Finite element modeling of ultrasonic-assisted turning: cutting force and heat generation

Abstract

Adding ultrasonic vibrations to conventional turning can improve the process in terms of cutting force, surface finish and so on. One of the most important factors in machining is the heat generation during the cutting process. In ultrasonic-assisted turning (UAT) the tool tip also vibrates at very high frequency and this sinusoidal motion causes complexity in heat modeling of the cutting system. Modeling and simulation of cutting processes can help to understand the nature of process and provides information to select optimum conditions and machining parameters. In this article, a finite element model has been developed for predicting tool tip temperature in UAT. The effect of machining parameters including cutting speed, feed rate and amplitude of vibration on the tool tip temperature has been investigated. In order to simplify the machining process, the cutting experiment has been carried out in dry condition. The results showed that by applying ultrasonic vibration to the cutting tool, the tool tip flash temperature increases but in some condition its average value could be less than the conventional machining.     

超声振动精密切削振幅对工件尺寸误差的影响

精密超声振动切削是将一定振幅的高频振动添加到刀具的运动过程中的一种加工方式,具有切削力小,加工精度高,加工表面质量好等特点。采用动力学分析方法利用二自由度的振动切削工件-刀具系统模型,并借鉴普通切削中对切削力的分析方法,首次从理论上实现了对振动切削中刀具振幅对工件变形影响的研究,并采用数值模拟的方法给出它的变化规律:在精密振动切削使用的振幅范围内,刀具振幅的变大会使工件的净位移减小、进而使工件的尺寸误差减小。同时,给出了不同刀具前角、切削速度和切削深度条件下,工件尺寸误差随振幅变化的规律。     

Tool wear prediction of machining hydrogenated titanium alloy Ti6Al4V with uncoated carbide tools

Tool wear is a problem in the turning of titanium alloy, and it is thus of great importance to understand and quantitatively predict tool wear and tool life. In this paper, a combined tool wear model including abrasive, adhesion, and diffusion wear has been implemented in a commercial finite element (FE) code to predict tool wear. Many key problems in tool wear simulation are presented and discussed such as temperature distribution, the updating of tool geometry, and the smoothing of wear boundary. Subsequently, a finite element method wear prediction model is built, and the results are compared with the experimental value; a good agreement was found. Simulated results showed that cutting force will decrease first and then increase with the increase of the concentration of hydrogen, while tool life varies in the opposite way; therefore, the optimum value of hydrogen content is about 0.3 %. The addition of 0.3 % hydrogen could improve tool life greatly, and its tool life is more than three times that of the as-received material. The hydrogenation process's favorable effect is limited by cutting parameters and cooling conditions. According to the numerical results, an appropriate machining speed and higher feed is the selection criterion for high-efficiency machining of hydrogenated titanium alloy. Furthermore, a reasonable range of cutting parameters is found; the cutting speed is in the range of 50–100 m/min, and the feed is in 0.15–0.25 mm/rev.     

Finite element modeling of 3D turning of titanium

The finite element modeling and experimental validation of 3D turning of grade two commercially pure titanium are presented. The Third Wave AdvantEdge machining simulation software is applied for the finite element modeling. Machining experiments are conducted. The measured cutting forces and chip thickness are compared to finite element modeling results with good agreement. The effects of cutting speed, a limiting factor for productivity in titanium machining, depth of cut, and tool cutting edge radius on the peak tool temperature are investigated. This study explores the use of 3D finite element modeling to study the chip curl. Reasonable agreement is observed under turning with small depth of cut. The chip segmentation with shear band formation during the Ti machining process is investigated. The spacing between shear bands in the Ti chip is comparable with experimental measurements. Results of this research help to guide the design of new cutting tool materials and coatings and the studies of chip formation to further advance the productivity of titanium machining.     

