金属切削加工中航空铝合金板材的本构模型

针对金属切削加工中材料的高温度、高应变、高应变率数据难以获取,无法建立动态本构模型这一技术难题,提出基于有限元模拟和"单因素"流动应力公式计算的联合建模策略.由"单因素"流动应力公式反复计算与模拟应变率对应的流动应力,基于新的流动应力有限元模拟迭代的进行并追求模拟值与实验结果的一致,获取能反映切削材料力学性能的"三高"数据和流动应力数据.数据分析表明,应变率对流动应力具有强化作用,温度对流动应力具有弱化作用,稳态变形后,各应力-应变曲线都变为一条趋于与应变坐标轴平行的直线.根据影响规律选取Zerilli-Armstrong经验模型,采用非线性回归分析建立起航空铝合金板材在铣削加工中的动态本构模型.最后进行实验验证,证明了该本构模型的正确性.     

镍铝青铜切削加工本构模型参数辨识（英文）

镍铝青铜材料因具有较高的强度、耐磨损及优异的抗应力腐蚀特性而广泛用于螺旋桨的制造中。为了建立其在高应变率条件下的本构关系,提出一种切削加工过程中Johnson-Cook模型参数辨识的新方法。该方法综合了SHPB动态压缩实验、可预测切削力模型及直角切削实验。首先,根据SHPB实验得到镍铝青铜在不同应变率和温度下的真实流变应力-应变曲线;然后,建立关于预测流变应力和实验流变应力的目标函数,将SHPB实验辨识的本构参数作为初值,采用PSO算法反演得到最终的本构参数;最后,对可预测切削力模型和有限元仿真获得的切削力进行对比,验证了所辨识参数的准确性。     

纯铁在高应变率下的流动应力特征及其动态塑性本构关系

利用MTS材料试验机和分离式Hopkinson压杆实验装置,对锻造后经930℃下退火2h的纯铁材料进行压缩实验,测定纯铁在准静态条件(10-3s-1~100s-1)和高应变率(650s-1~8500s-1)下的应力-应变曲线。实验结果表明,纯铁是应变率敏感材料,纯铁在高应变率条件下,具有应变率增强、增塑以及应变强化效应,高应变率下的塑性变形过程中产生的绝热升温对材料具有热软化作用。基于Johnson-Cook(J-C)本构模型,引入绝热温升软化项对模型进行修正,通过实验数据拟合得到了纯铁的动态塑性本构关系,模型计算结果和实验结果证明,该模型可以较好地预测纯铁在高应变率下的塑性流动应力。     

考虑高温再结晶Ti-6Al-4V合金的修正J-C本构模型

为了研究Ti-6Al-4V合金在高速切削下的真实流动应力-应变关系,针对当温度达到临界变化温度时,材料的流动应力会突然下降这一现象,建立了一种修正Johnson-Cook（J-C）本构方程。修正的J-C本构关系能够准确地描述加工温度范围内再结晶软化机制对材料流动应力的影响,预测结果与试验数据吻合良好,特别是在高温阶段,流动应力计算值与试验值误差在4%以内,正确地反映了Ti-6Al-4V合金各个温度下的真实流动应力变化。结果表明,修正后的J-C本构方程可以用于研究分析Ti-6Al-4V合金的流动应力特征与规律。     

基于Deform-2D的TC4合金的J-C模型参数优化选择

为了更加准确地了解TC4合金在切削过程中所发生的一系列变化,对3组TC4合金的J-C模型参数分别在传统和高速切削条件下进行仿真。通过将切屑形状以及切削力与实验结果进行对比,并进行迭代计算,对摩擦因数和材料的失效参数进行修正,并且将3组参数得到的仿真结果与实验结果进行比较,最终确定一组最佳本构模型参数。在传统切削和高速切削下,该组本构模型参数所得到的仿真结果在切屑形状和主切削力的精度上均占有绝对优势。研究结果为TC4合金材料的切削仿真提供了更为可靠的理论依据。     

再结晶软化效应对Ti-6Al-4V修正本构的影响

通过对分离式霍普金森压杆实验应力-应变数据的分析,考虑到再结晶软化效应对材料本构的影响情况,建立了J-C修正本构模型,该模型用2个表达式来表示不同临界应变值区间材料本构的特点;利用增量法建模,屈服服从Huber-Mises准则,应力更新采用径向回退法,使用Fortran语言编写了基于AdvantEdge FEM的子程序。通过对2种本构及高速铣削实验数据的分析与比较,证明了在表现高速切削Ti-6Al-4V合金的切屑形态时,修正J-C本构比J-C本构更适用。     

