Optimised Laser Material Deposition
Laser material deposition has already proven itself in various areas, such as when repairing tools or applying anti-corrosion coatings. However, the result depends considerably on how evenly the laser beam applies the powder. The process parameters, i.e. the speed and volume of the powder feed into the melt pool, play a decisive role. Nozzles and caustics must therefore be regularly checked, certified and calibrated before the process. The sequence of these work steps has up until now been very complex and cumbersome, however. Scientists at Fraunhofer ILT have therefore developed an inline process supported by a machine.
Integration into existing systems
The system solution consists of three main components: a camera module along with movable optics and illumination, all of which are mounted on the machining head. The nozzle is measured with a laser module, which is placed in the system. The two modules are controlled electronically either in a control cabinet or directly in the system. In order to detect and measure the particle density distribution and caustics of the powder jet, the jet is illuminated with a laser line perpendicular to the powder gas flow and observed by the coaxially arranged camera through the powder nozzle. The system changes the relative position of the laser and the machining head several times for further measurements. Finally, the evaluation of 2,000 to 3,000 images shows the statistical distribution of the particles in one plane. "If I use this method to gradually capture the so-called caustics – i.e. the focusing area in which the powder particle beam is bundled – it can be calculated and characterised very precisely in terms of the most important parameters, such as the minimum diameter and the density distribution," explains professional engineer Oliver Nottrodt, project manager for Process Control and System Technology at Fraunhofer ILT.
The measuring system enables standardised measurement and certification of the powder feed nozzles and complete characterisation of the respective powder jet. It helps set up the process by taking over a multitude of tasks from the user such as measuring and marking the positions of the processing laser, as well as documenting all work steps. Furthermore, the measuring system uses the geometric characteristics of the melt pool to monitor the laser metal deposition process, which the system also visualises and documents.