Chinese Journal of Mechanical Engineering: Additive Manufacturing Frontiers最新文献

The inherent capabilities of additive manufacturing (AM) to fabricate porous lattice structures with controllable structural and functional properties have raised interest in the design methods for the production of extremely intricate internal geometries. Current popular methods of porous lattice structure design still follow the traditional flow, which mainly consists of computer-aided design (CAD) model construction, STereoLithography (STL) model conversion, slicing model acquisition, and toolpath configuration, which causes a loss of accuracy and manufacturability uncertainty in AM preparation stages. Moreover, toolpath configuration relies on a knowledge-based approach summarized by expert systems. In this process, geometrical construction information is always ignored when a CAD model is created or constructed. To fully use this geometrical information, avoid accuracy loss and ensure qualified manufacturability of porous lattice structures, this paper proposes a novel toolpath-based constructive design method to directly generate toolpath printing file of parametric and controllable porous lattice structures to facilitate model data exchange during the AM preparation stages. To optimize the laser jumping route between lattice cells, we use a hybrid travelling salesman problem (TSP) solver to determine the laser jumping points on contour scans. Four kinds of laser jumping orders are calculated and compared to select a minimal laser jumping route for sequence planning inside lattice cells. Hence, the proposed method can achieve high-precision lattice printing and avoid computational consumption in model conversion stages from a geometrical view. The optical metallographic images show that the shape accuracy of lattice patterns can be guaranteed. The existence of “grain boundaries” brought about by the multi-contour scanning strategy may lead to different mechanical properties.

The application of titanium alloys in aerospace put forward the requirement for higher strength. Additive manufacturing is a promising method for the efficient and economical processing of titanium alloys. However, research on the additive manufacturing of ultrahigh-strength titanium alloys is still limited. The mechanisms of microsegregation for high alloying elements and poor plasticity are still not clear. In this study, an ultrahigh-strength titanium alloy Ti–4.5Al–5Mo–5V–6Cr–1Nb (TB18) was prepared using two methods: laser direct energy deposition (LDED) and forging. The LDEDed alloy contains three zones with similar grain morphologies but different microstructure. The microsegregation of the alloy is limited due to the rapid solidification and almost eliminated after the thermal cycle and solution treatment. With stress relief treatment, the LDEDed alloy exhibits anisotropic mechanical properties. After solution and aging treatments, its ultimate strength is enhanced; however, its plasticity is relatively lower than that of the wrought alloy with equally high strength. The excellent balance of the strength and plasticity of the wrought alloy can be ascribed to the formation of α_WGB and multiscale α laths, which provides enlightenment for optimizing the properties of the LDEDed alloy.

In this study, the thermal analysis theory of selective laser melting (SLM) was introduced, and different high-entropy alloy (HEA) specimens were prepared using the SLM technology. The effects of different powder sizes, elemental contents, and process parameters on the microstructure and mechanical properties of FeCoNiCrAl_x HEA specimens fabricated using SLM were analyzed. Moreover, hardness and tensile tests of these high-entropy alloys were performed. The results showed that with increasing laser power and hatch spacing, the hardness of the specimens initially increased and subsequently decreased; it also increased with increasing scanning speed. The FeCoNiCrAl_0.5 HEA specimens prepared using fine powder exhibited better tensile properties, followed by FeCoNiCrAl_0.8 HEA. However, the FeCoNiCrAl_0.5 HEA prepared using coarse powder exhibited the poorest tensile properties. A comparison of the tensile properties of the specimens at different heights revealed that the specimens formed at the middle height exhibited improved tensile properties.

Light-weight, high-strength metamaterials with excellent specific energy absorption (SEA) capabilities are significant for aerospace and automobile. The SEA of metamaterials largely depends on the material and structural design. Herein, inspired by the superior impact resistance of pomelo peel for protecting the pulp and the elevated SEA ability of a functionally graded structure, a graded bionic polyhedron metamaterial (GBPM) was designed and realized by 3D printing using a soft material (photosensitive resin) and a hard material (Ti-6Al-4V). Guided by compression tests and numerical simulations, the elevated SEA ability was independent of the materials. The fluctuation region appeared in hard-material-fabricated bionic polyhedron metamaterial (BPMs) and was absent in soft-material-fabricated BPMs in the stress–strain curves, resulting in the growth rate of the SEA value of the soft-material-fabricated GBPM being enhanced by 5.9 times compared with that of the hard-material-fabricated GBPM. The SEA values of soft- and hard-material-fabricated GBPM were 1.89 and 44.16 J/g, which exceed those of most soft- and hard-material-fabricated metamaterials reported in previous studies. These findings can guide the design of metamaterials with high energy absorption to resist external impacts.

