High-speed five-axis ball-end milling operations could achieve high efficiency, good surface integrity, and high accuracy in machining of complex components for many manufacture fields. This work concentrated on the machined surface properties and cutting performance produced by the multi-axis ball-end milling process in order to enhance the high performance application of this technology. Variations of the potential tool–workpiece contact zone; the cutting section area, and perimeter corresponding to eight types of tool posture; and the influence of the different tool postures on the machining characteristics were analyzed by geometrical modeling method. The tool postures with negative tilt angles, positive lead angles, or compound inclination angles with negative tilt angle and positive lead angle are beneficial to improve cutting effects with larger effective cutting speed. Discussions on the response analysis and optimization of the machined surface roughness, surface hardness, and the average and maximum cutting forces were conducted under up milling condition. Furthermore, the multi-objective coupling optimization for process performance and surface integrity and typical application in practical machining were carried out for high-speed multi-axis ball-end milling, and the optimization plans are validated by detection and analysis of the machined surface. The research results would promote the high performance application of the high-speed multi-axis ball-end milling operation.

Multilayer graphene (MLG)-reinforced Al2O3/TiC ceramics were fabricated through hot pressing sintering, and the reinforcing effect of MLG on the microstructure and mechanical properties of the composites was investigated by experiment and simulation. The simulation of dynamic crack initiation and propagation was investigated based on the cohesive zone method. The results show that the composite added with 0.2wt% MLG has excellent flexural strength and high fracture toughness. The major reinforcing mechanisms are the synergistic effect by strong and weak bonding interfaces, MLG pull-out, and grain refinement resulting from the addition of MLG. In addition, the aggravating of crack deflection, branching, blunting, and bridging have indispensable contribution to the improvement of the as-designed materials.

•Cr3C2/(Cr3C2+VC) ratios affect microstructure and mechanical properties of WC-based ceramics.•The two-step hot-pressing sintered functionally graded WC-TiC-Al2O3-Cr3C2-VC ceramics exhibit high mechanical properties.•Grains become fine and Al2O3 dispersion tends to be homogeneous with raised Cr3C2.•Functionally graded WC-based ceramics with a Cr3C2/(Cr3C2+VC) ratios of 0.6 can be used as high-speed cutting tools.•Surface residual compressive stress can greatly improve the mechanical properties of FGM.The effect of VC, Cr3C2 and combination (Cr3C2 and VC with varied weight ratios of Cr3C2/(Cr3C2+VC)) on the microstructure and mechanical properties of functionally graded WC-Al2O3-TiC composite synthesized employing two-step hot-pressing sintering (heated to 1700 °C and then immediately cooled to 1600 °C with a soaking time of 30min) was comprehensively investigated. Combined addition of VC and Cr3C2 with an appropriate ratio to WC-TiC-Al2O3 composite performed a more pronounced effectiveness on inhibiting grain growth and improving the homogeneous dispersion of Al2O3 nano-particulates in WC matrix than single addition of VC or Cr3C2 did. Furthermore, single Cr3C2 addition outperformed VC in grain refinement and uniform distribution of Al2O3. The experimental results show that excellent mechanical properties are achieved for Cr3C2-VC additions with Cr3C2/(Cr3C2+VC) weight ratio 0.6 with a hardness of 25.64 GPa, a flexural strength of 1209.6 MPa, a fracture toughness of 11.49 MPa mm1/2 and a surface residual stress of −591.9 MPa. High surface compressive stress, strong interface bonding, crack branching and bridging, crack deflection, microcracking and Al2O3 pullout are the major mechanisms contributing to the drastically enhanced flexural strength and fracture toughness. The five-symmetric-layer graded ceramics developed in this paper provide an exceptional combination of high toughness and high hardness, which are conducive to the application as metal cutting tools.

