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

Variable Polarity Plasma Arc welding has proved to be extremely successful in welding aluminum alloys despite their adherent refractory oxide. This success has been attributed to removal of the oxide during the reverse polarity cycle. In situ optical spectroscopy is used to measure the amount of hydrogen and oxygen in the plasma arc with a minimum detectable limit of less than 100 ppm. It was found that the amount of contamination is independent of surface preparation and torch speed. Using this information, it is proposed that the predominant mechanism for reverse polarity cleaning in aluminum is dielectric breakdown of the surface oxide ahead of the torch rather than by ion sputtering.

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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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The Effect of Weld Gas Flow Rate on Al-Li Weldability

Journal of Engineering for Industry ◽

10.1115/1.2901659 ◽

1993 ◽

Vol 115 (3) ◽

pp. 263-267

Author(s):

L. F. Martinez ◽

J. C. McClure ◽

A. C. Nunes

Keyword(s):

Flow Rate ◽

Arc Welding ◽

Gas Flow ◽

Plasma Arc Welding ◽

Plasma Arc ◽

Gas Flow Rate ◽

Welding Arc ◽

Variable Polarity ◽

Variable Polarity Plasma Arc

Adequate shield and plasma gas flow rate during plasma arc welding are crucial factors in achieving high quality welds. Too low a shield gas flow rate lets atmosphere enter into the arc and too high a rate wastes weld gas and may cause turbulence and entrain atmosphere. Sufficient plasma gas flow is required for keyhole welding and, as shown in this paper, can reduce hydrogen contamination in the weld. In-situ optical spectroscopy used to detect oxygen and hydrogen in the welding arc during variable polarity plasma arc (VPPA) welding of aluminum 2090 revealed that there is an easily detected critical shield gas flow rate needed to exclude atmosphere and that this critical rate can be used to automatically control gas flow rates during welding.

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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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