Wear and Tool Life of CBN Cutting Tools

The wide application of precise high-quality components made of advanced structural materials is directly related to the accelerating use of superhard materials and tools made of them. When machining with these tools, the optimal choice of cutting process parameters is important, as the requirements concerning the parts can often only be satisfied by cutting under extreme conditions (small chip cross-section, high cutting speed, special materials, new wear forms, etc.). Polycrystalline CBN tools are widely used for the fine turning of parts made of construction, stainless, heat-resistant, acid-resistant or even hardened (60–70 HRC) HS steels. The experimental T = T(vc) tool life curves are of "dromedary" type. The tool life maximum point moves up and down according to changes of depth of cut and feed-rate values. The reasons for polyextreme tool life curves and moving maximum tool-life points are discussed in the paper. A new general tool life Eq. is outlined which reflects the physical principles of cutting phenomena more completely and exactly. The suggested form describes the polyextreme structure of the tool life function, while the position of the extreme values (along the T- and vc-axis) depend on the cutting parameters. ID="A1" Correspondence and offprint requests to: Professor A. G. Mamalis, Manufacturing Technology Division, Department of Mechanical Engineering, National Technical University of Athens, 42 28th October Avenue, 106 82 Athens, Greece. E-mail: mamalis@central.ntua.gr     

Performance of Uncoated and Coated Carbide Tools in the Ultra-Precision Machining of Stainless Steel

Ultra-precision machines are widely used to turn aspherical or spherical profiles on mould inserts for the injection moulding of optical lenses. During the turning of a profile on a stainless steel mould insert, the cutting speed reduces significantly to 0 as the cutting tool is fed towards the centre of the machined profile. This paper reports experiments carried out to study the wear of uncoated and PVD-coated carbide tools (carbide tool coated with 2000 alternate layers of AlN and TiN, each layer 1.5 nm and carbide tool coated with 0.5 m TiN, 5.5 m TiCN and 0.5 m TiN) in the ultra-precision machining of STAVAX (modified AISI 420 stainless steel) at low speeds with and without lubricant. A sprayed mixture of compressed air, liquid paraffin oil and cyclomethicone was used as lubricant. Examination of the wear at the rake face of the tool suggests that during machining of the alloy with a hardness of 55 HRC without lubricant, the cutting edge is subjected to high compressive stress, resulting in fracture. Reducing the hardness of the alloy would therefore result in a lower stress acting on the cutting edge, thus rendering the tool less susceptible to fracture. Both the rake and the flank faces of the coated tools exhibited lower wear than the uncoated tools. This was due to the former tools possessing higher fracture resistance owing to the presence of the coating. The lubricant was effective in improving surface finish, preventing surface fracture and reducing flank wear.     

导电加热切削时刀具的热电磨损

导电加热切削时,由于强烈的电热效应,刀具磨损形态与传统切削加工方法有所不同。本文研究了导电加热切削的电热特性和电物理现象,分析了导电加热切削时刀具的热电磨损及其机理。     

Evaluation of machining performance of STAVAX with PCBN tools

A study was undertaken to investigate the wear characteristics of polycrystalline cubic boron nitride (PCBN) cutting tools and surface integrity during machining of STAVAX (specialised stainless steel) with and without coolant. Plastic deformation and formation of overtempered martensite and white layer (untempered martensite) were the dominant subsurface and surface defects. It was found that decreasing the hardness of the STAVAX from 55 HRC to 40 HRC could result in fracture on the flank face, leading to a deterioration of the surface finish. It was observed that low CBN content tools (60%CBN/40%TiN) exhibited greater fracture resistance than high CBN content tools (85%CBN/15%TiN, 90%CBN/10%Co). Although coolant could not bring about a reduction in the flank wear, it was effective in reducing the subsurface and surface defects, and in preventing chipping of the tool edge, leading to an improved surface finish. A superior surface finish (Ra<0.3 m) was obtained with cutting fluid using a tool with a radius of 0.8 mm, depth of cut of 0.05 mm and feed rate of 0.05 mm/rev.     

