Progressive cutting tool wear detection from machined surface images using Voronoi tessellation method

Tool condition monitoring by machine vision approach has been gaining popularity day by day since it is a low cost and flexible method. In this paper, a tool condition monitoring technique by analysing turned surface images has been presented. The aim of this work is to apply an image texture analysis technique on turned surface images for quantitative assessment of cutting tool flank wear, progressively. A novel method by the concept of Voronoi tessellation has been applied in this study to analyse the surface texture of machined surface after the creation of Voronoi diagram. Two texture features, namely, number of polygons with zero cross moment and total void area of Voronoi diagram of machined surface images have been extracted. A correlation study between measured flank wear and extracted texture features has been done for depicting the tool flank wear. It has been found that number of polygons with zero cross moment has better linear relationship with tool flank wear than that of total void area.     

The effect of machined topography and integrity on fatigue life

The paper reviews published data which address the effect of machining (conventional and non-conventional processes) and the resulting workpiece surface topography/integrity on fatigue performance, for a variety of workpiece materials. The effect of post-machining surface treatments, such as shot peening, are also detailed. The influence of amplitude height parameters (Ra, Rt), amplitude distribution (Rsk) and shape (Rku) parameters, as well as spatial (Std, Sal) and hybrid (Ssc) measures, are considered.There is some disagreement in the literature about the correlation between workpiece surface roughness and fatigue life. In most cases, it has been reported that lower roughness results in longer fatigue life, but that for roughness values in the range 2.5–5 μm Ra it is primarily dependent on workpiece residual stress and surface microstructure, rather than roughness. In the absence of residual stress, machined surface roughness in excess of 0.1 μm Ra has a strong influence on fatigue life. Temperatures above 400 °C reduce the effects of both residual stress and surface roughness on fatigue, due to stress relieving and the change in crack initiation from the surfaces to internal sites. The presence of inclusions an order of magnitude larger than the machined surface roughness generally overrides the effect of surface topography.     

GH4169超声辅助磨削表面完整性研究

为研究超声辅助磨削对GH4169表面完整性的影响,开展GH4169超声辅助磨削与普通磨削加工试验,研究超声振动及磨削参数对其显微硬度、残余应力与微观组织的影响。结果表明:GH4169磨削表面层均产生加工硬化与残余压应力,并生成晶粒细化层;与普通磨削相比,超声辅助磨削增大其表面层显微硬度,同时增加其表面层残余压应力与晶粒细化层厚度。砂轮转速增加使显微硬度最大值先减小后增大,残余压应力与晶粒细化层厚度增加;磨削深度增加使显微硬度最大值、残余压应力与晶粒细化层厚度同时增加;且位错密度的变化趋势与显微硬度变化趋势一致。      

Comparison of tool wear mechanisms and surface integrity for dry and wet micro-drilling of nickel-base superalloys

The study focuses on the surface integrity and wear mechanisms associated with mechanical micro-drilling of nickel-base superalloy (Inconel 718) under dry and wet cutting conditions. Mechanical and metallurgical characterization was undertaken using scanning electron microscopy (SEM), backscatter electron microscopy (BSE), electron backscatter diffraction microscopy (EBSD), transmission electron microscopy (TEM), focused ion beam (FIB) microscopy, nanoindentation, energy dispersive spectroscopy (EDS) and elemental analysis techniques. The surface integrity results revealed large scale near surface deformations with high dislocation density along with nanocrystalline grain structures both under wet cutting conditions, with evidence of recrystallisation and lower dislocation density for dry cutting. Cutting conditions play a significant role in determining the depth of the affected layer, the frequency of misorientations, the microstructures and the stored energy found there. The cutting temperature and use of coolant play a key role in the formation of the altered surfaces. Abrasion, diffusion and micro-chipping were found to be the main wear mechanisms for wet cutting compared to abrasion, high adhesion, macro-chipping and catastrophic failure for dry cutting. Adhesion of work-piece material to the tool associated with abrasion and diffusion processes is the main contributor to wear phenomena. The results are important in guiding the choice of cutting conditions for acceptable surface integrity.     

Variation of temperature at the bottom surface of a hole during drilling and its effect on tool wear

The temperature at the bottom surface of a hole being drilled is measured by using an infrared-radiation pyrometer equipped with two optical fibers. One of the optical fibers is inserted into the oil hole of an internal coolant carbide drill and passes through the machine-tool spindle. This optical fiber is connected to another optical fiber at the end of the spindle. Infrared rays radiating from the bottom surface of the hole being drilled are accepted and transmitted to the pyrometer by the two optical fibers. Temperature increases as drilling progresses, and it increases considerably near the bottom surface of the workpiece. In case of a 10-mm-thick carbon–steel workpiece, temperature reaches 190, 250, and 340 °C at drilling depths of 6, 8, and 10 mm, respectively. To investigate the effect of the increase in temperature on drill wear, a series of 10-mm-deep blind holes are drilled in workpieces with thicknesses of 10 and 25 mm. Tool wear is greater when the drill cuts a hole at the bottom of a 10-mm workpiece than that when the drill cuts a hole at the mid-depth of a 25-mm workpiece. This indicates that the rapid increase in temperature near the bottom of the workpiece effects the progress of drill wear.     

