查看更多>>摘要：The additive manufacturing process fabricates parts with various parameters and surface features, significantly impacting the structure and mechanical properties of the part. Polymers like Polyetheretherketone (PEEK) demonstrate excellent wear resistance, and it is feasible to be processed with high-temperature polymer additive manufacturing with different surface features for applications such as bearings. The variation in layer thickness of the 3D printed part will result in different surface features and influencing their contact characteristics and wear response. In applications requiring lubrication, like bush bearing, the 3D-printed samples with layered structures can be advantageous by providing space between layers for lubricant storage. The layer thickness affects crystallinity, indentation hardness, tensile strength, surface roughness and energy. Surface roughness impacts the contact mechanism, and surface energy affects the adhesion of 3D-printed cuboid samples with a bearing steel counter body during a dry sliding test using a pin-on-disc configuration for an hour. PEEK's friction coefficient and wear rate increase with layer thickness, and the maximum wear rate of 8.3 x 10-5 mm3/Nm and friction coefficient of 0.62 by the sample with 0.3 mm layer thickness. The space/grooves between layers were observed to accommodate wear debris and influence the wear process during the test. The transfer layer formation on the steel surface affects the wear rate and mechanism, which is influenced by the trapped debris between the grooves formed by stacked layers of the sample surface.
查看更多>>摘要：Arc-directed energy deposition (DED) can produce large-scale metal components with high deposition rates. However, large residual stress (RS) and deformation are formed in as-built parts since serious heat accumulation is generated due to considerable heat input, damaging the mechanical properties of deposited parts. This study aims at controlling stress and deformation of as-built thin walls by applying a double electrode arc-DED technique with lower heat input. By introducing an additional branch electrode to divert some current from the main wire, the heat input to deposited layers is reduced. Double electrode arc-DED has the potential to achieve higher deposition rates and lower heat input to deposited layers without compromising the forming quality. The novelty is that how the branch current affects the temperature, RS, and deformation of walls in double electrode arc-DED is revealed by using finite element simulation. A composite heat source model is developed to characterize the thermal effect of the double electrode arc. Experimental tests check the finite element model's effectiveness. The simulation results are in good agreement with the experimental results. Compared to conventional gas metal arcDED, the high-temperature zone on as-built layers shrinks, and the melt pool's peak temperature and length decrease in double electrode arc-DED. As the branch current increase from 0 to 105 A, the maximum longitudinal RS on as-built layers decreases from 292 to 265 MPa, and the maximum deformation on the substrate reduces by 1.5 mm, indicating that introducing a branch arc can effectively reduce the heat input, RS, and deformation in arc-DED. This study provides valuable guidelines on regulating RS and deformation in arc-DED from the perspective of decreasing heat input to as-built layers.
查看更多>>摘要：In the aerospace manufacturing industry, conventional laser welding often fails due to assembly errors, resulting in discontinuous long-straight welds in titanium cabin skin structures. This study introduced a novel oscillation laser beam welding (OLBW) approach, combined with a low-frequency, medium-duty cycle pulse waveform. We applied this method to fabricate tailor-welded blanks (TWBs) of Ti6Al4V alloy under reserved air gap conditions. Experiments involved various combinations of beam trajectory and pulse waveform parameters. Keyhole and weld pool dynamics were numerically simulated by developing a validated multi-phase thermo-fluid coupling model. Key findings include: At an oscillation frequency of 100 Hz, the process enhances metal bridge formation between workpieces, with the keyhole maintaining a normal shape and an opening area of 0.196 mm2-smaller than the focused beam spot-enabling continuous weld beads. At 200 Hz, however, the average metal bridge area drops by 23.2 % indicating a weakened gap bridging capacity, and the keyhole opening expands to over 0.8 mm2 after several cycles, creating a button-hole geometry. This is primarily due to insufficient hydrostatic pressure response on the keyhole's posterior wall under the rapid anterior wall's movement, along with a surface tension coefficient increasing from 1.1 N/m to 1.2 N/m. Introducing a 50 Hz square pulse waveform addresses this by promoting periodic keyhole collapse and weld pool cooling, keeping the keyhole in a semi-or full-penetration state and therefore suppressing the button-hole effect. Additionally, increasing beam oscillation frequency or incorporating pulse reduced alpha '-martensite grain size, primarily driven by an average cooling rate over 2.6 x 105 K/s or cyclic remelting in overlap regions.
