Wear behavior of some cutting tool materials in hard turning of HSS

This study presents an assessment of the performance of four cutting tool in the machining of medium hardened HSS: polycrystalline c-BN (c-BN+TiN), TiN coated polycrystalline c-BN (c-BN+TiN), ceramic mixed alumina (Al₂O₃+TiC), and coated tungsten carbide (TiN coated over a multilayer coating (TiC/TiCN/Al₂O₃)). The Al₂O₃+TiC and the coated carbide tools can outperform both types of c-BN at high cutting speeds. Raman and SEM mapping revealed an alumina tribo-layer that protects the surface of the Al₂O₃+TiC cutting tool. The high chemical and thermal stability of Al₂O₃ tribo-films protects the tool substrate because it prevents the heat generated at the tool/chip interface from entering the tool core.     

Wear characteristics of diamond tool in ultraprecision raster milling

Ultraprecision freeform raster milling is a very complex machining process, and long machining time is used for small components. Therefore, the diamond tool wear is a crucial factor that not only raises the machining cost but also limits the cutting performance in ultraprecision raster milling. In this paper, the methods of process monitoring and wear evaluating of single-crystal diamond tools during the raster milling of copper are studied in two types of cutting environment: with lubrication and without lubrication. Experimental results indicate that the impact and free vibration are important dynamic characteristics in raster milling process that result in the obvious microchipping wear on the cutting edge.     

高精度金刚石刀具研磨关键技术研究

金刚石刀具刃口锋利度对所加工零件的表面质量有着重要影响。通过确定合理的研磨设备结构和合理的研磨工艺参数,获得的刀具刃口锋利度从300 nm提高到了50nm,刀面表面粗糙度从15nm提高到了0.5nm,刀具刃口质量得到了明显改善。     

Mirror surface machining of high-alloy steels by elliptical vibration cutting with single-crystalline diamond tools: Influence of alloy elements on diamond tool damage

Elliptical vibration cutting with single-crystalline diamond tools is applied to mirror surface machining of high-alloy steels such as cold work die steels and high-speed tool steels with a hardness of more than 60 HRC. Although practical mirror surface machining of hardened die steels such as Stavax (modified AISI 420) with a hardness of 53 HRC has been realized with the elliptical vibration cutting, lives of single-crystalline diamond tools are not sufficiently long in machining of some high-alloy steels, that may be caused by a large amount of alloy elements. In order to clarify the influence of the alloy elements on the diamond tool damage, the elliptical vibration cutting experiments are conducted on six kinds of high-alloy steels and four kinds of pure metals which are the same as the alloy elements. Mechanical properties of the alloy steels, i.e. difference in hardness between carbides and matrices, and the number of small carbides, are measured, and their influence on the micro-chippings are investigated. The chemical states of the alloy elements in high-alloy steels are analyzed using an X-ray diffraction (XRD) and an electron probe micro analyzer (EPMA), and their influence on the tool wear is discussed. Based on the investigation, a mirror surface machining of DC53, which has a high hardness of 62.2 HRC and the best machinability in the tested high-alloy steels, is demonstrated, and a mirror surface with a roughness of Rt 0.05 μm is obtained successfully.     

金刚石刀具刃磨装夹系统的振动特性分析

在金刚石刀具的刃磨过程中,机床本身及其刃磨装夹系统的振动干扰会直接影响到刀具的锋锐度和表面粗糙度。本文通过对刃磨过程特征振动信号的分析,结合模态实验,对刃磨装夹系统结构的振动特性进行了分析和评价。     

Self-sensing of cutting forces in diamond cutting by utilizing a voice coil motor-driven fast tool servo

Cutting force measurement is important for monitoring the diamond cutting process. In this paper, a new measurement method of thrust cutting force associated with a voice coil motor (VCM) driven fast tool servo (FTS) system has been developed. Instead of integrating additional force sensors to the FTS which would influence the dynamics of the FTS, the force measurement in the proposed system is achieved associated with in-process monitoring the variation of the driving current of the VCM and pre-process determining the system parameters. In this way, the cutting forces are accurately obtained by subtracting the influences of the driving force, the spring force, the damping force and the inertial force associated with the system as well as the cutting process. Based on the proposed method, a microstructure array was machined using the developed VCM-FTS and the cutting force during the machining process was monitored in real time. The measured force signal was in good agreement with the machining result. The surface profile error of the fabricated microstructure could be clearly distinguished by the variation of the measured cutting force signal. This provides a new approach for in-process cutting force measurement associated with FTS based diamond cutting process.     

