Volodymyr Bushlya

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 (vc = 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.

EFFECTS OF CUTTING SPEED WHEN TURNING AGE HARDENED INCONEL 718 WITH PCBN TOOLS OF BINDERLESS AND LOW-CBN GRADES

Application of polycrystalline cubic boron nitride (PCBN) tools as an alternative for ceramic and cemented carbide tools in machining superalloys has been frequently identified as a solution for enhancing process efficiency but only a limited number of studies has been done in this area. The current study explores the effect of the cutting speed, which was varied in a wide range (2–14 m/s), on machinability of age hardened Inconel 718 with PCBN tools. Performance of binderless PCBN grade and grade with low-cBN content was evaluated in terms of tool life, tool wear, cutting forces and surface quality. Chip formation and process dynamics were analyzed as well. It was found that low-cBN grade provided 70–90% better surface finish and tool life than the binderless at moderate speeds (5–8 m/s). Performance of both grades at low and high speed ranges was non-satisfactory due to notching and flaking respectively. At low cutting speed adhesive wear plays a major role while as the speed increases a chemical wear becomes dominant.

Mechanical properties of superhard boron subnitride B13N2

Microstructure and mechanical properties of bulk polycrystalline rhombohedral boron sub-nitride B13N2 synthesized by crystallization from the B–BN melt at 7 GPa have been systematically studied by micro- and nanoindentation, atomic force microscopy and scanning electron microscopy. The obtained data on hardness, elastic properties and fracture toughness clearly indicate that B13N2 belongs to a family of superhard phases and can be considered as a promising superabrasive or binder for cubic boron nitride.

Modeling subsurface deformation induced by machining of Inconel 718

ABSTRACT Traditionally, the development and optimization of the machining process with regards to the subsurface deformation are done through experimental method which is often expensive and time consuming. This article presents the development of a finite element model based on an updated Lagrangian formulation. The numerical model is able to predict the depth of subsurface deformation induced in the high- speed machining of Inconel 718 by use of a whisker-reinforced ceramic tool. The effect that the different cutting parameters and tool microgeometries has on subsurface deformation will be investigated both numerically and experimentally. This research article also addresses the temperature distribution in the workpiece and the connection it could have on the wear of the cutting tool. The correlation of the numerical and experimental investigations for the subsurface deformation has been measured by the use of the coefficient of determination, R2. This confirms that the finite element model developed here is able to simulate this type of machining process with sufficient accuracy.

Theoretical shear strength and the onset of plasticity in nanodeformation of cubic boron nitride

The nanoindentation in the continuous stiffness measurement mode was used to investigate the onset of plasticity at the nanodeformation of cubic boron nitride (cBN). This technique allows us to reveal an elastic-plastic transition in the contact and to measure the yield strength of cBN at the nanoscale. An abrupt elastoplastic transition (a pop-in) was observed in the (111) cBN single crystal as a result of a homogeneous or heterogeneous nucleation of dislocations in the previously dislocations-free region under the contact. The analysis of the data obtained at the homogeneous nucleation of dislocations in the contact region made it possible to experimentally estimate the theoretical shear strength of cBN and its ideal (elastic) hardness. In a sample of the fine-grained cBN with a nanotwinned substructure a smooth elastoplastic transition was observed in consequence of the propagation and multiplication of already existing dislocations in the contact region.

HP-HT sintering, microstructure, and properties of B6O- and TiC-containing composites based on cBN

The article presents a study of the potential for the use of B6O superhard boron suboxide as a binder in composite materials with a low cBN content. Superhard B6O is characterized by higher mechanical properties than TiC widely used in commercial materials today. Composites containing 60 vol % cBN and different binder compositions that included B6O and TiC have been sintered in a toroid-type high-pressure apparatus at a pressure of 7.7 GPa in a temperature range from 1500 to 2000 °C. The microstructure, phase and elemental composition of the sintered materials have been examined via electron microscopy and X-ray diffraction analysis. Mechanical properties have been analyzed via indentation techniques. The performance of the cutting tools produced from the sintered composites has been evaluated in turning hardened cold work tool steel.

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.

Machinability of CuZn21Si3P brass

New brass alloys containing less or even no lead are being developed, decreasing the environmental impact of the material. One example of an alternative brass is CuZn21Si3P, which contains less than 0.09 wt-% Pb. The research presented in this article evaluates the machinability of CuZn21Si3P as compared to more common, lead-containing free-machining brasses. The results show a marked decrease in the machinability of CuZn21Si3P. When longitudinally turning CuZn21Si3P the cutting tool failed after 142 min of machining. This tool wear was to a large extent remedied through the use of a coating on the cutting tool. CuZn21Si3P appears as a viable substitute for lead-containing brasses, thus implying the possibility for improving the sustainability of modern production. This paper is part of a Themed Issue on Brass Alloys.

Influence of cutting speed and tool wear on vibrations and process stability when turning Inconel 718 with PCBN tools

Results of the study of cutting speed and tool wear influence on the vibrations and their nature during machining superalloy Inconel 718 with low cBN content (cBN-L) and binderless pcBN (bcBN) tools are presented. Cutting speed was varied from 2 to 14 m/sec while other cutting conditions were constant. The process evolution was studied with the wavelet transform of tool acceleration spectra. Behaviour of the dynamic system was found to vary with the cutting speed and the specifics of tool wear. It is shown that machining with bcBN tools was accompanied by appearance of significant vibration when cutting speed exceeded 5 m/sec, but the machining with cBN-L was characterised by the suppression of vibrations over the entire speed range. This was related to the difference of tool microgeometry development during the course of wear. The wear of bcBN tools, in contrast to cBN-L, was characterised by merger of crater and flank wear and formation of negative clearance angle. Such difference results in an increase of cutting forces 2-4 times as compared to cBN-L tools. Estimation of dynamic stability by 0-1 test confirmed the process instability when turning with bcBN tools at cutting speeds higher than 8 m/sec which concurs with chatter appearance.

Dynamic stability of the process of turning nickel superalloys using a toolholder produced by selective laser sintering

The paper presents the results of a comparative analysis of dynamic stability of SiC whisker reinforced alumina tools used in a conventional and prototype toolholders when turning a nickel-based superalloy Inconel 718. The use of the prototype toolholder with a cellular spatial structure is shown to significantly suppress vibrations during the machining operation and stabilize the cutting process within the cutting speed range between 200 and 500 m/min. Considering the identical nature of tool wear rate and the analytical ellaborations regarding the process dynamics, the above-mentioned benefits are related to damping properties of the proposed toolholder.