Finite element simulation and experimental investigation of tool temperature during ultrasonically assisted turning of aerospace aluminum using multicoated carbide inserts

This paper summarizes the results of thermal finite element simulation and experimental studies of tool temperature in ultrasonic-assisted turning (UAT) of aerospace aluminum using multicoated carbide inserts. At first, mathematical models were developed in order to study the effects of tool coating, rake angle, cutting speed, and feed rate on the friction coefficient. Then with respect to the kinematics of the process, the cutting velocity model would be presented. This velocity model is used in combination with the mathematical model to define the friction coefficient during UAT. The mentioned frictional model is used to write a user subroutine to incorporate the effect of friction coefficient as a function of cutting parameters in the finite element program Abaqus. The results of this simulation make it possible to determine cutting temperature patterns accurately. It is also used to study the effect of cutting parameters (cutting speed, feed rate, rake angle, and vibration amplitude) on UAT. Finally, the simulation results are compared with experimental measurements of cutting temperatures from ultrasonic-assisted turning tests. The results show that ultrasonic-assisted turning is able to lower the maximum cutting temperature in cutting tool, about 29 %, in low feed rates (≈0.14 mm/rev), with a vibration amplitude of ≈10 μm and work velocity of ≈0.5 m/s.     

振动频率对超声辅助切削的影响

对超声辅助切削而言,刀具振动频率是一项至关重要的影响因子。本文从理论上分析了刀具振动频率对超声切削的影响,并利用有限元软件MSC.Marc建立了超声切削的二维正交热力耦合模型,通过有限元仿真研究了刀具振动频率对切削应力和切削温度的影响规律。     

Design and experimental results of a tunable vibration turning device operating at ultrasonic frequencies

The development of a tunable ultrasonic vibration-assisted diamond-turning tool is described. The resonance operation method, which formerly served to achieve mechanical motion at ultrasonic frequencies, is now replaced by a newly developed pulse driving technique. The prototype tools allow for vibration frequencies from dc up to 40 kHz and vibration amplitudes from 0 to 10 μm. This paper reviews the design of the new tool system and summarizes the experimental results from diamond turning steel work materials. As in other studies on vibration-assisted machining, the results show that the surface turned with a vibrating tool contains scalloped geometric features superimposed on the tool marks left from conventional turning, resulting in a lower total surface roughness. Tool wear comparisons document advantages from the added vibration, and variations in the carbon content in the resulting chips were also examined.     

SiC陶瓷旋转超声振动套磨制孔有限元仿真及实验研究

为解决SiC陶瓷加工时容易出现崩边、裂纹等问题,结合仿真与实验对其进行旋转超声振动套磨制孔技术研究。根据SiC陶瓷宏观力学本构模型,建立SiC陶瓷制孔仿真有限元模型并进行加工过程仿真分析,相比常规制孔,超声振动制孔的仿真轴向力最大可减小26.1%。常规加工和超声振动加工的对比实验研究表明,旋转超声振动加工可减小轴向力达32.9%,可大幅减少陶瓷材料脆性断裂,显著改善孔壁表面质量。有限元仿真与实验研究所得的轴向力在超声振动下最大相差7.5%,常规条件下两者最大相差14%,验证了有限元模型的正确性。仿真和实验研究结果表明：超声振动加工可显著减小轴向力和刀具磨损、提高刀具耐用度、改善制孔质量、降低加工成本。     

Vibration-resistant interference microscope with assistant focusing for on-machine measurement of surface topography

The interference microscope is a powerful tool for surface topography measurement, but its high sensitivity to vibration hinders its application to on-machine use. To measure surface roughness on a machine for the ultra-precision machining, a vibration-resistant interference microscope (VRIM) with an assistant focusing function is developed. The basic principle of VRIM is an error-compensated phase-shifting interferometry. An iterative algorithm is presented to calculate the surface phase with the phase shift amounts as unknown variables, where the phase shift amounts are calculated and compensated with least-squares method. A narrow bandwidth illumination is employed to alleviate coherence envelop influence, and a simplified intensity model is established to decouple the variables. Assisting the microscope to find fringe quickly, the focusing is realized by introducing an off-axis thin beam to generate two spots, of which their relative position relates to the defocus. The focusing method is directional and determinant, and has a large range up to 0.3 mm. In the vibration disturbances of 0.2 μm and 0.4 μm amplitudes over 0 Hz to 20 Hz frequency region, the roughness accuracy and repeatability of measuring an ultra-precision machined surface are both up to the sub-nanometer level. The developed instrument is applied to a single-point diamond turning machine and achieves a sub-nanometer accuracy and repeatability.     

Modeling subsurface deformation induced by machining of Inconel 718

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.     

Stress Analyses of CBN Insert in Hybrid Machining of RBSN Ceramic

This article investigates the significant improvement in cutting tool life in machining of Reaction Bonded Silicone Nitride (RBSN), using cryogenic coolant. A finite element model is developed to analyze stress distributions in the Cubic Boron Nitride (CBN) cutting inserts used in a hybrid turning process. The analysis reveals that the decrease in cutting tool temperature caused by cryogenic cooling leads to a decrease of stresses in the cutting tool, especially when micro-cracks are present. It is found that a decrease in temperature from 1740 to 788°C leads to approximately 56% stress reduction at the flank face of the cutting tool.     