金刚石车刀抹平工艺参数优化实验研究

汽车轮毂是外观质量要求较高的工件。轮毂材料为铸造铝合金,由于铸造工艺的原因,毛坯内部有大量的细微气孔,车削以后微孔暴露于轮毂表面形成很多黑点,影响外观质量。为了消除轮毂表面的这些黑点,在精车后增加了一道抹平工序,采用了具有双重负倒棱的零度前角金刚石车刀对轮毂表面进行挤压,获得了很好的效果。 这里就应用抹平工艺过程中刀具的双重负倒棱的后角和切削厚度等参数进行了优化试验研究,找到了适合具体加工条件的最佳参数,并分析了刀具角度和切削厚度对抹平效果的影响。１ 实验设计 刀具主剖面的几何参数如图１所示,各参…     

Study of HPHT single crystal diamond as precision cutting tool material

High pressure high temperature (HPHT) synthetic diamond is rapidly replacing natural diamond in precision machining industry due to its consistency in quality and cost. It is believed by some manufacturers that HPHT diamond cutting tool is virtually free of impurities, inclusions and cracks. This paper is to analyze defects inside HPHT diamond crystal by density test, optical microscopy, SEM, Raman, and XRD. Results show that HPHT diamond is relatively clean, with less chemical elements inside in comparison with natural diamond. However, there are cracks, pit holes, and bubbles in/on the crystal, some tracing amount of cementite (Fe₃C), γ-Fe, and nickel based carbides also exist in the HPHT diamond crystal, causing less accurate cutting tool edge and surface integrity. Residual stresses in HPHT diamond are compressive but high in value, may lead to cutting tool brittleness and micro-chipping, which is a common reason for diamond tool failing in precision machining.     

Wear characteristics of circular diamond saws in the cutting of different hard abrasive rocks

Circular diamond saw of wear is affected by a range of factors. However, the principal factors that require consideration in predicting wear rates are the type of diamond saw, the saw operating parameters and the characteristics of the cut rock. A single rock property index is not a sufficient basis for predicting wear performance. A variety of ten types of rocks were cut in the laboratory with two types of circular diamond saw using a fully instrumented cutting rig at different feed rates, depths of cut and at constant peripheral speed. Quantitative determinations of a wide range of textural, mechanical and intact properties of the rocks were also made. Wear (weight loss and height loss) of saw were measured after a series of test in each rock type. The wear of saws can take many forms, however, the most common wear mechanism operating on saws during the rock cutting is abrasion. Impact loading and impact fatigue also accelerates the wear of saws. The analysis indicated that the statistical model for the rock saws have potential for practical application. The application of multiple regression analysis to diamond saw performance is novel and the technique shows promise for the prediction of saw wear in specific rock types. The ability of the technique to provide a mathematical characterization of the performance of new cutting saws in the specific rocks may prove to value to saw manufacturers and users.     

Investigation of diamond cutting tool lapping system based on on-machine image measurement

The profile tolerance of diamond cutting tool??s edge is one of the key factors in affecting machining accuracy. With the development of ultra-precision machining technology for optical free-form surfaces and optical microstructures, the demand for high-precision round nose diamond cutting tools is increasing. In this study, an on-machine image processing approach is applied to cutting edge geometry truing process, and profile data of cutting edge in sub-pixel precision is acquired using a series of image processing methods. According to the profile captured, the deviation from an ideal cutting edge is calculated and feedbacked to the controller. The lapping system is employed to lap the cutting edge pertinently using the deviation and the corresponding position captured, and the round edge of high accuracy is obtained efficiently. This method can avoid the error caused by the process of refixturing for offline measurement in the traditional lapping method of diamond cutting tool and reduce the influence of human factors. A truing experiment for cutting edge of the monocrystal diamond cutting tool is carried out at the developed lapping system based on on-machine image measurement, and round cutting edge of profile tolerance less than or equal to ±0.5???m is achieved.     

Wear mechanisms of several cutting tool materials in hard turning of high carbon–chromium tool steel

The present study illustrates the performance of three different cutting tool materials, namely: PCBN, TiN coated PCBN, and mixed aluminum ceramic (Al₂O₃+TiC) in the turning of medium hardened D2 tool steel (52 HRC). Formation of Cr–O tribofilms on the ceramic tool surface as a result of interaction with the workpiece material and environment (identified by X-ray Photoelectron Spectroscopy) leads to improvement of lubricating properties at the tool/chip interface. Obtained results revealed that the mixed alumina ceramic tool can outperform both types of PCBN under different machinability criteria.     

