Evaluating and understanding fill speed profiles is an important aspect of injection molding.
Polymer materials can flow by heating them to their melting range. Every polymer has a melt and mold temperature range, and within that range the polymers flow and can be injected into a mold.
Molten polymer is injected into the mold by moving the screw of the molding machine forward. The screw acts as a plunger and pushes the molten material into the cavity. The injection pressure has to overcome the material’s resistance to flow and the resistance to fill through the runner’s gates and cavity. The required pressure can vary during the fill process but it increases as the mold cavity is filled.
In general, the lower the melt and mold temperature and the thinner the flow path, the higher the required injection pressure. Conversely, the higher the melt and mold temperature and thicker the flow path, the lower the required injection pressure.
The goal is to achieve uniform temperature and pressure distribution throughout the cavity. When this is achieved, packing, cooling, shrinkage, and warpage behaviors can be optimized.
Molding a high-quality part starts with evaluating the best possible fill speed profile.