Plastic mould is a kind of tool used for processing plastic products, which gives plastic products a complete configuration and precise size. Plastic moulds have various types and structures, mainly depending on the plastic species, processing methods and the structure of plastic products. Plastic mould is a kind of plastic mould, which is widely used in compression moulding, extrusion moulding, injection moulding, blow moulding and low-foam moulding.
General plastic mould consists of two parts, the moving mould and the fixed mould, the moving mould is mounted on the moving template of the injection moulding machine, and the fixed mould is mounted on the fixed template of the injection moulding machine. During injection moulding, the moving mould and the fixed mould are closed to form the pouring system and the cavity, and when the mould is opened, the moving mould and the fixed mould are separated in order to take out the plastic products.
1. Classification of plastic molds
According to the different molding methods, plastic processing mold types corresponding to different process requirements can be divided, mainly including injection molding molds, extrusion molding molds, blister molding molds, high-expanded polystyrene molding molds, etc.
1.1 Plastic injection (plastic) mold
Plastic injection mold is the most commonly used molding mold in the production of thermoplastic parts. The corresponding processing equipment for plastic injection molds is a plastic injection molding machine. The plastic is first heated and melted in the heating barrel at the bottom of the injection machine. Then, driven by the screw or plunger of the injection machine, it enters the mold shape through the nozzle of the injection machine and the pouring system of the mold. cavity, the plastic is cooled and hardened to form, and the finished product is demolded.
Plastic injection molds usually consist of molding parts, pouring systems, guide parts, ejection mechanisms, temperature adjustment systems, exhaust systems, support parts, etc. Manufacturing materials usually use plastic mold steel modules. 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. Plastic products produced by the injection molding process are very wide, ranging from daily necessities to various complex machinery, electrical appliances, transportation parts, etc., are all molded with injection molds. It is the most widely used processing method in the production of plastic products.
1.2 Plastic compression moulds
Plastic compression moulds include two types of structural moulds: compression moulding and pressure injection moulding. They are a kind of moulds mainly used for moulding thermosetting plastics, and their corresponding equipment is pressure moulding machine.
Compression moulding method according to the characteristics of the plastic, the mould will be heated to the molding temperature (generally in 103 ° - 108 °), and then the measured pressure plastic powder into the mould cavity and charging chamber, close the mould, the plastic in the high heat, high pressure under the action of the soft viscous flow, after a certain period of time after the curing and shaping, to become the desired shape of the product. Pressure injection moulding and compression moulding is different from a separate charging chamber, the mould is closed before moulding, the plastic in the charging chamber to complete the preheating was viscous flow state, adjusted under pressure squeezed into the mould cavity, hardening and shaping.
Pressure injection mould is mainly composed of cavity, charging chamber, guiding mechanism, launching parts, heating system and so on. Pressure injection moulds are widely used in encapsulation of electrical components. The materials used in the manufacture of compression moulds are basically the same as those of injection moulds.
1.3 Plastic Extrusion Mould
Plastic extrusion mould is used to form the production of a continuous shape of plastic products of a class of moulds, also known as extruder head, widely used in pipes, rods, monofilament, sheet, film, wire and cable coverings, profiles and other processing.
With plastic extrusion mould corresponding to the production equipment is plastic extruder, the principle is that the solid plastic in the heating and extruder screw rotating pressure conditions, melt, plasticise, through a specific shape of the mouth of the mould and made of cross-section and the shape of the mouth of the mould of the same shape of the continuous plastic products.
Plastic extrusion mould manufacturing materials are mainly carbon structural steel, alloy tooling, etc. Some extrusion moulds in need of wear-resistant parts will also be inlaid with diamond and other wear-resistant materials. Extrusion process is usually only applicable to the production of thermoplastic products, its structure and injection moulds and compression moulds have obvious differences.
1.4 Plastic Blow Mould
Plastic blow mould is used to form plastic containers hollow products (such as beverage bottles, daily necessities and other packaging containers) of a kind of mould. The form of blow moulding according to the principle of the process are mainly extrusion blow moulding, injection blow moulding, injection blow moulding, injection extension blow moulding (commonly known as ‘injection pull blow’), multi-layer blow moulding, sheet blow moulding and other blow moulding. The equipment corresponding to blow moulding of hollow products is usually called plastic blow moulding machine, and blow moulding is only applicable to the production of thermoplastic products. The structure of blow moulds is relatively simple, and the materials used are mostly made of carbon.
