The study of wear of cutting tools of cBN-based composite material and the influence of tool wear on cutting forces in turning hardened steels

The paper presents some findings of the investigation of finish turning of KhVG hardened steel using a cutting tool with an insert made of a cubic boron nitride based composite (cBN-Si₃N₄ system). The behavior of tool wear throughout the machining time as well as the influence of the tool wear on cutting force components and resulting cutting force have been clarified.     

The study of the influence of wear of the cutting tool with an insert of cBN-based composite material on the tool vibrations in finish turning of hardened steels

It has been found out that wear of a cutting tool with an insert of cBN-based composite material has an effect on the tool vibrations in finish turning of hardened steels with various hardness values. The influence of the tool vibrations on the machined surface roughness has been studied.     

The study of the influence of cutting conditions on machined surface roughness in turning hardened steels with cutting tools of cBN-based composite

The paper presents some findings of the investigation of finish turning of KhVG hardened steel using a cutting tool tipped with a round insert made of a composite based on cubic boron nitride (cBN-Si₃N₄ system). Based on the analysis of machined surface roughness, the cutting conditions have been found which ensure a stable interaction between the cutting tool and the workpiece.     

Dynamic phenomena in finish turning of hardened steels with cBN-based tools

The paper presents some findings of the investigation of finish turning of KhVG hardened steel (60–62 HRC) using a cutting tool with an insert made of a cubic boron nitride based composite (cBN-Si₃N₄ system). The influence of machining process variables on the cutting force components, vibrations, and machined surface roughness is clarified. The authors propose some practical recommendations of how to choose machining modes and conditions.     

Wear and life of tools with inserts from cBN-based polycrystalline Superhard materials in the finish turning of hardened steels at heavy feeds

The results have been considered of experimental studies of the wear regularities of tools with polycrystalline superhard materials based on cubic boron nitride (PCBN) in high-performance finishing of hardened steel with oblique cutters. The effect of machining conditions on the life of such tools has been analyzed.     

The stressed-strained state in the chip forming zone during the finish turning of workpieces of hardened steels

The finite element method has been used for modeling the stressed-strained state in the chip forming zone in cutting workpieces of hardened steels by tools equipped with cutting inserts of cubic boron nitride-based polycrystalline superhard material (PCBN). Special features of the stressed-strained state in the chip forming zone when using tools with a flat and a cylindrical rake faces have been discussed.     

Investigation on diamond tool wear in ultrasonic vibration-assisted turning die steels

This paper presents comprehensive theoretical analyses and experimental investigations for evaluating the ultrasonic vibration-assisted turning (UVAT) of die steels with single-crystal diamond tools. The diamond tool wear was found to rely heavily on the feed rate and the cutting speed while being insensitive to the depth of cut and the tool relief angle under the cutting conditions used in the tests. The tool wear characteristics were further studied based on the observation of wear zone using Raman spectral analysis and energy-dispersive X-ray (EDX) analysis. The detection results of the tool worn topography, the phase transformation and the carbon diffusion of diamond crystals revealed that tool wear mainly occurred on the tool flank face due to the graphitization and the diffusion of the diamond tool. Analytical results of the function mechanisms of the ultrasonic turning indicated that the friction force between the tool flank face and the machined surface, which depended mainly on the ratio of the cutting speed and the vibration speed, could be effectively reduced in ultrasonic turning process. The analytical and experimental results indicated that compared with conventional turning (CT), the cutting performance, in terms of the tool life, was markedly improved by applying ultrasonic vibration to the cutting tool.     

Influence of tool material and tool wear on tool temperature in hard turning reconstructed via inverse problem solution

In this work the cutting tool temperature distribution that develops during turning of hardened cold-work tool steel is modeled on the basis of experimental data. The data obtained from a series of thermocouples, placed on a PCBN insert, into an anvil, and into a toolholder, were used as the input for the model. An inverse problem was solved, where the heat fluxes were computed. The temperature distribution was modeled for the case of new tools, as well as for the case of its development in the course of a tool wear. The reconstructed temperature distributions were in good agreement with the measured data. The heat flux through rake face was found to be reducing with the decrease of thermal conductivity of the tool material.     

Tool wear and tool life of PCBN,binderless cBN and wBN-cBN tools in continuous finish hard turning of cold work tool steel

The paper presents the results of comparative study of performance of cutting tools made of ceramic-bound, binderless cBN, and wBN-cBN tool materials. The tool performance was assessed by tool wear-resistance, values of cutting forces, parameters of machined surface quality, and the state of sub-surface layer generated in continuous turning of hardened cold work tool steel. The tests were carried out under conditions of high speed machining (v _c = 120–180 m/min) both with and without a coolant. The best tool performance by the above-mentioned criteria is provided by a low-cBN material with ceramic binder.     

Brittle-to-ductile transition in the fracture of steels hardened by thermomechanical treatment

This article describes the results of a comparative study of the brittle-to-ductile transition observed during the fracture of steel after quench-hardening and after thermomechanical treatment, with respect to the tempering and test temperatures. Substantial differences in the kinetics of the increase in ductility during the brittle-to-ductile transition were revealed by mechanical torsion tests and electron microscopic examination of fracture surfaces.     

An experimental study of the influence of tool material and fine turning conditions on the level of acoustic emission signals

The paper addresses the influence of cutting conditions on acoustic emission signals in fine turning of aluminum alloys. Each AE signal was split into two sections: the first one is associated mostly with the chip formation and the second one with the tool–workpiece friction. The tool materials were single crystals of natural and synthetic diamond as well as hardmetal WC–6Co. The experimental data demonstrate that in diamond turning the main signal is emitted during the chip formation, while in the case of hardmetal turning the portion of the signal emitted due to the tool flank friction is often larger and depends on the cutting conditions.     

