Designing for Metal Injection Molding

Metal injection molding (MIM) is a technology that addresses many current manufacturing challenges. OptiMIM utilizes the injection molding process to produce net-shaped parts, ideal for high-performance applications demanding exceptional density, strength, and corrosion resistance. These parts consistently outperform industry standards in mechanical and physical properties. Designing for MIM requires careful consideration of several factors to ensure project success. Continue reading to explore the distinctive variables incorporated into our award-winning components.

MIM Molding Variables

Designing for metal injection molding requires careful consideration of various factors. The mold can be a two-plate or three-plate design. When designing the part, it's essential to determine the placement of details and features, such as gating and gate location. In some cases, a single gate or multiple gates may be necessary, depending on the part's geometry.

Parting Lines

It's also crucial to consider the parting line and parting line witness. Every part has a parting line related to the molding process. However, it's important to be mindful of the application and understand how the parting line's location might affect the part's form, fit, or function. Ideally, the parting line should not be on a functional surface.

Ejector Marks

Another important consideration is ejector marks. All parts must be ejected from the mold, so the ejector location must be carefully evaluated in relation to the part's function. In certain instances, sleeve ejection can be used to minimize or eliminate ejector marks.

Wall Features & Wall Thickness

Additional factors to consider include thin wall features, especially those measuring 0.020 inches or less in thickness. When injecting thin features into a mold, there is a risk of breakage if the ejection process is not performed correctly. Our engineers carefully evaluate these factors and collaborate with clients prior to developing new programs.

For the full list of molding variables, download OptiMIM’s MIM Design webinar!

MIM Design Considerations

After we get past molding variables, we start looking at design considerations. And due to the complexity of the MIM process, there are quite a few design features that need to be addressed at each stage.

Drag Effect

g effect which is merely the fact that inherent to the MIM process, a part shrinks on the tiles when they’re placed into our sintering ovens. Keep in mind from the MIM 101 webinar, that on average, a MIM part will shrink about 20 percent. Specific shrink rates depend on the grade of the material and our engineering team designs the part with shrinking factored in.

Sag Effect

The second effect that occurs during the sintering process is the sag effect. During sintering, parts become relatively soft and because of gravity, cantilevered or unsupported features tend to want to run or sag. To design for the sag effect, we create a design that counters the effects of gravity. We can add special centers or ceramics that could be individual blocks, or custom machine ceramics to maintain those unsupported features.

Another option is working with you to modify your design to accommodate this goal without adding any additional costs. We look to add features like gussets on the part. Again, this would be ideal as long as it doesn’t affect your form, fit, or function of your application.

Draft Angles

The design characteristics for metal injection molding are very similar to plastic injection molding. However, the one main exception is the requirement of draft angles. In most cases for metal injection molding, we don’t require any draft angles at all. It’s a rare requirement.

The only time we might require a draft angle is if we have a high aspect ratio feature and we need to pull the mold, such as a thin wall section or a long core pin. We may introduce a half-a-degree draft just for additional relief, but for the most part, we don’t require a draft angle. The reason; we have a paraffin wax in the feedstock and that wax acts as a mold release agent so it allows us to have, for the most part, straight holes in the mold. There’s very little shrinkage that occurs at the molding stage. For that reason, it allows us to not require a draft angle.

Wall Thickness

Another thing about metal injection molding that’s very similar to that of plastic injection molding is uniform wall thickness. An ideal MIM part has similar wall thickness throughout so that we can control the shrinkage variability.

Undercuts

At OptiMIM, we design components with a collapsible core, a mold feature that enables us to incorporate undercuts directly into the molding process, thereby reducing the need for secondary operations and costs. Undercuts are often impractical or challenging with other manufacturing methods, but they are achievable with metal injection molding. Consulting with our engineering team prior to designing for undercuts is highly recommended.

To learn more about mold and design variables for the metal injection molding process, I invite you to download our free webinar. We’ll discuss the above topics in more detail and cover more on:

• Knurling
• Custom feedstock
• Gating
• Secondary operations
• Solving functional or assembly issues
• And more! 

OptiMIM works with many of the world’s most demanding manufacturers—from medical and defense to automotive and consumer electronics. They know we deliver the quality and performance they need to create better products, more consistently, whatever the volume. From the initial design stage all the way through to full production, let our team of experienced engineers help you drive your business forward—contact us today!