CIRP Journal of Manufacturing Science and Technology最新文献

Adjustable-ring-mode (ARM) laser welding displays great potential for improving the stability of the molten pool and the weld quality of aluminum alloys through the coaxial attachment of a large-sized ring-beam spot. In this paper, the author embarked on a systematic study on the impact of varied core powers, ring powers, and core/ring power ratios on the weld morphology, microstructure, and mechanical properties of Al-Mg alloy during the laser welding process with ARM. The results showed that the core power led to higher depth of penetration, and the superheating of the molten pool it created caused grain coarsening and reduced properties. The ring beam effectively decreased weld spatter and enhanced the surface roughness of the weld. Furthermore, the ring beam was more likely to obtain a wider columnar crystal zone and a more homogeneous grain size distribution. The welded joints possessed higher tensile strength values when ring beam power was increased from 1.5 to 2 kW due to the improvement of surface flatness and porosity defects by the ring beam.

This paper describes development of multi-layer deposition of Ti6Al4V added with 5 at% of Cr, 5 at% of Ni, and 2.5 at% of each Cr and Ni by μ-plasma powder arc additive manufacturing process. It presents findings on their microstructure, porosity, evolution of phases, microhardness, tensile strength, ductility, fracture morphology, fracture toughness, and abrasion resistance. Phase evolution found that α/α’-Ti and β-Ti phases are formed in all the alloys, intermetallic phase Cr₂Ti evolved in Ti6Al4V5Cr and Ti6Al4V2.5Cr2.5Ni alloys whereas intermetallic phase Ti₂Ni is formed in Ti6Al4V5Ni alloy. Their microstructure revealed that addition of chromium and nickel refined grains of their α-Ti and β-Ti phases. Elemental composition of the evolved phases found that at% of chromium, nickel, and vanadium in β-Ti phase is more than the α-Ti phase of the developed alloys. It enhanced their ultimate tensile and yield strength, and microhardness but reduced ductility. It changed the fracture mode from ductile to a combination of ductile and brittle mode possessing large size dimples, micropores, and cleavage facets. It is due to solid solution strengthening, evolution of intermetallic phases Cr₂Ti and Ti₂Ni, and grain refinement of β-Ti and α-Ti phases. Enhanced microhardness and presence of intermetallic phases improved fracture toughness and abrasion resistance of the developed alloys thus imparting them higher resistance to propagation of cracks and abrasive wear.

Automatic electroplating production lines have been widely used in electronics industries to reduce the labour intensity and improve the production efficiency. In the multi-variety and low-volume electroplating production, it is known that the task loading sequence and hoist scheduling are coupled with each other, and they codetermine the production efficiency, while all the existing scheduling methods consider them separately, and thus the optimal production schemes become unavailable. Therefore, this paper develops a Task sequence-Hoist scheduling Coupled Optimization (THCO) model which simultaneously considers the requirements and practical constrains of task sequence and hoist scheduling, having an optimization objective of minimizing the maximum completion time. For this model, a double-layer code is developed and an Improved Salp Swarm Algorithm (ISSA) is developed by introducing three improvement strategies: the random spare strategy which is used to increase the population diversity, the nonlinear adaptive weight strategy which is used to balance the exploration and exploitation capacities, and a golden sine algorithm which is used to improve the convergence rate. Experiments based on 23 benchmark functions are then conducted. The obtained results show that ISSA has better convergence and solving quality than existing algorithms. Furthermore, several production cases prove that THCO can generate production schemes that better meet the requirements of production lines.

Milling robots have the advantage of large workspace and high flexibility compared to machine tools, and are more suitable for machining large and complex surfaces. However, the stiffness of robots is significantly lower than that of machine tools, and they are more prone to chattering. Compared to machine tools, robots mainly occur mode coupling chatter. Analyzing chatter in robots is a great challenge due to the highly flexible and pose-dependent position of the robotic arm. Mode coupling chatter is caused by the most flexible and dominant structural modes of the robot milling system. Available methods are unable to identify the structural modal parameters of a milling robot at all poses in the actual working state. This paper proposes a modal analysis method for robots, which can realize the automatic traversal of the pose of the milling robot and the automatic identification of modal parameters. This paper analyzes the robot multi-joint flexibility characteristics, spatial structure characteristics, and machining vibration characteristics, correlates the joint motor control system and current power characteristics, finds the correlation between the current information and the vibration information, and identifies the modal frequency through the current signals, and realizes the modal frequency identification in the entire workspace. This method is capable of output-only complete mode shape identification, can quickly analyze the main vibration modes, and is of great significance for the study of robot milling chattering.

