International Journal of Machine Tools & Manufacture最新文献

High-speed electrochemical discharge drilling (ECDD) offers substantial benefits for efficient, high-quality fabrication of film cooling holes. One shortfall of this technique is the lack of a visual model for simulations. The determination of optimal machining parameters predominantly depends on trial-and-error methodologies. In order to develop a visual model for simulations, an in-depth analysis of the machining mechanism is necessary. This entails direct observation of the machining phenomena and a thorough understanding of the surface topography evolution processes. The study focuses on machining Ni-based single-crystal materials that are used in turbine blades, employing experiments to investigate the material removal mechanism. Based on the relevant conclusions, a visualized simulation model is developed for the first time. The results show that discharge and electrochemical dissolution occur alternately at the microscopic level. Besides, the discharge in low conductivity solutions is similar to pure electrical discharge drilling (EDD) rather than a gas film discharge. Discrepancies in the elemental distribution of the matrix and recast layer cause changes in the electrochemical dissolution behavior. The current efficiency of the recast layer is significantly lower than that of the matrix. Based on the mechanistic exploration, this study integrates discrete discharge with continuous electrochemical dissolution to construct a visual model of high-speed ECDD, by leveraging a dead grid method and explicit differential. This model can precisely anticipate the distribution of the recast layer and the diameter of the hole, thereby contributing valuable insights towards achieving zero recast layer machining and enhancing the use of ECDD in the aerospace industry.

Machine tool have traditionally been developed for the manufacture of new parts and to be operated in workshop environments. With a remit of addressing clearly defined tasks, the concepts/configurations of these are nowadays, somehow, standard. This perspective intends to flag up to the community the relatively unexplored topic of portable Robotised Machine (RoboMach) tools that address the need for in-situ maintenance and repair of industrial installations. By the immense variety of tasks that RoboMach are designed to fulfil, there is an open ground for exploring, at the confluence with other complementary research disciplines, novel machine tool configurations that could open fresh academic challenges.

Recent research has focused on laser in-situ additive manufacturing of metal matrix composites with spatially controllable microstructures (phases). This study, inspired by the process of inserting mesh fibers into reinforced concrete, synthesizes TiN in situ using laser powder bed fusion and N₂ gas. The laser-melted track, embedded with TiN particles, formed a spatially heterostructured Ti composite (SHTC) with a three-dimensional, artificially controlled architecture in a pure Ti matrix. The influences of process parameters on the mechanical properties of the spatially heterostructured Ti composite and the microstructural evolution of TiN/Ti were investigated emphatically. The results showed that the growth direction of the microstructure was changed by laser powder bed fusion additive manufacturing with alternating N₂–Ar gas under suitable N₂ concentration and melting track spacing. Among all spatially heterostructured Ti composites, the TiN–Ti heterolayer net-like structure achieved a high ultimate tensile strength of ∼1.0 GPa and elongation of 27 %, demonstrating a superior strength-ductility combination than intrinsic pure Ti and uniform TiN composites, as well as traditional layered structure Ti-based composites. During the tensile test, the deformation behavior was monitored in situ using digital image correlation, and the fracture mechanism was investigated. Hetero-deformation induced strengthening and toughening potentially explains the mechanism behind the strength enhancement of spatially heterostructured Ti composites. Furthermore, this work may stimulate research and development in additive manufacturing of spatial heterostructures with configurable structures, targeting synergistic regulation of strength and ductility in the integration of structure-material-function.

β-Ga₂O₃, known as a next-generation wide-bandgap transparent semiconducting oxide (TSO), has considerable application potential in ultra-high-power and high-temperature devices. However, fabricating a smooth β-Ga₂O₃ substrate is challenging owing to its strong mechanical strength and chemical stability. In this study, an atomic-scale smoothing method named plasma-enabled atomic-scale reconstruction (PEAR) is proposed. We find that three reconstruction modes, namely, 2D-island, step-flow, and step-bunching, can be identified with the increase in the input power; only the step-flow mode can result in the formation of an atomically smooth β-Ga₂O₃ surface (Sa = 0.098 nm). Various surface and subsurface characterizations indicate that the smooth β-Ga₂O₃ surface shows excellent surface integrity, high crystalline quality, and remarkable photoelectric properties. The atomic-scale density functional theory-based calculations show that the diffusion energy barrier of a Ga atom is only 0.46 eV, thereby supporting the atomic mass migration induced by high-energy plasma irradiation in the experiment. Nanoscale molecular dynamics simulations reveal that O atoms firstly migrate to crystallization sites, followed by Ga atoms with a lower migration rate; reconstruction mainly proceeds along the <010> direction and then expands along the <100> and <001> directions. The millimeter-scale numerical simulations based on the finite element method demonstrate that the coupling of the thermal and flow fields of plasma is the impetus for PEAR of β-Ga₂O₃. Furthermore, the smoothing generality of PEAR is demonstrated by extending it to other common TSOs (α-Al₂O₃, ZnO, and MgO). As a typical plasma-based atomic-scale smoothing method, PEAR is expected to enrich the theoretical and technological knowledge on atomic-scale manufacturing.

Parallel manipulators are generally associated with high speed, stiffness, and repeatability. Nonetheless, after decades of development, their industrial uptake is still limited when compared to serial architectures. In this paper, we investigate the reasons behind this gap between parallel machine tool potential and real-case applications with a critical analysis of the state of the art. This paper aims to provide machine tool users with the understanding of the functional and technological characteristics of parallel manipulators, as well as to help roboticists approach machining applications with an in-depth perspective and a curated collection of references. We outline fundamental modeling tools for parallel mechanisms and then explain how they can be applied to the development, optimization, and performance evaluation of machine tools, with a focus on kinematic and dynamic metrics, error analysis, and calibration. We then discuss the evolution of parallel machine tools in industry, highlighting successful designs and commercial applications. Finally, we provide our perspective of the field, summarizing the main characteristics, advantages, and disadvantages of parallel machine tools, highlighting the barriers preventing a more widespread implementation of these systems, outlining current research trends, and identifying potential future developments.

