Weld Topography Based on Laser Triangulation
Ahvenjärvi, Jani (2021)
2021
Teknis-luonnontieteellinen DI-ohjelma - Master's Programme in Science and Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2021-04-07
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202103052387
https://urn.fi/URN:NBN:fi:tuni-202103052387
Tiivistelmä
Objective of this thesis was to design and construct a topography measurement device prototype for welding. Purpose of the device was to measure the shape of the weld during welding process. Device was based on laser triangulation and small angles of 10◦ and 20◦ for triangulation were chosen to make device compact in size. Resolutions for different triangulation angles were investigated and performance in MAG welding situation was covered in this thesis. Work was done in collaboration with Cavitar Ltd.
Prototype was implemented as a modular line laser unit that can be used with various welding cameras. Prototype consists of line laser unit, camera unit and a spacer block which integrates line laser unit and camera unit. Line laser package inside line laser unit was optimized and minimized in size to dimensions of width 10 mm, height 8.5 mm an length 20 mm. Wavelength of the laser was 645 nm. Camera unit used in this thesis was Cavitar welding camera C200. Camera unit had filters to reduce light from the welding process. Integration was made by 3D printed spacer block which fixed triangulation angle between camera and laser. Two spacer blocks were made to have two options for angles of 10◦ and 20◦ between camera and laser. Maximum image acquisition frame rate of the prototype was 70 fps with resolution of 1440x1080 pixels.
Resolution of the triangulation device depends on the angle between laser and object surface. One pixel corresponded to height from 400 μm to 85 μm with angles from 0◦ to 60◦ between laser and object surface normal, when angle between camera and laser was 20◦. Corresponding heights for one pixel with angle of 10◦ between camera and laser were from 800 μm to 175 μm.
Prototype was tested in the MAG welding of steel and stainless steel with the laser line located 1 cm behind the meltpool. Visibility of the laser line during welding process was good even with large angles of 70◦ between laser and object surface normal. Welding process had hardly any effect on the measurement. Afterwards welds were measured with commercial laser scanner having a resolution of 36 μm to verify results.
Prototype was implemented as a modular line laser unit that can be used with various welding cameras. Prototype consists of line laser unit, camera unit and a spacer block which integrates line laser unit and camera unit. Line laser package inside line laser unit was optimized and minimized in size to dimensions of width 10 mm, height 8.5 mm an length 20 mm. Wavelength of the laser was 645 nm. Camera unit used in this thesis was Cavitar welding camera C200. Camera unit had filters to reduce light from the welding process. Integration was made by 3D printed spacer block which fixed triangulation angle between camera and laser. Two spacer blocks were made to have two options for angles of 10◦ and 20◦ between camera and laser. Maximum image acquisition frame rate of the prototype was 70 fps with resolution of 1440x1080 pixels.
Resolution of the triangulation device depends on the angle between laser and object surface. One pixel corresponded to height from 400 μm to 85 μm with angles from 0◦ to 60◦ between laser and object surface normal, when angle between camera and laser was 20◦. Corresponding heights for one pixel with angle of 10◦ between camera and laser were from 800 μm to 175 μm.
Prototype was tested in the MAG welding of steel and stainless steel with the laser line located 1 cm behind the meltpool. Visibility of the laser line during welding process was good even with large angles of 70◦ between laser and object surface normal. Welding process had hardly any effect on the measurement. Afterwards welds were measured with commercial laser scanner having a resolution of 36 μm to verify results.