Mold injection molding is a processing method used in mass production of certain parts with complex shapes. The specific principle refers to: the heated and melted plastic material is pushed by the screw of the injection molding machine and injected into the cavity of the plastic mold at high pressure. After cooling and solidification, a plastic molded product is obtained.
The plastic mold consists of two parts: a movable mold and a 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 the pouring system and cavity. When the mold is opened, the movable mold and the fixed mold are separated to facilitate removal of plastic products.
Although the structure of plastic molds may vary due to different types and properties of plastics, shapes and structures of plastic products, and types of injection machines, the basic structure is the same.
1. The plastic mold structure is divided by function and mainly consists of: pouring system, temperature adjustment system, molded parts system, exhaust system, guide system, ejection system, etc. Among them, the pouring system and molded parts are the parts that are in direct contact with plastics and change with the plastics and products. They are the most complex and changing parts of the mold and require the highest processing smoothness and precision.
1. Gating system: refers to the runner part before the plastic enters the cavity from the nozzle, including the main channel, cold material cavity, runner 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, the fixed mold and the cavity (concave mold), core (convex mold), forming rod, etc. The core forms the inner surface of the product, and the cavity (die) forms the outer surface shape of the product. After the mold is closed, the core and cavity form the cavity of the mold. According to process and manufacturing requirements, sometimes the core and die are combined from several pieces, sometimes they are made as a whole, and inserts are only used in parts that are easily damaged and difficult to process.
3. Temperature adjustment system: In order to meet the mold temperature requirements of the injection process, a temperature adjustment system is required to adjust the temperature of the mold. For injection molds for thermoplastic plastics, the cooling system is mainly designed to cool the mold (the mold can also be heated). The common way to cool the mold 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 the cooling water to pass hot water or hot oil, the heating of the mold can also be installed inside and around the mold. Electric heating element.
4. Exhaust system: It is established to exclude the air in the cavity and the gas generated by the melted plastic during the injection molding process out of the mold. When the exhaust is not smooth, air marks (air marks), scorch, etc. will be formed on the surface of the product. Bad: The exhaust system of a plastic mold is usually a groove-shaped air outlet opened in the mold to discharge the air in the original cavity and the gas brought in by the melt. When the molten material is injected into the mold cavity, the air originally existing in the mold 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 connections, and The mold filling is not satisfactory, and the accumulated air may even burn the product due to high temperature caused by compression. Under normal circumstances, the exhaust hole 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 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, a lot of molten material will not seep out of the vent hole, because the molten material will cool and solidify there and block the channel. The exhaust port must not be opened facing the operator to prevent the molten material from accidentally spraying out and injuring people. In addition, the matching gap between the ejector rod and the ejector hole, the matching gap between the ejector block and the stripping plate and the core can also be used to exhaust air.
5. Guide system: It is established to ensure that the movable mold and the fixed mold can be accurately aligned when closing the mold. Guide components must be installed in the mold. In injection molds, four sets of guide posts and guide sleeves are usually used to form the guide components. Sometimes it is necessary to set mutually matching inner and outer cones on the movable mold and the fixed mold to assist positioning.
6. Ejection system: Generally includes: ejection pin, front and rear ejection pin plates, ejection pin guide rod, ejection pin return spring, ejection pin plate locking screw, etc. When the product is formed and cooled in the mold, the front and rear molds of the mold are separated and opened. The ejection mechanism, the ejector pin, pushes the plastic product and its condensate in the runner out of the mold cavity and runner position under the push of the ejector pin of the injection molding machine. , in order to proceed with the next injection molding cycle.
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2. According to the structure, plastic molds generally consist of several parts such as mold base, mold core, auxiliary parts, auxiliary systems, auxiliary settings, and dead-end processing mechanisms.
1. Mold base: Generally, we do not need to design it. You can order it directly from the standard mold base manufacturer, which greatly saves the time required to design the mold, so it is called the plastic mold standard mold base. It forms the most basic frame part of the plastic mold.
2. Mold core: The mold core part is the core part of the plastic mold. It is the most important component of the mold. The forming part of the plastic product is inside the mold core, and most of the processing time is spent on the mold core. However, compared with some relatively simple molds, it does not have a mold core part, and the product is formed directly on the template. Most of the early plastic molds were like this and were relatively backward.
3. Auxiliary parts: Commonly used auxiliary parts for plastic molds include positioning rings, injection bushings, ejector pins, grab pins, support columns, ejection plate guide posts, guide bushes, garbage nails, etc. Some of them are standard parts and can Order it directly when ordering the mold base, and some parts need to be designed by yourself.
4. Auxiliary systems: There are four auxiliary systems for plastic molds: pouring system, ejection system, cooling system and exhaust system. Sometimes, because the plastic materials used need to be heated to a very high temperature, some molds will also have a heating system.
5. Auxiliary settings: The auxiliary settings of the plastic mold include lifting eye holes, KO holes (top stick holes), etc.
6. Dead Angle Treatment Structure: When a plastic product has a dead Angle, the mold will also have one or more dead Angle processing structures. Such as slider, inclined roof, hydraulic cylinder, etc. In most domestic books, this kind of mechanism for dealing with dead ends is called "plowing mechanism".
In fact, it is not difficult to make a plastic mold. No matter how the plastic product changes, for the mold used to form the plastic product, its structure is nothing more than the above aspects. The difference between molds is whether the mold is large or small? The positions or methods of each auxiliary parts, auxiliary settings, and auxiliary systems are different. The method, structure, size, etc. of dealing with dead corners have only changed. Of course, design experience is particularly important in order to make the designed mold simple to process, easy to assemble, long in service life, affordable, and have good formed products. With good experience, you can deal with problems that arise during design and processing, and you will be more confident about design changes.
3. Structural composition of the injection machine: A general-purpose injection machine mainly includes an injection device, a mold clamping device, a hydraulic transmission system and an electrical control system. The main function of the injection device is to plasticize the plastic evenly and inject a certain amount of melt into the cavity of the mold with sufficient pressure and speed. The injection device mainly consists of plasticizing parts (composed of screw, barrel and nozzle) as well as 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, ensure that the molding mold is reliably closed during injection, and remove the product. The mold clamping device mainly consists of the front and rear fixed templates, the movable template, the tie rods used to connect the front and rear templates, and the mold clamping cylinder. , connecting rod mechanism, mold adjustment device and product ejection device.
Hydraulic system and electrical control system: Their 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 ancillary equipment. 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 realization of the injection machine. control.
