Investigating the influence of target distance in laser offline measurement based on self-mixing interference and its potential for monitoring additive manufacturing processes

Abstract

Laser-based Directed Energy Deposition (LDED) is influenced by various factors such as process parameters during the layer-by-layer deposition process, which leads to severe defects and the unstable mechanical properties of the fabricated parts. Monitoring and measuring the dimensions and defects of the parts during the manufacturing process can facilitate real-time adjustments of process parameters to improve the yield of the manufacturing process. However, the existing LDED equipment imposes challenging environmental conditions for millimeter-range measurement methods, and the processing area sizes are different which require different measurement distances. Existing measurement methods often encounter issues such as reduced measurement accuracy or complex data processing when implementing centimetre-range measurements. Therefore, this paper proposes an offline measurement method based on laser self-mixing interference and investigates the influence of distance targets on the feedback signal received. Our in-house developed measurement device utilized a 200 mW near-infrared laser diode to measure the dimensions of a series of centimetre-sized single-wall samples processed with Polylactic Acid (PLA) polymer, 1064 Aluminium alloy, and 316L stainless steel. By processing the feedback signals, the dimensions of the defects within the target can be determined. Experimental results demonstrate that the measurement accuracy can reach up to 99.620 % for a target positioned within 300 mm. The results showcase the potential of our proposed measurement method in the field of additive manufacturing process monitoring.