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 the plastic injection molding 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 for the molten plastic 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 flow chart of plastic injection molding
The plastic injection molding process usually includes the following steps: feeding, plasticization, injection, pressure holding, cooling and mold release.
Plastic pellets or powders are fed into the injection hopper.
The plastic is heated in the barrel, and turned from solid pellets into a molten flow, which possesses great plasticity. This process is referred to as plasticization.
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 injection.
When the molten plastic 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 dense textured plastic product is produced. This step is known as pressure holding.
The in-mold cooling process of the plastic part usually refers to the entire process from the moment the molten plastic 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 is allowed when the plastic part is cooled to a certain temperature, through which the plastic part is pushed out of the mold by the ejectors.
The key parameters that determine the product molding quality include:
The plastic injection molding process boasts a diversity of advantages, among which the most significant ones are shown below:
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.
Eco Molding co., Ltd is one of the more well-known plastic injection molding companies in China. Our injection molding shop is equipped with 20 sets of high precision injection molding machines, ranging from 50 tons to 650 tons, They are mostly imported from Taiwan and Japan, our injection shop run 24 hours a day, 7 days a week, and provide production services.
We are experienced with various plastic products for many industrial, including automotive, medical, lighting, sports equipment, home appliances, and agriculture. We are an accredited an ISO9001-2008 company since 2004, We also have 5 IPQC people constantly watch our production and check part quality, This ensures our production maintains the highest level of quality. In the last 15 years, Eco Mold has established a strong reputation for producing high-quality tool and part at a reasonable price.We maintain strong business relationships with appx. 50 customers, mainly from the USA and Europe.
1. Causes and solutions for product burrs(flash) formed when the injection machine first starts, as well as an incomplete filling after a while of production:
When the machine first starts, the melting in the injection machine barrel flows smoothly with a lower stickiness thanks to a longer period of heating, so product burrs tend to occur. After a while of production, since the melting continuously takes the heat away, the product will not be fully injected due to great stickiness and poor liquidity. This problem can be solved by gradually increasing the temperature of the barrel after some time into the production.
2. In the production process, the product cannot be fully injected, even increasing injection pressure and velocity won’t work sometimes. Why and how to solve it:
In the production process, the melting continuously takes the heat away, so the product will not be fully injected due to great stickiness and poor liquidity. This problem can be solved by increasing the temperature of the injection machine barrel.
3. Causes and solutions for product becoming oval:
A product becomes oval is because the melting is not evenly fed, causing uneven pressure on the circumference of the product thus making it oval. The 3-point injection approach can be adapted to allow for even feeding.
More plastic injection molding question and answer in : https://www.ecomolding.com/plastic-injection-molding-faqs/