According to different types of gating system, plastic molds can be divided into three categories:

Runner and gate are on parting line and are demolded together with product when mold is opened. Design is the simplest, easy to process, and low cost, so more people use large nozzle system to work. Plastic mold structure is divided into two parts: movable mold and fixed mold. Movable part of injection machine is movable mold (mostly ejection side), injection end of injection machine is generally inactive and called fixed mold. Because fixed mold part of large nozzle mold is generally composed of two steel plates, this type of structural mold is also called "two-plate mold". Two-plate mold is the simplest structure in large nozzle mold.

Runners and gates are not on parting line, generally directly on product, so it is necessary to design an additional set of nozzle parting lines, design is more complicated, processing is more difficult. Generally, fine nozzle system should be selected according to product requirements. Fixed part of nozzle mold is generally composed of three steel plates, so this type of structural mold is also called "three-plate mold". Three-plate mold is the simplest structure in nozzle mold.

Structure of this type of mold is roughly same as that of nozzle. The biggest difference is that runner is in one or more hot runner plates and hot nozzles with constant temperature. There is no cold material demoulding, runner and gating. Port is directly on product, so runner does not need to be demolded. This system is also called a nozzleless system, which can save raw materials, is suitable for situations where raw materials are more expensive and products require higher requirements, design and processing are difficult, mold costs are high.
Hot runner system, also known as hot runner system, is mainly composed of a hot sprue sleeve, a hot runner plate, and a temperature control electric box. Our common hot runner system has two forms: single-point hot gate and multi-point hot gate. Single-point hot gate uses a single hot sprue sleeve to directly inject molten plastic into cavity. It is suitable for plastic molds with a single cavity and single gate; multi-point hot gate is to branch molten material into each sub-heat gate sleeve through hot runner plate and then enter cavity. It is suitable for single-cavity multi-point feeding or multi-cavity molds.

 

Plastic is first added to heating barrel of injection machine. Plastic is heated and melted. Driven by screw or plunger of injection machine, it enters mold cavity through nozzle and mold gating system. It is hardened and shaped into an injection molded product due to physical and chemical effects. Injection molding consists of a cycle consisting of injection, pressure holding (cooling) and demolding of plastic parts, so injection molding has periodic characteristics.
Molding cycle of thermoplastic injection molding is short, production efficiency is high, wear of melt on mold is small, plastic parts with complex shapes, clear surface patterns and markings, and high dimensional accuracy can be molded in large quantities; but for plastics with large wall thickness changes, it is difficult to avoid molding defects. Anisotropy of plastic parts is also one of quality problems, all possible measures should be adopted to minimize it.

Commonly known as compression molding, it is one of the earliest methods of forming plastic parts. Compression molding is to add plastic directly into an open mold cavity with a certain temperature, then close mold. Under action of heat and pressure, plastic melts and becomes a fluid state. Due to physical and chemical effects, plastic is hardened into a plastic part with a certain shape and size that remains unchanged at room temperature.
Compression molding is mainly used for molding thermosetting plastics, such as phenolic molding powder, urea-formaldehyde and melamine-formaldehyde molding powder, glass fiber reinforced phenolic plastic, epoxy resin, DAP resin, silicone resin, polyimide and other molding materials. It can also process unsaturated polyester material (DMC), sheet molding compound (SMC), prefabricated integral molding compound (BMC), etc. In general, according to matching structure of upper and lower molds of compression film, compression molds are divided into three types: overflow type, non-flooding type, and semi-flooding type.

