Research on the forming process and trial production of a box-shaped part with liquid-filled deep drawing
Liquid-filled forming technology is a new type of metal forming process, which is widely used in the production and manufacture of parts in the fields of automobiles, aviation, and aerospace. This article describes the process of using liquid-filled drawing technology to replace the traditional rigid die drawing process to form a box-shaped part. The method of numerical simulation is used to study the liquid-filled drawing process of typical box-shaped parts. The method of adjusting blank holder gap and blank holder force solves the problem of flange wrinkles in the trial mold. The results show that adjusting the blank holder gap can improve the forming quality of the part, but it cannot completely eliminate the wrinkles on the flange surface; the variable blank holder force method is adopted to eliminate the wrinkles on the flange surface by adjusting the blank holder force. Good moldability, meeting the requirements of forming technology.
Introduction to Liquid Filling Technology
Liquid-filled forming technology is an advanced flexible sheet metal forming technology, and one of the representative technologies of modern precision manufacturing. The liquid-filled forming technology uses liquid water, oil or viscous materials as the force-transmitting medium. During forming, the blank is closely attached to the mold under the action of the force-transmitting medium to form the designed part shape. According to the different shapes of the processed blanks, there are generally three types of liquid-filled forming technologies: sheet-filled forming, tube-filled forming, and shell-filled forming.
Figure 1 shows the comparison between liquid-filled deep drawing and ordinary deep drawing. The characteristic of liquid-filled deep drawing is that the concave mold is filled with liquid, and the punch is used to drive the sheet into the concave mold, thereby establishing reverse hydraulic pressure. The reverse hydraulic pressure reduces the hanging area of the blank between the convex and concave dies in the ordinary deep drawing forming, and makes this part of the blank close to the convex mold, thereby producing a “friction retention effect”, and alleviating the sheet metal at the round corners of the punch ( The radial stress of the dangerous section during traditional deep drawing can improve the bearing capacity of the force transmission zone, inhibit the thinning and cracking of the blank, which can effectively increase the forming limit and reduce the forming pass.
Figure 1 Comparison between liquid-filled drawing and ordinary drawing
During forming, the liquid overflows from the blank and the upper surface of the die, forming fluid lubrication between the surface of the blank and the die, thereby reducing the friction coefficient between the blank and the die. The protective effect of oil reduces the probability of scratches on the surface of the formed part, and at the same time reduces the radial stress required for flange deformation.
Part features and material properties
Figure 2 Three-dimensional digital model of box-shaped parts
Figure 3 Whether the box-shaped part can be drawn and formed at one time.
The expanded length of the curved part is:
The round corner radius R of the blank after the rounded drawing part is unfolded is:
And then get:
According to the above calculation results, the box-shaped part is located at the “red dot” position shown in Figure 4 and can be deep-drawn at one time.
Numerical simulation
From the theoretical calculation, it can be known that the part can be deep-drawn at one time. First, the numerical simulation software is used to simulate the rigid deep-drawing process of the box-shaped part. The numerical simulation parameters are as follows: punch fillet radius 16mm, blank holder fillet radius 10mm, concave model surface fillet radius 12.7mm, grid size 1.5mm. The coefficient of friction is set as follows: the male mold is 0.17 (rough), the female mold is 0.05 (lubricated), and the blank holder is 0.05 (lubricated). During the forming process, the blank holder gap is initially set to 1.76mm, and the gap between the convex and concave die is 2mm.