Fraunhofer Institute for Laser Technology ILTOnline / November 10, 2020 - November 12, 2020
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Additive manufacturing of large components using Laser Powder Bed Fusion (LPBF)
Conventional systems for Laser Powder Bed Fusion (LPBF) are limited in their size. When increasing the usable build-volume, the challenge is to realize a homogeneous shielding gas flow over the entire powder bed. In addition, an increase in productivity is necessary in order to be able to use such systems economically.
To meet these challenges, the Fraunhofer Institute for Laser Technology ILT has developed a novel LPBF machine concept (size: 1000x800x350mm³) for the production of large components as part of the lead project futureAM. This concept includes a processing head which is movable via linear axes. The processing head features a local inert gas system, thus creating process conditions which are easy to control. The latest development stage includes a processing head with a five-scanner system to ensure sufficient productivity of the process.
For the proof of concept, Rolls Royce Ltd. provided an oil transfer coupling of an aircraft engine as a demonstrator and redesigned it for additive manufacturing. With the help of the new machine concept, it was possible to manufacture the demonstrator with a bounding box of Ø600 x H280 mm³. The monolithically manufactured component thus replaces an assembly of originally 44 individual parts and will be presented to the public for the first time at Formnext 2020.
»PETIT«
The materials currently used in Laser Powder Bed Fusing (LPBF) are alloys designed for conventional manufacturing processes. However, this does not allow the advantages of the LPBF process to be fully exploited. New alloys must therefore be developed under LPBF conditions, which currently requires several costly and time-consuming production cycles of the powder material. To meet these challenges, Fraunhofer ILT has developed the miniaturized and modular process chamber »PETIT«. It is possible to process material samples with a significantly reduced powder material of < 40 cl, which makes a fast alloy development with elemental powder mixtures feasible. By integrating PETIT into existing LPBF systems to use their optical and laser systems, rapid screening of different alloy compositions with high transferability to processes on an industrial scale is possible.
Adaptive process control for Laser Powder Bed Fusion (LPBF)
During additive manufacturing using Laser Powder Bed Fusion (LPBF), process-related deviations of the actual part geometry of the component from the CAD target geometry occur. This is caused by movements of the laser-induced melt pool. Melt pool flows lead to sintering of powder particles to the surface of the component, while heat accumulation leads to bulges, especially in pointed contour areas. This leads to an increased cost-intensive post-processing effort, especially for precision components.
Fraunhofer ILT is therefore developing an adaptive process strategy within the framework of the BMBF-funded project IDEA, in which continuous (cw) and pulse-modulated (pw) laser radiation is used to manufacture macroscale components. By means of the pulse-modulated exposure of the component contour, smaller melt baths can be realised in comparison to cw exposure, which solidify independently of each other, thus reducing melt pool flows and movements. As a result, surface roughness as well as geometric accuracy and thus the quality of the component can be significantly improved.
Integration of sensors into LPBF parts
Additive Manufacturing allows for new approaches to integrate sensors into functional parts, as every position within the part is accessible during the manufacturing process. This allows to freely position sensors in previously inaccessible areas of parts.
Fraunhofer ILT develops process chains to integrate temperature and pressure sensors into laser powder bed fusion (LPBF) parts. The sensors are introduced during a process pause, connected to the part using the processing laser source and then fully integrated by finishing the part around it. The sensors are thereby well protected against harsh conditions.
Aside from free and precise positioning of the sensors, this new technology allows for faster response time in temperature measurement as well as measurement of internal mechanical stresses, that cannot be measured in any other way.
While this approach uses of the shelf sensors, the additive manufacturing of the sensors themselves during the process is currently investigated at Fraunhofer ILT.