刀具几何参数对铝合金车削性能的影响

根据刀具的主要几何参数设计了单因素实验,在Deform-3D中建立了铝合金7075的车削有限元模型,对车削过程进行仿真,通过数据处理,得出前角、主偏角、刃倾角、刀尖圆弧半径对切削力和切削温度的影响,结果表明:切削力随前角的增大而减小,随刀尖圆弧半径的增大而增大,主偏角和刃倾角对各方向上的力影响不同;切削温度随前角、刃倾角的增大而上升,随刀尖圆弧半径的增大而下降。     

金刚石刀具精密切削钛合金薄壁件试验研究

为满足航空发动机的减重、提高零部件的加工质量和对性能的要求,采用试验的方法,对航空用钛合金薄壁件进行精密切削加工研究,主要以表面加工质量为研究对象,并以其为约束,以提高效率为目的对切削参数进行优化,得到了较为可行的加工参数,并对表面粗糙度的变化规律进行分析研究,同时分析了金刚石刀具在精密切削钛合金薄壁件加工中,刀具磨损初期、中期和后期的磨损形式和成因,研究为实际型号钛合金薄壁零件的加工提供了一种改进加工工艺技术的方法。     

Wear behavior and cutting performance of nanostructured hard coatings on cemented carbide cutting tools in hard milling

The influence of nanolayer AlTiN/TiN and multilayer nanocomposite TiAlSiN/TiSiN/TiAlN hard coatings on the wear behavior and cutting performance of carbide cutting tools was investigated in face milling of hardened AISI O2 cold work tool steel (∼58 HRC) at dry conditions. Characterization of the coatings was performed using nanoindentation, scratch test, reciprocating multi-pass wear test. The chips forming during cutting process were also analyzed. Results showed that abrasive and oxidation wear are dominant tool failures. The nanolayer AlTiN/TiN coating gives the best adhesion to the substrate, the best wear resistance in machining and thus provides the longest lifetime with carbide inserts.     

An in situ method to evaluate the waviness of rounded cutting edge of diamond tool

The International Journal of Advanced Manufacturing Technology - An in situ measurement system is established to measure the waviness of rounded cutting edge of diamond tool, into which a...     

Development of a programmable vibration cutting tool for diamond turning of hardened mold steels

There are two drawbacks in the performance of the resonant vibration cutting tools currently available. One is that the vibration frequency cannot be changed arbitrarily and the other is that the cutting force is low. It is impossible to turn mirror plates with many kinds of materials using these resonant vibration cutting tools because they cannot match the desirable turning speeds that correspond to the machined materials and the vibration frequency needs to be increased or decreased to obtain the desired surface roughness. Resonant vibration cutting tools do not allow the vibration frequency to be set arbitrarily. The small cutting force of these tools also causes some difficulties in diamond turning of metals other than soft metals such as aluminum and copper. In this research, we developed a vibration cutting tool that can generate two-dimensional vibration shapes without distortion by placing two piezoelectric actuators at right angles. This tool can machine the many kinds of mirror plates with different materials to the desired surface roughness. It is also possible to machine hard materials such as mold steels because the amplitudes of the vibrations do not decrease, even when large cutting forces are required. In this paper, we describe the design of the nonresonant vibration cutting tool, and show by the diamond turning of oxygen-free copper and aluminum that our nonresonant vibration cutting tool can machine desired shapes. Finally, it is verified by actual machining experiments that the proposed vibration cutting tool can machine hardened mold steels such as STAVAX with HRC 54.     

Wear mechanisms of cutting tools in high-speed cutting processes

Contemporary cutting tools used for High Speed Cutting (HSC), made on the basis of micro-grained cemented carbides with multi-layer protective coating, allow for effective machining of hardened and tempered steels of hardness over 50 HRc. The characteristic wear of such tools is affected by the fact that the cutting speed is no longer the main influential factor on wear; the wear can also be the consequence of the high-speed tool movements in the feed direction. The paper presents some original research into the wear types, as well as the phenomena in the cutting zone and their relationships to the causes and main wear mechanisms (adhesion, abrasion and diffusion) for the tools used in HSC.     

TiN涂层刀具切削高锰钢的磨损破损研究

研究奥氏体高锰钢切削过程中TiN涂层硬质合金刀具的磨损、破损机制,测量了切削温度并得出后刀面磨损量与 切削时间和切削速度的关系曲线,以及刀具前、后刀面显微磨损、破损形貌和化学变化。结果表明,TiN涂层硬质合金刀 具切削奥氏体高锰钢时耐磨性优于单一硬质合金刀具,且适于低速切削(小于30m/min)。     

近年切削刀具品种及刀具材料的变化

刀具材料的发展和变化是推动金属切削工艺进展的重要因素之一。不同刀具材料的刀具销售值在刀具总销售值中的构成比能反应不同国家刀具应用水平的高低。本文分析“不同刀具材料的刀具销售值构成比”和“各种刀具大类品种构成比”的近年变化，以说明其现状与趋势。