How plastic molds work

How plastic molds work

The plastic is heated and melted in the heating barrel at the bottom of the injection machine, and then driven by the screw or plunger of the injection machine, it enters the mold cavity through the injection machine nozzle and the casting system of the mold. The plastic is cooled and hardened to form, and the product is demolded. Its structure is usually composed of molding parts, pouring system, guide parts, push-out mechanism, temperature control system, exhaust system, support parts and other parts. Manufacturing materials usually use plastic mold steel modules, and the commonly used materials are mainly carbon structural steel, carbon tool steel, alloy tool steel, high-speed steel, etc. The injection molding processing method is usually only suitable for the production of thermoplastic products. The plastic products produced by the injection molding process are very wide. From daily necessities to various complex machinery, electrical appliances, and transportation parts, they are all molded by injection molds. It is the most widely used processing method in the production of plastic products.

Plastic mould

Plastic molds are tools that are matched with plastic molding machines in the plastic processing industry to give plastic products a complete configuration and precise dimensions. Due to the wide variety of plastics and processing methods, and the complex and simple structures of plastic molding machines and plastic products, the types and structures of plastic molds are also diverse.

1 Basic introduction
basket mould

A combined plastic mold for compression molding, extrusion molding, injection molding, blow molding and low-foaming molding. It mainly includes a cavity with a variable cavity composed of a concave mold combined substrate, a concave mold component and a concave mold combined card board The concave mold is a convex mold with a variable core composed of a convex mold combined base plate, a convex mold component, a convex mold combined card board, a cavity cut-off component and a side cut combined board. Coordinated changes of mold convex, concave mold and auxiliary molding system. Series of plastic parts of different shapes and sizes can be processed. In the plastics processing industry, it is matched with plastic molding machines to give plastic products a complete configuration and precise size tools. Due to the wide variety of plastics and processing methods, and the complex and simple structures of plastic molding machines and plastic products, the types and structures of plastic molds are also diverse.

With the rapid development of the plastics industry and the continuous improvement of general and engineering plastics in terms of strength, the application range of plastic products is also expanding, and the amount of plastic products is also rising.

Plastic mold is a tool for producing plastic products. It is composed of several groups of parts, and there is a molding cavity in this combination. During injection molding, the mold is clamped on the injection molding machine, the molten plastic is injected into the molding cavity, and cooled and shaped in the cavity, then the upper and lower molds are separated, and the product is ejected from the cavity and out of the mold through the ejection system, and finally the mold is closed For the next injection, the entire injection molding process is carried out cyclically.

Generally, a plastic mold is composed of 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 a pouring system and cavity. When the mold is opened, the movable mold and the fixed mold are separated to take out the plastic crate mould products.

Although the structure of the mold may vary widely due to the variety and performance of plastics, the shape and structure of plastic products, and the type of injection machine, the basic structure is the same. The mold is mainly composed of a pouring system, a temperature control system, forming parts and structural parts. Among them, the pouring system and molded parts are the parts that are in direct contact with the plastic and change with the plastic and the product. They are the most complex and the most variable parts in the plastic mold, requiring the highest processing finish and precision.

The gating system refers to the part of the runner before the plastic enters the cavity from the nozzle, including the main runner, the cold slug, the runner, and the gate. Molded parts refer to the various parts that constitute the shape of the product, including movable molds, fixed molds and cavities, cores, molding rods, and vents.

China's plastic molds are driven by high technology and driven by the application needs of pillar industries, forming a huge industrial chain, from the upstream raw and auxiliary materials industry and processing, testing equipment to downstream machinery, automobiles, motorcycles, home appliances, electronic communications , Construction and building materials and other major application industries, the development of plastic molds is full of vitality.

With the rapid development of China's automobiles, home appliances, electronic communications, and various building materials.

"China's Plastic Mould Market In-Depth Research and Investment Prospect Analysis Report" consists of twelve chapters. First, it introduces the overall operation status of the world's plastic mold industry and the development environment of China's plastic mold industry market. Then it analyzes the current situation of China's plastic mold industry market operation, and then introduces the competition pattern of China's plastic mold market. Subsequently, the report made an analysis of the operating conditions of key enterprises in China's plastic mold industry, and finally analyzed the development trend and investment forecast of China's plastic mold industry. If you want to have a systematic understanding of the plastic mold industry or want to invest in the plastic mold industry, this report is an indispensable tool for you.

2 main categories

According to the different molding methods, the types of plastic processing molds corresponding to different process requirements can be divided, including injection molding molds, extrusion molding molds, blister molding molds, high-foamed polystyrene molding molds, etc.

1. Plastic injection (plastic) mold

It is mainly a molding mold that is most commonly used in the production of thermoplastic products. The corresponding processing equipment for plastic injection molds is a plastic injection molding machine. The plastic is first heated and melted in the heating cylinder at the bottom of the injection machine, and then melted in the screw of the injection machine. Or driven by the plunger, it enters the mold cavity through the nozzle of the injection machine and the pouring system of the mold, and the plastic is cooled and hardened to form, and the product is demolded. Its structure is usually composed of molding parts, pouring system, guide parts, push-out mechanism, temperature control system, exhaust system, support parts and other parts. Manufacturing materials usually use plastic mold steel modules, and the commonly used materials are mainly carbon structural steel, carbon tool steel, alloy tool steel, high-speed steel, etc. The injection molding processing method is usually only suitable for the production of thermoplastic products. The plastic products produced by the injection molding process are very wide. From daily necessities to various complex machinery, electrical appliances, and transportation parts, they are all molded by injection molds. It is the most widely used processing method in the production of plastic products.