高速切削刀具磨损寿命的研究

分析了高速切削时刀具的磨损形态 ,综述了各种高速切削刀具材料 (包括陶瓷刀具、立方氮化硼刀具、金刚石刀具、金属陶瓷刀具和涂层刀具 )高速切削时的磨损机理 ,讨论了高速切削铸铁、淬硬钢和镍基合金时刀具的磨损寿命。     

烧结条件对整体CBN烧结密实体的影响

通过以Al为粘接剂和CBN为原料的整体刀具材料在不同的烧结条件下的烧结,并对烧结体进行了密度、磨耗比测试和SEM电镜扫描的微观形貌分析,发现温度和压力对其性能有很大的影响。结果表明:在压力一定的情况下,存在一个最佳合成温度,烧结体的磨耗比达到最大值。     

Wear and Tribological Performance of Different Ceramic Tools in Dry High Speed Machining of Ni-Co-Cr Precipitation Hardenable Aerospace Superalloy

Tool wear is an important machinability criterion. To reduce total machining costs, this study demonstrates the wear and tribological performance of four ceramic tools in dry high-speed turning of Ni-Co-Cr precipitation hardenable superalloy (Inconel 100). Wear of the tool materials and the structural and phase transformations at the tool–chip interface were investigated. Results obtained reveal that SiAlON ceramic outperformed other ceramic tool materials at different cutting speeds due to the formation of a large amount of mullite tribofilms on the tool face, which serve as a thermal barrier layer. Alumina ceramic with the addition of ZrO₂ can be recommended for machining Inconel 100 at speeds above 150 m/min due to its ability to form thermal barrier ZrO₂ tribofilms, which decrease the coefficient of friction at the tool–chip interface. Mixed alumina and an alumina matrix reinforced with SiC_w were found to be unsuitable for machining age-hardened Inconel 100 superalloy.     

Stress Analyses of CBN Insert in Hybrid Machining of RBSN Ceramic

This article investigates the significant improvement in cutting tool life in machining of Reaction Bonded Silicone Nitride (RBSN), using cryogenic coolant. A finite element model is developed to analyze stress distributions in the Cubic Boron Nitride (CBN) cutting inserts used in a hybrid turning process. The analysis reveals that the decrease in cutting tool temperature caused by cryogenic cooling leads to a decrease of stresses in the cutting tool, especially when micro-cracks are present. It is found that a decrease in temperature from 1740 to 788°C leads to approximately 56% stress reduction at the flank face of the cutting tool.     

超精密加工技术的发展及对策

介绍超精密加工及其应用背景,发展动向,以及超精密加工关键技术的一些最新成果,从超精密加工技术推广应用的角度阐述其模块化,廉价化发展趋势,同时就如何发展诸如模块化部件,执行系统,测量控制和环境控制等超精密加工关键技术提出一些新的观点和方法。     

超精密加工精度分析

介绍超精密加工技术概要;从加工精度角度出发分析超精密加工技术国内外动态及今后发展的目标;探讨进一步提高主轴和导轨运动精度以及微进给和超精密测量精度等的可能性和关键技术问题;展望超精密加工技术在微细加工领域的发展前景。     

单颗CBN磨粒微切削硬质合金YG8磨损研究

微小孔用铰珩工具长径比大,刚度差,可以采用加工工艺方法对其进行修整.为揭示铰珩工具修整过程中CBN磨粒的磨损特性,采用光滑粒子流体动力学法,建立CBN磨粒微切削YG8硬质合金的仿真模型,并通过试验验证该模型的可行性.结果表明:在微切削YG8硬质合金过程中,随着累积材料去除体积的增加,CBN磨粒不断发生微破碎而使其磨损体...     

