Design,fabrication and properties of a self-lubricated tool in dry cutting

Micro-holes were made using micro-EDM on the rake and flank face of the cemented carbide (WC/Co) tools. Molybdenum disulfide (MoS₂) solid lubricants were filled into the micro-holes to form self-lubricated tools (ML-1 and -2). Dry cutting tests on hardened steel were carried out with these self-lubricated tools and conventional tools (ML-3). The cutting forces, the tool wear, and the friction coefficient between the tool–chip interface were measured. It was shown that the cutting forces with ML-1 and -2 self-lubricated tools were greatly reduced compared with that of ML-3 conventional tool, the ML-1 self-lubricated tool with one micro-hole in its rake face possessed the lower friction coefficient at the tool–chip interface; while the ML-2 self-lubricated tool with one micro-hole in its flank face revealed more flank wear resistance. The mechanism responsible was explained as the formation of a self-lubricating film between the sliding couple, and the composition of this lubricating film was found to be MoS₂ solid lubricant, which was released from the micro-hole and smeared on the rake or flank face, and can be acted as lubricating additive during dry cutting processes.     

Self-lubrication of sintered ceramic tools with CaF2 additions in dry cutting

An Al₂O₃/TiC ceramic cutting tool with the additions of CaF₂ solid lubricant was produced by hot pressing. The fundamental properties of this ceramic cutting tool were examined. Dry machining tests were carried out on hardened steel and cast iron. The tool wear, the cutting forces, and the friction coefficient between the tool–chip interface were measured. It was shown that the friction coefficient at the tool–chip interface in dry cutting of hardened steel and cast iron with Al₂O₃/TiC/CaF₂ ceramic tool was reduced compared with that of Al₂O₃/TiC tool without CaF₂ solid lubricant. The mechanisms responsible were determined to be the formation of a self-lubricating film on the tool–chip interface, and the composition of this self-lubricating film was found to be mainly CaF₂ solid lubricant, which was released and smeared on the wear track of the tool rake face, and acted as lubricating additive between the tool–chip sliding couple during machining processes. The appearance of this self-lubricating film contributed to the decrease of the friction coefficient. Cutting speed was found to have a profound effect on this self-lubricating behavior.     

Machining performance of pearlitic–ferritic nodular cast iron with coated carbide and silicon nitride ceramic tools

This paper concerns the fundamental cutting characteristics obtained in the turning of the pearlitic–ferritic nodular iron (EN-GJS-500-7 grade with UTS=500 MPa) when using carbide tools coated with single TiAlN and multilayer TiC/Ti(C,N)/Al₂O₃/TiN coatings, as well as silicon nitride (Si₃N₄) based ceramic tools. As a competitor, a P20 uncoated carbide grade was selected. The fundamental process readings include cutting and feed forces, the tool–chip interface temperature, Peclet number, friction coefficient and the tool–chip contact length as functions of cutting parameters. In particular, the measurements of cutting temperature were carried out using conventional tool–work thermocouple method and IR thermography. It is concluded based on many process characteristics that multilayer coated and ceramic tools can substantially improve the performance of nodular iron machining.     

织构化刀具表面摩擦磨损特性与减摩降磨机制研究

在刀具表面设计并加工出一定结构的微织构,可大幅改善刀具-切屑表面的摩擦状态。为了探究不同形态的织构刀具在干摩擦状态下的摩擦磨损特征,通过有限元仿真分析软件ABAQUS对不同织构类型的刀具进行分析,结合刀具的应力状态分布情况分析各类织构对减摩抗磨作用的影响。同时,利用飞秒激光器在刀具表面加工不同类型的织构并与钛合金磨球进行摩擦磨损实验,测定其摩擦因数,分析不同类型织构刀具表面的磨损情况和形貌。仿真及试验结果表明：刀具T1应力集中区分布广泛,应力集中严重;相对于T1,刀具T2、T3、T4、T5的等效应力值出现大幅降低,且应力分布较为均匀,其中刀具T4的表面等效应力值最低,且降温效果最优。上述结果表明：带有不同类型织构的刀具较无织构刀具的摩擦因数均有不同程度降低,一定程度上缓解了刀具表面的黏结磨损,其中T4摩擦因数降低最为显著,减摩效果最为突出。     

Cutting performance and failure mechanisms of an Al2O3/WC/TiC micro- nano-composite ceramic tool

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.     

