Jetting in Injection Molding: Causes And Solutions

1. Introduction

Injection molding is a widely used manufacturing process to produce various plastic parts and components. However, it's not without its challenges. One common issue that can mar the quality of molded products is jetting. In this blog, we'll delve into the causes of jetting in injection molding and explore effective solutions to overcome this defect.

2. What is Jetting?

Jetting is a surface defect in plastic injection molding. It occurs when molten plastic fails to adhere properly to the mold surface, resulting in visible lines or streaks on the finished product. These lines are often referred to as "jetting lines."

3. What are the Causes of Jetting in injection molding?

3.1 The gate is small

The size of the gate plays a crucial role in preventing jetting in injection molding. A small gate restricts the flow of molten plastic into the mold cavity. As a result, the plastic has limited space to flow and adhere to the mold surface, leading to jetting defects in injection molding.

3.2 Injection speed is fast

The speed at which molten plastic is injected into the mold can significantly affect the occurrence of jetting. High injection speeds cause the plastic to rush into the mold cavity too quickly. This rapid flow doesn't allow the plastic to properly adhere to the mold surface, resulting in jetting lines.

3.3 High viscosity / low fluidity

The viscosity of the plastic material used in injection molding is a key factor. High-viscosity plastics have low fluidity, making it challenging for them to flow and fill the mold cavity properly. When plastic has difficulty flowing, it may form jetting lines due to inadequate mold surface coverage.

3.4 Low holding pressure

Holding pressure is essential in keeping the molten plastic in the mold cavity to prevent jetting. If the applied holding pressure is too low, the plastic may not be adequately contained within the mold, allowing it to prematurely solidify and create jetting defects.

4. The solution to avoid Jetting in injection molding

4.1 Try to increase the gate size

Increasing the gate size is a practical solution to mitigate jetting. A larger gate allows for a more controlled and less restrictive flow of molten plastic into the mold cavity. This enables better adherence of the plastic to the mold surface, reducing or eliminating jetting defects.

4.2 Try to change the gate location

Altering the gate location can have a significant impact on preventing jetting. By moving the gate from a central position to a corner or edge of the part, you can encourage the plastic to flow more smoothly and uniformly. This change in gate location can promote better filling of the mold cavity, minimizing the chances of jetting.

4.3 Try to reduce the injection speed

Slowing down the injection speed is an effective strategy to counteract jetting. A reduced injection speed allows the plastic to enter the mold cavity more gradually, improving its ability to adhere to the mold surface. This measured flow reduces the likelihood of jetting lines forming.

4.4 Reduce resin viscosity

Lowering the viscosity of the plastic resin can enhance its fluidity and reduce the risk of jetting. Using materials with lower viscosity or adjusting processing temperatures to decrease viscosity can help promote smoother and more complete mold filling. This change in resin characteristics can lead to a better-quality finished product.

4.5 Check the holding pressure

Ensuring proper holding pressure is crucial in addressing jetting. Increasing the holding pressure can help maintain the molten plastic within the mold cavity until it solidifies. Adequate pressure ensures that the plastic flows uniformly and avoids premature solidification, reducing jetting defects.

5. Conclusion

Jetting injection molding defects can compromise the quality and appearance of molded plastic parts. By understanding the causes and implementing the right solutions, plasic injection molding manufacturers can achieve better results. Increasing gate size, adjusting injection speed, managing resin viscosity, and monitoring holding pressure are all effective ways to combat jetting and ensure a smoother, higher-quality injection molding process.