铣削加工对铝合金薄壁件残余应力的影响

研究了铣削加工对铝合金薄壁件残余应力的影响。在有限元软件MSC.MARC中建立了三维有限元模型,通过二次开发,编制了相应的子程序,分别用来向有限元模型中添加初始残余应力场,对节点施加铣削力,控制铣削路径和对模型的网格进行自适应细化,使用该模型进行薄壁零件的铣削仿真。结果表明:随着铣削的进行,试件余料内部应力不断释放,应力场出现重分布。通过比较不同铣削深度时的应力分布情况,得到了铣削加工对薄壁零件残余应力的影响规律。     

2024铝合金铣削加工表面残余应力仿真研究

为了研究不同的铣削参数对2024铝合金铣削过程中铣削加工表面残余应力的影响,采用有限元仿真与试验验证结合的方法,利用有限元建立2D铣削仿真模型,研究铣削过程中切削表面残余应力随切削参数的变化,并在相同的切削参数下进行铣削试验测量切削表面残余应力,采用正交试验和单因素试验对铣削参数进行优化。结果表明,有限元仿真的结果与试验的结果数据相近,验证了有限元模型的准确性,通过正交试验选出最优的铣削工艺参数为切削速度500m/min、每齿进给量0.05mm/z、铣削宽度10mm、铣削深度0.5mm;在切削2024铝合金时,在不影响生产的条件下,采用较低的切削速度,较低的进给量、铣削深度和铣削宽度,得到的表面残余应力值较小。     

钛合金拉伸铣削的机理与试验研究

对钛合金TC4(Ti6Al4V)在拉伸状态下进行铣削加工.建立平面应变的残余应力形成模型,分析了拉伸装夹改变加工表层残余应力的机理.研究了铣削对钛合金表面残余应力和表面粗糙度的影响,得到了在不同切削参数下钛合金表面残余应力和表面粗糙度的实验数据.实验结果表明,拉伸装夹基本不影响表面粗糙度,但可以大大提高加工表面残余压应力并增大残余压应力层的厚度.     

基于ABAQUS的航空叶轮铣削变形机理研究

高速铣削制造航空整体叶轮时,叶轮叶片的变形问题是影响叶轮加工精度的主要原因。而铣削过程中的铣削力、切削热、残余应力则是导致叶片变形的直接因素。为了探究叶片的变形机理,基于叶片的几何特征和加工工况,提出了将叶轮叶片简化为悬臂梁结构的分析方法,同时采用有限元分析软件ABAQUS建立反映叶片铣削过程高温、高应变率状态的铣削模型,模拟分析不同铣削参数下整体立铣刀铣削航空铝合金7075-T7451叶片的过程。叶片铣削模拟过程揭示了铣削速度、每齿进给量、径向铣削深度三个主要铣削参数对铣削力、切削热、叶片表面残余应力的影响,为制造整体叶轮时加工参数的选取、加工变形及震颤控制提供依据。     

钛合金高速铣削加工表面残余应力的模拟研究

采用有限元法建立了更接近实际的铣刀结构模型及三维铣削模型,对不同刀具参数和切削参数条件下高速铣削钛合金Ti6Al4V的表面残余应力进行了仿真分析,得到了各因素对表面残余应力分布的影响规律。结果表明:工件的残余应力在表层由拉应力迅速的转变为压应力,在100~200μm之间出现残余压应力的最大值。工件表层残余应力随刀具前角、切削速度和每齿进给量的增加而减小,切削深度对表层残余应力的影响不是很明显。     

高温合金GH4169球头刀铣削表面完整性测试实验研究

利用球头铣刀对高温合金GH4169试件进行铣削加工,并对其加工表面完整性指标进行检测。结果表明：在选取的实验参数条件下,线速度vc对于表面粗糙度Ra、表面显微硬度和加工表面残余应力等表面完整性指标的影响不明显;表面粗糙度Ra和加工表面显微硬度会随着切深ap和每齿进给量fz的增大而增大;高温合金GH4169球头刀铣削加工后的表面残余应力σH呈现为拉应力状态,范围为219.3~338.9 MPa;残余拉应力随着切深ap和每齿进给量fz的增大而减小,原因是随着切深ap和每齿进给量fz的增大,加工表面的塑性变形程度逐渐增加。     

Ti6Al4V零件铣削加工表面等效残余应力与作用深度的测量

为了预测Ti6Al4V零件因铣削加工所致表面残余应力而引起的变形,介绍了一种测量表面等效残余应力及其作用深度的方法。通过对被加工面的背面进行两次腐蚀剥层的操作,使得零件的厚度和中性层的位置发生变化,测量此过程中零件挠度和表面应变的变化,进而计算得到铣削加工引起的零件表面等效残余应力及其作用深度值。通过有限元分析验证,发现有限元计算得到的零件挠度和应变的变化与实际测量值非常吻合,因此可以断定该方法得到的结果是正确的。其可以正确评估铣削加工引起的表面残余应力性质和大小并能准确预测零件铣削加工后因表面残余应力而引起的工件的变形量,从而可以预测零件是否满足精度要求。     

