The effect of shielding gas on deep penetration high power fiber laser welding of thick plate steel for pipe line construction

During deep penetration laser welding, a keyhole is formed in the molten pool due to the intense recoil pressure of evaporation. The formation of the keyhole leads to a deep penetration weld with a high aspect ratio and this is the most advantageous feature of welding by high-energy-density beams. The configuration and characteristics of a keyhole are related to the welding stability. In a fiber laser butt-joint welding of Type 304 austenitic stainless steel plate with a high power 10 kW continuous wave fiber laser, an infrared sensitive high-speed video camera was used to capture the dynamic images of the molten pools. The configurations of a keyhole were analyzed through image processing techniques such as median filtering, wiener filtering and gray level threshold segmentation to obtain the edge of a keyhole. The width and the area of a keyhole were defined as the keyhole characteristic parameters, and the deviation between the laser beam and weld center as a parameter reflecting the welding stability. By analyzing the change of the keyhole characteristic parameters during welding process, it was found that these parameters were related to the welding stability. Welding experimental results and analysis of the keyhole characteristic parameters confirmed that the welding stability could be monitored and distinguished by a keyhole configuration during high-power fiber laser welding.

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Extraction of Characteristic Parameters of Keyhole during High Power Fiber Laser Welding

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.201-202.352 ◽

2012 ◽

Vol 201-202 ◽

pp. 352-355

Author(s):

Yong Hua Liu ◽

Xiang Dong Gao

Keyword(s):

Laser Welding ◽

Fiber Laser ◽

High Power ◽

Continuous Wave ◽

Welding Process ◽

Detection Methods ◽

Deep Penetration ◽

Welding Quality ◽

Characteristic Parameters ◽

Fiber Laser Welding

During deep penetration laser welding, a keyhole is formed in the molten pool. The characteristics of keyhole are related to the welding quality and stability. Analyzing the characteristic parameters of a keyhole during high power fiber laser welding is one of effective measures to control the welding quality and improve the welding stability. This paper studies a fiber laser butt-joint welding of Type 304 austenitic stainless steel plate with a high power 10 kW continuous wave fiber laser, and an infrared sensitive high-speed video camera was used to capture the dynamic images of the molten pools. A combination filtering system with a filter length of 960-990nm in front of the vision sensor was used to obtain the near infrared image and eliminate other light disturbances. The width, the area, the leftmost point, the rightmost point, the upmost point and the bottommost point of a keyhole were defined as the keyhole characteristic parameters. By using the image preprocessing method, such as median filtering, Wiener filtering, threshold segmentation and Canny edge detection methods, the characteristic parameters of a keyhole were obtained. By analyzing the change of the keyhole characteristic parameters during welding process, it was found that these parameters could reflect the quality and stability of laser welding effectively.

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Detection of Seam Offset Based on Molten Pool Characteristics during High-Power Fiber Laser Welding

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.549.1064 ◽

2012 ◽

Vol 549 ◽

pp. 1064-1068

Author(s):

Jian Bin Liang ◽

Xiang Dong Gao ◽

De Yong You ◽

Zhen Shi Li ◽

Wei Ping Ruan

Keyword(s):

Laser Welding ◽

Fiber Laser ◽

High Power ◽

Molten Pool ◽

High Energy ◽

High Energy Density ◽

Deep Penetration ◽

Characteristic Parameters ◽

Fiber Laser Welding ◽

Deep Penetration Welding

Laser welding includes the heat conduction welding and the deep penetration welding. Deep penetration welding can not only penetrate the material completely, but also can vaporize the material. An important phenomenon during deep penetration welding is that molten pool in the weldment will appear a keyhole. The formation of the keyhole leads to a deep penetration weld with a high aspect ratio and this is the most advantageous feature of welding by high-energy-density beams. Small focus wandering off weld seam may result in lack of penetration or unacceptable welds, and largely reduce heating efficiency. In a fiber laser butt-joint welding of Type 304 austenitic stainless steel plate with a high power 6kW continuous wave fiber laser, an infrared sensitive high-speed video camera was used to capture the dynamic images of the molten pools. The configurations of molten pools were analyzed through image processing techniques such as median filtering, partial Otsu threshold segmentation and Canny edge to obtain the edge of keyholes and molten pools. The circular degree and the area of keyholes and the width and average gray of molten pools were defined as characteristic parameters to reflect the seam offset between the laser beam and the weld center. By analyzing the change of characteristic parameters during welding process, it was found that these parameters were related to the seam offset. Welding experimental results and analysis of characteristic parameters confirmed that the seam offset could be monitored and distinguished by molten pools configuration during high-power fiber laser welding.

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