Comprehensive Guide to Mold Temperature in Injection Molding

Table of Contents

 Mold temperature refers to the temperature of the mold surface which is achieved through the mold temperature control system. The mold temperature needs to be optimized based on the properties of injection molding materials and product requirements. This parameter plays a crucial role in the injection molding process affecting part quality and consistency. 

Proper control and management of mold temperature ensures cost effective production of injection molded parts.The temperature of the mold affects the flow behavior of the molten material and influences the performance of the plastic product. It also determines the cooling rate of the molten material affecting part quality and consistency.

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Injection Mold Cooling System 

Understanding Mold Temperature

We have seen that mold temperature is often referred to as the temperature of the mold cavity surface during the injection molding process. Mold temperature is controlled using heating and cooling systems incorporated into the mold. These systems facilitate proper regulation of the temperature of the mold cavity surfaces to meet part specification. 

Mold temperature depends on various factors such as the plastic material being used, geometry of the part and the desired properties of the final product. Maintaining proper mold temperature is important for achieving consistent part quality, dimensional accuracy and surface finish.

Achieving uniformity and optimal mold surface temperature during the molding process is essential for producing high quality injection molded parts. The mold temperature plays a significant role in ensuring uniformity of cooling and the temperature of the mold. Uniform cooling prevents differential cooling which can lead to uneven shrinkage and warping of the part. 

Optimal temperature control allows for accurate regulation of the surface temperature which is essential for achieving the desired surface finish and texture. In addition it influences the release of the part from the mold by ensuring smooth ejection of the part without deformity.

Significance of Mold Temperature

The mold temperature is a very important parameter in the injection molding process. Below we are going to look at some of the benefits associated with the mold temperature.

Mechanical Properties

Mold temperature affects the crystallinity of the plastic material. Higher mold temperature enhances better molecular alignment and crystallization, leading to enhanced mechanical properties. Mold temperature should be kept moderate to reduce internal stress which eventually results in formation of stress cracks.

Part Quality

The mold temperature affects the dimensional accuracy of plastic material during cooling. Optimal control promotes uniform cooling reducing dimensional variations on the final product. The aesthetic of the final product is also impacted by the mold temperature. 

Higher mold temperature results in a smooth surface finish while lower mold temperature creates a textured finish. Proper control helps achieve the desired surface finish. In addition, consistent mold temperature minimizes the risk of part defects such as sink marks.

Mold Cycle

Molt temperature control promotes uniform cooling throughout the part minimizing cycle time by optimizing the cooling process. It plays a crucial part in solidifying the part and allowing for ejection. 

Uneven mold temperature distribution is a common issue in injection molding that results in various defects in the final products such as inconsistent shrinkage and internal stress.

Inconsistent Shrinkage

Uneven mold temperature distribution can lead to varying cooling rates across the molded part. Some areas cool faster and shrink at a different rate compared to other areas.The differential shrinkage results in dimensional inaccuracies in the final part.

Internal stress

Varying cooling rates due to uneven mold temperature distribution leads to internal stress within the molded part. As the part cools unevenly some parts contract at different rates leading to development of internal stress which affects the mechanical integrity of the part.


Uneven mold temperature distribution can result in part deformation. This occurs when some sections of a part cool rapidly resulting in differential shrinkage and other irregularities. For symmetrical parts, it is essential to maintain consistent mold temperature to ensure uniform cooling.

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Injection Molding Machine (Image Source: Pinterest)

Factors Influencing Mold Temperature Settings

Below are some factors that influence the setting of mold temperature in the injection molding process. The following factors need to be carefully considered and optimized to achieve the desired part quality and enhance productivity.

1. Material Characteristics

When determining the mold temperature, material characteristics play a significant role. Some of these properties are melt temperature, thermal conductivity and surface finish requirement. Different plastic materials have distinct characteristics that influence their optimal mold temperature requirement for injection molding. 

Acrylonitrile Butadiene styrene (ABS) requires a mold temperature range of 50C to 80C. ABS has good flow properties and high mold temperature enhances the material flow into complex geometry and facilitates uniform cooling minimizing shrinkage related defects. 

Polypropylene has a temperature range of 20C to 70C. In PP lower mold temperatures are used to prevent premature solidification and ensure proper flow into intricate features. The mold temperature influences the crystallinity, mechanical properties and aesthetic requirements of different plastics in the injection molding process.

For material like polypropylene (PP) higher mold temperatures promote faster crystallization enhancing the mechanical properties such as strength and stiffness. ABS have lower degrees of crystallinity due to their amorphous nature. Materials like ABS require higher mold temperature to achieve aesthetics requirements of parts.

2. Part Design and Geometry

The geometry of the part being molded affects mold temperature setting. Thicker sections of the part need higher mold temperature to enhance uniform cooling preventing sink marks. Thin sections may require lower mold temperature to improve the flow characteristics. 

Intricate designs in injection molded parts often need higher mold temperature to achieve the desired features effectively. The higher mold temperature improves the flow rate of molten material during injection molding. In addition proper mold temperature control helps in prevention of molding defects such as sink marks and dimensional inaccuracies. 

