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.     

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.     

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.     

A comparative study of the cutting forces in high speed machining of Ti–6Al–4V and Inconel 718 with a round cutting edge tool

Titanium alloy Ti–6Al–4V and nickel-based superalloy Inconel 718 have been widely employed in modern manufacturing. The published literature on high speed machining (HSM) of the two materials often involves different machining set-up, which makes it difficult to directly apply the research findings from one material to the other to select the most appropriate tool geometry and cutting conditions. A comparative experimental study of HSM of Ti–6Al–4V and Inconel 718 is conducted in this paper using the same machining set-up. The scope of this study is limited in high speed finish machining, where the tool edge geometry plays a significant role. The experimental set-up and the methods of measuring the cutting forces and the tool edge radius are introduced. A total of 40 orthogonal high speed tube-cutting tests were performed, involving five levels of cutting speeds and four levels of feed rates. Based on extensive experimental data, the similarities and differences between HSM of Ti–6Al–4V and Inconel 718 are quantitatively compared and qualitatively explained in terms of four quantities: (1) the cutting force F_c, (2) the thrust force F_t, (3) the resultant force R, and (4) the force ratio F_c/F_t. A total of 12 empirical regression relationships are obtained.     

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.     

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.     

Advanced coated ceramic tools for machining superalloys

The main limitation on the use of nickel-base superalloys, such as INCONEL 718, is the difficulty in conventional-type machining. The use of high cutting speed to achieve both machining adiabatic conditions and high productivity is necessary for their applications. This non-conventional type machining results in a short life-span of tools, even for those expensive ceramic ones with reinforced SiC whiskers (SiC_w) suitable for use at high cutting speeds. The aim of the paper is to present the results of a new idea proposed by the authors to obtain an increase in tool life at high cutting speed by minimizing the temperature effects on composite reinforcement mechanisms. The 2090 SiC whiskers reinforced A1₂O₃ tools were CrN and (Ti,AI)N coated using the PVD technique, and comparative machining tests on INCONEL 718 were carried out using uncoated and coated tools. After machining, the tools were observed with a scanning electron microscope (SEM), and EDAX (X-ray) semiquantitative analyses were performed. The behaviour of the CrN and (Ti,AI)N layers using various cutting conditions was analysed and different wear mechanisms along the tool chip contact length were observed. The cause and the mechanisms of wear were deduced and mathematic models linking tool life with process parameters were suggested.     

PcBN加工淬硬钢刀具材料的研究

介绍了立方氮化硼刀具材料( PcBN)的制备过程,并制备了六种不同配方的样品加工淬硬钢.通过切削实验和性能检测,发现PcBN刀片在加工淬硬钢时cBN浓度起着关键作用,切削同样的路程,低浓度PcBN的后刀面磨损量小.经扫描电镜观察,CoAl合金粉能够提高PcBN烧结刀具材料的致密度.测量耐磨性时,证明用于金刚石复合片PC...     

Microstructural changes in CVD κ-Al2O3 coated cutting tools during turning operations

This work is concerned with the microstructural evolution in CVD κ-Al₂O₃ coatings during high speed metal cutting. The wear characteristics and the κ-Al₂O₃ to α-Al₂O₃ phase transformation during metal cutting have been studied in detail by means of transmission electron microscopy and scanning electron microscopy. Based on the results of these investigations, the different wear mechanisms of κ-Al₂O₃ coated cemented carbide tools in metal cutting are discussed.Under the cutting conditions studied, flank wear depth developed at about twice the speed of rake face wear. No phase transformation occurred on the flank face, leading to wear of the non-transformed κ-Al₂O₃ of a more abrasive nature. On the rake face, a region of the κ-Al₂O₃ coating was transformed to α-Al₂O₃, and the wear crater was positioned inside the transformed α-Al₂O₃ area. The surface zone in the crater displayed a higher dislocation density, an indication of the occurrence of plastic deformation. It is concluded that the transformation from κ-Al₂O₃ to α-Al₂O₃, and the wear of the transformed α-Al₂O₃ by plastic deformation, are characteristic of the rake face wear.     

Machinability of titanium alloys (Ti6Al4V and Ti555.3)

Near-beta titanium alloys like Ti555.3 are increasingly being used in aeronautics replacing in some critical applications the most common Ti6Al4V. However, these near-beta titanium alloys have a poor machinability rating which needs to be overcome so as to maintain at least the same productivity levels as in Ti6Al4V.This paper presents the machinability results carried out for Ti555.3 compared with the commonly used Ti6Al4V. The aim of this research work is to understand tool wear mechanisms when machining Ti555.3. Analysis of variables such as cutting forces, chip geometry and tool wear shows that: (I) greater difficulty is encounterd when machining Ti555.3 alloy compared with Ti6Al4V alloy which can be machined at higher speeds up to 90 m min^?1; (II) there was a correlation between the mechanical properties of work material, tool wear, and component forces; (III) the occurrence of the diffusion process leads to the formation of a layer of adhered material composed of Ti and TiC on the tool's rake face for both Ti alloys.     