查看更多>>摘要：Nickel-based superalloys are widely used in important applications in various industries, including aerospace, defence, chemical processing, and marine. However, the difficulties encountered in machining these alloys pose specific challenges regarding the efficiency and quality of the parts. Thus, adopting economical and environmentally friendly cutting strategies during machining is essential for the environment and performance. For this purpose, silicon dioxide (SiO2) and aluminium oxide (Al2O3) nanoparticles were added to a base-cutting fluid to develop a novel hybrid nanofluid MQL (HNFMQL) cutting fluid, which is then applied during turning experiments. The thermo-physical characteristics, namely pH, thermal conductivity, and coefficient of friction of different fluid mixtures, are studied. The machining experiments are performed on Hastelloy C4 under conventional (dry, MQL, HNFMQL) and heat-assisted (HA) machining (HA dry, HA MQL, HA HNFMQL), and the cooling-lubrication ability is analyzed by measuring machining responses. Compared to HNFMQL and dry conditions, heat-assisted machining with HNFMQL reduced surface roughness by 20 % and 55.56 % and decreased tool wear by 14 % and 41.47 %. The SEM and EDX analysis of worn cutting tools revealed the efficacy of HNFMQL and HA HNFMQL with lower abrasive wear. Whereas, abrasion, adhesion, and chipping are observed under dry machining. The study of the material's microstructural behaviour using Electron Backscatter Diffraction (EBSD) revealed important details about its behaviour under various machining conditions. The EBSD investigation revealed a well-aligned microstructure, proving that heat impacts a limited region in heat-assisted machining.
查看更多>>摘要：This article presents the finite element modeling and simulation of machining with evolutionary friction, which was obtained from the interactive friction model (IFM). An empirical-numerical approach was used for IFM calibration, and the simulated annealing optimization was used to determine the IFM parameters. As the first step, the validated FEA simulations with constant friction coefficients were used to extract the interfacial parameters (i.e., pressure, sliding velocity, and temperature). Afterward, the interfacial parameters of the marginal nodes were fed into the IFM to optimize the model parameters. The evolution of the coefficient of friction obtained from the calibrated IFM was afterward used to generate the FEA model, which was validated with experimental cutting force. Finally, the performance of the IFM-based FEA model was compared with that of the constant friction coefficient. It was found that the inclusion of the evolution of friction with cutting time caused a shift in the FEA-simulation-based cutting force, feed force, thrust force, and temperature to move in the projected direction of friction. The adopted approach of IFM calibration can be helpful as an alternative to the friction data for machining interfaces, which are challenging to achieve through tribology tests.
查看更多>>摘要：The combined SSE-FE PROCESS was recently known as a new severe plastic deformation (SPD) method. In this process, the die wall's unique shape can create large strains without repeating the cycle. The samples are extruded gradually using direct punch pressure and are produced with a regular cross-sectional area. In this study, the upper bound (UB) theory method is proposed for the first time to estimate the forming force consumed in the CSSE-FE technique. The UB theory analysis is investigated for the deformation of 1050 aluminum alloy with a square cross-section. Also, the CSSE-FE process was studied experimentally and numerically using ABAQUS/Explicit 6.14 software to validate the results. In addition, the effect of the friction factor (m), the maximum deflection angle (alpha max), and the thickness of the die outlet channel on the force consumed was investigated. The numerical results and the upper bound theory showed that by increasing the friction factor from 0 to 0.4, the force increased by about 82.24 %. In this research, the upper bound method in force prediction caused a difference of about 10.2 % greater than the experimental results. The accuracy in calculating the force using theoretical, numerical, and experimental methods can be seen from an excellent correlation between their results.
查看更多>>摘要：The use of multi-positional X-ray Computed Tomography (XCT) has been shown to reduce metal artifacts when scanning multi-material assemblies. However, its effectiveness heavily relies on the choice of scan orientations to fuse. This paper presents a novel approach to determine the optimal combination of scan positions by taking a small number of simulated projections and deriving projection-based metrics to estimate the quality of the resulting data fusion. Two regression models, linear and Random Forest, were used and compared for prediction of the optimal combination. Results on an adaptation from an industrial case study showed that, while both models provide predictions that are well correlated to the actual ranked values on the test data (Spearman's rho of 0.841 for the linear model and 0.964 for the Random Forest), the Random Forest model performed better than the linear model on all the proposed evaluation metrics, and consistently ranked high quality combinations among its top predictions. These results highlight the effectiveness of the approach in finding optimal combinations of scan positions with little input data, providing a time-efficient solution for improving XCT reconstruction of multi-material objects.
