Process scheme for the stabilized standoff distance formation based on powder behavior during laser directed energy deposition

Abstract

Geometric defects, particularly for the uniformity interlayer height distribution due to fluctuations in standoff distance (SD), tend to occur in the laser directed energy deposition (DED-LB) forming of thin-walled parts, which can severely compromise the dimensional accuracy and quality of final manufactured parts. To address this challenge, a novel control framework is developed through the integration of real-time layer height monitoring and dynamic SD adjustment. First, the full analytical model of the laser-powder-melting pool interaction was solved using the finite difference method, and the optimal powder feeding process parameters for forming were obtained. Then, the geometric accuracy of thin-walled parts under different SD was analyzed. A Z-axis uplift compensation strategy was proposed to control the stability of the SD amount in DED-LB thin-walled part formation. Finally, experimental analysis was performed to validate the effectiveness of the control method for the geometric accuracy and material properties of the formed thin-walled parts. The results indicated that the flight speed and acceleration of the powder particles followed a linear trend. The highest powder utilization occurred during the zero SD deposition process. The optimal forming SD for the thin-walled parts was found to be 0 mm. Instability in energy input caused by fluctuating SD was identified as the primary factor contributing to the reduced geometric accuracy and performance of the thin-walled parts. Under stable zero SD (SZ-SD) control, the surface roughness of the thin-walled parts improved by 49.1 %, layer height uniformity increased by 38.5 %, and the forming height rose from 14.71 mm under unstable negative SD (UN-SD) to 19.37 mm, significantly boosting forming efficiency. Moreover, the high cooling rate refined the grain structure, reduced the harmful Laves phase and texture strength, leading to a 12.9 % increase in tensile strength and a more uniform hardness distribution. This study provides valuable theoretical and technical support for enhancing the forming quality and efficiency of DED-LB thin-walled parts, contributing to the advancement of intelligent manufacturing.