International Journal of Machine Tools & Manufacture最新文献

The edges of van der Waals materials exhibit unique physical and chemical properties, and they are promising for applications in many fields, such as optoelectronics, energy storage, and catalysis. Van der Waals material nanostructures with a controllable high density of edges are difficult to produce by current fabrication methods. In the present study, a simple nanomachining process to fabricate van der Waals nanowires with a high density of edges is proposed. This method used a linear-edge diamond tool to cut the basal plane of van der Waals film materials into a one-dimensional nanowire at the nanoscale. Experimental tests were performed to investigate the influences of the cutting thickness, film thickness, cutting direction, and material properties on the machining outcomes. The results showed that the van der Waals materials possessed low Young's moduli ranging from 24 to 238 GPa by cutting with a cutting thickness of larger than 30 nm, and the out-of-plane cutting direction led to the best machining quality and controllable preparation of van der Waals nanowires. To support the interpretation of the process outcomes, molecular dynamics simulation and transmission electron microscopy were performed to reveal the material-removal mechanism during nanocutting of van der Waals materials. From analysis of the chip-deformation process, interlayer slipping was found to dominate the plastic processing of the van der Waals materials, accompanied by intralayer bending and intralayer fracture in the out-of-plane cutting direction. By contrast, the brittle removal state occurred when cutting in the in-plane direction. This study provides important insights into the material-removal mechanism of van der Waals materials prepared by nanoscale mechanical cutting.

Static and dynamic analysis of key structural components of the machine tool is the crucial stage in transferring the physical to the virtual domain for digital manufacturing trends. The modeling technique of rolling kinematic joints with high nonlinearity can directly influence the accuracy and efficiency of prediction. Existing literature replicates the nonlinear static and dynamic characteristics considering the rolling element contact interface and proposes the theoretical modeling approach for the feed drives. However, there is a lack of systematic literature surveys. This paper reviews the current progress placed at the nonlinear analytical model of rolling kinematic joints, including ball screw feed drives, recirculating linear guideways, and ball screws. Advanced investigations on nonlinear dynamic stiffness and vibration response associated with ball screw feed drives are covered. Specifically, for linear guideways and ball screws, the stiffness and load distribution models can be divided into two categories: with and without consideration of the component structural deformations. Moreover, the corresponding detailed modeling process is introduced. The time-dependent modeling principle highlighting the recirculation motion of rolling elements is summarized, and friction and wear behavior is briefly discussed. The paper ends with the current research advancement and scarcity and recommends promising modeling tendencies. Particularly, the modeling tendencies require integrated model research on ball screw feed drives considering the more detailed nonlinear joint. Moreover, a fusion of multi-physics parameters is expected to achieve the high-fidelity mechanical model of key structural components for intelligent manufacturing demand.

Nanotwinned (nt) Cu has received much attention because of its superior mechanical and electrical properties, but only a few production processes can yield nt-Cu parts with uniform thickness and a homogeneous microstructure on the wafer scale. To solve this problem, a new precision electroforming process is proposed that combines auxiliary cathodes with pulse reverse current (PRC) electroforming, which provides a synergistic effect to increase the homogeneity of the thickness and a nanoscale twin structure. As a practical example of the proposed process, 4-inch nt-Cu lamina arrays were fabricated and numerically modeled to probe into the synergistic mechanisms. The intrinsic correlations among the array element spacing, current waveform, and main forms of thickness nonuniformity were determined. In addition, the effects of the processing parameters on the microstructural evolution and microhardness of the nt-Cu arrays were analyzed. The results indicated that such a significant improvement in thickness uniformity and microstructure homogeneity were due to the auxiliary-cathode/PRC combination, which enables maximization of the PRC leveling efficiency by inducing a uniform current distribution; this effectively ensures that the microstructures are uniform across all laminae on the wafer scale. Additionally, thick nt-Cu deposited on the current-crowding regions was preferentially stripped during the application of reverse current. This alleviates the adverse effects of the current redistribution resulting from the auxiliary cathode on the thickness uniformity of the laminae and offers additional possibilities for homogeneous growth of nt-Cu. The new precision electroforming process has significant potential to produce wafer-scale components with uniform thickness and specific microstructures.

