Aim: To develop a cost-effective monitoring and control system to be integrated in the LMD (Laser Metal Deposition) process for quality improvement and manufacturing cost reduction.
Challenges: Several thermal monitoring systems, using thermal cameras or pyrometry, and geometric monitoring systems based on vision cameras or triangulation systems have been incorporated into the LMD process. However, thermal and geometrical aspects have been generally controlled separately. In practice, both aspects are related, as for example the adjustment of the laser power for the modification of the workpiece temperature has a direct effect on the growth of the workpiece. This also leads to the need to incorporate two different measurement systems, which increases the overall cost and complicates the compatibility between the two systems due to space, control strategy problems and unification of the data processing unit. On the other hand, the height measurement of the part is in most cases performed after deposition of the clad or between the deposition of different layers, which requires a stop in the process that affects the duration, induces higher temperature fluctuations and micro-structural changes in the part.
Benefits: The main feature targeted in the experiment, which provides a high level of innovation, is the fusion, in the same monitoring system and control unit, of two of the main aspects of an additive process: the thermal and the geometrical ones. On the other hand, while real-time processing of thermal measurements by means of visible or thermal cameras is already established, the reliable measurement of the process geometry in-situ is a point that still needs to be solved. One of the approaches will be to use state-of-the-art line profile sensors together with stereoscopic vision and adequate optical filtering to combine the precise information of the line profile sensor with the on-line volumetric information of the weld seam from the stereo camera. Finally, the integration of the sensor in an automatic way in an industrial manufacturing environment is a clear difference with respect to other measurement systems which require the intervention of the machine user. One benefit will be to shorten the lead time of the parts manufactured by the LMD process, by reducing the number of failed parts towards zero, minimising the set-up time and guaranteeing a superior quality of the manufactured parts.
Activities & Present achievements: The proposed solution aims to develop a monitoring system that fuses geometric and thermal measurement sensors, acting on the process parameters that control the temperature of the deposited bead and its growth in a combined approach. This approach will be based on the hypothesis that the melt-pool monitoring will be done with the IR-camera, the quality of the powder stream could be analysed by the visual coaxial camera, the overall geometrical position will be acquired every several layers using the structured light sensor, the geometrical position of the previous layer as well as the correction of the current layer will be controlled by the line profile sensor and finally a real-time volume information of the part being processed will be acquired using stereoscopic vision. The control system developed will act in real time, adjusting the main process parameters (laser power, feed rate, nozzle-to-part distance), thanks to real-time FPGA processing.
Current Status: All three deliverables for the technology development phase of the project were completed on time and passed the acceptance criteria agreed with the mentor. Based on the understanding established a solution was proposed that fuses the monitoring of the thermal and geometrical aspects, responding to the main requirements of the process. In addition, a study of the market that this solution could have in potential users of the technology was conducted.