The Importance of Melt Temperature & Mold Temperature in Plastic Molding and How the Two Work Together

When it comes to plastic molding 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…

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.

*For information on defects caused by improper melt and mold temperatures and how to fix them see: Plastic Injection Molding: Temperature-Induced Defects & Solutions.*

U.S. Plastic Molding Company Specializing in Complex Projects for Mission-Critical Parts

Plastic Molded Concepts is a U.S. plastic molding company that uniquely specializes in molding with engineered resins. We provide all-inclusive plastic molding services, including pre and post-molding services.

We serve a wide range of industries requiring mission-critical parts, including aerospace & defense, automotive, electronics, filtration and more.

Our in-house Master Molders are technically trained and formally certified in plastic mold design, analysis, optimization, troubleshooting and issue resolution relating to complex molding projects.

Contact PMC now for plastic molding consulting assistance, or check out our case studies to see how we handle the most complex molding projects!