Flank wear prediction of ceramic tools in hard turning

Due to technical and economical factors, hard turning is competing successfully with the grinding process in the industries. Many practical applications require components to be hardened in order to improve their wear behavior. Higher productivity and good surface quality are the requirements of the modern industries. However, tool wear is the major problem in hard turning. The tool wear models, used to assess the performance of hard turning process, play an important role in predicting the surface quality. So, in the present work, an attempt has been made to develop an analytical tool wear model for the mixed ceramic inserts during the hard turning of bearing steel incorporating abrasion, adhesion, and diffusion wear mechanisms. The new model developed can reliably be used to assess the wear of the mixed ceramic tools within the domain of the parameters. It has been observed that tool wear is increasing with the increase in cutting speed, feed, and effective rake angle. However, it has been found to be slightly decreasing with the increase in nose radius. The proposed model was validated by conducting experiments. It could be seen that the model was capable of predicting the flank wear using the cutting parameters and tool geometry.     

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.     

The monitoring of flank wear on the CBN tool in the hard turning process

In precision hard turning, tool flank wear is one of the major factors contributing to the geometric error and thermal damage in a machined workpiece. Tool wear not only directly reduces the part geometry accuracy but also increases the cutting forces drastically. The change in cutting forces causes instability in the tool motion, and in turn, more inaccuracy. There are demands for reliably monitoring the progress of tool wear during a machining process to provide information for both correction of geometric errors and to guarantee the surface integrity of the workpiece. A new method for tool wear monitoring in precision hard turning is presented in this paper. The flank wear of a CBN tool is monitored by feature parameters extracted from the measured passive force, by the use of a force dynamometer. The feature parameters include the passive force level, the frequency energy and the accumulated cutting time. An ANN model was used to integrate these feature parameters in order to obtain more reliable and robust flank wear monitoring. Finally, the results from validation tests indicate that the developed monitoring system is robust and consistent for tool wear monitoring in precision hard turning.     

硬脆及黑色金属材料的单点金刚石车削加工技术综述

单点金刚石车削技术是产生纳米特征表面的光学元件重要制造工艺之一。此加工技术在空间科学、生物医学工程、军事、国防和光学等领域有着广泛的应用。然而,金刚石刀具在切削硬脆和黑色金属材料时受到限制,如刀具磨损加剧、刀具寿命缩短以及工件表面加工质量降低等。为了减少刀具磨损和提高工件表面加工质量,相关学者提出了不同的解决方案,将从单点金刚石车削辅助工艺、工件改性、刀具性能改善和超硬材料及刀具方面梳理面向提高硬脆和黑色金属材料加工质量的单点金刚石车削加工技术相关研究,分析当前各种加工技术的优势与局限,提出未来将多种能场辅助的单点金刚石车削技术和基于聚焦离子束改性的金刚石刀具技术作为研究的重点。     

Performance studies of multilayer hard surface coatings (TiN/TiCN/Al2O3/TiN) of indexable carbide inserts in hard machining: Part-I (An experimental approach)

In recent years, hard machining using CBN and ceramic inserts became an emerging technology than traditional grinding and widely used manufacturing processes. However the relatively high cost factors associated with such tools has left a space to look for relatively low cost cutting tool materials to perform in an acceptable range. Multilayer coated carbide insert is the proposed alternative in the present study due to its low cost. Thus, an attempt has been made to have an extensive study on the machinability aspects such as flank wear, chip morphology, surface roughness in finish hard turning of AISI 4340 steel (HRC 47 ± 1) using multilayer coated carbide (TiN/TiCN/Al₂O₃/TiN) insert under dry environment. Parametric influences on turning forces are also analyzed. From the machinability study, abrasion and chipping are found to be the dominant wear mechanism in hard turning. Multilayer TiN coated carbide inserts produced better surface quality and within recommendable range of 1.6 μm i.e. comparable with cylindrical grinding. At extreme parametric conditions, the growth of tool wear was observed to be rapid thus surface quality affected adversely. The chip morphology study reveals a more favorable machining environment in dry machining using TiN coated carbide inserts. The cutting speed and feed are found to have the significant effect on the tool wear and surface roughness from ANOVA study. It is evident that, thrust force (Fy) is the largest component followed by tangential force (Fz) and the feed force (Fx) in finish hard turning. The observations yield the machining ability of multilayer TiN coated carbide inserts in hard turning of AISI 4340 steel even at higher cutting speeds.     

