Design of the exhaust groove of the injection mold

Injection mold should be designed of exhaust groove and is a tool for producing plastic products; it is also a tool for giving plastic products a complete structure and precise dimensions. Injection molding is a processing method used in the mass production of some complex-shaped parts. Specifically, it refers to the high-pressure injection of the plastic melted by heat into the mold cavity by the injection molding machine, and the molded product is obtained after cooling and solidification.

Mold composition

Although the structure of the mold may vary widely due to the variety and performance of plastics, the shape and structure of plastic products, ਅਤੇ ਇੰਜੈਕਸ਼ਨ ਮਸ਼ੀਨ ਦੀ ਕਿਸਮ, ਬੁਨਿਆਦੀ structureਾਂਚਾ ਇਕੋ ਜਿਹਾ ਹੈ. The mold is mainly composed of a pouring system, a temperature control system, forming parts and structural parts.

Among them, the pouring system and molded parts are the parts that are in direct contact with the plastic and change with the plastic and the product. They are the most complex and the most variable parts in the plastic mold, requiring the highest processing finish and precision.

The injection mold is composed of a movable mold and a fixed mold. ਚਲਣਯੋਗ ਉੱਲੀ ਨੂੰ ਇੰਜੈਕਸ਼ਨ ਮੋਲਡਿੰਗ ਮਸ਼ੀਨ ਦੇ ਚੱਲਣਯੋਗ ਟੈਂਪਲੇਟ ਤੇ ਸਥਾਪਤ ਕੀਤਾ ਗਿਆ ਹੈ, ਅਤੇ ਫਿਕਸਡ ਮੋਲਡ ਇੰਜੈਕਸ਼ਨ ਮੋਲਡਿੰਗ ਮਸ਼ੀਨ ਦੇ ਸਥਿਰ ਟੈਂਪਲੇਟ ਤੇ ਸਥਾਪਤ ਕੀਤਾ ਜਾਂਦਾ ਹੈ.

ਇੰਜੈਕਸ਼ਨ ਮੋਲਡਿੰਗ ਦੇ ਦੌਰਾਨ, the movable mold and the fixed mold are closed to form a pouring system and a cavity. ਜਦੋਂ ਉੱਲੀ ਖੁੱਲ੍ਹ ਜਾਂਦੀ ਹੈ, the movable mold and the fixed mold are separated to take out the plastic products. In order to reduce the heavy workload of mold design and manufacturing, most of the injection molds use standard mold bases.

exhaust vent

It is a trough-shaped air outlet opened in the mold to discharge the original gas and the gas brought in by the molten material. When the melt is injected into the cavity, the air originally stored in the cavity and the gas brought in by the melt must be discharged out of the mold through the exhaust port at the end of the material flow, otherwise the product will have pores, poor connection.

Dissatisfaction with the filling of the mold, and even the accumulated air will burn the product due to the high temperature generated by the compression. Under normal circumstances, the vent can be located either at the end of the melt flow in the cavity or on the parting surface of the mold. The latter is a shallow groove with a depth of 0.03-0. 2mm and a width of 1.5-6mm on one side of the cavity.

During injection, there will not be a lot of molten material in the vent hole, because the molten material will cool and solidify at the place and block the channel. The opening position of the exhaust port should not be facing the operator to prevent accidental spraying of molten material and hurting people. ਇਸਦੇ ਇਲਾਵਾ, the matching gap between the ejector rod and the ejector hole, the matching gap between the ejector block and the stripper plate and the core can also be used for exhaust.

1. The role of the exhaust slot

The function of the exhaust groove mainly has two points: one is to remove the air in the mold cavity when the molten material is injected; the other is to remove various gases generated during the heating process of the material. The thinner the product, the farther away from the gate, the opening of the exhaust groove is particularly important.

ਇਸਦੇ ਇਲਾਵਾ, for small parts or precision parts, the opening of the venting groove should also be paid attention to, because it can not only avoid surface burns and insufficient injection volume, but also eliminate various defects of the product and reduce mold pollution. ਨੂੰ

So, how can the exhaust of the ਉੱਲੀ cavity be considered sufficient? ਜੇ ਆਮ ਗੱਲ ਕਰੀਏ, if the melt is injected at the highest injection rate, but no focal spots are left on the product, it can be considered that the exhaust in the cavity is sufficient.

2. Exhaust method

There are many ways to exhaust the mold cavity, but each method must be guaranteed: the size of the exhaust slot should be designed to prevent the material from overflowing into the slot while the exhaust slot is exhausted; secondly, it should prevent clogging. ਇਸ ਲਈ, when measuring from the inner surface of the cavity to the outer edge of the cavity, the height of the venting groove above 6-12mm should be about 0.25-0.4mm.

ਇਸਦੇ ਇਲਾਵਾ, too many exhaust grooves are harmful. Because if the clamping pressure acting on the parting surface of the mold cavity without opening the vent 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 venting the mold cavity on the parting surface, it can also achieve the purpose of venting by arranging an venting groove at the end of the material flow of the pouring system and leaving a gap around the ejector rod, because the venting groove If the selection of the depth, width and position of the opening is not appropriate, the flash burr produced will affect the appearance and accuracy of the product. ਇਸ ਲਈ, the size of the above gap is limited to prevent flash around the ejector rod.

Special attention should be paid here: when parts such as gears are exhausted, even the smallest flash may be undesirable. For this type of parts, it is best to use the following methods to exhaust:

(1) Completely remove the gas in the flow channel;

(2) Shot peening the mating surface of the parting surface with 200# silicon carbide abrasive. ਇਸਦੇ ਇਲਾਵਾ, the opening of the exhaust groove at the end of the material flow of the pouring system 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. Design method Based on many years of experience in injection mold design and product testing, this article briefly introduces the design of several exhaust grooves. For product molds with complex geometric shapes, it is best to determine the opening of the vent slot after several mold trials. The biggest disadvantage of the overall structure in the mold structure design is poor exhaust
4. There are several ways to vent the core of the integral cavity: (1) Use the groove or insert installation part of the cavity; (2) Use the side insert seam; (3) Partially make it into a spiral shape; ( 4) Install a slotted slat core and open a craft hole in the longitudinal position;

(5) When the exhaust is extremely difficult, adopt the mosaic structure, ਕਿਉਂਕਿ IC ਟਰੇ ਦਾ ਭਾਰ ਹਲਕਾ ਹੁੰਦਾ ਹੈ; if the dead corners of some molds are not easy to open the venting groove, first of all, the mold should be appropriately changed to the mosaic processing without affecting the appearance and accuracy of the product. , It is not only good for processing the exhaust groove, but sometimes it can also improve the original processing difficulty and facilitate maintenance.

4. Exhaust slot design when thermosetting plastics are molded. Exhaust of thermosetting materials is more important than thermoplastic materials. First of all, the runners in front of the gate should be exhausted. The width of the exhaust slot should be equal to the width of the runner, and the height should be 0.12mm. All sides of the mold cavityshould be exhausted. The exhaust slots should be 25mm apart, 6.5mm wide, and 0.075-0.16mm high, depending on the fluidity of the material. Softer materials should take lower values.
5. The ejector rod should be enlarged as much as possible, and in most cases, 3-4 flat surfaces with a height of 0.05mm should be ground on the cylindrical surface of the ejector rod, and the direction of the wear marks 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 there is a flash formed, it will adhere to the workpiece.

Conclusion Properly setting up the exhaust groove can greatly reduce the injection pressure, injection time, holding time and clamping pressure, and make the molding of plastic parts easy, thereby improving production efficiency, reducing production costs, and reducing machine energy. Consumption.

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