Effects of random aspects of cutting tool wear on surface roughness and tool life

The effects of random aspects of cutting tool flank wear on surface roughness and on tool lifetime, when turning the AISI 1045 carbon steel, were studied in this investigation. It was found that standard deviations corresponding to tool flank wear and to the surface roughness increase exponentially with cutting time. Under cutting conditions that correspond to finishing operations, no significant differences were found between the calculated values of the capability indexC _p at the steady-state region of the tool flank wear, using the best-fit method or the Box-Cox transformation, or by making the assumption that the surface roughness data are normally distributed. Hence, a method to establish cutting tool lifetime could be established that simultaneously respects the desired average of surface roughness and the required capability index.     

Improving machined surface textures in avoiding five-axis singularities considering tool orientation angle changes

This paper looks into the irregular machined surface textures appearing in the process of avoiding five-axis singularities using the C-space based tool orientation translation method. At first, the mechanism for the appearances of the irregular surface textures is analyzed. A cutting simulation in VERICUT reveals that irregular surface textures are actually caused by lacking control of the tool orientation angles in the orientation modification process. Realizing that, a modified particle swarm optimization (PSO) is intergraded into the previous tool orientation translation method. In the PSO, the particle evolving equations are redefined and a mutation operation is added. The objective of the PSO is to find an optimal translating vector in the C-space so that the changed tool orientation angles can reach minimum values. In this way, the surface textures can be controlled. Three comparative cutting experiments with fillet endmills are carried out to verify the effect of the proposed method. The experimental results show that: (1) with the tool orientation translation method, the five-axis singular problem can be well avoided; and (2) with the optimal translating vector found by the PSO, the machined surface textures can be greatly improved.     

Development of a new tool to generate compressive residual stress within a machined surface

Generally, critical machined parts such as aircraft parts require high fatigue strength and resistance to stress corrosion cracking. These machined parts almost all usually have tensile residual stress within the machined surface after milling. However, if the compressive residual stress within the machined surface can be obtained by a milling process alone, it is expected that fatigue strength and resistance to stress corrosion cracking of the machined components will be improved. The purpose of this study is to develop a new tool that can generate compressive residual stress within the machined surface concurrently with the milling process. This tool has cutting edges for material removal and a projection pin for a burnishing-like process. It was shown that the proposed cutter could generate effective compressive residual stress within the machined surface during the milling process. Residual stress levels were in the region of −100 to −200 MPa on the machined surface, and −300 to −400 MPa at 0.05 mm beneath the surface. These levels are almost comparable with those obtained by the shot peening process.     

Improving tool wear and surface covering in polishing via toolpath optimization

Polishing operations are commonly carried out manually, thus inducing variability on the surface quality. The aim of this paper is to automate the polishing of free-form surfaces in order to obtain high quality surfaces. Tool wear and toolpath surface covering have a great impact on surface properties. The current work proposes therefore a toolpath which optimizes both tool wear and surface covering. This toolpath is composed of an optimized elementary pattern repeated along a 5-axis carrier trajectory. Usually, trochoid patterns are used. Non uniform wear of the tool and uneven probability density function of the surface covering are the main inconvenients of such pattern. So, this paper proposes two optimized patterns: Spade and Triangular. Both of them lead to uniform tool wear. Our paper also demonstrates that the second solution provides a uniform probability density function. All presented computations are validated experimentally.     

考虑温变效应的搅拌工具磨损有限元分析

根据搅拌摩擦焊接过程材料热物参数温变特性，基于库伦摩擦做功和经典Archard磨损理论，分别建立了6061铝合金薄板搅拌摩擦焊热源修正模型和搅拌工具H13模具钢磨损模型，并嵌入到Deform有限元仿真软件中，模拟了有无考虑温变下搅拌工具的磨损量分布形貌和磨损规律. 结果表明，两种情况下搅拌工具磨损量分布形貌基本一致，温变效应使得搅拌工具和接头材料间力热作用加剧，在焊接过程中，搅拌工具的磨损系数对温变效应的敏感性要大于材料硬度的变化. 考虑温变效应的搅拌工具磨损模型能更加反映其磨损变化规律，具有较高的磨损预测精度.     

The effects of machined workpiece surface integrity on the fatigue life of γ-titanium aluminide

Tension–tension tests on turned, electro-chemical machined (ECM) and electro-discharge textured (EDT) specimens made from Ti–45Al–2Nb–2Mn+0.8 vol% TiB₂ alloy, showed the turned specimens to have a higher fatigue strength 475 MPa. It is likely that this was due to the presence of highly compressive surface residual stresses caused by the turning operation.     

Chatter stability of a slender cutting tool in turning with tool wear effect

An analysis of the chatter behavior for a slender cutting tool in turning in the presence of wear flat on the tool flank is presented in this research. The mechanism of a self-excited vibration development process with tool wear effect is studied. The components contributing to the forcing function in the turning vibration dynamics are analyzed in the context of cutting force and contact force. A comparison of the chatter stability for a fresh cutting tool and a worn cutting tool is provided. Stability plots are presented to relate width of cut to cutting velocity in the determination of chatter stability. Machining experiments at various conditions were conducted to identify the characteristic parameters involved in the vibration system and to identify the analytical stability limits. The theoretical result of chatter stability agrees qualitatively with the experimental result concerning the development of chatter stability model with tool wear effect.     