316LN高温热变形行为与热加工图研究

通过Gleeble热模拟实验机在1000~1200℃,应变速率为0.01~10 s~(-1)条件下的近等温热模拟压缩实验,建立了316LN双曲正弦的流动应力预测模型及其热加工图。该流动应力预测模型考虑了实验过程中塑性变形和摩擦引起的温升,对流动应力进行了修正,考虑应变对流动应力预测模型参数的影响,获得了统一流动应力预测模型,模型预测值与实验值的相关系数为0.992,平均相对误差为4.43%;热加工图基于Prasad动态材料模型分别获得了不同应变速率、温度条件下的能量耗散率和失稳系数;分析了应变量、温度和应变速率对于能量耗散率和失稳系数的影响。结果表明:实验条件下最大能量耗散率值为0.38,且高应变速率下失稳,并通过显微组织分析对热加工图进行了验证。     

TC4钛合金切削过程显微结构变化的研究

基于有限元仿真,研究了在干切削和低温冷却条件下切削TC4合金过程中零件加工表面微结构的变化。通过运用用户自定义的材料属性的程序,对材料的本构模型、在不同切削条件下微结构变化的特征,以及在切削过程中流动应力的变化进行定义,使得材料的流动应力在切削过程中可以根据实际的计算结果进行随时更新。通过实验的比较,证实了仿真结果的正确性。     

基于正交切削理论的航空钛合金切削加工本构模型构建

为弥补现有航空钛合金切削加工本构模型研究的不足,提出基于正交切削理论的材料本构模型构建方法。根据正交切削理论建立剪切区内应力、应变、应变率、温度以及二维切削力的数学模型,开发以剪切区长度和厚度比值为迭代变量的建模技术,结合动态压缩力学性能实验(SHPB实验)和直角铣削实验,通过对各变形参数的数学求解,建立航空钛合金切削加工本构模型。在此基础上,进行材料本构模型的分析和实验验证。结果表明:航空钛合金材料在切削加工中具有明显的应变硬化特性、温度敏感特性和应变率敏感特性;钛合金随着应变率的增大,流动应力的增量逐渐减小,材料的应变率敏感性降低。     

基于应变影响的7A09铝合金等温压缩流动应力模型

在Gleeble-1500型热模拟压缩机上研究7A09铝合金在温度为633~733 K、应变速率为0.01～10.0s-1、最大变形程度为60%条件下的高温流动行为;基于7A09铝合金高温压缩时的流动应力特征,建立反映应变影响的7A09铝合金流动应力模型.结果表明:随着变形温度的升高和应变速率的降低,合金的流动应力显著降低;当应变超过一定值后,随着应变的增加,高、低应变速率下合金的流动应力变化趋势不同;建立的流动应力模型的计算值与实验值之间的最大误差为7.77%,平均误差为2.69%;与不考虑应变影响的流动应力模型相比,该模型的拟合精度高,能较好地描述7A09铝合金高温变形过程中的流动行为,为铝合金高温变形过程的数值模拟奠定了较好的基础.     

Influence of the stress,strain, and temperature on the surface roughness of an AlSl 52100 steel due to an orthogonal cut

In recent years, the finite element method (FEM) has become the main tool for simulating the metal cutting process because research based on trial and error is time consuming and requires high investment. Early studies were done by different investigators. In this research AISI 52100, hardened steel (62 HRC) was selected for an orthogonal machining process as well as metal cutting simulation using the software DEFORM-2D. This software is based on a forging process and has been adapted to an orthogonal machining process. The results of simulated cutting forces were compared with experimental cutting force data to validate the orthogonal cut simulation. Also, the surface roughness was measured, and the influence of the stress, strain, and temperature on the surface roughness was studied.     

