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Cutting tool materials are the backbone of machining and play a vital role in the manufacturing industry. Innovation in cutting tools is important for customized and demanding applications. This state-of-the-art review is focused on innovations and future research directions for cutting tools covering i) tool materials/microstructure/property relationships, ii) coatings and their effect on tool performance, iii) cutting edge and functional surface preparation and effect on tool performance, iv) tool geometry for high performance and stable machining considering rapid machining, sustainability, and circularity aspects. The vision is to identify tool material/coating/geometry/functional surface relationships for significant improvement in machining performance. This paper includes perspectives from several research groups with a detailed discussion on current advances, capabilities, and challenges in engineered design of cutting tools, materials, coatings, structures and sets a new agenda for future tooling and research directions. [ABSTRACT FROM AUTHOR]

Manufacturing industries work towards the development of low toxic, eco-friendly, and sustainable alternatives to save the ecosystem from the harmful effects of traditional cutting fluids used for machining from long decades. The utilization of solid lubricants in machining is an advance alternative aimed at regulating the temperature in the machining zone without causing environmental pollution. The present study illustrates the machining performance of AISI 52100 steel employing solid lubricant-assisted machining (SLAM). The study evaluates the machining performance of SLAM with respect to cutting forces, vibration acceleration, tool wear, chip morphology, and surface roughness against dry machining (DM). The experimental findings indicate that utilizing SLAM leads to a notable decrease in cutting forces, ranging between 45% to 60%, a reduction in vibration acceleration by 14% to 29%, a decrease in tool wear by 11% to 17%, and a substantial improvement in surface finish ranging from 47% to 66% compared to DM. [ABSTRACT FROM AUTHOR]

The paper provides an analysis of the impact of the values of cutting tool inclination strategies and angles measured in the parallel and perpendicular to feed direction, radial depth of cut and feedrate on the surface roughness. The workpiece was made of the AISI H13 steel, hardness 50 HRC, and was machined using a ball-nosed end mill with CBN edges. The research methodology involved experiments conducted based on the Taguchi orthogonal array, optimization of parameters with the use of Taguchi method and process modelling using neural networks. Thanks to the use of neural networks, the analyses were performed for various levels of machining efficiency, obtained as a result of different radial depths of cut and feedrates. In order to obtain mathematical models welldescribing strongly nonlinear impact of the cutting tool inclination strategies and angles, a separate neural network learned for each tool inclination strategy. The prediction of results was made using a set of neural networks. The analyses and experiments resulted in surfaces with very low Ra parameter of 0.16 mm and mathematical models with a good fit to the experimental data. Values of the cutting tool inclination angle that allow obtaining the surface of specific surface roughness were specified for various levels of machining performance. [ABSTRACT FROM AUTHOR]

Purpose: Because many cutting fluids contain hazardous chemical constituents, industries and researchers are looking for alternative methods to reduce the consumption of cutting fluids in machining operations due to growing awareness of ecological and health issues, government strict environmental regulations and economic pressures. Therefore, the purpose of this study is to raise awareness of the minimum quantity lubrication (MQL) technique as a potential substitute for environmental restricted wet (flooded) machining situations. Design/methodology/approach: The methodology adopted for conducting a review in this study includes four sections: establishment of MQL technique and review of MQL machining performance comparison with dry and wet (flooded) environments; analysis of the past literature to examine MQL turning performance under mono nanofluids (M-NF); MQL turning performance evaluation under hybrid nanofluids (H-NF); and MQL milling, drilling and grinding performance assessment under M-NF and H-NF. Findings: From the extensive review, it has been found that MQL results in lower cutting zone temperature, reduction in cutting forces, enhanced tool life and better machined surface quality compared to dry and wet cutting conditions. Also, MQL under H-NF discloses notably improved tribo-performance due to the synergistic effect caused by the physical encapsulation of spherical nanoparticles between the nanosheets of lamellar structured nanoparticles when compared with M-NF. The findings of this study recommend that MQL with nanofluids can replace dry and flood lubrication conditions for superior machining performance. Practical implications: Machining under the MQL regime provides a dry, clean, healthy and pollution-free working area, thereby resulting the machining of materials green and environmentally friendly. Originality/value: This paper describes the suitability of MQL for different machining operations using M-NF and H-NF. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2023-0131/ [ABSTRACT FROM AUTHOR]

