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.

This study investigated the application of an in envelope additive/subtractive (LPBF) manufacturing method (Matsuura LUMEX-Avance-25) to fabricate IN718 benchmarking coupons. The coupons were then examined comprehensively for surface finish both with and without high-speed micro-machining. The microstructure of the manufactured IN718 coupons was investigated thoroughly in the as-fabricated condition and following three different standard and one non-standard post-processing heat treatments. As built coupons revealed columnar grain morphology mainly along the direction with a cellular dendritic sub-grain structure and without any strengthening precipitates. Grain size, aspect ratio, and texture were maintained after each of the applied four heat treatments. Only one of the standard heat treatments resulted in the δ phase formation. The other three heat treatments effectively dissolved the Laves phase preventing the δ formation while promoting the formation of γ′/γ″ precipitates. Despite the observed differences in their microstructures, all of the heat treatments resulted in similar yield and ultimate tensile strength values that ranged between 1103–1205 MPa and 1347–1387 MPa, respectively. These values are above the minimum requirements of 1034 MPa and 1241 MPa for the wrought material. The non-standard heat treatment provided the highest elongation of 24.0 ± 0.1% amongst all the heat-treated specimens without a significant loss in strength, while the standard heat treatment for the wrought parts resulted in the lowest elongation of 18.3 ± 0.7% due to the presence of δ phase.

The present work investigates the effectiveness of two heat treatment cycles—solution treatment + aging (STA) and direct aging (DA)—on optimizing the microstructure and enhancing the mechanical properties of 18Ni-300 maraging steel (300 MS) produced by additive–subtractive hybrid manufacturing (ASHM). The STA treatment led to a fully martensitic microstructure with minor remnants of the cellular substructures associated with the solidification conditions in ASHM. DA resulted in some reverted austenite and partial dissolution of the cellular morphologies into shorter fragments. Despite the contrasting microstructures, the tensile strength and the macro- and micro-hardness were comparable between STA and DA conditions. By contrast, the potential for improving the ductility was higher with the DA heat treatment. This is attributed to the higher reverted austenite content in the samples treated by DA, i.e., up to a maximum of 13.4% compared to less than 3.0% in the STA samples. For the DA sample with the highest reverted austenite content of 13.4%, the highest local and global fracture strain values of 30.1 and 5.9 ± 0.6% were measured, while the respective values were 23.4 and 4.4 ± 0.1% for the corresponding STA sample. This work suggests that DA of 300 MS produced by ASHM is sufficient to achieve comparable hardness and tensile strength to STA, whilst maintaining reasonable ductility. Avoiding the solution treatment cycle, with its appreciably higher temperatures, could benefit the dimensional stability and surface quality that are important for ASHM of 300 MS parts.

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.

Several applications require low torque pulsations as they can lead to mechanical vibrations and acoustic noise in the electric motor. Optimization of the rotor permanent magnet (PM) shape is one of the effective methods for reducing torque pulsations. Unfortunately, the low versatility of the magnet fabrication technologies limits the development of new motor geometries. Cold spray additive manufacturing can be used for shaping permanent magnets for the direct fabrication of motor parts without the need for additional assembly steps. This fabrication technique allows an increase in the design flexibility of electric machine geometries targeting improved performance. This paper investigates the performance of permanent magnet rotors fabricated using a cold spray additive manufacturing technique for radial flux surface permanent magnet synchronous machines (SPMSM). The permanent magnet rotors considered are conventional rectangular-shaped with unskewed magnets (Model A), skewed magnets (Model B), and sinusoidal-petal shaped magnets (Model C) along the axial direction. The magnitude of magnetization current pulse required to magnetize these rotors is calculated and an impulse magnetizer setup is designed for in-situ magnetization. The performance of the shaped cold sprayed permanent magnet rotors and their effects on back EMF, electromagnetic torque, and cogging torque are analyzed experimentally and comparisons are made between the different rotor designs.

The magnetic performance of NdFeB permanent magnets rapidly decreases as their operation temperature increases. This limits the power output of electric motors as their internal temperature quickly increases with the power demand. This is particularly problematic for applications where high peak power is required for a short period of time, for example during automobile highway acceleration or during an airplane lift-off. With the advances in additive manufacturing, one can envision to fabricate more complex motor geometries and magnetic structures, without additional costs, allowing for enhanced functionalities such as better thermal management. In this context, this paper investigates the feasibility of using phase changing materials (PCMs) to mitigate the temperature rise in permanent magnets (PMs) fabricated by additive manufacturing. The potential of PCM and its relevance was validated by modeling the thermal response of an electric motor during a representative electric vehicle driving scenario. It was found that segmented magnets with embedded phase changing materials would allow to efficiently control temperature rise. To validate the simulation results, PM test pieces with and without embedded PCMs were fabricated using cold spray additive manufacturing and tested using a custom laser thermal cycling setup.