•MLG-reinforced graded WC-based nono-composites were prepared through TSS.•53.3% enhancement in toughness was obtained by adding 0.1 wt.% MLG.•Significant tribological properties improvement were obtained by adding 0.1 wt.% MLG.•Toughening mechanisms and anti-friction and wear resistance mechanisms were studied.Mechanical and tribological properties of functionally graded multilayer graphene (MLG) reinforced WC-TiC-Al2O3 ceramics prepared employing two-step sintering (TSS) are determined in this paper. Results showed that MLG can act as not only an exceptional reinforcement phase, but also a superior lubricant phase. A 0.1 wt% MLG/WC-TiC-Al2O3 ceramics exhibits ~ 53.3% enhancement in fracture toughness, ~ 73.8% decrement in friction coefficient, ~ 82.65% improvement in wear resistance in comparison with monolithic ceramics. MLG bending, wrapping, interface debonding, MLG wall and network, MLG induced weak interface, grains bridging by MLG, MLG pullout, crack deflection, crack bridging and crack stopping are the major toughening mechanisms. The dramatic improvement in tribological performance is attributed to the self-lubrication of MLG and easily formed friction layer in the contact interface. Furthermore, the unrivalled thermal conductivity of MLG and its rather significant effect in inhibiting the grain growth are the important contribution to the improved tribological performance. Therefore, the functionally graded MLG/WC-TiC-Al2O3 ceramics are conducive to be engineered as high-speed cutting tools.Download high-res image (194KB)Download full-size image

The Al2O3−(W,Ti)C composites with Ni and Mo additions varying from 0vol% to 12vol% were prepared via hot pressing sintering under 30 MPa. The microstructure was investigated via X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS). Mechanical properties such as flexural strength, fracture toughness, and Vickers hardness were also measured. Results show that the main phases A12O3 and (W,Ti)C were detected by XRD. Compound MoNi also existed in sintered nanocomposites. The fracture modes of the nanocomposites were both intergranular and transgranular fractures. The plastic deformation of metal particles and crack bridging were the main toughening mechanisms. The maximum flexural strength and fracture toughness were obtained for 9vol% and 12vol% additions of Ni and Mo, respectively. The hardness of the composites reduced gradually with increasing content of metals Ni and Mo.

Compared with traditional grinding, hard turning with ceramic tools has lots of advantages such as lower cost, higher productivity, better machining accuracy, and elimination of cutting fluids. However, the catastrophic fracture of ceramic tool frequently occurs in turning of hardened steel. Hence, there is a need to recognize the evolution of machinability aspects (cutting forces and tool wear) in the whole turning process. An orthogonal experiment was designed to investigate the evolution of cutting forces and tool failure mechanisms in intermittent turning of hardened 20CrMnTi steel with Al2O3-TiC ceramic tool. The effects of cutting parameters on cutting forces were analyzed by Taguchi method and analysis of variance (ANOVA) during different tool wear stages. The results revealed that the influence of cutting parameters on cutting forces gradually declined with the increased tool wear, and the contribution of depth of cut on cutting forces gradually increased. The optimal cutting parameters of cutting forces were calculated for different wear stages. In addition, the fracture modes and mechanisms of tool under different cutting conditions were investigated. The fatigue striations and fatigue beaches were observed at the fracture surface. The propagation paths and mechanisms of fatigue cracks were analyzed under different cutting speeds. The results indicated that the fracture area of tool was mainly affected by mechanical stress, while the depth of crack propagation was determined by thermal stress.

Coated carbide tools are widely used in machining titanium alloys due to their excellent wear resistance, high strength, and hardness even at elevated temperature. The paper gives a special attention to the failure mechanisms of coated carbide cutting tools during high-speed intermittent cutting process. The effects of serrated chip formation on the instantaneous cutting forces, transient temperature, and thermal stress distributions on the cutting tool were investigated based on finite element method (FEM). The results show that the cutting tools undergo combined thermomechanical and high/low cycle fatigue loading during intermittent cutting process. Micro-crack propagation and coating delamination were observed on the cutting edge and rake face. Flank wear and brittle fractures on the cutting edge caused by crack propagation were identified as the main failure mode of coated carbide tools in intermittent cutting process. Intense tensile thermal stress on the cutting tool edge was found to be produced by differential cooling rates in the idle periods. The rapid alteration of stresses was believed to be the direct cause of crack propagation on the cutting edge.

