Robotic Fiber Printing and Voxel-Based Simulation Open New Doors in Composite Design

In structure and shape, composites behave more like fabric than metal. Composite parts are not chiseled or cut from blocks. Rather, they are built by stacking up layers of composite materials. Unlike traditional metal, composite materials are anisotropic. They do not stretch, bend, and break uniformly in all directions. Their warping behavior depends on how the fibers are woven at the microscopic level. Therefore, it is possible to engineer composite materials that are stronger in one direction (Z direction, for example) for a specific purpose. All these characteristics offer new possibilities and applications in automotive and aerospace, especially in the identifying ways to reduce weight.

But these complexities also make them difficult to simulate and analyze. Their nonuniform distortion tests the tried-and-true stress calculation methods employed to solve classic FEA (finite element analysis) scenarios. Some leading simulation software vendors have developed tools to address them. In this article, we explore a new frontier—the intersection of 3D-printed composites and algorithm-based optimization, better known as generative design.

Printing Composites

This year, Arris Composites grabbed the Red Dot Design Concept 2020 award with its Additive Molding Carbon Fiber Truss. The company says the product “doubles the specific stiffness of a steel I-beam while adding material benefits like corrosion resistance and the opportunity for functional integration into the structure. It is also 100% recyclable and highly scalable in size and quantity thanks to Arris’ innovative Additive Molding manufacturing process.”

For manufacturing and fabrication, Arris looks to Nature for inspiration. “The alignment of wood grains through a tree limb provides the highest structural strength and stiffness,” it explains in the announcement. “Similarly, Additive Molding allows designers to align glass and carbon fibers along the load paths within a complex 3-dimensional part.”

Additive Manufacturing (AM) is now an established term, but Additive Molding is a relatively new term. The use of additive, which suggests layering, contradicts the idea of molding, which describes forming a part by pouring liquid materials into hollow molds.

Founded in 2015, the startup Continuous Composites has been developing a new large-scale 3D printing method. “The process starts with a continuous dry fiber that is impregnated in-situ with a snap-curing thermosetting resin deposited by the end effector. The end effector is moved by a motion platform, driven by Continuous Composites’ proprietary toolpath generation software,” the company explains. 

The company employs automated robotic arms to bind the fiber and resin instantly upon extrusion. Finding the existing terms inadequate, it too came up with a new phrase to describe its process: Continuous Fiber 3D Printing (CF3D).

Yet another new term came from the Washington-based Electroimpact, which specializes in factory automation and tooling. The company said it has “integrated an in-situ out-of-autoclave thermoplastic AFP (automatic fiber placement) process and an advanced FFF (fused filament fabrication) 3D printing process into a unified Scalable Composite Robotic Additive Manufacturing (SCRAM) system.”

With SCRAM, Electroimpact expects to be able to produce large structures with complex contours, such as aerodynamic surfaces and flow-directing ducts. Its 6-axis robotic arm can deposit fiber in different orientations, allowing users to tailor the process to the specific applications.

Typical powder-bed 3D printers’ print chambers in the current desktop and production-grade 3D printers range from the size of a shoe box to an oven. But emerging applications from Arris Composites, Continuous Composites, Electroimpact, and others suggest future 3D-printed parts will grow larger, breaking out of the confines of the print chambers.

Furthermore, it shows the convergence of 3D printing with composites, changing the layer-like materials into a plastic-like medium that can be dripped from a print nozzle.

Generative Design and Large Format Printing

In an Autodesk University 2019 presentation titled “Advanced Manufacturing with Robotic Continuous Fiber Printing Technology,” Dominique Muller, an Autodesk research engineer, said, “Our research group developed a tool called Mimic. It’s a plug-in for Maya. You can download it for free. It uses the same concept as creating a movie—you can predefine the movement of the robot … you can define the robot’s toolpath, download it onto the robot, and the robot will follow the same path. It’s the same toolpath as animation, but we are translating it into robotic code.”

The company has undertaken a number of projects with its partner Moi to test what it calls Continuous Fiber Manufacturing (CFM). The outcome of the collaboration includes a BMX bike frame printed in glass fiber composite, resulting in a 40% weight reduction; and MAMBO, a 21-inch boat made of fiberglass. 

Mimic is an open-source Maya plug-in available from Github. The company also offers Autodesk Netfab software for AM design and manufacturing. 

A New Way to See

In visualization, the complexity of what can be 3D printed is testing the limits of the current mesh- and polygon-based 3D visualization technologies. The method describes 3D models made of primitive shapes as a series of knitted surfaces, but it starts to falter when describing 3D-printable lattice structures and membrane-like networks due to the inordinate amount of surfaces it needs to support.

Dyndrite, which offers a GPU-accelerated geometry kernel for AM hardware and software, is hoping to address it with its Voxel Application Program Interface (API). A voxel describes a 3D volumetric unit (as opposed to a 2D surface), thus many feel it is a better way to describe complex 3D models—the kind many hope to explore with AM. 

“This is the first voxel manipulation tool hyper-tuned for the accuracy and resolution needed in modern scientific and engineering workflows, including digital manufacturing,” said Harshil Goel, CEO and founder, Dyndrite at the Dyndrite Day, a virtual event held in October. “With the increasing sophistication of CT scanners, MRIs, and additive manufacturing print heads, developers require more powerful tools to realize the full capabilities and resolution of their hardware. We look forward to working with our partners and customers to put this power into the hands of their end-users.”

Dyndrite Day presenters include Renishaw, Ansys, and GPU maker NVIDIA, among others. In his presentation at the event, Mike Geyer, Industry Marketing Manager, NVIDIA, said, “Generative Design has a big opportunity to become useful. We’re seeing interesting stuff moving out of the physical, mechanical realm of Generative into more fluid-based applications … One area where we see a lot of benefits to applying the GPU is in CAE (computer-aided engineering) for simulation and analysis. Some have done a great job of leveraging the GPU to accelerate CFD.” Altair’s ulTraFluid X, which uses a voxel-based system, is one such software title.

The convergence of design optimization and AM is a new frontier, with many simulation software vendors paying close attention to new possibilities. While commercial products are few, R&D projects and Beta programs are accelerating, as attested by the speakers at the Dyndrite Day gathering.

Can voxel-based optimization offer new tools to automatically generate composite shapes ideally suited to be printed? Or help manufacturing engineers automatically generate composite printing strategies based on the desired shape? These may soon be answered.

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