Tool–chip thermal conductance coefficient and heat flux in machining : Theory, model and experiment

This study proposes a technique for determining a tool–chip thermal conductance coefficient and heat flux in machining. The technique is based on solving an inverse heat transfer problem (IHTP). Because the IHTP is ill-posed, a priori information is required for its effective solution. To derive this information, substantial qualitative and quantitative analysis of a mixed boundary value problem for the heat equation and an illustrative test case for IHTP are provided. It has been established that the averaged interfacial chip temperature is needed for an effective IHTP solution. Thermal imaging combined with a special experimental setup was used to determine chip temperature. It was also found that a function describing the heat flux time dependency belongs to a set of decreasing functions. Tool–chip thermal conductance coefficients were obtained for high-speed steel and cemented carbide tooling. On the microscale, this data was interpreted in terms of a conforming rough surface contact conductance model, where tool wear was found to govern variations in the thermal conductance coefficient

Correlation between edge radius of the cBN cutting tool and surface quality in hard turning

In this study, the attempt has been made to investigate the correlation between the cutting tool edge radius and surface quality in terms of the surface roughness and subsurface deformation through a FE simulation and experiment. Machining tests under different machining conditions were also conducted and the surface roughness and subsurface deformation were measured. Surface roughness and subsurface deformation were produced by the cutting tools with different edge radii under various cutting parameters. Both results from the FE simulation and machining tests confirmed that there was a significant influence on the surface quality in terms of both the surface roughness and subsurface quality from the edge radius. There is a critical edge radius of cBN tools in hard turning in terms of surface quality generated.У даному дослідженні було зроблено спробу дослідити взаємозв’язок між радіусом закруглення крайки різального інструменту і якістю поверхні, які оцінюються шорсткістю поверхні і деформацією підповерхневого шару, методами скінчено-елементного моделювання і експериментально. Було здійснено низку експериментів при різних умовах обробки з одночасним вимірюванням шорсткості поверхні і деформації підповерхневих шарів. Також застосовували різальні інструменти з різними радіусами різальної крайки при різних режимах різання. Результати моделювання і випробувань підтвердили значний вплив радіуса закруглення крайки на якість і шорсткість поверхні, а також якість підповерхневого шару. Виявлено оптимальний радіус округлення крайки інструменту з КНБ, який треба застосовувати при обробці надтвердих матеріалів для отримання найкращої якості поверхні.В данном исследовании была сделана попытка изучить взаимосвязь между радиусом скругления кромки режущего инструмента и качеством поверхности, оцениваемой шероховатостью поверхности и деформацией подповерхностного слоя, методами конечно-элементного моделирования и экспериментально. Были проведены испытания при различных условиях обработки с одновременным измерением шероховатости поверхности и деформации подповерхностного слоя. Применялись режущие инструменты с различными радиусами режущей кромки при различных режимах резания. Результаты моделирования и испытаний подтвердили значительное влияние радиуса скругления кромки на шероховатость поверхности, а также на качество подповерхностного слоя. При точении закаленной стали инструментом из сBN имеется оптимальный радиус режущей кромки инструмента, который следует применять при обработке сверхтвердых материалов для получения наилучшего качества поверхности

Using Barkhausen Noise to Measure Coating Depth of Coated High-Speed Steel

Coated high-speed steel tools are widely used in machining processes as they offer an excellent tool life to cost ratio, but they quickly need replacing once the coated layer is worn away. It would be therefore useful to be able to measure the tool life remaining non-destructively and cheaply. To achieve this, the work presented here aims to measure the thickness of the coated layer of high-speed cutting tools by using Barkhausen noise (BHN) techniques. Coated high-speed steel specimens coated with two different materials (chromium nitride (CrN), titanium nitride (TiN)) were tested using a cost-effective measuring system developed for this study. Sensory features were extracted from the signal received from a pick-up coil and the signal features, Root mean square, peak count, and signal energy, were successfully correlated with the thickness of the coating layer on high-speed steel (HSS) specimens. The results suggest that the Barkhausen noise measuring system developed in this study can successfully indicate the different thickness of the coating layer on CrN/TiN coated HSS specimens

Improvement of tool utilization when hard turning with cBN tools at varying process parameters