An ultra-fine grain carbide cutting tool material was fabricated by using Sinter-HIP technique. Four-tooth solid carbide end mills with a 20 mm diameter and a 0.8 mm corner-radius were manufactured and then coated with physical vapor deposition multilayer TiAlN and AlCrN coatings. Cutting performance of coated ultra-fine grain carbide end mills was investigated via high-speed wet milling tests on Ti-6Al-4V alloy with a TiAlN coated fine grain end mill commercially available for comparison. The transient and progressive cutting forces during wet machining were measured and the chip morphologies were analyzed. The results of the milling tests revealed that the TiAlN coated ultra-fine grain solid carbide end mill exhibited longer tool life, smaller progressive cutting forces, and better broken chips than the TiAlN coated fine grain end mill with the same cutting condition. In addition, the multilayer TiAlN coated end mill achieved higher tool wear resistance than the multilayer AlCrN coated end mill. The longer tool life of the new coated ultra-fine grain solid carbide end mill should be attributed to the smaller grain size of the tool substrate material with higher hardness, higher transverse rupture strength, and better thermo-mechanical fatigue properties, as well as higher wear resistance of TiAlN coating.

In the present study, high-speed side milling experiments of H13 tool steel with coated carbide inserts were conducted under different cutting parameters. The microhardness and microstructure changes of the machined surface and subsurface were investigated. A finite element model, taking into account the actual milling process, was established based on the commercial FE package ABAQUS/Explicit. Instantaneous temperature distributions beneath the machined surface were analyzed under different cutting speeds and feed per tooth based on the model. It was found that the microhardness on the machined surface is much higher than that in the subsurface, which indicates that the surface materials experienced severe strain hardening induced by plastic deformation during the milling process. Furthermore, the hardness of machined surface decreases with the increase of cutting speed and feed per tooth due to thermal softening effects. In addition, optical and scanning electron microscope (SEM) was used to characterize the microstructures of cross sections. Elongated grains due to material plastic deformation can be observed in the subsurface, and white and dark layers are not obvious under present milling conditions. The thickness of plastic deformation layer beneath the machined surface increases from 3 to 10 μm with the increase of cutting speed and feed per tooth. The corresponding results were found to be consistent and in good agreement with the depth of heat-affected zone in finite element analysis (FEA).

Si3N4-based composite ceramic tool materials reinforced with nanoscale Si3N4 and microscale (W, Ti)C were fabricated by hot pressing and sintering technology. The flexural strength, fracture toughness and hardness of the sintered composites were tested and the microstructure and indention cracks were observed. The experimental results showed that the Si3N4/(W, Ti)C nanocomposites containing 18 vol% of nanoscale Si3N4 and 20 vol% of microscale (W, Ti)C, which were sintered under a pressure of 30 MPa at 1700 °C in vacuum condition for 45 min, had the optimum comprehensive mechanical properties. The appropriate addition of microscale (W, Ti)C and nanoscale Si3N4 accelerated the formation of elongated β-Si3N4 grains and contributed to the improvement of mechanical properties. The strengthening and toughening mechanisms for the Si3N4/(W, Ti)C composite ceramic tool materials was a synergistic effect of intergranular and transgranular fracture, crack bridging, deflection and branching.

High-speed milling tests were carried out on Ti–6Al–4V titanium alloy with a polycrystalline diamond (PCD) tool. Tool wear morphologies were observed and examined with a digital microscope. The main tool failure mechanisms were discussed and analyzed utilizing scanning electron microscope, and the element distribution of the failed tool surface was detected using energy dispersive spectroscopy. Results showed that tool flank wear rate increased with the increase in cutting speed. The PCD tool is suitable for machining of Ti–6Al–4V titanium alloy with a cutting speed around 250 m/min. The PCD tool exhibited relatively serious chipping and spalling at cutting speed higher than 375 m/min, within further increasing of the cutting speed the flank wear and breakage increased greatly as a result of the enhanced thermal–mechanical impacts. In addition, the PCD tool could hardly work at cutting speed of 1,000 m/min due to the catastrophic fracture of the cutting edge and intense flank wear. There was evidence of workpiece material adhesion on the tool rake face and flank face in very close proximity to the cutting edge rather than on the chipped or flaked surface, which thereby leads to the accelerating flank wear. The failure mechanisms of PCD tool in high-speed wet milling of Ti–6Al–4V titanium alloy were mainly premature breakage and synergistic interaction among adhesive wear and abrasive wear.

