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

This study investigates the in vitro degradation of calcium-deficient hydroxyapatite powder after heat treatment at different temperatures and analyzes the calculated phase composition, particle size distribution, degradation rate, and bioactivity of the powder after heat treatment. A mixture of hydroxyapatite and β-tricalcium phosphate (BCP) coatings was prepared on the surface of a 3D-printed hydroxyapatite-whisker-strengthened hydroxyapatite scaffold (HA_w/HA) by vacuum impregnation and ultraviolet light curing combined with an optimized heat treatment process. The performance of the coatings under different methods was characterized. The composite scaffolds with highly interconnected pores and excellent mechanical properties were prepared, and their biodegradation performance, bioactivity, osteoconductivity, and osteoinductivity of the scaffolds were improved. The results showed that calcium-deficient hydroxyapatite began to transform into BCP between 600 °C and 800 °C, and the powder treated at 800 °C has better bioactivity. The BCP coating prepared by light curing was more uniform, resulting in a higher interfacial bonding strength, and has better osteoconductivity and osteoinductivity than that prepared by vacuum impregnation.

This paper presents an approach to achieve broadband absorption and temperature resistance using ceramic substrates. A specially formulated slurry suitable for additive manufacturing technology was developed to fabricate ceramic substrates with lattice structures. The lattice structure not only reduces the weight of the absorber but also facilitates the broadening of the absorption bandwidth. The experimental results demonstrate that the proposed structure exhibits absorption rates exceeding 88% within the frequency range of 19.9–30.41 GHz, with a relative absorption bandwidth of 41.8% under normal incidence. Furthermore, the absorber's performance was assessed under high temperatures of up to 200 ℃, revealing absorption spectra that closely match the initially measured spectrum. Additive-manufactured ceramic lattice structures present a promising avenue for designing multifunctional broadband microwave absorbers capable of withstanding elevated temperatures.

Transparent electromagnetic (EM) shielding glass with a metal mesh has significant potential for application in different fields of EM radiation and anti-EM interference light-transmitting observation windows. In particular, a transparent EM-shielding glass with a large-aspect-ratio metal mesh can effectively alleviate the contradictory problems of shielding effectiveness and light-transmission performance constraints. However, the fabrication of high-aspect-ratio metal meshes on glass substrates has problems such as high cost, complex processes, low efficiency, small area, and easy damage issues, which limit their application in the field of high-performance, transparent EM-shielding glass. Therefore, this paper proposes a composite additive manufacturing process based on electric-field-driven microjet 3D printing and electroplating. By fabricating metal meshes with an Ag-Cu core-shell structure on a glass substrate, EM-shielding glass with high shielding efficiency and light transmission can be manufactured without increasing the aspect ratio of the metal meshes. The prepared Ag-Cu composite metal mesh has excellent optoelectronic properties (period 250 μm, line width 10 μm, 90.1% transmission at 550 nm visible light, square resistance 0.21 Ω/sq), efficient electrothermal effect (3 V DC voltage can reach 189 °C steady-state temperature), stable EM-shielding effectiveness (average shielding effectiveness 23 dB at X-band), and acceptable mechanical and environmental stability (less than 3% change in square resistance after 150-times adhesion test and less than 6% and 0.6% change in resistance after 72 h in acid and alkali environments, respectively). This method provides a new solution for the mass production of high-performance large-area transparent electric heating/EM-shielding glass.

The use of composite sandwich structures with cellular cores is prevalent in lightweight designs owing to their superior energy-absorbing abilities. However, current manufacturing processes, such as hot-press molding and mold pressing, require multiple steps and complex tools, thus limiting the exploration of advanced sandwich structure designs. This study reports a novel multi-material additive manufacturing (AM) process that allows the single-step production of continuous fiber-reinforced polymer composite (CFRPC) sandwich structures with multiscale cellular cores. Specifically, the integration of CFRPC-AM and in situ foam AM processes provides effective and efficient fabrication of CFRPC panels and multiscale cellular cores with intricate designs. The cellular core design spans three levels: microcellular, unit-cell, and graded structures. Sandwich structures with a diverse set of unit-cell designs, that is, rhombus, square, honeycomb, and re-entrant honeycomb, were fabricated and their flexural behaviors were studied experimentally. The results showed that the sandwich structure with a rhombus core design possessed the highest flexural stiffness, strength, and specific energy absorption. In addition, the effect of the unit-cell assembly on the flexural performance of the CFRP composite sandwich structure was examined. The proposed design and fabrication methods open new avenues for constructing novel and high-performance CFRPC structures with multiscale cellular cores that cannot be obtained using existing approaches.

High-fidelity simulations of powder bed fusion (PBF) additive manufacturing have made significant progress over the past decade. In this study, an efficient two-dimensional frame was developed for simulating the electron beam PBF process with hundreds of tracks for the direct prediction of the build quality. The applicable parameter range of the developed model was determined by comparing the heat transfer with that in three-dimensional cases. Subsequently, powder deposition and selective melting were coupled for a continuous simulation of the multilayer process. Three powder deposition models were utilized to generate random powder particles, and their effects on the packing structure and the resultant simulated build quality were investigated. The predicted build quality was validated using experimental results from independent studies. By reproducing the building process, the defect development mechanism in a multilayer process was revealed for the coalescence behaviors of randomly distributed powder particles, which also confirmed the importance of simulation at the high-fidelity powder scale. The effects of key process parameters during multilayer and multi-track processes on the build quality were systematically investigated. In particular, the formation statuses of all tracks during the simulated building process were recorded and analyzed statistically, which provided crucial information on the printing process for understanding the building mechanism or performing uncertainty analysis.