Modeling and analyzing the effects of air-cooled turning on the machinability of Ti–6Al–4V titanium alloy using the cold air gun coolant system

This study provides the mathematical models for modeling and analyzing the effects of air-cooling on the machinability of Ti–6Al–4V titanium alloy in the hard turning process. A cold air gun coolant system was used in the experiments and produced a jet of compressed cold air for cooling the cutting process. The air-cooling process seems to be a good environment friendly option for the hard turning. In this experimental investigation, the cutting speed, feed rate and cutting depth were chosen as the numerical factor; the cooling method was regarded as the categorical factor. An experimental plan of a four-factor (three numerical plus one categorical) D-optimal design based on the response surface methodology (RSM) was employed to carry out the experimental study. The mathematical models based on the RSM were proposed for modeling and analyzing the cutting temperature and surface roughness in the hard turning process under the dry cutting process and air-cooling process. Tool wear and chip formation during the cutting process were also studied. The compressed cooling air in the gas form presents better penetration of the lubricant to the cutting zone than any conventional coolants in the cutting process do. Results show that the air-cooling significantly provides lower cutting temperature, reduces the tool wear, and produces the best machined surface. The machinability performance of hard turning Ti–6Al–4V titanium alloy on the application of air-cooling is better than the application of dry cutting process. This air-cooling cutting process easily produces the wrinkled and breaking chips. Consequently, the air-cooled cutting process offers the attractive alternative of the dry cutting in the hard turning process.     

Tool-wear mechanisms in hard turning with polycrystalline cubic boron nitride tools

Hard turning is a turning operation performed on high strength alloy steels (45R_a0.1 μm). Extensive research being conducted on hard turning has so far addressed several fundamental questions concerning chip formation mechanisms, tool-wear, surface integrity and geometric accuracy of the machined components. The major consideration for the user of this relatively newer technology is the quality of the parts produced. A notable observation from this research is that flank wear of the cutting tool has a large impact on the quality of the machined parts (surface finish, geometric accuracy and surface integrity). For components with surface, dimensional and geometric requirements (e.g. bearing surfaces), hard turning technology is often not economical compared with grinding because tool-life is limited by the tolerances required (i.e. high flank wear rate).

The aim of this paper is to present the various modes of wear and damage of the polycrystalline cubic boron nitrides (PCBN) cutting tool under different loading conditions, in order to establish a reliable wear modeling. Flank wear has a large impact on the quality of the parts produced and the wear mechanisms have to be understood to improve the performance of the tool material, namely by reducing the flank wear rate. The wear mechanisms depend not only on the chemical composition of the PCBN, and the nature of the binder phase, but also on the hardness value and above all on the microstructure (percentage of martensite, type, size, composition of the hard phases, etc.) of the machining work material. The proposed modeling is in a generalized form of the extended Taylor’s law allowing to prediction of the tool-life as a function of the cutting parameters and of the workpiece hardness. The effects of these factors on tool-wear, tool-life and cutting forces are discussed in the paper.     

Influence of the tool corner radius on the tool wear and process forces during hard turning

Hard turning has become an alternative machining process for grinding processes of hardened steels. One challenge during hard turning is the increasing wear during the operation time of the tool and the hereby influenced workpiece surface and subsurface properties. This causes unfavorable changes of the microstructure and residual stress state or rather damages of the subsurface. Important factors are the contact conditions between the tool and the workpiece. The width of flank wear land influences the size of the passive force significantly. This has a direct impact on the subsurface properties of the workpiece. One solution is to modify the contact conditions and thereby the specific mechanical and thermal loads that are applied to the tool as well as to the workpiece. This article presents an experimental approach of modified corner radius geometry of cutting tools for hard turning processes. Hereby, the size and direction of the contact length of the cutting edge are adjusted as well as the load impact during machining. The aim is to reduce the tool wear performance. The results show the potential of the load-specific tool design concerning the tool wear and the workpiece subsurface properties. Furthermore, a new approach for predicting the process forces during hard turning is presented.     

Performance comparison of conventional and wiper ceramic inserts in hard turning through artificial neural network modeling

Hard turning with ceramic tools provides an alternative to grinding operation in machining high precision and hardened components. But, the main concerns are the cost of expensive tool materials and the effect of the process on machinability. The poor selection of cutting conditions may lead to excessive tool wear and increased surface roughness of workpiece. Hence, there is a need to investigate the effects of process parameters on machinability characteristics in hard turning. In this work, the influence of cutting speed, feed rate, and machining time on machinability aspects such as specific cutting force, surface roughness, and tool wear in AISI D2 cold work tool steel hard turning with three different ceramic inserts, namely, CC650, CC650WG, and GC6050WH has been studied. A multilayer feed-forward artificial neural network (ANN), trained using error back-propagation training algorithm has been employed for predicting the machinability. The input?Coutput patterns required for ANN training and testing are obtained from the turning experiments planned through full factorial design. The simulation results demonstrate the effectiveness of ANN models to analyze the effects of cutting conditions as well as to study the performance of conventional and wiper ceramic inserts on machinability.     