微型刀具在高速加工中心上的应用

微型刀具应用在高速加工中心上是21世纪的一项高新技术。高速切削加工以高效率、高精度和高表面质量为基本特征,在机械制造行业获得了越来越广泛的应用,并已取得了重大的经济效益,是当代先进制造技术的重要组成部分。本文结合Datron高速加工中心,配以Datron刀具,介绍了高速加工的原理、实现高速加工所应具备的条件以及高速加工所带来的优越性。     

立方氮化硼刀具在切削加工中的应用

以立方氮化硼（CBN）刀具为研究对象,简要介绍了CBN材料物理机械性能,以及其具有的硬度高、稳定性好、耐磨、加工质量高等优势,阐述了CBN刀具在现代机械加工中的应用,并提出我国机械行业CBN刀具在切削加工中的应用及发展。     

加工烧结合金和铸铁的整体PCBN刀具的研制

博特PCBN刀具广泛应用于切削淬火钢、铸铁和烧结铁合金(sintered powder metal,简称PM材料)等硬质黑色金属材料,能提高生产效率和降低生产成本.针对烧结铁合金的加工性能差的特点,博特公司再次成功开发了整体CBN刀具BN-S100,与其他产品相比,CBN颗粒含量高达90%以上,CBN颗粒之间的结合更加...     

机械数控加工过程刀具高效使用优化分析

在数控加工中,刀具属于基础部件,对产品安全与质量具有直接影响。同时刀具使用情况与控制情况也会对数控加工经济效益产生一定影响。对此,本文介绍数控加工的刀具选择,充分阐述切削原理为刀具高效施工提供保障,并提出几点优化策略。     

高速数控机床在机械加工中的应用分析

伴随机械制造行业的深入发展,机械自动化技术在飞速进步,这在一定程度上提高机械加工的速度和质量。为了能够更好地提高数控机床的加工速度,高速数控机床应运而生,通过该技术能够更好地提高数控机床的工作速度,有利于提高产品品质。本文首先针对高速数控机床的概念、原理和特点进行阐述,然后对高速数控机床的分类进行论述,并且对数控机床的工艺以及高速数控机床的应用进行整体分析。     

浅谈非球面光学零件的超精密加工技术

对国内外非球面光学零件的超精密加工技术、设备以及发展状况进行了分析和总结,指出了我国与国外先进水平的差距,并对我国非球面超精密加工技术的发展提出了建议。     

磨料粒度对电镀CBN砂轮磨损影响的有限元仿真分析

以单颗CBN磨粒的磨损为例,对电镀CBN砂轮的磨损进行研究。针对磨削淬硬轴承钢GCr15,将单颗CBN磨粒适当简化成圆锥体,建立楔形滑擦模型,利用Deform 3D软件对单颗CBN磨粒的磨耗磨损进行仿真分析。仿真结果表明:不同粒度磨粒的磨损形式相似,均为前端面磨成弧形月牙洼形,尖端逐渐磨成平台;相同条件下磨粒的最大磨损量随着磨料粒度号的增大而减小。同时也说明了细粒度的电镀CBN砂轮的磨损较小。研究结果对进一步研究电镀CBN砂轮制造工艺有指导意义。     

Tool crater wear depth modeling in CBN hard turning

Hard turning has been receiving increased attention because it offers many possible benefits over grinding in machining hardened steel. The wear of cubic boron nitride (CBN) tools, which are commonly used in hard turning, is an important issue that needs to be better understood. For hard turning to be a viable replacement technology, the high cost of CBN cutting tools and the cost of down-time for tool changing must be minimized. In addition to progressive flank wear, microchipping and tool breakage (which lead to early tool failure) are prone to occur under aggressive machining conditions due to significant crater wear and weakening of the cutting edge. The objective of this study is to model the CBN tool crater wear depth (K_T) to guide the design of CBN tool geometry and to optimize cutting parameters in finish hard turning. First, the main wear mechanisms (abrasion, adhesion, and diffusion) in hard turning are discussed and the associated wear volume loss models are developed as functions of cutting temperature, stress, and other process information. Then, the crater wear depth is predicted in terms of tool/work material properties and process information. Finally, the proposed model is experimentally validated in finish turning of hardened 52100 bearing steel using a low CBN content tool. The comparison between model predictions and experimental results shows reasonable agreement, and the results suggest that adhesion is the dominant wear mechanism within the range of conditions that were investigated.     

干式切削用刀具涂层制备的新技术及新材料

干式切削是未来金属切削加工的重要发展方向之一,符合“绿色制造”新理念,有利于降低生产成本和保护环境。本文介绍了刀具涂层在于式切削中的应用,综述了干切削刀具涂层制备新材料及新技术。