Executive Summary : | Photo-diode based melt-pool monitoring can be a potential low-cost yet versatile alternative for quality assurance in laser based additive manufacturing and its allied processes. It can be used to detect several quality aspects such as lack of fusion/penetration, porosities, contaminations etc. in laser cladding process. Most of the commercially available process monitoring systems are either very expensive or generates computationally heavy data which needs additional high computational facilities to process the data. These restrict the wide-spread usage of such systems which plays a critical role in ensuring the desired mechanical and metallurgical properties of the products by laser-based metal additive manufacturing. Photo-diodes are relatively cheap and its response time is much less than a micro-second. Thus, it can be used to monitor and control the process in real-time. In this work, a prototype will be developed using an array of photo-diodes to capture the spectral emissions from the molten pool during the laser cladding process. These process signatures are not data heavy (in few kilobytes). Thus, processing of these data in real-time does not need any additional high computational facility. Along with the proper selection of different optical components, this array of photo-diodes arranged in a particular orientation will be used to capture the desired signals from the melt-pool generated during the interaction of the laser beam with the materials. Such system can be easily integrated with the laser processing heads (cladding/welding head) to monitor and capture the process signatures. Rigorous experiments with wide range of process parameters will be carried out to test the efficacy of the proposed process monitoring system. Any anomality in the captured signals while compared with that of a stable process can be analyzed and correlated back with the defects/un-desired properties of the deposited parts. The novelty of such system is that it does not require analysis of individual plasma emission lines which is computationally intensive, rather enables quantitative measurement of specific sensitivity of spectral emissions to certain defects. Further, the versatility of such system lies in the fact that it can be used as a probing tool for other laser material processing modalities such as laser welding, cutting, surface modifications etc. |