A graded ceramic tool material was fabricated by hot-pressing. Its cutting performance and failure mechanisms were investigated in dry face milling of Inconel 718 using round inserts at ultra high speeds ranging from 500 to 1600 m/min. The results showed that the microscopic chip shape was serrated type and the minimal cutting force was obtained at 900 m/min under this ultra high speed cutting conditions. Due to the enhanced mechanical properties and higher fracture resistance, the graded tool showed a self-sharpening characteristic. And the notch wear resistance of the graded tool was higher than that of the common reference tool under the same cutting condition. The failure mechanisms involved chipping, flaking, abrasive wear and adhesive wear. The mechanisms responsible for the higher cutting performance of the graded tool were determined to be the higher mechanical properties. The understanding of the failure mechanisms in ultra high speed milling processes can provide the guidance for the proper application of the tools, furthermore the guidance for tool materials design.

The slotting experimental method is not applicable for force coefficients identification considering inclination angle in ball-end finish milling. A new experimental method for force coefficients identification considering the inclination angle is proposed in this research. In this method, the start and exit radial immersion angles φst and φex in any cutting conditions are modeled based on different inclination angles. Based on the research of Gradisek et al., contrary to the slotting experimental method, the position of the cutting element on a ball-end mill edge could be approximately regarded as the only factor that affects the cutting force coefficients. Experiments have been conducted to calculate the cutting force coefficients based on the new method and slotting method respectively. The results show that, for finish milling, the new experimental method for force coefficients identification is better than the slotting experimental method.Graphical abstractHighlights► Slotting test cannot be used for force coefficients modeling in ball end finish milling. ► The force coefficients are different for different inclination angles of cutter. ► The different inclination angle corresponds to different cutting element and cutting speed.

This paper presents a detailed analysis of tool failure progression through an experimental study of high speed milling of Ti-6Al-4V alloy with CVD (Ti(C, N)-Al2O3)-coated carbide tools. The progressive tool failure characteristics under a variety of different cutting conditions were investigated. Cutting forces components and transient infrared temperature during the machining processes have been measured along with corresponding progressive tool wear when milling using coated carbide inserts under dry machining conditions. Optical microscope and scanning electron microscopic analysis results clearly show the different dominant wear regions at different stages of machining with coated carbide tools. The experimental results demonstrate that the cutting forces and the cutting temperature produced during the machining process showed an increasing trend with the tool failure progression, which in turns accelerated the tool wear progression and caused the change of the tool failure mechanisms. Furthermore, the progressive tool failure mechanisms were analyzed qualitatively. The cutting speed was correlated with progressive tool failure mechanisms, and the different conditions of friction and normal stresses caused by different cutting force and cutting temperature under different cutting speeds resulted in the varieties of progressive tool failure mechanisms.

The generation mechanism of machining-induced residual stresses is a complex nonlinear and thermal–mechanical coupling problem. The cutting forces and cutting temperature produced in machining process must be considered simultaneously. The influence of cutter orientation and feed per tooth on the cutting speed, cutting forces, cutting temperature, and residual stresses is discussed in the present study. Effective cutting speed in accordance with the inclination angle in feed direction is analyzed. The cutting forces are gained by milling experiment, and the cutting temperature is obtained by finite element method. Moreover, the influence of the effective cutting speed on the cutting forces and cutting temperature is stated, and the relationship among the cutting forces, cutting temperature, and residual stresses is discussed. The experimental and numerical methods are both adopted in this study to give a better understanding of the milling process. After analysis of the phenomenon, several conclusions are made. The inclination angle in feed direction affects the effective cutting speed, and then the cutting forces, cutting temperature, and residual stresses are affected. Priority selection of inclination angle in feed direction is suggested from 5° to 30° in order to reduce the cutting forces. The overall trend of the workpiece temperature presents the parabolic shape, while the chip temperature increases with the increasing inclination angle in feed direction. Residual stress in feed direction almost increases with the increasing feed per tooth, which is not obvious in the general scope of the feed rate. The inclination angle of 5° and 15° is the priority in order to produce residual compressive stresses in cross feed direction.

