Injection molding is a automatic process runned by injection molding machine. Plastic granules are melted and forwarded by a turnning screw shaft inside the box of injection molding machine. When the operator start the process, the molten plastic would be injected through the nozzle into the closed mold fixed on the machine, the injection process may take for seconds to make sure all the spaces of mold cavities are fully filled. After that, the cooling water will flow through the water channel in the mold to take the heat and make the moten plastic harden. Finally, the hardened part is ejected alone with opening of the mold.
Actually, there are several parameters which should be set rightly, then the process could be repeated again and again. Generally, the process could be divided into 3 phrases.
- Filling phrase – Time, speed, and pressure should be adjusted properly to make enough molten plastic flow go into the mold. The engineer have to consider the material property, product structure and mold type to adjust parameters.
- Holding phrase – Speed will be set low and pressure set just enough on this phrase to make the flow fill up the empty space in the mold.
- Cooling phrase – Pressure will be set low and cooling water runs to take the heat and make the molten plastic harden.
However, the right parameters is important for making high quality mass production. Environment change and operator’s mistakes will lead to failure of injection molding. So high quality mass production needs a strict quality system. Training of the workers, habit development and quality checking frequency are also important.