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刀具干车淬硬钢时倒棱前角对切削力和刀具磨损的影响

PCBN刀具磨出负倒棱是为了加强刀具的刃口强度，以减少刀具加工时可能出现的破损情况。本文通过对PCBN刀具加工淬硬轴承钢GCr15的一系列试验数据加以分析，得出倒棱前角和切削力、刀具磨损之间的关系，进而得出在实际加工情况下应该采用的最佳倒棱前角值。试验表明：当倒棱前角取15度且切削速度为125m／s时，刀具具有最好的加工效果，不但切削力可以达到最小值，刀具磨损最轻，而且刀具寿命也达到了最大值。     

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.     

Influence of tool edge preparation on performance of ceramic tool inserts when hard turning

Coating, as a form of tool edge preparation, changes the properties, geometry and roughness of the active parts of tool inserts. The performance of both uncoated and coated ceramics was tested in machining tests and the results were related to the tool edge and the machined surface as well as cost indices. The presented results show that tool edge preparation by coating does affect forces, tool wear and the machined surface, while friction force from scratch tests and the coating thickness and its hardness have been identified as being relevant to the results of machining tests. The relationship between the thickness of the surface layer and residual stress at the surface due to coating has been evaluated. Though the tool life of coated ceramics is shorter than that of cubic boron nitride, tool edge preparation by coating contributes to the reduction in machining costs due to the application of higher cutting speeds.     

Mechanics of high speed cutting with curvilinear edge tools

High speed cutting is advantageous due to the reduced forces and power, increased energy savings, and overall improved productivity for discrete-part metal manufacturing. However, tool edge geometry and combined cutting conditions highly affects the performance of high speed cutting. In this study, mechanics of cutting with curvilinear (round and oval-like) edge preparation tools in the presence of dead metal zone has been presented to investigate the effects of edge geometry and cutting conditions on the friction and resultant tool temperatures. An analytical slip-line field model is utilized to study the cutting mechanics and friction at the tool-chip and tool–workpiece interfaces in the presence of the dead metal zone in machining with negative rake curvilinear PCBN tools. Inserts with six different edge designs, including a chamfered edge, are tested with a set of orthogonal cutting experiments on AISI 4340 steel. Friction conditions in each different edge design are identified by utilizing the forces and chip geometries measured. Finite-element simulations are conducted using the friction conditions identified and process predictions are compared with experiments. Analyses of temperature, strain, and stress fields are utilized in understanding the mechanics of machining with curvilinear tools.     

A preliminary investigation of the effect of tool geometry on tool temperatures when turning steel at high speed

A new tool temperature technique has been successfully used to study the effect of simple geometry changes on the magnitude and distribution of temperature in cemented carbide inserts used to cut a 0.4% carbon steel at 200 and 250 m/min. The magnitude of the maximum rake face temperature, its positron from the cutting edge and the size of the heat affected zone increased with decreasing rake angle and was largest of all for the tools with a −5° rake angle and a 0.20 mm × −20° edge chamfer.     

PCD刀具加工有色金属的研究

本文主要研究PCD刀具加工有色金属时刃口及后刀面的刃磨质量对切削表面质量的影响。首先对PCD刀具切削有色金属模型进行了分析研究,然后分别采用金属结合剂金刚石砂轮、树脂结合剂金刚石砂轮和陶瓷结合剂金刚石砂轮刃磨出三把不同质量的PCD刀具进行了切削对比试验,并用扫描电镜对切削表面微观形貌进行了观察分析,发现加工有色金属时,PCD刀具后刀面与刃口刃磨质量对切削表面质量有着同等重要的影响作用。     

On-line monitoring of tool wear in turning using a neural network

Tool wear has long been identified as the most undesirable characteristic of the machining operations. Flank wear, in particular directly affects the workpiece dimensions and the surface quality. A reliable and sensitive technique for monitoring the tool wear without interrupting the process, is crucial in realization of the modern manufacturing concepts like unmanned machining centres, adaptive control optimization, etc. In this work an optoelectronic sensor is used in conjunction with a multilayered Neural Network for predicting the flank wear on the cutting tool. The gap sensing system consists of a bifurcated optical fibre, a laser source and a photodiode circuit. The output of the photodiode circuit is amplified and converted to the digital form using an A/D converter. The digitized sensor signal along with the cutting parameters form the inputs to a three layered, feed forward, fully connected Neural Network. The Neural Network, trained off-line using a backpropagation algorithm and the experimental data, is used to predict the flank wear. A geometrical relation is also used to correlate the flank wear on the cutting tool with the change in the workpiece dimension. The values predicted using the Neural Network and those calculated using the geometrical relation are compared with the actual values measured using a tool maker's microscope. Results showed the ability of the Neural Network to accurately predict the flank wear.     

