Injection Molding Gating and Ejector pins: how do gating and ejection optimize part quality and production efficiency?

How Do Gating and Ejection Optimize Part Quality and Production Efficiency?

Gating and ejector pins are essential components in the injection molding process, allowing plastic resin to enter the mold and molded parts to be effectively ejected. From our experience, there are several methods for gating and ejecting parts, and the optimal locations should be carefully considered before proceeding with tooling.

What Are Tab Gates and How Do They Work?

Tab gates are the most commonly used due to their optimal processing capabilities. They can be adjusted in size as needed, starting tapered down from the runner to the smallest point at the part's surface. This design creates a freeze point between the part and runner, removing heat from the part's surface and minimizing the risk of sink marks. After molding, the tab gate must be manually removed, leaving a gate vestige within 0.005 inches.

Figure 1: The yellow block on the left shows the size and shape of the tab gate, which can be moved to various locations on the part. The molded part on the right displays a rectangular blemish where the gate was placed.

What Are Sub Gates and Their Benefits?

Sub gates typically incorporate a tunnel gate into the side of the part or an ejector pin (post gate). Both styles tend to leave smaller vestiges on the part's exterior. Tunnel gates enter the part externally, midway down its surface, leaving less of a gate vestige. Post gates fill the part through an ejector pin close to the perimeter, leaving no visible vestige on the exterior. However, they may leave a cosmetic shadow on the opposite side due to heat and part thickness, so caution is advised for highly cosmetic parts with texture or high polish.

Why Are Hot Tip Gates Ideal for Balanced Fills?

Hot tip gates minimize part waste from sprue and runner systems, making them ideal for parts requiring balanced fills from the center to the edges. This balance prevents mold shift, a common issue with tab gates. Hot tip gates, with a diameter of about 0.050 inches, are often the most cosmetically appealing and can be hidden in a dimple or around a logo or text.

Figure 2: The yellow cylinder represents the gate location, as shown in an order confirmation. The result is a small raised bump on the surface of the finished part which can be trimmed by hand.

When Should You Use Direct Sprue Gates?

Direct sprue gates are the least cosmetically appealing and are used with specific materials that have a high glass content or for parts requiring secondary machining in the center. They have a large diameter, making manual removal difficult, often necessitating milling to remove the fixture.

Conclusion

When deciding on the gating and ejector pin options for your plastic resin parts, it's crucial to consider the design and production requirements carefully. Tab gates offer excellent processing capabilities, minimizing heat-related defects. Sub gates, including tunnel gates and post gates, can reduce gate vestige on the part's exterior, though post gates may leave a cosmetic shadow. Hot tip gates provide balanced fills and are aesthetically pleasing, while direct sprue gates are suited for specific materials or parts needing secondary machining. By selecting the appropriate gating and ejector pin options, you can optimize the quality and production efficiency of your plastic parts.

Choosing the right gating and ejection methods is not just about meeting immediate design needs; it's about ensuring long-term success and efficiency in your manufacturing process. Proper gating and ejection strategies enhance the structural integrity, aesthetic appeal, and overall performance of your parts. By understanding the benefits and applications of different gating techniques, you can make informed decisions that lead to better product outcomes and more efficient production cycles.