SUMMARY

Qualifying laser and optics systems in laser powder bed fusion (LPBF) additive manufacturing (AM) is critical to ensuring repeatable machine operation and predictable final component properties; a key to the widespread adoption of AM for producing safety-critical parts. In LPBF, an f-θ lens focuses a laser beam over some flat working region to melt and fuse powder material into a bulk component. The focal plane, defined as the surface on which the beam is focused by the f-θ lens, is nominally flat and coincident with the build plane, which is defined by the machine powder recoating system. The development and application of a low-cost, scalable, artifact-based method for measuring the focal plane deviation from the build plane over the working area for an LPBF system is presented. Anodized aluminum samples are etched at varying offsets from the nominal build plane and etched track widths are measured to estimate the beam diameter and generate a beam caustic over the build platform. The minimum location of a hyperbolic fit to the track width data is taken to be the focus location of the beam along the machine z-axis. The location of the focus point is mapped over the build platform. It is also demonstrated that focal plane orientation error can be evaluated with high accuracy, employing this measurement method to qualify the alignment of, and calibrate, LPBF optics systems. Additionally, the optimal materials and process parameters for this measurement method are identified. An anodized aluminum process map is generated for a set of laser power, scan speeds, and beam defocus. The track width and variation in track widths at each set of parameters are evaluated and establish an optimal parameter set for use with the focal plane error measurement method developed.