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.     

Effects of cutting geometry in turning with TiN-coated tools

The effects of cutting tool geometry on the performance of TiN-coated high-speed steel tools were studied. Turning tests were carried out with inserts made of conventional and powder metallurgical HSS. The workpiece material was a case hardening steel with a hardness of 170 HB. Two different cutting geometries were used. In addition to altering the cutting angles, the effect of honing the cutting edge before coating was studied. The results showed clearly that even small changes in the tool angles affect the performance of the TiN-coated tool. Honing the cutting edge significantly increased wear resistance by improving the edge strength and reducing microchipping. On the basis of the results the modification of cutting tool geometry for hard coatings is discussed.     

Cutting edge geometries

Tool life and performance are decisively determined by cutting edge geometry. An appropriate shape of the cutting edge improves wear resistance, tool life and process reliability. This paper reviews major developments in cutting edge preparation technologies and methods of cutting edge characterization. Moreover, the influences of cutting edge geometry on chip formation, material flow, as well as mechanical and thermal loads on the tool are discussed. The essential modeling and simulation approaches are presented. Effects on surface integrity are described. Finally, an overview of important perceptions for prospective research and development in this field is provided.     

Mechanisms involved in the improvement of Inconel 718 machinability by laser assisted machining (LAM)

The aim of the present research work has been to gain a broader understanding of how or why laser assisted machining (LAM) improves machinability of Inconel 718, a hard-to-machine material of interest in the aeronautic industry. This has been accomplished by, first, running short run tests to determine the laser parameters and configuration for which highest force reductions are obtained and also to determine the effect of cutting parameters (feed, cutting speed and depth of cut) on force reduction. Secondly, long run tests have been performed in order to analyze process variables such as cutting forces, tool wear and surface roughness. Temperatures and hardness have been also measured in order to gain a broader perspective of the process.Experimental results have demonstrated that LAM improves machinability of Inconel 718 since machining forces and final surface roughness are reduced. The novelty reached with the present research work is the identification of three mechanisms associated to the laser heating as the responsible of this machinability improvement: material yield strength reduction, material base hardness reduction (only in precipitation hardened Inconel 718) and elimination of the work hardening generated in previous machining passes. The reduction of the work hardening leads also to a lower notch wear that limits the risk of sudden failure of the cutting tool and thus the wear mode is changed to flank wear, which leads to a controllable tool life and better surface roughness.     

Evaluation of machinability in turning of microalloyed and quenched-tempered steels: Tool wear,statistical analysis,chip morphology

The machinability of microalloyed steel (30MnVS6) and quenched-tempered (QT) steels (AISI 1045 and AISI 5140), at different cutting condition, is presented in the paper. An experimental investigation was conducted to determine the effects of cutting speed, feed rate, hardness, and workpiece material on the flank wear land and tool life of coated cemented carbide inserts in the hard turning process. It was tried that for any test condition the hardness of these steels became almost identical by using appropriate heat-treatment processes. The statistical analysis was used for evaluation of different factors on cutting forces. Chips characteristics and chip/tool contact length were also investigated. The different sections (shear plane, microcrack, thickness and edge) of the chip were examined by scanning electron microscope (SEM). Shear planes and microcracks of the chips in microalloyed steel show that the chips of microalloyed steel are regular and discontinuous. Crater wear of the tools was studied by using video microscope in turning process. The results showed that the tool life and machinability of the microalloyed steel is better than the QT steels at identical cutting condition.     

