The Special Issue Machining—Recent Advances, Applications and Challenges is intended as a humble collection of some of the hottest topics in machining. The manufacturing industry is a varying and ...challenging environment where new advances emerge from one day to another. In recent years, new manufacturing procedures have retained increasing attention from the industrial and scientific community. However, machining still remains the key operation to achieve high productivity and precision for high-added value parts. Continuous research is performed, and new ideas are constantly considered. This Special Issue summarizes selected high-quality papers which were submitted, peer-reviewed, and recommended by experts. It covers some (but not only) of the following topics:
High performance operations for difficult-to-cut alloys, wrought and cast materials, light alloys, ceramics, etc.;
Cutting tools, grades, substrates and coatings. Wear damage;
Advanced cooling in machining: Minimum quantity of lubricant, dry or cryogenics;
Modelling, focused on the reduction of risks, the process outcome, and to maintain surface integrity;
Vibration problems in machines: Active and passive/predictive methods, sources, diagnosis and avoidance;
Influence of machining in new concepts of machine–tool, and machine static and dynamic behaviors;
Machinability of new composites, brittle and emerging materials;
Assisted machining processes by high-pressure, laser, US, and others;
Introduction of new analytics and decision making into machining programming.
We wish to thank the reviewers and staff from Materials for their comments, advice, suggestions and invaluable support during the development of this Special Issue.
A tribo-electrostatic separation was developed to produce protein concentrates from yellow pea flour. A mixed-level full factorial experiment followed by a multiple linear regression model was ...developed to assess the impacts of airflow rate, plate voltage, milling type, and screen size as operating factors on protein content, separation efficiency, and yield of the protein-enriched concentrates. Except for plate voltage, all factors showed significant impacts on protein content. The interaction of plate voltage and milling screen size was significant in protein content. Plate voltage was the only main effect statistically impacting protein separation efficiency; however, polynomial interactions of flow rate with plate voltage and flow rate with milling type and screen size were significant. The optimal parameters were laminar flow at ±6.5 kV electric field strength using pin-milled flour at the smallest tested milling screen size, which resulted in protein content of 57.1% and separation efficiency of 62%. Theoretical predictions agreed with experimental data.
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•Tribo-electrostatic separation was optimized for the protein enrichment of yellow pea.•Flow rate, voltage, milling type, and intensity were assessed as independent factors.•The impact of the pin and Ferkar milling at different intensities was investigated.•Pin milling was more efficient in the dissociation of protein and starch particles.•Pin milling at higher intensity greatly enriched pea flour under a laminar flow.
In present, five-axis numerical control (NC) machining center is used to process blisk, and the technology of plunge-milling and side-milling are widely adopted, which results in lower processing ...efficiency and high total cost. In the present study, first, a new machining technology of blisk is put forward, which is known as multi-milling, namely, disc-milling is used to remove the large margin of blisk’s channel, plunge-milling can expand the size of groove, further forming the surface of channel, and the corner and angle of the channel can be eliminated by side-milling. Second, with one-stage fan blisk of a certain type aircraft engine as an example, the processing efficiency of three different technologies (multi-milling, plunge-milling+side-milling, and side-milling) are studied by means of UG (Unigraphics NX) software. Third, based on the technology of multi-milling, the specific structure of multi-milling machine tool is designed. Last, the verification test is conducted, test results show that the processing efficiency of blisk can be enhanced drastically, finish cost can be reduced greatly with the multi-milling machine tool, which can give a great push to the development of aviation industry.
•Reduction of forces and improvement of efficiency during finish ball end milling.•Multi-criteria optimisation in terms of cutting forces and efficiency.•Relations between ball end milling process ...efficiency and surface inclination angle.•Optimised forces and process efficiency achieved for vc=375m/min and α=15°.
This paper proposes a method for the reduction of forces and the improvement of efficiency during finish ball end milling of hardened 55NiCrMoV6 steel. The primary objective of this work concentrates on the optimal selection of milling parameters (cutting speed – vc, surface inclination angle α), which enables the simultaneous minimisation of cutting force values and increased process efficiency. The research includes the measurement of cutting forces (Fx, Fy, Fz) during milling tests with variable input parameters and calculation of process efficiency accounting for cutting parameters and surface inclination. The paper then focuses on the multi-criteria optimisation of the ball end milling process in terms of cutting forces and efficiency. This procedure is carried out with the application of the response surface method, based on the minimisation of a total utility function. The work shows that surface inclination angle has a significant influence on the cutting force values. Minimal cutting forces and relative high efficiency can be achieved with cutting speed vc=375m/min and surface inclination angle α=15°.
