How much influence does mold temperature have on injection molding?

Mold temperature is the most important variable in injection molding - regardless of the type of plastic being molded, it must be ensured that a basic wetting of the mold surface is formed. A hot mold surface keeps the plastic surface liquid long enough to build pressure inside the cavity.

If the cavity is filled and the cavity pressure can press the soft plastic against the metal before the frozen skin appears to harden, then the cavity surface replication is high. On the other hand, if plastic entering the cavity at low pressure is suspended, no matter how briefly, then its slight contact with the metal can cause staining, sometimes referred to as gate smearing.


For each type of plastic and plastic part, there exists a mold surface temperature limit beyond which one or more undesirable effects can occur (e.g., the component can spill burrs). Higher mold temperatures mean less resistance to flow.

On many injection molding machines, this naturally means faster flow through the sprue, gate and cavity, because the injection flow control valve used does not correct for this change, and faster filling causes higher effective pressure in the sprue and cavity. This can cause overflow burrs.

Since the hotter model does not freeze the plastic that enters the overflow edge area before high pressures are developed, the melt can overflow around the ejector bar and spill into the parting line gap. This indicates the need for good injection rate control, and some modern flow control programmers can indeed do this.

Typically, an increase in mold temperature will reduce the amount of plastic that has a condensation layer in the cavity morning, allowing the molten material to flow more easily within the cavity, resulting in greater part weight and better surface quality. At the same time, the increase in mold temperature will also result in increased part tension strength.

Mold insulation method

If the mold is not insulated, as much heat can easily be lost to the air and the injection molding machine as is lost to the shot cylinder. To insulate the mold from the machine plate and, if possible, insulate the surface of the mold. If considering a hot runner mold, try to reduce the heat exchange between the hot runner section and the cooled injection molded part. This approach will reduce energy loss and preheating time.