Effect of chamfer angle on wear of PCBN cutting tool

In precision hard turning, a remaining problem is to minimise tool wear to maintain the accuracy of geometry and surface finish. Tool wear not only directly reduces the part geometry accuracy but also increases cutting forces drastically. The change in the cutting forces also causes instability in the tool motion, which results in more inaccuracy. PCBN cutting tools are often used in hard turning. However, they are still relatively expensive compared to ordinary carbide cutting tools. In order to attain sufficiently high production rates at minimum cost, increase of knowledge on cutting tool geometry is necessary. This article presents a study of the effect of chamfer angle on tool wear of PCBN cutting tool in the super finishing hard turning. The correlation between cutting force, tool wear and tool life were investigated. The optimised chamfer angle for PCBN cutting tool is suggested. Finally, the distribution of stresses and maximum principal stress working on the tool edge were calculated with the use of finite element method.     

Electro-erosion edge honing of cutting tools

Sink EDM of fine features necessitates the application of several tool electrodes to sequentially generate the required geometry, due to the inevitable localized wear of the tool that rapidly rounds-off sharp edges. Be that as it may, this phenomenon can be exploited to hone sharp edges of electrically conducting cutting tools by sinking the cutting edge into an appropriate counterface material. This paper presents the proof-of-concept and operating characteristics of this innovative process. Robust edge geometry generation, and a significant improvement in the life of high speed steel tools consequent to such preparation of the cutting edge are demonstrated.     

The preparation of cutting edges using a marking laser

During the machining process, high mechanical and thermal loads occur at the cutting edge. Such loads can cause tool failure. Specifically non-uniform and sharp cutting edges that have a low cutting edge stability lead to such failures. In order to enhance the tool performance, the cutting edges are prepared by manufacturing both a pre-defined cutting edge geometry, and an appropriate cutting edge roughness. This paper describes the use of a low-cost marking laser for the preparation of cutting edges as an alternative to conventional preparation techniques, such as brushing or blasting. Cutting edge radii of 9?C47 ??m can be prepared with a machining accuracy of 1.5 ??m. The maximum preparation time for an individual cutting edge is approximately 10 s. Uncoated indexable inserts manufactured in this way were tested in a face milling operation. The results of these investigations (using prepared cutting edges) show both an increase in tool life and an improved surface roughness of the machined workpieces compared to those using non-prepared cutting edges.     

Evaluation of HVOF-sprayed WC-Co coatings for wood machining

A great concern to save the amount of tungsten carbide used in various mechanical components has become important because of an increase of global demand and the resultant sharp rise in the price in recent years. Sintered tungsten carbide (WC) tools are usually used in woodworking industry because of their excellent combination of hardness and toughness. However, the actual area necessary for cutting is very small compared to the overall cutting tool body. In this work, three high-velocity oxy-fuel (HVOF) sprayed WC-Co coatings with different carbide size (0.2, 2, and 6 µm) on high speed tool steel substrates were fabricated and then grinded to produce cutting tools. Characterization of the deposited coating was done by scanning electron microscope, X-ray diffraction, hardness and indentation fracture toughness tests. The wood machining tests were performed on natural wood (Apitong) and medium density fiberboard (MDF) to study their performance as a cutting tool. The results showed that the hardness values of the coatings were approximately the same as that of sintered material, while the fracture toughness values were significantly lower. The wood machining tests on Apitong revealed that the coating tools were worn by the same level of edge recession as the sintered material. However, they showed numerous edge chippings over the worn surfaces and the level of edge chipping tended to increase with reducing the carbide size. The wood machining tests on MDF revealed that the coating tools were worn by the same level of edge recession in the low density wear zone as the sintered material but by a significantly higher level in the high density wear zone.     

Effect of the Cutting Edge Radius and its Manufacturing Procedure, on the Milling Performance of PVD Coated Cemented Carbide Inserts

The fatigue and wear behaviour of PVD coatings on cemented carbide inserts with various cutting edge radii are investigated experimentally and analytically in milling. The inserts with cutting edge radii from 8 up to 35 μm were manufactured by honing and micro-blasting. The tool wear progress was depicted through Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) microspectral analysis. The Finite Elements Method (FEM) simulation of the contact between the tool and the workpiece highlights the effect of the cutting edge radius on the first coating fracture and the further wear development. The wear behaviour of the cutting edge radii manufactured by honing, in comparison to the corresponding ones by means of micro-blasting, is significantly enhanced, whereas the cutting edge radius increasing can lead to a higher tool life.     