This paper investigates the textured surface generation mechanism in vibration-assisted micro milling through modelling and experimental approaches. To decouple the effects of tool geometry and ...kinematics of vibration-assisted milling, a surface generation model based on homogenous matrices transformation is proposed. On this basis, series of simulations are performed to provide insights into the effects of various vibration parameters (frequency, amplitude and phase difference) on the generation mechanism of typical textured surfaces in 1D and 2D vibration-assisted milling. Furthermore, the wettability tests are performed on the machined surfaces with various surface texture topographies. The fish-scale textured surfaces are found to exhibit better wettability than those with wavy-structure. The results indicate that vibration-assisted milling is an effective method to generate certain surface textures with controllable wettability.
•Results showed that the vibration reduced the mean cutting force and increased its deviation.•The simulation confirmed the existence of torsional vibration which caused intermittent cutting.•Most ...effective parameter for mean forces (FX and FY) was feed and the deviation was rotational speed.
Ultrasonic assisted milling (UAM) is one of the advancements in the area of conventional milling process. Literature suggests that superpositioning of ultrasonic vibration with milling process improves its efficacy by reducing forces and improving surface finish. In the present study experimental investigations were carried out to evaluate the effect of process parameters (power of ultrasonic vibration (UP), rotational speed, axial depth of cut (DOC) and feed rate) on the cutting responses (average cutting force and the standard deviation in cutting forces). An experimental setup was designed and developed to perform UAM process with axial vibrations. The end mill used in this setup was designed by performing harmonic analysis on ANSYS workbench. UAM experiments based on central composite design (CCD) technique were performed on Al6063 aluminum alloy. Analysis of variance (ANOVA) was performed and regression equations were obtained. Further, the obtained results were analyzed to study the effect of machining parameters on the responses. The developed models were then validated by performing experiments on random and optimized set of process parameters. The ANOVA results suggested that the most effective parameter for cutting forces was feed rate, however its standard deviation was affected by rotational speed. Also the assistance of axial vibration reduced the average cutting force and increased its standard deviation. In order to evaluate the effect of axial ultrasonic vibrations, simulations were performed to study the cutting kinematics in UAM process. The simulations showed that the presence of torsional vibration at the cutting tip, caused intermittent cutting during UAM.
Recently, mechanical micro-milling is one of the most promising micro-manufacturing processes for productive and accurate complex-feature generation in various materials including metals, ceramics, ...polymers and composites. The micro-milling technology is widely adapted already in many high-tech industrial sectors; however, its reliability and predictability require further developments. In this paper, micro-milling related recent results and developments are reviewed and discussed including micro-chip removal and micro-burr formation mechanisms, cutting forces, cutting temperature, vibrations, surface roughness, cutting fluids, workpiece materials, process monitoring, micro-tools and coatings, and process-modelling. Finally, possible future trends and research directions are highlighted in the micro-milling and micro-machining areas.
Coatings usually play an important role in terms of machining tool behaviour and lifespan. TiAlN is a well-known PVD coating but, the permanent need for improved performance is inducing new ...compositions around this coating. In this work, the wear behaviour of different PVD coated tools with different geometries was analysed, in the milling of pre-hardened tool steel. The selected tools had two different geometries, namely ball nose end mill and end mill tools. Additionally, these were coated with two different PVD coatings, TiAlSiN and TiAlN. These tools were employed in milling operations of W 1.2711 pre-hardened tool steel. The cutting parameters were defined in a way to enable a valid comparison between the milling tools, varying only feed and cutting length, to analyse the influence of these parameters on the tool's wear mechanisms. Cutting force data was collected during the milling tests using a dynamometer in order to identify the different wear stages of the tool, and surface roughness was measured after each test. Furthermore, after the milling tests the tools were submitted to a SEM analysis, in order to analyse the wear mechanisms of each coated tool. The main wear mechanisms that were identified in both coatings are adhesion and abrasion, followed by coating delamination. Moreover, the analysed wear was less significant in the TiAlSiN PVD coated tools used, mainly in the ball-nose tools, providing as well very good surface roughness of the machined surface. The surface morphology of the tool and the direction of the grooves left on the tool surface after grinding operations of the uncoated tool showed a significant influence on the coating wear mode. The best machining conditions have been established, taking into account the lowest surface roughness obtained on the machined surface and the lowest wear rate of the tool.
