In situ calibration of galvanometric scanning head for laser powder bed fusion machines based on a vision system

• Published in: International journal of advanced manufacturing technology Vol. 111; no. 5-6; pp. 1767 - 1783
• Main Authors: Le, Van Thao, Quinsat, Yann
• Format: Journal Article
• Language: English
• Published: London Springer London 01-11-2020; Springer Nature B.V; Springer Verlag
• Subjects: CAE) and Design; Calibration; Computer-Aided Engineering (CAD; Data acquisition; Delay time; Engineering; Engineering Sciences; Engraving; Galvanometers; Geometric accuracy; In situ measurement; Industrial and Production Engineering; Laser beams; Lasers; Mathematical analysis; Measurement methods; Mechanical Engineering; Mechanics; Media Management; Melting; Original Article; Powder beds; Rapid prototyping; Scanners; Scanning; Vision systems; Laser powder bed fusion; Galvanometric scanning system; Vision system; Additive manufacturing; Image processing; calibration; In- situ calibration
• ISSN: 0268-3768; 1433-3015
• DOI: 10.1007/s00170-020-06189-7

In laser powder bed fusion (LPBF) additive manufacturing machines, a laser galvanometric scanning system is used to control the movement of the laser beam, which melts material powders layer-by-layer in a powder bed. Errors between desirable positions and actual positions of the laser in the work plane of the machine directly affect the geometry accuracy of built parts. Therefore, calibrating the laser galvanometric scanning system of LPBF machines is a very important task. This system is generally calibrated by calculating correction tables for its joint components. However, most existing calibration methods require a measuring phase of actual positions of laser engraved on a calibration plate. This phase was generally performed by a measuring system in another location, thus requiring a delay time and causing an interruption of the calibration process. In the current study, an
in situ
calibration method for the laser galvanometric scanning head of LPBF machines was developed based on a vision system. The vision system (i.e., a high-resolution monochrome camera) was used to acquire experimental data rapidly during the calibration process, thereby avoiding the laser marking and the measuring phases of laser marks in another location. The acquired experimental data was subsequently used to calculate the correction tables/matrices for calibrating the optical chain of an LPBF machine prototype. The obtained results show that the developed measurement method is acceptable for the
in situ
measurement with a good accuracy. After the calibration process, errors between the positions generated by the identified LPBF machine and those measured by the proposed method are very small with an average error of 0.03 mm, and about 80% of positions present an error less than 0.04 mm in the calibration region.