2. Plastic compression mould

It includes two structural mold types: compression molding and injection molding. They are a type of molds mainly used to mold thermoset plastics, and their corresponding equipment is a pressure molding machine. According to the characteristics of the plastic, the compression molding method heats the mold to the molding temperature (generally 103°-108°), then puts the measured compression powder into the mold cavity and the feeding chamber, and closes the mold. The plastic is under high heat and high pressure. It is a softened viscous flow, solidified and shaped into the desired product shape after a certain time. The difference between pressure injection molding and compression molding is that there is a separate feeding chamber. The mold is closed before molding. The plastic is preheated in the feeding chamber and is in a viscous flow state. It is adjusted and extruded into the mold cavity under pressure to harden and form. Compression molds are also used to mold some special thermoplastics such as hard-to-melt thermoplastics (such as polyvinyl fluoride) blanks (cold molding), resin lenses with high optical performance, slightly foamed nitrocellulose car steering wheels, etc. . The compression mold is mainly composed of a cavity, a feeding cavity, a guiding mechanism, an ejecting part, a heating system, etc. Injection molds are widely used for packaging electrical components. The material used in the manufacture of compression molds is basically the same as that of injection molds.

3. Plastic extrusion mould

A type of mold used to mold and produce continuous-shaped plastic products, also called extrusion molding heads, is widely used in the processing of pipes, rods, monofilaments, plates, films, wire and cable coatings, and profiled materials. The corresponding production equipment is a plastic extruder. The principle is that the solid plastic is melted and plasticized under heating and the screw of the extruder is rotated and pressurized, and the cross-section is the same as the shape of the die through a specific shape of the die. Continuous plastic products. Its manufacturing materials mainly include carbon structural steel, alloy tools, etc. Some extrusion dies will also be inlaid with wear-resistant materials such as diamond on the parts that need wear-resistant. The extrusion process is usually only suitable for the production of thermoplastic products, and its structure is obviously different from injection molds and compression molds.

4. Plastic blow mould

It is a kind of mold used to form plastic container hollow products (such as beverage bottles, daily chemical products and other packaging containers). The forms of blow molding are mainly extrusion blow molding hollow molding and injection blow molding hollow molding according to the process principle. , Injection stretch blow molding hollow molding (commonly known as "injection stretch blow"), multilayer blow molding hollow molding, sheet blow molding hollow molding, etc. The corresponding equipment for blow molding of hollow products is usually called a plastic blow molding machine. Blow molding is only suitable for the production of thermoplastic products. The blow mold structure is relatively simple, and the materials used are mostly made of carbon.

5. Plastic blister mold

It is a kind of mold that uses plastic plates and sheets as raw materials to form some simpler plastic products. The principle is to use the vacuuming method or compressed air molding method to fix the plastic plates and sheets on the concave or convex mold. Under the condition of heating and softening, it deforms and sticks to the cavity of the mold to obtain the desired molded product, which is mainly used in the production of some daily necessities, food, and toy packaging products. Due to the low pressure during forming, the blister mold is made of cast aluminum or non-metallic materials, and the structure is relatively simple.

6. High foamed polystyrene molding die

It is a mold that uses expandable polystyrene (beads composed of polystyrene and foaming agent) raw materials to form various desired shapes of foam packaging materials. The principle is that the expandable polystyrene can be steam molded in the mold, including two types of simple manual molds and hydraulic straight-through foam plastic molds, which are mainly used to produce industrial packaging products. The materials used to make this type of mold include cast aluminum, stainless steel, bronze and so on.

3 design elements

Mold design and manufacturing are closely related to plastic processing. The success or failure of plastic processing depends largely on the effect of mold design and mold manufacturing quality, and plastic mold design is based on the correct design of plastic products.

The structural elements to be considered in plastic mold design are:

① Parting surface, that is, the contact surface where the concave mold and the convex mold cooperate with each other when the mold is closed. The selection of its location and form is affected by factors such as product shape and appearance, wall thickness, molding method, post-processing technology, mold type and structure, demolding method and molding machine structure.

②Structural parts, namely sliders, inclined tops, straight top blocks, etc. of complex molds. The design of structural parts is very critical, related to the life of the mold, processing cycle, cost, product quality, etc. Therefore, designing the core structure of a complex mold requires a designer to have a higher comprehensive ability, and strive to be simpler, more durable, and more economical. Design.

③Mold precision, namely avoiding jams, precise positioning, guide posts, positioning pins, etc. The positioning system is related to the appearance quality of the product, mold quality and life. According to the different mold structure, different positioning methods are selected. The positioning accuracy control mainly depends on processing. The internal mold positioning is mainly considered by the designer to design a more reasonable and easy-to-adjust positioning the way.

②The pouring system, that is, the feed channel from the nozzle of the injection molding machine to the cavity, including the main runner, the runner, the gate and the cold cavity. In particular, the selection of the gate position should be conducive to the molten plastic filling the cavity in a good flow state. The solid runner and gate cold material attached to the product are easy to eject from the mold and be removed when the mold is opened. Except for road model).

③The shrinkage rate of plastics and various factors that affect the dimensional accuracy of products, such as mold manufacturing and assembly errors, mold wear, etc. In addition, when designing compression molds and injection molds, the matching of the process and structural parameters of the molding machine should also be considered. Computer-aided design technology has been widely used in plastic mold design.