Selection and advantages and disadvantages of gate position and structure of MIM injection mold
time：2020-05-11Views：549 Author：Best Seiko
The gate, also known as the feed port, is a channel connecting the runner and the melt in the cavity. Choosing the right gate is directly related to whether the injection products are intact and injection molded with high quality. Gate design includes the determination of gate cross-sectional shape and size and the choice of gate location. Regarding the determination of the shape and size of the gate cross section, many textbooks have mentioned it, which will not be repeated here. Best now compares the differences of various types of gates according to the characteristics of different injection molded products, and discusses the methods and principles of gate position and structure selection. The location of the gate plays a decisive role in the shape of the melt flow front and the effect of holding pressure, so it also determines the strength and other properties of the injection molded product. The factors that affect the determination of the gate location include the shape, size, wall thickness, dimensional accuracy, appearance quality and mechanical properties of the product. In addition, the difficulty of gate processing, demoulding, and gate removal should also be considered. The correct gate position can avoid the foreseeable problems. 1. The type and location of the gate In the injection mold design, according to the structure and characteristics of the gate, the commonly used gate forms are the following 11 types. 1. Straight gate: It is the mainstream gate, which is a non-limiting gate (1) Advantages: the plastic melt enters the cavity directly from the large end of the mainstream channel, so it has low flow resistance, short flow and long replenishment time Features. Such a gate has a good melt flow state, and the melt flows from the center of the bottom surface of the cavity to the parting surface, which is conducive to exhaust; this gate form makes the projected area of the injection molded product and the pouring system on the parting surface very large Small size, compact mold structure, and even pressure on the injection molding machine. (2) Disadvantages: There is a large residual stress at the feed, which is easy to cause warpage and deformation of the injection molded products. At the same time, the gate is large, it is difficult to remove the gate traces and the traces are large, which affects the appearance, so this type of gate is mostly used for Injection molding large and medium-sized long process, deep cavity, cylindrical or shell injection products are very suitable for polycarbonate, polysulfone and other high-viscosity plastics. In addition, this type of gate is only suitable for single cavity molds. When designing this type of gate, in order to reduce the gate area where it contacts the injection molded product and prevent defects such as shrinkage and deformation, on the one hand, the taper angle of the main channel should be selected as small as possible (from 2 to 4) °), on the other hand, the thickness of the fixed template and fixed mold base should be minimized. 2. Side gate: The side gate is called a standard gate in foreign countries. The side gate is generally opened on the parting surface.The plastic melt fills the mold cavity from the inside or the outside.The cross-sectional shape is mostly rectangular (flat groove).Change the gate width and thickness to adjust the shear rate and pouring of the melt. The freezing time of the mouth. This type of gate can choose its position according to the shape characteristics of the injection molded product, and it is convenient to process and trim, so it is widely used. (1) 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 injection products of various shapes, but it is not suitable for slender barrel-shaped injection products. (2) Disadvantages: Injection products and gates cannot be separated on their own, there are welding marks, injection pressure loss is large, and it is unfavorable for the exhaust of deep cavity injection products. 3. Fan-shaped gate: The fan-shaped gate is generally opened on the parting surface and feeds from the outer side of the cavity. The gate gradually widens in the feeding direction and the thickness gradually decreases. The wave front of the plastic melt entering the cavity from the gate is relatively straight, which can reduce warpage and deformation, and is suitable for forming a plate-shaped plastic product with a large width. 4. Thin gate: also known as flat seam gate. The distribution runner of the gate is parallel to the side of the cavity, and its length is usually greater than the width of the plastic product. (1) Advantages: The plastic melt enters the cavity uniformly at a low speed through the thin gate. The material flow is parallel, which can avoid warpage and deformation. It is often used to form flat large-area thin-walled plastic products. (2) Disadvantages: It is difficult to remove the gate, which increases the production cost of plastic products. 5. Ear protector gate: The ear protector gate is mainly used for highly transparent flat plastic products and plastic products with little deformation requirements. (1) Advantages: The ear protection gate is provided with ear grooves on the side of the cavity. The melt generates frictional heat on the side of the ear grooves through the gate impact, thereby improving the fluidity. After adjusting the direction and speed, the ear protection is uniform and Entering the cavity smoothly can avoid jet flow. (2) Disadvantages: gate removal is more difficult and gate traces are larger.