Plastic injection molding is a very popular term in the manufacturing industry. As the name suggests, it refers to the process where plastic parts are manufactured from various thermosetting, and thermoplastic materials. The plastic injection molding process is employed in various industries such as aerospace, toys, medical, packaging, and construction for producing smallest to the largest part. Are you keen to know what goes in this process? Read this post to know more. Here we will discuss the entire process of plastic injection molding.
Introduction to Injection Molding Process Cycle –
An injection molding machine, a mold, and a raw plastic material are requisites for injection molding process. The process cycle for injection molding lasts between 2-4 seconds, and consists of 4 stages, as given below:
- Clamping: The mold used for the process consists of two halves. In this step, the two halves are clamped using the hydraulically powered clamping unit. One-half of the mold is attached to the injection molding machine, while the other is allowed to slide. The clamping unit pushes the mold halves, and exerts sufficient force to secure them during the material injection. The clamping force required is directly related to the resin property, as well as the injection pressure required to fill the molded cavity. Thicker resins have low flow rates, and require high pressure to eject. However, thin resins have high flow rates, and thus require less pressure.
- Injection: The resin in the injection barrel liquefies under the combination of pressure and heat. The barrel features heat bands, which are designated to increase the temperature to the correct melting points. Accurate temperature is the most important feature of this process. If the temperature is too high, the shear stress, and fill speed will be affected, subsequently affecting the product quality. On the other hand, if the temperature is too low, the product resin will not properly liquefy. Once, the resin is liquefied, the screw within the injection barrel pushes the molten material through the nozzle, and fills the mold cavity. The success of this stage depends on three factors: fill speed, packing and sink mark displacement, and shear stress.
- Cooling: The liquefied plastic inside the mold cools down when it touches inner mold surfaces. As the plastic cools, it takes up the shape of the desired part. Also, during cooling, some shrinkage may occur. Proper packing of the material in the injection phase helps reduce the material shrinkage in this phase. The mold is kept closed until the required cooling time has passed. The cooling time is determined from thermodynamic properties of the resin, and the thickness of the wall part.
- Ejection: The molded part is ejected from the mold, once it completely solidifies. A huge force is applied to the ejected part during the cooling time. This helps prevent the part from sticking to the mold due to shrinkage. In order to facilitate smooth release, a mold release agent is sprayed to the mold cavity surface, prior to the material injection. After ejecting the mold, it is clamped until the next shot.
After reading the above post, you will get an idea that precision of an injection molded part depends on the process. This means to get it right you need to approach an expert in the field like Veejay Plastic. The company provides injection molding services for various industries.