In the context of satisfying sustainability requirements nowadays, dry machining is one of the ideal strategies to eliminate the environmental and human health burdens of machining processes. In addition, micro-textured cutting tools are used to improve the performance of dry machining processes. Micro-textures reduce the chip-tool contact length and thus reduce friction and heat, which results in fewer cutting forces and temperature. However, the action of micro-cutting of the bottom side of the chip, which is known as derivative cutting, cuts down the gains of using textured tools, where derivative cutting leads to higher cutting forces, heat, and tool wear. This study aimed to investigate the effects of significant texture design parameters (i.e., micro-groove width) when cutting AISI 1045 steel using different machining parameters (i.e., 75 m/min and 150 m/min of cutting velocity, 0.05 and 0.10 mm/rev of feed). Three different textured cutting tool designs were prepared using the laser texturing technique and then utilized in machining experiments. In addition, the measured machining outputs were forces, power consumption, flank wear, and surface roughness. There were no marks for the derivative cutting when using the textured cutting tool with the narrowest micro-grooves according to the obtained microscopical images after the machining tests. In addition, the textured cutting tool, which included the narrowest micro-grooves, showed better performance compared to the non-textured cutting tool and the other textured tool designs in terms of cutting and feed forces, power consumption, flank tool wear, and surface roughness at the used cutting conditions. This confirmed that the careful optimal design of the micro-textured tools can reduce or eliminate the severity of the derivative cutting, and thus improve the overall machining performance. [ABSTRACT FROM AUTHOR]

The rigidity and natural frequency of machine tools considerably influence cutting and generate great forces when the tool is in contact with the workpiece. The poor static rigidity of these Vertical Machining Centre machines can cause deformations and destroy the workpiece. If the natural frequency of the machines is low or close to the commonly used cutting frequency, they vibrate considerably, resulting in poor workpiece surfaces and thus shortening the lifespan of the tool. The main objective of this study was to develop an experimental technique for measuring the effect of machine tool stiffness. The static rigidity of the X-axis was found to be 2.20 kg/μm, while the first-, second-, and third-order natural frequencies were 27.3, 34.4, and 48.3 Hz, respectively. When an external force of 1000 N was applied, the Y-axis motor load was found to be approximately 2740 N-mm. In this study, the finite element method was mainly used to analyze the structure, static force, modal, frequency spectrum, and transient state of machine tools. The results of the static analysis were verified and compared to the experimental results. The analysis model and conditions were modified to ensure that the analysis results were consistent with the experimental results. Multi-body dynamics analyses were conducted by examining the force of each component and casting of the machine tools and the load of the motor during the cutting stroke. Moreover, an external force was applied to simulate the load condition of the motor when the machine tool is cutting to confirm the feed. In this study, we used topology optimization for effective structural optimization designs. The optimal conditions for topology optimization included lightweight structures, which resulted in reduced structural deformation and increased natural frequency. [ABSTRACT FROM AUTHOR]

The present study investigates the microstructure of monolayer TiAlSiN and bilayer AlTiN/TiAlSiN coatings deposited on WC-Co inserts through magnetron sputtering. Further, a comparative study on the tool life and wear characteristics of uncoated, monolayer and bilayer coated inserts was performed through dry turning of tempered EN-8 steel under extreme cutting conditions. The TiAlSiN coating showed a dense fine morphology whereas the AlTiN/TiAlSiN coating showed a mixed morphology with a columnar structure for the intermediate layer of AlTiN followed by a dense nanocrystalline structure for the top layer of TiAlSiN. The dry turning experiments show that the major form of wear mechanism observed during machining was crater wear. Both monolayer and bilayer coated inserts showed promising cutting performance and the bilayer coated inserts showed better tool life than the monolayer coated inserts under most of the cutting conditions. [ABSTRACT FROM AUTHOR]