The measurement of milling tool-tip frequency response functions (FRFs) in rotating conditions is challenging in practice. Methods based on the receptance coupling substructure analysis (RCSA) can obtain rotating tool-tip FRFs using normal modal test devices; thus, they have received extensive attention in the research community. The typical RCSA framework first adopts a calibration rod for measuring rotating FRFs. Then, it analytically calculates the desired tool-tip FRFs through the RCSA theory. As the calculation process involves matrix inversion, high-quality FRF data is required. However, experimentally measured FRFs in rotating structures contain severe noise, leading to an unreliable calculation. This paper presents a novel error analysis model to investigate the propagation mechanism of measurement errors in the typical RCSA framework. Results show that measurement errors would cause errors in the length of the coupled substructure while introducing scaling effects. The calibration rod is found to be vital for RCSA calculation reliability. The patterns of the calculation error are opposed when adopting a short or long calibration rod. Then, a calibration rod selection strategy is proposed. The strategy makes full use of the high measurement quality near the resonance in rotating FRFs and achieves the dominant mode frequency matching between the clamped rod and the clamped tool by adjusting the rod length. Simulations validate the error analysis model and the calibration rod selection strategy. Experimental results also show that the optimal selection of the calibration rod could improve the calculation reliability of rotating tool-tip FRFs in the typical RCSA framework.

An ultrahigh voltage is frequently required in electrochemical jet machining (EJM) to produce extreme current densities (>900 A/cm² for this study) to achieve maximum dissolution rates. However, such a high electric field easily induces a cathodic discharge at the nozzle, and the generation mechanism and characteristics remain unexplored. For the first time, this study shows a direct visualisation of the hydrogen evolution and cathodic discharge in EJM using high-speed photography. An in-depth analysis of the discharge behaviour was carried out based on electrical monitoring, temperature measurement, and characterisation of the resulting changes in the electrode surface. It was revealed that the current density threshold determines the discharge ignition. Discharge occurs preferentially at the inner edge of the nozzle end face, which can cause nozzle wear and reduce localisation of anode workpiece dissolution. The discharge intensity can be controlled by varying the applied voltage and pulse frequency. The electrolyte flow velocity and gap distance influence the discharge behaviour. With appropriate process control, cathodic plasma can enhance the EJM performance while minimising its negative impact. Furthermore, cathodic discharge can be significantly suppressed by designing the geometry of the nozzle tip to avoid local electric field concentration.

The construction of stability diagrams of interrupted milling cases is generally carried out by means of time-consuming numerical methods in either frequency or time domain, since the period doubling lobes arising under interrupted cutting are omitted by the time-averaged parametric scan of the traditional zeroth order approximation. This paper presents a novel seminalytic method in the frequency domain for interrupted milling. Taking advantage of their analytical chatter frequency distribution, this method adds the period doubling lobes calculated in a single frequency scan to the existing Hopf limits of the zeroth order solution. This, together with intelligent selection of scanning frequency ranges and truncation to the minimum set of harmonics, allows very fast calculation of the stability charts of interrupted milling cases while retaining the analytical basis and advantages of the zeroth order algorithm. The method accurately describes the stability limits at period doubling dominated zones and improves the existing zeroth order solution, but exhibits slight inaccuracies in the prediction of Hopf boundaries due to mode interaction and harmonic truncation effects.

Advanced technologies for the calibration of machine tools are presented. Kinematic errors independently of their causes are classified into errors within one-axis as intra-axis errors, errors between axes as inter-axis errors, and as volumetric errors. As the major technological elements of machine tool calibration, the measurement methods, modeling theories, and compensation strategies of the machine tool errors are addressed. The criteria for selecting a combination of the technological elements for machine tool calibration from the point of view of accuracy, complexity, and cost are provided. Recent applications of artificial intelligence and machine learning in machine tool calibration are introduced. Remarks are also made on future trends in machine tool calibration.

