Abstract
Lack of fusion can often occur during ultra-thin sheets edge welding process, severely destroying joint quality and leading to seal failure. This paper presents a vision-based weld pool monitoring method for detecting a lack of fusion during micro plasma arc welding (MPAW) of ultra-thin sheets edge welds. A passive micro-vision sensor is developed to acquire clear images of the mesoscale weld pool under MPAW conditions, continuously and stably. Then, an image processing algorithm has been proposed to extract the characteristics of weld pool geometry from the acquired images in real time. The relations between the presence of a lack of fusion in edge weld and dynamic changes in weld pool characteristic parameters are investigated. The experimental results indicate that the abrupt changes of extracted weld pool centroid position along the weld length are highly correlated with the occurrences of lack of fusion. By using such weld pool characteristic information, the lack of fusion in MPAW of ultra-thin sheets edge welds can be detected in real time. The proposed in-process monitoring method makes the early warning possible. It also can provide feedback for real-time control and can serve as a basis for intelligent defect identification.
Highlights
Edge joint weld is a type of welding joint that is commonly used in ultra-thin-walled precision metal parts and components in industries of aircraft, aerospace, nuclear power, petrochemical, metallurgy, etc., such as the bellows-type accumulator in launch vehicle [1,2,3]
This paper proposed an effective vision-based weld pool monitoring method for detecting lack of fusion during micro-plasma arc welding (MPAW) of ultra-thin sheets edge welds
The morphology of mesoscale weld pool and its tiny dynamic variations can be successfully observed and stably monitored in MPAW of ultra-thin sheets edge welds, which are crucial for reliable process monitoring and defects detection
Summary
Edge joint weld is a type of welding joint that is commonly used in ultra-thin-walled (thickness ≤ 0.15 mm) precision metal parts and components in industries of aircraft, aerospace, nuclear power, petrochemical, metallurgy, etc., such as the bellows-type accumulator in launch vehicle [1,2,3]. These welds are generally welded by precision welding, like micro-plasma arc welding (MPAW), micro-tungsten inert gas welding, or laser welding, which have concentrated energy distributions and narrow heat affected zones [4,5,6]. Several common factors are known to be in favor of the occurrence of this defect, including unstable arc, variation in heat sink, excessive thermal distortion, weld misalignment, impurities on workpiece surface, improper heat input, dimensions out Sensors 2018, 18, 2411; doi:10.3390/s18082411 www.mdpi.com/journal/sensors
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