查看更多>>摘要：Thermoset composites like Carbon fiber-reinforced thermoset plastic (CFRTS) have significantly transformed the aviation, automotive, and construction sectors due to their lightweight nature, exceptional stiffness-to-strength ratio, corrosion resistance, and enhanced thermal stability, particularly when cross-linking thermosets are used as matrix materials. Despite these advantages, traditional manufacturing methods often struggle to achieve precise fabrication control and optimize material properties, creating a critical gap in the effective production of these composites. In contrast, laser-assisted manufacturing (LAM) presents a promising alternative, leveraging the unique capabilities of laser energy for accurate material processing. This review systematically examines recent advancements in LAM techniques for carbon fiber-reinforced thermoset composites, addressing the underlying principles, diverse processes, and applications within the automotive and aerospace industries. Specifically, it explores the intricate mechanisms by which laser processing enhances the precision and quality of composite fabrication, including the effects of laser parameters on material properties and their implications for end-use performance. The novelty of this study lies in synthesizing existing knowledge while highlighting significant research gaps in the current literature, such as the limited investigation of laser-material interactions specific to thermoset composites and the need for standardized testing methodologies. Furthermore, this review identifies opportunities for interdisciplinary research, combining insights from materials science, mechanical engineering, and manufacturing technology to develop innovative solutions that maximize the potential of laser-assisted manufacturing. By elucidating the physical behavior of thermoset composites and evaluating the effectiveness of laser processing, this study not only contributes to a deeper understanding of this rapidly evolving field but also serves as a roadmap for future research directions. It emphasizes the importance of collaborative efforts to overcome existing challenges and optimize the integration of laser technology in composite manufacturing, thereby fostering advancements that could lead to more sustainable and efficient production practices.
查看更多>>摘要：The penetration depth is an important indicator for evaluating the laser penetration ability in the laser welding process. Plume is the main information carrier of welding process signals. In this paper, by synchronously collecting the plume vision signal and the plume particle signal (based on the principle of self-mixing interference, SMI), and combining the algorithms of ensemble empirical mode decomposition and fast Fourier transform (EEMD-FFT) to extract the time-domain and frequency-domain features of the plume signals, a method designed for penetration depth monitoring through the fusion of multiple plume signals is introduced. The results show that both the plume area and the total intensity of the SMI signal are positively correlated with the weld penetration depth, and the frequency-domain features of the plume signal have a higher correlation than the time-domain features. Compared with the peak frequency, the centroid frequency of plume signal has higher sensitivity and adaptability to working conditions when reflecting the changes in the penetration depth. The SMI signal has obvious advantages in signal processing efficiency. Its storage space is only 0.47 % of that of visual signal, and the overall processing time can be shortened by 93.4 %. The two types of signals have good complementarity in terms of information. The signal strategy can be flexibly selected according to actual needs to achieve a balance between the efficiency and accuracy of welding monitoring. The research can provide a novel technical scheme for the in-situ monitoring during laser welding.
查看更多>>摘要：The self-piercing riveting (SPR) is an ideal process for joining dissimilar materials such as carbon fiber-reinforced plastics (CFRP) and aluminum alloys. However, piercing CFRP with a rivet leg causes significant damage, thereby reducing joint performance. To address this issue, this study proposes a novel process called flat electromagnetic self-pierce riveting with no concave die (FE-SPR) to join 2.0-mm-thick CFRP and 5052 aluminum alloy sheets. This method is an improvement based on traditional semi-hollow rivets to enhance structural strength and reduce CFRP damage. A comparative analysis of cross-sectional quality, quasi-static mechanical properties, forming mechanisms, and failure behavior were conducted between joints fabricated with traditional semi-hollow rivet (T-rivet) and novel semi-solid rivet (N-rivet). The results showed that the N-rivet joint, unlike the T-rive joint, exhibited upsetting deformation of the rivet shank and secondary expansion of the rivet leg. These features help suppress CFRP damage and increase undercuts. The average area of CFRP damage for T-rivet joint was 33.99 mm2, 135.1 % higher than the N-rivet with 5 degrees. The peak load and energy absorption of the Nrivet with 5 degrees were 4154 N and 11.81 J, 18.3 % and 13.5 % higher than T-rivet joints, respectively. All joints exhibited one failure mode, characterized by rivet pull-out from the aluminum plate while maintaining adhesion to the CFRP plate. This study offers a reliable solution for lightweight multi-material structures in automotive and aerospace applications.
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Elsevier