•TiAlSIN coating presented better results in pre-hardened tool steel milling than TiAlN coated tools (end-mill and ball-nose tools’ geometry).•Wear mechanisms follow this sequence: adhesion, abrasion, and delamination. The cycle is repeating itself, increasing systematically.•For the conservative set of parameters used, low machining forces were registered, and no significant variations were observed.•The first signals of tool failure happened after 2 m cutting length.•TiAlSiN coated tools provided lower roughness of the machined surfaces, showing a better suitability for finishing operations.•Best cutting conditions: 80 m/min cutting speed, 0.0147 mm/edge feed rate, 3 mm depth of cut under dry machining conditions.
The primary objective of this study is to explore the fabrication of a hybrid nanocomposite (HNC) composed of ZnAl40Cu2 alloy, graphene, and B4C particles, while also determining the optimal graphene ...reinforcement ratio for enhanced properties. Our methodology entails the production of HNC powders (HNPs) through mechanical milling, where we combine graphene nanoplatelets with B4C microparticles into ZnAl40Cu2 alloy powders. Throughout this process, we maintain a constant B4C content of 1.5 wt%, while varying the graphene content at 1.5 wt%, 3 wt%, and 4.5 wt%. Following the characterization of all produced powders, which includes an assessment of powder morphology, powder size distribution, and powder microhardness, we proceed to hot-press the HNPs to create bulk HNC samples. After consolidating the specimens, a comprehensive series of tests are carried out to determine microstructural, mechanical (hardness and tensile strength) and tribological properties. Our results reveal that the HNC specimen with graphene content of 3 wt% (referred to as A2) displays the most notable enhancements in properties. Specifically, A2 exhibits an impressive hardness of 163 HB, surpassing the hardness of the ZnAl40Cu2 matrix alloy, which measures at 133 HB. Furthermore, its ultimate tensile strength significantly outperforms the ZnAl40Cu2 matrix alloy, with a remarkable value of 223 MPa compared to 157 MPa. However, it is worth noting that the improvement in wear resistance for HNCs is most pronounced up to a certain threshold of graphene content, which is 3 wt%.
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•This study is the first to determination of comprehensive tribological properties of ZnAl40Cu2 based HNCs.•The effect of Gr on the mechanical and tribological properties of ZA40 based HNCs was investigated for the first time.•This study is the first to find the optimal Gr content for improved properties in ZnAl40Cu2 alloy HNCs.•Low wear rates were obtained, which is actually comparable to some ZA and Al-based materials.
•A pose optimization method is presented to eliminate the redundant freedom along a given five-axis CNC tool path aiming at increasing the robot stiffness, resulting in improved machining accuracy.•A ...new frame-invariant performance index is proposed to evaluate the stiffness of the robot at a certain posture.•The redundancy elimination problem is formulated as a one-dimensional optimization problem in consideration of the constraints of joint limits, singularity avoidance and trajectory smoothness.•The one-dimensional optimization problem is solved by a simple discretization search algorithm.
Industrial robot provides an optimistic alternative of traditional CNC machine tool due to its advantages of large workspace, low cost and great flexibility. However, the low posture-dependent stiffness deteriorates the machining accuracy in robotic milling tasks. To increase the stiffness, this paper introduces a pose optimization method for the milling robot when converting a five-axis CNC tool path to a commercial six-axis industrial robot trajectory, taking advantage of a redundant degree of freedom. First, considering the displacements of at least three points on the end effector of the robot, a new frame-invariant performance index is proposed to evaluate the stiffness of the robot at a certain posture. Then, by maximizing this index, a one-dimensional posture optimization problem is formulated in consideration of the constraints of joint limits, singularity avoidance and trajectory smoothness. The problem is solved by a simple discretization search algorithm. Finally, the performance index and the robot trajectory optimization algorithm are validated by simulations and experiments on an industrial robot, showing that the machining accuracy can be efficiently improved by the proposed method.
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