In this study, a reduced-order crystal plasticity finite element (CPFE) model was developed to study the effects of the microstructural morphology and crystallographic texture on the mechanical anisotropy of selective laser melted (SLMed) Ti-6Al-4V. First, both hierarchical and equiaxed microstructures in columnar prior grains were modeled to examine the influence of the microstructural morphology on mechanical anisotropy. Second, the effects of crystallographic anisotropy and textural variability on mechanical anisotropy were investigated at the granular and representative volume element (RVE) scales, respectively. The results show that hierarchical and equiaxed CPFE models with the same crystallographic texture exhibit the same mechanical anisotropy. At the granular scale, the significance of crystallographic anisotropy varies with different crystal orientations. This indicates that the present SLMed Ti-6Al-4V sample with weak mechanical anisotropy resulted from the synthetic effect of crystallographic anisotropies at the granular scale. Therefore, combinations of various crystallographic textures were applied to the reduced-order CPFE model to design SLMed Ti-6Al-4V with different mechanical anisotropies. Thus, the crystallographic texture is considered the main controlling variable for the mechanical anisotropy of SLMed Ti-6Al-4V in this study.

Additive remanufacturing technology, as one of the key technologies of remanufacturing engineering, can realize the integrated repair of the structure and function of high value-added key metal parts of large and complex equipment, which can significantly reduce the use and maintenance costs, save labor and time costs. It applies to the on-site repair and remanufacturing of key parts in the aerospace, energy and chemical industry, heavy haul machinery, and other fields, as well as the on-site rapid repair of parts in special environments such as tunnels, open seas, and space. Additive remanufacturing technology can promote the reform of the maintenance and support mode of weapons and equipment and become the research hotspot of major military-developed countries. This paper expounds on the connotation and characteristics of additive remanufacturing technology and introduces its evolution process. The research achievements of the author in the development of additive remanufacturing platforms, material design, and process optimization were summarized. Given the problems (such as control shape, control performance, and control position) in the additive remanufacturing process, the author puts forward solutions and looks forward to the future development direction of additive remanufacturing technology.

Laser powder bed fusion (L-PBF)-processed high-silicon steel has great advantages in freely designed electric engines, and various studies have been conducted in this field. However, the analysis of both the mechanical and magnetic properties, focusing on the multiscale microstructure under as-fabricated and heat-treated conditions, which is indispensable for industrial applications, has not been performed. In this study, an Fe–Ni–Si sample was fabricated using the L-PBF process. Subsequently, the following hot isotropic pressing (HIPing) process was employed as a post heat treatment step for the Fe–Ni–Si alloys. The effects of HIPing on the microstructure were investigated, focusing on the metastable stable phase transformation in the Fe–Ni–Si system. X-ray diffraction results showed single-phase fcc γ (Fe, Ni) in the L-PBF-processed samples before and after HIPing. Moreover, the acicular Ni/Si-rich structure (formed in the as-fabricated L-PBF sample because of its high cooling rates) transformed to the equilibrium austenite, Ni₃Si, and FeNi₃ phases during HIPing. After HIP, the compressive modulus and strength increased from 11 GPa and 650 MPa to approximately 18 GPa and 900 MPa, respectively. The magnetic properties were evaluated via a hysteresis loop, and the coercivity increased from 1.8 kA/m and to 2.9 kA/m after the HIPing process.

Proprietary metal 3D printing is still relegated to relatively expensive systems that have been constructed over years of expensive trial-and-error to obtain optimum 3D printing settings. Low-cost open-source metal 3D printers can potentially democratize metal additive manufacturing; however, significant resources are required to redevelop optimal printing parameters for each metal on new machines. In this study, the particle swam optimization (PSO) experimenter, a free and open-source software package, is utilized to obtain the optimal printing parameters for a tungsten inert gas-based metal open source 3D printer. The software is a graphical user interface implementation of the PSO method and is designed specifically for hardware-in-loop testing. It uses the input of experimental variables and their respective ranges, and then proposes iterations for experiments. A custom fitness function is defined to characterize the experimental results and provide feedback to the algorithm for low-cost metal additive manufacturing. Four separate trials are performed to determine the optimal parameters for 3D printing. First, an experiment is designed to deposit and optimize the parameters for a single line. Second, the parameters for a single-layer plane is optimized experimentally. Third, the optimal printing parameters for a cube is determined experimentally. Fourth, the line optimization experiment is revised and reconducted using different shield gas parameters. The results and limitations are presented and discussed in the context of expanding wire arc additive manufacturing to more systems and material classes for distributed digital manufacturing.