Keyhole Diameter Research Articles

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

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.

Real-time image processing of keyhole puddle in variable polarity plasma arc welding

In a previous study, a simple and practical image-sensing system comprising a narrow band filter and neutral filters was developed to acquire front-side keyhole puddle images in variable polarity plasma arc welding (VPPAW) of aluminium alloys. However, during actual welding, oxides existing on the puddle surface and variations in image quality with respect to keyhole puddle size complicate the processing of images. In this paper, an image-processing method based on an α-cutting-average-median filter, minimum filter, direction enhancement operators and local statistical characteristics enhancement is developed to tackle the various shapes and appearances of the keyhole puddle. Also, an effective edge-tracing method is developed to detect the edge of the visible keyhole. The geometric sizes of the visible keyhole, such as area, width and height, are acquired with sufficient accuracy, which can be used to calculate the keyhole diameter during the welding process. Experiments show that satisfying results can always be obtained with the developed image-processing method regardless of the original image quality. Processing one image frame takes less than 220ms.

Stability of keyhole in plasma arc welding

Stability of the keyhole plays a fundamental role in producing quality welds in keyhole plasma arc welding. Some studies have assumed that keyhole diameter is a stability measurement. However, recent experimental observation by the authors revealed that width is not correlated with stability. To measure stability, this study uses the keyhole width as the lower limit of the weld pool width required to prevent keyhole collapse. Because the maximal width of the weld pool before burn-through is approximately fixed for particular applications, it can be used as the upper limit of the weld pool width for preventing burn-through. Hence, the margins of the keyhole process from collapse and burn-through can be measured based on how close the pool width is to its upper and lower limits. The stability distance and stability factor are then defined based on the margins to quantity the state of the stability of the keyhole process.

大出力レーザ溶接に関する研究 (第1報)

The high power laser welding is performed with very complicated physical phenomena. These physical phenomena should be visualized using several quantitative measurement methods to get a highly reliable welding process. In this experiment, plasma cloud was investigated using a high speed camera and a measuring device to get a plasma voltage. A moltenpool and keyhole was visualized by CCD camera while irradiating N2 laser on the surface. It was found that plasma size was constant even if welding speed changed at both He and Ar gas atmosphere within this experimental condition. Keyhole diameter on the surface was changed from approximately 1 mm to 1.5 mm while varing welding speed and power. Absorption ratio of stainless steel SUS 304 on keyhole welding, also was measured by calorimetric method by measuring the temperature rise of copper block in which SUS 304 test piece was press-fitted. It was found that the absorption ratio shows an almost constant value of 0.7-0.8 even if input energy (J) has been varied.

Enthalpy technique for solution of stefan problems: Application to the keyhole plasma arc welding process involving moving heat source

A computational methodology is carried out to predict the transient development of the weld pool and the temperature histories in the workpiece during plasma arc welding (PAW) of type AISI-304. One aim of this paper is the modelling of conduction heat transfer with phase change where the thermal conductivity and specific heat in the solid region are nonlinear functions of temperature. A stable numerical solution in a two dimensional fixed grid domain is demonstrated when an implicit time scheme, back substitution procedure is used to solve the governing equation. The influence of the different parameters such as, welding speed, keyhole diameter, thermal properties, distance between the nodes in the region of interest and the time steps on the welding quality and numerical consideration are studied.