Oxide scales formation in nano-crystalline TiAlCrSiYN PVD coatings at elevated temperature

Nano-crystalline TiAlCrSiYN plasma vapor deposited (PVD) coatings were developed for oxidation and wear protection at elevated temperatures. Compositional tuning of the coatings was performed to enhance oxidation protection at elevated temperatures.The oxidation kinetics of the coatings has been studied over 180 h at 900 °C in air. Post-oxidation microstructural examinations of specimens were performed using transmission electron microscopy (TEM), secondary electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and glow discharge optical emission spectroscopy (GDOES). Micro mechanical characteristics of the coating were studied using a micro materials nanotest system. Wear resistance of the coatings were studied during turning of Inconel 718.Experimental results clearly indicate that the aluminum-rich PVD TiAlCrSiYN coatings with 60 at.% of Al can improve oxidation resistance of titanium aluminide alloy at the temperature 900 °C as well as wear resistance during machining of Inconel 718. It was shown that during oxidation, continuous protective alumina-based oxide films form on the surface. These oxides are predominantly (Al,Cr)₂O₃-based films. Self-healing behavior of the TiAlCrSiYN coatings was observed in its ultra-fine nano-crystalline structure.     

Structure of the Al–Ni intermetallic layers produced on nickel alloy by duplex treatment

Hard and wear and corrosion resistant Al–Ni type intermetallic layers, with an external Al₂O₃ zone, were successfully produced on Inconel 600 using a duplex method. The duplex method combines glow discharge assisted oxidizing with pre-coating the Inconel substrate with aluminum by magnetron sputtering. The oxidizing process carried out at 560 °C for 4 h leads to a diffusion-induced transformation of the aluminum coating and adjacent Inconel into a 15 μm thick composite layer of Al₂O₃+AlNi+AlCr₂+AlNi₃+Cr(Fe,Ni)+Ni(Cr,Fe,Al). The structure of the layer was examined in cross-section by transmission electron microscopy (TEM). The surface zone of the layer is constituted by nanocrystalline Al₂O₃ covering the main zone of the AlNi layer. In this zone, near its border with the oxide zone, are small agglomerates of nanocrystalline Al₂O₃. The upper and thicker part of the AlNi zone also contains precipitates of the AlCr₂ phase. The AlNi zone is separated from Inconel by a diffusion zone of Ni(Cr,Fe,Al). In this region grains of AlNi₃ are found with groups of Cr(Fe,Ni) phase grains. As a consequence, the region is locally strongly enriched with chromium. This suggests that the formation of AlNi induces an uphill diffusion of chromium into the Inconel substrate.     

PcBN刀具连续车削淬硬钢性能的研究

为了研究PcBN刀具在干式连续车削条件下刀具的性能,选用两种不同的PcBN刀具,在不同切削速度及不同工件硬度条件下,对淬硬钢进行车削试验。在此基础上,对刀具前、后刀面的显微形貌特征进行了观察,分析了刀具的失效机理。结果表明:切削速度对刀具的切削寿命影响很大,随着切削速度的增加刀具寿命几乎线性下降。硬度也是影响刀具切削寿命的重要因素之一,当v190 m/m in时,刀具切削硬度为(64±1)HRC工件的寿命比相同条件下切削硬度为(61±1)HRC工件的寿命下降约40%~60%。刀尖温度随着切削速度的增加不多,切屑温度要比刀尖温度高出许多。在本试验中,刀具的失效判据为崩刃或后刀面平均磨损超过0.3 mm。     

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.     

切削Inconel718时新型陶瓷刀具JX-2-Ⅰ的切削性能研究

JX－2－Ⅰ是最新研制的碳化硅晶须（SiCw）增韧和碳化硅颗粒（SiCp）弥散增强氧化铝（Al2O3）新型陶瓷刀具。本文详细研究了该刀具加工Inconel718时的切削性能，结果表明，在低速干切时的刀具抗磨损能力为YG8＞JX－2－Ⅰ＞JX－1＞JX－2－Ⅱ；在105m／min的高速湿式切削时，JX－2－Ⅰ的切削性能与JX－1差不多，但是在42m／min的速度时JX－2－Ⅰ的切削性能好于JX－1（Al2O3＋SiCw）。同时发现在用JX－2－Ⅰ中高速切削Inconel718时必须使用冷却液。由于切削温度对工件材料加工硬化的影响，以及对工件材料高温强度屈服拐点的影响而存在一个切削速度的最佳选取范围。SEM分析表明，刀具磨损的主要形式是后刀面磨损、边界磨损、切深沟槽磨损和前刀面月牙洼磨损；刀具磨损的主要机理是粘结磨损、磨粒磨损和塑性变形磨损。     