Effect of femtosecond laser pretreatment on wear resistance of Al2O3/TiC ceramic tools in dry cutting

A femtosecond pulsed laser (pulse width: 120 fs, wavelength: 800 nm and repetition rate: 500 Hz) was used for the pretreatment on the rake face of Al₂O₃/TiC ceramic cutting tools. The evolution of surface morphology of pretreated cutting tools irradiated with different pulse energies was measured by scanning electron microscope (SEM) and atomic force microscope (AFM). Dry cutting tests were carried out with these pretreated tools and conventional tools on hardened steel. The effect of pulse energy on the wear resistance of these pretreated tools was investigated. Results show that the cutting forces have no significant difference between laser pretreated tools and the conventional tool; the cutting temperatures of laser pretreated tools were slightly reduced compared with the conventional tool. Meanwhile, we found that the laser pretreated tools increased the adhesions of chips on the rake face, but they can significantly improve the wear resistance of the rake face; and laser pulse energy was found to have a profound effect on the wear resistance of the laser pretreated tools.     

Documentation of tool wear progress in the machining of nodular ductile iron with silicon nitride-based ceramic tools

Nowadays, the HPM of cast irons is based on silicon nitride ceramic and CBN cutting tools. This paper characterizes and correlates several outputs of the cutting process of nodular cast iron using uncoated and Al₂O₃/TiN coated Si₃N₄ ceramic tools resulting from wear progress and destruction of tool faces. Investigations include tool wear curves, tribological behaviour of the tool–chip interface and tool wear mechanisms occurring on contact surfaces. The image-based characterization of worn surfaces employs such techniques as SEM, BSE and EDX analysis. The occurrence of various wear mechanisms, such as abrasive, adhesive and chemical wear was revealed.     

复合织构刀具切削铝合金的性能∗

基于铝合金材料切削的现状和需求,针对单一织构刀具存在的抗黏减摩性能不足的问题,将不同织构应用于刀-屑接触区域,提出刀具前刀面分区异构的思想。利用皮秒激光在刀具黏结区与滑移区分别加工凹坑和沟槽,并调整沟槽的取向(平行 / 垂直于主切削刃),得到上下型(SXDV 和 SXDP)和左右型(ZYDV 和 ZYDP)四种复合织构刀具。对 6061 铝合金进行湿切削试验,研究不同区域内添加不同织构对刀-屑接触表面摩擦状态的影响。研究结果表明,对比无织构和单一织构刀具, ZYDP 复合织构刀具展现了更好的切削性能。具体表现如下：与无织构刀具相比,ZYDP 刀具的主切削力降低 30.7%,刀面黏结面积减少 63.9%,切屑卷曲半径减少 27.4%。合理的复合织构方案可以明显改善刀具切削过程中的黏结磨损问题,延长了刀具寿命。复合织构方案的提出以及相应的激光加工过程可为织构刀具的设计及实际应用提供新思路。     

Unlubricated friction and wear behaviors of Al2O3/TiC ceramic cutting tool materials from high temperature tribological tests

The unlubricated friction and wear behaviors of Al₂O₃/TiC ceramic tool materials were evaluated in ambient air at temperature up to 800 °C by high temperature tribological tests. The friction coefficient and wear rates were measured. The microstructural changes and the wear surface features of the ceramics were examined by scanning electron microscopy. Results showed that the temperature had an important effect on the friction and wear behaviors of this Al₂O₃ based ceramic. The friction coefficient decreased with the increase of temperature, and the Al₂O₃/TiC ceramics exhibited the lowest friction coefficient in the case of 800 °C sliding operation. The wear rates increased with the increase of temperature. During sliding at temperature above 600 °C, oxidation of the TiC is to be expected, and the formation of lubricious oxide film on the wear track is beneficial to the reduction of friction coefficient. The wear mechanism of the composites at temperature less than 400 °C was primary abrasive wear, and the mechanisms of oxidative wear dominated in the case of 800 °C sliding operation.     