Suppression of notch wear of a whisker reinforced ceramic tool in air-jet-assisted high-speed machining of Inconel 718

This paper describes the notch and flank wear specific to a SiC whisker reinforced alumina tool in air jet assisted (AJA) turning of nickel-base superalloy Inconel 718 at high cutting speeds. An AJA machining experiment has revealed that the air jet applied to the tool tip in addition to coolant dramatically reduces the depth-of-cut notch wear. As a result, the width of flank wear, but not the size of notch wear, determined the life of a ceramic tool in AJA machining of Inconel 718. This is a reason for the large extension and small variation of the tool life when high speed AJA machining is adopted. The maximum tool life length reached 2160 m at a cutting speed of 660 m/min under the given cutting conditions. Finally, the mechanisms of the notch and flank wear of a SiC whisker reinforced alumina tool in AJA machining are discussed from the viewpoints of tribochemical reactions and tool wear anisotropy.     

Multi-objective optimization of oblique turning operations using finite element model and genetic algorithm

Multi-objective optimization of oblique turning operations while machining AISI H13 tool steel has been carried out using developed finite element (FE) model and multi-objective genetic algorithm (MOGA-II). The turning operation is optimized in terms of cutting force and temperature with constraints on required material removal rate and cutting power. The developed FE model is capable to simulate cutting forces, temperature and stress distributions, and chip morphology. The tool is modeled as a rigid body, whereas the workpiece is considered as elastic–thermoplastic with strain rate sensitivity and thermal softening effect. The effects of cutting speed, feed rate, rake angle, and inclination angle are modeled and compared with experimental findings. FE model is run with different parameters with central composite design used to develop a response surface model (RSM). The developed RSM is used as a solver for the MOGA-II. The optimal processing parameters are validated using FE model and experiments.     

TX1600镗铣加工中心立柱动态特性分析

用Sofidworks软件建立三维实体模型,在三维实体模型的基础上建立了TX1600镗铣加工中心立柱模态分析的有限元模型,用ANSYS有限元分析软件对它进行模态分析,通过求解得出前4阶固有频率和相应的主振型。为了解各阶频率对结构动载荷的响应情况,论文还将对TX1600数控加工中心立柱进行谐响应分析,结果得出数控中在受外部激振力下的动态响应特性,并在此基础上指出了机床存在的不足。     

FINITE ELEMENT ANALYSIS FOR CHIP FORMATION IN HIGH SPEED TURNING OPERATIONS BY ARBITRARY LAGRANGIAN EULERIAN METHOD

A two-dimensional finite element (FE) model for the high speed turning operations when orthogonally machining AISI H13 tool steel at 49HRC using poly crystalline cubic boron nitride (PCBN) is described. An arbitrary Lagrangian Eulerian (ALE) method has been adopted which does not need any chip separation criteria as opposed to the traditional Lagrangian approach. Through FE simulations temperature and stresses distributions are presented that could be helpful in predicting tool life and improving process parameters. The results show that high temperatures are generated along the tool rake face as compared to the shear zone temperatures due to high thermal conductivity of PCBN tools.     

Analytical prediction of cutting tool wear

An analytical method is presented which enables the crater and flank wear of tungsten carbide tools to be predicted for a wide variety of tool shapes and cutting conditions in practical turning operations based only on orthogonal cutting data from machining and two wear characteristic constants. A wear characteristic equation is first derived theoretically and verified experimentally. An energy method is developed to predict chip formation and cutting forces in turning with a single-point tool from the orthogonal cutting data. Using these predicted results, stress and temperature on the wear faces can be calculated. Computer simulation of the development of wear is then carried out by using the characteristic equation and the predicted stresses and temperatures upon the wear faces. The predicted wear progress and tool life are in good agreement with experimental results.     