Experiments and finite element simulations on micro-milling of Ti–6Al–4V alloy with uncoated and cBN coated micro-tools

This paper presents experimental investigations and finite element simulations on micro-milling of Ti–6Al–4V alloy with fine grain uncoated and cBN coated micro-end mills. Micro-milling of Ti–6Al–4V using uncoated and cBN coated tungsten carbide micro-end mills are conducted; surface roughness, burr formation and tool wear are measured. Effects of machining parameters on surface roughness, burr formation, and tool wear for uncoated and cBN coated micro-tools are investigated. Finite element modelling is utilized to predict forces, temperatures, and wear rate for uncoated and cBN coated micro-tools. Predicted temperature and tool wear contours for uncoated and cBN coated micro-tool edges reveal advantages of cBN coatings. Optimization studies on the experimental results are also conducted to identify the optimum process parameters which minimize both surface roughness and burr formation concurrently.     

Preparation of polycrystalline cubic boron nitride compact by high-pressure infiltration using cemented carbide

Polycrystalline cubic boron nitride (PcBN) compacts, using the infiltrating method in situ by cemented carbide (WC–Co) substrate, were sintered under high temperature and high pressure (HPHT, 5.2 GPa, 1450 °C for 6 min). The microstructure morphology, phase composition and hardness of PcBN compacts were investigated by using scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). The experimental results show that the WC and Co from WC–Co substrate spread into cubic boron nitride (cBN) layer through melting permeability under HPHT. The binder phases of WC, MoCoB and Co₃W₃C realized the interface compound of PcBN compact, and the PcBN layer formed a dense concrete microstructure. Additionally the Vickers hardness of 29.3 GPa and cutting test were performed when sintered by using cBN grain size of 10–14 μm.     

Effect of sintering temperature on the structure and properties of polycrystalline cubic boron nitride prepared by SPS

The polycrystalline cubic boron nitride (PcBN) with Si₃N₄–AlN–Al₂O₃–Y₂O₃ ceramic system as binding agents was prepared by spark plasma sintering (SPS). The starting materials Si₃N₄, AlN, Al₂O₃, Y₂O₃, and cBN in the ratio of 22:14:10:4:50 were heated to a sintering temperature between 1250 °C and 1450 °C at a heating rate of 300 °C/min, with a holding time of 5 min in nitrogen atmosphere. The microstructure, phase constitution, microhardness and fracture toughness of the prepared PcBN were then studied. It was shown that the Si₃N₄–AlN–Al₂O₃–Y₂O₃–cBN polycrystalline materials were densified in a very short sintering time resulting in materials with relative densities of more than 95%. When the sintering temperature increased, the microhardness and fracture toughness of prepared PcBN were also increased. The microhardness of PcBN prepared at 1250–1450 °C was between 28.0 ± 0.5 GPa and 48.0 ± 0.9 GPa, and its fracture toughness K_IC was from 7.5 ± 0.2 MPa m^1/2 to 11.5 ± 0.3 MPa m^1/2. Microstructure study showed that the ceramic-binding agents bonded with cubic boron nitride particles firmly. Our work demonstrated that spark plasma sintering technology could become a novel method for the preparation of PcBN cutting materials.     

Self-bonding mechanism of pure polycrystalline cubic boron nitride under high pressure and temperature

Cubic boron nitride (cBN) powders with different grain size were used as a starting material, and the pure polycrystalline cubic boron nitride (PcBN) samples were sintered under the same conditions at 7GPa, 1700 °C, 270 s. Abrasion resistance and compressive strength of sintered pure PcBN samples were tested, and the microstructure was observed and analyzed by SEM, HRTEM, XRD and Raman spectrum. The results show that the particle size of cBN has not only a great influence on microstructure and property of the sintered pure PcBN un-der the same conditions but also influence on the bonding mechanism of the cBN particles. The inner stress of the pure PcBN sintered with the cBN particle size of 10 μm during the high pressure sintering process is about 199–222% higher than that of the sample with the cBN size of 1 μm. The wear ratio and the compressive strength of PcBN samples sintered with 10 μm cBN was increased by 47.7% and 39.7% than that of the sintered sample with 1 μm cBN respectively. The coarser-grained PcBN contains serious deformation and crushing, which can be attributed to the twin boundary and the stacking faults in the samples. As a consequence, the abrasion ratio and compressive strength of the pure PcBN are dramatically increased. It is assumed that self-bonding mechanism generated from plasticity deformation, which is a main bonding mechanism for the high pressure sintering of pure cubic boron nitride.