Designing for metal injection moulding

Metal injection moulding (MIM) is a technology that addresses many current manufacturing challenges. OptiMIM utilises the injection moulding process to produce net-shape 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 metal injection moulding requires careful consideration of several factors to ensure project success. Continue reading to explore the distinctive variables incorporated into our award-winning components.

Metal injection moulding design – moulding variables

Designing for metal injection moulding requires careful consideration of various factors. The mould can be a two-plate or three-plate design. When designing the part, it is 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 is also crucial to consider the parting line and parting line witness. Every part has a parting line related to the moulding process. However, it is important to consider 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 mould, so the ejector location must be carefully evaluated in relation to the part's function. In certain instances, sleeve ejection can be used to minimise 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 mould, there is a risk of breakage if the ejection process is not performed correctly. Our engineers carefully evaluate these factors and collaborate with clients before developing new programmes.

For the full list of moulding variables, download OptiMIM's MIM Design webinar!

Metal injection moulding design considerations

After considering moulding variables, we begin looking at metal injection moulding design considerations. 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

The drag effect is simply the result of a part shrinking on the tiles when placed in our sintering ovens, which is inherent to the MIM process. Keep in mind from the MIM 101 webinar that, on average, a MIM part will shrink by about 20 percent. Specific shrink rates depend on the grade of the material, and our engineering team designs the part with shrinkage 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 run or sag. To design for the sag effect, we create a design that counteracts the effects of gravity. We can add special centres or ceramics, which could be individual blocks, or custom-machined 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 seek to add features such as gussets to the part. Again, this would be ideal as long as it does not affect the form, fit or function of your application.

Draft angles

The design characteristics for metal injection moulding are very similar to plastic injection moulding. However, the main exception is the requirement for draft angles. In most cases for metal injection moulding, we do not require any draft angles at all. It is a rare requirement.

The only time we might require a draft angle is if we have a high aspect ratio feature and need to pull the mould, such as a thin wall section or a long core pin. We may introduce a half-degree draft for additional relief, but for the most part, we do not require a draft angle. The reason is that the feedstock contains paraffin wax, which acts as a mould release agent, allowing us to have, for the most part, straight holes in the mould. Very little shrinkage occurs at the moulding stage. For that reason, we do not require a draft angle.

Wall thickness

Another aspect of metal injection moulding that is very similar to plastic injection moulding is uniform wall thickness. An ideal MIM part has similar wall thickness throughout so that we can control shrinkage variability.

Undercuts

At OptiMIM, we design components with a collapsible core, a mould feature that enables us to incorporate undercuts directly into the moulding 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 moulding. Consulting with our engineering team before designing for undercuts is highly recommended.

To learn more about mould and design variables for the metal injection moulding process, we invite you to download our free webinar. We will 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 defence 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 through to full production, let our team of experienced engineers help drive your business forward—contact us today!