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.     

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.     

PCBN刀具高速切削淬硬轴承钢的磨损机理研究

采用美国D.I.公司生产的BZN9000作为刀具材料制成PCBN刀具,在沈阳机床厂生产的CA6140A车床上对GCr15淬硬轴承钢进行高速切削试验。对切削试验后刀具的前、后刀面进行SEM形貌观察和EDS能谱分析,结果表明:PCBN刀具在高速切削过程中,机械磨损、黏着扩散磨损和化学磨损是刀具磨损的主要形式;前刀面磨损主要为月牙洼磨损,切削刃处、月牙洼后、前刀面处的黏着元素扩散比月牙洼底部还要严重;对后刀面的WDS线能谱分析证实,切削刃处的黏着元素扩散比后刀面要严重。      

Influence of oxygen on the tool wear in machining

High temperatures generated in machining are known to facilitate oxidation wear. A controlled atmosphere chamber was developed to investigate the effects of oxygen on tool wear and high speed machining tests were conducted on air and in argon. Cemented carbide, cermet and cubic boron nitride tooling was used on alloyed steel, hardened tool steel and superalloy Alloy 718. Machining in argon resulted in higher flank wear, higher cutting forces, and larger tool–chip contact length on the rake face. However, in hard machining, argon atmosphere reduced rake cratering. Transmission electron microscopy of tools worn on air showed formation of nanocrystalline Al₂O₃ film on the rake when machining aluminium containing Alloy 718, while no oxide films was detectable in the other cases.     

Tool wear and chip formation during hard turning with self-propelled rotary tools

This paper presents a performance assessment of rotary tool during machining hardened steel. The investigation includes an analysis of chip morphology and modes of tool wear. The effect of tool geometry and type of cutting tool material on the tool self-propelled motion are also investigated. Several tool materials were tested for wear resistance including carbide, coated carbide, and ceramics. The self-propelled coated carbide tools showed superior wear resistance. This was demonstrated by evenly distributed flank wear with no evidence of crater wear. The characteristics of temperature generated during machining with the rotary tool are studied. It was shown that reduced tool temperature eliminates the diffusion wear and dominates the abrasion wear. Also, increasing the tool rotational speed shifted the maximum temperature at the chip–tool interface towards the cutting edge.     

Machinability of hardened steel using alumina based ceramic cutting tools

Alumina based ceramic cutting tool is an attractive alternative for carbide tools in the machining of steel in its hardened condition. These ceramic cutting tools can machine with high cutting speed and produce good surface finish. The wear mechanism of these ceramic cutting tools should be properly understood for greater utilization. Two types of ceramic cutting tools namely Ti[C,N] mixed alumina ceramic cutting tool and zirconia toughened alumina ceramic cutting tool are used for our investigation. The machinability of hardened steel was evaluated by measurements of tool wear, cutting forces and surface finish of the work piece. These alumina based ceramic cutting tool materials produce good surface finish in the machining of hardened steel. In this paper an attempt is made to analyse the important wear mechanisms like abrasive wear, adhesive wear and diffusion wear of these ceramic cutting tool materials and the performance of these ceramic cutting tools related to the surface finish is also discussed here.     

Performances of micro-textured WC-10Ni3Al cemented carbides cutting tool in turning of Ti6Al4V

Cutting performances of micro-textured WC-10Ni₃Al cutting tools compared with micro-textured WC-8Co cutting tools in turning of Ti6Al4V was investigated in this study. Cutting forces, cutting temperature, and tool life based on the criterion of a 300 μm flank wear were measured. The wear tracks of the rake face and flank face for micro-textured WC-10Ni₃Al cutting tools were analyzed. It is found that WC-10Ni₃Al cutting tools had smaller heat damages during LST compared with WC-8Co cutting tools, which was benefit for avoiding premature tool failure during Ti6Al4V machining process. Micro-textures on the rake face could effectively reduce cutting forces, cutting temperature, adhesion on the rake face, and hence increase tool life, especially at higher cutting speed.     

The influence of the microstructure of hardened tool steel workpiece on the wear of PCBN cutting tools

Due to the recent developments of advanced cutting tool materials in the superbarasive family, such as cubic boron nitride (CBN) tools, the interest in cutting hardened steels has increased significantly. High flexibility and ability to manufacture complex workpiece geometry in one set up is the main advantage of hard turning compared to grinding. The focus of this study is to investigate the performance and wear behavior of CBN tools in finish, dry turning of four different hardened steels, treated to the same hardness R_c = 54. The following four materials were machined: X155CrMoV 12 cold work steel (AISI D2), X38CrMoV5 (AISI H11) hot work steel, 35NiCrMo16 hot work steel and 100Cr6 bearing steel (AISI 52100). A large variation in tool wear rate was observed in the machining of these steels. The tool flank grooves have been correlated to the microstructure of these steels, namely the presence of various carbides. The chip study reveals that there is presence of different amounts of white layers in machining these steels.     

