(Last Updated On: September 28, 2018)

Although the structure of the mold will change because of the change of the plastic variety and performance.

plastic products shape and structure ,the type of injection molding machine. But the basic structure is the same.Mold is mainly composed of gating system, temperature control system, molded parts and structural parts. The gating system and molded parts are in direct contact with the plastic and they will change with plastic and products.They are the parts which are the most complex ,the greatest change, the most demanding machining finish and highest precision in the mold.
The injection mold is composed of two parts of the movable mold and the fixed mold. The movable mould is mounted on the moving mould plate of the injection molding machine. The fixed mould is mounted on the fixed mould plate of the injection molding machine. When injection molding,the movable mould and the fixed mold is closed to constitute gating system and mold cavity.When the movable die and the fixed mold separate in order to remove the plastic products.In order to reduce the heavy workload of mold design and manufacturing, injection molding mostly uses standard mold…

 

below above mold

 

 

Gating system
Gating system refers to the channel section that the plastic from the nozzle enters into the front of the mold cavity, including  main sprue, cold-slug, runner and gate, etc.
Gating system is also called as the runner system. It is a group of feed channels that lead plastic melt from injection machine nozzle to cavity.It is composed of sprue, runner, gate and cold slug well. It is directly related to the quality of plastic products molding and productivity.

 

gate_system

 

Sprue
It is a part of the channel in the mold that connects the injection nozzle and the runner or the cavity . The top of the spure is concave in order to connect with the nozzle. The sprue inlet diameter should be slightly larger than the diameter of the nozzle (0.8mm) to avoid overflowing, and prevent the interception because of cohesion atypia. Inlet diameter is according to the size of the product,generally 4-8mm. The sprue diameter should be enlarged inward 3 degrees to 5 degrees, so that the flow superfluous material strip.

Cold slug
It is a hole that locates at the end of spure to trap cold material between the two injection of the nozzle end. In order to prevent the blockage of the runner or the gate. If cold material once mixes in the cavity,then products are easy to produce internal stress.Cold slug diameter is about 8-10mm,and depth is 6mm.For ease of stripping, the bottom is usually borne by a release lever.The top of the release bar should be designed as zigzag hook-shaped or sunken grooves, in order to pull the sprue superfluous successfully when the release.

Shunt
It is a channel in the multi-slot die that connects main channel to each cavity.In order to make melt with velocity fill the cavities.The shunt channel in the mold should be be symmetrical arranged and equally spaced.The shape and size of the shunt flow cross-section have influence on the plastic melt flowing, products releasing and difficulty of mold manufacturing.
If by the the flowing of equal quantity, the flowing channel resistance of circular cross section is least.But the surface area of cylindrical flow path is small which is negative for cooling of shunt warts.And this shunt must be installed on the two mold halves what are both labor intensive and difficult to align.
Therefore we often use trapezoidal or semi-circular cross-section shunt which are installed on the half mold with release lever.The runner surface must be polished to reduce the flow resistance and to provide a faster mold filling speed. The size of the flow channel is determined by the plastic variety, size and thickness of products.For most thermoplastics,the section width of the split channel does not exceed 8m,especially large up to 10-12m, especially small 2-3m. In the premise of meeting the needs,cross-sectional area should be minimized in order to increase the shunt warts and extend the cooling time.

Runner
It is a channel that connects the main road (or shunt) to the cavity.Sectional area of the channel is equal to the main channel (or shunt),but are usually reduced. So it is the smallest part in the whole cross-sectional area of the flow path system.Gate shape and size have a great impact on the product quality.

The role of the runner :
A.control material flowing rate
B.In the injection,because melt curdles early to prevent backflowing.
C.Make melt rise temperature because of strong shear, thereby reduce the apparent viscosity to improve liquidity.
D.It is convenient for separate products and runner system.The gate shape, size and position are depend on the nature of plastic, size and structure of the products. Cross-sectional shape of the gate is generally rectangular or circular.Cross-sectional area area should be small and the length should be short.This is not only based on the above-mentioned role, but also it is easy for small gate to enlarge.The position of gate generally should not affect the appearance and thickness of product.
Gate size should be designed to consider the nature of the plastic melt.Cavity is space to mold plastic products.Molded parts are component to constitute the cavity.
Each molded parts often have special names.Die is molded parts to constitute the articles. Core or punch constitutes internal shape of the product. Design molded parts should according to performance of plastic,the geometry of the article, dimensional tolerances and requirements to sure the overall structure of the cavity.
To ensure the surface smooth of plastic products,and ease of stripping,the surface where be contact with the plastic must ensure the roughness more than 0.32um and resistant to corrosion.Molded parts generally use heat treatment to increase the hardness and select corrosion-resistant steel.

Temperature regulation system
In order to meet the injection molding process,there needs Temperature regulation system to adjust the temperature of the mold.For thermoplastics,cooling system is mainly designed to make mold cool.The common method of cooling mold is setting cooling water passage to take the heat of the mold.In order to heat mold,we can install electric heating elements inside and around the mold.

cooling system

 

 

 

Molded parts
Molded parts refer to various parts to constitute the articles shape,including movable mold and the fixed mold, cavity, core, forming stem and exhaust vent.Molded part is composed of core and die.The core forms the inner surface of the article,and the die forms the outer surface shape of the article.After clamping,core and cavity will form the mold cavity.According to process and manufacturing requirements, sometimes core and die are made up of several pieces, sometimes makes into whole part.There are inserts on easily damaged,difficult to machine parts.

molded parts

 

Exhaust vent
It is one kind of groove outlet in the mold to discharge the original gas and brought gas.When the molten material inject into the cavity, the original gas stored in the cavity and brought gas must be discharged at the end of the stream through the exhaust vent. Otherwise it will cause products with stoma, poor contact,filling dissatisfaction.
Under normal circumstances, vent can both be installed at the end of melt flowing in the cavity,and the parting surface of the mold.The latter sets shallow grooves at the side of the die deep 0.03-0.2mm, width 1.5-6mm.In injection process,there will not be a lot of melt leakage.Because the melt will cool and solidify there to block channel.The exhaust vent never faces to the operator to prevent melt accidental discharging to wound people.In addition, it can also use the coordination gap in eject lever and eject hole or the coordination gap in the block and stripper plate to exhaust.

Structural parts
It refers to various parts of constituting the mold structure, including guide, ejection, core pulling and typing of the various parts. For example,the context plywood,context deduction templates, bearing plate, bearing columns, guide posts, stripper plate, the release lever and return lever and so on.
1.The guide member
To ensure that the movable mold and the fixed mold accurate alignment,it must set guide member.In injection mold,we usually use four sets of guide pin and the guide sleeve to form the guide member. And sometimes should separately set the inner and outer cone on the movable mold and the fixed mold to assist positioning.
2.Release mechanism
In the mold-opening process,release agency pushes out or pulls out the slug in the runners and plastic products.Release fixing plate and push plate to hold the push plate.There is reset lever fixing on the putter.The reset lever makes the push plate reset when the movable mold and fixed mold clamping.
3.side core-pulling mechanism
Some plastic products with side concave or side holes must be side parting first before being pushed out.After extracting the core side can successfully release, this time need to set the side core-pulling mechanism in the mold….