Principles for Gate Layout in Injection Molding
The gate is the passage that connects the runner and the cavity in an injection mold. Its location and form significantly affect the quality of the molded part, production efficiency, and mold life. A reasonable gate layout ensures smooth filling of the cavity with the melt, reduces defects, and improves product quality.
1. Ensure a Balanced Melt Flow
The gate should be positioned in a way that promotes the plastic melt filling the entire cavity via the shortest path and at a uniform speed. For multi-cavity molds, it is especially important to ensure that the flow distance from each gate to the furthest point of the cavity is equal. This helps avoid issues such as uneven filling, air traps, or scorching caused by unbalanced flow.
2. Minimize Shear Heat Effects
The gate design should avoid generating excessive shear heat, as this may lead to plastic degradation and negatively impact the mechanical properties and appearance of the molded part. By adjusting the gate's size, shape, and position, the melt flow speed can be controlled to reduce shear forces, thereby maintaining the optimal physical properties of the plastic.
3. Facilitate Removal of Gate Marks
The selection of the gate position should take into account the ease of removing gate marks during subsequent processing. An ideal gate design places the gate mark in a non-critical area of the part, making it easy to remove through trimming, cutting, or ultrasonic methods without affecting the product's final use or appearance.
4. Reduce Stress Concentration
The gate should be avoided in areas of the part where stress concentration is expected, such as sharp edges, thin walls, or areas that will bear high loads. Improper gate placement can lead to cracks or deformation in these areas, negatively impacting the product's structural strength and durability.
5. Consider Mold Venting
The gate layout should coordinate with the mold’s venting system to ensure that gases generated during the melt flow can be smoothly evacuated. Properly positioning venting channels near the gate can improve injection efficiency and product quality.
