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.     

Tool force model development for diamond turning

Accurate determination of forces in the three-dimensional turning process is important for the development of a model to describe diamond turning (DT). This paper describes a dynamometer system which measures force magnitude in steady-state cutting. To build a quantitative model, the forces are experimentally separated into components. The response of these components to a variation of cutting parameters is explained in part by a hardness gradient near the part surface. This gradient is due to work hardening by the tool during previous passes. The extent of plastic work, and thus the hardness gradient, is dependent on the tool edge sharpness (≈ 100 nm). Therefore, the turning forces are strongly influenced by the condition of the tool edge. This paper illustrates the feasibility of finding the connection between edge sharpness and tool forces. It also demonstrates the ability to monitor tool forces over extended periods of time. These relationships are important in predicting the diamond tool edge condition from tool forces during a turning operation.     

刀具磨损图像监测法中的积屑瘤自动识别与去除方法的研究

积屑瘤是金属切削加工中常见的现象,在刀具磨损区域的图像中,积屑瘤部分和磨损区域是连在一起的,为保证刀具磨损带真实图像的提取,必须在图像系统中对积屑瘤部分进行自动识别和去除。本文选取了Canny算子对图像进行边缘检测,得到了包含有效边缘的清晰骨架。针对标准Hough变换存在的问题,提出了一种改进的算法,实现了直线的有效、快速检测,在刀具磨损图像中有效地去除了积屑瘤部分,获得了刀具磨损带真实图像。     

Tool wear and chip analysis after the hard turning of AISI D6 steel assisted by LN2

Abstract

Sustainability is a concept which is widely considered nowadays, including in factories where machining operations are present. The search for methods able to improve the performance of industrial processes without damaging the environment or the worker’s health has been the main goal of several investigations. In this context, cryogenic machining is a technique that has been studied as an alternative to the use of mineral oil-based cutting fluids, mainly in the machining of titanium and nickel alloys. Investigations on the cryogenic machining of hard tool steels are still scarce in the literature. This article presents results from a series of turning trials under dry and cryogenic conditions using a hardened AISI D6 tool steel bar (57 HRC) as the workpiece. For the cryogenic machining tests, liquid nitrogen was delivered to the flank face, rake face and on both faces of PCBN inserts. The main cutting parameters (cutting speed, feed rate, and depth of cut) were kept constant during the trials. Tool wear and chip morphology were the output variables studied. The results show that the liquid nitrogen was able to reduce the cutting tool wear, providing a tool lifetime around 50% longer compared with the dry process. Moreover, the frequency of chip segmentation was diminished under cryogenic conditions in comparison with the dry process.     

基于小波分析和模糊控制理论的铣刀磨损监控方法

研制了一种铣刀磨损的监控方法.在该系统中信号采集采用声发射传感器,信号的特征提取采用小波分析的方法,将变换后的尺度系数和各个频段的小波系数作为特征,采用自行设计的Sugeno模糊控制系统进行状态识别,模糊控制系统的输出是刀具磨损的具体值.     

Modeling of tool wear during hard turning with self-propelled rotary tools

In this paper, an attempt is made to evaluate the self-propelled rotary carbide tool performance during machining hardened steel. Although several models were developed and used to evaluate the tool wear in conventional tools, there were no attempts in open literature for modeling the progress of tool wear when using the self-propelled rotary tools. Flank wear model for self-propelled rotary cutting tools is developed based on the work-tool geometric interaction and the empirical function. A set of cutting tests were carried out on the AISI 4340 steel with hardness of 54–56 HRC under different cutting speeds and feeds. The progress of tool wear was recorded under different interval of time. A genetic algorithm was developed to identify the constants in the proposed model. The comparison of measured and predicted flank wear showed that the developed model is capable of predicting the rate of rotary tool flank wear progression.     

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.     

Tool wear monitoring in drilling using force signals

Utilization of force signals to achieve on-line drill wear monitoring is presented in this paper. A series of experiments were conducted to study the effects of tool wear as well as other cutting parameters on the cutting force signals and to establish the relationship between force signals and tool wear as well as other cutting parameters when drilling copper alloy. These experiments involve four independent variables; spindle rotational speed ranging from 600 to 2400 rev min⁻¹, feed rate ranging from 60 to 200 mm min⁻¹, drill diameter ranging from 5 to 10 mm, and average flank wear ranging from 0.1 to 0.9 mm. A statistical analysis provided good correlation between average thrust and drill flank wear. The relationship between cutting force signals and cutting parameters as well as tool wear is then established. The relationship can then be used for on-line drill flank wear monitoring. Feasibility studies show that the use of force signal for on-line drill flank wear monitoring is feasible.     

