Whether the drawing die can produce the panel with qualified dimensional accuracy, small dimensional fluctuation and qualified surface quality, and whether it can be produced in batch stably plays a decisive role in the production of main engine plant. Therefore, in the process of die debugging, it is necessary to recognize the relationship between drawbead and binder surface, and to distinguish which is more important, and to have a clear understanding of the role of the two elements in the whole forming process. In this paper, combined with experience and theory, the drawbead and binder surface are analyzed, which has a certain guiding significance for general drawing die debugging.
Relationship between drawbead and pressing surface
(1) drawbead.
Drawbead is an important part of drawing die. According to the form of drawbead, it can be divided into semicircular rib, square rib, sill rib, etc. Generally speaking, the feeding drawing die is designed as semicircular rib, and the bulging drawing die is designed as square rib or rib. Semicircular reinforcement can be divided into single reinforcement and double reinforcement, and double reinforcement is usually designed for those requiring larger feed resistance.
The elements of drawbead include height, width and R angle. The bar height and R angle directly determine the feeding resistance of the bar, and the width of the bar is generally designed according to the standard.
(2) pressing surface.
The blank holder surface is an annular closed surface on the blank holder ring, and the blank holder surface is an indispensable element of the drawing die. It forms a rib groove system with the drawbead to jointly control the feed quantity and provide conditions for drawing qualified parts.
The elements of pressing surface include management surface, rib groove R angle and external pressing surface. Taking the reinforcement as the boundary, the inner side of the reinforcement is defined as the management surface, also known as the internal pressing material surface, and the outer side of the reinforcement is defined as the external pressing material surface.
(3) the relationship between drawbead and pressing surface.
The relationship between drawbead and pressing surface can be summarized as follows: drawbead is the main component of feeding resistance, and the pressing surface is the secondary part of providing resistance. They cooperate with each other to output a stable feed resistance with small fluctuation, so as to adjust the change of flow rate caused by the fluctuation of Mechanical properties of sheet metal, air cushion pressure, drawing oil, material thickness and other factors.
Adjustment of drawing die
(1) to recognize the relationship between drawbead and pressing surface plays a decisive role in the adjustment of drawing die.
The general principle of the study of pressing surface is “tight inside and loose outside”. The inner part is the management surface, and the management surface is solid color, that is, the inner side of the drawbead is close to the side of the punch. When the strip is coated with blue oil (the coloring agent used for grinding), it is 100% compacted and pressed white. Theoretically, the gap between the management surface is slightly less than one material thickness, and the external pressing material surface has virtual color, that is, the blue oil shows that the contact point is like fog, that is, there is no white compaction point The blank holder surface is slightly larger than one material thickness, and the blank holder ring balance block is installed to keep the gap constant.
(2) the height of drawbead has the greatest influence on the sheet resistance.
For ultra-low carbon steel sheet (commonly used automobile brands are DC04, dc06, DC07), the height of the rib is generally 5mm, the width is 10mm, and the minimum effective plane width of the management surface is 8mm; for aluminum plate, the rib height is generally 6mm, the width is 12mm, and the minimum width of the management surface is 8mm. In the process of research and preparation, it is not easy to adjust the reinforcement and rib groove R angle and height. When the pressing material surface coloring is qualified, adjust the pull piece according to the part defects, such as reducing the drawing rib height, enlarging the rib groove R angle, etc., until the qualified parts are debugged.
In this process, the sheet metal is in a completely free and uncontrollable state during the period from just contacting the ribs to the completion of forming. In addition, the automotive deep drawing parts basically belong to the closed cylindrical parts, so there must be radial tensile stress and tangential compressive stress at the corner of the sheet metal. Under the action of the tangential compressive stress, the blank pressing surface will produce very “random wrinkling”. The degree of wrinkling is closely related to the height of drawbead. The higher the rib is, the greater the deformation is and the bigger the wrinkling is. On the contrary, the lower the rib is, the smaller the deformation is and the smaller the wrinkling is. If the rib is lowered, the wrinkling can be reduced. The empirical data is that when the height of the rib is reduced to 1.5 ~ 2mm, the wrinkling is basically eliminated when it is less than 1.5mm. At this time, the resistance coefficient of the rib is equivalent to AutoForm In other words, the feeding resistance of the reinforcement is very small. At this time, the feeding resistance is mainly provided by the pressing surface. However, due to the increase of temperature, the friction coefficient increases and the stability of the surface is greatly reduced.
Therefore, the most important factor in drawing die debugging is drawbead. The height of drawbead has the greatest influence on sheet metal resistance, followed by rib R angle and rib groove R angle, the management surface has less influence, and the external pressing material surface has the least influence. Therefore, when these factors need to be adjusted, priority should be given to the unimportant elements, and the adjustment of the most influential factors should be cautious.
The order of adjustment should be as follows: external pressure material surface → management surface → reinforcement groove R angle → reinforcement R angle → reinforcement height.
2020-10-17