Additive Manufacturing Strategies

Multi-Material 3D Printing: 3D Print Me a Sandwich (Structure)

ST Medical Devices

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There are these developments that we all feel are coming (YouTube, second nozzles, inexpensive desktop SLA) and there are those that are head-splitting-ly obvious when announced (Dirk van der Kooij’s mounting of an extrusion head on a robot arm). Things that are unexpectedly ingenious or impossible (LIFT). Things that are so obvious that they take a special kind of genius to make them real (Z Unlimited). Thanks to a recent paper from researchers at the University of Alberta, I’ve discovered a new category: things that are so obvious that they are dismissed and therefore underdeveloped.

A paper by David Moises Baca Lopez and Rafiq Ahmad of the University of Alberta points to a way of making multiple material 3D prints very accessible indeed. By letting go of the idea of true functionally gradient parts, where every voxel can be determined and designed for effect, the team has a super simple way of letting us all experiment with multiple materials. They suggest simply extruding sandwiched structures of ABS, HIPS, and PLA to obtain different properties.

The University of Alberta paper resulted in some interesting findings with PLA, ABS, and HIPS. They stated that, “In general, these three types of specimens showed higher ultimate strength and elastic modulus when fabricated with the sandwich configuration compared to a single material.” Also, “Among these specimens, the combination of PLA-ABS-PLA had the best tensile strength and Young’s modulus with means of 44.40 and 1364.57 MPa, respectively. ” What’s more, “it was observed that combining these two materials as a sandwich structure where PLA was printed as the outer skins and ABS as the inner core of the specimen provided a significant performance combining their properties.”

The team concluded that, “the use of the sandwich structure applied to conventional 3D printing materials gain applicability in generating functional parts that can withstand tensile loading for longer periods over single homogenous materials by integrating the properties of two different materials in the same part. It can also provide higher elongation at break, which can absorb energy and therefore give long-term use before failing. The advantages of multi-material and sandwich structures methods are suitable to implement and able to achieve the requirements of various applications using low-cost materials.”

This is already possible with dual extruders and also possible on one printer with one nozzle and some patience. In support materials, this has been done and there has been experimentation in this area already. But the paper from these researchers really made me think that this super simple approach deserves a lot more attention than it has been getting. Precisely because it is so accessible and so under-explored, this is something that you at home or work could be and, perhaps, should be working on.

3D printed gradient and multi-material parts have been a constant research topic over the years. By being able to 3D print different densities or materials at every, voxel gradient components, materials or processes can produce a single part on a machine in a single material that can be flexible in some areas, hard in others and soft in another. The possibilities in design and engineering beg belief. Stratasys-Objet has been able to jet gradient parts for many years now. People are looking at Arcam electron beam melting, powder bed fusion, and other technologies to do the same. Aerosint allows you to 3D print gradients, as does Fabrisonic and others.

In this post, I go into functionally graded materials, why it has been so difficult to do, and why it’s a perennial next big thing, rather than a big thing. Complex, expensive, and difficult to get your head around—how can we make functionally gradient materials more accessible and experiment with them?

We can all print different materials atop of another at home right now. Indeed, many already do it with supports. At the same time, maybe quite a few have tried at one point to play around with PLA and ABS together to get them to stick and work. But, we haven’t fundamentally looked, tried, and tested this enough to extract the real benefits.

By mixing sandwich layers of prints together, we can develop and obtain a plethora of different properties in parts—much more so than the hereto-limited exploration of using “polypropylene as a soft layer and ABS as a hard one” has brought to some applications.

I really believe that a thorough extension and a much deeper look into the sandwich layering of print materials will get us an incredible return on our invested time. And this is before we experiment with different infill percentages and infill structures in different layers. Of course, what we can also do is add fiber and fiber matts in between parts to reinforce them and change properties. To me, this area is one of the most exciting in desktop FDM at the moment and is super under-explored.

I know that we already use some TPU and other flexible materials printed onto parts to make them flex or seal. But, given the material library that we now have at our disposal in FDM, there should be many more results, combinations, and properties that we can still uncover and use. I think that this is a completely overlooked area whereby a lot more higher performance 3D printed parts can be made than are currently possible. Whats more these parts can be made using current 3D printers and current machines. This sandwich structuring needs to be explored more by research institutes, companies and users at home. So please make yourself a sandwich.

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