The cutting tool stresses in finish turning of hardened steel with mixed ceramic tool

Precision hard machining is an interesting topic in manufacturing die and mold, automobile parts, and scientific research. While the hard machining has benefit advantages such as short cutting cycle time, process flexibility, and low surface roughness, there are several disadvantages such as high tooling cost, need of rigid machine tool, high cutting stresses, and residual stresses. Especially, tool stresses should be understood and dealt with to achieve successful performance of finish hard turning with ceramic cutting tool. So, the influence of cutting parameters on cutting stresses during dry finish turning of hardened (52 HRC) AISI H13 hot work steel with ceramic tool is investigated in this paper. For this aim, a series finish turning tests were performed, and the cutting forces were measured in tests. After literature procedure about finite element model (FEM), FEM is established to predict cutting stresses in finish turning of hardened AISI H13 steel with Ceramic 650 grade insert. As shown, effect of the cutting parameters on cutting tool stresses in finish turning of AISI H13 steel is obtained. The suggested results are helpful for optimizing the cutting parameters and decreasing the tool failure in finish turning applications of hardened steel.     

Precision radial turning of AISI D2 steel

This paper compares finite element model (FEM) simulations with experimental and analytical findings concerning precision radial turning of AISI D2 steel. FEM machining simulation employs a Lagrangian finite element-based machining model applied to predict cutting and thrust forces, cutting temperature and plastic strain distribution. The results show that the difference between the experimental and simulated cutting force is near 20%, irrespectively of the friction coefficient used in the simulation work (approximately 19.8% for a friction of 0.25% and 18.4% for the Coulomb approach). Concerning the thrust force, differences of about 22.4% when using a friction coefficient of μ?=?0.25 and about 56.9% when using the Coulomb friction coefficient (μ?=?0.378) were found. The maximum cutting temperature obtained using the analytical model is 494.07°C and the difference between experimentation and simulation methods is 15.2% when using a friction coefficient of 0.25 and when using the Coulomb friction only 3.1%. Regarding the plastic strain, the differences between analytical calculations and FEM simulations (for the presented friction values) suggest that the finite element method is capable of predictions with reasonable precision.     

超声振动铣削加工参数对切削力的影响

为了改善传统铣削钛合金的加工条件,研究了进给方向超声振动辅助铣削对切削力的影响。定值计算了不同振动频率、振幅、铣削速度时的净切削时间比,建立了对工件施加超声振动的铣削加工三维有限元模型,根据仿真结果讨论了加工参数对进给方向切削力瞬时值的影响,并结合净切削时间比分析了加工参数对三个方向切削力平均值的影响。研究表明:施加超声振动后切削力明显减小;振动频率小于40kHz和振幅小于30μm时切削力平均值同净切削时间比变化趋势一致,当频率或振幅超过上述值时,刀具、工件间的摩擦力对切削力平均值的影响显著。     

Theoretical and experimental study of the chatter vibration in wet and MQL machining conditions in turning process

Turning is one of the most commonly used cutting processes for manufacturing components in production engineering. The turning process, in some cases, is accompanied by intense relative movements between tool and workpiece, which is called chatter vibrations. Chatter has been identified as a detrimental problem that adversely impacts surface finish, tool life, process productivity, and dimensional accuracy of the machined part. Cooling/Lubrication in the turning process is normally done for some reasons, including friction and force reduction, temperature decrement, and surface finish improvement. Wet cooling is a traditional cooling/lubrication process that has been used in machining since the past. Besides, a variety of new cooling and lubricating approaches have been developed in recent years, such as the minimum quantity lubrication (MQL), cryogenic cooling, nanolubrication, etc., due to ecological issues. Despite the importance of cooling/lubrication in machining, there is a lack of research on chatter stability in the presence of cutting fluid in cutting processes. In this study, the chatter vibration in turning process for two cooling/lubrication conditions of conventional wet and MQL is investigated. An integrated theoretical model is used to predict both the metal cutting force and the chatter stability lobe diagram (SLD) in turning process. This model involves deriving a math equation for predicting metal cutting force for both wet and MQL conditions using experimental training force data and a Genetic Expression Programming (GEP)-based regression model. Also, the traditional single degree of freedom chatter model is used here for predicting the SLDs. The chatter model is discussed and verified with experimental tests. Then, the experimental results of the tool's acceleration signal, work surface texture, surface roughness, chip shape, and tool wear are presented and compared for wet and MQL conditions. The results of this study show that the cooling/lubrication systems such as wet or MQL have a considerable effect on the SLDs. Also, the predicted results of metal cutting force and SLD for both wet and MQL techniques are in good agreement with the experimental data. Therefore, it is recommended that for each lubrication condition including wet, or MQL, the SLD be determined to achieve higher machinability.