Machining optimization has been studied for low machining cost, high production rate, and energy saving. Nevertheless, most of the studies did not consider the part geometry. The complex part geometry results in varying contact conditions between the cutting tool and the workpiece. Therefore, the conventional tool life equation may not be applicable, and it is impossible to expect the same performance of machining different parts even with the same cutting parameters. In addition, the amount of material removal is different from part to part. Either the underuse or overuse of the tool is considered production loss in machining process. As a result, it is better for the cutting tool to be utilized until it reaches the end of its life when the operation is completed. Taking the conditions above into considerations, an objective function including the machining cost and the loss of tool usage is proposed in this study. Three turning operations, one straight turning and two profiling, were investigated to show the effect of part geometry on the machining optimization and tool wear. The results showed the different optimization processes and tool wear patterns although the initial cutting parameters and the amount of material removal were identical. The optimization processes were converged in 5 iterations. The cost of three cases reduced 34%, 33%, and 19%, respectively, with different optimized cutting parameters, and the tool approached the end of its life when the operation was done. [ABSTRACT FROM AUTHOR]

In the present investigation, machining performance of Ti6Al4V is studied under dry environment, pressurized air supply and distilled water based Minimum Quantity Lubrication (MQL). Machining (turning) performance is assessed in purview of cutting force (tangential component) magnitude, tool-tip temperature, width of tool flank wear progression, morphology of evolved chips and severity of vibrations at varied cutting speeds as well as cooling media. Characteristic features of spatial temperature distribution profile (at the vicinity of tool-tip) as influenced by varied cooling media are studied with the help of thermographs of the cutting zone. Mechanisms of cutting tool wear are studied as well. It is experienced that amongst three cutting environments tested, application of water-MQL is beneficial for machining of Ti6Al4V at low cutting speed. Severity of vibrations gets 50.39% reduced during machining under water-MQL than dry condition. Consequently, as compared to dry machining, water-MQL causes 79% reduced tool flank wear and 82% reduced crater wear at low cutting speed. Under water-MQL, reduced tool-tip temperature (66% reduced than dry condition) suppresses severity of tool wear. In comparison with high cutting speed, performance of water-MQL is found much better at low cutting speed. 'Unaffected zones' are identified at the worn-out tool rake face under water-MQL. High amplitude of vibration (maximum absolute mean value) causes low chip-segmentation ratio. On the contrary, chip reduction coefficient gets truncated with decrement in vibration amplitude. Vibration amplitude has positive influence on degree of chip-curl. [ABSTRACT FROM AUTHOR]

The performance of the PVD coated carbide insert with micro-holes is experimentally compared with that of the conventional inserts while machining Inconel 718 under Dry and MQL condition (Canola Oil, 0.25% Gr with Canola Oil). The machining performance of textured tool is found to be relatively good when compared to untextured tool in terms of the cutting force, surface roughness, flank wear and crater wear occurred on the cutting inserts. It is being inferred that Canola oil with 0.25% Gr-nanoparticle has improved the cutting force by 17.39%, decreased the flank wear and surface roughness by 20% and 36.23% respectively while machining with the textured tool. [ABSTRACT FROM AUTHOR]

Wave form end mills with variable rake and helix angles are new in the machining industry, and limited information is available on their machining performance. In this study, the machining performance of wave form end mills with variable rake and helix angles on the helical cutting edge on AISI 316L austenitic stainless steel which is in the difficult-to-cut materials due to work hardening, high tool wear and build-up edge (BUE) was investigated. In this context, five different carbide cutting tools, which are wave form tools with different wavelengths (mm) and wave amplitudes (µm) (6-550, 8-250, 4-450, and 8-650) and the standard tool, were evaluated through both experimental and statistical approaches in consideration of cutting forces, surface quality, tool life criteria. In terms of cutting forces and surface quality; wave form tools exhibited higher cutting forces and surface roughness values than the standard tool in all machining conditions, due to the predominance of machining negativity in negative rake angle regions despite the advantages provided by the positive rake angle regions. On the other hand, in 8-250 and 8-650 waveform tools with smaller positive and negative rake angles (+4°, -2°, -3°) were observed low tool wear values 17.2% and 6.9%, respectively compared to the standard tool. As a result, it is thought that 8-250 and 8-650 wave form tools can be a solution in rough milling processes for the low tool life problem caused by high mechanical strength and high work hardening properties that make difficult-to-cut AISI 316L material. [ABSTRACT FROM AUTHOR]

