Structure of plastic mold

Mold injection molding is a processing method used in batch production of certain complex-shaped parts. The specific principle is: the heated and melted plastic raw materials are pushed by the injection molding machine screw and injected into the mold cavity of the plastic mold under high pressure. After cooling and solidification, the plastic molded product is obtained.

The plastic mold consists of two parts: the movable mold and the fixed mold. The movable mold is installed on the movable template of the injection molding machine, and the fixed mold is installed on the fixed template of the injection molding machine. During injection molding, the movable mold and the fixed mold are closed to form a pouring system and a cavity. When the mold is opened, the movable mold and the fixed mold are separated to remove the plastic product.

Although the structure of the plastic mold may vary due to different types and properties of plastics, the shape and structure of plastic products, and the type of injection molding machine, the basic structure is the same.

1. The structure of the plastic mold is divided by function, mainly consisting of: pouring system, temperature control system, molding parts system, exhaust system, guide system, ejection system, etc. Among them, the pouring system and molding parts are the parts that are in direct contact with the plastic, and they change with the plastic and the product. They are the most complex, most variable, and require the highest processing finish and precision in the mold.

1. Pouring system: refers to the flow channel part before the plastic enters the cavity from the nozzle, including the main channel, cold material hole, branch channel and gate, etc.

2. Molding parts system: refers to the combination of various parts that constitute the shape of the product, including the movable mold, fixed mold and cavity (concave mold), core (convex mold), molding rod, etc. The core forms the inner surface of the product, and the cavity (concave mold) forms the outer surface shape of the product. After the mold is closed, the core and cavity constitute the cavity of the mold. According to the process and manufacturing requirements, sometimes the core and the concave mold are composed of several pieces, and sometimes they are made as a whole, and only inserts are used in parts that are easy to damage and difficult to process.

3. Temperature control system: In order to meet the requirements of the injection process for the mold temperature, a temperature control system is required to adjust the temperature of the mold. For injection molds for thermoplastics, the main thing is to design a cooling system to cool the mold (the mold can also be heated). The common method of mold cooling is to open a cooling water channel in the mold and use the circulating cooling water to take away the heat of the mold; in addition to using cooling water to pass hot water or hot oil, electric heating elements can also be installed inside and around the mold to heat the mold.

4. Exhaust system: It is set up to exhaust the air in the cavity and the gas generated by the melting of plastic during the injection molding process out of the mold. If the exhaust is not smooth, the surface of the product will form gas marks (gas marks), burns and other defects; the exhaust system of the plastic mold is usually a groove-shaped air outlet opened in the mold to exhaust the original cavity air and the gas brought in by the molten material. When the molten material is injected into the cavity, the air originally stored in the cavity and the gas brought in by the melt must be discharged to the outside of the mold through the exhaust port at the end of the material flow, otherwise the product will have pores, poor connection, incomplete filling, and even the accumulated air will be compressed to generate high temperature and burn the product. Generally, the exhaust hole can be set at the end of the molten material flow in the cavity or on the parting surface of the mold. The latter is to open a shallow groove with a depth of 0.03-0.2mm and a width of 1.5-6mm on one side of the die. During injection, there will not be much molten material leaking out of the exhaust hole, because the molten material will cool and solidify there and block the channel. The exhaust port should not be opened facing the operator to prevent the molten material from accidentally spraying out and injuring people. In addition, the clearance between the ejector rod and the ejector hole, the clearance between the ejector block and the stripper plate and the core can also be used to exhaust.

5. Guide system: It is set up to ensure that the movable mold and the fixed mold can be accurately aligned when the mold is closed, and a guide component must be set in the mold. In the injection mold, four sets of guide pins and guide sleeves are usually used to form the guide component. Sometimes, inner and outer cones that match each other are set on the movable mold and the fixed mold to assist positioning.

6. Ejector system: generally includes: ejector, front and rear ejector plates, ejector guide rod, ejector return spring, ejector plate locking screw and other parts. When the product is molded and cooled in the mold, the front and rear molds of the mold are separated and opened, and the ejector mechanism-the ejector pushes or pulls the plastic product and the condensed material in the runner out of the mold cavity and runner position under the push of the ejector rod of the injection molding machine, so as to carry out the next injection molding cycle.
2. Plastic molds are generally composed of mold frames, mold cores, auxiliary parts, auxiliary systems, auxiliary settings, dead angle processing mechanisms and other parts according to their structures.

1. Mold frame: Generally, we do not need to design it, and we can order it directly from the standard mold frame manufacturer, which greatly saves the time required for designing the mold, so it is called the standard mold frame of plastic molds. It constitutes the most basic frame part of the plastic mold.

2. Mold core: The mold core part is the core part of the plastic mold, and it is the most important component in the mold. The forming part of the plastic product is in the mold core, and most of the processing time is also spent on the mold core. However, compared with some simpler molds, it does not have a mold core part, and the product is formed directly on the template. Most of the early plastic molds are like this, which is relatively backward.

3. Auxiliary parts: Common auxiliary parts of plastic molds include positioning rings, sprue bushings, ejectors, grab pins, support columns, ejector plate guide columns and guide sleeves, garbage nails, etc. Some of them are standard parts and can be ordered directly when ordering mold frames, and some need to be designed by yourself.

4. Auxiliary system: There are four auxiliary systems of plastic molds: pouring system, ejection system, cooling system and exhaust system. Sometimes, because the temperature of the plastic material used needs to be heated to a very high temperature, some molds will also have a heating system.

5. Auxiliary settings: The auxiliary settings of plastic molds include ring holes, KO holes (ejector rod holes), etc.

6. Dead corner processing structure: When the plastic product has a dead corner, the mold will also have one or more structures to handle the dead corner. Such as sliders, inclined ejectors, hydraulic cylinders, etc. In most domestic books, this mechanism for dealing with dead angles is called "core extraction mechanism".

In fact, plastic molds are not difficult. No matter how the plastic product changes, for the mold used to form this plastic product, its structure is nothing more than the above-mentioned aspects. The difference between molds lies in whether the mold is large or small? The positions or methods of various auxiliary parts, auxiliary settings, and auxiliary systems are different. The methods, structures, sizes, etc. for dealing with dead angles have changed. Of course, to make the designed mold simple to process, easy to assemble, long life, moderate price, and good molded products, design experience is particularly important. Good experience can handle problems that arise in design and processing, and it is also more confident in dealing with design changes.

3. Structural composition of injection molding machine: A general-purpose injection molding machine mainly includes injection device, mold clamping device, hydraulic transmission system and electrical control system. The main function of the injection device is to plasticize the plastic evenly and inject a certain amount of molten material into the mold cavity with sufficient pressure and speed. The injection device is mainly composed of plasticizing parts (screw, barrel and nozzle), hopper, transmission device, metering device, injection and mobile cylinder, etc.

Mold clamping device: its function is to realize the opening and closing of the mold, to ensure that the molding mold is reliably closed during injection, and to eject the product. The mold clamping device is mainly composed of front and rear fixed templates, mobile templates, tie rods for connecting the front and rear templates, mold clamping cylinders, connecting rod mechanisms, mold adjustment devices, and product ejection devices.

Hydraulic system and electrical control system: its function is to ensure that the injection machine works accurately and effectively according to the predetermined requirements (pressure, speed, temperature, time) and action sequence of the process. The hydraulic system of the injection machine is mainly composed of various hydraulic components and circuits and other auxiliary equipment, and the electrical control system is mainly composed of various electrical appliances and instruments. The hydraulic system and the electrical system are organically organized to provide power and control for the injection machine.