At Xiris we are all about viewing weld processes in ways you’ve never seen before. Surely most people have not seen the imaging capabilities of a weld camera in a Schlieren application, which is why we wanted to share it.
Schlieren is defined as the “discernible layers in a transparent material that differ from the surrounding material in density or composition.”1 These layers can be captured with the high dynamic range of a weld camera when used in a schlieren optics setup.
The physics behind it is quite simple. A light source is set up to point directly at a concave mirror, and that light refracts off the mirror. However, due to the schlieren effect the light will travel back in different directions depending on the density, temperature or pressure of the air, meaning it no longer passes through the same focal point. Using a razor blade edge set at precisely the right point, it is able to bisect the new focal point so that less dense air gets completely rejected whereas the light refracted through denser air passes through. A weld camera with high dynamic range is then set up to focus on the refracted light that does pass through, capturing inhomogeneities in the air of an object that is placed directly in front of the concave mirror, such as the flow of shielding gas in a weld process.
Diagram of the Schlieren Optics Set Up (courtesy of Harvard University)2
Recently, our friends at ESAB Sweden have been experimenting with their own Schlieren photography using a Xiris Weld Camera. With a 500 mm focal length concave mirror, a red LED light and a razor blade they were able to construct a DIY Schlieren optics set up. It is quite tricky to get the set up exactly right, but once perfected, the goal is to capture the flow of shielding gas during a welding process. Other potential applications of this set up exist as well, such as visualizing the shielding gas and heat flow in GMAW welding processes, while also being able to monitor the details of the melt pool and drop forming. The result is a clean and crisp video of the complete welding process that has rarely been seen before.
Image of the Weld Camera Capturing the Welding Gun in the Schlieren Optics Set Up
Image of the Schlieren Optics Setup with a Xiris Weld Camera
And here is a short video of their Schlieren Imaging Set Up:
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