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How does the mold temperature control system work in injection molding?

2026/08/19 By le zhan

How does the mold temperature control system work in injection molding

A stable mold temperature is one of the most critical conditions in the injection molding process. It directly affects the filling of molten plastic into the cavity, heat transfer to the mold, the solidification and shrinkage processes, and the dimensional accuracy and surface quality of the final product. Therefore, a mold temperature control system is not merely an auxiliary device for heating or cooling the mold, but rather a thermal management system; It continuously removes process heat, supplements heat when necessary, and ensures that the mold remains within the set operating temperature range throughout the entire production process.

In actual injection molding production, it operates through a controlled circulation loop. The principle is quite simple:

Heat the mold when the temperature is too low → Maintain circulation at the target temperature → Remove excess heat when the mold temperature is too high → Continuously repeat the above cycle.

Simply put, the mold temperature controller heats or cools a heat-transfer medium—such as water or oil—and then uses a pump to circulate it through the mold’s internal runners. As the medium circulates, it exchanges heat with the mold.

What exactly is the role of a mold temperature control system in injection molding?

The mold temperature control system regulates the thermal state of the injection mold by circulating a controlled heat transfer medium through the mold’s dedicated runners.

Its primary purpose is not merely to make the mold “hot” or “cold,” but to maintain the mold temperature at a stable and repeatable level to meet the requirements of specific materials, mold designs, and production processes. This is its most critical function!

During the injection molding process, the thermal load constantly changes. The mold may also lose heat to the surrounding environment. Without active temperature control, the mold temperature would fluctuate continuously. The mold temperature controller is specifically designed to compensate for these variations.

The most common thermal control loop for a mold temperature controller consists of five basic steps:

  1. Heating or cooling: The controller adjusts the heat transfer medium to the target temperature.
  2. Pumping: A circulation pump delivers the medium from the controller to the mold.
  3. Heat exchange: The medium flows through machined or integrated runners inside the mold, exchanging heat with the mold steel.
  4. Return: After absorbing or releasing heat, the medium flows back to the controller.
  5. Feedback and Correction: Sensors monitor the temperature, and the controller adjusts the heating or cooling output based on the deviation between the measured value and the setpoint.

This forms a closed-loop temperature-control process rather than a simple one-time heating operation.

What exactly is the role of a mold temperature control system in injection molding

How does the mold temperature control system exchange heat with the mold?

The principle of heat exchange is simple: the heat transfer medium transfers thermal energy between the temperature controller and the mold.

Taking the mold heating process as an example, the specific process is as follows:

The temperature controller heats the medium, and a pump delivers it into the mold’s temperature-controlled flow channels. The higher-temperature medium transfers heat to the cooler mold steel. As the mold temperature rises, the temperature difference between the medium and the mold gradually decreases. When the mold reaches the target temperature, the temperature controller reduces the heating power.

The cooling process is the reverse. The medium absorbs heat from the mold and carries it back to the temperature controller, where the system dissipates it through the cooling circuit.

This process can be summarized as:

Temperature Controller → Heat Transfer Fluid → Mold Runners → Mold → Return Fluid → Temperature Controller

So, we can conclude that a mold temperature controller’s circulation efficiency depends on more than just heater power. Factors such as flow rate, heat transfer fluid properties, runner design, pressure, temperature differences, and circulation uniformity also play an important role.

How Is the Set Temperature Maintained?

A mold temperature controller does not simply turn the heater on and off based on a single temperature reading; instead, it continuously compares the target temperature with the actual process temperature.

For example:

Set temperature = 80°C
Actual temperature = 76°C

The controller detects a 4°C temperature difference and increases the heating output.

As the actual temperature approaches 80°C, the controller gradually reduces the heating demand. If the mold temperature subsequently rises to 82°C due to additional heat from the molten plastic, the controller switches to cooling.

This feedback process is typically implemented using PID control. The goal is to prevent the system temperature from repeatedly exceeding or falling below the target value.

How Is the Set Temperature Maintained

How does the mold temperature control system interact with the injection molding cycle?

Mold temperature control extends throughout the entire injection molding cycle.

  • During the injection phase, molten plastic enters the mold and transfers a significant amount of heat to the cavity surfaces.
  • During the holding phase, the plastic remains under pressure, and additional material may enter the cavity; heat exchange between the polymer and the mold continues.
  • During the cooling phase, the mold dissipates heat from the polymer, allowing the part to reach sufficient rigidity for demolding.
  • During the mold opening and demolding phases, the mold is temporarily exposed to the surrounding environment, which constitutes another stage of heat loss.

