International Journal of Machine Tools & Manufacture最新文献

Non-traditional laser and fluid jet processes exhibit time-dependent material removal characteristics. The feedrate profile must be planned carefully along the toolpath for accurate surface profile generation while ensuring that the kinematic limits of machine tools are not violated. Conventional methods iteratively solve a deconvolution/convolution problem on the dwell-time density (reciprocal of the feedrate profile) that is computationally heavy, may leave significant residual processing errors, and even generate infeasible feed profiles with the manufacturing equipment. This paper proposes a novel approach that fully addresses the shortcomings above. Dwell-time density is first expressed as a continuous B-spline profile. The associated dwell basis functions (DBF) are convolved with the process influence function (PIF) to generate new process basis functions (PBF). This approach conveniently allows the posing of the problem as a concurrent linear least-squares problem on the control points shared by the DBFs and PBFs while ensuring the numerical stability of the solution and smoothness of the feed profile. To mitigate excessive acceleration peaks and any ringing effect around the edges of the toolpath, this paper also presents methodologies for stabilizing the scheduled feedrate profile by introducing knot vector adjustments (adaptive knot dropping) and linear edge constraints. The effectiveness of the proposed method is demonstrated and validated through simulation case studies and experimentally in fluid jet processing of precision optics. Results indicate that the proposed technique overcomes the limitations of conventional strategies and allows high-frequency surface components beyond the first zero-power frequency of the process footprint to be tracked while still generating a smooth feed profile within the acceleration limits of a machine tool. This ability stems from the localization characteristics associated with the basis functions. By improving the accuracy of high-frequency components, the proposed method exhibits the potential to fabricate topographies with sharper edges, which has been a challenge for conventional techniques.

Cemented carbide inserts coated with CVD α-alumina, particularly those exhibiting a (0001) texture, have proven highly effective in steel turning. Despite the established superior performance of (0001) textured alumina coatings, the underlying reasons remain unclear. This study explores the influence of the crystallographic texture of alumina on wear mechanisms in various chip-tool contact zones on the insert rake face. The objective is to establish a fundamental understanding of the active degradation mechanisms and machining performance by relating coating texture to the orientation and deformation of individual Al₂O₃ grains. Two multilayered coatings, Al₂O₃ on Ti(C,N), featuring (0001)- and $\left(11\bar{2}0\right)$-textured CVD α-alumina, were assessed in dry turning of a bearing steel. The wear rate of the $\left(11\bar{2}0\right)$ coating was double that of the (0001) coating. Worn coatings exhibit nano-terrace formation at the insert edge, likely due to chemical etching. In the sticking zone, plastic deformation leads to larger facets for grains oriented with the chip flow direction, while rounded surfaces result if this condition is not met. In the transition zone, both (0001) and $\left(11\bar{2}0\right)$ textured coatings undergo increased plastic deformation accompanied by sub-surface dislocations. (0001) texture deforms more by basal slip creating a wavy coating pattern with steps present at larger misalignments of the lattice planes in neighboring grains while $\left(11\bar{2}0\right)$ texture deforms by several slip systems creating elongated ridges and ruptured-like areas resulting in rougher surface. This difference in surface morphology is then inherited by the abrasion of submicron coating fragments embedded in the chip (more in $\left(11\bar{2}0\right)$ texture) in the sliding zone resulting in an even rougher surface. Chemical reaction with the hot chip may also contribute to wear acting as an additional mechanism. This fundamental understanding contributes to the potential enhancement of steel machining using texture-controlled CVD alumina coatings, ultimately improving coated cutting tool performance.

Laser-induced forward transfer (LIFT) has emerged as a versatile technique for printing high-resolution metal microstructures. However, a common drawback of this method is the inadequate coalescence of the deposited metal microdroplets, which results in inferior electrical and mechanical properties. This paper proposes a novel approach for fabricating high-performance metal micropillars using a single-pulsed laser to alternately deposit and remelt metal microdroplets. Specifically, an ultraviolet nanosecond laser was used to induce the deposition of copper microdroplets, forming a patterned powder bed with high resolution. Subsequently, a laser pulse train was applied to fuse the patterned powder bed. The results showed that voids and microdroplet delamination were eliminated in the printed copper micropillars, whose yield strength and elastic modulus increased threefold, approaching 63% of those of the bulk metal. The remelting behavior of the deposited microdroplets was elucidated by modelling and analysing the thermal accumulation effects of a laser pulse train. A remelting map was proposed, including the non-melting, remelting, and vaporizing regimes. According to the depth of melt pool, the evolutions of morphology and microstructure in the depositing and remelting process were elucidated. Hence, this study advances the LIFT process for fabricating high-performance metal microstructures.

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.