Surface Integrity and Machineability in Intermittent Hard Turning

Despite the large amount of research on hard turning, there are few results on intermittent hard turning. In this paper, the feasibility of internal intermittent hard turning has been investigated. First, the cutting tools with different cubic boron nitride (CBN) contents were evaluated, based on machineability: tool wear, surface roughness, and cutting forces. In the case of intermittent turning, low CBN content tools had better machineability than high CBN content tools. The depth of the machining damaged layer and the magnitude and distribution of residual stress were evaluated. The experimental results showed that intermittent hard turning can produce surface integrity which is good enough for replacing the grinding process.     

精密硬车加工轴承套圈的表面完整性试验研究

针对磨削加工中套圈精密加工存在的不足,进行精密硬车削加工轴承套圈新工艺的开发,通过加工试验分析了精密硬车加工轴承套圈的表面完整性,探究了基准面平面度、刀具磨损量等工艺参数与加工精度的对应关系。基于精密硬车削套圈试样的表面粗糙度、沟道圆度、显微硬度、热损伤、金相组织、残余应力分布、加工效率等方面的研究,得出了精密硬车削可达到磨削加工精度的结论,且金相组织稳定,不易存在热损伤,具有可控的残余应力分布和较高的加工效率,有利于产业化生产高精密轴承。利用磁性卡盘装夹套圈,分析试样基准面平面度对精密硬车削套圈沟道圆度的影响,发现提高基准面平面度可以有效提高加工套圈的沟道圆度;分析了刀具磨损对硬车削套圈加工精度的影响,得出在精密加工阶段刀具磨损量是控制套圈圆度的重要监控工艺参数的结论。     

涂层刀具磨损对工件表面质量的非线性影响关系

在高速硬态切削过程中,涂层刀具高速切削失效形态分为非正常磨损（破损）与正常磨损两种。刀具非正常磨损失效发生在低速切削时,而高速切削过程中的刀具失效形式倾向于后刀面磨损、边界磨损和切削刃斜面磨损等多种一常磨损彤式的组合。本文通过涂层刀具高速车削45#钢的试验,研究了刀具磨损对工件表面质量的影响。试验表明：提高切削速度,工件已加工表面质量并未随刀具磨损情况加剧而呈线性下降,刀具磨损对已加工表面质量负面影响作用的减轻,使表面质量在一定程度上得到了改善。     

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.     

Environmentally conscious hard turning of cemented carbide materials on the basis of micro-cutting in SEM: stressing four kinds of cemented carbides with PCD tools

Environmentally conscious hard turning and technology has placed more importance on the machining process. In this research, the possibility of environmentally conscious hard turning of cemented carbides was studied. The effects of cutting methods of dry and wet (vegetable oil mist, and mineral oil) and work material on cutting resistance and wear characteristics of cutting tools were experimentally investigated. The turning and micro-cutting process in SEM was carried out by using four kinds of tungsten carbides with the PCD cutting tools. Specifically, an emphasis was put on the effect of WC and Co additives in four kinds of cemented carbides on machinability and tool wear characteristics. The tool wear width and the cutting resistances were measured, and the worn flank was observed.     

Modelling of CBN tool crater wear in finish hard turning

The wear of cubic boron nitride (CBN) cutters, commonly used now in the finish turning of hardened parts, is an important issue that needs to be addressed for hard turning to be a viable technology due to the high costs of CBN cutters and the down-time for tool change. Chipping and tool breakage, which lead to early tool failure, are both prone to take place under the effect of crater wear. The objective of this study is to develop a methodology to model the CBN tool crater wear rate to both guide the design of CBN tool geometry and optimise cutting parameters in finish hard turning. First, the wear volume losses due to the main wear mechanisms (abrasion, adhesion, and diffusion) are modelled as functions of cutting temperature, stress, and other process attributes respectively. Then, the crater wear rate is predicted in terms of tool/work material properties and cutting configuration. Finally, the proposed model is experimentally validated in finish turning of hardened 52100 bearing steel using a low CBN content insert. The comparison between the prediction and the measurement shows reasonable agreement and the results suggest that adhesion is the main wear mechanism over the investigated range of cutting conditions .     

Environmentally conscious hard turning of cemented carbide materials on the basis of micro-cutting in SEM (2nd report): stress turning with three kinds of cutting tools

Environmentally conscious hard turning and technology have placed increasing importance on the machining process. Cutting fluids have a significant impact on the environment, thus numerous research works are being performed to minimize their use. However, tool wear is very severe in hard turning cemented carbides without the use of cutting fluids. In this research, the effects of dry and wet cutting methods (vegetable oil mist and mineral oil) and tool material on cutting resistance and wear characteristics of cutting tools were experimentally investigated to study the possibility of creating an environmentally conscious hard turning of cemented carbides. Mist and wet cutting of the cemented carbides using poly-crystalline diamond (PCD) cutting tools were adopted to investigate how tool wear on the basis of micro-cutting in the Scanning Electron Microscope (SEM) can be reduced. Additionally, the poly-crystalline cubic boron nitride (PcBN) and the usual cBN cutting tools were compared with the PCD cutting tools. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.recommended for publication in revised form by Associate Editor Dae-Eun Kim HEO Sung Jung was born in Busan, R. O. K., in 1958. He received the Ph.D. in Mechanical Engineering from Osaka University, Osaka, Japan. He is a Full Professor of Mechanical Engineering at Doowon Technical College, Ansong -si, Gyonggi-do, Republic of Korea. His current research interests are in the areas of cutting of difficult-to-cut materials, environmentally conscious machining and cutting tool design.     

