Abstract
In this study a new approach to laser polishing with periodic modulated laser power in the kilohertz regime is introduced. By varying the modulation frequency and modulation time, different periodic laser power curves with varying minimum, peak and average laser power can be created. The feasibility of the method is shown by polishing of vertical built AlSi10Mg L-PBF parts with an initial roughness of Ra = 12.22 µm. One polishing pass revealed a decreasing surface roughness with increasing energy density on the surface up to Ra = 0.145 µm. An increasing energy density results in a rising remelting depth between 50 and 255 µm and a rising relative porosity of 0.3% to 4.6%. Furthermore, the thermal process stability, analysed by the melt pool length in scanning direction, reveals a steadily increasing melt pool dimension due to component heating. Multiple laser polishing passes offers a further reduced surface roughness, especially at higher modulation frequencies and provides an improved orientation independent roughness homogeneity. The process stability regarding varying initial surface roughness revealed an almost constant relative roughness reduction rate with an achievable roughness variation after two polishing passes between Ra = 0.13–0.26 µm from an initial state of Ra = 8.0–19.2 µm.
Highlights
Laser powder bed fusion (L-PBF) is the most common additive manufacturing technique for rapid prototyping and industrial manufacturing of complex individual metal parts with small batches
This paper introduces a new approach to laser polishing by modulated laser power
Laser power modulation of continuous wave laser systems is done by means of the modulation of the pump modules of the resonator
Summary
Laser powder bed fusion (L-PBF) is the most common additive manufacturing technique for rapid prototyping and industrial manufacturing of complex individual metal parts with small batches. Due to the low absorptivity in the near infrared wavelength, which causes high back reflections and an unstable melt pool, laser surface processing of aluminium alloys is challenging and requires high beam intensities [42,43]. Laser polishing of L-PBF-Aluminium AlSi10Mg parts with pulsed and continuous laser radiation can reach high roughness reduction rates up to 98% Ra [44,45,46,47,48]. Pulsed and continuous mode laser polishing of L-PBF surfaces with varying initial roughness by changing fabrication angle revealed a constant relative roughness reduction ability [49]. The process stability and roughness reduction ability at varying initial roughness, caused by different fabrication angles, are analysed and compared to the common continuous and pulsed laser operation modes
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