Drawing (also known as drawing, deep drawing) is a common process in stamping process because it is applicable to all walks of life and has wide applicability. From blank to stretch forming, it needs to be completed in multiple steps, primary stretching → secondary stretching →... → forming. Various problems will occur during the drawing process of the die, such as wrinkling, top R cracking, side wall cracking, product surface damage, drawing height too high or too low, etc. Therefore, the drawing process is also a difficult point in the stamping die.

The following describes the general characteristics of the drawing die:
1、 Stretch concept:
1. stretching: press the plate into a hollow part (the wall thickness is basically unchanged).
2. stretching process: the material on the plane (flange) is transferred to the cylindrical (box) side wall, so the overall dimension of the plane changes greatly.
3. stretching coefficient: the ratio of stretching diameter to rough embryo diameter "m" (deformation degree from rough embryo to workpiece).
Introduction and characteristics of drawing die
2、 Main factors affecting tensile coefficient:
1. mechanical properties of materials (yield strength - elastic deformation; tensile strength - plastic deformation; elongation coefficient; reduction of area).
2. relative thickness of materials.
3. stretching times.
4. stretching method.
5. fillet radius of male and female die.
6. finish, lubrication condition, clearance, etc. of tensile working surface.
7. stretching speed.
3、 Stretching process arrangement:
1. parts with thinner material and larger drawing depth than diameter: reduce the cylindrical diameter to increase the height, and the fillet radius can be reduced step by step.
2. for parts with thick material and similar drawing depth and diameter, the fillet radius can be reduced during the process of gradually reducing the cylindrical diameter by maintaining the same height.
3. the flange is very large and the circle radius is very small: it should be achieved through multiple shaping.
4. if the flange is too large, bulge forming method shall be adopted if necessary.
Introduction and characteristics of drawing die
In order to embody the principle of "constant flange", the flange formed in the first drawing will not participate in the subsequent drawing deformation. The material (i.e. the material forming the wall and bottom) of the wide flange drawing minus the material first inserted into the die should be 3~10% more than the actual material required for the final drawing.
Note: if the number of stretching times is calculated by area, the upper limit shall be taken; otherwise, the lower limit shall be taken. These excess materials will be returned to the flange in the subsequent stretching steps, which will cause the flange to become thicker but can prevent the head from cracking. The locally thinned area can be corrected by shaping. Therefore, it is very important to strictly control the drawing height of each drawing.
4、 Box stretch
The corner part is equivalent to the stretching of the cylindrical part, and the straight wall part is equivalent to the bending deformation;
5、 Stretch lubrication
In the process of drawing, there is friction between the material and the die, so special stamping and drawing lubricating oil should be provided. The high friction will not only increase the drawing coefficient, increase the drawing force, but also wear, and scratch the surface of the die and the workshop. Therefore, it is harmful to use the deformation potential of the force transmission area under the lubrication conditions to compensate for the non-uniformity, which can not only improve the bearing capacity of the force transmission area, but also promote the smooth plastic deformation of the whole deformation area. Therefore, the lubrication condition is necessary in stretching.

The above is a brief introduction and characteristics of the drawing die. Although some problems of drawing dies are indeed a headache, there are solutions to them. As long as we master the two points of "force" and "gap", many problems can be solved.

Hebei Zhongtian Cemented Carbide Co., Ltd. en.hebzhongtian.cn  was established in 1988. Over years of honest management, vigorous exploration and continuous growth, Hebei Zhongtian Cemented Carbide Co., Ltd. was formally established in 2021. The company has passed ISO9001 quality management system certification. The company covers a land area of over 10,000m2, has over 50 employees, over 20 low speed wire cut machines, machining centers, lathe-mill combined machines, fine grinders, polishers and other domestic and overseas advanced equipment, and the Detection Department has three-coordinate measuring instruments and automatic image measuring instruments. We make every effort to produce each product to satisfy customers. 

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