Design method of venting grooves for injection molds

When injection molding, the venting hole will not have a lot of melt oozing out, because the melt will cool and solidify at that place to block the channel. The venting hole should not be open to the operator to prevent the melt from accidentally ejecting. In addition, you can also use the ejector rod and the ejector hole with the gap, the top block, and stripper plate, and the core with the gap to exhaust.

1、The role of the exhaust slot

The role of the exhaust slot has two main points

a, in the injection of molten material, to exclude the air in the mold cavity.

b, to exclude the material in the healing process of various gases.

The more thin-walled products, the move away from the part of the gate, the opening of the exhaust slot is particularly important.

    In addition, for small parts or precision parts, also pay attention to the opening of the exhaust slot, because it can avoid the product surface burns and insufficient injection volume, but also can eliminate various defects of the product, reduce mold pollution, etc. 

    So, how is the exhaust of the mold cavity considered adequate? Generally speaking, if the melt is injected at the highest injection rate and no scorch is left on the product, the exhaust of the cavity is considered sufficient.

2、Exhaust method

    There are many methods of cavity exhaust, but each method must ensure that: the exhaust tank in the exhaust at the same time, the size of the design should be able to prevent material overflow into the tank; secondly, to prevent blockage.

    Therefore, from the inner surface of the cavity to the direction of the outer edge of the cavity body, the length of 6-12mm or more exhaust slot part, slot height should be put about 0.25-0.4mm. In addition, the number of exhaust slots is too much is harmful. This is because, if the clamping pressure acting on the parting surface of the mold cavity without the venting groove is very large, it is easy to cause cold flow or cracking of the mold cavity material, which is very dangerous. 

    In addition to exhausting the mold cavity on the parting surface, the purpose of exhausting the mold cavity can be achieved by setting an exhaust slot at the end position of the material flow of the casting system and leaving a gap around the ejector rod, because the depth and width of the exhaust slot and the location of the selection, if not appropriate, the resulting flying burr will affect the beauty and accuracy of the product. Therefore, the size of the above clearance is limited to prevent the flying edge around the ejector rod.

Special attention should be paid here to the fact that even the smallest flutter may be undesirable in the exhaust of such parts like gears, which are best exhausted in the following manner.

a. Thoroughly remove the gas in the runner.

b、Blasting the mating surface of the parting surface with silicon carbide abrasives with a particle size of 200#.

c. Open an exhaust slot at the end of the material flow of the casting system, mainly the exhaust slot at the end of the manifold, the width of which should be equal to the width of the manifold, and the height varies depending on the material.

3、Design method

   For the complex geometry of the product mold, the opening of the exhaust slot is best to be determined after several mold trials. And the mold structure design in the form of the overall structure, its biggest drawback is the exhaust bad. For the overall cavity mold core, there are several exhaust methods as follows.

a. Using the slot or insert mounting part of the cavity.

b、Use of side insert joints.

c, partially made into a spiral shape.

d, in the longitudinal position with a slotted slatted heart, open process hole.

When the exhaust is extremely difficult, the use of inlay structure, etc.; If some of the dead ends of the mold are not easy to open the exhaust slot, the first should not affect the appearance and accuracy of the product, the mold should be properly changed to inlay processing, so that not only conducive to the processing of exhaust slot, and sometimes can improve the original processing difficulties and ease of maintenance.

4、Conclusion

    Properly opening the exhaust slot, can greatly reduce the injection pressure, injection time, holding time, and clamping pressure, so that the molding of plastic parts from difficult to easy, to improve production efficiency, reduce production costs and reduce the energy consumption of the machine.