Many previous researches on high-speed machining have been conducted to pursue high machining efficiency and accuracy. In the present study, the characteristics of cutting forces, surface roughness, and chip formation obtained in high and ultra high-speed face milling of AISI H13 steel (46–47 HRC) are experimentally investigated. It is found that the ultra high cutting speed of 1,400 m/min can be considered as a critical value, at which relatively low mechanical load, good surface finish, and high machining efficiency are expected to arise at the same time. When the cutting speed adopted is below 1,400 m/min, the contribution order of the cutting parameters for surface roughness Ra is axial depth of cut, cutting speed, and feed rate. As the cutting speed surpasses 1,400 m/min, the order is cutting speed, feed rate, and axial depth of cut. The developing trend of the surface roughness obtained at different cutting speeds can be estimated by means of observing the variation of the chip shape and chip color. It is concluded that when low feed rate, low axial depth of cut, and cutting speed below 1,400 m/min are adopted, surface roughness Ra of the whole machined surface remains below 0.3 μm, while cutting speed above 1,400 m/min should be avoided even if the feed rate and axial depth of cut are low.

An Al2O3-based composite ceramic tool material reinforced with WC microparticles and TiC nanoparticles was fabricated by using hot-pressing technique. The cutting performance, failure modes and mechanisms of the Al2O3/WC/TiC ceramic tool were investigated via continuous and intermittent turning of hardened AISI 1045 steel in comparison with those of an Al2O3/(W, Ti)C ceramic tool SG-4 and a cemented carbide tool YS8. Worn and fractured surfaces of the cutting tools were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results of continuous turning revealed that tool lifetime of the Al2O3/WC/TiC ceramic tool was higher than that of the SG-4 and YS8 tools at all the tested cutting speeds. As for the intermittent turning, tool life of the Al2O3/WC/TiC ceramic tool was equivalent to that of YS8, but shorter than that of the SG-4 at lower cutting speed (110 m/min). However, tool life of the Al2O3/WC/TiC ceramic tool increased when the cutting speed increased to 170 m/min, becoming much longer than that of the SG-4 and YS8 tools. The longer tool life of the Al2O3/WC/TiC composite ceramic tool was attributed to its synergistic strengthening/toughening mechanisms induced by the WC microparticles and TiC nanoparticles.

In this paper, the formulae of transient temperature field and transient thermal stress field in an infinite sandwich plate with double-sided functionally graded coatings (FGM coatings) under the convective boundary condition are derived via an asymptotic solution approach. The thermo-physical properties of the two symmetrical graded coatings are assumed to have distributions of power forms along the thickness direction of the plate. Numerical calculations of transient thermal stresses for a TiC–Al2O3 FGM coating/Al2O3 substrate/Al2O3–TiC FGM coating system under different Biot numbers in cold shock are performed in contrast to a sandwich plate with homogeneous coatings and a homogeneous plate. The effects of the thermo-physical property distributions of the FGM coatings on the thermal shock resistance of the plate are analyzed. And consequently some design rules for the sandwich plate with FGM coatings are put forward, which may be used to design FGM coated cutting tools with high thermal shock resistance.

This paper presents analyses of the transient temperature fields in an infinite plate, an infinite solid cylinder and a solid sphere made of functionally graded materials (FGMs) under convective boundary conditions. The composition and the thermo-physical properties of the infinite FGM plate, the infinite FGM solid cylinder and the FGM solid sphere are of planar symmetric, axially symmetric and spherically symmetric distributions, respectively. The analytical formulae of the one-dimensional transient temperature fields for the three FGM solids are obtained respectively by using the separation-of-variables method and the variable substitution method. Numerical results reveal that the transient temperature fields of the FGM components exhibit similar shape effect to that of homogeneous components. The present work provides valuable basis for the investigation of the thermal shock resistance of FGMs with various shapes.

In this paper, an analysis of the transient thermo-mechanical behavior of a solid cylinder of functionally gradient material (FGM) under the convective boundary condition is presented theoretically. The analytical formula of the unsteady temperature distribution is derived by using the separation-of-variables method and hence the maximum thermal stress attained at the surface of the FGM solid cylinder as well as its time of occurrence can be calculated. Based on a local tensile stress criterion, the expression of critical temperature change ΔTc leading to the local tensile strength at the surface, which is designated as the thermal shock resistance parameter for FGM solid cylinder, is obtained. The effects of the radial distributions of thermo-physical properties on the thermal shock resistance of the FGM solid cylinder are investigated via numerical calculations in contrast to homogeneous solid cylinder, from which some suggestions on design of FGM solid cylinders with high thermal shock resistance are put forward.

