injection mold

- Apr 17, 2018-

          The injection mold has the advantages of high production efficiency, low labor intensity, long service life, and the ability to form complex shapes of plastic products, etc. 

          The structure of the injection mold is determined by factors such as the form of the injection machine and the complexity of the product. Although the injection mold has Various structural forms, but can be divided into two parts: moving mold and fixed mold. When injection, the movable mold and the fixed mold close together to form the cavity and the pouring system. When the mold is opened, the movable mold separates from the fixed mold, and the product is taken out. 

         The fixed mold is mounted on the fixed template of the injection machine and is directly in contact with the nozzle mouth or the sprue bushing. The moving mold is installed on the moving template of the injection machine and moves along with the template to separate or close the fixed mold part. The core pulling and ejection mechanism are generally in this part. (Figure 1-1 shows a typical injection mold, Usually consists of the following parts. 

1. Mold cavity 

        The mold cavity is the part of the mold directly molded into a plastic product. It is usually composed of a punch (formed product internal form, a die (formed product external shape), a core or a molding bar, inserts, etc. The relevant parts of the mold and the fixed mold are combined (as shown in Figure 1-1, the cavity is composed of 13 and 14). In order to ensure that the surface of the plastic product is smooth and beautiful and easy to release, the roughness of the cavity surface that is in contact with the plastic should generally be Very small, preferably less than Ra0.2.

2. Casting system           The pouring system refers to the part of the plastic melt that flows from the nozzle of the injection machine into the flow path of the mold cavity. It consists of the main flow channel, the runner, the gate, and the cold material hole.

2.1 Mainstream:         The main channel is a section of the channel connecting the injection machine nozzle to the runner or cavity. The top of the main channel is concave spherical, so as to connect with the nozzle, the inlet diameter is slightly larger than the nozzle diameter, generally 4~8mm, to avoid flash, and Gradually increase along the feeding direction, the magnification angle is generally 3°~5°, which facilitates the stripping of the flow channel debris.2.2 runners:          The runner is the channel connecting the main channel and the gates in the multi-cavity. To make the molten material fill the cavity at equal speed, the runners should be arranged symmetrically and equidistantly in the mold.

2.3 gate:           The gate is the channel connecting the runner (or the main channel) and the cavity. Common gates are: direct gate, side gate, disk gate, ring gate, spoke gate, fan gate, point Sprue, latent gate, ear gate, etc. The role of the gate is to control the material flow, so that the molten material injected from the flow channel fills the mold cavity and does not flow backwards, facilitating the separation of the product and the flow channel. According to the above effect, the gate cut The area should be small and should not be large, should be short and not easy to long. Gate location is generally selected in the thickest product without affecting the appearance of the place.2.4 cold material points:            The cold hopper is a cavity at the end of the main channel to trap the cold material produced between two injections at the tip of the nozzle to prevent blockage of the runner or gate, and to prevent the cold material from entering the cavity. The formation of the product of the internal stress. The diameter of the cold material cavity is generally 8 ~ 10mm, 6mm deep. In order to facilitate the release of the main channel material, the bottom of the cold material cavity is often used to have a curved hook or sinker groove head stripping support .3. Guidance section           The fixed mold and the movable mold part of the mold are respectively installed on the fixed mold of the injection molding machine and on the moving mold plate. During the injection molding process, it is in a reciprocating closed and open state. It is designed to ensure accurate centering between the movable mold and the fixed mold mold. The guide parts usually have guiding columns, guide holes or internal and external taper surfaces that are matched with each other on the movable mold fixed mold. Some injection mold ejection devices are provided to prevent skewing of the ejector plate during ejection process. Parts, keep the ejector board horizontally.

4. Sub-type pull core mechanism           Products with outside recesses or side holes must be laterally typed before pulling out, pull out the side punches or pull out the side cores before they can easily escape.5. Ejector           Also known as demoulding device. After the product is cooled and set in the mold, in order to take out the product, the ejector is generally set on the mold. Some eject the product from the mold in the mold opening process, and some eject the product after the mold is opened. This is related to the type of ejector installed on the injection machine and the mold used.6. Cooling heating system            In order to meet the injection mold temperature requirements, the mold is equipped with a cooling or heating system. The cooling system generally opens a cooling channel in the mold, heating is installed inside or around the mold heating assembly, such as electric heating rod, electric heating plate, electric heating ring, etc. .7. Exhaust system           In order to discharge the original air in the cavity during the injection process, an exhaust groove is often provided on the parting surface. However, the small-size product has a small displacement, and it can directly use the parting surface to exhaust, and the top or shape of many molds can be used. The clearance between the core and the mold can act as an exhaust, so it is not necessary to open the exhaust slot.8. Mold mounting parts           The mold mounting part has two functions. Firstly, the mold is reliably mounted on the template of the injection machine. Second, the thickness of the mold is adjusted by using the mounting part so that the mold thickness meets the requirements of the injection machine used.