Defining additive composite manufacturing and its integration with traditional processes provides new solutions and a way forward. #continuousfiberAM #feature #specialreport

This composite drive shaft demonstrator, made by combining 3D printing and tape-wound LCC, uses 3D printed load introduction elements at the end fittings and spiral longitudinal ribs to the other end. Laser-assisted tape winding combines these elements to form an in-situ reinforced continuous carbon fiber reinforced exterior. Different materials were tested, including PC, PA and LM PAEK, short fiber reinforced printer filament and UD carbon fiber reinforced tape. Photo source, all images: Technical University of Munich, Chairman of Carbon Composites (LCC)

In October 2020, CW reported on the use of continuous fibers for 3D printing of composite materials, and provided an overview of the technologies being developed and the classification of the processes used. The latter was contributed by the research assistant and expert of additive manufacturing at the Technical University of Munich and the chairman of carbon composites (Lehrstuhl für Carbon Composites, or LCC, Munich, Germany).

CW is again working with LCC, but this time focusing on the larger area of ​​Additive Manufacturing (ACM), especially the process developed at the interface between traditional composite materials and Additive Manufacturing (AM). "We are seeing more and more technologies going beyond our continuous fiber 3D printing classification, but combining automated composite manufacturing with AM and providing new solutions that have been impossible so far," LCC researcher Thomas Wettemann Pointed out.

Evolving prospects: Combining continuous fiber ACM with traditional composite material processes Although powder-based additive manufacturing (ACM) processes exist, they lack the performance of continuous fiber reinforced materials. For the latter, material extrusion is the main process, but now it is combined with a highly automated placement process to open up new markets and provide solutions that point to new manufacturing paradigms. Note: The icon in the figure shows the selected supplier and is not a complete list. Image credit: Alexander Matschinski, Technical University of Munich, Chairman of Carbon Composites (LCC)

LCC itself blurs the boundaries between traditional processes and 3D printing by combining automatic fiber placement (AFP) and filament winding (FW) with extrusion-based ACM (see "Future Composite Manufacturing-AFP and Additives manufacture"). "We have also switched from traditional thermoplastic extrusion to 3D printing using thermoset plastics by using the technology we developed for resin transfer molding [RTM] combined with ultrasonic technology," said Dr. Swen Zaremba, deputy director of LCC. At the same time, LCC is working hard to formulate ACM standards and improve its materials and processes.

Note that there are broader prospects for ACM, including chopped fiber-filled filaments extruded using Fused Deposition Modeling (FDM), powder fiber materials processed using selective laser sintering (SLS), and the use of magnetically oriented fillers and numbers Highly customized parts for light processing (DLP), the latter developed by Fortify (Boston, MA, USA). These processes do produce composite parts and open up new markets and applications, but this discussion will stay in the field of continuous fiber reinforcement.

"We usually discuss this issue first and the motivation for developing these new technologies," Zaremba said. As Wettemann explained in his SAMPE speech in January 2019, the motivation is that cost-effective production beyond mass production—including mass production—can also save resources, minimize or eliminate waste, and be environmentally friendly. And climate friendly. "It also provides a way to fully digitize the composite material process chain," he added. "This is the first step in the path of decades of change."

The key components of LCC's ACM definition include:

"ACM concentrates the long processing chain that used to be more or less at one point, a kind of manufacturing in a box," Zaremba said. Therefore, Matschinski adds, “You are processing the material and giving the part shape inside the box without using forming tools.” Both parties agree that the “box” may be a very large ACM unit, such as Electroimpact (Mukil, Washington, U.S. Theo) SCRAM unit launched in 2020. "ACM may also be used outside of a single box," Zaremba said. "For example, our job is to add local reinforcement and smaller functions to larger AFP components."

However, Wettemann points out, “We now see examples of the entire composite material process chain contained in an automated production line or cell, but this is not what we define as ACM.” In contrast, through in-situ consolidation (ISC) Thermoplastic AFP head combined with fuse manufacturing [FFF, another term for FDM] 3D print head, SCRAM unit can process material and give shape without tools. "For us, this in-situ consolidation using AFP is really the beginning of ACM in LCC, because you create a cured/consolidated composite when you perform placement or laying," Zaremba said.

This brings us to the second key point of LCC's definition of ACM. “Before, you always had a global integration step. Ideally, the material handling and history of the part is the same as when it is molded in an autoclave, oven, heating tool, or press,” Zaremba explains. "With ACM, we perform this heat treatment and reinforcement locally when manufacturing parts."

Wettemann pointed out that ISC provides an entry point from automated composite manufacturing into the AM world, "but it also brings real challenges to materials and processing, because this partial material treatment is also a regular heat treatment. Please note, In the beginning, we only used injection molding materials for 3D printing. But then we realized that it was not really optimized for FFF printing. Therefore, the company began to modify the materials of its printing system to cope with the repeated heating and cooling of the resin. And the required speed and the need to bond the layers together and avoid warping. The latter is also the reason why more and more companies are seeking to adopt continuous fibers."

Hybrid solutions This drive shaft demonstrator shows how LCC uses Additive Composite Manufacturing (ACM) to create new solutions for continuous fiber composites.

However, the integration of continuous fibers can also cause problems. "This is one of the reasons we were attracted to ACM," Zaremba said. "The 3D printing process promised a lot of results, but the results did not provide the type of quality we expected for structural or aerospace applications. We can see the gap between advanced composite materials using continuous fibers and what AM technology can provide. The goal of LCC is to bring these worlds together, realize the promised potential, and combine technology to realize new solutions."

