High Speed Videography of Welding — Part 2: Applications with Front- and Backlighting

This paper is the second of a three-part series covering the field of high-speed videography in welding. This second part provides a comprehensive discussion of two of the most common techniques of high-speed imaging of welding: backlighting and frontlighting, including broad and narrow-spectrum lighting (lasers in the case of backlighting) with both techniques. In all cases, building on the foundations laid out in Part 1, detailed descriptions of appropriate setups are provided together with examples of published practical implementations. The welding processes addressed include laser beam welding, gas tungsten arc welding, gas metal arc welding (GMAW), flux cored arc welding, and submerged arc welding. The advantages and disadvantages of front- and backlighting are explored in detail. Frontlighting is especially useful for processes with high dynamic range, such as short-circuit metal transfer in GMAW. Backlighting is less used with modern digital cameras; however, small amounts of backlighting can highlight features such as the electrode extension when using natural radiation lighting. Narrow-spectrum sources such as lasers are especially useful in combination with narrow bandpass filters to eliminate unwanted radiation sources. The implementations of front- and backlighting reviewed in this paper, together with those for natural radiation lighting in Part 3 and the fundamental concepts and resulting quantitative guidelines provided in Part 1, provide welding researchers with a previously inexistent compilation of criteria to select proper equipment, accessories, and parameters for high-speed imaging of a vast variety of phenomena in welding, laser welding, and associated processes such as additive manufacturing or cutting.