The Fraunhofer Institute for Laser Technology (ILT) and the Chair of Technology of Optical Systems (TOS) at RWTH Aachen University have announced a collaboration aiming to create a state-of-the-art test machine enabling them to flexibly investigate complex laser beam profiles in power classes up to 2 kW, a capability that allows customised solutions for industrial partners. This platform is designed to integrate Laser Beam Powder Bed Fusion (PBF-LB) Additive Manufacturing processes more efficiently and robustly into industrial production as demand grows.

PBF-LB machines often use 300-400 w lasers, but the Gaussian laser beam used can have significant disadvantages, explains ILT. The high concentration of power in the beam centre leads to local overheating and undesirable material evaporation as well as process instability, both of which can impair component quality due to spatter and pores. These issues significantly limit the scalability of the process, meaning that the laser power available in PBF-LB machines – often up to 1 kW – cannot be utilised for most materials.

“One way to speed up the process is to use several lasers and optical systems in parallel,” states Marvin Kippels, PhD student in the Laser Powder Bed Fusion Department at Fraunhofer ILT. “However, the costs scale at least proportionally to the number of systems installed.”

In addition, these machines cannot always be utilised homogeneously in real applications, which means that productivity cannot be increased proportionally to the power. A promising approach is to improve the productivity of the single-beam process, which can also be transferred to multi-beam PBF-LB machines.

The role of beam shaping

Previous studies have shown that even simple beam shapes with rectangular, ring-shaped or a combination of two Gaussian distributions produce promising results for both component quality and process speed. Fraunhofer ILT is now conducting comprehensive investigations into the potential of more complex beam shapes, something mostly unexplored.

“The interaction of laser beam and material in the process is so complex due to its dynamics that simulations can only provide indications of the actual melt pool behaviour,” explains Kippels, who is currently setting up a new type of machine that uses LCoS-SLMs (Liquid Crystal on Silicon – Spatial Light Modulator), which will enable researchers to investigate almost any beam profile in the PBF-LB process.

With a laser power of up to 2 kW, Fraunhofer’s machine is a platform for testing new beam shapes at very high power levels in the PBF-LB process. This allows suitable machine technology to be identified for an individual PBF-LB task. “We can optimise the [PBF-LB] process in a targeted manner,” explains Kippels. He refers specifically to less material evaporation, less spatter formation, reduced melt pool dynamics, smoothened melt track surface, and increased process efficiency by adapting the melt track geometry.

Flexible beam profiles for specific requirements

Currently, machine technology is often promoted as able to produce specific beam shapes such as ring or top hat profiles. However, the choice of these beam shapes is not based on an in-depth understanding of the underlying process mechanisms, which is reflected in the sometimes contradictory literature on the subject. Only by understanding the processes can research specifically define which adjustments achieve a designated target, such as a certain melt track geometry.

This means that a beam shape must be developed and optimised for the application, which can then ideally be implemented in the company without needing Liquid Crystal on TLCoS-SLM technology. Using Fraunhofer ILT’s research platform, industrial customers and project partners can leverage this flexibility in researching the laser-beam tool.

“We are still at the very beginning, but we can already see the enormous potential that beam shaping can offer for the [PBF-LB] process,” says Marvin Kippels. “There is no one perfect beam shape; every application has its own requirements. Thanks to our flexible beam shaping, we can find the ideal distribution for each process, the best process parameters for the task in question.” To achieve this goal, several departments at the Aachen Institute support the work of Kippels and his team.