Throughout all of the above phases, the mold temperature controller operates continuously to ensure the mold remains at the required temperature during each production cycle.

How does a water-type mold temperature controller work in injection molding?

A water-type mold temperature controller uses water as the heat transfer medium. Its operating principle can be summarized as follows:

Water tank or circulation loop → Pump → Heater/cooling circuit → Mold → Return flow → Temperature sensing → Control and regulation

When the mold needs heating, an electric heater raises the water temperature. A circulation pump delivers hot water to the mold runners, where it transfers heat to the mold before returning to the water-type mold temperature controller. When the mold temperature is too high, the temperature controller activates the cooling circuit or the corresponding cooling function to remove excess heat from the circulating water. The cooled medium then flows back to the mold. The primary advantage of water-type mold temperature controllers is their highly efficient heat-transfer capability, making them suitable for a wide range of standard and precision injection molding processes.

How does a water-type mold temperature controller work in injection molding

Heating Principle of Water-Type Mold Temperature Controllers

Electric heaters transfer energy to the circulating water. Because water has a high heat capacity, it can transport a large amount of thermal energy between the temperature controller and the mold.

The basic process is as follows:

Electrical energy → Heater → Water → Mold

When the water temperature is below the set target, the heating power increases; as the temperature approaches the target, the PID control algorithm reduces the heating demand.

When the mold temperature or circulating water temperature rises above the setpoint, the system immediately starts the cooling process. Depending on the system configuration, the controller activates the cooling function via a separate cooling circuit or a cooling valve. The process circulating water transfers heat to the cooling medium, which then carries the heat out of the system.

We can intuitively understand this process:

Mold heat → Circulating water → Heat exchanger/cooling circuit → External cooling water → Environment

The cooling rate of a water-type mold temperature controller depends on the temperature difference, flow rate, mold design, cooling channel efficiency, and the capacity of the cooling source. Therefore, water-type mold temperature controllers are particularly suitable for processes that require fast thermal response and continuous control within the operating range of a water-type system.

How Do Oil-Type Mold Temperature Controller Work in Injection Molding

How Do Oil-Type Mold Temperature Controller Work in Injection Molding?

Oil-type mold temperature controllers follow the same basic closed-loop control principle but use heat-transfer oil instead of water as the heat-transfer medium.

The process works as follows:

Heat transfer oil is heated → Circulates → Heat exchange with the mold → Heat transfer oil returns → Temperature is measured → Control adjustment.

When the system needs to heat the process, the electric heater raises the temperature of the heat transfer oil. A high-temperature circulation pump delivers the heat transfer oil to the mold runners; the hot oil transfers heat to the mold and then returns to the mold temperature controller.

When the mold temperature is too high, the system uses the oil circulation and cooling mechanisms to remove excess heat.

The primary difference between water-type and thermal oil systems lies in their operating temperature ranges.

Water-type systems work well for medium-temperature applications. However, when the required mold or process temperature exceeds the practical operating range of a water-based system, a thermal oil system provides greater advantages.

Temperature Control Method for Oil-Type Mold Temperature Controller

The circulation of the heat transfer oil must remain stable, as it serves as the carrier of thermal energy. Oil-type mold temperature controllers monitor the circulating oil’s temperature and adjust the heater’s output power based on the difference between the actual temperature and the setpoint. When cooling is required, the system removes heat from the oil circuit.

Final takeaway: How Does a Mold Temperature Control System Work?

The operating principle of a mold temperature control system in injection molding involves continuously circulating a temperature-controlled heat transfer medium inside the mold while monitoring the actual temperature and comparing it to the set temperature, thereby automatically adjusting the heating or cooling mode to maintain the desired temperature conditions.

Water-type mold temperature controllers use water as the heat transfer medium and are typically suitable for standard and precision molding applications within their specified temperature range.

Oil-type mold temperature controllers use heat-transfer oil and are designed for applications requiring higher temperatures. They provide an effective temperature control solution for situations where water-type systems are no longer suitable.

Therefore, the role of a mold temperature controller goes beyond simply heating or cooling the mold. Its core purpose is to achieve predictable and repeatable thermal control, thereby ensuring that the injection molding process delivers stable filling, controlled cooling, consistent dimensional accuracy, reliable surface quality, and repeatable production cycles.

 

 

 

 

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