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Plastic Injection Mold It Consists Of Two Parts, Dynamic Mode And Fixed Mode
Oct 30, 2017

Injection mould is a kind of processing method used in mass production of some complicated shape parts, which is mainly used in industrial field. Injection mold process for the melting of the material by high-pressure injection into the mold cavity, after cooling and solidification, to get the forming products; According to the molding characteristics of the thermosetting plastic mold, thermoplastic plastic mold two kinds.

The injection mold is composed of two parts, the dynamic mode and the fixed die, the movable mould is installed on the moving template of the injection molding machine, and the fixed die is installed on the fixing formwork of the injection moulding machine. During injection molding, the casting system and the mold cavity are formed by closing the die and fixed die, and the mould is separated to remove the plastic products.

Although the structure of the mould may be changeable due to the variety and properties of plastic, the shape and structure of plastic products and the type of injection machine, the basic structure is consistent. The mold is mainly composed of pouring system, thermostat system, forming parts and structural parts. wherein the gating system and the molded parts are directly contacting with the plastic, and vary with the plastic and the products, is the most complex in the plastic mold, the change is the biggest, requires the processing smoothness and the highest precision part.

The pouring system refers to the flow passage part of the plastic from the nozzle into the cavity, including the main channel, the cold material hole, the Distributary channel and the gate. The forming part is a kind of various parts which form the shape of the product, including the movable mode, the fixed mode and the cavity, the core, the forming rod and the exhaust port. Typical mold structure such as diagram.

Pouring system

The gating system, also known as the Runner system, is a group of feeding channels which will lead the plastic melt into the cavity by the injector nozzle, which is usually composed of the main channel, the Distributary channel, the gate and the cold material hole. It is directly related to the molding quality and production efficiency of plastic products.

Mainstream Road

It is a section of the mold connecting the injection molding machine nozzle to the shunt channel or the type cavity. The top of the main channel is concave to connect with the nozzle. Inlet diameter of main channel should be slightly larger than nozzle diameter (O. 8mm) to avoid spillage and prevent the interception of the two due to the connection is not allowed. The import diameter depends on the size of the product, generally 4-8mm. The diameter of the main channel should be enlarged to the angle of 3° to 5°, in order to release the flow passage.

Cold Material hole

It is a hole located at the end of the main channel to capture the cold material produced between the two injections at the end of the nozzle to prevent clogging of the shunt or gate. If the cold material is mixed into the cavity, the internal stress is easily produced in the product. The diameter of the cold material hole is about 81 Lomm, the depth is 6mm. In order to facilitate demoulding, the bottom is often borne by the ejection rod. The top part of the ejection rod should be designed into a zigzag hook shape or a sunken groove, so that the stripping of the main road can be successfully pulled out.

Shunt Road

It is a channel connecting the mainstream channel and the various cavities in the multi-slot die. In order to fill the cavity with equal speed, the arrangement of the Distributary channel on the plastic mould should be symmetrical and equidistant. The shape and size of the cross-section of the shunt channel have an effect on the flow of the plastic melt, the demoulding of the product and the manufacture of the mould. The flow path resistance of the circular cross-section is minimized if the flow of the equivalent material is measured. However, because of the smaller than the surface of the cylindrical runner, it is unfavorable to the cooling of the diverting material, and the shunt channel must be set in two halves, which is both both a and an easy alignment. As a result, it is often used in trapezoidal or semicircular section of the shunt channel, and is opened in the mold with the ejection rod half of the die. The surface of the runner must be polished to reduce the flow resistance to provide a faster mold filling speed. The size of the runner is determined by the size and thickness of the plastic product. For most thermoplastics, the cross-sectional width of the manifold is no more than 8m, with a maximum size of 10,112 m, and a small 2-3m. In order to meet the needs of the premise should be as far as possible to reduce the cross-sectional area, so as not to increase the shunt passage and prolong the cooling time.


It is access to the main channel (or shunt path) and the cavity. The cross-sectional area of the channel can be equal to the sprue (or shunt path), but it is usually reduced. So it is the smallest section of the whole channel system. The shape and size of the gate have a great effect on the quality of the products.