Analysis of orthogonal finish machining using tungsten carbide and diamond tools of different heat transfer coefficients

An orthogonal cutting model for finish machining, using diamond and tungsten carbide tools which have different coeffficients of thermal conductivity, was simulated and analyzed. It was assumed that the tool had a minute amount of tool flank wear. The distribution of strain rate and stress within the machined workpiece and the determination of the cutting force were obtained after simulation. The generation and distribution of temperature and stress within the chip through cutting of the workpiece were also acquired. In addition, the temperature of the tool, the workpiece and the chip during finish machining by the two different tools, that show the effects of the different friction coefficients of the diamond tool and the tungsten carbide tool on cutting, were compared. Finally, the cutting forces predicted by the model for orthogonal finish machining were compared with those obtained by experiment, and it appears that the present orthogonal finish machining model is reasonable.     

A Hybrid Cutting Force Model for High-speed Milling of Titanium Alloys

In this paper, the Johnson-Cook (JC) strength model is used to describe the flow stress of Ti6AI4V and to estimate two important parameters in Oxley's model: the strain-rate constant and the angle made by the resultant force and the shear plane. The JC model is also incorporated into a finite element method (FEM) simulation for the deformation process of T16AI4V. Finally, a hybrid cutting force model based on the FEM simulation and Oxley's theory is proposed to predict cutting forces when machining Ti6AI4V. Experimental results are found to substantiate the developed model.     

Milling force prediction using a dynamic shear length model

Modelling of cutting forces in milling is often needed in machining automation. In this paper, a new method for the determination of the cutting forces in face milling is presented, which applies a predictive machining theory originally developed for orthogonal cutting to milling operations, with a dynamic shear length model developed and incorporated. The proposed dynamic shear length model is developed based on the analysis for the true tooth trajectories of a milling cutter, taking into account of the characteristic wavy surface effects in milling. The prediction for the cutting forces is carried out at each step of the angular increment of cutter rotation from input data of fundamental workpiece material properties, tool geometry and cutting conditions. Cutting forces at a cutter tooth can be predicted once the shear angle, shear length, shear plane area, and the shear flow stress along the shear length have been determined. The milling force prediction using the dynamic shear length model is verified through milling experimental tests. The sensitivity of the difference between the static and dynamic shear length models with respect to the feed per tooth and the cutter diameter is discussed.     

Simulation of 3D chip shaping of aluminum alloy 7075 in milling processes

By adopting an equivalent geometry model of machining process and considering thermo-plastic properties of the work material, a finite element method（FEM） to study oblique milling process of aluminum alloy with a double-edge tool was presented. In the FEM, shear flow stress was determined by material test. Re-meshing technology was used to represent chip separation process. Comparing the predicted cutting forces with the measured forces shows the 3D FEM is reasonable. Using this FEM, chip forming process and temperature distribution were predicted. Chips obtained by the 3D FEM are in spiral shape and are similar to the experimental ones. Distribution and change trend of temperature in the tool and chip indicate that contact length between tool rake face and chip is extending as tool moving forward. These results confirm the capability of FEM simulation in predicting chip flow and selecting optimal tool.     

Finite element modeling for the cutting process of the titanium alloy Ti10V2Fe3Al

By producing of critical components in the aerospace industry is widely used the β-titanium alloy Ti10V2Fe3Al (Ti-1023) due to its extremely high ratio of strength to density, its great resistance to fatigue, its excellent resistance to corrosion and fracture toughness. This material is characterized by significant difficulties in machining. Substantial assistance in the study of the titanium alloy Ti-1023 machinability can provide a simulation of machining by numerical modeling. This paper presents the results regarding the creation of the FEM models for the cutting processes of the titanium alloy Ti-1023. The created FEM cutting models were constantly verified with experimental tests of the kinetic machining characteristics and analyses of the chip morphology by orthogonal and oblique cutting as well as flat end milling with different depths of immersion. A Johnson–Cook model was used as material model of the workpiece and the damage mechanism of the workpiece is reproduced with the Cocroft and Latham model. The parameters of material and fracture model were determined by DOE study. Comparing the experimentally established and the simulated kinetic machining characteristics and chip morphology confirms that the created FEM models are of a good quality. The size of error for simulating the chip dimensions does not exceed 10 % and ranges between 10 and 30 % for simulating the resultant forces.     

