Plastic mold. Principle of parting surface selection

Plastic mold. Principle of parting surface selection

The general principle of parting surface selection

The selection of parting surface is not only related to molding and demoulding of plastic parts, but also related to mold structure and manufacturing cost. Therefore, we must pay attention to the selection of parting surface. Generally speaking, there are three general principles for the selection of parting surface:

1. To ensure the quality of plastic parts. This is the most basic one, must make the quality of plastic parts meet the predetermined requirements.

2. Easy to release plastic parts. Easy to release mold, can increase productivity, plastic parts are not easy to deformation, improve the rate of authenticity.

3. Simplify mold structure. The same plastic parts, because of the different choice of parting surface, the complexity of the structure is very different, reasonable choice, can simplify the mold structure.

How to choose parting surface.Plastic Mold

The relationship between mold cavity and mold can be divided into three categories: mold cavity is completely in the moving mold; The cavity is completely in the fixed die. The cavity is in moving and fixed die respectively. Due to the various shapes of plastic parts, the selection of parting surface changes a lot, in order to make you have a basic understanding of the selection of parting surface, the following introduces some typical parting surface selection.

1. Classification of long members is shown in the figure below. If the length of plastic parts is long, such as tubular, cylindrical, bar shaped plastic parts, such as the cavity in a template, it will make the stripping Angle too large (figure a), if the cavity is arranged in the moving, fixed mold (figure b), can reduce the stripping Angle, so that the plastic parts at both ends of the size difference is not too large.

Plastic mold-img

A)parting with too large stripper slope;

B)mold parting to reduce the parting Angle.

2. The parting of the plastic part on the moving mold side is shown in the figure below. Leaving the plastic part on the side of the moving mould, it is easy to set up and manufacture the demoulding mechanism with simple structure. Therefore, try to keep the plastic part in the moving mold side. For the cover shaped plastic parts, the parting surface is reasonably selected according to figure a. For plastic parts with embedded parts, the parting surface can be selected according to figure b, because the embedded parts will not shrink and the core will be tight. If the core of plastic parts symmetrical distribution, according to the figure. Parting, forcing the plastic parts to stay on the moving mold; If there is a plastic part with side holes, it should be divided according to figure d to avoid core pulling.

Plastic mold-img

  1. plastic cover parts;
  2. plastic parts with embedded parts;
  3. symmetrical plastic parts with molded cores;
  4. plastic parts with side holes.

3. To ensure the appearance quality of plastic parts typing, as shown in the figure below. The appearance quality of plastic parts needs to be guaranteed. Careful consideration should be given to the selection of parting surface. For example, the parting surface should not be set on smooth surface or circular curved surface as far as possible.

Plastic mold-img

  1. type making the surface smooth;
  2. reduce the parting of flaps;
  3. reduce the classification of spillage.

4. It is conducive to exhaust classification, as shown in the figure below. The parting surface is often used as the exhaust channel in the injection mold. In order to exhaust smoothly, the parting surface should be located at the end of the melt flow material, and it should not be blocked at the end. The structures of figures b and d are more reasonable than those of figures a and c.

Plastic mold-img

5. Ensure coaxiality parting, as shown in the figure below. Many plastic parts have coaxiality requirements, in the mold design should ensure this requirement, should make plastic parts have coaxiality requirements of the part of the design in the same move template, in order to meet the precision requirements.FIG. A can meet the requirements of coaxiality, while FIG. B is not accurate and cannot meet the requirements of coaxiality. (1 movable mode 2 - fixed mode)

Plastic mold-img

  1. type separation to ensure coaxiality;
  2. type separation difficult to ensure coaxiality.

6. The typing with side holes is shown in the figure below. When selecting parting surface, side core pulling or parting should be avoided as far as possible. If necessary, the following principles can be referred to. Figure a places side core on the moving die to facilitate core pulling. According to figure c, it is more reasonable to place the long distance of core pulling in the direction of mold opening and the small distance of core pulling in the side. However, if the type is divided according to figure d, it will bring difficulties to the demoulding.(1 - moving mode 2 - fixed mode)

Plastic mold-img

6. Type classification to ensure accuracy, as shown in the figure below. In plastic parts on some surface precision requirements, such as thread surface, mating surface, etc., this time the surface cannot pass through these surfaces, otherwise it will affect the precision of plastic parts, even difficult to use. The typing in FIG. A guarantees the accuracy of thread, while the typing in FIG. B cannot guarantee the accuracy of thread through the thread axis. The typing of FIG. C guarantees the integrity and smoothness of the circular surface, while d has an obvious seam line around it, which affects the appearance and use.

Plastic mold-img

  1. typing to ensure screw thread accuracy; 
  2. typing that cannot guarantee the precision of thread;
  3. ensure that the plastic parts have smooth appearance;
  4. the parting of plastic parts with smooth appearance cannot be guaranteed.

8. The classification of thin-walled plastic parts with uniform wall thickness is required, as shown in the figure below. To make the wall thickness uniform, the normal plane is not used as the parting surface, but the tapered step parting surface as shown in FIG. A. Plastic mold.

Plastic mold-img

  1. tapered step parting surface;
  2. plane parting surface.
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