The role of the gate is:

A, control material flow speed:

B, in the injection can be deposited in this part of the melt premature condensation to prevent backflow:

C, so that the passing of the melt by a strong shear and increase the temperature, thereby reducing the apparent viscosity to improve liquidity:

D. Easy to separate the products from the runner system. The design of the gate's shape, size and position depends on the nature of the plastic, the size and structure of the product. Generally, the cross-section of the gate is rectangular or circular, and the cross-sectional area should be small and short in length, which is not only based on the above effect, but also because the small gate becomes larger and easier, while the large gate is very difficult to shrink. The gate position should generally be selected at the thickest of the product without affecting the appearance of the place. The design of the gate size should take into account the properties of the plastic melt. Cavity It is the space of forming plastic products in the mould. Components used as constituent cavities are collectively referred to as molded parts. Each molding part has a special name. The forming part of the form of a product is called a concave die (also called a yin die), forming the inner shape of the product.

(such as holes, grooves, etc.) called the core or convex die (also known as Master). The overall structure of the cavity must be determined according to the properties of the plastics, the geometrical shape of the products, the tolerances of the dimensions and the requirements of the use of the molded parts. The second is to choose the parting surface, the gate and the exhaust hole position and the Demoulding method according to the definite structure. At last, the design of each part is carried out according to the size of the control product and the combination method of each part is determined. The plastic melt enters the cavity to have the very high pressure, therefore the forming part must carry on the reasonable material selection and the strength and the rigidity check. In order to ensure the smooth appearance of plastic products and easy demoulding, where the surface with plastic contact, its roughness ra>0. 32um and corrosion resistant. The forming parts are generally made by heat treatment to improve the hardness and the use of corrosion-resistant steel.

Thermostat System

In order to meet the requirements of the injection process on the mold temperature, the thermostat system needs to adjust the temperature of the mould. For thermoplastic plastic injection mold, mainly designed cooling system to make the mold cooling. The common method of mould cooling is to open the cooling water channel in the mould, to take the heat of the mould with the circulating cooling water, and the heating of the mould can be used in addition to hot water or steam in the cooling water channel, and the electric heating element can be installed inside and around the mould.

Forming parts

The forming part is composed of a core and a concave die. The core forms the inner surface of the product, and the concave mold forms the exterior surface shape of the product. The mold cavity is formed after the die-clamping core and the cavity. According to the process and manufacturing requirements, sometimes the core and die are composed of several pieces of tile, sometimes made into a whole, only in easily damaged, difficult to process parts of the insert.

Exhaust port

It is opened in the mold of a groove-shaped vent, used to discharge the original and the molten gas brought into. When the melt is injected into the cavity, the air that is stored in the cavity and the gas that is brought in by the melt must be discharged through the vent to the die at the end of the material flow, otherwise the product will have the blowhole, the bad, the mold dissatisfaction, and even the accumulated air will be burned by compression to produce high temperature. In general, the vent hole can be located at the end of the melt flow in the cavity, or on the fractal surface of the mold. The latter is opened on the side of the concave die 0. 03-0. 2mm, Width 1. 5-6mm Shallow groove. In the injection, the vent hole will not have a lot of molten material leakage, because the molten material will be cooled and solidified at the place to block the passage. The opening position of the exhaust outlet should not be on the operator, in case of accidental spraying of the molten material. In addition, the clearance between the ejector rod and the ejector hole, the top block and the release plate and the core are combined to exhaust the air.

Structural Parts

It refers to a variety of parts that make up the mold structure, including: Guide, demoulding, core-pulling and various parts. such as front and rear splint, front and Back button template, bearing plate, bearing pressure column, guide column, stripping formwork, demoulding rod and return rod.

1. Guide Parts

In order to ensure that the dynamic mode and the fixed die can be accurately aligned in the die, the guide part must be set in the mold. In the injection mold, four sets of guide pillars and guide sleeve are usually used to form the guiding parts, and sometimes the inner and outer cone of each other should be arranged on the dynamic mode and fixed die respectively to assist the positioning.

2. Launch of the agency

In the process of opening the mold, there is a need for the introduction of plastic products and its in the runner's condensate in the introduction or Pull-out. A fixed plate and a push plate are introduced to clamp the putter. In the push rod is usually fixed with a reset rod, the reset bar in the dynamic, fixed die clamping when the push plate reset.

3. Side core pulling mechanism

Some with side concave or side hole plastic products, before being introduced must carry on the side parting type, pulls out the lateral type core to be able to smooth demoulding, at this time needs to set the side core pulling mechanism in the mold.

Standard mould Holder

In order to reduce the heavy mold design and manufacturing workload, most of the injection mold used a standard mold frame.