虚拟轴机床刀具运动轨迹的直接控制

本文提出了虚拟轴机床刀具运动轨迹的直接控制方法,该方法可根据可信息和加工工艺信息,直接生成刀具希望轨迹和虚轴运动指令,并通过虚实变换对实轴的联动控制,从而有效保证刀具轨迹与希望轨迹一致,所得结果为开发新型虚拟轴机床控制系统奠定了基础。     

基于狄利克雷混合模型的刀具磨损量在线估计

提出了一种基于狄利克雷混合模型的刀具磨损状态监测和磨损量估计的新方法。该方法将刀具磨损过程描述为磨损量的累积过程,通过对磨损增量的连续估计获得刀具当前的磨损量估计。首先对原始力信号进行特征提取,接着在不确定磨损增量状态数量的前提下采用狄利克雷混合模型对特征自动分类,然后利用吉布斯采样方法确定模型参数,最终得到描述力信号特征与磨损增量映射关系的刀具磨损状态混合模型。根据该混合模型以及当前的力信号信息即可完成刀具磨损量的在线估计。真实应用案例证明了该方法能自适应学习磨损状态并有效估计刀具的连续磨损值。     

Assessment and visualisation of machine tool wear using computer vision

Tool wear monitoring is an integral part of modern CNC machine control. Cutting tools must be periodically checked for possible or actual premature failures, and it is necessary to record the cutting history for a tool’s full life of utilisation. This means that an on-line monitoring system would be of great benefit to overall process control in manufacturing systems. Computer vision has already shown promise as a candidate technology for this task. In this paper, we describe the use of digital image processing techniques in the analysis of images of worn cutting tools in order to assess their degree of wear and thus remaining useful life. It is shown that a processing strategy using a variety of image texture measures allows for effective visualisation and assessment of tool wear, and indicates good correlation with the expected wear characteristics.     

Influence of tool wear on surface roughness in hard turning using differently shaped ceramic tools

Hard turning has been applied in many cases in producing bearings, gears, cams, shafts, axels, and other mechanical components since the early 1980s. Mixed ceramics (aluminum oxide plus TiC or TiCN) is one of the two cutting tool materials (apart from PCBN) widely used for finish machining of hardened steel (HRC 50–65) parts, especially under dry machining conditions and moderate cutting speed ranging from 90 to 120 m/min. This paper reports an extensive characterization of the surface roughness generated during hard turning (HT) operations performed with conventional and wiper ceramic tools at variable feed rate and its changes originated from tool wear. Moreover, it compares some predominant tool wear patterns produced on the two types of ceramic inserts and their influence on the alteration of surface profiles. After the hard turning tests, the relevant changes of surface profiles and surface roughness parameters were successively registered and measured by a stylus profilometer. In this investigation, a set of 2D surface roughness parameters, as well as profile and surface characteristics, such as the amplitude distribution functions, bearing area curves and symmetrical curves of geometrical contact obtained for the machined surface, were determined and analyzed. A novel aspect of this research is that the notch wear progress at the secondary cutting (trailing) edges was found to produce the substantial modifications of the individual irregularities, and constitute the altered surface profiles. Moreover, this research contributes to practical aspects of HT technology due to exploring the relations between the tool state at different times within the tool life and the relevant surface roughness characterization.     

棱体成形车刀廓形的简化设计与制造

通过建立成形车刀廓形设计的数学模型,探讨了棱体成形车刀廓形简化设计与制造的新方法,比起传统的方法有很大改进,对工厂技术人员有重要参考价值。     

Tool wear in turning of titanium alloy after thermohydrogen treatment

The influence of hydrogen contents on the tool wear has been mainly focused on the flank wear of the common tool,and the influence of hydrogen contents on the rake crater wear(main wear type) of the tool,particularly for the fine granular material tool,has been less investigated comprehensively.In this paper,for the purpose of researching the influence of hydrogen contents on tool wear,the titanium alloy Ti-6Al-4V is hydrogenated at 800 ℃ by thermohydrogen treatment technology and the turning experiments are carried out by applying uncoated WC-Co cemented carbide tool.The three-dimensional video microscope is used to take photos and measure tool wear.The results show that both of crater wear depth(KT) and average flank wear width(VB) firstly decreases and then increases with the increasing of hydrogen content.The maximum reducing amplitude of KT and VB is about 50% and 55%,respectively.Under the given conditions,the optimum hydrogen content is 0.26%.It is considered that the reduction of cutting temperature is an important factor for improving tool wear after the Ti-6Al-4V alloy is properly hydrogenated.Furthermore,the reasons of hydrogen effect on the tool wear are chiefly attributed to comprehensive effect of hydrogen contents on microstructure,physical properties and dynamic mechanical properties of the Ti-6Al-4V alloy.The proposed research provides the basic data for evaluating the machinability of hydrogenation Ti-6Al-4V alloy,and promotes practical application of thermohydrogen treatment technology in titanium alloys.     

