Injection moulding quality
Injection moulding quality and the optimisation of the runner system’s design.
Injection moulding is a widely used manufacturing process to produce high-quality plastic components with excellent dimensional accuracy and surface finish. However, the process is highly complex, and any deviation in the material flow can significantly affect the consistency and quality of the final product. Therefore, it is crucial to optimise the runner system’s design and control the material flow to ensure uniform filling and minimise defects. In this article, we will discuss the control of material flow in a runner system to optimise injection moulding quality. This guide is intended for engineers, product designers, mould designers, toolmakers, and mould makers seeking to improve their injection moulding processes and achieve consistent, high-quality results.
1. Importance of Runner System Design
The runner system is a crucial component in the injection moulding process and the injection moulding quality. A well-designed runner system can ensure consistent material flow and minimise defects. It is essential to consider factors such as gate types, gate locations, and runner size when designing the runner system. A small gate can lead to high injection pressure and poor part quality but does allow for a faster cycle time and the potential for self-trimming gates such as sub gates which reduce part cost. A large gate can increase cycle time and slow down production and will also need a separate trimming operation. Therefore, selecting the right gate type and location is critical for achieving optimal injection moulding quality.
2. The Role of Material Properties
Another essential factor that can affect material flow is the material properties. It is crucial to understand the viscosity and flow rate of the material being injected to optimise the runner system design. The material’s viscosity can impact the gate size, while a low flow rate can increase dwell time and affect the melt’s temperature. Therefore, it is essential to choose the right material and adjust the runner system design accordingly to achieve optimal injection moulding quality. The type of material is also a consideration a Crystaline or semi-crystalline material will behave very differently to an amorphous material, and this will often impact the gate and runner design and type chosen for the application.
3. Simulation Software
Simulation software can aid in designing a runner system by predicting the flow of the material within the mould. It allows designers to simulate various scenarios and optimise design parameters before creating the final mould. By simulating the injection moulding process, designers can predict potential issues such as weld lines, air traps, and flow hesitation. This approach helps in reducing the iterations required during the mould design process and optimising the runner system design for optimum injection moulding quality.
4. Sustainable Runner System Design
In recent years, there has been a growing interest in sustainable manufacturing practices and reducing waste in the injection moulding process. Runner systems can contribute to material waste, as they are often discarded after each cycle. One solution is to design a cold runner system, where the runners are not ejected with the part and can be re-processed and fed back into the machine to use in subsequent cycles. Another option is to create a hot runner system, where the runner material is kept melted and reused in the next cycle, reducing waste and energy consumption. Sustainable runner system design not only benefits the environment but can also lead to cost savings and increased efficiency.
5. Runner Balancing
Balancing the runner system is crucial for achieving consistent material flow and preventing defects in the final product. This stage is often overlooked by toolmakers and imbalanced runners can lead to variations in filling time and pressure, causing issues such as short shots, sink and warpage. Balancing the runner system involves adjusting the runner length, diameter, and placement to ensure equal pressure and material flow to each cavity. This process can be time-consuming but is essential for achieving optimal injection moulding quality.
6. Design for Manufacturability
Design for manufacturability (DFM) is a concept that involves designing parts and moulds that are optimised for the injection moulding process. By considering DFM principles, designers can ensure that the part is mouldable, with appropriate wall thickness, draft angles, and gating locations. These factors can impact the runner system design and ultimately affect the part’s quality. Designing for manufacturability can reduce lead times, decrease costs, and improve quality control in the injection moulding process.
In summary, controlling material flow in a runner system is crucial to achieving optimal injection moulding quality. A well-designed runner system, consideration of material properties, simulation software and using well-established practices to ensure the runner is designed properly, can significantly impact the final product’s consistency and quality. Optimising the injection moulding process requires a thorough understanding of the runner system and its role in the overall process. By following these guidelines, engineers, product designers, mould designers, toolmakers, and mould makers can improve their injection moulding processes and achieve consistent, high-quality results.
In conclusion, there are various factors to consider when designing a runner system for injection moulding. optimising the runner system design can result in consistent material flow, reduced defects, and improved product quality. Using simulation software and designing for sustainability and manufacturability can also improve the injection moulding process’s efficiency and reduce waste. Balancing of the runner system is also crucial for ensuring optimal quality and preventing downtime. By following these guidelines, manufacturers can achieve consistent, high-quality results in their injection moulding processes.
For more information about runner system design and injection moulding quality, please contact Benn Simms, benn.simms@ledwellplastics.com Managing Director of Ledwell
