Working on DFM (Design for Manufacturing) projects is a primary focus for our engineers here at Kickr Design. One of the key components of this process is the draft analysis required for injection molded parts.
Draft angles are crucial to the design process, ensuring the part can smoothly release from the mold during production. This usually requires a progression of adjustments and testing different draft angles, sometimes as minimal as 1 to 3 degrees, to achieve the desired result.
A draft is not always added to the part as it is being designed, and it is not needed at all for 3D printing. In some cases, a draft can lead to undesirable effects in the parts. Additionally, adding a draft too early in the design process can create problems later if the part design undergoes significant changes.
Here’s more about what that process looks like, using images of an active Kickr Design project as an example.
Image Color Key:
- Blue indicates a positive draft in the direction of pull.
- Red indicates a negative draft, which ideally turns green if the pull direction is reversed.
- Yellow indicates that a particular area does not meet the draft setting being analyzed.
The Process For Draft Angle Analysis
Based on the general design of the part, we will determine the mold parting line very early in the design process for plastic injection molded parts. The parts are typically oriented parallel to the mold cavity separation, but not always.
Some specific features will require a non-standard orientation to maintain the part’s aesthetic or to accommodate a feature or function. The texture of the part defines how much draft it needs to be smoothly ejected from the mold. A coarse texture will require a greater draft angle.
Three degrees is the industry standard rule of thumb for lightly textured parts, and a draft as minimal as 1/2 degree is often sufficient for small parts. These standards may not always be suitable for larger projects, as they can lead to exterior surface flaws. This represents only a good starting point to show the general draft approach and assessment.
Determining Sufficient Draft Angles
The texture or roughness of the part dictates how much draft the part should have. High gloss parts also require some draft, though less than more coarse products. Draft helps to prevent drag marks and scraping as the parts are ejected from the mold.
For some projects, a zero draft cannot be avoided, though it’s generally not recommended. Zero-draft projects often require side pulls, which can increase the cost of the mold tooling. This change can impact the overall cost of the part, but can be amortized into the run.
Why Care About Drafts In DFM for Injection Molding?
Draft analysis is directly related to manufacturability. Without a functional design that accounts for mold removal, you risk manufacturing challenges later on. Understanding draft analysis boosts the confidence engineers have that a part or product can be easily produced at scale. The ability to consistently manufacture parts and products is key before going to market or entering full-scale production.
If you have an idea for a new product or need an existing part to perform better, we can help. We’re happy to walk you through all the options and help you make informed decisions in custom product development. Reach out here and receive a free cost estimate.