LCC has seen many such new solutions, such as the Additive Molding process developed by Arris Composites (Berkeley, California, USA) and the Fusion Bonding cell developed by 9T Labs (Zurich, Switzerland) for 3D printing, both of which have a high-volume process. "These processes do not give the shape of the final part in the additive process, but use a mold and the second step in that mold," Matschinski said. "So, this does not fit our definition of ACM. However, both provide interesting solutions that combine traditional composite manufacturing and AM technology."

"9T Labs is definitely using a 3D printer," Wettemann pointed out, "but it is necessary to create a prefab, and then process it in the digital molding process to create a new lightweight thermoplastic composite component, and to solve the previously unavailable composite technology. Market.” Here, he mentioned 9T Labs’ goal of replacing metals in parts where injection molding cannot provide sufficient performance. "At LCC, we also studied how to introduce endless fibers into injection molding, but it is difficult to accurately position endless fibers during the injection molding process." In contrast, 9T Labs' technology seems to provide an easy-to-implement method for high-performance parts. Production method.

Arris Composites has a different approach, but achieves some similar goals, although the goal is to increase the volume of the part by an order of magnitude. Riley Reese, co-founder and chief technology officer of Arris Composites, said: "We can not only achieve mass production of continuous fiber components, but also increase the versatility of unlocking dynamic component integration." The component of the component becomes one part, while increasing the strength and the radio transparency and other characteristics. We are cost-competitive in compression molding-for example, SMC [sheet molding compound]-but with continuous fibers."

Arris Composites describes its process as "additive molding." Image source: Arris Composites

Going back to LCC's definition of ACM, the third key component recognizes the dispute between using and not using molding tools for manufacturing. "The direct method is where the final shape is obtained from the printed matter-I never had the tools," Wetterman said. "The advantage is that there is no need for tool manufacturing at all. As long as we have molds, we will talk about indirect processes, or we are talking about more traditional composite manufacturing, and then additive manufacturing technology will help."

Wettemann pointed out that this hybrid approach can help resolve factors such as integration and processing, which can increase the cost and time of traditional composite manufacturing. “We have seen the development of the Digital Manufacturing and Design Center of Singapore University of Technology and Mikrosam [Macedonia Prilep] between 2015 and 2017, where automated robots were developed to produce advanced composite parts in AFP-type processes, but without Tools," he explained. "Therefore, this is moving in the direction of ACM, because these two methods have successfully achieved digital manufacturing in free space without tools, but further development is still needed. Reducing the need for tools is the key, because This also provides us with new possibilities for manufacturing composite parts and the types of parts that can be manufactured." For example, the very organic load path output by topology optimization and generative design software does pursue the efficiency of biological structures such as bones and trees, but They are difficult to manufacture from continuous fibers.

LCC researcher Patrick Consul said: "In direct part manufacturing, we see the same as you show in the landscape, the lines become blurred, and we are moving to a more hybrid manufacturing method" (see "3D printing CFRP for RTM molds for flaperons, exoskeletons, etc."). Earlier this year, his team completed the first experiment of a hybrid method that combines material extrusion and directed energy deposition [DED], using a laser-based prototype machine for pre-reinforced laminates and laminates without a heating chamber. Print on very large 3D prints. "We are also committed to combining ACM with milling and AFP, which are very suitable because they both rely on complex tool paths," he said. "The conversion between them has become quite simple, you don't need too much additional training." Therefore, the process chain is shortened, digitized and simplified.

Thermoset ACM LCC is working to compress the process chain of traditional composite materials using thermoset (TS) AFP to one point. The technology developed for RTM will be compatible with the use of ultrasound and the extrusion of cheap fast-curing epoxy resin materials developed for automotive applications. Combine.

LCC also promotes a hybrid approach by combining technologies developed for RTM and 3D printing. "The result is similar to fast curing, but we want to get rid of UV curable resins because they are a bit too expensive when you want to make larger parts," Zaremba explains. "Instead, we used a new type of ultrasonic mixing technology developed for RTM and now apply it to a typical extruder with cheap, fast curing epoxy resin developed for the automotive industry."

Matschinski further explained this technique: “When we deposit impregnated fibers during the printing process, we use ultrasonic vibration to mix and cure epoxy resin almost immediately.” This is in contrast to the DLR composite structure and What is the difference between the ultrasound used in the Adaptive System Research Institute (see "Reducing the Cost of Continuous Fiber 3D Printing Materials")? Matschinski explained: “DLR is using ultrasonic vibration to improve the penetration of the thermoplastic matrix into the expanded fibers to create continuous fiber-reinforced 3D printer filaments, which are then extruded using traditional materials for printing. We are using ultrasound to harden the continuous fibers to enhance the thermosetting properties. Silk."

“For example, organizations such as Arris Composites, 9T Labs, and our team at LCC are interesting because their roots and employees come from the composite world and the AM world,” Wettemann said. "They are working together to create new technologies that can now help us escape from a future economy that may be constrained by resources and growth to fight the climate crisis. They provide the path to the solutions we need."

Tool manufacturers and original equipment manufacturers are adopting additive manufacturing for customized quick tools, masters and fixtures.

Airbus subsidiary CTC GmbH Stade has researched Orbital Composites' patented coaxial extrusion process and has made progress in terms of speed, scale, materials and versatility, as its goal is very large structures.

The additive manufacturing startup MarkForged aims to achieve this goal and is already marketing the system.

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