Thermal error is one of the primary factors affecting the machining accuracy of precision machining tools. Therefore, it is important to study the transient thermal characteristics of machine tools and the thermal-error control strategies. Thus far, a transient analytical modelling method for characterising the thermal characteristics of machine tools was proposed and an active error control strategy was provided. First, temperature-field modelling was conducted using an analytical method based on the Fourier series method and partial differential equations of heat conduction. Second, using the derived temperature field, the thermal deformation field was calculated based on finite element theory. Subsequently, the continuous real-time effect of the thermal power per unit heat source on the temperature and deformation fields of precision machine tools was studied. The proposed analytical modelling method not only predicts the machine tool heat deformation based on the working conditions of the heat source, but also matches the thermal control source power with the demand of the machine tool heat deformation. The optimal real-time power of the thermal control source is dynamically iterated and matched, such that the thermal deformation caused by the heat and thermal control sources can be balanced in real time at the displacement control point. Finally, the volumetric thermal error was actively controlled by adjusting the temperature field of the machine tool.

The simulated and experimental results indicate that the transient analytical model can accurately predict the real-time thermal characteristics of the machine tool and that the real-time active thermal control method can effectively reduce volumetric thermal errors. Using active thermal control, the squareness error in the YZ-plane was reduced by approximately 45%, the spindle thermal elongation was reduced from 23 μm to 7 μm, and the volumetric thermal error in the X, Y, and Z directions were reduced by approximately 16, 14, and 17 μm, respectively.

Laser-assisted machining is a promising method to achieve high efficiency and low damage when machining high-strength alloys. To explore the surface formation in laser-assisted grinding high-strength alloys, laser-assisted scratching was performed on a typical high-strength TC17 titanium alloy material using molecular dynamics simulations and experiments at different laser powers. The scratch force, material removal efficiency based on the scratched surface, and subsurface damage were analysed to determine the laser effects. A smaller scratch force can be achieved by laser assistance, and an appropriate laser power can enhance the material removal efficiency. The molecular dynamics simulation results were consistent with those of the experiments, and the subsurface formation process could be characterised by molecular dynamics simulations. In the laser-assisted scratched subsurface, three layers were found to differ from the matrix: amorphous, ultra-refined, and refined layers. The ultra-refined and refined layers were governed by continuous and discontinuous dynamic recrystallisation mechanisms, respectively, accompanied by different features through transmission electron microscopy analysis. These layers were shallower than those in the conventional scratched subsurface because of the annealing effect and smaller scratch force. In particular, annealing plays an important role in the amorphous layer of the machined surface. Laser-assisted belt grinding experiments were conducted for validation. This study provides significant insights into the low surface damage mechanism of high-strength alloys using laser-assisted machining.

In metal cutting, severe sliding contact at the tool-chip interface is unavoidable by a conventional cutting tool, which results in sloth motion of chip, higher chip thickness, formation of stagnation zone, higher power consumption, and poor surface finish. To overcome this limitation, rolling motion is introduced at the tool-chip interface by mounting a roller at the tip of a cutting tool – termed as Rotating Tip Cutting Tool (RTC-tool). The roller in RTC-tool rotates during cutting and establishes rolling-sliding contact. A model in-situ experimental configuration is used to study the plane strain flow characteristic of pure copper, notoriously known for higher chip thickness and power consumption, during cutting at low speed. The performance of RTC-tool is compared with sharp cutting-edge and blunt cutting-edge tools (fixed curvature and stationary-roller-tip tool). It is found that rolling motion at the tool-tip decreases the chip thickness and average plastic strain within the chip by about two times than sharp tool and more than two times than the blunt tools. Additionally, there is a significant improvement in surface roughness than the sharp tool. The digital image correlation techniques reveal that flow characteristics within the chip and near the tool-tip interface (retardation region) are influenced by the non-laminar plastic flow of materials. As opposed to the unstable retardation region and periodic cracking at the tool-tip of sharp tool, additional rolling motion at the tool-tip cuts the chip at the incipient stage, forms a stable retardation region, and increases the average velocity of the material in this region. Large retardation region and sloth motion of materials within the retardation region produce large chip thickness during cutting by blunt edge tool. As the chip thickness rather power consumption of the sharp tool is less than the blunt tool, force measurement in nearly orthogonal cutting configuration of RTC-tool compared with the sharp cutting edge. These tests are performed at moderate speed range in a lathe machine. The force measurement data and post-cutting characterization are aligned with the in-situ observations. As the frictional resistance of the roller controls the chip thickness further improvement in the performance of the RTC-tool is possible by reducing the frictional resistance of the roller.