Effect of micro-textured tools on machining of Ti–6Al–4V alloy: An experimental and numerical approach

In this work, an attempt is made to reduce the detrimental effects that occurred during machining of Ti–6Al–4V by employing surface textures on the rake faces of the cutting tools. Numerical simulation of machining of Ti–6Al–4V alloy with surface textured tools was employed, taking the work piece as elasto-plastic material and the tool as rigid body. Deform 3D software with updated Lagrangian formulation was used for numerical simulation of machining process. Coupled thermo-mechanical analysis was carried out using Johnson-cook material model to predict the temperature distribution, machining forces, tool wear and chip morphology during machining. Turning experiments on Ti–6Al–4V alloy were carried out using surface textured tungsten carbide tools with micro-scaled grooves in preferred orientation such as, parallel, perpendicular and cross pattern to that of chip flow. A mixture of molybdenum disulfide with SAE 40 oil (80:20) was used as semi-solid lubricant during machining process. Temperature distribution at tool–chip interface was measured using an infrared thermal imager camera. Feed, thrust and cutting forces were measured by a three component-dynamometer. Tool wear and chip morphology were captured and analyzed using optical microscopic images. Experimental results such as cutting temperature, machining forces and chip morphology were used for validating numerical simulation results. Cutting tools with surface textures produced in a direction perpendicular to that of chip flow exhibit a larger reduction in cutting force, temperature generation and reduced tool wear.     

基于微磨削方法的微织构刀具制备与切削性能研究

目的研究表面微织构对硬质合金刀具切削性能的影响。方法采用微磨削方法在硬质合金刀具前刀面加工出具有不同结构参数的横向、纵向和交叉微织构,通过AL6061切削试验和有限元切削仿真,研究表面微织构对硬质合金刀具的切削温度及刀具磨损的影响。结果采用V形金刚石砂轮微磨削方法能够加工出几何形状规则且表面质量良好的表面微织构。与无织构刀具相比,微织构刀具的切削温度明显降低,高温区域明显减少,其中横向织构刀具降温效果最为显著。微织构刀具的切削温度随沟槽间距的增大而升高,沟槽间距为150μm时,切削温度最低。表面微织构能够有效减轻刀具前刀面的粘结磨损,横向织构刀具减摩抗粘效果最好,且采用较小的沟槽间距更利于减轻刀具的粘结磨损。随着切削速度的增加,表面微织构的抗粘结作用更加明显,当切削速度为150 m/min时,沟槽间距为150μm的横向织构刀具的切屑粘结面积最小。结论在横向、纵向和交叉织构刀具中,沟槽间距为150μm的横向织构刀具切削性能最好,即降温效果、抗粘结性能最为显著。     

Topography of the flank wear surface

In many applications, topography represents the main external features of a surface. This paper describes the topography of the flank wear surface and also presents the relationship between the maximum flank wear and the topography parameters (roughness parameters) of the flank wear surface during the turning operation. A modern CNC lathe machine (Okuma LH35-N) was used for the machine turning operation. Three-dimensional surface roughness parameters of the flank wear surface were measured by a surface texture instrument (from Talysurf series) using surface topography software (Talymap). Based on the resulting experimental data, it is found that as the flank wear increases, the roughness parameters (sR_a, sR_q, and sR_t) on the flank surface increase significantly. The greater the roughness value of the flank wear surface, the higher the friction of the tool on the workpiece and the greater the heat generation that will occur, thus ultimately causing tool failure. On the other hand, positive skewness (sR_sk) indicates the presence of a small number of spikes on the flank surface of the cutting tool, which could quickly wear off during the machining process.     

