The gate is an opening in the mold that allows molten plastic to flow into the mold cavity. It connects the part to the feed system. There are many different types of gates to choose from, and many different locations on the part where the gate can be placed. This video explores how the type of gate that is chosen and the gate’s placement affect the quality of the parts you design, as well as the importance of communicating your ideas with the toolmaker.
Mold base types and degating methods are important considerations when choosing a gate design. Two-plate molds allow for gating on the edge of the part, whereas three-plate molds allow for gating on the top surface of the part. Gate placement will influence the part’s aesthetics, shrinkage, dimensional stability, and performance due to the way the part packs out. It will also determine weld line locations. Because there is little to no mixing of polymer melt at weld line locations, they cause a localized decrease in mechanical properties, as well as a cosmetic defect. Another consideration is having a balanced fill pattern. This is preferred because it will generally lead to lower injection pressure requirements, and more consistent molecular or fiber orientation, which will help reduce the potential for warpage.
These factors allow you to determine which gating option will result in the highest quality part. If these ideas are clearly communicated with the toolmaker, it will help them build a mold that meets your specifications. By understanding the basics of gate design and placement, you can design higher quality, more robust plastic parts.
Gate locations can be compared with mold-filling simulation software, such as Moldflow. Click here to learn about Moldflow analysis and manufacturing support at The Madison Group.
Want to learn more check out How Does Gate Size Affect Part Dimensions and Performance and Introduction to Hot and Cold Runners for Injection Molded Parts.