Plastic Injection Molding

Plastic Injection Molding

What is Plastic Injection Molding?


After the plastic material is heated and plasticized in the injection barrel, the molten plastic flow will be injected into the mold cavity through the sprue and runner system, and finally, take shape after being cooled. This process is defined as plastic injection molding.
 

The Detail of the Process


During the molding process, the plastic pellets will be first delivered into the high-temperature injection barrel through the hopper, where they are heated, melted and plasticized into a sticky molten flow, which will then be injected into a lower temperature closed mold through the injection nozzle at a high speed under the great pushing pressure exerted by the plunger or the screw.
 
Under the great pressure, the molten plastic will fill the entire cavity and will also be compacted. After that, the plunger or the screw will return after a period of pressure holding. At this point, it is possible to flow back from the cavity into the sprue and runner system. When the mold opens after cooling and forming, the product will be released from the mold cavity.
 
The common process usually includes the following steps: feeding, plasticization, injection, pressure holding, cooling and mold release.
 
Feeding: Pellets or powders are fed into the hopper.
 
Plasticization: The plastic is heated in the barrel and turned from solid pellets into a molten flow, which possesses great plasticity.
 
Injection: The plasticized molten flow will be pushed to the forepart of the barrel by the plunger or the screw, and then injected to fill the mold cavity through the injection nozzle and sprue & runner system of the mold. This step is called an injection.
 
Pressure holding: When the molten material is shrinking inside the mold due to cooling, the plunger or the screw will continuously force the molten material in the barrel into the mold for replenishment, to ensure that a complete structured and the densely textured product is produced. This step is known as pressure holding.
 
Cooling: The in-mold cooling process usually refers to the entire process from the moment the molten material at the gate is fully solidified to the plastic part is ejected from the mold cavity; but actually the cooling step starts the minute the molten plastic flows into the cavity, covering the time period from completion of injection, pressure holding to the moment before mold release starts.
 
 
Mold release/Ejection: Mold release is allowed when is cooled to a certain temperature, through which the plastic part is pushed out of the mold by the ejectors.
 

Why Choosing Plastic Injection Molding?


Injection molding process boasts a diversity of advantages, among which the most significant ones are shown below:
 
The process is able to be fully automated to realize high production efficiency (injection molding can be used to mass-produce parts in a very effective way).
 
The process makes it possible to produce the immensely detailed or complicatedly designed parts. What you need is an engineering design company or an internal design department to develop great designs. Yet, the moment apart is manufactured via the injection molding process, there would be little finishing work needing to be done because the produced parts look extremely finished.
 
To gain the desired material properties in your final products, you are allowed to select a wide range of materials in the plastic injection molding process or mix different materials for a combined outcome. The combined use of more than 1 material (usually 2 different materials) is referred to as co-injection molding. Generally speaking, very little waste will be produced in the injection molding process, because excessive materials are able to be easily recycled.
 
Mold inserts can be used to produce a new part (through this process, you can change the internal cavity without complete redesigning or re-machining of the steel or aluminum tools by CNC). Apparently, the life cycle of the tooling will be dependent on the injection molding materials, and particularly on the geometry of the part and the barrel temperature of the materials. To be specific, high temperatures and delicate (thin) geometric shapes will shorten the service life of the tooling.
 
However, the injection molding process also has some distinct disadvantages. For example, the tooling costs are too high that it is not easy for average independent designers to reach them. Keep this in mind; you will know how to choose the alternatives.
 

What Kinds of Material We Use For?


It is an important decision for you to choose the proper plastic materials for your customized injection molding project. You have to consider multiple factors before selecting the right materials, such as part application, function, flexibility, durability, and color. Different plastic molding materials look and behave differently, so the materials you choose will have a direct influence on your products' performance and features. You even need to consider the material's shrinkage rate.
 
If a plastic injection molded part is made out of a single material for the initial production run, the part dimensions may be affected if you change the material for future productions. This is because different materials show different shrinkage performance.
 
Zetar offers a wide range of plastic materials to be used for the process. We will also welcome you if you make requests for special resin materials. However, if what you need is not included in the list, please don’t hesitate to contact us and we will do what we can to meet your personalized material needs. The material we often use as below: ABS, PA6, PA66, PP, PC, PC/ABS, PS, POM, PPS and so on.

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