Additive manufacturing letters最新文献

Conventional robotic wire arc additive manufacturing technologies enable the rapid production of moderate-sized components using low-cost wire feedstocks and robotic welding systems. Efforts to date have primarily focused on single robot solutions. However, new configurations are possible with coordination of multiple robots and multi-degree of freedom positioners. This paper describes a new multi-agent control paradigm that enables multiple robots to work collaboratively on manufacturing a single component on a rotating platform. The advantages of this approach are increased deposition rate and productivity. This paper demonstrates this control strategy on a 19 degrees-of-freedom platform based on three wire arc additive systems surrounding a single rotating platform.

This study investigates the fabrication of conductive structures for electronics applications using embedded 3-D printing coupled with Volumetric Additive Manufacturing (VAM). Electrically conductive carbon grease was suspended within a resin matrix, and the samples underwent VAM printing and post-processing. The resulting three dimensional conductive structure was measured to have a resistance of 4.5 kΩ, corresponding well with the material specifications. The results showed the importance of complete encapsulation of the conductive material within the resin to preserve the conductive structure. The resistivity of the conductive grease remained unaffected, indicating no interaction with the resin. Potential enhancements to improve the structure's fidelity and broaden its range of applications is discussed. This research highlights the potential of embedded 3-D printing for fabricating conductive structures in VAM. The fabrication method allows for unprecedented avenues in developing electronic applications, such as smart sensing, smart drug delivery and cyborganics.

A single-phase Ni-superalloy (Hastelloy X) was fabricated by laser powder bed fusion (L-PBF) using different layer-thicknesses (i.e., 40, 60, 80, and 120 µm), by implementing different optimized volumetric laser energy densities (i.e., VED of 67, 44, 31, and 35 J/mm³). As-built (AB) microstructure, grain morphology, and the recrystallization kinetics were systematically dependent on VED which generally decreases by increasing layer thickness. An increased VED led to a columnar grain morphology, strong texture, large lattice micro-strain, high fraction of low angle boundaries, and increased yield strength. Electron back scattered diffraction (EBSD) analysis revealed that also the recrystallization kinetics was significantly dependent on VED. By decreasing the VED, recrystallization was largely suppressed because of the lower dislocation density in the AB state. A processing map to study the recrystallization as a function of VED, and solution annealing temperature is proposed.

Freeze-dry pulsated orifice ejection method (FD-POEM) shows great potential in producing spherical refractory or multi-component alloy powders. However, addressing the dispersibility issue of high-concentration slurries is required to broaden the application scope of FD-POEM in additive manufacturing. To this end, this study proposes the use of ultrafine bubble (UFB) water as an economical additive to improve slurry dispersibility without introducing impurities. A refractory MoSiBTiC alloy with complex compositions was chosen as an example to demonstrate the effect of UFBs on the dispersibility of the slurry mixture and the morphology of the FD-POEM powders. The underlying mechanism of the improved slurry dispersibility was elucidated through calculations of repulsive forces. Consequently, the operational range for the FD-POEM process was significantly expanded from 10 to 20 % when using UFB water. In addition, the MoSiBTiC alloy build was fabricated via laser powder bed fusion (L-PBF) using FD-POEM-produced powders with UFB additives, exhibiting uniform dendrites and fine TiC nanoparticles distributed in the matrix. This study not only expands the potential applications of UFB water in powder fabrication but also paves the way for the processability of Mo-based parts with advanced microstructures by combining FD-POEM with L-PBF.

Wire laser additive manufacturing (WLAM) is an emerging process to build rapidly metal parts of low complexity. In this paper, single beads of low alloy carbon steel, ER120, were welded with a filler on a S355J2 substrate to reproduce the conditions met in WLAM. The impact of the process parameters (power, wire feedrate, travel speed, spot size) on the stability and geometry of the beads were investigated. A configuration with a dual spot was also studied and found to give analogous results to a single, larger spot of the same area. For each bead dimension (height, width, area, depth) a power law relationship with the process parameters is fitted. Descriptors based on volume energy density and enthalpy were proposed to describe the transition from a conduction mode welding to a keyhole stage, which can lead to the creation of pores in the part.