The thermo-elastic response of functionally gradient ceramics is investigated by means of the calculations of unsteady temperature fields and unsteady thermal stresses for an infinite functionally gradient ceramic plate with symmetrical structure under the convective boundary condition. A new strength-based fracture criterion for thermal shock of functionally gradient materials (FGM) ceramic plate is put foreword and consequently a new expression of critical temperature difference ΔTc, leading to the local fracture strength at the surface as the thermal shock resistance parameter for infinite FGM ceramic plate with symmetrical structure is obtained. The effects of the distributions for thermo-physical properties on the thermal shock resistance of the functionally gradient ceramics are analyzed via numerical calculations in contrast to homogeneous ceramics, from which some suggestions on design of functionally gradient ceramics with high thermal shock resistance are made.

•Failure patterns of coated carbide tool are investigated by high-speed face milling of hardened steel SKD11.•The fatigue morphologies, including river patterns, fatigue steps and fatigue striations, are found on failure surface.•The location of fatigue source and the propagation paths of fatigue crack are investigated.•The influence of tool damage on cutting forces and machined surface roughness are introduced.Failure patterns of coated carbide tool were investigated by high-speed face milling of the hardened steel SKD11. Tool failure surface morphology, cutting force and machined surface roughness were also analyzed to reveal the failure mechanisms. The results indicated that the dominant failure pattern of coated carbide tool was breakage. The primary mechanism of tool breakage was fatigue fracture. Under different cutting speeds, the distinctive morphologies of fatigue fracture were presented on the failure surfaces. At low cutting speeds, many fatigue sources were observed on the rake face. The distance between fatigue sources and tool nose was approximately two times of the depth of cut. With the increase of cutting speed, the fatigue striations and riven patterns were observed at the fracture surface. In addition, the fatigue steps and crack deflection were found under high cutting speeds. The main fracture mode was intergranular fracture at lower cutting speeds. However, it was transgranular fracture at higher cutting speeds. Furthermore, the irregular fracture surfaces at low cutting speeds and at high cutting speeds contribute to a larger cutting force increment compared with the medium cutting speeds. The increment of surface roughness in the initial and severe wear stages was lower than that in the steady wear stage, while the deviation of surface roughness was relatively large.

•Machined surface plastic deformation was simulated by FEM simulation.•Microstructural texture evolution was simulated and analyzed by VPSC code.•Crystal plasticity theory was used in surface texture evolution.•Pole figures and ODF diagrams under different cutting speeds were investigated.•The machining simulation was validated by cutting tests.When high speed machining polycrystalline metal, severe plastic deformation usually undergoes in the machined surface layer, accompanied by the microstructural variation of the crystallographic orientation. In the present paper, the machined surface plastic deformation and microstructural texture evolution during high speed machining of titanium alloy Ti-6Al-4V were investigated using finite element method (FEM) simulation. Firstly, a two dimensional FEM model was established, and was validated in terms of cutting forces and chip shape characteristics with experimental results of orthogonal machining. The plastic deformation on the machined surface was analyzed on the basis of finite element simulation. Results revealed that the plastic shear strain was much larger than the other strains in different directions. In addition, the variation of plastic shear strain and strain rate versus cutting time was obtained. When the feed rate was constant, the strain decreased and the maximum strain rate increased as cutting speed increased. Finally, the machined surface texture was simulated and analyzed using the Viscoplastic Self-consistent (VPSC) program based on the variation of plastic shear strain and strain rate, combined with polycrystalline plasticity theory. The machined surface texture evolution during machining was expressed by pole figures and orientation distribution function (ODF) diagrams. And the cylinder texture was identified from the pole figures. Four typical shear textures, including Y, C1, C2, and B fiber textures, were obtained from the ODF diagrams. Meanwhile, the orientation density of texture decreased with the increasing of cutting speed.