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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.

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 plastic 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, cooled and shaped in the cavity, and 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 a cavity. When the mold is opened, the movable mold and the fixed mold are separated to take out the plastic 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, cold material cavity, runner and gate, etc. 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.

Driven by high technology and driven by the application demand of pillar industries, plastic molds have formed a huge industrial chain, from upstream raw and auxiliary materials industry and processing, testing equipment to downstream machinery, automobiles, motorcycles, home appliances, electronic communications, Several major application industries such as building materials, plastic mold development is full of vitality.

The Main Classification Of Plastic Mould

According to the different molding methods, the types of plastic processing molds corresponding to different process requirements can be divided, mainly 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, 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 form thermosetting plastics, and their corresponding equipment is a pressure forming 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 period of time. The difference between 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 moulds is basically the same as that of injection moulds.

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, profiled materials, etc. The corresponding production equipment is a plastic extruder. The principle is that the solid plastic is melted and plasticized under the conditions of heating and the screw of the extruder to rotate and pressurize, 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 parts that require 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 structure of the blow mold 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. Its principle is to use the vacuum method or compressed air molding method to make the plastic plates and sheets fixed on the concave mold or the convex mold. Under the condition of heating and softening, it is deformed and pasted on 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. The blister mold is made of cast aluminum or non-metallic materials because of the low pressure during molding, and the structure is relatively simple.

6.High-expansion polystyrene molding die

It is a mold for using 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-formed in the mold, including two types of simple manual operation 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 are cast aluminum, stainless steel, bronze and so on.

The Design Elements Of Plastic Mould

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 the design of plastic molds is based on the correct design of plastic products.

The structural elements to be considered in the design of plastic molds are:

  • 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.
  • Structural 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.
  • Mold 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-adjustable positioning the way.
  • Gating 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 cavities. 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).
  • Plastic shrinkage rate 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.

Mould Accessories

Punch needle, punch, guide post, guide sleeve, precise positioning, ejector pin, thimble, cylinder, slider device, inclined top device, steel ball sleeve, date stamp, plastic mold spring, sealing ring, cooling joint, water plunger, Positioning ring, sprue bushing, pull pin, pull rod, limit nail, garbage nail, support column, shutter, mold opening sequence controller (mold clamping buckle assembly), etc.

The Structural Parts Of Plastic Mould


The structure of blow molds, casting molds and thermoforming molds is relatively simple.

Compression molds, injection molds, and transfer molds are more complicated in structure, and there are many parts that make up this type of mold.

The basic parts are:

  • Molding parts, including concave molds, convex molds, and various molding cores, are parts of the inner and outer surfaces or upper and lower end faces, side holes, undercuts and threads of the molded product.
  • Support fixed parts, including mold base plate, fixed plate, support plate, cushion block, etc., to fix the mold or support pressure.
  • Guiding parts, including guide posts and guide sleeves, are used to determine the relative position of the movement of the mold or ejection mechanism.
  • Core-pulling parts, including diagonal pins, sliders, etc., are used to pull out the movable core when the mold is opened to demold the product.
  • Push out parts, including push rod, push tube, push block, push piece plate, push piece ring, push rod fixing plate, push plate, etc., to demold the product. Standard mold bases are commonly used for injection molds. This mold base is a complete set of basic parts that have been standardized and serialized in structure, form, and size. The mold cavity can be processed by itself according to the shape of the product. The use of standard mold bases is beneficial to shorten the molding cycle.

2.The role of common mold base parts

Fixed mold base plate (panel): Fix the front mold on the injection molding machine.

Runner plate (nozzle plate): Remove the waste handle when opening the mold to make it fall off automatically (three-plate mold).

  • Fixed mold plate (A plate): the front mold part of the molded product.
  • Movable mold fixing plate (B plate): the back mold part of the molded product.
  • Cushion: Mould foot, its function is to make the top plate have enough space for movement.
  • Push plate: When opening the mold, push out the product from the mold by pushing out parts such as ejector pins, top blocks, and inclined tops.
  • Movable mold base plate (bottom plate): Fix the back mold on the injection molding machine.
  • Guide post and guide sleeve: play the role of guiding and positioning, assisting the opening of the front and rear molds, and the basic positioning of the mold.
  • Support column (support head): Improve the strength of the B plate, effectively avoiding the deformation of the B plate caused by long-term production.
  • Top plate guide column (Zhong Tuo Division): guide and position the push plate to ensure smooth ejection.

The Material Requirements Of Plastic Mould

The working conditions of plastic molds are different from those of cold stamping dies. Generally, they must work at 150°C-200°C. In addition to being subjected to a certain pressure, they also have to withstand temperature. According to the different use conditions and processing methods of plastic molding molds, the basic performance requirements of steel for plastic molds are roughly summarized as follows:

1.Sufficient surface hardness and wear resistance

The hardness of the plastic mold is usually below 50-60HRC, and the heat-treated mold should have sufficient surface hardness to ensure that the mold has sufficient rigidity. When the mold is working, due to the filling and flow of the plastic, it has to withstand greater compressive stress and friction. The mold is required to maintain the accuracy of the shape and the stability of the dimensional accuracy to ensure that the mold has a sufficient service life. The wear resistance of the mold depends on the chemical composition and heat treatment hardness of the steel, so increasing the hardness of the mold is beneficial to improve its wear resistance.

2.Excellent machinability

In addition to EMD processing, most plastic molding molds require certain cutting processing and fitter repairs. In order to extend the service life of cutting tools, improve cutting performance, and reduce surface roughness, the hardness of the steel used for plastic molds must be appropriate.

3.Good polishing performance

For high-quality plastic products, the surface roughness of the cavity is required to be small. For example, the surface roughness value of the injection mold cavity is required to be less than Ra0.1~0.25, and the optical surface requires Ra<0.01nm. The cavity must be polished to reduce the surface roughness value. For this reason, the selected steel requires less material impurities, fine and uniform structure, no fiber directionality, and no pitting or orange peel defects during polishing.

4.Good thermal stability

The shape of the parts of the plastic injection mold is often complicated and difficult to process after quenching. Therefore, it should be selected as much as possible with good thermal stability. When the mold is formed by heat treatment, the linear expansion coefficient is small, the heat treatment deformation is small, and the dimensional change caused by the temperature difference The rate is small, the metallographic structure and the mold size are stable, and the processing can be reduced or no longer needed to ensure the mold size accuracy and surface roughness requirements.

45 and 50 grades of carbon steel have certain strength and wear resistance, and are mostly used as mold base materials after quenching and tempering. High-carbon tool steel and low-alloy tool steel have higher strength and wear resistance after heat treatment, and are mostly used for forming parts. However, high-carbon tool steel is only suitable for manufacturing small-sized and simple shaped parts due to its large heat treatment deformation.

With the development of the plastics industry, the complexity and precision of plastic products have become more and more demanding, and higher requirements have been placed on mold materials. For the manufacture of complex, precise and corrosion-resistant plastic molds, pre-hardened steel (such as PMS), corrosion-resistant steel (such as PCR) and low-carbon maraging steel (such as 18Ni-250) can be used, all of which have good Cutting processing, heat treatment and polishing performance and high strength.

In addition, when selecting materials, you must also consider preventing scratches and bonding. If there is relative movement between the two surfaces, try to avoid selecting materials with the same structure. Under special conditions, one side can be plated or nitrided to make the two sides have different The surface structure.

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