The influence mechanism of variable polarity plasma arc pressure on flat keyhole welding stability

The keyhole digging process associated with variable polarity plasma arc (VPPA) welding remains unclear, resulting in poor control of welding stability. The VPPA pressure directly determines the dynamics of the keyhole and weld pool in the digging process. Here, through a high speed camera, high frequency pulsed diode laser light source and X-ray transmission imaging system, we reveal the potential physical phenomenon of a keyhole weld pool. The keyhole depth changes periodically corresponding to the polarity conversion period if the current is same in the electrode negative (EN) phase and electrode positive (EP) phase. There exist three distinct regimes of keyhole and weld pool behavior in the whole digging process, due to the arc pressure attenuation and energy accumulation effect. The pressure in the EP phase is smaller than that of the EN phase, causing the fluctuation of the weld pool free surface. Based on the influence mechanism of energy and momentum transaction, the arc pressure output is balanced by separately adjusting the current in each polarity. Finally, the keyhole fluctuation during the digging process is successfully reduced and welding stability is well controlled.

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Experimental Analysis of Welding Parameters on Variable Polarity Plasma Arc Pressure

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.651.355 ◽

2013 ◽

Vol 651 ◽

pp. 355-360 ◽

Cited By ~ 7

Author(s):

Yi Jiang ◽

Ming Liu ◽

Yao Hui Lu ◽

Bin Shi Xu

Keyword(s):

Arc Welding ◽

Gas Flow ◽

Welding Current ◽

Welding Parameters ◽

Plasma Arc Welding ◽

Plasma Arc ◽

Arc Pressure ◽

Variable Polarity ◽

Reversed Polarity ◽

Variable Polarity Plasma Arc

Variable polarity plasma arc welding has been widely used to manufacture industries. The effects of welding current and plasma gas flow as the most important parameters on variable polarity plasma arc pressure were discussed experimentally. To welding current, two experimental were designed to discuss the effects of straight polarity current and reversed polarity current on arc pressure respectively. It could be concluded that arc pressure is quadratic with welding current. To plasma gas flow, both experimental and numerical analysis are used to discuss the mechanisms of plasma gas flow to arc pressure, and it could be conclude that arc pressure is quadratic with plasma gas flow rather than linear.

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Experimental Analysis on the Variable Polarity Plasma Arc Pressure

Chinese Journal of Mechanical Engineering ◽

10.3901/cjme.2011.04.607 ◽

2011 ◽

Vol 24 (04) ◽

pp. 607 ◽

Cited By ~ 14

Author(s):

Yi JIANG

Keyword(s):

Experimental Analysis ◽

Plasma Arc ◽

Arc Pressure ◽

Variable Polarity ◽

Variable Polarity Plasma Arc

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Physical mechanism of material flow in variable polarity plasma arc keyhole welding revealed by in situ x-ray imaging

Physics of Fluids ◽

10.1063/5.0036587 ◽

2021 ◽

Vol 33 (1) ◽

pp. 017121

Author(s):

Bin Xu ◽

Shujun Chen ◽

Shinichi Tashiro ◽

Fan Jiang ◽

Manabu Tanaka

Keyword(s):

Material Flow ◽

Physical Mechanism ◽

Plasma Arc ◽

X Ray ◽

Keyhole Welding ◽

X Ray Imaging ◽

Variable Polarity ◽

Variable Polarity Plasma Arc

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Prediction of the Weld Pool Stability by Material Flow Behavior of the Perforated Weld Pool

Materials ◽

10.3390/ma13020303 ◽

2020 ◽

Vol 13 (2) ◽

pp. 303

Author(s):

Ruiqing Lang ◽

Yongquan Han ◽

Xueyu Bai ◽

Haitao Hong

Keyword(s):

Weld Pool ◽

Material Flow ◽

Flow Behavior ◽

Maximum Velocity ◽

Plasma Arc ◽

Mechanical Coupling ◽

Arc Pressure ◽

Variable Polarity ◽

Weld Pools ◽

Variable Polarity Plasma Arc

This article presents the application of a computational fluid dynamics (CFD) finite volume method (FVM) model for a thermo-mechanical coupling simulation of the weld pool used in variable polarity plasma arc welding (VPPAW). Based on the mechanism of the additional pressure produced through self-magnetic arc compression and the jet generated from mechanical plasma arc compression, and considering the influence of arc height and keyhole secondary compression on arc pressure, a three-dimensional transient model of variable polarity plasma arc (VPPA) arc pressure was established. The material flow behaviors of the perforated weld pools were studied. The results show that three kinds of flow behavior existed in the perforation weld pools and it is feasible to predict the weld pool stability by the material flow behaviors of the perforated weld pools. The weld pools can exist stably if the material flow in the bottom of the perforated weld pools can form confluences with moderate flow velocities of 0.45 m/s, 0.55 m/s and 0.60 m/s. The weld pools were cut when the material flowed downward and outward with the maximum velocity of 0.70 m/s, 0.80 m/s. When the maximum material flow velocity was 0.40 m/s, the weld pool collapsed downward under the action of larger gravity. The thermo-mechanical coupling model was verified by the comparison of the simulation and experimental results.

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Material flow in variable polarity plasma arc keyhole welding of aluminum alloy

Journal of Manufacturing Processes ◽

10.1016/j.jmapro.2018.10.023 ◽

2018 ◽

Vol 36 ◽

pp. 480-486 ◽

Cited By ~ 5

Author(s):

Zhaoyang Yan ◽

Shujun Chen ◽

Fan Jiang ◽

Ning Huang ◽

Suolai Zhang

Keyword(s):

Aluminum Alloy ◽

Material Flow ◽

Plasma Arc ◽

Keyhole Welding ◽

Variable Polarity ◽

Variable Polarity Plasma Arc

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On-line monitoring of the keyhole welding pool in variable polarity plasma arc welding

Proceedings of the Institution of Mechanical Engineers Part B Journal of Engineering Manufacture ◽

10.1243/095440502760291817 ◽

2002 ◽

Vol 216 (9) ◽

pp. 1265-1276 ◽

Cited By ~ 7

Author(s):

H Wang ◽

R Kovacevic

Keyword(s):

Arc Welding ◽

Plasma Arc Welding ◽

Plasma Arc ◽

Ann Model ◽

Image Processing Algorithm ◽

Welding Pool ◽

Keyhole Welding ◽

Variable Polarity ◽

Close Relationship ◽

Variable Polarity Plasma Arc

This paper presents a technique to monitor the weld penetration in real time by the front-side image sensing of the keyhole welding pool in variable polarity plasma arc welding (VPPAW) of a 6061 aluminium alloy. A novel optical system is developed to acquire the keyhole welding pool images from two sides of the plasma arc welding torch. The geometric sizes of the visible keyhole can be accurately obtained by using the developed image-processing algorithm. The variation in sizes of the visible keyhole has a close relationship with the real diameter of the keyhole. An artificial neural network (ANN) model is established to describe the relationship between the keyhole diameter and the geometrical sizes of the keyhole welding pool obtained from the image.

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