The objective of this experimental study is to evaluate the performance of three tool materials (mixed ceramic (CC650), PVD-coated carbide tool (GC1025) and CVD-coated carbide tool (GC4015)) during hard turning process of bearing steel 100Cr6 (66HRC) under dry environment. To do this, long-term tests used out to determine the tools life, productivity and machined surface quality in relationship with variation of the cutting speed and feed. The admissible parametric of cutting conditions has been obtained in order to reach a compromise tool life, its productivity and machined surface quality of part. Results showed that cutting speed is the most important factor affecting tool life but surface roughness was mainly influended by feed. Second order regression models was developed to find out the relationships between cutting speed and tools life time in the one hand and the correlation between tools life time and feed rate on the other hand. The results were compared to the litterature. For comparative study, the results showed that ceramic tool has been characterized by a good productivity and better surface quality compared to PVD-coated carbide tool. The latter was in turn more efficient than CVD coated carbide tool, which beyond the cutting speed 75 m/min was unproductive. [ABSTRACT FROM AUTHOR]

Electric discharge machining (EDM) is a nontraditional machining process based on the thermal erosion of the electrically conductive workpiece and tool electrodes. The product cost manufactured by the EDM process mainly depends on the tooling cost, which comprises the cost of tool material, tool fabrication, and tool maintenance. The properties of tool material affect the machining performance parameters like material removal rate (MRR), tool wear rate (TWR), and surface roughness. The performance parameters are also influenced by the tool geometry, tool fabrication method, and the way by which both tools and workpiece interact with each other. In the EDM process, tool wear is difficult to avoid and high TWR decreases the accuracy of the machined parts. Therefore, to obtain the desired accuracy it is necessary to calculate TWR and provide wear compensation. The tool electrode fabrication method also decides the TWR. Tool electrodes are generally manufactured by metal forming techniques like forging and drawing, other than that, powder metallurgy, additive manufacturing are also being used. The process performance of the tool can be improved by cryogenic treatment and coating of the tool electrodes. This review provides the literature survey about the different types of tools used in the EDM process, methods of fabrication, tool wear types; measurement and compensation techniques. [ABSTRACT FROM AUTHOR]

Cemented carbide inserts coated with CVD α-alumina, particularly those exhibiting a (0001) texture, have proven highly effective in steel turning. Despite the established superior performance of (0001) textured alumina coatings, the underlying reasons remain unclear. This study explores the influence of the crystallographic texture of alumina on wear mechanisms in various chip-tool contact zones on the insert rake face. The objective is to establish a fundamental understanding of the active degradation mechanisms and machining performance by relating coating texture to the orientation and deformation of individual Al 2 O 3 grains. Two multilayered coatings, Al 2 O 3 on Ti(C,N), featuring (0001)- and (11 2 ‾ 0) -textured CVD α-alumina, were assessed in dry turning of a bearing steel. The wear rate of the (11 2 ‾ 0) coating was double that of the (0001) coating. Worn coatings exhibit nano-terrace formation at the insert edge, likely due to chemical etching. In the sticking zone, plastic deformation leads to larger facets for grains oriented with the chip flow direction, while rounded surfaces result if this condition is not met. In the transition zone, both (0001) and (11 2 ‾ 0) textured coatings undergo increased plastic deformation accompanied by sub-surface dislocations. (0001) texture deforms more by basal slip creating a wavy coating pattern with steps present at larger misalignments of the lattice planes in neighboring grains while (11 2 ‾ 0) texture deforms by several slip systems creating elongated ridges and ruptured-like areas resulting in rougher surface. This difference in surface morphology is then inherited by the abrasion of submicron coating fragments embedded in the chip (more in (11 2 ‾ 0) texture) in the sliding zone resulting in an even rougher surface. Chemical reaction with the hot chip may also contribute to wear acting as an additional mechanism. This fundamental understanding contributes to the potential enhancement of steel machining using texture-controlled CVD alumina coatings, ultimately improving coated cutting tool performance. [Display omitted] • The wear rate of (0001)-textured α-alumina coating is half of that of the (11 2 ‾ 0) -textured coating. • Generation of a flat tool/chip contact surface gives less coating plastic deformation. • Slip systems parallel to the wear surface generate a microscopically flat surface. • Steps are created at larger misalignment of the lattice planes in neighboring grains forming a wavy pattern. • Wear surface morphologies are coupled to the number and direction of activated slip systems. [ABSTRACT FROM AUTHOR]