Determination of workpiece flow stress and friction at the chip–tool contact for high-speed cutting

This paper presents a methodology to determine simultaneously (a) the flow stress at high deformation rates and temperatures that are encountered in the cutting zone, and (b) the friction at the chip–tool interface. This information is necessary to simulate high-speed machining using FEM based programs. A flow stress model based on process dependent parameters such as strain, strain-rate and temperature was used together with a friction model based on shear flow stress of the workpiece at the chip–tool interface. High-speed cutting experiments and process simulations were utilized to determine the unknown parameters in flow stress and friction models. This technique was applied to obtain flow stress for P20 mold steel at hardness of 30 HRC and friction data when using uncoated carbide tooling at high-speed cutting conditions. The average strain, strain-rates and temperatures were computed both in primary (shear plane) and secondary (chip–tool contact) deformation zones. The friction conditions in sticking and sliding regions at the chip–tool interface are estimated using Zorev's stress distribution model. The shear flow stress (k_chip) was also determined using computed average strain, strain-rate, and temperatures in secondary deformation zone, while the friction coefficient (μ) was estimated by minimizing the difference between predicted and measured thrust forces. By matching the measured values of the cutting forces with the predicted results from FEM simulations, an expression for workpiece flow stress and the unknown friction parameters at the chip–tool contact were determined.     

Determination of flow stress properties of machinable materials with help of simple compression and orthogonal machining test

This paper describes a possible method for predicting values of orthogonal metal cutting properties such as shear angle, cutting force etc., on a basis of the well known Hollomon equation, using a simple compression test in order to avoid any cutting experiments. There are two possibilities: the flow stress properties can be obtained from an independent material test; or by measuring the active and passive cutting forces from the orthogonal machining test itself. This paper is concerned with a material flow stress equation, including the effects of strain (ε), strain rate ( ) and temperature (T), which is one of the five equations that have to be solved in simulation analysis with the finite element method. In finding a solution for those five equations, it is necessary to dispose of flow stress properties by rearrangement of the Hollomon equation and so making it usable for cutting process investigation. The rearrangement is described in this paper.     

The prediction of cutting force in ball-end milling

Due to the development of CNC machining centers and automatic programming software, the ball-end milling have become the most widely used machining process for sculptured surfaces. In this study, the ball-end milling process has been analysed, and its cutting force model has been developed to predict the instantaneous cutting force on given machining conditions. The development of the model is based on the analysis of cutting geometry of the ball-end mill with plane rake faces. A cutting edge of the ball-end mill was considered as a series of infinitesimal elements, and the geometry of a cutting edge element was analysed to calculate the necessary parameters for its oblique cutting process assuming that each cutting edge was straight. The oblique cutting process in the small cutting edge element has been analysed as an orthogonal cutting process in the plane containing the cutting velocity and chip flow vectors. And with the orthogonal cutting data obtained from end turning tests on thin-walled tubes over wide range of cutting and tooling conditions, the cutting forces of ball-end milling could be predicted using the model. The predicted cutting forces have shown a fairly good agreement with test results in various machining modes.     

Modeling of cutting forces in near dry machining under tool wear effect

A predictive model for the cutting forces in near dry machining, in which only a small amount of cutting fluid is used, is developed based on considerations of both the lubricating effect and the cooling effect. For the lubricating effect, with the material properties, lubricating parameters, and cutting conditions, the friction coefficient in near dry machining is calculated based on the boundary lubrication model for use in a modified Oxley's approach to determine the cutting forces. For the cooling effect in near dry machining, a moving heat source method is pursued to quantify the primary-zone shear deformation heating, the secondary-zone friction heating, and flank face air–oil mixture cooling. These two effects are considered collectively to estimate cutting forces under the condition of sharp tools. The predicted variables of flow stress, contact length, and shear angle obtained from the model are used to predict the cutting forces due to the tool flank wear effect based on Waldorf's model. Comparisons are made between predicted and experimental cutting forces for sharp tools and worn tools in the cutting of AISI 1045 with uncoated carbide tools. The results show that the proposed model provides average prediction errors of 14% in the tangential cutting force direction, 21% in the axial directions, and 30% in the radial directions within the experimental test condition range (cutting speeds of 45.75–137.25 m/min, feeds 0.0508–0.1016 mm/rev, and depth of cuts 0.508–1.016 mm). It is also found that the cutting forces in near dry machining are generally lower than those under dry machining condition. Under cutting speeds of 91.5 and 137.25 m/min, the deviations of the predicted forces between near dry machining and dry machining range from 5% to 39% for axial cutting forces, 3% to 36% for radial cutting forces, and 1% to 32% for tangential cutting forces. It suggests that the lubricating mechanism has a stronger effect on cutting forces than the cooling mechanism when cutting AISI 1045 with uncoated carbide tools.