Three-dimensional (3D) printing of carbon fiber-reinforced thermoplastic composites (CFRTPs) provides an effective method for manufacturing the CFRTPs parts with complex structures. To increase the mechanical performance of these parts, a 3D printing technology for short-continuous carbon fiber synchronous-reinforced thermoplastic composites (S/C-CFRTPs) has been proposed. However, the synchronous reinforcement that existed only at particular positions led to a limited improvement in the mechanical performance of the 3D-printed S/C-CFRTP part, which made it challenging to meet the engineering requirements. To solve this problem, two methods for achieving synchronous reinforcement at all the positions of the 3D-printed S/C-CFRTP part are proposed. To determine a suitable printing process for the S/C-CFRTP part, a comprehensive comparison between the two methods was conducted through theoretical analysis and experimental verification, involving the printing mechanism, fiber content, impregnation percentage, and mechanical performance. The results indicated that the towpreg extrusion process was suitable for manufacturing the 3D-printed S/C-CFRTP part. Compared with the in situ impregnation process, the towpreg extrusion process led to a fiber content increase of approximately 7% and void rate reduction of approximately 6%, resulting in 19% and 20% increases in the tensile and flexural strengths of the 3D-printed S/C-CFRTPs, respectively. Additionally, an optimized process parameter setting for fabricating an S/C-CFRTP prepreg filament with excellent mechanical performance was proposed. The findings of this study can provide a new approach for further improving the mechanical performance of the 3D-printed advanced composites.

This paper presents a customized design method for ergonomic products via additive manufacturing (AM) considering joint biomechanics. An ergonomic customized design model can be built based on kinesiology involving human joint biomechanics. Manifolds of the human bone can be reconstructed from X-rays, computed tomography (CT), magnetic resonance imaging (MRI), and direct 3D scanning. The conceptual and detailed design of customized products were implemented on ergonomic shoes and insoles. A lightweight lattice structure with variable porosity was generated via structural topology optimization for an ergonomic customized design. Notably, the upper surface of the custom-made insole may adhere perfectly to the plantar surface of the patient, resulting in a lower peak plantar pressure. Finite element analysis (FEA) can be employed to simulate the static or dynamic biomechanical characteristics. The conceptual ergonomic products were forwarded to the machine and fabricated via AM, driven by visual digital twin techniques. The experiments proved that a customized design suitability method for wearable ergonomic products via 3D printing is specifically tailored to the rehabilitation needs of individual customers, while consuming the least cost, time, and materials.

In recent years, innovations in 3D/4D printing techniques for continuous fiber-reinforced polymer composites (CFRPCs) have opened new perspectives for the integrated design and manufacture of composites with customized functions. This paper reviews the current state of 3D/4D printed functional composites, including the materials, shape memory/changing effects, self-monitoring/healing behaviors, and challenges surrounding additive-manufactured functional composites. Specifically, continuous fibers and matrices that provide functional roles are classified and discussed in detail. 4D printed shape memory and changing CFRPCs can retain their original shapes from a designed shape upon exposure to different external stimuli, including heat, electricity, humidity, and multi-stimuli activation. Furthermore, self-monitoring of structural health is achieved through the piezoresistive features of reinforced fibers in 3D printed CFRPCs. Finally, this review concludes with an outlook on the future research opportunities for 3D/4D printed functional CFRPCs.

Laser powder bed fusion (LPBF) is the most widely used metal additive manufacturing process. It is a novel layer-by-layer manufacturing technique based on a geometrical model that provides a suitable alternative for material processing. This mode is widely used in laser and electron beam welding. Nickel (Ni) alloy preparation using the LPBF method has attracted considerable attention in several areas, owing to the high corrosion resistance and good mechanical properties of the prepared alloys. The specific conditions of solidification through the metal fused during the selective laser fusion process and its layer deposition induces microstructural peculiarities, including the formation of a supersaturated solid solution,extreme microstructural refinement, and the generation of residual stress. Consequently, heat treatment and hot isostatic pressing, which are generally applied to conventionally manufactured Ni alloys, may need to be altered to adapt to the metallurgical properties of Ni alloys manufactured using direct metal laser deposition and address particular issues resulting from the process itself. Several studies have been conducted on this topic over the past few years, suggesting different approaches for addressing different alloying systems. This review summarizes the latest scientific findings in the area of thermal treatment for selective laser sintering of additively manufactured Ni alloys.

Metamaterials are artificial structures that have been engineered to exhibit properties that do not occur naturally in conventional materials. They were firstly made up of periodic unit cells that interact with electromagnetic (EM) waves to manipulate their behavior, showing extraordinary phenomena like EM cloaking, negative index, beam deflection and so on. In recent years, the concept of metamaterial has been penetrating in various physical domain and various metamaterials with versatile functionalities have been proposed and fabricated by 3D printing technology to manipulate the interactions between matter and electromagnetic, thermal, acoustic, and mechanical energy. With the increasing of structural complexity, material types, precision additive manufacturing serve as a powerful tool to achieve novel metamaterials with extraordinary performance and fusion of functionalities. In this paper, we reviewed the remarkable properties enabled by 3D printed metamaterials in different fields, and analyzed the consilience relationship between structure, function, and manufacturing process.