Improvement on Ultra-short pulse laser ablation process

The part cutting based on ultra-short pulse laser ablation process is directly linked to the manufacturing problems addressed by the industrial end-user Micreon, working with femtosecond (fs) laser systems. In this case, different difficulties related to the high process dynamics have been tackled as: instabilities on the laser source output, the identification of the laser focal position of the part and the need for in-line information regarding the workpiece state (cut width, part temperature) so the final workpiece quality could be estimated. In this case, the Laser Zentrum Hannover (LZH) has worked on the implementation of different methods for the in-line process monitoring. On the one hand, a simple and cheap device for the measurement of the energy from single laser pulses down to 20 fs has been developed. Also, a system for the in-line identification of the cut width has been developed, obtaining accuracy values bellow 2 µm when working with feed rates up to 400 mm/min. Besides, a commercial auto-focus device has been implemented to work properly within a fs-laser context and, finally, a thermo-camera has been implemented on the machining set-up so part temperatures above 80 ºC can be identified and avoid the burning or the workpieces. Once the different monitoring devices were developed, the LZH has worked on the development and implementation of an adaptive process control scheme. Employing the in-line data obtained by the monitoring devices, rules for the actuation on the laser machine parameters have been developed. Fig. below depicts the capability of the developed control to modify the laser output and stabilize the desired process variable. Thanks to this control scheme, the process parameters can be modified in real-time in order to generate the desired quality on the machined part. Besides the adaptive process control approaches defined for this process, the development of statistical tools for the analysis of process trends and the prediction of non-controllable process deviations has been undertaken too. The University of Leuphana has worked on the analysis of the data provided by the auto-focus system implemented by LZH. Based on this data, the identification of high focal deviations is carried out. Thanks to this, it is possible to detect a part that would require too many corrections to attain the desired quality and suggest its scrapping to avoid excessive costs.