Advances in in-situ monitoring technology for laser processing

Laser processing is an advanced non-contact processing technology. Photo-physical and photo-chemical reactions are mainly responsible for the processing of matter during the laser-matter interaction. Nowadays, laser processing has vast application values in many fields, such as aeronautics and astronautics, automobile manufacturing, health and medical community, instrument and apparatus and nuclear industry. With constantly deepening industrialization, higher demands for processing efficiency and quality are raised for laser processing. Comparing to high-cost ultra-short pulsed laser, it is more reasonable and affordable to apply monitoring technology to observe and regulate the laser processing, which can achieve similar outcomes. The conventional off-line monitoring technology analyzes the machining process and detects when the laser processing is finished, resulting in the poor timeliness and low working efficiency. This technology cannot be applied in mass industrial production when dealing with complex working condition as well as workpiece with diversified structures and components. Hence, in-situ monitoring technology has been widely employed as a necessary supplementary means for laser processing. In this paper, the interaction mechanism between laser and matter is firstly analyzed in the time scale. Various physical phenomena during the interaction between the laser with different pulse durations and matter are clarified, from which the pointcut for in-situ monitoring technology is specified. Systematic reviews on the applied in-situ monitoring technology during laser processing home and abroad are established. The working principle, system configuration as well as advantages and disadvantages of the in-situ monitoring technologies based on individual acoustic sensor, spectrometer, photodiode, visual sensor and temperature sensor are analyzed in detail. Meanwhile, the application status including the combination of these sensors and the combination of these sensor and artificial intelligence are elaborated. The development trend of the in-situ monitoring technology for laser processing based on the existing deficiencies is prospected.