Laser Powder Bed Fusion (LPBF) has become increasingly important in recent years as an additive manufacturing technology for metal components in industrial production. However, the current LPBF machine technology is limited in terms of the maximum achievable build volume, especially concerning the build area of the powder bed. Enlarging the build area makes it increasingly challenging to maintain uniform process conditions across the entire powder bed regarding the shielding gas flow and the optical system.
In this work, these challenges are addressed by decoupling the process conditions from the size of the build area. For this purpose, a novel machine concept based on a movable processing head is investigated. The underlying principle is that the processing head is equipped with a local shielding gas flow and a laser scanner system. By means of a linear axis system, the processing head is moved across the powder bed.
Based on this machine concept, a large-format machine has been realized, comprising a movable 5-scanner processing head and a build area of 1000 mm x 800 mm. To ensure uniform process conditions across the build area, methods for the calibration and adjustment of the relevant machine subsystems are introduced. Regarding the geometric accuracy of the machine, geometry models are developed which help to analyze how errors of the linear axis system affect the positioning accuracy of the laser spots in the processing plane. In addition, a novel camera-based method for scan field calibration and multi-scanner alignment is proposed. As a basis for the CAM system for this machine type, algorithms for balancing the workload among multiple laser scanner systems and for path planning of the processing head across the powder bed are introduced.
Finally, demonstrator parts manufactured with the large-format machine are presented, with the largest part having outer dimensions of 600 mm in diameter and 280 mm in build height. These demonstrators exhibit consistently high part quality across the large part dimensions, proving the suitability of the machine concept and the effectiveness of the methods developed.