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Views: 50 Author: Site Editor Publish Time: 2024-06-27 Origin: Site
The holes, slots, and depressions in plastic parts are essential for assembly, ventilation, and even adding aesthetic appeal to some products. These features are created by the core, the mold's protruding section. During injection molding, a core with excessive height or length endures greater impact from the molten plastic, which can easily cause core displacement and result in significant dimensional errors in the hole features. Here are eight design tips for injection molded holes to enhance part quality and minimize potential deformation.
Holes in plastic parts generally fall into three categories: blind holes, through holes, and stepped holes. Through holes are simpler to produce than blind holes because the cores can be positioned on both sides of the mold, allowing for greater depth. For very deep holes, using a stepped hole technique in the molding process can be a more effective solution.
1.For blind holes, if D<5mm, then h≤2D.
2.For blind holes, if D>5mm, then h≥3D.
3.For through holes, if D<5mm, then h≤4D.
4.For through holes, if D>5mm, then h≤6D.
The bottom thickness of blind holes should be no less than 0.2 times the hole diameter. A thin bottom may lead to a fragile blind hole and surface imperfections on the reverse side. To maintain strength, consider thickening the bottom if it is too thin.
a) The bottom height of blind holes should be at least 0.2x the blind hole diameter, i.e.: h≥0.2D.
b) Consider strengthening the bottom of blind holes.
It is advised to keep a minimum distance of at least 1.5 times the hole diameter or the wall thickness, whichever is greater, between holes and between holes and the edge of the part. Therefore, s≥1.5t or 1.5D should be observed.
Since holes are formed by removing material from the parts, they weaken the overall strength. Consequently, areas with multiple holes are susceptible to weld marks, further compromising the part's strength. It is best to avoid placing too many holes in load-bearing areas of the parts.
To enhance the strength of a hole and prevent deformation, a boss feature can be incorporated around the hole's edge. This design can also be applied to long holes or slots needing additional strength. Typically, reserving at least 0.3-0.5mm of boss ensures a sturdy hole structure and allows sufficient space for other potential elements or coatings.
a) The original hole design is prone to deformation.
b) Add the boss to hole edge to strengthen the part.
When designing holes, it is advisable to avoid complicating the mold structure. To keep the mold design simple and cost-effective, avoid incorporating side holes that are perpendicular to the parting direction. These side holes require additional side actions or side pulls, which add complexity to the mold and increase production costs.
A deep hole is characterized by its long and narrow shape. It is crucial for the direction of the elongated hole to align with the flow of the molten plastic. If the hole is perpendicular to the flow, it can obstruct the plastic's movement, potentially causing defects and inconsistencies in the finished product.
a) The hole direction is perpendicular to the flow direction.
b) The hole direction is consistent with the flow direction.
Vent holes are frequently needed in products to allow for heat dissipation. Typically, round vent holes are preferred as the mold core is cylindrical, simplifying the manufacturing process and keeping mold costs low. On the other hand, hexagonal vent holes are harder to produce and do not always offer superior ventilation. An excessive number of vent holes can weaken the part, so adding ribs or bosses around the vent holes can help increase the strength of the part.
