Reliability in generative manufacturing

© Felizitas Gemetz/Fraunhofer IWM

A generatively manufactured and bionically inspired chair's load-bearing capacity is being tested at the Fraunhofer IWM. Model size: 40% of original.

Generative production processes are becoming more important in the production of small series, customized components and the manufacture of complex component structures. The transition from rapid prototyping to rapid manufacturing requires that produced parts be subjected to reliable and defined quality control. To do this, we experimentally and computationally define the internal stresses and shape distortions that arise from the layered structure of components in selective laser melting (SLM) processes or in stereolithography. Using finite elements methods and »computer aided optimization«, we also investigate the mechanical properties of complex structures which can be produced through generative processes. Load-oriented and function-optimized design make functional components for the »Internet of things« possible.

Jaeger, R.; Koplin, C.; Brand, M.; Meiners, W.; Jansen, S.; Improving the Reliability in Rapid Manufacturing of metallic Components, in Proc. of Euro-uRapid 2007, International User’s Conference on Rapid Prototyping and Rapid Tooling and Rapid Manufacturing (2007)

Koplin, C.; Gurr, M.; Mülhaupt, R.; Jaeger, C. R.; Shape accuracy in stereolithography: A material model for the curing behavior of photo-initiated resins, in Proc. of Euro-uRapid International 2008, User’s Conference on Rapid Prototyping and Rapid Tooling and Rapid Manufacturing (2008) 315-318 Link

Design for generative manufacturing technology and bionic structures

 

Biomimetic structures inspired by nature can be easily produced with additive manufacturing processes due to their geometry. As a demonstration of a generatively manufactured component with a cell structure, a bionically designed cantilever chair was designed at the Fraunhofer IWM. Software was specially developed for »computer aided optimization (CAO)«, which efficiently evaluates the cellular structure of even large components and optimizes the loads accordingly.

Artificial venous systems and blood vessel replacement

 

Supplying tissue with nutrients through a venous system (vascularization) is a current challenge in tissue engineering. The Fraunhofer IWM is involved in projects whose goal is additive manufacturing of a vascular system to supply tissue grown in vitro. We determine the optimum topology of the vascular system and optimize the local geometry of the branches to achieve optimal fluid mechanical flow conditions. The mechanical properties of artificial blood vessels and the diffusion of nutrients through hydrogels and nonwovens to supply cells are experimentally investigated. The artificial blood vessel system should make the »biofabrication« of tissue models and transplants possible in the future.

The customer as designer

 

Additive manufacturing processes are becoming a significant driver of participatory production, »mass customization« and »open innovation«. Individualized products or replacement parts can essentially be designed by anyone on a computer and then generatively manufactured with their own 3D printer, in a fab lab, or by a contract manufacturer. But not everyone is a capable engineer or a good designer. We are working on the foundations for software tools that simplify the load-oriented design of components by the end user. 

© Fraunhofer Institute for Mechanics of Materials IWM

Components made of All-PE composites: using a catalyst, different unbranched PE chains are produced (top) and the fiber structures produced in the 3D pressure nozzle are deposited in the desired orientation in the printed component.

Completely recyclable, lightweight, single Component Composite Material for Injection-Molded Components

 

Previously, polyethylene (PE) had to be reinforced with carbon or glass fibres in order to be used in lightweight construction. The need to add e.g. glass fibres to PE to improve its mechanical and tribological properties has made production and recycling more difficult and costly.

Polyethylene (PE) without such additives has a very good energy, environmental and cost balance. It can be recycled easily and almost infinitely often: used product is rasped, melted and formed into new components with consistently good quality.

In cooperation with the FMF Materials Research Center at the University of Freiburg and the polyolefin manufacturer LyondellBasell, the Fraunhofer IWM has produced and qualified a sustainable, all-PE single component composite. The reinforcing fiber structures are also made of PE and form during injection-molding.

Using a specific catalyst, the FMF pioneered the synthesis of a blend of PE with various chain lengths in the chemical reactor, including a fraction of ultra high molecular weight PE. These »reactor blends« form fibre-like nanostructures which reinforce the material. Due to the resulting mechanical properties of the material, it can be used in lightweight construction and is 100% recyclable. In the injection moulding process, the fibre structures are formed when high shear stresses occur in the injection moulding tool. In the 3D printing process, the fibre structures of the new material can also form in the nozzle. This allows the fibre alignment to be specifically adjusted during 3D printing.

An attractive combination of high stiffness, tensile strength and impact strength could be observed by FMF for the newly developed all-PE composites. The Fraunhofer IWM evaluated the behavior under crash loading (i.e. under high strain rates) and the tribological characteristics of the novel composites. Reactor blends with a suitable composition reach a similar wear resistance as poly(amides).

As a result, many new applications for this recyclable material are conceivable: in addition to light weight gear wheels in automobiles or for the food industry, it is also possible to produce nestling robot grippers which adapt to the shape of a part, medical orthoses or connectors.

 

Hees, T.; Zhong, F.; Koplin, C.; Jaeger, R.; Mülhaupt, R., Wear resistant all-PE single-component composites via 1D nanostructure formation during melt processing, Polymer 151 (2018) 47-55 Link

All-Polyethylene single Component Composite Material: Recyclable lightweight single Component Composite Material developed for Injection-Molded Components

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