There are many stamping processes, and stretching is one of them. This process has a wide range of applications, and it has a certain effect on some covers, covers, and electrical instrument housings of automobiles and decorative shells, as well as many daily necessities. There are three kinds of geometric shapes for stretched parts: rotating body parts, box-shaped parts and complex surface parts.
Requirements for stamping and stretching processing:
1. The shape of the stretched parts should be as simple and symmetrical as possible
In the circumferential direction, the axisymmetric stretched parts will be uniformly deformed, and the molds made at this time are relatively easy to process, and the manufacturability at this time is also the best. For stretched parts of other shapes, sharp contour changes should be avoided as much as possible. For example, the rear cover of the automobile muffler, under the premise of ensuring the use requirements, the simplified shape will change the production process from multiple processes to one or two processes, and the consumption of materials will also be reduced by half.
2. The size ratio of each part of the stretched part should be appropriate
The design of flanges and deep drawing parts should be avoided as much as possible, because such workpieces require more drawing times. For example, the size of the upper part of the workpiece is too different from the size of the lower part, which does not meet the requirements of the drawing process. If you want to make it composite, you can divide it into two parts, process and manufacture them separately, and then connect them. If the cavity of the workpiece is not deep, but the diameter of the flange is large, it will be very difficult to manufacture, and annealing treatment is required in the middle. If the flange diameter is reduced, intermediate annealing may be omitted. The outline of the flange of the workpiece should preferably be similar to the outline of the drawn deep part. If the width of the flange is inconsistent, not only the drawing is difficult, but additional processes are required, and the trimming margin needs to be relaxed to increase metal consumption.
3. The fillet radius of the stretched part should be appropriate
In order to facilitate forming and reduce the number of stretches, the fillet radius of the stretched part should be increased as much as possible. The fillet radius between the bottom and wall of the tensile part, the flange and the wall, and the four walls of the rectangular part must meet the requirements.
4. The unevenness of the thickness of the stretched parts should be considered
On the inner and outer walls of workpieces that have been stretched multiple times or on the flange surface of stretched parts with flanges, impressions produced during the stretching process should be allowed. Unless the workpiece has special requirements, the method of shaping or catching up can be used to eliminate these marks
5. The holes on the stretched parts should be arranged reasonably
Set the holes on the stretched part on the main structural surface, keep it on a plane, or make the hole wall perpendicular to the plane, so that punching and trimming can be completed in one process at the same time.
6. The dimensional accuracy of stretched parts should not be too high
The manufacturing accuracy of the stretched parts includes the accuracy in the diameter direction and the accuracy in the height direction. In general, the precision of the drawn parts should not exceed the specified value. The size on the product drawing needs to indicate the guaranteed external size or inner cavity size, and the inner and outer dimensions cannot be marked at the same time.
7. Selection of stretching oil
In the selection of drawing oil, in addition to the lubricity and cooling properties of the drawing oil, the rust resistance, cost and easy maintenance of the drawing oil should also be considered. The drawing oil is easy to choose base oil with relatively low viscosity to add anti-friction additives, which can not only achieve lubrication and anti-friction, but also have good cooling and easy filterability. However, the problems of stretching oil are low flash point, high temperature during stamping, easy deformation, high risk factor, and fast volatilization, and the user's use cost is correspondingly high. Highly abrasive stretching oil.