It is a molding method in which plastic in a viscous flow state passes through a die with a specific cross-sectional shape under a high temperature and a certain pressure, then is shaped into a continuous profile with a desired cross-sectional shape at a lower temperature. Production process of extrusion molding includes preparation of molding materials, extrusion molding, cooling and shaping, traction and cutting, post-processing of extruded product (tempering or heat treatment).
In extrusion molding process, pay attention to adjusting temperature of each heating section of extruder barrel and temperature of die head, screw rotation, traction speed and other process parameters in order to obtain qualified extruded profiles. Special attention should be paid to adjusting rate of polymer melt extruding from die of die. Because when extrusion rate of molten material is low, extrudate has a smooth surface and uniform cross-sectional shape; but when extrusion rate of molten material reaches a certain limit, surface of extrudate will become rough, lose its luster, appear shark skin, orange peel, and shape distortion. When extrusion rate is further increased, surface of extrudate is distorted, even splits and breaks into melt fragments or cylinders. Therefore, control of extrusion rate is very important.

Also known as die casting. It is to put plastic raw materials into preheated feeding chamber, then put pressing column into feeding chamber to lock mold, apply pressure to plastic through pressing column, plastic melts into a flowing state under high temperature and high pressure, enters cavity through casting system to gradually solidify into a plastic part. This type of molding method is also called transfer molding. Transfer molding is suitable for plastics that are lower than solid plastics. In principle, plastics that can be compression molded can also be molded by injection molding. But it is required that molding material has good fluidity in molten state when temperature is lower than solidification temperature, and has a larger solidification rate when temperature is higher than solidification temperature.

It is to fix tube or sheet blank material made by extrusion or injection, which is still in plasticized state, in forming mold, immediately pass in compressed air to force blank material to expand and stick to wall of mold cavity. After cooling and shaping, it is demoulded, which is a processing method for obtaining required hollow products. Plastics suitable for hollow molding are high-pressure polyethylene, low-pressure polyethylene, rigid polyvinyl chloride, soft polyvinyl chloride, polystyrene, polypropylene, polycarbonate, etc. According to different molding methods of parison, hollow molding is mainly divided into two types: extrusion blow molding and injection blow molding. Advantage of extrusion blow molding hollow molding is that structure of extruder and extrusion blow molding die is simple, but disadvantage is that wall thickness of parison is inconsistent, which easily causes wall thickness of plastic product to be uneven.
Advantage of injection blow molding hollow molding is that wall thickness of parison is uniform and there is no flash. Because injection parison has a bottom surface, bottom of hollow product will not produce seams, which is not only beautiful but also high in strength. Disadvantage is that molding equipment and molds used are expensive, so this molding method is mostly used for mass production of small hollow products, and it is not widely used in extrusion blow molding.

Die casting mould is also called transfer mould. Plastic raw materials are added to preheated feeding chamber, then pressure is applied to pressure column. Plastic is melted under high temperature and high pressure, enters cavity through casting system of mold, gradually hardens into shape. This molding method is called die-casting. Mold used It is called a die-casting mold. This kind of mold is mostly used for molding of thermosetting plastics.
In addition, there are foam molding molds, glass fiber reinforced plastic low pressure molding molds, and so on.

 

With help of a heating device, plastic in gating system will not solidify and will not be demolded with product, so it is also called a runnerless mold.
Advantage:
1) No waste
2) Injection pressure can be reduced, and multi-cavity mold can be used
3) Molding cycle can be shortened
4) Improve quality of products. Features suitable for hot runner molding compound:
5) Melting temperature range of plastics is wide. At low temperature, it has good fluidity, and at high temperature, it has better thermal stability.
6) Sensitive to pressure, no flow without pressure, but can flow when pressure is applied.
7) Good specific heat, so that it can be cooled quickly in mold.
Available hot runner plastics are PE, ABS, POM, PC, HIPS, PS.
There are two commonly used hot runners: 1) heated runner mold 2) adiabatic runner mold.

Steel plates used in inner mold parts need to be heat treated after being purchased, such as quenching and carburizing, to meet requirements of use. Such injection molds are called hard molds. For example, inner mold parts are made of H13 steel, 420 steel, and S7 steel.

Steel used in inner mold part does not need to be heat treated after being purchased, and it can meet requirements of use. Such injection molding is called soft mold. For example, inner mold uses P20 steel, Ace steel, 420 steel, NAK80, aluminum, and beryllium copper.