Batch Size 1 in the patient's best interest

Prof. Jürgen Fleischer and Jörg Dittus team up with ARBURG to implement additive manufacturing of fiber-reinforced plastics with continuous fibers. This new production technology could make it easier to customize prostheses in the future.

The first attempts to replace missing body parts with prosthetic devices and thus maintain functionality date back to the Etruscans in antiquity. They used gold wires to attach lost teeth in order to bridge disruptive interdental gaps. Thanks to advances in medical technology, much more complex and functional prostheses and implants are no longer a rarity: such devices replace body parts, like prosthetic legs, or independently take over vital functions within the body, like heart valve implants.

To date, steel and titanium have been the materials of choice when it comes to the load-bearing capacity and biocompatibility of artificial substitutes. Due to the demand for cost-effective production, metallic prostheses are usually produced in large quantities in a mass-compatible geometry. Customized products are associated with considerable additional costs.

"Additive manufacturing is a technological development that is comparatively recent. Being able to help shape such a new field and thus impact the production technology of tomorrow is a great motivation for me"

Jörg Dittus

Researchers Prof. Jürgen Fleischer and Jörg Dittus from KIT's wbk Institute of Production Science, supported by specialists from the mechanical engineering company ARBURG GmbH + Co KG, are using a groundbreaking additive manufacturing technique for fiber-reinforced plastics (FRPs) to create the best conditions for customized medical prostheses and medical products made of printable fiber composites."Additively manufactured fiber-reinforced plastics offer advantages in terms of flexibility and customization due to their material properties. Compared to metal components, we achieve high weight-specific strength and performance," explains Dittus, whose doctoral research focuses on the additive manufacturing of fiber composite components for lightweight construction. Using the proprietary ARBURG Plastic Freeforming (APF) process and a fibre feed unit specially developed for fiber reinforcement, the project partners at the KIT ARBURG Innovation Center at have succeeded in additively manufacturing FRP parts from plastic with so-called continuous fibers made of glass or carbon - 3D printing for fiber-reinforced plastic parts, so to speak.

"The continuous fibers are implemented directly into the component with the help of a fiber feed unit during the layer-by-layer application of the plastic. Until now, industrial-grade processing has only existed for short fibers," says Dittus. "Additive manufacturing with continuous fibers is an understudied field. We have built up the process technology expertise and incorporated it into prototype development." The prototype of the fiber feed unit was integrated into the "freeformer", ARBURG's additive manufacturing system, and is currently undergoing a test phase for process reliability. With a strong partner such as ARBURG and the wide application range of the APF process, numerous plastics and special plastics, specifically for medical technology, are already available as standard granulate.

Additive manufacturing is particularly advantageous whenever components need to be manufactured profitably in customized one-offs or small batches. "We see great potential in the field of medical technology. The goal here is to produce precisely one customized and robust prosthesis in batch size 1 that is optimally adapted to the patient," specifies Prof. Fleischer. Using FRP, it is possible to produce solid functional components from which highly stressable prostheses with low weight can be manufactured. Not only medical technology manufacturers would benefit from this, but above all the patients: Custom-fit prostheses increase wearing comfort and ensure perfect functionality. Martin Neff, department manager for plastic free forming at ARBURG reports: "Some of our customers who use fiber-reinforced materials in injection molding want to offer added value with additive manufacturing. This is because it does not replace established subtractive or injection molding processes but is a useful addition to them." Whether this process will facilitate prototype testing for prostheses in workshops in or even produce marketable prostheses for patients will be determined in the future.

At the ARBURG Innovation Center at KIT: Prof. Dr. Jürgen Fleischer (Director of the wbk), Martin Neff (Head of the Plastics Free-Form Department at ARBURG) and the scientists from the wbk's Lightweight Manufacturing working group Florian Baumann, Sven Coutandin (Senior Engineer Lightweight Manufacturing) and Jörg Dittus (from left to right).

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Bilder v.o.n.u.: Apple‘s Eyes Studio / Shutterstock, bearbeitet von DER PUNKT | Patrick Langer / KIT

Fiber-reinforced plastics in use

Additively manufactured plastic parts can show their strengths in a wide variety of industries: Automotive body parts, electronics as well as packaging and handles through to medical technology applications.

Fiber-reinforced plastics (FRP) are a relatively young group of materials - composites consisting of technical fibers, such as glass, carbon or aramid, embedded in a polymer matrix. Combining fibers and matrix agent, the fiber composite achieves robust properties with high specific stiffness and strength through mutual interaction and adhesive and cohersive forces.

The material properties of the fiber-plastic composite can be adjusted by fiber angle, fiber volume fraction and layer sequence, among others.

The areas of application for fiber-reinforced plastics are steadily increasing, also due to the development of new additive production methods. In many cases, they have already replaced the metallic materials traditionally used. In the following, we will introduce two common fiber composites with their specific areas of application.

Composite material with glass fibers

Glass fiber-reinforced plastic, or GFRP, is the most commonly used fiber composite reinforcing material. The basic advantage of GFRP is low cost, lightweight, high stability and corrosion resistance. GFRP is non-absorbent, easy to wash off and disinfect.