Performance of carbide tools with textured rake-face filled with solid lubricants in dry cutting processes

Surface texturing with different geometrical characteristics was made on the rake face of the WC/Co carbide tools, molybdenum disulfide (MoS₂) solid lubricants were filled into the textured rake-face. Dry cutting tests were carried out with these rake-face textured tools and a conventional tool. The effect of the texture shape on the cutting performance of these rake-face textured tools was investigated. Results show that the cutting forces, cutting temperature, and the friction coefficient at the tool-chip interface of the rake-face textured tools were significantly reduced compared with that of the conventional one. The rake-face textured tool with elliptical grooves on its rake face had the most improved cutting performance. Two mechanisms responsible were found, the first one is explained as the formation of a lubricating film with low shear strength at the tool-chip interface, which was released from the texturing and smeared on the rake face, and served as lubricating additive during dry cutting processes; the other one was explained by the reduced contact length at the tool-chip interface of the rake-face textured tools, which contributes to the decrease of the direct contact area between the chip and rake face.     

Failure mechanisms of TiB2 particle and SiC whisker reinforced Al2O3 ceramic cutting tools when machining nickel-based alloys

In this paper, Al₂O₃/TiB₂/SiC_w ceramic cutting tools with different volume fraction of TiB₂ particles and SiC whiskers were produced by hot pressing. The fundamental properties of these composite tool materials were examined. Machining tests with these ceramic tools were carried out on the Inconel718 nickel-based alloys. The tool wear rates and the cutting temperature were measured. The failure mechanisms of these ceramic tools were investigated and correlated to their mechanical properties. Results showed that the fracture toughness and hardness of the composite tool materials continuously increased with increasing SiC whisker content up to 30 vol.%. The relative density decreased with increasing SiC whisker content, the trend of the flexural strength being the same as that of the relative density. Cutting speeds were found to have a profound effect on the wear behaviors of these ceramic tools. The ceramic tools exhibited relative small flank and crater wear at cutting speed lower than 100 m/min, within further increasing of the cutting speed the flank and crater wear increased greatly. Cutting speeds less than 100 m/min were proved to be the best range for this kind of ceramic tool when machining Inconel718 nickel-based alloys. The composite tool materials with higher SiC whisker content showed more wear resistance. Abrasive wear was found to be the predominant flank wear mechanism. While the mechanisms responsible for the crater wear were determined to be adhesion and diffusion due to the high cutting temperature.     

Adhesion phenomena in the secondary shear zone in turning of austenitic stainless steel and carbon steel

This paper aims to increase the understanding of the adhesion between chip and tool rake face by studying the initial material transfer to the tool during orthogonal machining at 150 m/min. Two types of work material were tested, an austenitic stainless steel, 316L, and a carbon steel, UHB 11. The tools used were cemented carbide inserts coated with hard ceramic coatings. Two different CVD coatings, TiN and Al₂O₃, produced with two different surface roughnesses, polished and rough, were tested. The influences of both tool surface topography and chemistry on the adhesion phenomena in the secondary shear zone were thus evaluated. Extensive surface analyses of the inserts after cutting were made using techniques such as Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS), and Transmission Electron Microscopy (TEM). As expected, cutting in the stainless steel resulted in a higher amount of adhered material, compared to cutting in the carbon steel. Remnants of built-up layers were found on the surfaces of the 316L chips but not on the UHB 11 chips. Moreover, it was shown that for both materials the tool roughness had a profound effect, with the rougher surfaces comprising much higher amounts of adhered material than the polished ones. Non-metallic inclusions from both types of workpiece steels accumulate in the high temperature area on the inserts. The general tendency was that higher amounts of transferred material were found on the TiN coating than on the Al₂O₃ coating after cutting.     

