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Injection Moulding Process – The Vital Role of Mould Temperature

Jul 21, 2023


Injection Moulding Process and Mould Temperature

Plastics Injection Mould Tool

Injection moulding is a popular technique in manufacturing, enabling the production of a vast array of components with intricate designs and diverse materials. Given the efficiency of the injection moulding process and its adaptability, it is used across numerous sectors, including automotive, electronics, and healthcare.

One of the most important aspects of injection moulding is mould temperature, this factor can significantly impact the quality of the production and the parts that are being produced. Effective temperature control is critical for preventing quality issues such as shrinkage, stresses and warping from developing in the plastic. It is important that a balance between temperature of the cooling fluid and the rate of mould cooling is controlled.

This article delves into the importance of mould temperature in the injection moulding process, exploring its influence on the various stages and the resulting outcomes.

Defining Mould Temperature

Mould temperature refers to the temperature of the mould surface itself. It is a crucial factor during the injection moulding process as it determines how the product heats up and cools down. This temperature fluctuation significantly affects the final look, feel, and quality of the product.

Importance of Mould Temperature Control

The precision of mould temperature control is a vital aspect of the injection moulding process. The goal is to maintain the mould surface temperature within a specific range to ensure optimal conditions for the plastic material to flow, fill the mould cavity, and solidify into the desired shape.

The mould temperature is typically controlled using cooling or heating channels within the mould. These channels carry a coolant, often water, that regulates the mould’s temperature by either removing or adding heat. The design of these channels, including their diameter, number, location, and distance from the mould’s surface, is crucial to the performance of the moulded part.

Mould Temperature and Material Behaviour

The mould temperature plays a significant role in determining the behaviour of the plastic during the injection moulding process. For instance, in amorphous polymers like Acrylonitrile Butadiene Styrene (ABS) and polycarbonate, higher mould temperatures result in lower levels of moulded-in stress. Consequently, the final product has better impact resistance, stress-crack resistance, and fatigue performance.

On the other hand, in semi-crystalline plastics, the mould temperature is a key factor in determining the degree of crystallinity in the polymer. The degree of crystallinity influences many performance parameters, including creep resistance, fatigue resistance, wear resistance, and dimensional stability at elevated temperatures.

Mould Temperature and Injection Pressure

The mould temperature also impacts the injection pressure required during the injection moulding process. The injection pressure is the force that propels the plastic to flow, and it varies depending on the mould temperature. A higher mould temperature reduces the viscosity of the molten plastic, making it easier to flow and fill the mould. Conversely, a lower mould temperature increases the plastic’s viscosity, requiring a higher injection pressure to fill the mould.

Mould Temperature and Injection Time

Another critical parameter influenced by mould temperature is the injection time, which refers to the time taken for the plastic melt to fill the cavity. The injection time must be carefully adjusted according to the mould temperature to ensure that the mould is completely filled before the plastic solidifies. This precision in setting the injection time is crucial for improving the surface quality of the products and reducing dimensional variance.

Importance of Mould Locking Pressure

To resist the injection pressure, it is necessary to use mould locking pressure. The objective is to calculate a suitable value considering the projected area. The projected area of injection moulded parts is the maximum area seen from the direction of the clamping force. The appropriate mould locking pressure helps to maintain the integrity of the mould and ensure that the moulded part accurately represents the design.

Back Pressure and Its Role

Back pressure refers to the pressure that must be produced and exceeded before the screw retreats. Although a high back pressure is beneficial for pigment dispersion and plastic melting, it prolongs the screw’s return time, reduces the length of the fibre in the filled plastic, and increases the stress on the injection moulding machine. Therefore, the back pressure should be as low as possible, generally not exceeding 20% of the injection pressure.

Mould Temperature and the Cooling Process

A significant phase of the injection moulding process influenced by mould temperature is the cooling process. The objective of the cooling process is to lower the temperature of the moulded plastic to the point where it solidifies. Once the plastic solidifies, it can be demoulded. The cooling process needs to be carefully controlled to minimise warpage, twisting, or other shrinkage-related problems.

Mould Temperature and Its Impact on Final Products

The mould temperature significantly affects the final properties of a moulded product. A product cooled too quickly could become brittle and crack under pressure or force. On the other hand, slow cooling could result in a part with lower stress resistance and a higher propensity for warping or distortion. Hence, the mould temperature should be carefully regulated to balance these factors and produce a high-quality moulded part.

Key Takeaways

In conclusion, mould temperature plays a pivotal role in the injection moulding process. It influences the behaviour and transformation of the material, the injection pressure and time, the cooling process, and the final properties of the moulded part. By carefully controlling the mould temperature, manufacturers can optimise the injection moulding process to produce high-quality, durable, and precise moulded parts. Therefore, understanding and managing mould temperature is a critical aspect of successful injection moulding production.

To find out more about the injection moulding process, mould temperature control and mould tool design please contact Benn Simms benn.simms@ledwellplastics.com Managing Director of Ledwell

Injection Moulding

 

Summary
Injection Moulding Process and Mould Temperature
Article Name
Injection Moulding Process and Mould Temperature
Description
Injection moulding is a popular technique in manufacturing, enabling the production of a vast array of components with intricate designs and diverse materials. Given the efficiency of the injection moulding process and its adaptability, it is used across numerous sectors, including automotive, electronics, and healthcare.
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Publisher Name
Ledwell Plastics Ltd
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