GFRP is mainly used in the automotive, aerospace and naval industries where it is commonly found in body parts or structural components. GFRP is also suitable for use in wind turbines or bridges. Furthemore, the material’s high versatility allows it to be used as a container in plant engineering and pipe power construction. GRFP is also interesting for the electrical industry because of its good insulation properties. In everyday life, GRFP is used in clothing and sanitary units, such as bathroom sinks or shower trays. In the leisure sector, you can find GRFP in caravan and motor home construction or GRFP profiles as tent poles or sail battens.

Composite material with carbon fibers

Carbon-fiber-reinforced plastics, or CFRP, are tried and tested for components with high thermal and mechanical requirements. CFRP components demonstrate tensile and flexural strength, impact resistance and the ability to sustain loads. They are also lighter than all-metal parts and resistant to very high temperatures. For this reason, CFRP is used especially for heavy-duty, very rigid components.

CFRP components are expensive to manufacture compared with commercially used metal components of the same load-bearing capacity. They are therefore used particularly where stable lightweight structures are required and where low mass combined with high stiffness is accepted for increased costs, i.e. mostly for special applications.

The use of CFRP is widespread in aerospace engineering, yacht building, medical technology and high-quality automotive parts. CFRP is also used in boat building, for example for rotor blades, or in the sporting goods industry for professional sports equipment, such as golf clubs, bicycle components or ski equipment, due to its good material properties.

Picture: ARBURG GmbH + Co KG

TRADITION MEETS HIGH-TECH IN 3D FREEFORMS

At the ARBURG Innovation Center at KIT, scientists of the wbk Institute of Production Science are conducting joint research with ARBURG GmbH + Co KG into new technologies for additive manufacturing. Based on the ARBURG freeformer, an additive manufacturing of continuous fiber-reinforced plastic elements has been put into practice.This process allows building up any three-dimensional plastic components layer by layer from plastic droplets. A specially designed fibre feed unit rotates around the plastic discharge nozzle during the printing process, and as the plastic is discharged, it places the fibres in a position that allows them to be directly carried into the component by the plastic itself. The novel manufacturing technique is particularly suitable for prototyping and the production of individual small batches.

You can read the full report on the cooperation in KIT's innovation newsletter RESEARCH TO BUSINESS.

Pictures: Patrick Langer / KIT

PROF. DR.-ING. JÜRGEN FLEISCHER

Prof. Jürgen Fleischer studied mechanical engineering and earned his doctorate in 1989 in the field of production engineering at the former University of Karlsruhe (TH), now known as KIT. From 1992 to 1999, following his doctorate, he held various management positions in research, development and production in the Daimler-Chrysler Group. In 2003, he returned to the University of Karlsruhe as Professor and Head of the wbk Institute of Production Science.

From 2008 to 2010, Prof. Fleischer was granted a leave of absence from his university duties in the interest of the state of Baden-Württemberg, as he was appointed "Chairman of the Executive Board" by the company MAG Industrial Automation Systems. In 2010, he returned to KIT as professor and Head of the Institute of Production Science and also served as Dean of the Faculty of Mechanical Engineering until 2014. In his research, Prof. Fleischer focuses on manufacturing automation and machine tool engineering. His main areas of interest are mechatronic components and lightweight construction.

Since 2012, Fleischer also holds a visiting professorship at Tongji University in Shanghai, China. Prof. Fleischer is also an active member of several professional organizations and groups: He is a member and chairman of the scientific committee of the German Academic Association for Prodution Technology (WGP), a member of the International Academy for Production Engineering (CIRP) in Paris, a member of the Senate for the field of production science of the German Research Foundation (DFG) and a member of the selection committee for the Baden-Württemberg State Research Award.

JÖRG DITTUS

Jörg Dittus graduated with a Master of Arts degree in "Mechanical Engineering" from the Karlsruhe Institute of Technology (KIT). While completing his studies, he worked as an auxiliary research assistant at the wbk Institute of Production Science. His work there focused on automating the production chain of a resin transfer molding process as well as the production and optimization of fiber composite plastic parts. After graduating in Mechanical Engineering, Dittus stayed on at the institute as a research assistant and, since 2018, has been working there on his doctoral thesis in polymer engineering. In his current research projects, he is concentrating on the field of lightweight construction and additive manufacturing of continuous fiber-reinforced plastics.

DIP.-ING. (FH) MARTIN NEFF

Martin Neff has been with ARBURG since 1996. In his role as project engineer, he was initially responsible for the project management of fully automated production cells for seven years. From October 2003 to January 2007, he was a technical consultant in the "International Technical Support" department for ARBURG's international sales organisations, with a focus on the Asia-Pacific region.

In July 2007, he moved to the US subsidiary ARBURG, Inc. as Project and Engineering Manager, where he headed the engineering department. In January 2010, he took over as Sales and Engineering Manager of the ARBURG Technology Center Midwest in Elgin, IL.

In July 2013, he returned to ARBURG's German headquarters in Lossburg, Germany, and took over as Head of the Technology Consulting Plastics Free Moulding Group. Since the beginning of 2017, he has been responsible for the development of the freeformer's machine and process technology as department manager.

Bilder v.o.n.u.: wbk Institut für Produktionstechnik / KIT | Daniel Kuntze / die FotoFabrik | ARBURG GmbH + Co KG