FEM analysis of edge preparation for chamfered tools

The chamfer enhances the performance of the tool by strengthening the edge and reducing the possibility of tool wear and breakage. The strength of the chamfered tool can be investigated by analysis of process variables. This research investigates the effects of chamfer width and chamfer angle on process variables (force, stress, tool temperature and tool stress) in machining of a mild carbon low alloy steel by a cemented carbide tool using finite element method. The simulations show that the dead metal zone created under the tool acts as the effective cutting edge of the tool and increases the cutting forces. The predicted results show that the effect of chamfer width and angle is more pronounced on the thrust force than the cutting force. It also investigates the effect of chamfer on the effective shear angle and chip thickness, and comparison with available experimental results is presented. Tool temperatures are also predicted which suggests the presence of an optimum chamfer angle from the viewpoint of maximum tool temperature.     

Finite element simulations of ultrasonically assisted turning

Ultrasonically assisted turning is a promising machining technology, where high frequency vibration (f≈20 kHz) with an amplitude a≈10 μm is superimposed on the movement of the cutting tool. Ultrasonic turning yields a noticeable decrease in cutting forces, heat and noise radiation, as well as a superior surface finish, comparing to the conventional machining technology. The present study utilizes both experimental techniques and numerical (finite element) simulations to analyze the microstructural processes at the cutting tool–chip interface. High-speed filming of the chip–tool interaction zone during cutting and microstructural and nanoindentation analyses of the machined surfaces are used to compare process zones and deformation processes for both conventional and ultrasonically assisted technologies. The suggested finite-element (FE) model, which utilizes MSC Marc/Mentat general FE code, provides a transient analysis for an elasto-plastic material, accounting for the frictionless contact interaction between a cutter and workpiece as well as material separation in front of the cutting edge. A detailed analysis of cutting for a single cycle of ultrasonic vibration is carried out for isothermal conditions. Differences between conventional and ultrasonic turning in stress distribution in the process zone and contact conditions at the tool/chip interface are investigated.     

Modeling and multi-response optimization of machining performance while turning hardened steel with self-propelled rotary tool

There are many advanced tooling approaches in metal cutting to enhance the cutting tool performance for machining hard-to-cut materials.The self propelled rotary tool(SPRT) is one of the novel approaches to improve the cutting tool performance by providing cutting edge in the form of a disk,which rotates about its principal axis and provides a rest period for the cutting edge to cool and allow engaging a fresh cutting edge with the work piece.This paper aimed to present the cutting performance of SPRT while turning hardened EN24 steel and optimize the machining conditions.Surface roughness(R_a) and metal removal rate(r_(MMR)) are considered as machining performance parameters to evaluate,while the horizontal inclination angle of the SPRT,depth of cut,feed rate and spindle speed are considered as process variables.Initially,design of experiments(DOEs) is employed to minimize the number of experiments.For each set of chosen process variables,the machining experiments are conducted on computer numerical control(CNC) lathe to measure the machining responses.Then,the response surface methodology(RSM) is used to establish quantitative relationships for the output responses in terms of the input variables.Analysis of variance(ANOVA) is used to check the adequacy of the model.The influence of input variables on the output responses is also determined.Consequently,these models are formulated as a multi-response optimization problem to minimize the R_a and maximize the r_(MMR)simultaneously.Non-dominated sorting genetic algorithmII(NSGA-II) is used to derive the set of Pareto-optimal solutions.The optimal results obtained through the proposed methodology are also compared with the results of validation experimental runs and good correlation is found between them.     

Thermomechanical finite element simulations of ultrasonically assisted turning

Ultrasonically assisted turning (UAT) is studied with finite element (FE) simulations and compared with conventional turning (CT) using both computational results and infrared thermography experiments. The two-dimensional thermomechanically coupled FE model of both UAT and CT utilizes MSC MARC general FE code and incorporates temperature dependent material properties, strain rate effects, heat generated due to plastic flow, contact interaction and friction at the cutter/workpiece interface. Material separation in front of a cutting edge and automatic remeshing of distorted elements are implemented in the developed computational scheme. Influence of friction on resultant temperatures and chip shapes in turning for both UAT and CT is discussed. Temperature fields in the cutting region and in the cutting tool for CT and UAT are studied and compared with the experimental data. A role of various heat transfer parameters on thermal processes in UAT and CT is investigated.     

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.     

Theoretical and empirical coupled modeling on the surface roughness in diamond turning

In this work, a theoretical and empirical coupled method is proposed to predict the surface roughness achieved by single point diamond turning, in which the surface roughness is considered to be composed of the certain and uncertain parts. The certain components are directly formulated in theory, such as the effects of the kinematics and minimum undeformed chip thickness. The uncertain components in relation to the material spring back, plastic side flow, micro defects on the cutting edge of diamond tool, and others, are empirically predicted by a RBF (radial basis function) neural network, which is established by referring to the experimental data. Finally, the particle swarm optimization algorithm is employed to find the optimal cutting parameters for the best surface roughness. The validation experiments show that the optimization is satisfied, and the prediction accuracy is high enough, i.e. that the prediction error is only 0.59–10.11%, which indicates that the novel surface roughness prediction method proposed in this work is effective.     

