When it comes to Injection plastic mold manufacturing, proper melt temperature and mold temperature are paramount for ensuring your part’s final properties meet its performance requirements.

Below, our in-house Master Molders cover the various aspects of melt temperature, mold temperature, and how the two can work together during the plastic molding development process in order to produce a higher quality part at a lower cost.

Melt Temperature
In plastic molding, melt temperature must be carefully monitored throughout the molding process as temperature (and thus resin properties) can change as the resin works its way through the process.

Melt Temperature Impacts…
How does temperature affect a mold? Depending on the type of resin used, melt temperature can have varying impacts on properties, such as:

Resin Viscosity
Resin’s Final Molecular Weight in the Molded Part
Melt Temperature Considerations
When determining melt temperature you must consider:

Engineered Resin Chosen
Residence Time
Screw and Barrel Design
Mechanical Work Imparted to the Material
Final Property Requirements
Melt Temperature Issues
Melt Temperature is Inconsistent
Melt Temperature is not Homogenous
Example of Melt Temperature Effects on a Part
When parts that are molded in polypropylene have a melt temperature of 400 F vs 480 F, they have better impact resistance, have a shorter mold cycle time, and consume less energy during the plastic molding process.

*Example provided by Plastics Technology

Mold Temperature
In plastic molding, improper mold temperature can result in defects, such as mold warpage, sink marks and jetting.

Mold Temperature Impacts…
Depending on the type of resin used, mold temperature can impact properties, such as:

Molded-in Stress
Creep Resistance
Fatigue Resistance
Wear Resistance
Molecular Weight
Dimensional Stability
Mold Temperature Issues
Mold Temperature is Inconsistent
Mold Temperature Non-Uniform to Part Cavity Proximity
Example of Mold Temperature Effects on a Part
When parts that are molded in Polycarbonate have a higher mold temperature they will have lower levels of molded-in stress, which results in improved resistance to stress cracking, impact and fatigue.

Plastic Molding Melt Temperature AND Mold Temperature Considerations
Understanding how melt temperature and mold temperature work together to produce final part properties is essential.

In most cases a lower melt temperature combined with a higher mold temperature will produce optimal performance.

However, many button-pushing plastic injection molders do not have the technical expertise to implement and monitor these two critical aspects of plastic molding. Instead they see high melt temperature as the only solution for reducing resin viscosity.

Higher Melt Temperatures can Cause…
Unfortunately, higher melt temperatures can result in:

Resin Degradation
Longer Cooling Cycles
Increased Energy Consumption
Now, these plastic molders are forced to reduce the mold temperature in order to regain the lost productivity caused by long cooling cycles necessitated by higher melt temperatures. This high melt temperature to low mold temperature ratio often results in compromised part properties and an unstable part.

Instead, if they combined a lower melt temperature with a higher mold temperature they would likely create a part with better final properties and shorter cycle time, which would improve part quality and reduce costs.

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