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

The general characteristics of metal drawing die are introduced as follows:

First, the concept of stretching:

1. stretching: pressing the sheet 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-shaped) side wall, so the size of the plane changes greatly.

3. Tensile coefficient: the ratio of tensile diameter to blank diameter "m" (deformation degree from blank to workpiece). ?

Second, the main factors affecting the tensile coefficient:

1. Mechanical properties of materials (yield strength-elastic deformation; Tensile strength-plastic deformation; Extension coefficient; Area shrinkage).

2. The relative thickness of materials.

3. Stretching time.

4. Stretching method.

5. Radius of fillet of punch and die.

6. Smoothness, lubrication and clearance of drawing surface.

7. Stretching speed.

Third, the drawing process arrangement:

1. Parts with thin material and drawing depth greater than diameter: The fillet radius can be gradually reduced by reducing the cylinder diameter to increase the height.

2. Parts with thick materials and similar drawing depth and diameter: Under the condition of keeping the height unchanged, the fillet radius can be reduced in the process of gradually reducing the cylinder diameter.

3. The flange is very big and the circle radius is very small: it needs to be reshaped many times.

4. When the flange is too large, strain bulging method shall be adopted if necessary.

In order to embody the principle of "unchanged flange" and prevent the flange formed in the first drawing from participating in the subsequent drawing deformation, the material of the wide flange after drawing thinning (that is, the material forming the wall and bottom) should be 3~ 10% more than the material actually needed in the final drawing.

Note: When calculating the stretching multiple by area, the upper limit is taken, otherwise the lower limit is taken. These extra materials will return to the flange in the later drawing step, which will cause the flange to thicken but avoid the head cracking. The local thinning area can be corrected by shaping. Therefore, it is very important to strictly control the stretching height of each stretching.

Fourthly, the box-shaped part is stretched.

The corner part is equivalent to the stretching of the cylindrical part, and the straight wall part is equivalent to the bending deformation;

Verb (abbreviation for verb) stretch lubrication

In the process of drawing, there is friction between the material and the die, so special stamping and drawing lubricating oil is needed. High friction will not only increase the drawing coefficient, but also increase the drawing force, which will wear and scratch the surface of the mold and workshop, so it is harmful. Therefore, it is necessary not only to improve the bearing capacity of the force transfer zone, but also to compensate the unevenness by using the lubrication conditions to promote the smooth plastic deformation of the whole deformation zone. Therefore, lubrication conditions are necessary in drawing.

The above is the brief introduction and characteristics of the drawing die. Although some problems with wire drawing dies are really a headache, there are also solutions. As long as we master the "strength" and "gap", many problems can be solved.