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.     

表面微织构在切削过程中的研究进展

在切削过程中,临近切削刃的刀具前刀面与切屑、刀具后刀面与已加工表面接触区存在的高温高压情况严重影响了刀具服役寿命和工件表面完整性。表面微织构技术是一种先进的表面改性技术,在刀具表面制备不同尺寸参数、形状参数、分布参数的表面织构能够显著影响刀具的切削性能。当刀具表面微织构制备方法不同时,微织构所呈现的性能也不同。首先从制备技术的原理、制备过程、制备技术特点等方面对当前最先进的刀具表面微织构制备技术进行了综述。然后从切削力、切削温度、刀具磨损、切屑形成、工件表面完整性等角度分析了微织构对刀具切削性能的影响规律与机理。在分析切削力、切削温度、刀具磨损、切屑形成等4个指标时重点关注了刀具前刀面微织构所起的作用,在分析工件表面质量时,同时考虑了刀具后刀面微织构、前刀面微织构的影响。最后,介绍了当前微织构的研究热点,主要包括微织构技术与钝化刃口、润滑剂的协同作用对切削性能的影响,以及微织构刀具在切削过程中发生的衍生切削行为。通过对文献的归纳、总结与深入分析,给出了表面微织构未来的研究方向,为刀具进一步优化提供设计参考。     

Effect of Tool Wear on Roughness in Hard Turning

This paper attempts to make a contribution to wear estimation of CBN tools when turning hardened steels.It is well known that cutting edge geometry deteriorates with wear. Although many authors have considered tool wear process has a random nature, detailed tool examination has proved that wear has some deterministic features in these processes. Thus, plastic deformation exists in the early stages while gradual abrasion makes the cutting edge recede.On the other hand, it has also been found that there is a good replication of the tool on the roughness profile. Therefore, cutting edge state might be predicted with reasonable accuracy through roughness parameters. This strategy allows fast tool wear estimation by simple roughness measurements using a shop floor instrument.     

Experimental study on turning of TC9 titanium alloy with cold water mist jet cooling

Titanium alloys, as difficult-to-cut materials, have poor machinability due to their superior mechanical properties, heat resistance and corrosion resistance. High cutting temperature that will greatly accelerate tool wear often occurs in titanium alloy cutting process. In this paper, cold water mist jet (CWMJ) cooling method, an eco-friendly cooling method, was used to obtain a lower cutting temperature during TC9 titanium alloy turning process. The effects of CWMJ were mainly discussed as compared with cold air jet and flood cooling methods. A comprehensive evaluation on the cooling effects of CWMJ was carried out by hydrodynamic tests, heat transfer tests and turning tests, respectively. Experimental results indicated that CWMJ had better cooling effects as compared with other two cooling methods. Cutting temperature was greatly reduced, and tool life was improved with CWMJ during TC9 turning process. Machined surface quality and chip morphology were also acceptable.     

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.     

Experimental and finite element simulation based investigations on micro-milling Ti-6Al-4V titanium alloy: Effects of cBN coating on tool wear

Micro-milling process is a direct and flexible fabrication method in producing functional three dimensional micro-products. The advance of micro-milling process ultimately depends on the development of micro cutting tools since it is a tool-based process. Therefore, in this study an attempt to improve the performance of carbide micro-end mills by applying cubic boron nitride (cBN) coating was carried out. Experiments and finite element method (FEM) based simulations were used to study the effect of cBN coated tool in micro-machining of Ti-6Al-4V titanium alloy. The experiments were conducted to compare the performance of cBN coated and uncoated micro-end mills in terms of surface roughness, burr formation and tool wear. FE simulations were employed to investigate chip formation process in micro-milling to reveal the effects of cBN coated micro-end mills with increased edge radius in terms of cutting force generation, tool temperature and contact pressure, sliding velocity and hence tool wear rate. The simulation results were further utilized for estimating tool life using a sliding wear rate model and compared with experiments. This study clearly showed that the cBN coated carbide tool outperformed the uncoated carbide tool in generation of tool wear and cutting temperature.     