Hard turning of helical gear hubs produced from low-carbon alloyed steel with a bulk hardness of HRC 35, and case hardened up to HRC 60–63 with PCBN tools was considered in this study. The workpieces after heat treatment are characterized by a non-uniform thickness of the hardened surface layer which results in a high variation of measured HRC hardness. The deviation of surface microhardness is even greater (HV 314–742) due to the presence of an oxidized layer that should be removed before measurements. When also considering workpiece run-out and deviations in depth-of-cut due to the distribution of the workpiece diameter, all those factors result in a non-uniform development of tool wear that leads to a large deviation in tool life. To uphold quality and avoid scrap, industry uses a fixed conservative tool life (number of parts machined), which leads to many inserts being underutilized, which in turn, means extra expenses considering the price of PCBN tools. The present study addresses the development of different strategies for monitoring of tool wear and prediction of tool life aimed to increase productivity. Laboratory machining tests are performed to optimize the type and number of sensors necessary for data acquisition, to estimate the significance of the data used for the development of prediction model, as well as the efficiency of machine learning algorithms for the selected data and strategies to increase the algorithm's accuracy

Effect of cutting edge radius on surface roughness and tool wear in hard turning of AISI 52100 steel

Performance of cutting tool in hard turning is significantly influenced by its microgeometry, such as edge radius. This study presents an experimental exploration to understand the effect of cutting edge radius on machining performance in terms of surface roughness and tool wear. The cutting tools (CBN) with three groups of nominal edge radius, 20, 30, and 40 μm, were used in the study. The cutting edge radii were characterized with an Alicona optical microscope, and variation of the edge radius was evaluated in this study. The machining tests were then conducted to experimentally assess the effect of cutting edge radius on surface quality and tool wear under different machining conditions. Three-level and two-factor experiments were designed in the test. The results in this study suggest that there is noticeable variation in the edge radius on a cutting tool with a certain nominal value of edge radius. The variations tend to be smaller with increase of the nominal value of edge radius. Besides, the results can be drawn that edge radii have a significant influence on surface roughness and tool wear. Considering all factors, the cutting tool with nominal edge radius of 30 μm demonstrate better machining performance among three groups of cutting tool in hard turning of AISI52100 steel

Tool Wear and Vibrations Generated When Turning High-chromium White Cast Iron with pCBN Tools

Dynamic behavior and stability of system 'tool-workpiece' when machining HCCI with pCBN tools are determined by the processes which occur in cutting zone. The cutting process is characterized by formation of tool protection layer (TPL) on the chip contact area but its stability depends on the workpiece material composition, tool material and cutting conditions. The higher content of Si in the HCCI promotes the TPL formation and its stability. The presence and stability of TPL, besides the cutting edge protection, provides the system with additional damping resulting in the suppression of vibrations. A low Si content and low cutting speed leads to increase of cutting forces that in turn causes the self-generated vibration occurrence

Особливості формування структури та фазового складу в процесі реакційного спікання кубічного нітриду бору зі сполуками Ti, Cr, V

Influence of sintering temperature on both phase composition and structure of ceramic matrix composites based on cubic boron nitride with binders in a form of Al and the Ti, Cr, V carbides are investigated by methods of physical materials science. As the object of study, three cBN–TiC–Al, cBN–Cr3C2–Al, cBN–VC–Al compositions containing 60% vol. cBN are selected. The composites are obtained by high-pressure high-temperature (HPHT) sintering in high-pressure apparatus AVTT-30 in the temperature range of 1600– 2450°C under pressure of 7.7 GPa. In the process of HPHT sintering of composites in the cBN–TiC–Al and cBN–Cr3C2–Al systems, the formation of titanium and chromium diborides is found at the temperatures of sintering Тsint ≥ 1850°С and Тsint ≥ 2150°С, respectively, simultaneously with the formation of alu-minium nitride

Correlation between edge radius of the cBN cutting tool and surface quality in hard turning

cBN cutting tools with superior mechanical properties are widely used in machining various hard materials. The microgeometry of cBN cutting tools, such as the edge radius, has great influence on the surface quality of components and tool life. For optimized tool geometry, it is crucial to understand the influence of the cBN cutting tool microgeometry on the machined surface quality. In this study, the attempt has been made to investigate the correlation between the cutting tool edge radius and surface quality in terms of the surface roughness and subsurface deformation through a FE simulation and experiment. Machining tests under different machining conditions were also conducted and the surface roughness and subsurface deformation were measured. Surface roughness and subsurface deformation were produced by the cutting tools with different edge radii under various cutting parameters. Both results from the FE simulation and machining tests confirmed that there was a significant influence on the surface quality in terms of both the surface roughness and subsurface quality from the edge radius. There is a critical edge radius ofcBN tools in hard turning in terms of surface quality generated