Draft angles are one of the most important parts of mold design. Without draft angles, your part may struggle to get ejected from the mold, causing damage to the part or, worse, the mold itself. So, what are draft angles, and how and when should you incorporate them into your mold design? Here’s what you need to know about draft angles in injection molding.
Draft angles are tapers on part faces that help them eject from the mold properly. They are calculated as a degree measurement from the vertical axis of a mold, and they help account for the fact that injection molded parts shrink as they cool.
Without a draft angle, parts are more likely to stick to the mold and warp or break when they’re removed. Draft angles help reduce friction between the finished part and the side of the mold.
Here are some things to keep in mind when adding draft angles to your mold design.
Draft angles may not seem important when you’re designing a prototype that will be made using a 3D printer or some other process besides injection molding. However, draft can alter the form and fit of a part during assembly and its overall aesthetic, leading to major design overhauls.
Adding draft to your design right from the beginning can save you time, trouble, and money down the road when you move beyond basic prototypes.
There isn’t a single draft angle that is ideal for all injection molded parts. Instead, every part will have it’s own requirements. Generally, parts up to 2” long require 2° of draft. Anything longer than 2” should have an additional degree of draft for each inch of the mold depth. This is just a general rule of thumb, however. In some instances, you may need as much as 5° of draft for even a small part, and in some cases, you may be able to use as little as 1/2° of draft. It can be confusing, but we’ve designed thousands of projects and can help advise on the right draft for your product.
Textured parts are more likely to stick to the mold, so they need more draft to help remove them from the mold in one piece.
In general, using a core-cavity approach to your mold speeds up manufacturing, opens up the mold cavity and core for polishing, and makes the molding process easier compared to using a deep-rib approach.
Every surface of your part has the potential to stick to the mold, so it’s crucial to add draft to every component of your part, and not just the primary walls.
Depending on your mold design, you may need to add draft on both sides of the part rather than just one. For solid cylinders and other components with the parting line in the middle, there are two mold release actions, and each one needs a draft.
While it may seem like a part would look or function better without any draft, there are very few instances where a perfectly straight, zero-degree draft angle is required. Even if you can’t factor in the recommended 1 degree of draft per inch of mold depth, every little bit of draft helps, even if it’s only 1/2°.
At Universal Plastic Mold (UPM) in California, we’ve been a leading manufacturer of large part injection molding for more than 50 years. We can help you create the most efficient mold for your part incorporating draft angle and many other considerations to help you avoid design flaws that could lead to problems.
For more information on how UPM can be your injection molding partner or to request a quote, click here or call 1-888-893-1587.