Measuring procedures of cutting edge preparation when hard turning with coated ceramics tool inserts

In this paper, the authors introduce the methodology of combined studies on cutting edge preparation and tool performance testing. Five main fields of research on cutting edge preparation are identified in this study of cutting edge preparation while cutting edge microgeometry consists of data associated with tool edge and rake face. Uncoated and TiN coated mixed oxide ceramics inserts have been tested concerning their microgeometry and wear resistance and there is presented a sequence of measuring to identify cutting edge preparation and properties of coating. Authors propose the sequence which considers cutting edge preparation as a factor controlling performance of cutting edge in hard turning operations. Four steps in the sequence of performance testing include measurements with effects of wear criterion and machining time. Measured results show that combined effects of both preparation and coating reduce considerably friction forces in scratch tests and there is very negligible change of microhardness of uncoated and coated ceramics. Relationships between cutting edge microgeometry and acceptable machined surface roughness which results from the sequence in tool performance testing have been identified. Finally, tool performance indices are based on units which characterize machined surface roughness, tool edge wear and forces when hard turning.     

Effect of tool edge wear on the cutting forces and vibrations in high-speed finish machining of Inconel 718: an experimental study and wavelet transform analysis

High-speed machining has been receiving growing attention and wide applications in modern manufacture. Extensive research has been conducted in the past on tool flank wear and crater wear in high-speed machining (such as milling, turning, and drilling). However, little study was performed on the tool edge wear??the wear of a tool cutting edge before it is fully worn away??that can result in early tool failure and deteriorated machined surface quality. The present study aims to fill this important research gap by investigating the effect of tool edge wear on the cutting forces and vibrations in 3D high-speed finish turning of nickel-based superalloy Inconel 718. A carefully designed set of turning experiments were performed with tool inserts that have different tool edge radii ranging from 2 to 62???m. The experimental results reveal that the tool edge profile dynamically changes across each point on the tool cutting edge in 3D high-speed turning. Tool edge wear increases as the tool edge radius increases. As tool edge wear dynamically develops during the cutting process, all the three components of the cutting forces (i.e., the cutting force, the feed force, and the passive force) increase. The cutting vibrations that accompany with dynamic tool edge wear were analyzed using both the traditional fast Fourier transform (FFT) technique and the modern discrete wavelet transform technique. The results show that, compared to the FFT, the discrete wavelet transform is more effective and advantageous in revealing the variation of the cutting vibrations across a wide range of frequency bands. The discrete wavelet transform also reveals that the vibration amplitude increases as the tool edge wear increases. The average energy of wavelet coefficients calculated from the cutting vibration signals can be employed to evaluate tool edge wear in turning with tool inserts that have different tool edge radii.     

PCBN刀具干湿切削淬硬钢对比试验研究

通过PCBN刀具干、湿切削淬硬轴承钢GCr15对比试验,对两种条件下的切削力随刀具磨损的变化、刀具寿命及被加工工件表面粗糙度进行了对比。试验表明:干切削状态下金属软化效应占主导地位,湿切削可获得更好的表面粗糙度,切削液在刀具磨损后期开始发挥作用。     

纳米K2Ti4O9晶须增强型固体润滑涂层在切削加工中的应用

为了减少切削加工中切削液的排放 ,改善环境 ,本研究用固体润滑剂代替切削液。在高温摩擦试验机上对四种固体润滑剂进行了摩擦试验和效果对比 ,筛选出纳米钛酸钾增强型复合固体润滑剂 ;将其涂覆在刀具表面进行 4 0Cr钢切削试验 ,干切削中切削速度为 14 0m/min时涂层刀具的后刀面磨损量是未涂层刀具的 1/ 6 ,比使用切削液时的磨损量也略有降低 ;随着切削速度的升高 ,涂层刀具的后刀面磨损量有所增加 ,但仍比未涂层的低 ,比使用润滑液的有所增高。AFM、SEM和EDX对摩擦表面的分析结果表明 :固体润滑膜涂覆在刀具表面 ,可改善刀具的润滑状况 ,有效地防止切屑和刀具的粘附 ,明显减少刀具的磨损