Injection molding is an integral component of plastic molding processes; around 30% of raw plastic material goes toward this method and 40-44% of production from all plastic machinery is distributed via this route.
Injection molding is an efficient tool used for producing plastic products, consisting of various sets of parts including a mold cavity. Once mounted onto an injection molding machine, this mold allows molten plastic to enter its cavity where it cools before solidifying – this ejects off through an ejection system after both mold halves have been separated from one another.
Process Flow of Injection Molding
As shown above, injection molding is a cyclic process comprised of three distinct stages – pre-molding, injection molding and cooling and curing – each performing its part to complete its cycle.
(1) Pre-molding Stage;
The screw begins rotating and conveys plastic from its hopper into its front face, where it is plasticized at high temperature by shear force before gradually gathering at its front cylinder face. As more plastic accumulates at once, its pressure increases until finally overpowering back pressure of screw and pushing back. When plastic in front barrel reaches required injection volume level, screw stops retracting/rotating thus ending pre-molding stage.
(2) Injection Stage;
Whilst under the action of the injection cylinder, a screw moves forward pushing plastic stored at various speeds and pressures back towards the front of the feed tube and ultimately into an enclosed mold cavity via runners and gates.
(3) Cooling and Curing;
When injection molding plastic, pressure must remain inside of the mold cavity until solidification has taken place and pressure has dissipated completely in order to stop backflow. Cooling and curing time constitutes the majority of production processes.
