Frankfurt a. M., Germany / 11/19/2019 - 11/22/2019
In laser powder bed fusion (LPBF), the laser is used to build components layer by layer from a powder bed. Mechanical stresses, however, are caused by temperature differences in the component. Depending on the geometry and material, they can even result in the material cracking.
For these reasons, experts from the Fraunhofer Institute for Laser Technology ILT have joined forces with industrial partners to implement ideas in which the component is heated from above. As early as 2018, vertically emitting laser bars (VCSEL) were presented as part of the research campus for Digital Photonic Production (DPP) at RWTH Aachen University. Each VCSEL emits 1 kW of power into the chamber from above.
Now, the Fraunhofer ILT team has developed a solution together with its partner adphos GmbH, in which a near infrared (NIR) emitter is attached to the scraper and heats the material in the process plane with broadband radiation.
With a power of up to 12 kW, the NIR emitter achieves temperatures of 500 to over 800 °C in the component. The NIR illumination is homogeneous and can also be scaled very well.
Due to its electrical conductivity, high-purity copper is particularly in demand for current-carrying components and in heat management. Thus, it plays an important role in electrical engineering, mechanical engineering and electro mobility.
Metallic 3D printing with high-purity copper using Laser Powder Bed Fusion (LPBF) and infrared light has been difficult to implement so far, as low build-up rates and inhomogeneous component quality are not satisfactory for end users.
This problem can now be solved by using a new laser beam source in the “green” spectral range. For the first time, components made of high-purity copper could be constructed with a relative material density of more than 99.8 % and a high specific electrical conductivity of 58 MS/m.
Fraunhofer ILT is doing research on the influence of green and blue wavelengths on powder-bed-based Additive Manufacturing. The focus is on highly reflective materials such as copper and its alloys. It is also being investigated whether green and blue laser beam sources can be used to increase process quality, productivity and efficiency for the additive manufacturing of established materials in metallic 3D printing.
Within the BMBF-funded project ProLMD, the Fraunhofer Institute for Laser Technology is developing new system technology and processes with which, for example, reinforcements and other geometric elements can be applied to case or forged parts with laser material deposition (LMD).
A processing head for coaxial Wire-LMD with a ring shaped beam plays an important role here. The optical system was developed at Fraunhofer ILT and is now being refined for use within the collaborative ProLMD project.
The main advantages of the new processing optics are its independence of direction and the uniform intensity distribution of the laser beam ring. Thanks to the use of reflective optics (copper), high powers of up to 4 kW can be used for a wide wavelength range. Large components can therefore also be produced in a very high quality without pores and with very little post-processing. In addition, the new head enables welding on 3D surfaces. As with most LMD processes, the new optics is also suitable for repairing components.
Laser material deposition (LMD) has established itself for the repair and manufacture of metallic components in additive manufacturing (AM) and for the application of protective coatings. In this process, a powdery filler material is introduced into the melt generated by the laser beam via a nozzle, thus creating a layer metallurgically bonded to the workpiece.
In order to guarantee high process quality, the »powder gas jet« needs to be characterized and documented. Until now, this was not possible.
The “Powder Jet Monitor (PJM)” has now been developed at Fraunhofer ILT. For the first time, the “Powder Jet Monitor” makes it possible to document nozzle wear and adjust the powder nozzle. In addition, users can investigate how the parameters of the powder feed influence the part to be manufactured. With the PJM, the institute has provided the industry with a system for measuring the powder gas jet and enables manufacturer to produce more efficiently.
The process is already being used for the optimization of Extreme High-Speed Laser Material Deposition (EHLA).
The Fraunhofer-Gesellschaft has created the lighthouse project futureAM to systematically and continuously develop the Additive Manufacturing (AM) of metallic components. For this purpose, six institutes – all with a wealth of experience in the field of Additive Manufacturing – have entered into a strategic project partnership pursuing two fundamental goals:
1. Establish a comprehensive cooperation platform for the highly integrated cooperation and use of the decentrally distributed resources of the Fraunhofer-Gesellschaft in the field of AM.
2. Create the technological prerequisites to increase scalability, productivity and quality of AM processes in a way relevant to praxis for the production of tailor-made metal components.
The focus project has set itself ambitious goals, e.g.:
novel software for automated AM component identification and optimization
a scalable LPBF plant concept increasing productivity (by a factor > 10)
a process and system technology for generating spatially resolved, customized multi-material properties
an autonomous manufacturing cell for the post-treatment of AM components
The cooperation platform has not only been created through intensive cooperation in and between the individual fields of activity, but in particular through the establishment of a "Virtual Lab". For this purpose, all partners will participate in developing technology demonstrators.