In your daily life, there are easy to see various types and colors of plastic parts everywhere. what is plastic injection molding? How does a plastic injection mold work? Plastic injection mold is one of the three major elements of injection molding, which include plastic material, plastic injection mold, plastic injection moulding machine. Current, Plastic Injection mold widely used in automotive, medical, industrial equipment, etc. as a custom plastic injection molding service provider, we have fluent experience with mold manufacturing and moulding.
What is Plastic Injection Molding
Plastic injection molding, also called as injection molding. it is a manufacturing process to fabricate plastic parts. using a specialized hydraulic or electric injection machine, the process melts, injects and fabricate plastic into the pre-shaped of a metal mold that’s fitted into the machine.
Plastic Injection Molding Structure
The structure of plastic injection tooling is mainly composed of: Pouring system, Cooling system, molding parts , Venting system, Guiding system, Ejecting system, etc. according to the function. Among them, the pouring system and molding parts are in direct contact with the plastic pellets, and with the material and products and changes, is the most complex in the mold, the biggest change, requires the highest processing finish and accuracy of the part. Below please find the detail.
1. Pouring Systems
Pouring system: It is the part of the flow channel before the plastic enters the cavity from the injection nozzle, including the Sprue Runner, Runner, Sub-runner, Slug well and gate, etc.
2. Cooling Systems
In order to meet the mold temperature requirements of the injection Molding process, a Cooling system is required to adjust the mold temperature. For thermoplastic injection molds, the cooling system is mainly designed to make the mold cool down(the mold can also be heated). The common way to cool the mold is to open a cooling water channel in the mold, using the circulating cooling water to take away the heat from the mold; the mold can be heated by hot water or hot oil in addition to the cooling water, but also by installing electric heating elements in and around the mold.
3. Molding Parts
Including moving die, fixed die and cavity, core, forming rod and other components. According to the process and manufacturing requirements, sometimes the core and cavity are combined by a number of blocks, sometimes made into a whole, only in the easily damaged, difficult to process parts using inserts.
4. Venting
Is in order to injection molding process in the cavity of the air and plastic melting generated by the gas out of the mold and set up, the Venting is not enough when the surface of the product will form gas marks (air lines), Burning and other undesirable; plastic mold venting system is usually opened in the mold of a slot-shaped air outlet, to discharge the original cavity air and the melt into the gas.
General, we will machining a shallow slot 0.03-0.2mm deep and 1.5-6mm width to solve it.
5. Guiding
In order to ensure the accurate centering of the core side and the cavity side when closing the mold, guiding parts must be set in the mold. In the injection mold, four sets of guide pillars and guide bushings are usually used to form the guiding parts, and sometimes the inner and outer taper surfaces are set on the moving side and the fixed side respectively to assist in positioning.
6. Ejection
It generally includes: ejector pin, front and rear ejector plate, ejector pin guide bar, ejector pin reset spring, ejector plate locking screw and several other parts. When the product is molded and cooled in the mold, the Moving and Fixing mold is separated and opened, and the plastic product are pushed out or pulled out of the mold by ejector pin; in order to carry out the next injection molding work cycle.
Plastic Injection Mold Type
A. 2-Plate Mold
2-plate mold is very common mold. easy to manufacturing, Model price is relatively cheap.The required injection pressure is also low. Very wide range of applications.
B. 3-Plate Mold
Through above picture, you can find, 3-plate mold has one more stripper plate than the 2 plate die.The cost of 3-plate mold is relatively high. Both 2-plate and 3-plate mold are cold runner mold.
| 2-plate Mold | 3-plate mold | |
| Mold size | Normal | bigger |
| Mold Cost | Low | Higher |
| Injection Machine | Small | bigger |
| Structure | Stronger | Weak |
| Injection Time | Short | Long |
| Injection Pressure | Low | Higher |
| Gate Size | Small | bigger |
| Gate Cutting | Based on Gate Type | Auto cut down |
C. Hot Runner Mold
Hot runner molds are molds that use heating devices to keep the pellets melt in the runner from solidifying. Because it will save more material, keep cycle time more shorter. However, the mold price is expensive and precision. so the hot runner mold in today’s industrial countries and regions of the world are extremely widely used
Plastic mold according to the structure is generally divided by the mold base, mold cavity, assistance parts, assistance systems, assistance equipment, dead-end processing mechanism and other parts.
- Mold Base
Mold base is an important mold support parts, it needs to have certain hardness and precision, and the production process is more and more demanding, now most of them are purchased from professional mold base manufacturers, such as LK Moldbase; this saves a lot of time and energy for our mold manufacturing process, and professional things professional companies do. This ensures the mold accuracy, time and cost.
2. Mold Cavity and Core
mold cavity: mold cavity and core is the core part of the plastic mold, it is the most important part of the mold inside. Plastic products forming part in the mold cavity inside, most of the time processing is also spent on the mold core. However, there are some relatively simple molds, which do not have a mold core, the product is directly on mold base, we called it prototype molding or fast molding. Most of the early plastic molds so, relatively backward. So the mold material is very important, processing precision requirements, technology, such as to run spark, CNC, Wire cut and so on, plus post-processing also more, such as Texture, polishing, heat treatment.
3. Assistance Systems
plastic mold assistance system has the following four: injection system, ejector system, cooling system and venting system. Sometimes, because the plastic materials used need to be heated to a high temperature, so, some molds will also exist a heating system. Such as hot runner systems.
4. Assistance Equipment
injection mold Assistance setting to help set the lifting eye-bolt , KO hole and so on.
5.Dead-end processing
when the plastic products have dead-end, the mold will also have one or more dead-end processing structure. Such as slider, lifter, hydraulic cylinder, etc.. Most of us called “core pulling mechanism”.
In fact, the plastic mold is not difficult, no matter how the plastic products change, for the molding of this plastic product mold, its structure is nothing more than the above-mentioned aspects. And the difference between the mold is the mold is large or small? The position or the way of each assistance components, assistance system is different. The method, structure, size, etc. of dealing with dead ends just change. Of course, design experience is especially important to make the designed mold easy to process, easy to assemble, long life, affordable price, and good formed product. With good experience, you can deal with the problems that arise in the design and processing, and you can be more sure about the design changes.