Influence of the direction and flow rate of the cutting fluid on tool life in turning process of AISI 1045 steel

High-pressure coolant (HPC) delivery is an emerging technology that delivers a high-pressure fluid to the tool and machined material. The high fluid pressure allows a better penetration of the fluid into the tool–workpiece and tool–chip contact regions, thus providing a better cooling effect and decreasing tool wear through lubrication of the contact areas.The main objective of this work is to understand how the tool wear mechanisms are influenced by fluid pressure, flow rate and direction of application in finish turning of AISI 1045 steel using coated carbide tools.The main finding was that when cutting fluid was applied to the tool rake face, the adhesion between chip and tool was very strong, causing the removal of tool particles and large crater wear when the adhered chip material was removed from the tool by the chip flow. When cutting fluid was not applied to the rake face, adhesion of chip material to the face did occur, but was not strong enough to remove tool particles as it moved across the face, and therefore crater wear did not increase.     

Cutting temperature of ceramic tools in high speed machining of difficult-to-cut materials

This paper deals with an experimental and analytical investigation into the different factors which influence the temperature distribution on Al₂O₃---TiC ceramic tool rake face during machining of difficult-to-cut materials, such as case hardened AISI 1552 steel (60–65 Rc) and nickel-based superalloys (e.g. Inconel 718). The temperature distribution was predicted first using the finite element analysis. Temperature measurements on the tool rake face using a thermocouple based technique were performed and the results were verified using the finite element analysis. Experiments were then performed to study the effect of cutting parameters, different tool geometries, tool conditions, and workpiece materials on the cutting edge temperatures. Results presented in this paper indicate that for turning case hardened steel, increasing the cutting speed, feted, and depth of cut will increase the cutting edge temperature. On the other hand, increasing the tool nose radius, and angle of approach reduces the cutting edge temperature, while increasing the width of the tool chamfer will slightly increase the cutting ege temperature. As for the negative rake angle, it was found that there is an optimum value of rake angle where the cutting edge temperature was minimum. For the Inconel 718 material, it was found that the cutting edge temperature reached a minimum at a speed of 510 m/min, and feed of 1.25 mm/rev. However, the effect of the depth of cut and tool nose radius was almost the same as that determined in the turning of case hardened steel. It was also observed in turning Inconel 718 with ceramic tools that, cutting forces and different types of tool wear were reduced with increasing the feed.     

Mechanical property and cutting performance of yttrium-reinforced Al2O3/Ti(C,N) composite ceramic tool material

Effects of yttrium on the mechanical property and the cutting performance of Al₂O₃/Ti(C,N) composite ceramic tool material have been studied in detail. Results show that the addition of yttrium of a certain amount can noticeably improve the mechanical property of Al₂O₃/Ti(C,N) ceramic material. As a result, the flexural strength and the fracture toughness amount to 1010 MPa and 6.1 MPam^1/2, respectively. Cutting experiments indicate that the developed ceramic tool material not only has better wear resistance but also has higher fracture resistance when machining hardened #45 steel. The fracture resistance of the yttrium-reinforced Al₂O₃/Ti(C,N) ceramic tool material is about 20% higher than that of the corresponding ceramic tool material without any yttrium additives.     

Development of flank wear prediction model of Zirconia Toughened Alumina (ZTA) cutting tool using response surface methodology

Flank wear is an important criterion for machinability assessment of a material. The present study is an attempt to evaluate the influence of factors such as cutting speed, feed rate and depth of cut on flank wear during hard turning of EN 24 steel with newly developed transformed toughened nano-composite Zirconia Toughened Alumina (ZTA) ceramic inserts. ZTA provides a cost effective materials solution to the most demanding applications which require wear resistance, corrosion resistance, high temperature stability and superior mechanical strength. Several machining experiments were performed and mathematical models for flank wear have been postulated by using Response Surface Methodology (RSM). The analysis was based on a first order model in which the flank wear (V_b) is expressed as a function of three independent variables i.e. cutting speed (V), feed rate (F) and depth of cut (T). Analysis of Variance (ANOVA) was applied to check the adequacy of the mathematical model and their respective parameters. Key parameters and their interactive effect on flank wears have also been presented in graphical contours which may help for choosing the process parameters and predict the cutting condition for maximum tool life.     

Hard machining of hardened bearing steel using cubic boron nitride tool

In many cases, hard machining remains an economic alternative for bearing parts fabrication using hardened steels. The aim of this experimental investigation is to establish the behaviour of a CBN tool during hard turning of 100Cr6-tempered steel. Initially, a series of long-duration wear tests is planned to elucidate the cutting speed effects on the various tool wear forms. Then, a second set of experiments is devoted to the study of surface roughness, cutting forces and temperature changes in both the chip and the workpiece. The results show that CBN tool offers a good wear resistance despite the aggressiveness of the 100Cr6 at 60HRC. The major part of the heat generated during machining is mainly dissipated through the chip. Beyond 280 m/min, the machining system becomes unstable and produces significant sparks and vibrations after only a few minutes of work. The optimal productivity of machined chip was recorded at a speed of 120 m/min for an acceptable tool flank wear below 0.4 mm. Beyond this limiting speed, roughness (R_a) is stabilized because of a reduction in the cutting forces at high speeds leading to a stability of the machining system. The controlling parameter over roughness, in such hard turning cases, remains tool advance although ideal models do not describe this effect rationally. Surface quality obtained with CBN tool significantly compared with that of grinding despite an increase in the advance by a factor of 2.5. A relationship between flank wear (VB) and roughness (R_a) is deduced from parametric analysis based on extensive experimental data.     