Additive manufacturing with local composition control is uniquely suited for the development and exploration of advanced materials with compositionally graded structures. A fused filament fabrication printer was designed with in situ composition control facilitated by using an active-mixing hotend. Stepper motors drive three filament extruders and a mixing rod in proportions instructed by a print file to control composition and material distribution within extrusions. Composition tailoring was demonstrated by printing specimens with twelve distinct regions each consisting of unique filament mixtures. Local control of composition was demonstrated by printing a variety of specimens with composition gradients having horizontal, vertical, radial, and circumferential orientations. The tensile properties of printed materials were modified by printing with mix ratios of polylactic acid and thermoplastic polyurethane. Eight blend ratios were tested in tension and have tensile moduli ranging from 17.3 to 3480 MPa. These methods demonstrate advanced capabilities that are well suited for manufacturing functionally graded structures.

Processing of soft magnetic materials with additive manufacturing has shown capability to deliver good magnetic properties and increased silicon content of Fe-6.5 wt%Si, however methods must be used to reduce the eddy currents in large bulk cross-sections in components created by additive manufacturing. Geometrical design has been shown to do this effectively, however stochastically cracked parts show similar magnetic performance with a large increase in stacking factor. To enable their use in electrical machines the mechanical properties of this material must be understood. Therefore, this study uses uniaxial tensile testing to understand the mechanical performance. The ultimate tensile strength of the material in the as-built condition was 17.9 MPa (σ = 4.5 MPa), which was improved by 40% to 25.5 MPa (σ = 5.7 MPa) by infiltrating the cracks with a low viscosity resin. This brings the material strength to more than three standard deviations from the required strength of 7 MPa to be used in a specific axial flux machine. The material exhibited an elongation to failure of 8-10%, showing that the suppression of ordered phases by high cooling rates has improved the ductility of the material. Hence, the stochastically cracked parts have sufficient properties to be used in the 3D magnetic circuits of electrical machines.

A report on twinning-induced plasticity in 316L stainless steel manufactured by metal additive manufacturing (AM) is presented. A tapered tensile test geometry was used which enabled the investigation of twin formation over a range of strain levels in a single specimen. Hardness and twinning concentration were observed to increase with strain up to peak values of 380 ± 10 HV and 28 ± 4%, respectively. Furthermore, twin formation was found to be regulated by grain size and crystal texture. This methodology can be applied to new AM materials development and will inform the design of energy-absorbing structures that maximise the benefits of AM design and strain-hardenable materials.

Fe-Co alloys are an important class of soft magnetic materials that often pose challenges in their fabrication because of the brittle B2-ordered phase. We show that laser beam powder bed fusion (PBF-LB), owing to its rapid cooling rates, offers an avenue for the fabrication of these alloys by suppressing the disorder →order phase transformation at room temperature. We use neutron diffraction to understand the phase transformations in a Fe-50 %Co alloy fabricated via PBF-LB. We report that the disorder→order phase transformation in this alloy occurs concurrently via homogeneous ordering and classical nucleation and growth.

In the current study, the effects of different post-processing methods, including heat treatment (HT) and electro-chemical polishing (ECP) as well as their combination on the surface texture, porosity, microstructure, mechanical properties, and rotating bending fatigue behavior of U-notched laser powder bed fused AlSi10Mg specimens were comprehensively investigated. In addition, to better understand the effects of the applied post-processing methods on the sensitivity of the notched specimen to surface and near-surface defects, finite element analysis was performed. Chemical treatment was found to be very influential on surface texture modification of the very narrow notched parts, for which the application of other treatments can be quite challenging. It was also found that the fatigue behavior of the notched specimens was more sensitive to the surface texture rather than to the near-surface defects. The hybrid treatment involving HT+ECP was the most effective for fatigue behavior improvement due to simultaneous homogenization of the microstructure, released tensile residual stresses, enhanced ductility and high surface texture modification.