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How to Properly Set Venting Slots in Injection Moldings?

During the injection molding process, there will not be a large amount of melt coming out of the vent hole because the melt will cool and solidify there, blocking the passage. The opening position of the vent should not be towards the operator to prevent injury from accidentally spraying molten material.

Function of vent groove in injection molding

The main function of the vent groove is to remove the air and various gases generated during the heating process of the material in the mold cavity during injection molding. The opening of the vent groove is particularly important for small or precision parts, in order to avoid surface burns, insufficient injection or product defects, and reduce mold contamination. Generally speaking, if the injection speed of the melt is the highest and no scorched spot remains on the product, it can be considered that the venting in the mold cavity is sufficient.

Venting methods for injection molding

There are many ways to vent the mold cavity, but each method must ensure that the size of the vent groove should be designed to prevent material from overflowing into the groove during venting, and to prevent blockage. Too many vent grooves are harmful; if the clamping pressure is high on the part of the split surface without vent grooves, it is easy to cause cold flow or cracking of the mold cavity material, which is very dangerous. Vent grooves can be set at the end of the material flow in the gating system, and a gap can be left around the ejector pin to vent the mold cavity. The choice of depth, width and position of the vent groove can affect the appearance and accuracy of the product. Therefore, the size of the gap is limited to prevent flashing around the ejector pin.

Design methods for injection molding

For molds of products with complex geometries, it is best to determine the opening of the vent groove after several mold trials. However, the biggest drawback of the entire structure in mold structure design is poor venting. There are several venting methods for the entire mold cavity and core, such as using a groove or insert block installed in the cavity, utilizing a side insert block joint, making it into a spiral shape locally, installing a slotted bar-type core in the longitudinal position, and opening a process hole.

If the vent groove is difficult to open in some dead corners of the injection molding and the venting is extremely difficult, using insert and splice structures, appropriate opening of the vent groove can greatly reduce injection pressure, injection time, holding pressure time and clamping pressure, making plastic molding from difficult to easy, thereby improving production efficiency, reducing production costs, and reducing machine energy consumption.

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