Characteristics of the wear process in the cutting of free-cutting steels

The paper brings some interesting results of the investigation of the cutting edge wear at cutting of free cutting steels by cemented carbide plates. These steels are characterized by the additions of sulphur and lead to increase machinability. The experimental results have shown that the additives of sulphur and lead can strongly affect not only chip generation but also the form and rate of wear. Previous investigations have indicated clearly that the criterion of wear on the clearance faces provides too little information on tool life. The experimental results have also shown that at equal wear on the clearance face the form and rate of wear on the rake face differ essentially.     

Application of response surface methodology for determining cutting force model in turning hardened AISI H11 hot work tool steel

This experimental study is conducted to determine statistical models of cutting forces in hard turning of AISI H11 hot work tool steel (∼ 50 HRC). This steel is free from tungsten on Cr–Mo–V basis, insensitive to temperature changes and having a high wear resistance. It is employed for the manufacture of highly stressed diecasting moulds and inserts with high tool life expectancy, plastic moulds subject to high stress, helicopter rotor blades and forging dies.     

The influence of manganese on the fracture toughness of nickel steels

The effect of manganese content on the fracture toughness of a high-purity martensitic 0.6% C, 5% Ni steel has been determined after tempering below 350°C. The intergranular mode, characteristic of the brittle fracture of material with only trace manganese content, was eliminated by the addition of between 0.1% and 0.6% of that element. However, the purposeful addition of manganese introduced slow crack growth along an intergranular path prior to fast fracture which could in turn, be eliminated by testing in a dry environment. Although this environmental sensitivity prevented the full potential toughness of the material being realised in normal atmospheres the manganese addition effectively improved the toughness, and it is suggested that this is consequential to a change in the fracture criterion.

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Résumé L'effet de la teneur en manganèse sur la ténacité à la rupture d'un acier martensitique de haute pureté à 0,6% C et 5% Ni a été déterminé après revenu à 350°C.En procédant à des additions de manganèse de 0,1% à 0,6%, on a pu éliminer le mode intergranulaire qui caractérisait la rupture fragile de l'acier ne comportant que des traces de cet élément.Toutefois, ces additions intentionnelles de manganèse provoquent une tendance à la croissance lente de fissures le long d'un parcours intergranulaire, suivie d'une rupture brutale, qui peut, à son tour, être éliminée en travaillant dans une atmosphère sèche.En dépit du fait que la sensibilité à l'environnement pénalise la ténacité potentielle du matériau en atmosphère normale, des additions de manganèse améliorent effectivement la ténacité, et l'on suggère que ceci est dû à une modification du critère de rupture.

     

The fracture toughness of borides formed on boronized cold work tool steels

In this study, the fracture toughness of boride layers of two borided cold work tool steels have been investigated. Boriding was carried out in a salt bath consisting of borax, boric acid, ferro-silicon and aluminum. Boriding was performed at 850 and 950 °C for 2 to 7 h. The presence of boride phases were determined by X-ray diffraction (XRD) analysis. Hardness and fracture toughness of borides were measured via Vickers indenter. Increasing of boriding time and temperature leads to reduction of fracture toughness of borides. Metallographic examination showed that boride layer formed on cold work tool steels was compact and smooth.     

Experimental investigation of cutting parameters influence on surface roughness and cutting forces in hard turning of X38CrMoV5-1 with CBN tool

This experimental investigation was conducted to determine the effects of cutting conditions on surface roughness and cutting forces in hard turning of X38CrMoV5-1. This steel was hardened at 50 HRC and machined with CBN tool. This is employed for the manufacture of helicopter rotor blades and forging dies. Combined effects of three cutting parameters, namely cutting speed, feed rate and depth of cut, on the six performance outputs-surface roughness parameters and cutting force components, are explored by analysis of variance (ANOVA). Optimal cutting conditions for each performance level are established. The relationship between the variables and the technological parameters is determined through the response surface methodology (RSM), using a quadratic regression model. Results show how much surface roughness is mainly influenced by feed rate and cutting speed. The depth of cut exhibits maximum influence on cutting force components as compared to the feed rate and cutting speed.     

A study on the determination of actual cutting time in NC turning

In NC-lathe operation, the spindle speed is programmed for the spindle revolutions per minute or the unit length per minute for the constant circumferential cutting speed. Additionally, the tool feed can be coded in terms of the unit length per minute or per revolution. This paper describes the derivation of formulas which enable calculation of tool movement time when the real tool feederate with velocity unit varies during linear and/or circular interpolation with the most widely used cutting conditions, that is, cutting speed in terms of the length unit per minute and feed in terms of length unit per spindle revolution.     

Design and construction of a dynamometer to evaluate the influence of cutting tool rake angle on cutting forces

In this study, the influence of cutting tool rake angle on the cutting forces developed during turning operation was evaluated. For this purpose, a dynamometer was designed and constructed to measure cutting forces. In this dynamometer design, measurement of the cutting tool deflection under the cutting forces was aimed using two beam type load cells located suitably according to the cutting tool. In order to examine the influence of rake angle, turning tests were carried out on AISI 1040 steel workpiece using eight different rake angles. The turning tests at each rake angle were conducted at five different cutting speeds while depth of cut and feed rate were kept constant. The results showed that cutting forces decreased with increasing the rake angle.