TPT May 2012

I nspection & T esting

Monitoring of precision welding MOST open arc welding processes, regardless of the technology used, generate an extremely bright light source at the tip of the weld torch that makes proper monitoring and control of the weld process difficult. A view of the environment around the weld arc is important to ensure that the weld arc is properly sized and aligned with the work pieces it is welding. It is also important to monitor the weld seam and pool after the weld head to make sure that they are properly formed during the welding process. In a manual welding process, an operator uses a weld mask with extremely dark filters to attenuate the light from the weld arc sufficiently to provide detail of the light tip. However, this is not possible for an automated welding cell. Instead, an adaptive camera based system that can properly image the very bright weld arc when in operation, while still being able to see the background areas around the weld, would be of great assistance to the welding industry for automated welding cells. Typically a weld arc might be as much as 10,000,000 times brighter to a camera than the metal area around it. Such a large range of light requires special technology to be applied to see the bright areas of the weld arc while still seeing the darker areas in the background. Early attempts at solutions demonstrated that camera systems can monitor and record the welding process. However, generic CCD sensor technology does not allow for reliable evaluation of the welding process due to over- or under-exposure of the weld environment. Typical solutions involve closing the camera aperture down to only see the weld arc while making the background completely black, or opening the aperture large enough to see the background clearly while making the area of the weld arc super saturated, causing all definition to be lost. Very wide dynamic range cameras have been developed that are capable of imaging about 140-150dB range of brightness (or a ratio in excess of 10,000,000:1 of the brightest pixel to the darkest pixel), whereas most existing cameras are capable of only 50-60dB (about 1,000:1). A camera that is able to accommodate the entire range of light found in a welding environment could be used as a set up tool, a quality control tool or process control tool, resulting in production cost savings and reduced defects in the finishedwelded product. While all types of welding processes can use such technology, automatic welding systems especially benefit, as they are typically too congested or dangerous to have an operator directly monitor the welding process while under operation. In such cases, a camera mounted at the welding arc with a remote monitor allows the operator to view the welding process remotely, improving productivity while minimising health and safety issues. Xiris Automation Inc – Canada Email: sales@xiris.com Website: www.xiris.com

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M ay 2012