Improving tool life by varying resilience and damping properties in close proximity of the cutting edge

During straight turning of workpieces with non-cylindrical geometry or during milling operations on workpieces with hard surfaces such as the scale layer on cast iron the cutting edge has to withstand high recurrent impact loads. These loads can destroy the cutting edge rather spontaneously than by continuous wear. Commonly used criterions such as a flank or crater wear are not suitable. As part of the research presented in this paper mechanical system properties such as resilience and damping are varied and the influence on tool life is presented. Variation was done passively by changing the material of a shim which was positioned directly under the cutting insert and actively by using a piezo actuator to change the pressure of an oil reservoir close to the cutting insert. The results of this research confirm the potential advantages of a properly adjusted resilience close to the cutting edge. However, a single set of optimal properties for different machining operations or workpiece/tool combinations cannot be derived.     

Predictive modeling of surface roughness and tool wear in hard turning using regression and neural networks

In machining of parts, surface quality is one of the most specified customer requirements. Major indication of surface quality on machined parts is surface roughness. Finish hard turning using Cubic Boron Nitride (CBN) tools allows manufacturers to simplify their processes and still achieve the desired surface roughness. There are various machining parameters have an effect on the surface roughness, but those effects have not been adequately quantified. In order for manufacturers to maximize their gains from utilizing finish hard turning, accurate predictive models for surface roughness and tool wear must be constructed. This paper utilizes neural network modeling to predict surface roughness and tool flank wear over the machining time for variety of cutting conditions in finish hard turning. Regression models are also developed in order to capture process specific parameters. A set of sparse experimental data for finish turning of hardened AISI 52100 steel obtained from literature and the experimental data obtained from performed experiments in finish turning of hardened AISI H-13 steel have been utilized. The data sets from measured surface roughness and tool flank wear were employed to train the neural network models. Trained neural network models were used in predicting surface roughness and tool flank wear for other cutting conditions. A comparison of neural network models with regression models is also carried out. Predictive neural network models are found to be capable of better predictions for surface roughness and tool flank wear within the range that they had been trained.Predictive neural network modeling is also extended to predict tool wear and surface roughness patterns seen in finish hard turning processes. Decrease in the feed rate resulted in better surface roughness but slightly faster tool wear development, and increasing cutting speed resulted in significant increase in tool wear development but resulted in better surface roughness. Increase in the workpiece hardness resulted in better surface roughness but higher tool wear. Overall, CBN inserts with honed edge geometry performed better both in terms of surface roughness and tool wear development.     

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.     

PCBN刀具切削性能和磨损机理研究综述

聚晶立方氮化硼(PCBN)刀具是继聚晶金刚石刀具之后的又一种超硬刀具,以其独特的“以车代磨”、“硬态加工”、“干式切削”等方式被誉为21世纪的绿色环保刀具。PCBN刀具在金属切削方面具有广泛的应用,主要用来加工各种淬硬钢、耐磨铸铁等铁基材料。本文介绍了PCBN刀具成分、几何形状、切削参数等对其切削性能的影响,在此基础上分析了不同材料加工时刀具的主要磨损机理,还简单对比了硬质合金和PCBN刀具切削性能上的差异。      

切削奥氏体不锈钢(1Cr18Ni9Ti)时JX-2新型陶瓷刀具的切削性能

此文研究了新型陶瓷刀具JX－2（JX－2－Ⅰ和JX－2－Ⅱ）切削不锈钢（1Cr18Ni9Ti）时的切削性能，并同JX－1刀具进行了比较，结果表明，其抗磨损能力次序为：JX－2－Ⅲ＞JX－2－1＞JX－1，但JX－2－1和JX－1的磨损相差不大；同时研究了切削速度v和送给量f，对JX－2－Ⅰ刀具磨损的影响，发现u＝20m／min，f＝0．15～0．25mm／r时刀具磨损最小；SEM分析表明，刀具的主要失效形式为后刀面磨损、前刀面月牙洼磨损和刀刃微崩，刀具磨损的主要讲理是粘结磨损和磨粒磨损。     

PCBN刀具高速切削淬硬钢材料的研究

以PCBN复合片为刀具材料进行相关力学性能分析,并将其制成SNGN120408型刀具后在刀具机床上进行淬硬钢切削试验.分析结果表明:PCBN复合片的结合剂主要为TiN和TiB2,其内部结构均匀,且有良好的致密性.切削试验表明:在干式切削淬硬钢的试验中,切削进给量以及切削速度对PCBN刀具的磨损有较为明显的影响.相比于切...     

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.