In the machining process, the machining performance which mainly refers to machined surface quality and cutting forces is hard to predict under different tool wear status. In this work, an improved case-based reasoning (ICBR) method is proposed to predict both the cutting force and machined surface roughness. With the emergence of new problem, ICBR method obtains solutions to new problem through case retrieval and reuse. In case retrieval stage, K similar cases to the new problem were retrieved using K nearest neighbor method. By means of the K similar cases, support vector regression machine (SVR) model was established to give the solution of the new problem in case of the reuse stage of ICBR method. Artificial neural network (ANN) was introduced to estimate the influence of machining parameters and tool wear on machining performance. As the ANN and SVR models contain unknown parameters, the novel particle swarm optimization algorithm was proposed to train these models for its capability of fast convergence and global optimum. The proposed ICBR method was used to predict the surface roughness and cutting force. The results showed the proposed ICBR method can give superior prediction accuracy and lower Mean square error than other popular intelligent models. Meantime, the ICBR method possesses good robustness and can be used for the actual machining process. [ABSTRACT FROM AUTHOR]

Recently, PcBN tooling have been successfully introduced in machining Ni-based superalloys, yet our knowledge of involved wear mechanisms remains limited. In this study, an in-depth investigation of PcBN tool degradation and related wear mechanisms when machining Inconel 718 was performed. Diffusional dissolution of cBN is an active wear mechanism. At high cutting speed oxidation of cBN becomes equally important. Apart from degradation, tool protection phenomena were also discovered. Oxidation of Inconel 718 resulted in formation of γ-Al 2 O 3 and (Al,Cr,Ti) 3 O 4 spinel that were deposited on the tool rake. Also on the rake, formation of (Ti,Nb,Cr)N takes place due to cBN-workpiece interaction. This creates a sandwich tool protection layer forming continuously as tool wear progresses. Such in operando protection enabled counterbalancing tool wear mechanisms and achieved high performance of PcBN in machining. [ABSTRACT FROM AUTHOR]

The topic of sustainable machining has in recent times emerged as a significant and impactful area of research focus as it directly deals with environmental health and protection, economic growth and prosperity, and societal wellbeing with greater health and wellness. More specifically, sustainable machining at product, process, and system levels deals with reducing negative environmental impact, offering improved energy and resource efficiency, generating a minimum quantity of wastes, providing operational safety, and offering improved personal health. This paper summarizes recent efforts by the world research community in sustainable machining with a systematic approach for the analysis of machining processes that are broadly classified as sustainable, beginning with dry machining, and then near-dry (also known as minimum quantity lubrication (MQL)) and cryogenic machining processes. The paper also extends its analysis to a hybrid mode of sustainable machining that effectively combines cryogenic and MQL machining processes for improved productivity and machining performance. While a significant part of this paper presents experimental analysis, the progress being made in modeling and optimization has also been discussed in the paper. In particular, major challenges involved in model development for practical implementation, with a view to selecting optimum cutting conditions and cutting tool selection, are primarily discussed in the paper. The need for continued modeling efforts for achieving deployable optimized conditions for sustainable machining is highly recognized, and further research is required in numerous fronts integrating the various convergent disciplines such as materials, mechanics, computational sciences, economics, environmental sciences. [ABSTRACT FROM AUTHOR]