Wire arc additive manufacturing (WAAM) is increasingly gaining attraction from researchers and industries worldwide due to its low cost and the ability to produce intricate parts in a shorter time. In this study, the bimetallic wall of aluminium alloys (ER5356/ER4043) is fabricated by cold metal transfer based WAAM technique using two deposition directions (unidirectional and bidirectional) and three current combinations (115 A/90 A, 120 A/95 A, 125 A/100 A). The effect of deposition direction and current on microstructure evolution, mechanical properties, and residual stress has been investigated. Experimental results displayed better properties in bi-directional wall build at a current combination of 115 A/90 A. This is confirmed by optical microstructure as well as field emission scanning electron microscopy, which shows equiaxed grains on the ER4043 layer, fine grains on the ER5356 layer, and columnar-fine grains at the interface of the bi-directional wall while discontinuous dendritic grains is displayed in ER5356 layer of unidirectional wall. Energy dispersive spectroscopy analysis indicates a main difference in weight percentage for Si and Mg contents at the interface layer of the bidirectional wall than the unidirectional wall, with X-ray diffraction analysis specifying the intermetallic compounds like α-Al, Al₁₂Mg₁₇, Mg₂Si, AlMg, and Al_3.21Si_0.47 in both depositional directions. Tensile strength at the interface layer of the bi-directional wall surpasses the tensile strength of the unidirectional wall's interface layer, with fracture morphology indicating ductile fracture in all specimens. The microhardness test reveals an increase in hardness in the transverse direction at the current combination of 115 A/90 A and also in the bidirectional deposition wall compared to the unidirectional wall. Bidirectional deposition has generated less residual stress than unidirectional walls.

Due to the poor surface characteristics of additively manufactured parts, the necessity for post-process surface enhancement is crucial. Among the prevalent post-processing techniques, the acoustic cavitation-based surface finishing technique has recently emerged. Despite a considerable amount of focused research on the material removal mechanisms of this technique, less attention has been devoted to addressing its limitations associated with enhancing the process capability towards achieving a better surface finish. The driving force behind the acoustic cavitation technique is the bubble implosion through cavitation streaming, and the cessation of the acoustic cavitation streaming beyond a certain length is the main limitation. It has restrained the process capability towards finishing both external and internal surfaces. Hence, this research aims to unravel novel ways of employing the acoustic cavitation-generating parameters and achieving better-quality surface finishing of additively manufactured (AM) components. A study has been conducted on different AM materials, including Inconel 625 and aluminum alloy, by introducing various methods associated with acoustic amplitude, working mediums, temperature, and external vibration. The results reveal a significant reduction in average surface roughness for both materials. The topographical and morphological observations confirm the qualitative improvement on the surfaces. In addition, the conical bubble structures that frame the acoustic cavitation streaming are elucidated by implementing high-speed imaging techniques, and their enhancement at different parametric conditions is delineated. Henceforth, the findings suggest a notable insight into the potential of the employed approaches in enhancing the acoustic cavitation streaming for achieving a better surface finish of AM components.

In the realm of Digital Twins (DTs), industry experts have emphasised the pivotal concept of the Federation of Twins, envisioning seamless collaboration across sectors driven by shared semantics. In response to this challenge, the Cognitive Digital Twin (CDT) integrates the DT framework with formal semantics, specifically ontologies. This paper introduces a comprehensive five-step methodology for CDT development. Furthermore, it becomes possible to incorporate human expertise into the DT ecosystem by adopting an ontological approach. The CDT enhances DT services with advanced reasoning capabilities, leading to a profound semantic enrichment of the data. The presented methodology has been validated using a use case where the CDT is employed to detect malfunctions, significantly reducing manual intervention. This paper advocates for the adoption of CDTs, which represent a harmonious fusion of formal semantics and human expertise, enhancing system efficiency and operational performance.

This paper proposes a model to predict the tensile characteristics of metal fused filament fabricated (MFFF) components. The proposed model consists of mathematical, experimental, and finite element (FE) models. The mathematical model was constructed based on the composite laminate theory and was combined with experiments for basic layup of 0° and 90° raster angle to describe the behavior of MFFF parts. The FE model was built to simulate the behavior of MFFF parts in a virtual environment and its validity was verified using independent experiments for a more common layup of +45°/−45°.

Due to severe deformation, noise, and occlusion, the registration problem of non-rigid point sets in rolling formed metal workpieces poses challenges, and the demand for real-time data storage and registration during the rolling forming process makes this problem even more prominent. This paper proposes an enhanced nonrigid point set registration algorithm based on the Coherent Point Drift (CPD) framework, introducing novel methods to improve accuracy and efficiency. A refined local distance calculation method combining spatial distance has been proposed to improve matching accuracy. In contrast, an optimized shape context method introduces a new driving force criterion to expedite initial registration and reduce subsequent errors. Leveraging the Expectation-Maximization (EM) algorithm, the approach iteratively solves point correspondences, demonstrating robustness in handling complex scenarios like non-rigid deformation and noise. Experimental validation using real production datasets shows superior accuracy and efficiency over classical algorithms, showcasing a practical solution for non-rigid point set registration challenges in roll forming applications.