressing force caused by the change of the material thickness on the material deformation. The adjustment of the gap of the pressing surface mainly has the following two methods. : As shown in Figure 1, the principle of tightening and loosening is adopted. At the die mouth, the linear bending deformation zone and the elongation deformation zone should allow the pressing surface to be tight and loose. The material thickness does not change during the deformation process. Thinning, which causes the press gap to become relatively large, which is actually equivalent to reducing the pressing force. When the sheet flows through the tight zone, the presser ring weakens the presser action, while the tighter outer presser surface balances the presser force. As the material flows, the beading ring always maintains a pressing action to prevent defects such as wrinkles. As shown in Fig. 2, in the compression deformation zone, the material is in a radially stressed, tangentially stressed state of stress, and the blank is compressively deformed in the circumferential direction. As the material flows, the thickness of the material tends to increase, which causes the gap of the binder surface to be relatively reduced to increase the feed resistance, and the material is easily broken by the tensile stress. Therefore, when adjusting the gap of the die pressing surface, the inner side of the inner loose should be used.

The method eliminates the adverse effect of increased material thickness on material deformation.

(4)Cutting for drawing blanks

During the drawing die adjustment process, for some structurally asymmetrical coverings, due to the uneven deformation of the parts during the stretching, the workpiece has different feeding resistance around the die, except that the drawing is controlled by the drawbeads. According to the characteristics of various deformations, the sheet material is properly cut or blanked before stretching, and the cutting or blanking must be carried out according to the following principles:

(1) The surface area of the blank is approximately equal to the surface area of the workpiece..

(2) The shape of the blank should be similar to the cross-sectional shape of the workpiece..

(3)The outline of the blank should be smooth and streamlined,and there should be no protrusions and sharp corners. Generally, the flange edge with a large deformation amount can be kept smaller, and the flange edge with a smaller deformation can be left larger. The feed resistance is coordinated with the degree of deformation. In addition, the test should be based on the principle of small to large, that is, the small blank is used for the cracked place, and the material is enlarged if the wrinkle is applied. In short, with the continuous advancement of the automotive industry, the requirements for the appearance quality of automotive exterior parts are becoming higher and higher, which requires mold design and manufacturing personnel to continuously improve the design and manufacturing level, while accumulating rich mold adjustment. Experience, in order to manufacture and debug qualified stamping dies, in order to obtain the ideal stamping parts and improve the appearance quality of the car.