Dual-wire additive manufacturing (AM) couples traditional wire-based AM for part fabrication and the molten pool metallurgy for material-preparation with high deposition efficiency and material utilization. However, compared with traditional single-wire AM technology, it has a more complex and sensitive dual-droplet transition distance (TD), which not only affects the forming quality but also the metallurgical quality. Therefore, it is necessary and urgent to monitor and control its TD value online. In this study, we systematically investigated the sensing, controlling, and influential mechanism of the TD value in dual-wire AM technology, and Ti₂AlNb was taken as the target alloy owing to its great application prospects in the aerospace field. Specifically, a deposition experiment with different initial TD value was conducted to study the effect on the morphology and composition distribution of the as-printed part. Based on the optimal distance, the related image extraction algorithms and closed-loop control methods are developed. The closed-loop controlled verification experiment on the slope and step substrate, as well as the multi-layer deposition test, were carried out and analyzed. The results indicate that the developed system can control the TD to the desired value with good robustness. In addition, the controlled deposited multi-layer part exhibited good morphology and composition homogenizing in the post-characterization experiment. This study is of great significance for the intelligent and industrial development of dual-wire AM technology.

As one of the most novel additive manufacturing methods, currently selection and optimization of processing parameters in additive friction stir deposition (AFSD) have mainly relied on experiments and subsequent characterization of microstructural and mechanical properties. Such approaches are both time- and resource-consuming. Therefore, an ultrasound elastography enhanced gradient process parameter optimization method was applied in the present work to obtain a window of optimized processing parameters for AFSD processing of aluminum alloy by varying both rotational and linear deposition speeds. The quality of AFSD processed layer was investigated for physical nature of surface, dynamic elastic modulus, and microstructural aspects in cross-sections of the deposited layer. The efficiency in exploring process parameters was significantly enhanced by implementing a high-throughput screening experimental design based on application of gradient process parameters and continuous ultrasound elastographs. In addition, the applied ultrasonic elastography technique assisted in evaluating the homogeneity in microstructure and mechanical properties of AFSD sample over the entire gradients of the process parameters. The techniques adopted in current work can be further extended to identify suitable parameters for AFSD fabrication of components with desired mechanical properties such as hardness, fatigue, etc.

Aluminium alloy (Al-alloy) tubes, especially large-diameter thin-walled tubes with a tough bending radius, have been widely utilised in different industrial clusters owing to their high strength-to-weight ratio and good corrosion resistance. However, achieving such extreme specifications is challenging because severe and nonuniform bending deformation may cause tension and compression instabilities, such as overthinning, cracking, and wrinkling. Considering possible improvements in mechanical properties and friction behaviours of Al-alloy at cryogenic temperature (CT), the cryogenic bending potential of the 6061-O tubes with an extreme ratio of D/t of 89 (diameter/wall thickness) was explored at different deformation temperatures, including room temperature (RT) 20 °C, −60 °C, −120 °C, and −180 °C. First, the cryogenic mechanical properties and friction behaviour of the tubes were characterised. It was found that the overall mechanical properties of the Al-alloy tube were improved because of sub-grain formation and a more uniform distribution of dislocations at CT. The coefficient of friction between the tube and tooling exhibited a varying degree of reduction owing to the sensitivity of the tubes and the lubricant to CT. Subsequently, an innovative experimental platform for cryogenic bending was designed, and a finite element model of cryogenic bending was established. Third, cryogenic tube bendability and mechanism were explored. It was found that 6061-O tube formability can be effectively improved by cryogenic bending; however, there is no monotonic relationship between the bendability improvement and temperature decrease. The temperature to obtain the best bendability is −60 °C, at which the average wrinkle height is decreased by 81.4 %, and the average wall thickness reduction rate is reduced by 23.8 %. The bending limit represented by the bending radius is reduced from a 3.0D bending radius at RT to 1.0D at −60 °C, which is realised by the different or even opposite effects of the mechanical properties of tubes and the friction coefficient between the multiple contact interfaces on wall thinning and wrinkling.

Owing to hetero-deformation induced (HDI) strengthening and HDI work hardening, heterostructured materials with both “hard” and “soft” features have been proven to achieve strength–ductility synergy. Laser-directed energy deposition (LDED) has shown tremendous potential in the fabrication of heterostructured materials, but faces challenges in accurately placing the required structures or materials at specific times and locations. This study developed a novel Ti₂AlC (MAX phase)-modified Inconel 718 composite material (MAX/Inconel 718) with multiscale precipitation (γ’, carbides, Laves phase) characteristics during solidification, highly sensitive to changes in cooling rates, and exhibiting excellent controllability of strength. A method called multibeam diameter laser-directed energy deposition (MBD-LDED), which allows the dynamic adjustment of the beam diameter during the building process to alter the cooling rate during solidification, is proposed. This enabled the placement of MAX/Inconel 718 with different strengths at suitable positions within the part. Different combinations of beam diameters can form periodic distributions and spatial interlocking structures with alternating “soft” and “hard” features perpendicular and parallel to the building direction. Compared to commercial Inconel 718, MAX/Inconel 718 demonstrated excellent manufacturability, strength, and high-temperature oxidation resistance. This study provides new insights into the design and performance optimisation of heterostructures using homogeneous materials and offers guidance for the integrated manufacturing of heterostructured components in the context of comprehensive material–structure–performance design.