The injection moulding procedure can be automated and it is suitable for manufacturing moulded parts of high dimensional stability and complexity, as well as of different sizes. Injection moulding can be applied for low-viscous liquids (e. g. integral-polyurethane foams) or polymeric melts (e. g. thermoplastic melts).
Before, the main principle of injection was piston injection, and today it is injection moulding with screw. The material enters a heated melting cylinder through a funnel, where it is caught by the screw. The material melts, and gathers at the top of the screw. When enough molten material is collected, the whole screw moves forwards and injects the melt through a nozzle into the mould feed system. At the beginning of cooling the material contracts and the melt continues to remain under post-pressure. Later, the screw returns into the initial position and prepares for the new quantity of material, and the mould opens and the product is demoulded