Surface integrity generated by oblique machining of steel and iron parts

In this study the surface integrity produced by oblique turning of a range of iron-based materials including C45 carbon, 41Cr4 low-alloy hardened, X6CrNiTi18-10 stainless steels and EN-GJS-500-7 spheroidal iron was quantified by means of 2D and 3D surface roughness parameters, strain-hardening effects and associated residual stresses. Surfaces were produced by a special straight-edged cutting tool with large inclination angle of 55° equipped with carbide and mixed Al₂O₃–TiC ceramic cutting tool inserts. It was documented that oblique machining performed with relatively higher feed rate allows obtaining lower surface roughness and, in general, better bearing characteristics. Moreover, compressive stresses with the maximum value located close to the machined surface and parabolic profile can be induced into the surface layer. The magnitude of stresses depends on the strain-hardening rate of the surface layer.     

Model of quality management of hard coatings on ceramic cutting tools

For the development and introduction of new coated cutting tools (i.e. new combinations of cutting materials and hard coatings), it is necessary to carry out a number of studies with the purpose of optimizing the coatings composition and processing procedures, and also to test new tools under working conditions. The aim of this paper is to establish a common model for environmentally oriented quality management in the use and development of coated ceramic cutting tools with new coating systems. The paper also presents an investigation of the results of tribological and cutting properties of the coatings deposited with the PVD and CVD techniques on cutting inserts made from (Al₂O₃ + TiC) tool ceramics. Tests were carried out on ceramic inserts, uncoated and PVD or CVD-coated, with gradient, mono-, multi- (nano) layers and multicomponent hard wear resistant coatings composed of TiN, Ti(C, N), (Ti, Al)N, (Ti, AlSi)N and Al₂O₃ layers.     

Chip formation, cutting forces, and tool wear in turning of Zr-based bulk metallic glass

The chip light emission and morphology, cutting forces, surface roughness, and tool wear in turning of Zr-based bulk metallic glass (BMG) material are investigated. Machining results are compared with those of aluminum 6061-T6 and AISI 304 stainless steel under the same cutting conditions. This study demonstrates that the high cutting speeds and tools with low thermal conductivity and rake angle activate the light emission and chip oxidation in BMG machining. For the BMG chip without light emission, serrated chip formation with adiabatic shear band and void formation is observed. The cutting force analysis further correlates the chip oxidation and specific cutting energy and shows the significant reduction of cutting forces for machining BMG at high cutting speeds. The machined surface of BMG has better surface roughness than that of the other two work materials. Some tool wear features, including the welding of chip to the tool tip and chipping of the polycrystalline cubic boron nitride (PCBN) tool edge, are reported for turning of BMG. This study concludes that BMG can be machined with good surface roughness using conventional cutting tools.     

Wear behavior of Al2O3/Ti(C,N)/SiC new ceramic tool material when machining tool steel and cast iron

Design, fabrication and application of ceramic cutting tools are one of the important research topics in the field of metal cutting and advanced ceramic materials. In the present study, wear resistance of an advanced Al₂O₃/Ti(C,N)/SiC multiphase composite ceramic tool material have been studied when dry machining hardened tool steel and cast iron under different cutting conditions. Microstructures of the worn materials were observed with scanning electronic microscope to help analyze wear mechanisms. It is shown that when machining hardened tool steel at low speed wear mode of the kind of ceramic tool material is mainly flank wear with slight crater wear. The adhesion between tool and work piece is relatively weak. With the increase of cutting speed, cutting temperature increases consequently. As a result, the adhesion is intensified both in the crater area and flank face. The ceramic tool material has good wear resistance when machining grey cast iron with uniform flank wear. Wear mechanism is mainly abrasive wear at low cutting speed, while adhesion is intensified in the wear area at high cutting speed. Wear modes are dominantly rake face wear and flank wear in this case.