Mahmoud Osman

This research study investigated the hybrid processing of 316L stainless steel using laser powder bed (LPB) processing with high-speed machining in the same build envelope. Benchmarking at four laser powers (160 W, 240 W, 320 W, and 380 W) was undertaken by building additively with machining passes integrated sequentially after every ten deposited layers, followed by the final finishing of select surfaces. The final geometry was inspected against the computer-aided design (CAD) model and showed deviations smaller than 280 µm for the as-built and machined surfaces, which demonstrate the good efficacy of hybrid processing for the net-shape manufacturing of stainless steel products. The arithmetic average roughness values for the printed surfaces, Ra (linear) and Sa (surface), were 11.4 um and 14.9 um, respectively. On the other hand, the vertical and horizontal machined surfaces had considerably lower roughness, with Ra and Sa values ranging between 0.33 µm and 0.70 µm. The 160 W coupon contained layered, interconnected lack of fusion defects which affected the density (7.84 g·cm⁻³), yield strength (494 MPa), ultimate tensile strength (604 MPa), Young’s modulus (175 GPa), and elongation at break (17.3%). By contrast, at higher laser powers, near-full density was obtained for the 240 W (7.96 g·cm⁻³), 320 W (7.94 g·cm⁻³), and 380 W (7.92 g·cm⁻³) conditions. This, combined with the isolated nature of the small pores, led to the tensile properties surpassing the requirements stipulated in ASTM F3184—16 for 316L stainless steel.

Hybrid manufacturing is often used to describe a combination of additive and subtractive processes in the same build envelope. In this research study, hybrid manufacturing of 18Ni-300 maraging steel was investigated using a Matsuura LUMEX Avance-25 system that integrates metal additive manufacturing using laser powder bed fusion (LPBF) processing with high-speed machining. A series of benchmarking coupons were additively printed at four different power levels (160 W, 240 W, 320 W, 380 W) and with the integration of sequential machining passes after every 10 deposited layers, as well as final finishing of selected surfaces. Using non-contact three-dimensional laser scanning, inspection of the final geometry of the 18Ni-300 maraging steel coupons against the computer-aided design (CAD) model indicated the good capability of the Matsuura LUMEX Avance-25 system for net-shape manufacturing. Linear and areal roughness measurements of the surfaces showed average Ra/Sa values of 8.02–14.64 µm for the as-printed walls versus 0.32–0.80 µm for the machined walls/faces. Using Archimedes and helium (He) gas pycnometry methods, the part density was measured to be lowest for coupons produced at 160 W (relative density of 93.3–98.5%) relative to those at high power levels of 240 W to 380 W (relative density of 99.0–99.8%). This finding agreed well with the results of the porosity size distribution determined through X-ray micro-computed tomography (µCT). Evaluation of the static tensile properties indicated that the coupons manufactured at the lowest power of 160 W were ~30% lower in strength, 24% lower in stiffness, and more than 80% lower in ductility relative to higher power conditions (240 W to 380 W) due to the lower density at 160 W.