What if we told you that, in some cases, you can actually make a part stronger by printing it in multiple, separate pieces?

A few of my Markforged colleagues and I recently published a research paper in the Rapid Prototyping Journal, where we tested how additively manufactured co-part assemblies perform in tandem with our Continuous Fiber Reinforcement (CFR) process.

On their own, CFR and co-part assemblies lead to substantial strength improvements compared to equivalent parts. Together, they make parts even stronger — and in some cases are able to hold up to 6.4x the ultimate load of an equivalent Onyx part without CFR or a strategic co-part assembly.

Interested in learning how to maximize part strength with these techniques? This might not always be necessary — but if you have an edge case or need additional strength for a heavy load, this is for you.

I’ll explain the CFR process, why co-part assemblies are used to improve Z-strength, then walk you through a real world example of how to properly design, print, put together, and test a co-part assembly.

Printers and materials matter!

When it comes to the strength of parts, choosing the right 3D printers and materials makes all the difference. While many 3D printers can print common plastics such as PLA, ABS, and Nylon, the resulting parts are not suitable for many industrial uses that demand qualities such as strength, stiffness, heat and chemical resistance, plus durability.

While a number of 3D printers can print in stronger carbon fiber, Markforged 3D printers in particular can achieve even greater strength improvements. Markforged composite printers combine a base material discontinuously reinforced with carbon fiber (Onyx) with reinforcing continuous fibers laid through the part.

Continuous Fiber Reinforcement (CFR)

Continuous Fiber Reinforcement (CFR) is a proprietary process that allows Markforged printers to produce impressively strong composite parts. Reinforcing fiber materials include Carbon Fiber, Fiberglass, HSHT (High-Strength High-Temperature) Fiberglass, and Kevlar®.

How strong is CFR?

  • Adding proprietary CFR allows a composite part to hold up to 2.5x the ultimate load of an equivalent Onyx part without CFR. Onyx with CFR has a yield strength up to 800 MPa in the printed plane — nearly a 20x improvement from Nylon.
  • Combining CFR with a co-part strength design optimization allows parts to hold up to 6.4x the ultimate load of an equivalent Onyx part without CFR.

Markforged Eiger software lets you customize placement of continuous fibers within your part. There are basic and advanced strategies for reinforcing parts with fiber that you can learn more about here.

Why co-part assembly?

A huge advantage of 3D printing is the ability to design and print your part as a single unit. So, why would you want to go through the trouble of splitting your part into separate components, printing in multiple jobs, and assembling into the final part.

The answer is anisotropy. With fused filament fabrication printing, or FFF for short, parts are fabricated layer by layer. This means the X (left to right) and Y axes (front and back) will inherently have more strength than the Z axis (up and down).

This is primarily due to the bonds of thermoplastic materials within layers being stronger than the bonds between each different layer. While the orientation of a part can help mitigate some of the effects of anisotropy, a single part often has distinct features that demand a conflicting orientation to print properly.

So, for any part that falls into this scenario, we can break it into two or more parts and print them separately in their optimal orientations to minimize anisotropy — ultimately ending up with a stronger, more durable part.

Co-part assembly example: mounting plate

This is a mounting plate designed to secure a tent pole to the ground. The plate is secured to the ground through four holes, while the tent pole is secured to this boss through this hole. This is a common case where the direction of the load is perpendicular to the plane that the part is mounted to.

If we printed this as a single part horizontally, the bottom plate would be strong — however, the part would fail in the plane with the lowest cross-sectional area when enough load is applied.

Read the article in full here.