Injection Molding Draft Angle

Developing plastic injection molded parts is a delicate process, and applying draft to the parts' faces is critical to improving their moldability. Without it, they may end up with poor cosmetic finishes and/or warp due to the plastic cooling.The absence of draft also prevents parts from ejecting from the mold, which can lead to costly and time-consuming repairs.

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Injection Molding Draft Angle Guideline

Injection Molding Draft Angle Guideline

Developing plastic injection molded parts is a delicate process, and applying draft to the parts' faces is critical to improving their moldability. Without it, they may end up with poor cosmetic finishes and/or warp due to the plastic cooling.The absence of draft also prevents parts from ejecting from the mold, which can lead to costly and time-consuming repairs.

Injection Molding Draft Angle Guideline that Can Improve Part Moldability

Draft Early

When designing plastic injection molded parts, ignoring the draft early in the process can result in poor results.Since 3D-printed parts are typically built with a layer-by-layer method, they do not require special considerations for their moldability.Ideally, it should be the case that a prototype should be designed into a part from the very beginning, even though it may not be needed at that time. Doing so can help avoid potential issues and provide a better overall design.

Design for the future instead of the present. Having the draft already integrated can speed up the process.When a part is ready to be manufactured, it can move from 3D printing or machining to injection molding with the draft already integrated.

Generally, when designing a part, try applying as much draft angle as possible. However, this guideline can change depending on the cavity depth and other factors.

● 0.5 degrees on all vertical faces is strongly advised.

● 1 to 2 degrees works very well in most situations.

● 3 degrees is minimum for a shutoff (metal sliding on metal).

● 3 degrees is required for light texture (PM-T1).

● 5 or more degrees is required for heavy texture (PM-T2).

When draft may affect a part's performance, it is possible to design parts with as little as 0.5 degrees of draft.The smallest draft that is possible is discussed with the manufacturer first before going with the broadest draft.

Many injection mold tools are made from aluminum and are commonly used to mill the parts' cavities and core.Having fewer manufactured parts and having a wall thickness of less than 10 millimeters may result in additional draft and wall thickness.The increase in draft and thickness typically won’t affect the parts, and it may actually improve the performance of eventual production mold

Implement a Core-Cavity Approach

Having the draft applied to the outer and inside walls can create issues if it is not applied correctly. Doing so can prevent deep ribs in the mold.A core-cavity approach can help minimize the risk of forming deep ribs in the mold. It can also accelerate the manufacturing process.

Leverage (free) DFM Analysis

One of the most valuable tools that TEAM MFG offers is our free DFM analysis. This tool can be utilized for analyzing 3D models and designing injection molded parts.Within a few hours, we'll provide a quote that highlights the draft angles that are in need of adjustment. This step helps us identify potential issues and prevent future issues.

Before using it, please upload a 3D model of the part and get in touch with one of our experts. We cam offer a complete analysis at team-mfg.com.

Factor in Surface Finish

The draft's effect on a part's surface finish is similar to how it affects the surface finish of a car.The buildup of surface tension created by the plastic cooling during injection molding can prevent the part from loosening during ejection.This tension creates small scratches in the polished surface, and it’s even worse for textured surfaces—if draft is missing.

The texture of a part's walls can vary depending on the method used to apply it. However, if the draft is applied correctly, it can lock the part in place.By applying a draft, a part can move a short distance away from the mold to minimize the risk of scratches and mold drag. On finishes, this should be 3 degrees for light bead-blast finishes and 5 degrees for medium bead-blast finishes.On finishes, TEAM MFG generally requires a minimum 3 degrees of draft for a lighter bead-blast finish and 5 degrees for a medium bead-blast.