How do injection molding manufacturers control mold temperature?

 

During the injection molding process, mold temperature is a critical factor affecting quality. Mold temperature control is crucial. A hot mold surface maintains the surface of the semi-finished product liquid for a long enough period of time to build pressure within the mold cavity. A mold temperature controller maintains a constant temperature of the heat transfer fluid within a range of 1°C to 3°C, depending on the quality requirements of the molded part. So, how do injection molding manufacturers control mold temperature? HUIWEN Injection Molding shares some insights.

If the cavity is filled before the frozen surface hardens, and the cavity pressure presses the soft-injected semi-finished product against the metal, the cavity surface replication rate is very high. On the other hand, if the plastic entering the cavity under low pressure is suspended, even the slightest contact with the metal, even for a short time, can cause stains, sometimes called gate smears.

 

The Purpose of Mold Temperature Control and Its Impact on Molded Parts: In the injection molding process, the primary purpose of mold temperature control is to heat the mold to operating temperature and maintain a constant mold temperature at that operating temperature. This optimizes cycle time and ensures consistent, high-quality molded parts. Mold temperature affects surface quality, flow, shrinkage, injection cycle time, and deformation.

 

Excessive or insufficient mold temperature has different effects on different materials. For thermoplastics, higher mold temperatures generally improve surface quality and flow, but increase cooling time and injection cycle time. Lower mold temperatures reduce shrinkage within the mold but increase shrinkage of the molded part after demolding. For thermosets, higher mold temperatures generally reduce cycle time, which is determined by the time required for part cooling. Furthermore, in plastics processing, higher mold temperatures can also reduce plasticizing time and cycle times.

 

For each plastic and plastic part, mold surface temperature has a limit. Above this limit, one or more adverse effects may occur; for example, the component may flash and burr. Higher mold temperatures reduce flow resistance. In many injection molding machines, this naturally means faster flow through the gate, sprue, and cavity. Because the injection flow control valve used cannot correct for this variation, faster fill rates result in higher effective pressures in the gate and cavity. Generally speaking, increasing mold temperature reduces the plastic condensation layer within the mold cavity, allowing the molten material to flow more easily within the mold cavity, resulting in a heavier part and better surface quality. Furthermore, increasing mold temperature also increases part tensile strength. Many molds, especially those for engineering thermoplastics, operate at relatively high temperatures. If the mold is not insulated, heat loss to the air and the injection molding machine can be as great as heat loss to the injection cylinder. Therefore, the mold should be insulated from the machine plate. If possible, the mold surface should also be insulated. If hot runner molds are being considered, minimize heat exchange between the hot runner components and the cooled, injected part.

 

This concludes our discussion on how injection molding manufacturers control mold temperature. To learn more about precision injection molding, please visit HUIWEN Plastic Injection Mold Factory. With over 20 years of experience in custom precision injection molding, we are a comprehensive service provider integrating mold design, R&D, injection molding, production, and sales. Located in Liaobu, Dongguan, we welcome your interest and welcome a consultation.