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.     

KDP晶体单点金刚石切削脆塑转变机理的研究

加工超光滑表面的KDP晶体是现代超精密加工技术领域的重点研究课题。实验采用维氏压痕法研究KDP晶体脆性材料(001)面不同晶向的硬度、断裂韧性的变化规律。通过建立KDP晶体脆塑转变临界切削厚度模型,研究了KDP晶体金刚石切削脆塑转变机理。结果表明,脆塑转变临界最小切削厚度出现在断裂韧性最小而硬度最大的[110]方向;脆塑转变临界切削最大厚度出现在断裂韧性最大而硬度最小的[001]方向。并利用超精密机床加工了KDP晶体,加工结果与理论推导结论相符合,在[001]方向加工出表面粗糙度为7.5nm(RMS)的超光滑表面。     

Semi-orthogonal turning of hardmetal with CVD diamond and PCD inserts at different cutting angles

Thick CVD diamond brazed inserts and PCD cutting tools were compared in dry turning of WC-18 wt% Co bars. Machining of hardmetal by chip removal is a recent alternative technology to wheel grinding, aiming the reduction of the operation time, the elimination of cooling lubricants and single step shaping of complex geometries. Two cutting angle configurations were used: i) neutral (0°) rake angle and 11° clearance angle; ii) negative (−6°) rake angle and 6° clearance angle, named here as TP and TN, respectively. Roughing and finishing operations were performed with adequate cutting parameters. In roughing conditions, the TP-CVD inserts presented the best performance regarding the cutting forces, tool wear and workpiece surface quality, while no significant differences were found between the TP-CVD and TN-CVD tools in the hardmetal finishing. Contrarily to CVD diamond, the currently available commercial option, the PCD tool, was not able to machine such an abrasive material, not only due to its lower hardness but also because adhesion wear is promoted by the presence of the common cobalt binder of the hardmetal and the PCD composite.     

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 wire-EDM textured conventional tungsten carbide inserts in machining of aerospace materials (Ti–6Al–4V alloy)

Importance of this present investigation is to identify the influence of modified tool (tool with texturing) on the process of orthogonal turning of Ti–6Al–4V work material. To achieve the enhanced turning conditions, four different types of textures (plain conventional, cross, perpendicularly textured and parallel textured tool to the chip flow direction) were fabricated on the rake face of the tool insert and the lubricant used during the machining process is molybdenum disulfide (MoS₂). Machining forces (the force of cutting and feed), angle of shear, chip morphology, temperature distribution between tool and chip were measured. Shear strain and strain rate were also computed and compared with all type of cutting tools. Experimental results revealed that the cross-textured cutting tool exhibit an effective reduction in cutting force, friction, shear strain and strain rate. The favorable metal removal condition of curling chip with low diameter was achieved through cross-textured tool.     

Influence of cryogenic coolant on turning performance characteristics: A comparison with wet machining

Machining of 17-4 Precipitation Hardenable Stainless Steel (PH SS) is one of the difficult tasks because of its high cutting temperatures. Conventional cutting fluids are used to overcome the high cutting temperatures, but these are not acceptable from the health and environmental sustainable points of view. Cryogenic cooling is one of the potential techniques to overcome such problems. In the current work, comparison is made of cryogenic turning results, such as tool flank wear, cutting forces (feed force, main cutting force), cutting temperature, chip morphology and surface integrity characteristics with wet machining during machining of heat-treated 17-4 PH SS. The result showed that in cryogenic machining, a maximum of 53%, 78%, 35% and 16% reductions was observed in tool flank wear, cutting temperature, surface roughness and cutting force, respectively, when compared with wet machining. It was also evident from the experimental results that cryogenic machining significantly improved the machining performance and product quality even at high feed rates.     

Influence of nanofluids application on contact length during hard turning

The length of tool–chip contact area (L_c) is considered as a considerable parameter in metal cutting process. Mechanical stresses and high temperature at this region may easily lead to abrasion or even breakage of cutting tool. Up to now, several solutions have been presented to overcome these limitations. Using cutting fluids is one of the solutions to reduce friction, stresses, and temperature over this area. This paper presents experimental investigation and finite element simulation of tool–chip interface in hard turning AISI 4140 using TiO₂ nanofluids. Nanofluids are newly class of engineering fluids developed by distributing nanometer solid particles in a base fluid. The main reason to use nanofluids in cutting process is to increase heat transfer capabilities and also its tribological attributes. At first, the effects of cutting speed, nanoparticles’ size, and nanofluid concentration on L_c have been experimentally investigated. Then, a numerical model has been developed to simulate the contact area length in case of nanofluids application. Comparing the results with that of the experimental tests shows that TiO₂ nanofluids are able to decrease L_c, about 35%, in feed rate of 0.11 mm/rev, nanoparticle size equal to 10 nm, and nanofluid concentration equal to 3.0 wt%.     

