Experimental Study on Hard Turning Hardened GCr15 Steel with PCBN Tool

This paper discusses experimental results of turnin g experiments on GCr15 bearing steel hardened to 60～64 HRC. The objective was to d etermine the effect of the cutting parameters on cutting force, chip morphology and resultant workpiece surface quality, more specifically surface texture, micr ostructure alterations, changes in microhardness and residual stresses distribut ion. The changing rules of the main cutting force was shown in this paper which feature a increasing tendency with the improvement of the workpiece hardness wit hin the cutting parameter scope. The rule of cutting force changing with the wor kpiece hardness is accord to the traditional metal cutting theory. Stress value decrease with increasing cutting speed and workpiece hardness. The comparison of the machined surface roughness and harden layer depth of machined surface for d ifferent hardness is shown in Fig.1. The machined surface roughness is the worst when the workpiece hardness is around 50HRC. When the workpiece hardness is ove r 50HRC, the surface roughness value shows a descending tendency with the additi on hardness. The machined superficial harden layer depth shows an increasing ten dency with the improvement of the workpiece hardness. When the workpiece hardnes s is 50HRC the machined superficial harden layer depth is tiptop. When the workp iece hardness is over 50HRC the depth changes little with the addition of workpi ece hardness. The remnant stress status of the machined surface is shown in Fig. 2, which is press stress status both in surface and in base for less cutting par ameters under two kinds of cutting condition. But experiment results show that t ensile stress can be produced under uncomfortable cutting conditions. The deform ation created by the chip formation is reduced whereduce with [TPP126A,+35mm77mm,Z,PY#]Depth from surface (μm) ■ v=200m/min,f=0.24mm/r,ap=0.8mm,60HRC ● v=200m/min,f=0.15mm/r,ap=0.5mm,60HRC Fig.1 The subsurface residual stress between the two experimentsHardness (HRC) Fig.2 The surface finish vs. workpiece hardness the workpiece hardness is improved.

Cutting Temperature and Tool Wear of Hard Turning Hardened Bearing Steel

A study was undertaken to investigate the performan ce of PCBN tool in the finish turning GCr15 bearing steel with different hardness between 30～64 HRC. The natural thermocouple was used to measure the cutting tem p erature, tool life and cutting temperature were investigated and compared. The m aterial can be heated by this instrument which using low voltage and high elec trical current, while PCBN can’t be heated by electrifying directly, so the ke ntanium layer coating over the PCBN is heated, so the PCBN is heated and its th ermoelectric property is got by this method. [TPP129,+60mm88mm,Y,PZ#] Fig.1 Effect of cutting depth and workpiec hardness on. the cutting temperatureThe objective was to determine the influence of the workpiece hardness on change s in cutting temperature and tool wear characterize. It can be found from Fig.1 that the cutting temperature show an increasing tendency with the improvement of workpiece hardness within the cutting speed scope when the workpiece hardness i s under HRC50. And on the other hand, it is found that the cutting temperature s how the downtrend with the improvement of workpiece hardness when the workpiece hardness is over HRC50. According to experimental results, the critical hard ness when turning hardened GCr15 bearing steel with PCBN tool is about HRC50. Th e wear causes of PCBN tool have been found out through taking photos on the micr o-shape of PCBN poly-laminate initial surface as well as face and flank of wea r tool and analysis on chemical elements. It is discovered that the PCBN tools a re not suitable for cutting the workpiece at nearly critical hardness, because n ear the critical hardness, PCBN wear at the highest speed. For researching the w ear rule of PCBN tool, the tool wear experiments have been carried on by using b earing steel GCr15 at hardness HRC40 and HRC60 with changing cutting speed. The indexes of tool life equations is gained under two kinds of conditions w hich are bigger than 0.6, so the effects of cutting speed on the PCBN tool are m uch less than that of carbide tool and ceramic tool.

Effect of nanoparticles on the performance of magnetorheological fluid damper during hard turning process

Magnetorheological(MR)fluid damper which allows the damping characteristics of the damper to be continuously controlled by varying the magnetic field is extensively used in metal cutting to suppress tool vibration.Even though magnetorhelogical fluids have been successful in reducing tool vibration,durability of magnetorhelogical fluids remains a major challenge in engineering sector.Temperature effect on the performance of magnetorhelogical fluids over a prolonged period of time is a major concern.In this paper,an attempt was made to reduce temperature and to improve viscosity of magnetorhelogical fluids by infusing nanoparticles along with MR fluids.Aluminium oxide and titanium oxide nanoparticles of 0.1%and 0.2%concentration by weight were considered and experimental tests were conducted to study the influence of nanoparticles on the performance of magnetorheological fluid.From the experimental results it was observed that the presence of nanoparticles in MR fluid reduces temperature and increases the viscosity of MR fluid thereby increasing the cutting performance during turning of hardened AISI 4340 steel.

Comparative investigation towards machinability improvement in hard turning using coated and uncoated carbide inserts： part Iexperimental investigation

The investigation of low cost uncoated andcoated carbide insert in the hard turning of hardened AISID2 steel （≥55 HRC） will definitely open up a new arena asan economical alternative suitable to industrial machiningsectors. Thus, this paper reports the comparative machin-ability assessment for the hard turning of AISI D2 steel（（55 ± 1） HRC） by coated and uncoated carbide insert in adry environment. Micro hardness and abrasion tests werecarried out to assess resistance capability against wear. Theabove test results confirmed the greater wear resistanceability of AIaO3 coated carbide insert over uncoated car-bide. Based on the extensive investigation of comparativemachinability, the coated carbide insert （TiN-TiCN-A12O3）outperformed the uncoated carbide insert with regard tosurface roughness, flank wear, chip-tool interface temper-ature, and chip morphology. Abrasion and diffusion wereobserved as the principal tool wear mechanisms in theinvestigated range. The uncoated carbide failed completelydue to the severe chipping and quick dulling of the cuttingedge, which led to its unsuitability for machining hardenedsteel.

