International Journal of Machine Tools & Manufacture最新文献

Simultaneously improving the formability and post-formed strength of high-strength aluminum (Al) alloys, such as Al–Zn–Mg–Cu alloys, is essential in manufacturing complex-shaped panel components. The strict requirements on heat-treatment condition and high tooling costs limit the applications of current forming methods. A novel process called integrated reversion ageing and forming (IRAF) is proposed to form naturally aged (NA or T4 tempered) Al alloys. A principle-based concept analysis and systematic thermo-mechanical-metallurgical study of the IRAF process were performed. Additionally, tensile tests were conducted to evaluate the effects of parameters including heating rate, holding time, and forming temperature on formability and baked strength. The deformability of the AA7075-T4 alloy can be significantly enhanced through rapid heating to the reversion ageing temperature (150–300 °C), followed by short-term holding, as evidenced by the reduced yield strength of 200 MPa and increased uniform ductility. An instant strength increase to a value close to that of the T6 state was obtained after a short bake hardening (BH) treatment. Further, temperature-time-property (TTP) diagrams were established based on the correlation between the measured mechanical properties and through-process microstructure evolution to explain the mechanism underlying the optimised processing window of IRAF. The results indicate that fast-heating rate (>300 °C/min) promotes the reversion of NA clusters and inhibits re-precipitation of solutes, thereby improving the warm formability. Reversion ageing above 240 °C could induce the formation of coarse η'/η phases, leading to a considerably declined BH response. To accurately predict the strength evolution and deformation behavior during IRAF, a physical-based unified constitutive model was constructed by considering the reversion of NA clusters and solute re-precipitation. The bending and drawing tests on the AA7075-T4 alloy sheets verified that IRAF in the most-reverted state enabled optimum formability. The findings inspire promoting the reversion of pre-existing metastable particles to improve warm formability and post-formed age hardening.

The present study proposes a novel method of ultrasonic vibration assisted-abrasive peening for the enhancement of residual stress on the surface of metals and their alloys. The system employs a vibrating sonotrode that drives the formation and collapse of bubbles within a fluid medium. The imploding bubbles produce pressure waves which transfer momentum to the abrasives which are uniformly distributed in the fluid medium. The abrasives bombard a targeted surface along with intense pressure waves. This induces compressive residual stress through local plastic deformation in a short period. The capability of the ultrasonic-assisted abrasive peening setup is analysed in terms of residual stress by altering the abrasive concentration, peening time, and stand-of-distance between the bottom of the sonotrode and the exposed surface to be treated. The process is able to induce significant residual stress at around 67 % of yield strength for hard material Ti–6Al–4V and more than 80 % of yield strength for ductile materials, Al-6061 and OFHC-Cu. A numerical method coupled with a finite element model is employed to predict the dynamics of the process from cavitation of the bubble to the plastic deformation of the work material. At first, the model estimates the magnitudes of high-pressure waves at the bubble implosion near the solid surface, micro-jet velocity, and abrasive velocity. This information is then fed to Abaqus for numerical modelling of the deformation of work material. The impact of high-speed abrasives in the range of 100 m/s, pressure waves and microjets at the material surface are simulated through the FE model. The simulated results are verified with experimental findings in terms of surface residual stress for different materials, deviating within 10 %.

Ni–Ti alloys based on triple-periodic minimal surface lattice metamaterials have great application potential. In this work, the triply periodic minimal surface (TPMS) lattice structures with the same volume fraction from a normal Gyroid lattice to an octuple interlacing Gyroid lattice were prepared by the laser powder bed fusion (LPBF) technique. The influence of the interlacing-cell number on manufacturability, uniaxial compression mechanical behaviors, and hyperelastic responses of Ni–Ti lattice structures are analysed by experiments. The stress distributions and fracture mechanism of multicell interlacing lattice structures are illustrated by the finite element method. The obtained results reveal that when the volume fraction is the same, the specific surface area of the lattice structure increases with increasing interlacing-cell number, and the curvature radius of the single-cell strut reduces, which leads to the decrease in the manufacturability of the lattice structure. Meanwhile, the diameter of the single cell strut decreases, and the stress it can bear decreases, which leads to a decline in the compressive mechanical property of the lattice structure. However, the number of struts increases with the increase of interlacing cells, which makes the stress distribution of the lattice structure more uniform. The cyclic compression results indicate that with increasing interlacing-cell number, the proportion of the hyperelastic recoverable strain increases, and the residual strain in the cyclic compression test decreases. For the lattice structure with a chiral arrangement of single cells, the manufacturability, compressive mechanical properties, and hyperelasticity are comparable to those with a normal arrangement. Notably, the Ni–Ti Gyroid TPMS lattice structures have superior hyperelasticity properties (98.87–99.46 % recoverable strain).

Directed energy deposition (DED) with a coaxial wire-laser configuration has gained significant attention in recent years for the production of large-scale metallic components because of its low directional dependence, fast deposition rate, high feedstock efficiency, and low manufacturing costs. This work studies the coaxial wire-laser DED process of Inconel 718 alloy under a stable deposition condition with a relatively low input volumetric energy density (55.5 J/mm³). Post characterization reveals a cluster of refined grains at the center-bottom region of the as-printed track. Operando high-energy synchrotron X-ray experiments and multi-physics modeling are applied innovatively to study the fundamental mechanism responsible for the formation of this microstructure. The X-ray diffraction experiment provides direct evidence, which is supported by the simulation, that the feeding wire can reach the melt pool bottom and release solid particles (primarily carbides) near the mushy zone owing to insufficient melting. Consequently, these sub-micron sized particles suppress the growth of large columnar grains and cause the formation of unique microstructural heterogeneity. This discovery offers new opportunities for tailoring the solidification microstructure by controlling the melting state of the feedstock wire in DED process, in addition to commonly known factors such as the thermal gradient and solidification velocity.

Although the intermittent contact by the ultrasonic vibration-assisted cutting explained the machinability advantages, there exists a research gap in concentrating the effects of high-frequency ultrasonic vibration-assisted cutting (HFUVAC). This work clarified the differences of the micro/nano incremental material removal mechanisms between conventional cutting (CC) and high-frequency ultrasonic vibration-assisted cutting of 316 L stainless steel. The machinability advantages and microstructure features were compared and analyzed through the ultra-precision cutting experiments. Compared with the continuous contact mode of the conventional cutting, the incremental effect of the high-frequency ultrasonic vibration-assisted cutting achieved superior machinability, which included cutting force decreasing, tool wear reduction, surface defects suppression, and chips undergoing from discontinuous quasi-shear state to continuous multiple-shear state. As the nominal cutting speed increased in the high-frequency ultrasonic vibration-assisted cutting, the surface defects and surface roughness showed an increasing trend, which was indispensable to control the normal cutting speeds below 5 m/min, or the cutting stroke in each vibration cycle less than 800 nm to obtain the defect-free surface. The grain refinement and severe elongation deformation were observed at the chip bottom and machined surface of the conventional cutting due to strong mechanical friction loads. While the microstructure features of chips and the machined surface in the local deformation layer were the results of friction reduction, dynamic recrystallization, and twinning/stacking formation induced by the incremental effects of the high-frequency ultrasonic vibration-assisted cutting. The results help to improve surface quality and optimize the ratio of cutting speed to vibration frequency to enhance the efficiency.

Linear friction welding is a solid-state, near-net shape manufacturing method for metallic alloys which is characterised by complex deformation and metallurgical actions at the weld interface. However, a lack of understanding of the welding parameter interaction and subsequent welding mechanisms is hindering the joint integrity enhancement of dissimilar linear friction welding. In this study, we investigated the influence of various process parameters on macro/micro-formation, microstructural evolution, and properties to establish optimal welding conditions for the sound linear-friction-welded joint integrity of dissimilar superalloys, IN718, and the powder metallurgy FGH96. Increased oscillation frequency or decreased applied pressure promoted continuous dynamic recrystallisation and grain refinement, although discontinuous dynamic recrystallisation remained dominant. Enhanced dissolution of the strengthening phases (γ′ phase on the FGH96 side and δ phase on the IN718 side) was observed from the thermomechanically affected zone to the interface. The subsequent correlation between the microstructure and mechanical properties indicated that solid–solution strengthening was the dominant mechanism for enhancing interfacial bonding, which was promoted by mutual material deformation on both sides. Accordingly, to achieve synergistic plastic deformation in dissimilar linear friction welding, an optimisation strategy of welding parameter combination was proposed and validated by investigating hot compressive dissimilar Ni-based superalloys. The results of simulations of sub-size workpieces showed that using linear friction welding to manufacture bimetallic bladed disks, from conception to completion, was feasible. The paper offers an integrated solution for the full-scale manufacturing of an IN718/FGH96 blisk using linear friction welding based on microstructure–property interactions and relevant simulations, which can ideally serve as the basis for future bimetallic bladed disk manufacturing.

Grain refinement and arrangement is an effective strategy to enhance tensile and fatigue properties of key metallic components. Laser shock peening (LSP) is one of surface severe plastic deformation methods in extreme conditions, with four distinctive features, namely, high pressure (1 GPa–1 TPa), high energy (more than 1 GW), ultra-fast (no more than nanosecond scale), and ultra-high strain rate (more than 10⁶ s⁻¹), and generates a deeper compressive residual stress (CRS) field and the formation of a gradient nanostructure in the surface layer to prevent the crack initiation of metallic materials and alloys, which is widely used in aerospace, overload vehicle, ocean engineering, and nuclear power. Despite some investigations of LSP on surface integrity, microstructural evolution, and mechanical properties of metallic materials and alloys, there is a lack of a comprehensive perspective of LSP-induced microstructural evolution, mechanical properties for metallic materials and alloys in the last two decades. Furthermore, the relationship between the mechanical properties of metallic materials and alloys and the LSP processing parameters is presented. In particular, LSP-induced featured microstructure and grain refinement mechanisms in three kinds of crystal structures, for instance, face-centred cubic, body-centred cubic, and hexagonal close-packed metals, are present and summarised for the first time. In addition, some new emerging hybrid LSP technologies and typical industrial applications as important chapters are shown. Finally, the faced challenges and future trends in the next 10–20 years are listed and discussed. Results to date indicate that LSP, as an emerging and novel surface modification technology, has been increasingly used to surface layer of metallic components. These topics discussed could provide some important insights on researchers and engineers in the fields of surface modification and advanced laser manufacturing.

Single-crystal silicon carbide (SiC) is one of the most attractive materials for electronics and optics but extremely difficult to cut owing to its hard and brittle properties. While in previous studies, the focus has been placed on machining flat surfaces, in this study, the mechanisms of tool-workpiece interaction in cutting curved microstructures on 4H–SiC (0001) were explored through the ultraprecision diamond turning of micro-dimples. The surface/subsurface of both machined workpieces and used diamond tools were characterized, and the machining characteristics, such as chip formation and cutting forces, were also investigated. It was found that microcracks occurred easily in the feed-in/cut-in area of the dimples, which is caused by a large friction-induced tensile stress due to a large thrust force. The dimples located on the secondary cleavage directions <10−10> (S-dimples) were easy to produce crack-free surfaces, while the dimples located on the primary cleavage directions <−12−10> (P-dimples) were very prone to cause cracks on surfaces, even though the chips were formed in a ductile mode. The dimples located on the in-between direction (I-dimples) were moderately prone to surface cracking. It was also found that although the S-dimple has a crack-free surface, it has the thickest subsurface damage (SSD) layer containing a disordered layer, dislocations, and stacking faults; the SSD layer of the P- and I-dimples do not contain stacking faults; and the SSD layer of the I-dimple is the thinnest. Flank wear with nanoscale grooves on the diamond tool was significant without edge chipping and diamond graphitization detected. By optimizing the cutting conditions, a crack-free micro-dimple array was fabricated with nanometric surface roughness. The findings from this study provide guidance for the manufacture of curved SiC parts with high surface integrity, such as molds for replicating microlens arrays and other freeform surfaces on glass.

To meet the various and critical manufacturing requirements including high precision, low cost, good manufacturability, and more demanding from product service and performance aspects such as high performance, light-weight, less energy consumption and low carbon emissions in today's era of rapid product development with short product life circle, it is crucial to re-innovate and re-invigorate metal forming technologies and enable it to play an even more important role in manufacturing arena. Historically, introducing new kinds of energy fields into the forming process drives the innovative advance and rejuvenating of forming technologies due to the physically interactive mechanisms of energy field and certain material deformation behaviors such as thermal-mechanical coupling effects. In this paper, a classification of energy-aided metal forming processes is orchestrated and presented, and three kinds of energy-assisted metal forming technologies, viz., electrically-assisted forming, ultrasonic vibration assisted forming, and electromagnetic field supported forming, are reviewed and delineated as they are currently receiving a widespread attention with promising application potentials. In this paper, the physical essence and the effects of these introduced energy fields on deformation behavior, process performance, microstructure evolution are elucidated and analyzed. The constitutive modeling of these forming processes is recapitulated, and the newly established energy field assisted metal forming technologies are exemplified and discussed. Based on the advantages and limitations of these unique metal forming processes assisted by additional energy fields, the process capacity and application potentials are unraveled and examined. Finally, from the aspects of exploring physical mechanisms, establishing high-fidelity models, coupling the multiple energy fields, and developing intelligent equipment and realizing these forming processes, the current challenges and future prospects were discussed, summarized and articulated in such a way to present a panorama of the research, development and application of the energy-assisted forming technologies.