A Study Of The Multi-sensor Real-time Monitoring System For Laser Welding

Laser welding describes a process of jointing two (or more) pieces of metal together using a laser beam. Many factors have effects on the stability of the welding process. In order to increase the stability and the quality of laser welding, the laser welding process should be monitored and controlled in real time. In this article, the real-time monitor system of laser welding process is completely studied on both hardware and software. The main functions of the system's hardware include converting the acoustic emission signal and the energy of heat and light radiation into electric signals, the transmission and A/D converting of these electric signals. The software of this system can analyze the signals that are collected during laser welding and it can also show the characteristics of the signals directly and deeply. It is known that the plasma generated during laser welding emit light with a main wavelength between 190 and 400 nm, and the high temperature weld pool emits light with a main wavelength between 1000 and 1600 nm. As the dominant light of plasma is in the ultra-violet range and that of the high temperature weld pool in the infrared range, suitable light sensors should be used for their measurement. In this study, the measurement was carried out using a UV sensor, an IR sensor and a elect ret sensor which consist of a three channels real-time data collecting system. The software design is base on the LabVIEW platform. The main functions include data collecting, storing and processing. A series of laser welding experiments were carried out to study the relationship between the characteristics of the signals(UV, IR, AE signal) and the stability of laser welding. During the experiments, the laser power was stepwise increased from 1000W to 1800W, the welding speed was stepwise increased from 0.8m/min～3.4m/min, the assistant gas flow was stepwise decreased from 1.5m3/h～0.5m3/h and the distance between the lens and the work piece was stepwise increased from 123mm～126.5mm. At the same time the real-time monitor system collected the UV, IR and acoustic emission signals. Through the analysis of the collected signals, it clearly shows that the real-time monitor system is reliable and stable. The experiments also prove that the real-time monitor system is sensitive with the change of the welding parameters such as laser power, welding speed and so on. Above all,the experiments show that the system can meet all the requirements of the real-time laser welding monitoring system.