Design Injection Molding

Design spotlight: Adapting from additive to injection molding

By June 3, 2020
IM Face Shields Hero scaled

As the COVID-19 pandemic hit the United States, our team at Fast Radius quickly pivoted a significant portion of our additive manufacturing capabilities to producing face shields. To date, we’ve made and shipped thousands of additively manufactured face shields to protect frontline workers from the coronavirus. The shield is reusable, extremely durable, easy to assemble, and comfortable, but demand has far exceeded our additive production capacity.

Face shields black and white render
The Fast Radius additively manufactured face shield

To make our product available to more people, we decided to shift production to injection molding. Injection molding makes the shield more accessible on two counts; it allows us to produce a much higher volume, and injection molding brings the cost of the product down significantly because of lower material costs and speedier manufacturing.

In our work with customers, we often use additive technology to manufacture parts while ramping to injection molding production. Our own story is a strong example of how to use digital manufacturing technology to redesign an additive product for injection molding.

Rapid design iteration with simulation tools

We needed to make significant modifications to the additive design of the shield “halo” (or headband) to make it suitable for injection molding, while also maintaining its performance. We knew that the stiffness had to be optimized to reduce thin steel conditions that could cause tool damage during molding operations. Since we knew the stiffness of the current halo worked well, we simulated the fluctual displacement of the additive halo and used that displacement as a goal for the stiffness of the injection molded design.

To understand the elements contributing to stiffness, we used Finite Element Analysis (FEA) to pinpoint the design variables that produced better results. We relied on the simulation package within Autodesk 360, a tool that we use for a variety of purposes, including design, analysis, and simulation. We tested both the crown and ribbing patterns on the front of the outer ring. While the ribbing added some stiffness, we found that adding height to the crown was a more effective way to minimize displacement.

Top down view of halo
FEA focused on the outer ring of the halo
Halo Crown
This image indicates the crown on the halo’s outer ring

Adding height to the crown, however, could create poor tool conditions (thin tool steel) between the outer and middle rings. The slot where the shield itself is inserted is very thin — as thin as one to two millimeters; the taller the sections in the crown, the more thin steel would be needed for the tool, making it more likely that the tool steel would get damaged during molding operation.

We needed to find the optimal crown height that would reduce thin steel while preserving stiffness in the outer ring of the halo. To determine this, we ran 16 simulations, adjusting the design slightly to improve performance each time. At this stage in the design process, we had already met our goal and had many designs with similar or better displacement than the additive halo.

Rapid prototyping with HP Multi Jet Fusion (MJF)

From the concepts we simulated, we chose three to print with HP MJF, since that’s the technology we used to produce our original additive halo. Normally, it would take three days for an MJF part to cool enough to be usable, but our team of manufacturing engineers packed the build in a way that allowed us to have our parts in hand the next day.

Concepts printed
We printed three concept designs

The operations team at the Fast Radius Chicago factory wore the three concept halos and compared them to the original additively manufactured version to compare comfort and ease of assembly. Concept 10 (see above, third design) accepted the shield the easiest, but they suggested several modifications to improve comfort and make assembly easier. The resulting design (see below) was used to produce the injection molding tooling that will make the next version of our face shield halo.

Final halo design
Final halo design

Ultimately, switching from additive manufacturing to injection molding will make the halo much more accessible to those who need it. We were able to cut the price by 55%.

When we started making additive halos, we were meeting a demand we had no way to predict. When it became clear we could make our product more accessible, we modified our additive design for injection molding and got a tool into production in only three days.

Our team worked around the clock to get this important product to market. We accomplished this remarkable timeline thanks in large part to simulation software, digital manufacturing, and our agile working model. This pandemic has forced us to become more flexible with product development cycles, a trend that we think will continue on long past the pandemic.

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