Tool wear and form accuracy in ultrasonically machined microchannels

Quantifying wear on the basis of weight at micro levels may be erroneous. Moreover, information about wear distribution cannot be obtained on the basis of weight monitoring. Thus, quantification on the basis of linear measurements is an effective solution at micro levels. This paper presents a mathematical model for quantifying wear measured in two dimensions and subsequently converting it to a three dimensional wear model. The efficacy of the model was verified through machining data from ultrasonic micromachining of glass with tungsten carbide tools. The tool wear values obtained for the model was then correlated with the form accuracy of the machined microchannel which were found reasonable. Further, the effects of different process parameters like abrasive concentration, power rating, abrasive size and workpiece feed were studied on the tool wear behaviour and presented vis-a-vis microchannel form accuracy. High power rating and high abrasive concentration resulted in more tool wear and increased form inaccuracy; coarse abrasives resulted in higher form inaccuracy. Longitudinal wear resulted in decreased microchannel depth while lateral wear led to tapered microchannel walls and edge rounding wear yielded rounded corners in the fabricated microchannels.     

Analysis of tool wear and surface finish in hard turning

Hard turning is a profitable alternative to finish grinding. The ultimate aim of hard turning is to remove work piece material in a single cut rather than a lengthy grinding operation in order to reduce processing time, production cost, surface roughness, and setup time, and to remain competitive. In recent years, interrupted hard turning, which is the process of turning hardened parts with areas of interrupted surfaces, has also been encouraged. The process of hard turning offers many potential benefits compared to the conventional grinding operation. Additionally, tool wear, tool life, quality of surface turned, and amount of material removed are also predicted. In this analysis, 18 different machining conditions, with three different grades of polycrystalline cubic boron nitride (PCBN), cutting tool are considered. This paper describes the various characteristics in terms of component quality, tool life, tool wear, effects of individual parameters on tool life and material removal, and economics of operation. The newer solution, a hard turning operation, is performed on a lathe. In this study, the PCBN tool inserts are used with a WIDAX PT GNR 2525 M16 tool holder. The hardened material selected for hard turning is commercially available engine crank pin material.     

PCD刀具切削颗粒增强铝基复合材料时刀具磨损研究

通过高颗粒含量铝基复合材料切削加工时PCD刀具的磨损试验,研究了切削该种材料时PCD刀具的磨损形态及磨损机理。刀具磨损区微观形貌的检测分析结果表明,PCD刀具的磨损形态主要表现为前刀面磨损和后刀面磨损,造成刀具磨损的主要原因是磨料磨损和粘结磨损。采用超声波振动切削技术可减小刀具磨损。     

PCBN刀具断续切削磨损机理的研究

研究了BN250断续车削淬火钢SAE8822十字轴的磨损现象。试验结果显示微崩刃是断续车削中导致刀具失效的主要因素,工件与BN250刀具元素之间的化学反应和扩散作用削弱了结合剂与CBN基体直接的结合强度,是导致刀具破损发生的主要因素。     

陶瓷刀具车削TC4钛合金磨损特性的研究

为研究陶瓷刀具切削钛合金的磨损机理,采用CC6060陶瓷刀片对TC4钛合金进行了干式车削试验。结果表明:陶瓷刀具干式切削TC4钛合金时,磨损形貌以前刀面月牙洼磨损、后刀面沟槽磨损和刀尖破损为主,磨损机理主要是粘结磨损和氧化磨损。随着切削速度的增加,刀具磨损加剧,刀具寿命降低。CC6060陶瓷刀片干式切削钛合金时的使用寿命很低,不适于干式切削钛合金。     

数控机床刀具磨损监测实验数据处理方法研究

数控机床刀具磨损监测对于提高数控机床利用率,减小由于刀具破损而造成的经济损失具有重要意义.有针对性地回顾了国内外各种分析刀具磨损信号方法的研究工作,详细叙述了功率谱分析法、小波变换、人工神经网络以及多传感器信息融合技术的实现形式.通过比较各种数据处理方法的优缺点,提出基于混合智能多传感器信息融合技术是数控机床刀具磨损监测实验数据处理的未来发展的主要方向.