Predictive model of tool wear in milling with coated tools integrated into a CAM system

The coated tool wear evolution in milling at constant cutting conditions can be described analytically based among other factors on the cutting edge entry impact duration. A tool wear predictive mathematical model for milling parts of complicated geometry was created employing this methodology and a commercial CAM system. Parameters of the developed model were determined based on experimental results. In this way, the expected tool wear growth during numerically controlled milling can be estimated, considering the cutting penetrations along the tool paths, the process up or down kinematic and other factors. The application of the introduced model is demonstrated through appropriate examples.     

Analysis of tool wear and residual stress of CVD diamond coated cemented carbide tools in the machining of aluminium silicon alloys

Aluminium alloys have found increasing applications in the automotive and aeronautical industries in recent years. Due to their extraordinary properties however, the machining of these alloys still poses difficulties, and requires the optimized combination of cutting tool material and geometry. The potential of CVD diamond coated carbide tools has been demonstrated in recent years, however tool wear and short tool life remain as issues to be resolved. Key to increasing the tool life of CVD diamond coated tools is the further development of the coating process to optimize the coating adhesion. An understanding of the substrate and coating residual stress profiles must be gained in order to achieve this. Compressive residual stresses in cutting tools can lead to a higher crack resistance, but also to early coating delamination and tool failure. To analyze the influence of residual stresses on the coating quality and tool life, the residual stress profiles of tungsten carbide substrates and CVD diamond coatings were measured using X-ray and synchrotron radiation. The influence of the tungsten carbide substrate type and the CVD diamond coating process on the residual stress profiles was thus determined. In order to analyze the performance of the coated tools and the influence of the residual stresses on the tool lifetime, machining tests were performed with two aluminium silicon alloys. The tool wear, tool lifetime and workpiece quality were examined. Finally, many of the commonly used wear tests used to analyze the wear resistance of tool coatings cannot be implemented for CVD diamond coatings due to their high hardness. An impact test was therefore constructed to allow the determination of the wear resistance of CVD diamond tools.     

聚晶立方氮化硼刀具磨损与寿命研究综述

聚晶立方氮化硼(PCBN)是一种超硬刀具材料,由于其具有硬度高、化学稳定性和热稳定性好等优点,已经被广泛应用于汽车、航空航天、能源等领域的机械零部件加工。文中分析了PCBN刀具的主要磨损形式及其原因,并从刀具材料构成和几何形状、工件材料以及切削条件3个方面总结了影响PCBN刀具磨损和寿命的主要因素,最后介绍了切削参数优化和添加涂层等方法在提高刀具耐磨性与寿命方面的应用。     

Application of foil electrodes for electro-erosion edge honing of complex-shaped carbide inserts

Electro-erosion honing is a novel process that exploits the undesirable but inevitable phenomenon of localized electrode wear in sink electrical discharge machining that rapidly rounds off sharp edges, for the edge honing of cutting tools. The process essentially entails the sinking of a sharp edge of a cutting tool into a counterface of an appropriate material to generate the round edge geometry. This paper proposes the innovative application of a foil counterface, with a view to expanding the capability of this process in the honing of tools with such geometric features as nose radii and curved edges. Such a configuration involves no particular alignment requirements, and facilitates the simultaneous processing of a batch of inserts. In consideration of their industrial significance, the process is evaluated in the honing of cemented carbide inserts. The novel process is demonstrated to address the limitation of the conventional brush honing process in being capable of generating consistent edge geometry, while delivering comparable tool life.