Last updated on Mar 27, 2024

How can valve gated molds improve cycle time and part quality in injection molding?

Injection molding is a widely used process for producing plastic parts, but it can also pose some challenges in terms of cycle time and part quality. One way to overcome these challenges is to use valve gated molds, which are molds that have valves to control the flow of molten plastic into the cavities. In this article, you will learn how valve gated molds can improve cycle time and part quality in injection molding, and what factors to consider when choosing them.

1 Benefits of valve gating

Valve gating can offer several advantages for injection molding, such as reducing cycle time, improving part quality, enhancing aesthetic appearance, and increasing design flexibility. This is accomplished by eliminating the need for cooling and trimming the runners, preventing drooling, stringing, and cold slugs, and eliminating gate marks. Additionally, valve gating allows for different gate locations, sizes, and shapes, as well as sequential or simultaneous filling of multiple cavities.

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Anurag Mohanan

Project Manager @Prosohm Projects | Automotive Mold Design | Tooling Expert | NX Expertise | North American tooling standards expertise
Precise control over the injection process and the controlled flow of plastic material facilitated by the valve-gated system helps control the timing and flow rate of material into the mold cavity, which can reduce cooling time which in turn positively impacts cycle time. It also minimizes or even eliminates common injection molding defects such as flow marks, weld lines, and air traps. They also offer better filling of thin-walled parts without causing issues such as over-packaging or flash. Finally, sequential valve gated systems even further help better the process by allowing molding a wider range of part geometries and materials.
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2 Types of valve gates

When it comes to valve gates, there are two main types: hydraulic and pneumatic. Hydraulic valve gates utilize hydraulic cylinders to open and close the valves, while pneumatic valve gates use compressed air. The advantages and disadvantages of each type depend on the application and mold design. For instance, hydraulic valve gates can offer more precise and consistent control, but require more maintenance, space, and cost than pneumatic valve gates. On the other hand, pneumatic valve gates can operate faster and quieter than hydraulic valve gates; however, they have less accuracy and repeatability, and can be impacted by air pressure fluctuations and moisture.

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3 Factors to consider

When choosing valve gated molds, you need to take into account several factors, such as the material properties and processing parameters of the plastic resin, the part geometry and dimensions, the production volume and frequency, and the quality and appearance standards. These factors can influence the flow and solidification of the molten plastic in the mold, the gate location, size, and shape, as well as the filling and cooling behavior of the part. Additionally, they can determine the cost-effectiveness and durability of the valve gated molds, as well as their maintenance and cleaning requirements. Ultimately, they may also vary depending on the end-use and customer expectations of the part.

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4 Best practices

To get the most out of valve gated molds, you need to design the mold with sufficient cooling channels, venting slots, and alignment features to ensure optimal thermal management, air evacuation, and mold alignment. Additionally, it is important to select the appropriate valve gate system based on the material, part, and production specifications. Furthermore, it is necessary to adjust the valve gate timing, speed, and pressure according to the mold and process conditions in order to achieve the desired filling and packing patterns. Lastly, it is essential to monitor and inspect the valve gate performance, wear, and leakage regularly to prevent any issues or defects.

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Adriano Inacio

Assistente Administrativo
During the process of design, they can ensure the structural integrity of the mold and optimize thermal management, air evacuation and proper alignment. This is essential for maximizing the efficiency of the injection molding process, reducing costs and improving part quality. Furthermore, by selecting and adjusting the valve system correctly, they ensure uniform and consistent filling, adapted to material and production specifications. Through regular monitoring and careful inspections, they can detect and correct any potential problems, ensuring optimal mold performance over time.
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5 Common challenges

Valve gated molds can present some common issues, such as valve gate sticking, flashing, or balance. When valve gate sticking occurs, the valve pin may not retract or extend properly due to dirt, damage, or misalignment, leading to incomplete or excessive filling of the cavities. Valve gate flashing is when molten plastic escapes through the gap between the valve pin and the bushing, creating thin films or excess material on the part or mold. Valve gate balance is when molten plastic does not fill the cavities evenly or simultaneously due to unequal or inconsistent valve gate opening and closing. To avoid or solve these problems, troubleshoot and maintain the valve gate system regularly and seek technical support from the mold maker or the valve gate supplier.

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