Customized photonic devices for defectless laser based manufacturing

CUSTODIAN aims the development of a disruptive methodology which will allow to adapt the geometry and power distribution of the laser beam, in order to subject the material to an ideal thermal cycle during its processing.

This methodology includes the determination of the optimal thermal cycle for each material/application; the development of a photonic system that emits a reconfigurable laser that allows to reproduce the optimal thermal cycle; and the design of a real-time monitoring and control system.

The successful achievement of the proposed objectives will allow the fabrication of optimized-performance pieces at the first attempt, with the consequent savings in terms of associated delivery times and costs.

The CUSTODIAN methodology has been deployed and demonstrated in three relevant applications:
- Laser beam welding of austenitic steel parts for exhaust systems in automotive sector: the aim was to increase the robustness and flexibility of the process, in order to absorb variations in the gap of the parts to be welded. A beam shape consisting in a circular primary beam and a rectangular secondary beam was proposed and tested. Dynamicity was obtained by a variable secondary beam width, and adjustable power ratio between primary and secondary beams. Demo parts were tested for leakage and hot fatigue resistance under conditions similar to the real ones withstand by the exhaust system. Regarding hot fatigue testing, the CUSTODIAN solution provided much better results (32% - 83%), independently of the gap between parts (between 0 and 0.4 mm), compared to the standard LBW. On the other hand, the monitoring and control system has been successfully tested, showing its capacity to adjust the laser power to maintain the heat input constant, when the welding speed is reduced, and to tune the secondary beam width, when the melting pool collapses inside the gap.
- Laser-based powder bed fusion of nickel-based alloys (PBF-LB/M) for power generation (IN713LC) and aeronautical (CM247LC) industries: The aim was to demonstrate the possibility of processing these alloys by PBF-LB/M, avoiding hot cracking phenomenon. Two concentrical primary and secondary beams have been proposed and tested. A balling phenomenon was identified in the contour area of the coupons. It was clearly observed that the finer the powder is, the more remarkable the balling issue. The dynamic beam shaper was focused on balancing the power distribution between primary and secondary beams. It was found that certain processing conditions can dramatically reduce the amount of cracks. Further investigations should be conducted to obtain crack-free samples. On the other hand, the inline process control system has been demonstrated a success to control and feed-back process variables, as the laser power in a layer-by-layer manner, which could be useful not only for the alloys tackled within the CUSTODIAN project, but even for standard materials as more stable conditions could be achieved.
- Laser cutting of steels: A static MPLC solution has been tested successfully, showing very good results on surface roughness, mainly due to the ability of this technology to obtain a focus depth similar to the thickness of the steel plates to be cut. To dramatically increase the cutting speed further calculations and tests will be carried out in the very next future. It is important to remark, that the maximum average laser power used in laser cutting has dramatically increased over the last years. So, MPLC is still the unique approach to shape the beam based on fully reflective components and, thus, with minimum absorption and thermal load.

Main benefits from CUSTODIAN can be summarised as follows:
- By increasing the robustness and flexibility of Laser-based processes, it will allow a better material and energy efficiency, higher productivity and less scrap generation.
- By enabling the broader and cost-effective implementation of advanced materials.

This way, CUSTODIAN will have a significant impact in reducing GHG emissions.

Main CUSTODIAN results can be summarised as follows:

- The successful development of the CUSTODIAN methodology, based on MPLC technology, which has been applied and demonstrated in three different application use cases, becoming a very promising approach to solve many industrial laser application challenges that cannot be faced by using conventional laser systems. This methodology will be exploited by part of CUSTODIAN partners, that have signed an agreement in this sense.
- The viability of MPLC tech for beam shaping has been demonstrated, being in one of the most equilibrated alternatives among those already available in the market, or even under development, in terms of shaping quality and flexibility, power handling, dynamicity, and price.
- The multi-physics simulation carried out in CUSTODIAN has demonstrated how much useful could be to find out the most promising beam shapes to be tested, saving a lot of resources in experimental testing. This is being already exploited by one of the CUSTODIAN partners as a service.
- The development of a monitoring and control system based on SWIR/MWIR sensors and FPGA, which ensures that the beam shape designed by combined metallurgy and simulation approach, and deployed by beam shaper, has constant quality in order to guarantee the material processing conditions.
- CUSTODIAN results have been disseminated in different congresses and events. A final workshop was organised by the end of the project. Link to the workshop is available at Youtube channel: https://www.youtube.com/watch?v=P9JtaNwN5DY

CUSTODIAN’s groundbreaking approach is to work in the concurrent multiprocessing including pre- and post-heating of a small area applied by a beam shaper around the melt pool, looking to generate a temperature gradient which cuts down the high solidification rates. The revolutionary capacities of beam shaping offered by MPLC together with the high capacity of beam modelling and multi-physics simulation open the possibility to tailor the beam shape to exact thermal history in the material and avoid the combination of brittle temperature range and scan-induced stresses. Moreover, CUSTODIAN has also developed a cutting-edge complex control system for LBW and PBF-LB/M processes, composed by SWIR/MWIR sensors and FPGA which will ensure that the beam shape designed by combined metallurgy and simulation approach and deployed by beam shaper has constant quality in order to guarantee the material processing conditions.

Periodic Reporting for period 2 - CUSTODIAN (Customized photonic devices for defectless laser based manufacturing)

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