Through this manufacturers are able to produce high quality parts that meet the requirement for complex application.

Setting the Right Mold Temperature

Setting the right mold temperature is important for achieving high quality injection molded parts. Here are some steps to help you determine the appropriate mold temperature.

Understand Material Requirement

It is important to understand the material specification and requirements for the plastic being used in the injection molding process. Different materials have varying mold temperature ranges based on their specific characteristics.

Consider Part Design and Geometry

Evaluate the design and geometry of the part being molded. Some factors such as wall thickness, intricate features and aesthetics requirements influence mold temperature settings. All these factors need to be put into account to ensure the final product meets the desired requirements.

Review Material Data Sheets

These sheets have recommendations from the supplier on the mold temperature range to use based on the material type. It is important to follow the guidelines given making sure that the material used is processed under optimum injection molding process parameters.

Conduct Mold Trial 

To evaluate different mold temperature settings on part quality, dimensional accuracy and surface finish you need to conduct mold trials. This ensures you meet the desired mold temperature and specification before actual production of parts.

Monitor Cooling Uniformity 

Through the use of temperature sensors you can monitor the temperature distribution across the mold surface during the molding process. This helps identify any deviation in the injection process and the necessary adjustments are made to achieve desired part requirement.

Through following these steps and carefully evaluating material requirement and part design you can set the right mold temperature to ensure high quality injection molded parts.

Effects of Mold Temperature on Injection Molding

In injection molding the mold temperature influences various aspects of the process and quality of the molded parts. Here are some effects of mold temperature on injection molding.

1. Appearance and Surface Finish

Mold temperature influences the crystallinity of plastics. Higher mold temperature results in shinier finishes while on the other hand low temperatures cause dull and improperly filled parts. For instance with ABS low mold temperature results in a less glossy product finish. 

When the mold temperature is too low it can cause the plastic to grip the mold too tightly risking damage during ejection especially if the part has intricate features. At high mold temperature the plastic material composition is close to the surface leading to proper filling and shinier finish. However, excessive high mold temperature can cause the plastic to stick to the mold and produce blemishes on the part.

Finding the optimal temperature is essential for achieving the desired glossiness and surface quality of parts. When this is attained the flow rate balances with the cooling rate to achieve uniform filling of the mold cavity.This results in parts with consistent and aesthetically pleasing surface finish.

2. Dimensional and Mechanical Properties

The mold temperature has a great impact on shrinkage rate, dimensional stability and mechanical properties. High molding temperature can lead to thermal decomposition of the molten plastic resulting in higher shrinkage rate reducing the part size. On the other hand, lower mold temperature leads to reduced shrinkage resulting in a larger part. 

Temperature influences the crystallinity and molecular structure of the plastic. Alower mold temperature can result in invisible weld lines on the plastic part affecting its strength. A higher degree of crystallinity increases the tendency for stress cracking. 

For non crystalline plastics raising the mold temperature can help reduce the internal stress. It is crucial to put this into consideration to ensure dimensional stability of the final products 

Improper design of the cooling system or poor temperature control can lead to insufficient cooling of the plastic part leading to warping or deformation. It is essential to maintain a uniform mold temperature to ensure uniform cooling. 

Optimizing mold temperature setting to achieve a balance between cooling rates and material characteristics is essential for preventing warpage or deformation.

Mold Temperature Control Techniques

Below are some of the commonly used mold temperature control techniques for achieving consistent and precise temperature during injection molding.

Cooling System and Channels

Cooling channels are designed and strategically placed within the mold to facilitate the even distribution of coolant and heat extraction from the mold. This ensures uniform cooling throughout the mold surface.

Baffle Plates and Inserts

They are incorporated into the mold cavity to control coolant flow and optimize temperature distribution. They help direct coolant flow to specific areas of the mold ensuring uniform cooling avoiding temperature variation.

Advanced Control Systems

Automation and monitoring systems can be used to monitor and control mold temperature in real time. Through this deviation from the expected results can be noted and addressed promptly to meet the desired part requirement. 

Proportional integral derivative can be used to adjust coolant flow and temperature accordingly based on feedback from the temperature sensors. These systems offer precise control over the mold temperature.

Heat Exchanger 

These are devices that are used to transfer heat between the coolant and a secondary fluid. Plate heat exchangers are commonly used in injection molding to ensure efficient heat exchange and precise temperature control.they provide flexibility in temperature regulation and optimizing cooling efficiency.

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Injection Process Mold (Image Source: Pinterest)


Accurate mold temperature control is essential in ensuring optimal injection molding processes. Precise control of mold temperature ensures consistency and part quality by minimizing variations in dimensions. This enhances mechanical integrity of the part. It also contribute to cycle time optimization by balancing cooling rates with production requirement increasing production efficiency

Continuous monitoring and adjustments of mold temperature contribute greatly in ensuring manufacturers maintain consistent part quality and efficiency of the injection molding process. Through prioritizing mold temperature control and process optimization measures, manufacturers can deliver high quality products and maximize efficiency.


Steven Paul

Steven Paul

Steven Paul is the Technical Director in TDL, he has more than 15 years experience in Injection molding design.

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