A Study of Cutting Performance in Turning Plain Carbon Steel Using TiN-Coated, TiCN-Coated, and Uncoated Cemented Carbide Tools with Chamfered Main Cutting Edge

A special tool holder and its geometry was designed for this study. The tool holders, made of medium carbon steel, were milled and ground to various specifications. Tools of three kinds, i.e., TiN-coated, TiCN-coated and uncoated with chamfered main cutting edge (CMCE) were used in turning of carbon steel and pure aluminum to study the mechanism of secondary chip formation. According to the overall performance, the coated CMCE tools were better than the uncoated CMCE tools. In regard to the values of cutting forces and current consumption, the surface roughness of the work piece and the temperature of the tip surface, the levels of coated CMCE tools were all smaller than for the uncoated ones. The cutting force for the TiCN-coated CMCE tools was smaller than that of the TiN-coated ones. From the surface roughness of the work piece, the TiN-coated CMCE tools showed better results. From the color of the main chip and the hardness of the secondary chip, the temperature of the secondary chip was determined to be higher than that of the main chip. We postulate that CMCE tools may be transferring cutting heat more easily from the tip surface than the conventional tools.     

An experimental analysis of effective high speed turning of superalloy Inconel 718

Superalloy, Inconel 718 is widely used in the sophisticated applications due to its unique properties. However, machining of such superior material is difficult and costly due its peculiar characteristics. The present article is an attempt to suggest Taguchi optimization technique to study the machinability of Inconel 718 with respect to cutting force, cutting temperature, and tool life in high speed turning of Inconel 718 using cemented tungsten carbide (K20) cutting tool. Therefore, the objective of this work is divided into two phases: (i) to demonstrate a correlation between cutting speed, feed, and depth of cut with respect to cutting force, cutting temperature, and tool life in a process control of high speed turning of Inconel 718 in order to identify the optimum combination of cutting parameters; (ii) to show the effect of high speed cutting parameters on the tool wear mechanism and chip analysis. These correlations were obtained by multiple linear regressions. The confirmation tests were carried out to make a comparison between the experimental results and mathematical models proposed. The proposed models agree well with the experimental results.     

Molecular dynamics study on surface formation and phase transformation in nanometric cutting of β-Sn

Atomic motion and surface formation in the nanometric cutting process of β-Sn are investigated using molecular dynamics (MD). A stagnation region is observed that changes the shape of the tool edge involved in nanometric cutting, resulting in a fluctuation in the cutting forces. It is found that single-crystal tin releases the high compressive stress generated under the tool pressure through slip and phase transformation. The tin transformation proceeds from a β-Sn structure to a bct-Sn structure. The effects of the cutting speed, undeformed chip thickness (UCT) and tool edge radius on material removal are also explored. A better surface is obtained through material embrittlement caused by a higher speed. In addition, a smaller UCT and sharper tool edge help reduce subsurface damage.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-022-00399-w     

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.     

硬质合金车刀改进前后切削能对比研究

在金属切削过程中,能量的产生与耗散时刻存在,这会直接影响加工材料的形变与加工质量。以硬质合金车刀为研究对象,借助结合理论计算、切削实验与仿真分析的研究手段,对改进的硬质合金微槽车刀和原车刀在切削高强合金钢过程中切削能的产生、传递与耗散展开研究,从能量角度揭示硬质合金微槽车刀的降温机理。研究发现,硬质合金微槽车刀较原车刀降低了切削过程的能耗,其单位总输入能、单位摩擦能、单位剪切能的降幅分别为5.1%,10.4%和3.4%;从能量耗散角度分析发现,硬质合金微槽车刀切削区平均温度低于原车刀,且理论计算和实验分析结果与仿真结果一致。研究结果为硬质合金微槽车刀的深入研究提供了理论支持,为其它类似金属加工过程中切削能量的对比研究提供了有效的参考。     

Adiabatic shear fracture prediction in high-speed cutting at various negative rake angles and feeds

The critical characteristics of adiabatic shear fracture (ASF) that induce the formation of isolated segment chip in high-speed machining was further investigated. Based on the saturation limit theory, combining with the stress and deformation conditions and the modified Johnson-Cook constitutive relation, the theoretical prediction model of ASF was established. The predicted critical cutting speeds of ASF in high-speed machining of a hardened carbon steel and a stainless steel were verified through the chip morphology observations at various negative rake angles and feeds. The influences of the cutting parameters and thermal-mechanical variables on the occurrence of ASF were discussed. It was concluded that the critical cutting speed of ASF in the hardened carbon steel was higher than that in the stainless steel under a larger feed and a lower negative rake angle. The proposed prediction model of ASF could predict reasonable results in a wide cutting speed range, facilitating the engineering applications in high-speed cutting operations. The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-018-0212-2