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

2002 ◽  
Vol 216 (9) ◽  
pp. 1265-1276 ◽  
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.

Feasibility study of acoustic sensing for the welding pool mode in variable-polarity plasma arc welding

2002 ◽  
Vol 216 (10) ◽  
pp. 1355-1366 ◽  
Author(s):  
H Wang ◽  
R Kovacevic
Keyword(s):  
Acoustic Signal ◽  
Arc Welding ◽  
Welding Process ◽  
Plasma Arc Welding ◽  
Plasma Arc ◽  
Welding Pool ◽  
Power Spectral ◽  
Variable Polarity ◽  
Short Time ◽  
Variable Polarity Plasma Arc

The relationships between the acoustic signal and the modes of the welding pool, such as no-keyhole (melt-in), keyhole and cutting, in variable-polarity plasma arc welding are investigated. The Welch power spectral density (PSD) estimate and short-time Fourier transformation are implemented to analyse and identify the different modes of the welding pool. The results show that the no-keyhole mode (melt-in welding process) can be clearly distinguished from the keyhole and the cutting modes. The keyhole size is inversely proportional to the Welch PSD estimate of the acoustic signal.

Experimental Analysis of Welding Parameters on Variable Polarity Plasma Arc Pressure

2013 ◽  
Vol 651 ◽  
pp. 355-360 ◽  
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.

Workpiece Cleaning During Variable Polarity Plasma Arc Welding of Aluminum

1994 ◽  
Vol 116 (4) ◽  
pp. 463-466 ◽  
Author(s):  
Q. Pang ◽  
T. Pang ◽  
J. C. McClure ◽  
A. C. Nunes
Keyword(s):  
Arc Welding ◽  
Dielectric Breakdown ◽  
Surface Preparation ◽  
Refractory Oxide ◽  
Plasma Arc Welding ◽  
Plasma Arc ◽  
Reverse Polarity ◽  
Variable Polarity ◽  
Variable Polarity Plasma Arc

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.

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

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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