For those of us who are new to injection molding, we at NICE Rapid thought that we would describe some important aspects of the molding process and some of the terms that you might have heard being discussed. This week we will be talking about ‘gates’ and their different types.
Types and Importance of Gates
What are gates, why are they important and where should we put them? The term ‘gate’ is used to describe the area of the mold into which the liquid resin flows. This is something that will be visible on the final product, so it is important to ensure that it is either in an inconspicuous place or is sited where it is of little detriment to the cosmetics of the part. Obviously, in parts that are used in car manufacturing or something similar, this is dependent on where the part will be located. A part visible to the consumer will have to be produced so that the gate is hidden, whereas if a part is located within the bodywork and is not visible to the consumer, this will not be of importance. The location of the gate also impacts on the structural integrity of the finished part and this is of paramount concern if the part is safety critical or of high cost.
Below is a description of the types of gates you may find on an injection molded part:
- Sprue: This gate is easy to locate, but there is a high stress area around the gate and it is required to be manually trimmed, adding time and cost to the production process. It is suitable for large parts and because the gate can be easily placed, it is able to be located where there is less cosmetic impact on the part itself.
- Side: This type of gate is easier to locate and remove than a Sprue Gate, but still cannot be trimmed automatically, however, it can be unsightly and this should be taken into consideration with cosmetically delicate parts. It can be used for many types of part, but is unsittable for barrel-shaped designs due to its location.
- Point: This gate is able to be located in many positions and can be removed from the part automatically. There is lower stress around the gate itself and it leaves a smaller footprint on removal than the other types. Downsides are that the gate is fairly complicated to incorporate into the initial design and it requires a high injection pressure to achieve the best results.
Gates Placement Considerations
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Cosmetic Impact: The gate’s location is crucial in determining the final appearance of the molded part. Since the gate leaves a visible mark on the product, it is important to place it in an area that is either hidden or cosmetically insignificant. For consumer-facing parts, such as those used in automotive exteriors, the gate should be placed where it won’t be visible, while for internal or non-visible parts, this may not be as important.
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Structural Integrity: Gate placement directly influences the part’s structural strength. Improperly placed gates can create weak spots, particularly in high-stress areas. This is especially important for parts that are safety-critical or have high-cost implications. The placement needs to ensure uniform resin flow to avoid defects such as warping or inconsistent material distribution.
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Flow Path and Resin Distribution: The gate should be positioned to optimize the flow of the molten resin into the mold, ensuring even distribution and minimizing flow lines or air traps. Poor gate placement can result in incomplete filling, uneven pressure, or voids, affecting the quality and durability of the final part.
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Ease of Removal: The type of gate and its location determine how easily it can be removed after molding. Some gates, like the Sprue Gate, require manual trimming, adding to the production time and cost. Gates that can be trimmed automatically, such as Point Gates, are preferable in designs where efficiency and speed are essential.
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Part Design and Geometry: The shape and design of the part also affect where the gate can be placed. For example, side gates may not be suitable for barrel-shaped parts. The gate must be placed in a way that complements the design, allowing for smooth resin flow without causing defects or stress points.