Composite 3D Printing 101 | Anisoprint

Composite 3D Printing 101

Composite 3D printing is a relatively new trend in additive manufacturing. It is an innovative technology that allows creating 3D printed parts with enhanced parameters of strength, stiffness, and durability due to fiber component added to plastics.

There are two ways to add fiber to plastics: fill with chopped fiber or reinforce with continuous strands,  here we describe continuous fiber reinforcement specifically, as chopped fibre does not contribute to the properties equally and does not add to the quality and strength as much.

As part of the overview (101 stands for novice course), we will study the benefits of composites compared to both plastics and metals, look inside the existing composite 3D printing technologies, investigate the nowadays market and dwell on Anisoprinting.

Continuous carbon fiber reinforcement enhances mechanical properties of printed parts unlocking a wide range of applications in aerospace, automotive, aviation, and medical industries, and we will make a special case on it.

What is a composite?

Basically, a composite is a combination of two or more materials with dissimilar properties, provided these properties work together to make a single advanced material. When we speak about continuous fiber 3D printing, a composite means particularly fiber tows impregnated and covered by plastics. Typically these are a base polymer, referred to as a matrix, and reinforcing fiber of any type (carbon, basalt, glass, etc) bound together to produce a particular set of desirable resulting characteristics.

Whether filled with chopped or reinforced with continuous fibers, such materials feature improved parameters of stiffness and strength compared to pure plastics, though exhibit different anisotropic behavior. The interest in composite fiber 3D printing is accounted for by the fact that stiffness and strength parameters are by an order of magnitude greater than those of non-reinforced plastic, by contrast, chopped fiber filling at best only doubles this parameter for the resulting part.

Benefits of Composite 3D Printing

There exists a variety of methods to manufacture composite products, though many of them are costly, time-consuming, and labor-intensive. Unlike traditional ways with a manual layup of the plies inside molds, composite 3D printing opens up an opportunity to automate the process. Once the parameters are set and the model is sliced (prepared for printing), it does all the work without any further effort.

Fast prototyping and cost-saving

Here we approach the most prominent advantage of Composite 3D Printing — the speed of prototyping. Using CAD for creating a part one goes from the design straight to manufacturing without the need to start a whole production line and adjust the models on the go, without any extra costs or a waste of material. This is critical for SMEs, as in small production runs of customizable parts it will drop the price for the end-user.

Composite 3D Printing Technologies on the Market

By now the technology market is only emerging. Even though progress accelerates rapidly, there is only a handful of companies with ready solutions for composite 3D printing.

Most products feature a head with one or two nozzles, the head may be designed for fused filament fabrication, FFF (suitable for filaments from pure or carbon filled plastic), or have special construction for continuous fiber printing where it needs to operate with long fibers too. The head moves over the platform to build up the part layer by layer. FFF is used interchangeably with FDM (fused deposition modeling).

Continuous carbon fiber 3D printing technologies are collectively called continuous filament fabrication (CFF).

There is a couple of methods where dry fiber is impregnated with a thermoplastic either while it is transported into the print head or inside it — in-situ and inline impregnation respectively.

There are two more methods that make use of already prepared towpreg for extrusion, one as is, the other — in combination with a laser that heats the deposition area and a roller that presses the  fiber in.

Another technology recently was introduced by Anisoprint: CFC.

Composite fiber coextrusion assumes binding together the thermoset impregnated fiber and a plastic matrix at the moment of printing, it allows customizing the feed speed thus varying fiber volume ratio. Options for customization are numerous in terms of part complexity, fiber fraction, and choice of the matrix material. CFC allows any type of polymer as a matrix, for instance, PETG, ABS, PC, PLA, and nylon, resulting in thermal or chemical resistance, impact, wear, fatigue resistance, or particular friction properties depending on the goal.

Anisoprinting

CFC technology recently launched in production offers the most flexibility for composite manufacturing. The core of Anisoprinting technology is adding a plastic to a towpreg at the time of printing. The towpreg here is carbon fiber pre-impregnated with a thermoset. There are several reasons for that; it is cheap, it is the industry standard, and most importantly it does not allow pores between the single fibers in a bundle due to low viscosity providing good adhesion — due to capillary effect, or wicking, it fills in all the spaces between fibrillas quickly and fully. This is a central issue for all composite products since pores as we see below are notorious for making the material brittle and give rise to a whole number of complex problems. 

