Abstract
Optical techniques for real-time full-penetration monitoring for Nd:YAG laser welding have been investigated. Coaxial light emission from the keyhole is imaged onto three photodiodes and a camera. We describe the spectral and statistical analyses from photodiode signals, which indicate the presence of a full penetration. Two image processing techniques based on the keyhole shape recognition and the keyhole image intensity profile along the welding path are presented. An intensity ratio parameter is used to determine the extent of opening at the rear of a fully opened keyhole. We show that this parameter clearly interprets a hole in formation or a lack of penetration when welding is performed on workpieces with variable thicknesses at constant laser power.
Highlights
Laser welding is of increasing interest for aeronautics applications, because of the inherent low distortion of the process and its suitability for automation
In this paper we describe optical techniques based on the analysis of signals detected with both a camera and a single-point sensor, allowing real-time monitoring of full penetration
The ability to detect and use the optical emissions from the weld-pool area for penetration monitoring and control has been examined by many authors.[1,2,3,4,5,6,7,8,9]
Summary
Laser welding is of increasing interest for aeronautics applications, because of the inherent low distortion of the process and its suitability for automation In such safety-critical applications, it is vital that every weld can be assured to be free of defects; the requirement for process monitoring and control in order to detect (and where feasible, eliminate) possible defects in the weld (e.g., lack of penetration or porosities). Such a system would ensure a consistent process and reduce scrap and rework. We investigate their relative merits for preventing the formation of a hole while maintaining full penetration when welding variable thickness workpieces at high power
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