Analysis of hard turning process： thermal aspects

In manufacturing sector, hard turning has emerged as a vital machining process for cutting hardened steels. Besides many advantages of hard turning operations, one has to implement to achieve close tolerances in terms of surface finish, high product quality, reduced machining time, low operating cost and environmental friendly characteristics. In the study, three dimensional （3D） computer aided engineering （CAE） based simulation of hard turning by using commercial software DEFORM 3D has been compared to the experimental results of stresses, temperatures and tool forces in machining of AISI D3 and A1SI H13 steel using mixed ceramic inserts （CC6050）. In the following analysis, orthogonal cutting models are proposed, considering several processing parameters such as cutting speed, feed and depth of cut. An exhaustive friction modelling at the tool-work interface is carried out. Work material flow around the cut- ting edge is carefully modelled with adaptive re-meshing simulation capability of DEFORM 3D. The process simulations are performed at constant feed rate （0.075 mm/r） and cutting speed （155 m/min）, and analysis is focused on stresses, forces and temperatures generated during the pro- cess of machining. Close agreement is observed between the CAE simulation and experimental values.

Effect of PCBN cutting tools wear on surface integrality in high-speed hard turning

In this paper, the effect of of flank wear polycrystalline cubic boron nitride （PCBN） tools on residual stresses, white layer and roughness of machined workpiece surfaces is studied. Experimental results indicate that with the increase of the tool wear, the surface of the machined workpiece tends to generate tensile residual stresses, and white layer becomes clearly thicker and uneven on the workpiece surface. The effect of the flank wear on the surface roughness is less within some range of flank wear value. The results show that it is possible to produce ideal surface integrality levels by controlling the tool flank wear.

Comparative study on machinability improvement in hard turning using coated and uncoated carbide inserts： part II modeling, multi-response optimization, tool life, and economic aspects

The present study focused on mathematical modeling, multi response optimization, tool life, and eco- nomical analysis in finish hard turning of AISI D2 steel （（55 4- 1） HRC） using CVD-coated carbide （TiN/TiCN/ A1203） and uncoated carbide inserts under dry environ- mental conditions. Regression methodology and the grey relational approach were implemented for modeling and multi-response optimization, respectively. Comparative economic statistics were carried out for both inserts, and the adequacy of the correlation model was verified. The experimental and predicted values for all responses were very close to each other, implying the significance of the model and indicating that the correlation coefficients were close to unity. The optimal parametric combinations for A1203 coated carbide were dl-fl-v2 （depth of cut = 0.1 mm, feed = 0.04 mm/r and cutting speed = 108 m/min）, and those for the uncoated tool were dl-（0.1 mm）-fl （0.04 mm/r）-vl （63 rn/min）. The observed tool life for the coated carbide insert was 15 times higher than that for the uncoated carbide insert, considering flank wear criteria of 0.3 mm. The chip volume after machining for the coated carbide insert was 26.14 times higher than that of the uncoated carbide insert and could be better utilized for higher material removal rate. Abrasion, diffusion, notch- ing, chipping, and built-up edge have been observed to be the principal wear mechanisms for tool life estimation. Use of the coated carbide tool reduced machining costs by about 3.55 times compared to the use of the uncoated carbide insert, and provided economic benefits in hard turning.

Forces in Hard Turning of 51CrV4 with Wiper Cutting Tool

For precision machining, the hard turning process is becoming an important alternative to some of the existing grinding processes. This paper presents an analytical model for predicting cutting forces in hard turning of 51CRV4 with hardness of 68 HRC. The cutting tool used is made from cubic boron nitride （CBN） with a wiper cutting edge. Formulas for differential chip loads are derived for three different situations, depending on the radial depth of cut. The cutting forces are determined by integrating the differential cutting forces over the tool-workpiece engagement domain. For validation, cutting forces predicted by the model were compared with experimental measurements, and most of the results agree quite well.

White Layer of Hard Turned Surface by Sharp CBN Tool

White layers in hard turned surfaces were identified and measured as a function ot turning parameters based on the Taguchi method. It reveals that white layers generate on the machine surface in the absence of tool flank wear, and white layer depth varies with the different combinations of hard turning parameters. Turning speed has the most important impact on white layer depth, feed rate follows, and cutting depth at last. The white layer generation consequently suggests a strong couple relation to the heat generation and thermal process of hard turning operation. White layer disappears under an optimal combination of turning parameters by Taguchi method. It suggests that a superior surface integrity without white layer is feasible under some selected combinations of turning parameters by a sharp CBN cutting tool.

FFT and Wavelet-Based Analysis of the Influence of Machine Vibrations on Hard Turned Surface Topographies

With hard turning, which is an attractive alternative to existing grinding processes, surface quality is of great importance. Signal processing techniques were used to relate workpiece surface topography to the dynamic behavior of the machine tool. Spatial domain frequency analyses based on fast Fourier transform were used to analyze the tool behavior. Wavelet reconstruction was used for profile filtering. The results show that machine vibration remarkably affects the surface topography at small feed rates, but has negligible effect at high feed rates. The analyses also show how to control the surface quality during hard turning.