Fraunhofer Institute for Laser Technology (ILT), Aachen, Germany, will showcase a new metal Additive Manufacturing process in which the component in the powder bed is heated with laser diodes to reduce distortion, enabling the production of taller parts in new materials. ILT will exhibit the new technology in cooperation with the Chair for Technology of Optical Systems (TOS) at RWTH Aachen University.
Laser Beam Powder Bed Fusion (LB-PBF) Additive Manufacturing can produce internal stresses caused by temperature gradients in the generated component. In the laser spot, temperatures above the melting point prevail, while the rest of the component cools rapidly. Depending on the geometry and material, this temperature gradient can lead to cracks in the material.
To avoid this, the component is usually heated from below via the substrate plate. However, with taller structures this may not be sufficient. As part of the Digital Photonic Production (DPP) research campus, a funding initiative of the German Federal Ministry of Education and Research (BMBF), Fraunhofer ILT and RWTH TOS Chair are working together with their partner Philips Photonics to develop solutions for this task.
Developed as part of this project, titled DPP Nano, the new heating process uses an array of six vertical-cavity surface-emitting laser bars (VCSEL) of 400 W each, installed inside the process chamber. By emitting infrared radiation at 808 nm, this array can heat the device from above to several hundred degrees Celsius during the build process. The bars can be controlled individually, making sequences in different patterns possible, and the heating process is monitored using an infrared camera.
To test the VCSEL heating technique, project engineers have constructed parts in Inconel 718 which it is reported demonstrated significantly reduced distortion, with the component being heated up to 500°C. The use of VCSEL heating reduces the thermal gradient, and by extension the internal stresses, making it possible to produce taller parts with a minimised risk of distortion or cracking.
The new method also offers opportunities the Additive Manufacturing of particularly difficult materials, and the project engineers expect to begin testing with titanium aluminides in the near future. For this material, the component will be heated to approximately 900°C using the VCSEL method.
Titanium aluminides are are commonly used in components for turbomachinery, such as in the hot gas section of turbochargers. In addition to turbomachinery, the process also opens up new potential applications in other industrial sectors where thermally induced stresses in AM processes have to be reduced.
In addition to exhibiting the technology on Fraunhofer ILT’s stand during Formnext, the institute’s Andreas Vogelpoth will present a paper on ‘VCSEL-Based Preheating for LPBF’ at the TCT Conference @ Formnext on November 15, 2018.