Computational modelling of 3D turning: Influence of edge micro-geometry on forces,stresses, friction and tool wear in PcBN tooling

In this paper, computational modelling of 3D turning process in the presence of variable design cutting tool inserts is studied. Turning of alloy steel, AISI 4340, which utilized in high strength mechanical components for automotive and aerospace industry steel with uniform and variable edge design Polycrystalline cubic Boron Nitride (PcBN) inserts is performed. In the experiments chip geometry, forces and tool wear are measured. 3D computational modelling is utilized to predict chip formation, forces, stresses, temperatures and tool wear on uniform and variable edge design tools. Influence of variable edge tooling on resultant pressure-dependent friction has been investigated by utilizing 3D process simulations. Predicted forces are compared with experiments until pressure-dependent shear friction factor is solved. In general, a lower friction concentration is found for variable edge tooling. The temperature and stress distributions and tool wear contours reveal the advantages of variable edge micro-geometry design.     

PCBN刀具切削镍基合金时的氧化与扩散磨损分析

通过切削试验研究PCBN刀具切削镍基合金的磨损机理,结合物质吉布斯自由能函数法分析了刀具前、后刀面氧化磨损的反应发生机理的差异性,得出发生氧化磨损的主要氧化反应方程式;并运用热力学溶解理论模型计算氮化硼在镍基合金不同元素中的溶解度,得出前、后刀面扩散磨损过程发生机理的差异性。结果表明:刀具的前、后刀面都发生严重的氧化磨损和扩散磨损,元素的扩散溶解加剧了扩散磨损的发生。      

Performance of cryogenically treated WC drill using tool wear measurements on the cutting edge and hole surface topography when drilling CFRP

Drilling CFRP poses major challenges from the perspective of rapid tool wear and poor hole quality, with the development of higher strength fibers further accentuating these problems. Cryogenic treatment is one way of increasing tool hardness thereby improving tool life and hole quality through longer retention of cutting edge sharpness. In this study, tool wear is monitored by measuring flank wear, cutting edge flatting (CEF), peak flatting (PF) and cutting edge surface roughness (CESR). While flank wear is unable to distinguish the better performance of the cryo-treated drill from the untreated drill, the other wear parameters are able to account for the better hole quality (exit delamination) produced by this drill. CEF and PF are direct measures of the extent of cutting edge blunting unlike flank wear which measures wear along the flank due to rubbing. Fiber pullout is the primary reason for deterioration in surface finish and Rz and Rv are better measures than Ra in estimating surface quality.     

电镀金刚石圆柱铣刀在数控石材加工中磨损实验研究

本文采用正交实验方法,对电镀金刚石涂层刀具在数控石材加工中进行试验,研究加工参数和金刚石颗粒性能对电镀金刚石刀具磨损量的影响,并利用体式显微镜对磨损后的刀具表面形貌进行了分析.试验结果表明:影响金刚石铣刀磨损量的主要因素是金刚石粒度,加工参数中影响较大的是径向切深,其次是主轴转速,进给速度影响较小.刀具底面的磨损比侧面严重,刀具底面的磨损形式主要是犁沟,金刚石主要以脱落为主;侧面的磨损形式主要是磨平,金刚石颗粒以破碎为主.     