This paper presents the result of pulsating lubrication strategy (PLS), an alternative metalworking fluids approach to improve machining performance. The formation of built-up edge (BUE) and built-up layer (BUL) is among the problems encountered during the machining of aluminum alloy, which degrades cutting performance and thus affects the machined surface quality. This study focuses on chip removal effectiveness by jetting a coolant intermittently of PLS on the cutting tool to create a hydraulic shock. The water stream coolant was set to pulsate at 2000 pulse/min with the pressure of 0.76 MPa. Applying this method improves chip evacuation. Hence, minimizing the formation of BUE and BUL more effectively than dry cutting. [ABSTRACT FROM AUTHOR]

Since the 1960s, the Inconel Alloy 718 has been a standard nickel-based superalloy due to its high strength, balanced mechanical properties, and strong corrosion resistance at relatively low costs and has been widely used in critical aircraft engine components. With the aim of improving productivity and product quality by implementing advanced tools and new process designs, models such as the FE model are utilized to predict the machining performance such as the cutting forces, the tool life, and the surface integrity. In the research area of FEM chip formation simulation, the influence of flank wear on predictions has not been investigated, especially not on the underestimation of the cutting normal force. In this paper, a 2D FEM chip formation model with the coupled Eulerian-Lagrangian (CEL) method has been built to predict cutting forces as well as other material loadings (Brinksmeier et al. Procedia CIRP 13:429–434, 2014; Buchkremer and Klocke Wear 376-377:1156–1163, 2017) in the machining of Direct Aged 718. In order to validate the performance of the FE model, fundamental investigations have been performed in orthogonal cutting with different cutting parameters. Two kinds of cemented carbide cutting tools with different cobalt contents have been applied to achieve different tool wear behaviors. Moreover, the underestimation of the cutting normal force by FEM chip formation simulation has been investigated and solved in consideration of the flank wear. The introduced FE-modeling approach shows precise predictions in terms of the cutting forces and the chip formation. [ABSTRACT FROM AUTHOR]

New-generation aerospace alloys gain more interest due to their advanced properties. Ti-5553 alloy can be categorised as new-generation aerospace alloys, but it is also difficult-to-machine material. For this reason, machining performance and the role of cutting parameters on machining of this particular alloy needs to be well investigated. This study aims to contribute to understand machining performance of Ti-5553 under various cutting parameters including cutting speed, feed rate and depth of cut. Machining performance tests were carried out without using any cooling and lubricant. Tool wear, cutting forces, chip breakability and surface quality were considered as measured machining performance criteria. This study reveals that the depth of cut and cutting speed have a profound effect on the machining performance of this material by substantially affecting tool wear and cutting temperature and thus all measured machining performance outputs. [ABSTRACT FROM AUTHOR]

In machining, cutting tools suffer from severe surface wear, especially in the cutting of difficult-to-cut materials. A major cause of tool wear is the friction generated at the tool-work and tool-chip interfaces, which produces a great deal of frictional heat and abrasion. In order to extend tool life and improve the quality of machined components, a host of techniques have been applied to modify the rake and flank faces of cutting tools. These techniques aim at providing cutting tools with improved resistance to external loading, better tribological performance and/or better chemical stability. This article presents a review of the fundamentals behind which the friction and wear in machining are reduced by modifying the cutting tool surface with the commonly used techniques, such as surface coating, high energy beam treatment, and surface texturing. The effects of these surface modifications on improving the cutting performance are also analyzed. Future research directions are finally discussed. [ABSTRACT FROM AUTHOR]

