Injection molding gate type and how to desgin
The injection molding gate refers to the channel connecting the runner and the melt of the cavity, which is the entrance of the resin into the cavity. There are some kinds of injection molding gate types which should be choose exactly for producing the suitable plastic parts. Therefore, the injection molding gate design, including the size, quantity and location, has a significant impact on the quality of the plastic molding parts.
The injection molding gate types are generally divided into two types: unrestricted gates and restricted gates. It can be divided into the following types.
Sprue gate (Direct gate)
It is unrestricted gate. Its characteristic is that the plastic melt flows directly into the cavity, the pressure loss is small, the feeding speed is fast, the molding is easy, and it is suitable for all kinds of plastics. It has the advantages of good transmission pressure, strong pressure holding and shrinking effect, simple and compact mold structure, and convenient manufacturing. However, it is difficult to remove the gate, the gate traces are obvious, and large internal stress is easily generated near the gate, so that surface shrinkage marks are generated. Suitable for large plastic parts, thick wall plastic parts, etc.
When designing this type of gating system, in order to reduce the gate area where it contacts the injection molded product and prevent defects such as shrinkage and deformation at the site, on the one hand, the taper angle of the main channel with a smaller taper should be selected °), on the other hand, the thickness of the fixed template and fixed mold base should be minimized.
Restricted gate refers to the connection between the glue and the runner with a short distance and small cross section. It can adjust the thickness of the gating and also the solidification.
The side gate in the injection molding process is generally located on the parting surface and feeds from the outer side of the plastic part. The side gate is a typical rectangular cross-section gate. It is easy to adjust the shear rate and gate closing time during filling, so it is also called a standard gate.
Advantages: The gate section is small, which can reduce the consumption of molten material in the pouring system, the gate is easily removed, and the trace is not obvious. It is suitable for the parts of various shapes, but not for slender barrel-shaped plastic parts.
Disadvantages: Injection products and gates cannot be separated by themselves, there are welding marks, and the injection pressure loss is large, which is not conducive to the exhaust of deep cavity injection products.
It is often used to form plate-shaped plastic parts with larger width. The gate gradually widens along the feed direction, and the thickness gradually decreases to the thinnest. The plastic melt is evenly distributed in the width direction, which can reduce the internal stress of the plastic parts and reduce the warpage and deformation; however, it is difficult to remove the gate and the trace is obvious.
It is also a variation type of the side gate, which is commonly used to form large-area flat plastic parts. The distribution runner of the gate is parallel to the side of the cavity, called the parallel runner, and its length can be greater than or equal to the width of the plastic part. The plastic melt is evenly distributed in the parallel flow channel, and then flows in parallel at a low linear velocity, evenly entering the cavity, so the internal stress of the plastic part is small, reducing the warpage deformation that should be oriented, and Good exhaust. However, the gate removal work is heavy and the trace is obvious.
Pin point gate
Pin point gates are especially suitable for barrel-shaped, shell-shaped and box-shaped plastic products. For larger flat plastic products, multiple point gates can be set to reduce warpage. For thin-walled plastic products, the shear rate near the gate is too high, the residual stress is large, and it is easy to crack, which can locally increase the wall thickness at the pin point gate.
Advantages: The position of the point gate is limited, the gate trace is small, and the gate can be automatically broken when the mold is opened, which is conducive to automatic operation.
Disadvantages: The injection pressure is large. In most cases, the three-plate mold structure must be used. The mold is relatively complicated and the molding cycle is long.
The tunnel gate is evolved from the pin point gate. The injection runner is located on the parting surface. The type of injection gate dives into the bottom of the parting surface and enters the cavity in an oblique direction. In addition, the tunnel gate is generally hidden in the inner surface or side of the plastic part, so it does not affect the appearance of the plastic part, the plastic part and the runner are separately provided with a pushing mechanism, the gate is automatically cut off when the mold is opened, and the runner condensate fall off automatically.
Advantages: The position of the tunnel gate is more flexible, and it can be glued on the inner and outer surfaces of the plastic products. The latent gate mold structure is simpler than the three-plate mold structure, which greatly improves production efficiency and reduces costs.
Disadvantages: It is not suitable for plastics that are too tough (such as PA type) or too brittle (such as PS type), which can easily cause gate clogging.
The banana gate is an injection molding gate type with a circular arc-shaped tunnel gate structure. It is generally used in the two-plate mold. It adopts the parting surface directly into the glue to form two pieces of inserts. The split runner and gate are both designed on inserts.
Advantages: It can be glued on the bottom of the product. It has the characteristics of a point gate. The gate trace is small. It can be automatically broken when ejected, which is easy to realize automation. The head of the ejector pin is tapered, and the ejection mechanism is provided in the flow channel to facilitate ejection.
Disadvantages: The shape is more complicated, and the gate needs to be processed with electrodes.
The main principles of gate design of injection molding as follows:
1) The gate should be located in the thicker section of the plastic part, so that the melt flows from the thick material section to the thin section to ensure the complete filling of the mold;
2) The choice of gate location should reduce the plastic filling process to reduce pressure loss;
3) The location of the gate should be selected to facilitate the removal of air from the cavity;
4) The gate should not allow the molten material to directly punch into the cavity, otherwise it will produce vortex flow, leaving a spiral trace on the plastic parts, especially the narrow gate is more prone to this defect;
5) The location of the gate should be selected to prevent stitching on the plastic surface, especially in circular or cylindrical plastic parts, and a cold material well should be opened at the melting point of the gate surface;
6) The gate position of the injection mold with a slender core should be far away from the molding core to avoid deformation;
7) When forming large or flat plastic parts, multiple gates can be used to prevent warpage, deformation, and lack of material;
8) The gate should be opened as far as possible without affecting the appearance of the plastic parts, such as the bottom of the edge;
9) The size of the gate depends on the size, shape and performance of the plastic parts;
10) When designing a multi-cavity injection mold, consider the balance of the gate in combination with the balance of the flow channel, and try to achieve the uniform filling of the molten material at the same time.
To make sure that you choose the right types of injection molding gate in the, which will save much time and cost in the production process. In this step it is important that you are working with the experienced engineering team. Lushi-Molding has more than 50 engineers in the development for the injection mold design, so that we can surely give you some suggestions for your injection molding projects.
More Infos Please Contact Us: