International Journal of Machine Tools & Manufacture最新文献

Laser powder bed fusion (LPBF) technology enables the development of NiTi alloys with complex geometries and tunable phase-transformation temperatures (PTTs). This technology is increasingly acknowledged as promising in the field of elastocaloric (eC) refrigeration. However, the mechanisms governing the manner in which this technology tunes the eC performance remain ambiguous. This study evaluated the fine-tuning of the eC properties by regulating Ni evaporation through laser manipulation. Our results demonstrate that although adjusting Ni loss via laser heat input can effectively control the PTTs, inappropriate combinations of laser parameters may result in lower than anticipated cooling capacity (ΔT_ad) and coefficient of performance (COP_mat) of produced samples. An excessive heat input results in Ni evaporation and in grain coarsening through the remelting and combination of fine grains owing to overlapping molten pools. Lower Ni enhances the phase-transformation enthalpy (ΔH_tr). However, larger grains increase the energy dissipation and thereby, counteracting ΔT_ad improvements. Theoretical analysis and experiments revealed that finer grains increase the misorientation angles. This hinders the dislocation motion and thereby, enhances the mechanical properties. Meanwhile, coarser grains can more conveniently promote PT and thereby, increase ΔH_tr. Thus, based on the naturally controllable grain size heterogeneity in LPBF-manufactured NiTi alloys, we propose optimizing the eC properties by controlling the morphology of the molten pool. Thermal-history simulations could balance this relationship. Ultimately, we developed two NiTi alloys for both high-temperature (70 °C) and room-temperature (25 °C) refrigeration. This study has provided effective insights for customizing high-performance eC components such as multistage caloric cascade regenerators, using additive manufacturing.

Despite the remarkable achievements in single-energy field-assisted diamond cutting technology, its performance remains unsatisfactory for processing high-entropy alloys (HEAs), targeted for next-generation large-scale industrial applications due to their exceptional properties. The challenge lies in overcoming the limitations of current single-energy field-assisted processing to achieve ultra-precision manufacturing of these advanced materials. This study proposes a multi-energy field-assisted ultra-precision machining technology, the magnetic and ultrasonic vibration dual-field assisted diamond cutting (MUVFDC), to address the current challenges. The phenomenological aspects of the dual-field coupling effect on HEAs are explored and investigated through comprehensive characterization of the workpiece material, ranging from macroscopic surface morphology to microscopic structural features. These analyses are performed based on experimental results from four different processing technologies: non-energy field, magnetic field, ultrasonic vibration field, and dual-field assisted machining. Research results demonstrate that MUVFDC technology effectively combines the advantages of a vibration field, which enhances cutting stability, and a magnetic field, which improves the machinability of materials. Additionally, this coupling technology addresses the challenges associated with single-energy field machining: it mitigates the difficulty of controlling surface scratches caused by tiny hard particles in a vibration field and suppresses the rapid tool wear encountered in a magnetic field. Furthermore, the gradient evolution of the subsurface microstructure reveals that the vibration field suppresses the severe matrix deformation induced by magnetic excitation. Simultaneously, the magnetic field reduces the size inhomogeneity of recrystallized grains caused by intermittent cutting. Overall, MUVFDC technology enhances surface quality, suppresses tool wear, smooths chip morphology, and reduces subsurface damage compared to single-energy field or non-energy-assisted machining. This work breaks through the performance limitations of traditional single-energy field-assisted processing and advances the understanding of the dual-field coupling effects in HEAs machining. It also presents a promising processing technology for the future ultra-precision manufacturing of advanced materials.

Bobbin-tool friction stir welding is a variant of friction stir welding with high process flexibility that has garnered considerable attention from the community. The reliability of the weld is sensitive to the macrostructure and texture of the stir zone, which must be carefully tailored. The macrostructure of the stir zone is governed by the refill behaviour of the plasticised metal associated with the bobbin-tool; refill occurs preferentially near the upper and lower shoulders, creating a triangular gap at the mid-thickness level that is subsequently closed by the confluence of the layered refilling plasticised metal from the upper and lower levels. Volumetric defects easily develop in this triangular confluence region because the symmetrical confluence of the layered refilling metal has the inherent characteristic of limited intermixing. The visual appearance of the triangular region, featuring limited voiding, was improved by tapering the stirring probe. This modification reduced the volume of displaced metal, leaving a smaller gap to be refilled during welding. Concurrently, the symmetrical confluence pattern was altered to an asymmetrical pattern, which enhanced the intermixing of the layered refilling metal from the upper and lower levels and promoted gap closure. For defect-free welds, macroscopic deformation inhomogeneity under tensile loading was observed due to the presence of a strong basal texture in the stir zone. The texture was scattered by disrupting the regular shear deformation pattern in the stir zone, which was achieved by modifying the tool profile. The activation capability of both basal slip and extension twinning among various local regions across the stir zone was substantially reduced through texture tailoring, resulting in more homogeneous tensile deformation. Consequently, elongation was enhanced by 66 %. This study highlights an easy-to-perform and generic strategy that can improve the quality of bobbin-tool friction stir welds.

Voronoi-based architected metamaterials have gained significant recognition as promising candidates for bone defect repair implants. However, the demanding requirements for reliable and adjustable load-bearing capacity pose challenges in applying irregular Voronoi-based architected metamaterials in implant applications. In this study, we propose a lattice-inspired design methodology for these metamaterials, enabling precise control over topologies and porosities to enhance their mechanical properties. We demonstrate the influence of unit cell topology on the printability, mechanical properties, and permeability of lattice-inspired Voronoi-based metamaterials (LIVMs) fabricated via laser powder bed fusion (LPBF) additive manufacturing. The LPBF-printed LIVMs exhibited yield strengths ranging from 3.35 to 17.59 MPa and specific energy absorption ranging from 3.81 to 14.29 J/g. Through finite element modeling and experimentation, we show that the deformation behavior of LIVMs with various topologies plays a crucial role in enhancing mechanical performance through mechanisms such as homogeneous load transfer between unit cells and multistage-contact strengthening within a unit cell. Additionally, we analyze the impact of unit cell type and porosity on the mass-transport behavior of LIVMs using computational fluid dynamics simulations. The LIVMs achieved experimental permeability values ranging from 3.88 × 10⁻⁹ to 16.83 × 10⁻⁹ m² (consistent with trabecular bones), indicating that multiple fluid flow channels can be utilized to enhance mass transport by distributing flow pressure and increasing fluid mobility. The proposed design method effectively achieves a favorable combination of superior mechanical properties and tunable permeability in Voronoi-based architected metamaterials. These findings provide valuable theoretical guidance for the development of architected metamaterials for bone implant applications.

The complexity of the interaction between the workpiece and abrasives, the characterisation difficulty of the strain-rate effect, and the analytical difficulty of brittle-ductile coexistence removal pose significant challenges in surface micro-morphology modelling of brittle-solid grinding. To overcome these bottlenecks, a theoretical model of the normal scratching force driven by the strain-rate effect was developed to verify the strain-rate sensitivity coefficients of gallium nitride (GaN) crystals. Impact scratching tests with a single grit further emphasised that the brittle-to-ductile transition and subsurface damage behaviour of GaN crystals exhibited a distinct strain-rate dependence. Subsequently, a theoretical model of the surface micro-morphology involved in the grinding of GaN crystals was developed by comprehensively considering the strain rate, abrasive coupling effect, time evolution, abrasive randomness, and elastic-to-plastic and brittle-to-ductile transition depths. The simulated results of the model agreed well with the experimental results, with an average error of <10 %. The model indicated that the ground surface micro-morphology and roughness were insensitive to variations in the grinding depth. Under the allowable conditions of the grinder stiffness and dynamic balance, appropriately increasing the wheel speed and grinding depth, decreasing the feed speed, and refining the abrasive size could effectively improve the proportion of ductile removal during the grinding of brittle solids. The results not only enhance the understanding of the abrasive coupling effect on surface micro-morphological evolution, material removal, and damage accumulation, but also provide theoretical guidance for the parameter optimisation involved in the grinding of brittle solids.

Laser shock peening, an advanced technology for severe surface plasticity peening, encounters challenges such as shallow hardened layers and surface spalling when dealing with difficult-to-machine materials. In this study, we introduced a high-frequency electropulsing-assisted laser shock peening (HFEP-LSP) technique that coupled laser shock peening with high-frequency electric pulses to achieve a significant and deeper plastic deformation layer. In the HFEP-LSP technique, we first considered the dual “skin effect”, which coupled the skin effect of high-frequency electric pulses with the “skin effect” of the mechanical effect induced by the laser shock wave. An integrated experimental platform comprising an electric pulse generator, laser shock peening equipment, and a control system was built. A >1.6 mm deep compressive residual stress layer was obtained, and the depth of the plastic deformation layer increased by 83.3 %. Furthermore, we elucidated the dual “skin effect”-induced complex heterostructure and β_m phase transition. A comprehensive analysis revealed the factors contributing to the deeper strengthening layer induced by HFEP-LSP, including the compressive residual stress and plastic deformation layers. In addition, the effects of laser shock peening and HFEP-LSP on the mechanical properties were investigated. Compared to the annealed samples, the ultimate tensile strength and elongation of the HFEP-LSP-treated samples were increased by 12.3 % and 57.1 %, respectively, with a fatigue life improvement of 176.4 %. The mechanism of synergistic improvement in strength and ductility was demonstrated.

The hot forged Ti–6Al–4V alloy demonstrates well constructed microstructure and balanced mechanical properties, which promotes its wide application in aviation field. However, its relative poor resistance to wear and foreign object impact usually leads to the cumulative damage, causing sudden failure and serious accident. Laser shock peening (LSP) is a novel surface plastic deformation technique, which could strengthen the surface layer of components through gradient grain structure. Nevertheless, the specific mechanism of microstructure evolution and mechanical properties enhancement of LSP processed hot forged Ti–6Al–4V alloy is still obscure, and its corresponding explanation would help the wide application. In the present research, the hot forged Ti–6Al–4V alloy was processed by LSP to regulate its superficial microstructure and improve mechanical properties, helping to understand the inner mechanism. The results reveal that LSP could simultaneously result in the merging of ultrafine α-Ti grains and refinement of coarse α-Ti grains, which reconstruct the dual-size grain structure. The crystal tilting and transformation promoted by the generation and movement of dislocations benefit the merging of ultrafine grains. Due to the different slip systems in dual phases, β-Ti phases exhibit much greater response to slip under surface plastic deformation, which are enforced to deform and construct the shell structure by sliding and phase transformation, while the α-Ti phases act as the core to synergistically construct ‘core-shell’ like structure. The increase of LSP impact time promotes the well wrapping of the ‘core-shell’ like structure and strengthens it by abundant dislocations, which also forms the gradient grain structure from surface to inner. Since the microstructure regulation and crystal defects engineering, the LSP improves the surface damage resistance and mechanical properties of the hot forged Ti–6Al–4V alloy obviously. Such results indicate a new technology to increase the properties of the hot forged Ti–6Al–4V alloy component further.

Avoiding wrinkling defects is extremely difficult in the sheet metal forming of ultra-thin components made from high-strength aluminum alloys. A novel cryogenic forming is thus proposed for solving this very challenging problem, wherein a thicker cladding blank is stacked above the thinner target blank to establish interface shear stress for reducing the hoop compressive stress, so that the critical wrinkling stress is increased. The enlarged radial deformation is transferred and withstood by the increasing hardening and ductility at cryogenic temperatures. The wrinkling suppression mechanism is revealed through mechanical and numerical analyses. Systematic experiments were conducted for studying the feasibility of high-strength AA7075 in cryogenic forming with different stacking sequences of cladding and target blanks, cladding blanks including three material strength levels (AA1060-O, AA5052-O, and SUS-304), two thicknesses (3.0, and 2.0 mm), and blank-holder forces. The effects of the cladding blank and blank-holder forces were clarified as reflected by forming defects, thickness, and strain distributions. The mechanical and numerical analyses can indicate that contact pressure can be produced by the wrinkling tendency of thinner target blank and limitation of cladding blank to wrinkling, which is accompanied by a decrease in the hoop compressive stress and increase in the critical wrinkling stress. Therefore, applying a relatively thicker blank on the punch side can prevent the wrinkling of ultra-thin components. The wrinkling tendency decreases with increasing strength and thickness of the cladding blank, which results in an increase in deformation or even splitting, which can be solved by the cryogenic temperature. The thickness of the cladding blank can be reduced by increasing the blank-holder force, which further reduces the material cost. AA5052-O, which has a strength similar to that of the target blank, is more suitable as a cladding blank for AA7075-W because the balance preventing wrinkling, improving thickness uniformity, and controlling the forming force. A Φ200 mm hemispherical shell with an initial thickness of 0.3 mm was formed successfully, and the corresponding thickness-to-diameter ratio reached 0.8‰, which almost increased one time on the basis of direct cryogenic forming. This new approach can be used for fabricating ultra-thin components from high-strength aluminum alloys.

The measurement of five degrees-of-freedom (5-DOF) error motions, including radial, axial, and tilt motions, is crucial for ultra-precision rotary axes, which are key components of ultra-precision machine tools and instrumentation. In this study, we propose an interference-enhanced micro-vision technique to concurrently derive the 5-DOF error motions from a single-shot two-dimensional image, which was captured by a standard industrial camera equipped with an interference objective lens. By consolidating the essential features into a single optical path, the interference-enhanced micro-vision technique ingeniously merges machine micro-vision and modified white-light interference to detect in-plane and out-of-plane motions. Numerical simulations demonstrated, the basic principle for deriving the 5-DOF error motions, and the magnification of objective lens had inconsistent effects on the measurement accuracy for the radial and tilt motions, i.e. higher magnification led to higher radial accuracy but lower tilt accuracy. As practical application, the error motion detection capability was demonstrated by simultaneously measuring the 5-DOF synchronous and asynchronous error motions for a typical air bearing spindle at rotation speeds of 8.33, 108.33, and 308.33 rpm. The synchronous errors were nearly identical at various spindle speeds. However, because of system dynamics, increased vibrations were observed to be superimposed on the basic tilt error motions as the spindle speeds increased, which were verified by the vibration marks imprinted on the turned surfaces. For the 5-DOF motion measurements, the least-square fitting using large-volume edge and greyscale data of the captured image enabled super-high resolutions, despite using a camera with a relatively large pixel size and low bit depth. These results demonstrate that the proposed interference-enhanced micro-vision technique is a simple and effective tool for measuring spatial error motions in ultra-precision rotary axes.

The high-performance multi-DoF forming process (MDFP) necessitates a 6-DoF forming machine tool with high normal and lateral stiffness to bear large normal and lateral forming force of millions of Newton (MN). However, the payload of parallel kinematic machine (PKM) is generally limited to thousands of Newton (kN), which restricts its application in MDFP. Therefore, this paper aims to develop a novel heavy load PKM with high stiffness for MDFP. To maximise the normal stiffness, a 6-PSS PKM with zero base angle and horizontal driver is proposed. Further, the inner force transfer model of 6-PSS PKM is established, indicating that the normal stiffness will be maximised when the link force approaches to be vertical. Consequently, a design criterion for maximising normal stiffness, i.e., the root mean square error (RMSE) for horizontal projection of all links should be minimised, is established. To maximise the lateral stiffness, general force balance equations of 6-PSS PKM are derived, indicating that lateral force can cause unintended negative force of links, significantly reducing the lateral stiffness. Thus, a novel auxiliary 3-SPS configuration is employed to provide additional force system to mitigate this negative force via hydraulic links. Correspondingly, a design criterion for maximising lateral stiffness, i.e., all link force should remain positive, is proposed. By combining aforementioned design criterion and kinetostatic models, a near-singular 6-PSS PKM with maximising normal stiffness is achieved, and dimension parameters of 3-SPS PKM with maximising lateral stiffness are optimised. On this basis, a novel flexible redundant 6-PSS/3-SPS PKM with both high normal and lateral stiffness is proposed, and a novel heavy load Nonapod with payload of 8 MN and payload-mass ratio of 40 is developed, showing good stiffness performance. The plastic deformation mechanisms of multi-DoF formed aviation bevel gear are revealed, and experimentally formed aviation bevel gear in the new Nonapod achieves good accuracy, microstructure and mechanical performance. This work provides a new methodology for synthesis of heavy load PKM with high normal and lateral stiffness, and has significant application prospect in PKM under heavy load working condition.