Coolant is a substance that applied in a machining process for the efficient machining of materials. The application of coolants is based on the several factors including the types of machining process, workpiece material, cutting tool and cost. Coolant helps to dissipate the heat that can be generated during the machining operation, induce lubricating effects to decrease the friction caused by the interfaces of two surfaces, flush away chips and offer corrosion protection. With the right type of coolants used, the performance of machining applications and the attributes of workpieces can be remarkably enhanced. The objective of the study to provides a critical review on the mechanism of coolant penetration, functions, variety of coolants, cooling actions, effectiveness, applications, and the additives that alter the ability and properties of coolants. Furthermore, the critical review also addresses the new technology cryogenic machining that uses cryogenic gases as coolants instead of conventional coolants. [ABSTRACT FROM AUTHOR]

Austenitic stainless steel during machining still faces several challenges in terms of poor machinability and severe tool wear. In this work, different rake surface restricted contact tools with an inconstant tool-chip contact length are designed and fabricated. An in-depth investigation is then performed to comprehend the influence of the variable-length restricted contact tools on the machining performance and tool wear during dry cutting of AISI 316L austenitic stainless steel. The results indicate that considerable improvements in tribological properties and tool life are achieved with the developed tools. The cutting force, cutting temperature, chip curl radius, and chip thickness decrease compared to traditional restricted contact tools. A dramatic reduction in flank wear of up to 44.18% is obtained in variable-length restricted contact tools compared with traditional restricted contact tools. Variable-length restricted contact structures also reduce the adhesion rate and abrasion damage of tool wear processes. The insights in this study exhibit an efficient method of dry machining stainless steel and may provide a basis for designing cutting tools for green machining of difficult-to-cut materials. • The inconstant restricted contact length is designed for the cemented carbide tool. • The function of variable-length restricted contact patterns is found in machining. • The restricted contact shape is critical to the chip flow direction. • Variable-length restricted contact tools demonstrate better wear resistance. [ABSTRACT FROM AUTHOR]

The ideal cutting-tool coating material is characterized by unique chemical and physical properties to achieve excellent cutting performance, a good thermal barrier effect, and a high-quality machined surface. Diamond-like carbon (DLC) coating, as a kind of cutting-tool coating material, has been used in cutting various materials due to its low coefficients of friction and thermal expansion, high hardness, and good chemical inert and thermal conductivity. This article mainly focuses on the modification methods for the DLC coating and their application in machining different materials. Firstly, the methods employed to improve the mechanical properties of DLC coating are reviewed and analyzed, including the multilayer structure design, transition layer, and doping other elements. Secondly, the machining performances of DLC-coated tools in the application of different materials are summarized. This review provides knowledge of modification mechanisms regarding DLC coating and its effects on mechanical properties. For machining different materials, it provides a reference to make a suitable selection and design of DLC coating to obtain better machining performance. [ABSTRACT FROM AUTHOR]

• Radial high-speed ultrasonic vibration cutting (R-HUVC) is developed for improving machining performance of hardened steel. • Surface generation mechanisms of R-HUVC and boundary conditions for micro-dimples overlapping are analyzed. • Cutting force of R-HUVC is reduced by up to 80% compared to conventional cutting (CC). • Tool life in R-HUVC was longer than in CC during finish turning of hardened steel. Hardened steel has been widely used in the aviation and automotive fields owing to its unique properties. However, the poor machining performance for finishing hardened steel owing to low attainable cutting speeds and rapid tool wear has become a bottleneck in the functional performance and range of applications. In this study, a radial high-speed ultrasonic vibration cutting (R-HUVC) process was adopted for improving the machining performance of finishing hardened steel. R-HUVC involves the use of radial ultrasonic vibrations which ensure the separation of the tool and workpiece. The kinematics of R-HUVC were analyzed through a theoretical model, and its surface generation mechanisms in the intermittent cutting mode were studied. Then, finish turning experiments were conducted on the cutting force, surface roughness, and tool life to validate its machining performance compared to that of conventional cutting (CC) for a wide range of finishing conditions. The experimental results showed that R-HUVC can realize a lower cutting force, longer tool life, and better surface roughness compared to CC. It was verified that R-HUVC can be applied to high-speed machining for the finish turning of hardened steel because it improves the machining performance. [ABSTRACT FROM AUTHOR]