Appropriate opening of the injection mold air vent can greatly reduce the injection molding pressure, injection molding time, holding time, and injection mold clamping pressure, making the plastic parts from difficult to easy, thereby improving production efficiency, reducing production costs, and reducing the energy consumption of the machine.

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How To Design Injection Mold Air Vent?
The air vent of injection mold
It is a kind of groove-shaped air outlet opened in the injection mold to discharge the original gas
brought by the melt. When the molten material is injected into the cavity, the air originally in the
cavity and the gas brought by the melt must be discharged out of the injection mold through the
exhaust port at the end of the flow, otherwise, the product will have air holes, poor connection,
Dissatisfaction with mold filling, even accumulating air burns the product due to high
temperature caused by compression.
Under normal circumstances, the vent hole can be placed either at the end of the melt flow in
the cavity or on the parting surface of the injection mold. The latter is a shallow groove with a
depth of 0.03-0. 2mm and a width of 1.5-6mm.
During injection molding, there will not be a lot of molten material leaking from the vent hole,
because the molten material will cool and solidify at this place, blocking the channel. The
opening of the exhaust port must not face the operator to prevent accidental injection molding
of molten material and injury. In addition, the matching gap between the ejector pin and the
ejector hole, the matching gap between the top block and the stripper plate, and the core can
also be used for air venting.
1. The role of the air vent of the injection mold
The function of the air venting is mainly two points: one is to exclude the air in the injection mold
cavity when the molten material is injected; the second is to exclude all kinds of gases generated
by the material during the heating process. The more thin-walled products, the farther away

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from the gate, the opening of the exhaust slot is particularly important.
In addition, for small parts or precision parts, we must pay attention to the opening of the air
venting, because it can avoid product surface burns and insufficient injection volume, it can also
eliminate various defects of products and reduce mold pollution.
So, what is the exhaust of the mold cavity? Generally speaking, if the melt is injected at the
highest injection rate without leaving a focal spot on the product, it can be considered that the
exhaust in the injection mold cavity is sufficient.
2. Air venting method of injection mold
There are many ways to evacuate the mold cavity, but each method must ensure that: the air
venting is exhausted at the same time, its size should be designed to prevent the material from
overflowing into the groove; secondly, it must prevent blockage. Therefore, from the inner
surface of the injection mold cavity to the outer edge of the mold cavity, the length of the
exhaust groove of 6-12 mm or more, the groove height should be placed about 0.25-0.4 mm.
In addition, too many exhaust slots are harmful. This is because, if the injection mold clamping
pressure acting on the part of the injection mold cavity parting surface without the air venting is
too large, it is easy to cause cold flow or cracking of the injection mold cavity material, which is
very dangerous.
In addition to venting the injection mold cavity on the parting surface, you can also achieve the
purpose of venting by providing a vent groove at the end of the flow of the die casting system
and leaving a gap around the ejector rod, because the vent groove The selection of the depth,
width, and location of the opening, if not appropriate, will produce flash burrs that will affect the
aesthetics and accuracy of the product. Therefore, the size of the gap is limited to prevent
flashing around the ejector rod.
Special attention should be paid here: when exhausting parts such as gears, even the smallest
flash may be undesirable. Such parts are best exhausted in the following ways:
Completely remove the gas in the flow channel;
Shot-blasting the matching surface of the parting surface with silicon carbide abrasive with a
particle size of 200#;
The air venting is set at the end of the flow of the pouring system, which mainly refers to the
exhaust groove at the end of the runner. Its width should be equal to the width of the runner,
and the height varies depending on the material.
3. The design method of injection mold air venting
Based on many years of experience in injection mold design and product trial mold, this article
briefly introduces the design of several injection mold air venting.
For product molds with complex geometries, the opening of the exhaust groove is best
determined after several trial molds. The overall shortcoming of the overall structural form in
mold structure design is the poor exhaust.
For the overall cavity core, there are the following exhaust methods:
Use the groove or insert installation part of the cavity
Use the side insert seams

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Partially made into a spiral shape
Install slotted slat core in longitudinal position and open process holes
When exhausting is extremely difficult, use mosaic structure, etc.
If the dead corners of some injection molds are not easy to open the air vent, first of all, the
injection mold should be appropriately changed to inlay processing without affecting the
appearance and accuracy of the product. This is not only conducive to processing the air venting
but also sometimes improves the original Processing difficulty and easy maintenance.
4. Air vent design of injection mold during thermosetting plastic molding
The venting of thermosetting materials in injection molds is more important than thermoplastic
materials. First, all the runners in front of the gate should be vented. The width of the air venting
should be equal to the width of the shunt, and the height is 0.12mm. All sides of the mold cavity
should be exhausted, and the exhaust slots should be separated by 25mm, the width is 6.5mm,
and the height is 0.075-0.16mm, depending on the fluidity of the material.
Softer materials should take lower values. The ejector pin should be enlarged as much as possible,
and in most cases, 3-4 planes with a height of 0.05 mm should be ground on the cylindrical
surface of the ejector pin, and the direction of the wear scar should be along the length of the
ejector rod. Grinding should be carried out with a fine-grained grinding wheel. The end face of
the ejector rod should be ground with a chamfer of 0.12mm so that if flash is formed, it will
adhere to the workpiece.
5. Conclusion
Appropriate opening of the injection mold air venting can greatly reduce the injection molding
pressure, injection molding time, holding time, and injection mold clamping pressure, making the
plastic parts from difficult to easy, thereby improving production efficiency, reducing production
costs, and reducing the energy consumption of the machine.