Plastic injection molding is one of the most widely used manufacturing processes for making complex, high-quality plastic parts. It is a multi-step process that requires specialized equipment, skilled operators, and careful design consideration to produce parts that will have the desired physical, mechanical, and chemical properties.
A key step in the plastic injection molding process is Design for Manufacturability (DFM). Working with an experienced, professional plastic injection molder during the product development phase can help to ensure that the part design is optimized for production. This helps to avoid costly design changes and to reduce cycle time, lowering overall manufacturing costs.
Injection molding is a highly automated manufacturing process, with multiple stages that involve heating, melting, and cooling plastics. It is the preferred method for producing parts with a high level of detail and tight tolerances. It is also a cost-effective option for producing large volumes of identical parts and is suitable for a wide range of applications.
During the injection molding process, pelletized raw materials are fed into a heated barrel of the injection unit. Here, the heat melts and homogenizes the material by increasing its thermal energy state, weakening Van der Waals forces between individual chains, and reducing its viscosity.
The molten plastic is then transferred from the barrel to the mold using the injection nozzle and injection screw. It is injected into the cavities at high pressure until they are 95% filled. This pressure is influenced by the flow characteristics of the molded plastic, the mold dimensions, and the injection speed. Too low an injection pressure will result in early solidification of the molten plastic, and too much will create excessive pressure inside the cavity.
After the injection, the molded plastic is allowed to dwell in the cavities for a short period of time. This is to allow the evaporation of any residual molten plastic and to compact it during the cooling process. A coolant system within the mold provides this cooling function, as well as to compensate for any shrinkage that may occur during the dwelling step.
Once the molded plastic has sufficiently cooled, it is ejected from the mold using the ejection system. This typically leaves a pattern of marks on the finished plastic part known as gate marks, sprue marks and ejector pin marks, which are caused by variations in temperature, wear between the molding tools and their clamping units, gaseous vents, clearances between adjacent tooling parts and their relative motion during the molding process.
Depending on the application of the molded plastic, it may need additional treatment to improve its performance or appearance. This might include surface abrasion, chemical treatments, or the use of a release agent. This is to help facilitate a smoother, cleaner part removal and prevent premature deterioration of the molded plastics. It is also important to choose a plastic that offers the performance attributes required by the end user, and to consider any future maintenance or repair requirements.