1.5 Plastic Blister Mould
Plastic suction mould is a plastic plate, sheet material as raw material forming some simple plastic products of a mould, the principle is to use vacuum bloom method or compressed air forming method to make the fixed in the concave or convex mould plastic plate, sheet, in the case of heating softening deformation and paste in the mould cavity to get the required molded products, mainly used in the production of some daily necessities, food, toys, packaging products. Blister mould for forming pressure is low, so the mould material is mostly used cast aluminium or non-metallic materials, the structure is relatively simple.
1.6 High foaming polystyrene moulding moulds
The high foaming polystyrene mould is a kind of mould which applies the raw material of expandable polystyrene (bead material composed of polystyrene and blowing agent) to mould various foam packaging materials in the required shapes. The principle is that the evaporable polystyrene can be shaped into steam inside the mould, including two types of simple hand-operated moulds and hydraulic press straight-through foam moulds, which are mainly used for the production of packaging products for industrial goods. The material for manufacturing this kind of mould is cast aluminium, stainless steel, bronze and so on.
2. The working principle of plastic mould
Plastic mould is generally composed of mould seat (fixed mould), mould core (moving mould), ejector pin, ejector rod and other components. Its working principle is that the plastic material is heated and melted and injected into the mould, and then moulded by pressure, temperature and other factors.
In the first step, the plastic material is heated to a certain temperature so that it becomes molten and can be injected into the mould.
In the second step, the plastic material in the molten state is injected into the mould.
Third step, wait for the plastic material to solidify and mould, and unload the finished product.
3. Plastic Mould Making Process
The production of plastic mould can be divided into three stages: mould design, mould processing and mould trial. Among them, mould design is one of the most important links, it needs to fully consider the shape, size, thickness, structure and other factors of the plastic products, according to the actual needs of the design of a suitable mould structure.
Mould processing stage, need to rely on CNC machining equipment and a variety of cutting tools to complete. Usually, the precision of mould processing is very high to ensure that the final quality of the plastic products produced is good.
Mould trial stage is to check whether the mould is working properly, usually using plastic raw materials for mould trial to check whether the mould meets the actual production needs.
4. Material requirements of plastic mould
The working conditions of plastic moulds and cold punching moulds are different, generally have to work at 150 ° C - 200 ° C, in addition to a certain pressure, but also to withstand the effects of temperature. According to the use of plastic moulding mould conditions, different processing methods will be the basic performance requirements of plastic mould steel is summarized below.
- sufficient surface hardness and wear resistance
Plastic mould hardness is usually below 50-60HRC, after heat treatment of the mould should have enough surface hardness to ensure that the mould has enough stiffness. Mould in the work due to the filling and flow of plastic to withstand greater compressive stress and friction, the requirements of the mould to maintain the shape of the precision and stability of dimensional accuracy, to ensure that the mould has sufficient service life. The wear resistance of the mould depends on the chemical composition of the steel and the hardness of the heat treatment, so improving the hardness of the mould is conducive to improving its wear resistance.
- excellent cutting processability
Most plastic forming moulds, in addition to EMD processing also need to carry out a certain amount of cutting processing and clamp repair. In order to extend the service life of cutting tools, improve cutting performance and reduce surface roughness, the hardness of steel for plastic moulds must be appropriate.
- good polishing performance
High-quality plastic products, the requirements of the cavity surface roughness value is small. For example, injection mould cavity surface roughness value is required to be less than Ra0.1 ~ 0.25 level, the optical surface requires Ra<0.01nm, the cavity must be polished, reduce the surface roughness value. For this reason, the choice of steel requires less material impurities, tissue microfine uniform, no fibre directionality, polishing should not appear pitting or orange peel defects.
- good thermal stability
Plastic injection mould parts are often complex shape, hard to process after quenching, so should try to use a good thermal stability, when the mould forming process after heat treatment due to the coefficient of linear expansion is small, heat treatment deformation is small, the rate of change of the dimensions caused by the temperature difference is small, the metallurgical organization and the mould dimensions are stable, can be reduced or no longer be processed, you can ensure that the mould dimensional accuracy and surface roughness requirements.
5.The use of plastic mould
Plastic moulds are used in daily necessities manufacturing, industrial manufacturing, medical apparatus, plastic packaging boxes and other fields.
- Daily necessities manufacturing. Plastic moulds are widely used in the manufacture of daily necessities, such as plastic cups, plastic bowls, plastic chopsticks and so on.
- Industrial Manufacturing. Plastic moulds also play an important role in industrial manufacturing. For example, automobile manufacturing,