PCBN刀具干湿切削淬硬钢表面完整性研究

本文以采用PCBN刀具切削淬硬轴承钢GCr15为试验，对干、湿切削两种润滑条件下，工件表面粗糙度及表面白层（一种在加工表面形成的晶相组织发生变化的结构）进行了对比研究。实验结果表明：干、湿切削都可获得较好的表面粗糙度，湿切削表面粗糙度Ra稍低；湿切削没有发现明显的白层产生，干切削白层生成较早，且白层与黑层的厚度随着刀具磨损的增加而逐渐增加。     

Effects of the cutting edge microgeometry on tool wear and its thermo-mechanical load

Tailored cutting edge micro geometries lead to a significant enhancement of the cutting tool performance and increase its tool life. This paper presents the influence of honed cutting edge geometries on the tool wear behavior, process forces and thermal load of the inserts during turning operations. Tool life maps, which show the influence of the honed cutting edge on the wear behavior, are developed for different thermomechanical load profiles of the cutting tool. Furthermore, an approach for space resolved temperature measurements near the cutting edge via two-color ratio pyrometer is presented.     

放电能量对线切割加工表面质量的影响

在电火花线切割加工中,放电能量(电流的峰值和脉宽)在很大程度上影响被加工面的表面粗糙度,为了找出它们之间的规律,用有限元法对电火花线切割的加工蚀除进行了热分析,分析和实验结果表明,具有相同脉冲能量的放电电流,虽然表面粗糙度一样,但表面形貌不一样,在精加工时,更适合选用窄脉宽、高峰值的放电电流。     

Built-up edge effect on tool wear when turning steels at low cutting speed

In any machining process, it is very important to control the cutting variables used during the process because these will affect, for example, tool life and workpiece surface roughness. Since the built-up edge (BUE) increases the wear of the tool and affects the surface roughness of the workpiece, the study of this phenomenon is very important in predicting and minimizing the wear of a cutting tool. This research studies the influence of the BUE formation for coated carbide tools when turning medium- and high-strength steels. Different mathematical expressions were obtained to quantify this effect. Mathematical expressions for uncoated carbide tools were not possible to obtain, due to the fact that for these tools an increase in the wear and their premature fracture was observed.     

球墨铸铁轧辊表面镍基激光合金化层及其磨损性能

采用激光合金化技术在球墨铸铁QT600-3表面制备镍基合金强化层,通过XRD、SEM和摩擦磨损试验等研究了不同激光扫描速率对合金化层物相、微观结构、力学性能、常温和高温摩擦学性能的影响,并使用Raman光谱仪对磨痕进行分析。结果表明:Ni合金化层与基体冶金结合好、显微硬度高(高达720 HV0.1)、高温摩擦因数低至0.305、高温磨损率低至7.55×10^-6 g·N^-1·m^-1。随着扫描速率的增加,显微组织更加致密,显微硬度先升高后降低,700 ℃耐磨性能提高,但合金化层裂纹率增加。高温摩擦磨损过程中,合金化层的磨损机制以磨粒磨损为主,同时还存在疲劳磨损和氧化磨损。同时,扫描速率的增加可细化晶粒和提高显微硬度。而Ni合金化层表面在高温摩擦过程中形成的氧化产物和碳化物在高温下会对提高其耐磨性能产生积极作用。     

Influence of coating thickness on tool life and wear

Tools containing high speed steel were coated with a titanium nitride layer by applying the reactive pulse plasma method. In order to choose the most effective layer thickness out of those used and to estimate its best value, investigations of tool wear for coated and uncoated edges were carried out. The best thickness of TiN_x-Ti film for test ranges of the cutting parameters was calculated using a computer program. On this basis it was confirmed that the best thickness of TiN_x-Ti film is 5.74 μm for the test range of cutting speeds and 5.42 μm for the range of feeds.     

Correlating surface roughness,tool wear and tool vibration in the milling process of hardened steel using long slender tools

High speed milling is an operation frequently used in finishing and semi-finishing of dies and molds. However, when it is necessary to produce molds with deep cavities and/or with small corner radius, long tools with small diameters are required. This represents a challenge for manufacturing professionals: how to minimize tool vibration using a tool with such low rigidity and obtain good workpiece surface quality and long tool lives. This paper attempts to answer this question. Milling experiments on hardened AISI H13 steel were carried out using integral and indexable insert tools with different tool overhangs and different diameters. Tool wear, workpiece surface roughness and cutting forces were measured and these parameters were correlated with the frequency response function (FRF) obtained with the tools fixed in the machine tool. The main conclusion of this study is that good workpiece surface roughness allied to long tool lives for long tools with small diameters can be achieved, provided the tooth passing frequency used in the milling process (and its harmonics) does not produce high FRF values.