From Geometric Precision to Performance: Improved Online Monitoring System for Thin-Walled Parts by Fine Wire Laser Directed Energy Deposition

Difficulties in the geometric and performance control of wire laser additive manufacturing have hindered its widespread application. In this study, an in situ process monitoring system that combines a machine vision-based interlayer height controller (IHC) and P-controller-based melt pool temperature controller (MTC) was developed to improve the vertical dimensional accuracy and mechanical properties of off-axis fine-wire laser-directed energy deposition (OAFW-LDED) for 316 L thin-walled parts. The IHC effectively mitigates external defect inheritance, while its synergy with the MTC ensures process stability, improving the vertical dimensional accuracy to ±0.2 mm. Grain refinement was achieved by controlling the thermal input to optimize the thermal history and heat accumulation. A heterogeneous microstructure with alternating coarse and fine grains was observed and intergranular thermal cracking was suppressed. The yield and tensile strengths increased from 262 to 416 MPa to 313 and 516 MPa, respectively, with improved consistency in the yield strength between the top and bottom sections. However, excessive laser heat input caused interlayer cracks. Conversely, increasing the heat input through substrate preheating did not induce additional cracks and improved the overall hardness consistency of the thin-walled samples. Therefore, this study proposes a new formability control strategy for OAFW-LDEDs of thin-walled parts.