Development of a new rapid characterization method of hob's wear resistance in gear manufacturing—Application to the evaluation of various cutting edge preparations in high speed dry gear hobbing

Gear hobbing remains a cutting technology mainly dedicated to large-scale productions of gears for the automotive industry. The improvements in hobbing tool design are problematic due to the very long duration of wear tests and due to the application of special machine tools only available in production plants. In order to overcome these limitations and to accelerate the efficiency of the investigations, a new rapid testing method called “flute hobbing” has been developed on a standard five-axes milling machine widely present in research laboratories. This testing method has been associated with a software providing the geometry of each chip in hobbing. The correlation of the chip geometry with the wear of each tooth enables to discriminate the critical teeth of a hob in order to focus the development in this area of the cutting zone. This new methodology has been used to investigate the influence of the cutting edge preparation on the wear resistance of gear hobs made of PM-HSS in the context of dry high speed manufacturing. The application of the AFM technology to generate defined edge preparation has shown its efficiency to improve the tool wear resistance and has confirmed previous results.     

Development of monitoring system on the diamond tool wear

Recently, ultra-precision machining using a single crystal diamond tool has been developing very rapidly, especially in the fields of production processes for optical or magnetic parts such as magnetic discs, laser mirrors, polygon mirrors and copier drums. As a result, it has been successfully extended to machine various soft materials, generating mirror-like surfaces to sub-micron geometric accuracy with the ultra-precision CNC machine and the single crystal diamond tool. With the real cutting operation, the geometric accuracy and the surface finish attainable in machined surfaces are mainly determined by both of the sharpness of a cutting tool and stability of the machine vibration. In this study, for monitoring the progress of machining state for assuring the machining accuracy and the surface quality, a new monitoring method of machining states in face-cutting with diamond tool is proposed, using the frequency response of multi-sensors signal, which includes wear state of tool in terms of the energy within the specific frequency band. A magnetic disc is machined on the ultra-precision lathe.     

Effect of tool edge geometry and cutting conditions on experimental and simulated chip morphology in orthogonal hard turning of 100Cr6 steel

Understanding chip formation mechanisms in hard turning is an important area of research. In this study, experiments with varying cutting conditions and tool edge geometry were performed concurrently with finite element simulations. The aim was to investigate how the two mechanisms reported in literature namely—surface shear-cracking (SCH) and catastrophic thermoplastic instability (CTI) contribute to overall chip geometry and machining forces. By varying tool edge geometry and cutting conditions predominance of one over another is discussed. The calculation prescribed by Recht [Recht, R., 1964. Catastrophic thermoplastic shear. J. Appl. Mech. 31, 189–193] for representative cutting conditions resulted in a small critical cutting speed of 0.034 m/min indicating CTI was operative in the range of cutting conditions tested. FEM simulations were conducted on a subset of experimental conditions. Chip geometry and forces were compared between experiments and simulations. The experimental results indicated that SCH predominated in a majority of conditions. However, formation of saw-tooth chips in the FEM simulations established the occurrence of CTI also. Specifically, the edge radius did not alter chip geometry parameters. However, machining forces decreased with cutting speed and chip formation frequency increased linearly with cutting speed. A more negative rake angle also increased the chip pitch. The findings also indicate that only an intrinsic length scale governs saw-tooth chip formation in hard turning.     

The influence of working parameters on the response of a capacitive sensor used in-process for the measurement of tool wear

In a previous research work, a no contact capacitive sensor was obtained which could check superficial characteristics of workpieces during working. This sensor can relate variations of capacity to superficial finishing of the workpiece directly.The present study aims at finding a method for interfacing the capacitive sensor to a system of data acquisition and for deciding the substitution of the tool, automatically. It has been necessary to value the influence of cutting parameters on sensor's response in order to find the threshold value, characterizing by itself an anomalous working state owed to regular or irregular tool wear.     

2.05 m/min高拉速低碳钢FC控流结晶器的应用

板坯高速连铸因具有减少设备投资、增产增效和降低物料消耗的优势而受到越来越多的关注。为解决低碳钢浇铸周期与精炼周期的匹配问题和进一步提高生产效率,某钢厂开展了结晶器电磁制动参数优化的高速连铸工艺技术研究,施加磁场后,随着上线圈电流由模式A增加到模式C,结晶器表面的钢液流速由0.35 m/s减小至0.21 m/s,结晶器内上部流场流速减弱,在高拉速下可明显起到降低表面流速的作用,随着吹氩流量从12 L/min增加至20 L/min,钢液表面流速增加,随着水口浸入深度的增大,结晶器内的流场形态变化不明显,2.05 m/min拉速下夹杂物指数较1.8 m/min拉速夹杂物指数明显降低。