Theory And Method Of Quality Detection Based On Microphone Array In Laser Welding Processing

Acoustic signal generated in laser welding processing is suitable parameter of thequality procedure detection. It has the advantages of fast response and non-contactmeasurement and contains a large number of welding processing information, such aswelding molten pool, keyhole, metal vapor and plasma.However, its application is limited to some extent in laser welding, due to itsvulnerability to environmental noise. Recent study shows that microphone arraytechnology and signal processing method could eliminate background noises andlocalized sound sources, which provide a new way for quality procedure detection.This thesis is mainly focused on the research of the quality procedure detectionin laser welding. The new signal processing technology-blind signal separation isused to extract the feature acoustic signal of the laser welding. the source foridentification, tracking and locations is achieved based on the beamforming algorithmof microphone array technology.Firstly, the source mechanisms of keyhole and the plasma jet have beenresearched. Then, the model of the keyhole and pool is established based on thetheory of heat transfer and fluid dynamics. Finally, the distribution of sound field inlaser welding processing is calculated by the acoustic software.The relationship between the acoustic signals and different welding processparameters is researched by the experimental methods based on the study of sourcemechanism. And the standard source signal library is established.Blind signal separation algorithm is used to extract the feature acoustic signal ofthe laser welding based on the selected optimization criteria and the appropriatecomparison function. At the same time, the identification and location of the source inlaser welding processing is achieved according to the receiving the time and thelocation alternate.In order to verify feasibility of microphone array technology for sourceidentification and blind signal processing in applications of quality proceduredetection, the welding tests are implemented on the400Wlow-power laser,2kWmedial-power laser and12kW high-power CO₂laser.