5 Rules for Injection Molding
In the modern world, plastics reign supreme. From disposable cutlery to SpaceX helmets, not one person in today's society can say they don't regularly encounter plastic products. Plastics are cheap, easy to work with, and with modern advancements, they are becoming increasingly environmentally sound. But for all their benefits, successful plastic production—particularly through injection molding—requires precision and a deep understanding of the process. Here are five essential rules to help you master injection molding and create top-quality parts.
1. Maintain Uniform Wall Thickness
Consistency is key in injection molding. A uniform wall thickness ensures that the molten plastic flows evenly within the mold, preventing defects like warping, shrinkage, or weak spots. Aim for wall thicknesses between 1.2 mm and 3 mm, depending on the material you choose. This balance helps avoid issues like cooling delays and structural weakness.
2. Incorporate Draft Angles for Easy Ejection
Plastic parts can be stubborn when it comes to mold release. To make the ejection process smooth and avoid damage, you need to add draft angles—slight tapers that allow the part to slide easily out of the mold. A draft angle of 2° to 5° is usually enough to prevent drag marks or ejection difficulties.
3. Avoid Undercuts Whenever Possible
While undercuts might seem like a necessary design feature, they add complexity and cost to the molding process. They require additional mechanisms like side actions or cam systems, which increase tooling costs and the risk of defects. Simplifying designs to avoid undercuts will save time and resources while improving part quality.
4. Optimize Rib and Boss Design for Strength
Instead of thickening walls to improve part strength, use ribs. Ribs can strengthen a structure without requiring excessive material, but it’s crucial to keep them at about 40% to 60% of the wall thickness to prevent sinking or distortion. Bosses, which are raised sections for screws or fasteners, should be reinforced with ribs to avoid issues like voids.
5. Strategic Gate Placement and Mold Design
The placement of gates—the entry points where plastic is injected into the mold—is critical. Position them in thick sections of the part to ensure proper filling and prevent weak areas. Venting is also vital, allowing trapped air to escape and avoiding defects like burn marks or short shots.
By following these rules, you'll not only optimize your parts for functionality but also improve production efficiency and reduce costs.
Sources
Protolabs: Injection Molding Bascis