The process is called coextrusion as the towpreg and the plastic filament (the matrix) are heated, mixed within the printing head, and extruded simultaneously during the printing process. Thermoset cannot melt, which makes the core fiber string stable and set within the plastic. 

 

This sort of composite is referred to as bi-matrix, as the resulting part will contain two matrix materials: a thermoset and a thermoplastic. One works as impregnation, the other as a binder between the layers. In our case, the second plastic can be any, the choice of this plastic will be a marker of other properties (in addition to mechanical) for the future part, one can opt for non-flammable plastic, or different colors, resistant to heat or a chemical impart. 

 

Together with it we can, as we have a separate supply of fiber and plastic, at each point locally change the volume of fiber and plastic. We can feed less plastic, so increase the fiber volume, we can feed more plastic and it decreases. This way we can control the degree of anisotropy and, more importantly, print lattice structures with fiber intersections within a single layer. That is, we can stack reinforcing fibers on top of each other, at any angle we need, within each layer individually. At the same time, the thickness of the layer at the intersection point is not growing; only the volume fraction of fibers in this very place changes.

Applications of Composite 3D Printing

Three major features, flexibility, weight, and strength pave the way to a number of industrial uses where speed counts.

The first and most important parameter, light weight, makes composite parts a reliable substitution for metal ones in aircraft engineering. A lot of internal equipment like wall brackets, seat supports, and other constructional elements produce a substantial surplus mass when in bulk, thus adding extra expenditure and fuel consumption. Replaced by composite, such elements save 38% of the weight.

Original part: 400 g.
Anisoprinted part: 250 g.

Naturally, cost reduction drives innovation to electric vehicle production industries, from electric cars to gyrocopters, robotics technology, and belt systems.
Another application stems from effortless customization, where individual design is paramount. Here extra strong and light equipment tailored specifically for the user becomes affordable and easy to produce. Sportbikes parts design, wearable medical equipment, prototyping for narrow R&D areas, etc. have a broader horizon with 3D printed composites.

Let us discuss a sportbike suspension part. The composite rocker was printed on the Composer 3D printer, it exhibits the same performance as the metal one adding 40% material/cost savings, and is 35% lighter at the same time.
It is impacted by flexural tension during the exploitation. Traditionally produced with CNC technology, the guaranteed strength results in a high cost of manufacturing. Continuous fiber 3D printing removes this problem and reduces weight in addition.
Original part: 500g, €380
Anisoprinted part: 250g, €250

Another example of importance of ergonomic shape is designing blades that convert mechanical motion of a liquid or gas into kinetic energy. Applications are numerous: impellers, turbines, turbo pump units, fans, etc. There is a whole bunch of parameters to change and adjust — cross-section, thickness, inclination angle, even minor changes in shape are capable of changing performance in a significant way. Each iteration takes developing and creating a new metal stamp that gives shape to the new blade, here we offer an advantage in speed and design flexibility. Faster and cheaper development and testing plus operation efficiency of the blades sum up and lead to both immediate and long-term benefits. Using composite 3D printing makes the tool 8 times lighter allowing to use cheaper equipment and saving power spent for operation. It sums up with a 40% cost reduction on material in comparison to metal parts of the same strength and performance under heavy-duty working conditions. Moreover, printing tools on the Composer 3D printer let one control the production process, showing the exact TAT for a given part before the start.
Original part: 31 kg, €200
Anisoprinted part: 4 kg, €700

Another example of importance of ergonomic shape is designing blades that convert mechanical motion of a liquid or gas into kinetic energy. Applications are numerous: impellers, turbines, turbo pump units, fans, etc. There is a whole bunch of parameters to change and adjust — cross-section, thickness, inclination angle, even minor changes in shape are capable of changing performance in a significant way. Each iteration takes developing and creating a new metal stamp that gives shape to the new blade, here we offer an advantage in speed and design flexibility. Faster and cheaper development and testing plus operation efficiency of the blades sum up and lead to both immediate and long-term benefits. Using composite 3D printing makes the tool 8 times lighter allowing to use cheaper equipment and saving power spent for operation. It sums up with a 40% cost reduction on material in comparison to metal parts of the same strength and performance under heavy-duty working conditions. Moreover, printing tools on the Composer 3D printer let one control the production process, showing the exact TAT for a given part before the start.
Original part: 31 kg, €200
Anisoprinted part: 4 kg, €700

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