钛合金铣削加工表面残余应力有限元仿真

为了分析铣削工艺参数对钛合金已加工表面残余应力的影响,根据金属切削有限元分析的相关理论,以钛合金Ti6Al4V为工件材料,建立了铣削加工的有限元模型。采用正交试验设计法对钛合金Ti6Al4V铣削仿真的工艺参数进行优化,并用极差法分析不同的铣削速度、铣削深度、铣削路径对钛合金Ti6Al4V工已加工表面残余应力的影响。研究表明:在钛合金Ti6Al4V铣削过程中,对工件已加工表面残余应力影响因素由小到大依次为:铣削深度<铣削路径<铣削速度,切削深度对已加工表面残余应力影响较小,铣削速度对已加工表面残余应力影响最大;在研究范围内,随着铣削速度的增大,已加工表面残余应力逐渐增加。     

数控高速铣齿加工过程的有限元法仿真研究

在预先获得工件材料特性参数的基础上,并根据铣削加工的特点,利用有限元软件Deform 3D建立了铣削加工齿轮的有限元模型,基于此模型对高速铣齿加工过程中的切削力和温度进行了有限元模拟。通过铣削力试验测得了相同加工条件下的铣削力值,与仿真结果相差较小,证明了所建有限元模型的正确性,也表明了采用此模型进行的温度的模拟结果是可信的。铣齿加工过程的有限元仿真研究为下一步铣齿加工精度的提高奠定了基础。     

2024铝合金结构件残余应力的评估与变形预测

为了研究毛坯初始残余应力和铣削加工引入的表面残余应力对2024铝合金结构件加工变形的影响,通过有限元模拟和铣削试验对两框整体梁的加工变形进行了研究。考虑了毛坯的初始残余应力、铣削加工引入的表面残余应力以及这两个影响因素的综合作用对两框整体梁加工变形的影响。研究结果表明,毛坯的初始残余应力是两框整体梁产生加工变形的主要影响因素,初始残余应力与铣削加工引入的表面残余应力的综合作用加剧了变形,其中,由初始残余应力引起的变形占整体梁总变形的92%,表面残余应力引起的变形占整体梁总变形量的8%左右。并最终通过对两框整体梁的铣削加工试验验证了有限元模拟结果的准确性,对实际生产具有一定的参考价值。     

Ti(C,N)基金属陶瓷刀具切削加工有限元模拟

介绍了本课题组研制的一种新的刀具材料--T(iC,N)基金属陶瓷的成分组成及其力学性能;基于大变形-大应变理论、增量理论以及更新拉格朗日算法、采用几何断裂分离准则,建立了二维弹塑性金属正交切削有限元模型,对金属正交切削过程进行了数值模拟;改变刀具前角,得出在不同的刀具前角下T(iC,N)基金属陶瓷刀具在正交切削过程中切削力以及刀具后刀面等效应力变化;分析了切削力、刀具表面等效应力对刀具磨损的影响;模拟结果与相关研究的实验数据吻合。本文的研究为后期研制新的刀具材料提供了理论依据,降低实验成本。     

FEA modeling and simulation of shear localized chip formation in metal cutting

The finite element analysis (FEA) has been applied to model and simulate the chip formation and the shear localization phenomena in the metal cutting process. The updated Lagrangian formulation of plane strain condition is used in this study. A strain-hardening thermal-softening material model is used to simulate shear localized chip formation. Chip formation, shear banding, cutting forces, effects of tool rake angle on both shear angle and cutting forces, maximum shear stress and plastic strain fields, and distribution of effective stress on tool rake face are predicted by the finite element model. The initiation and extension of shear banding due to material's shear instability are also simulated. FEA was also used to predict and compare materials behaviors and chip formations of different workpiece materials in metal cutting. The predictions of the finite element analysis agreed well with the experimental measurements.     

The transient beginning to machining and the transition to steady-state cutting

Knowledge of the physics behind the separation of material at the tip of the tool is of great importance for understanding the mechanisms of chip formation. How material separates along the parting line to form the chip and cut surface is still not well understood, yet it is of great importance for improving the robustness, enhancing the predictability and extending the application of currently existing finite element computer programs. This paper attempts to provide some answers to these issues by means of a combined numerical and experimental investigation of the transient beginning to machining and the transition to steady-state orthogonal metal cutting. Numerical modelling was performed by means of an updated-Lagrangian approach based on the finite element flow formulation and experiments were carried out on lead specimens under laboratory-controlled conditions. Forces and displacements are given for the initial indentation phase during which material is displaced up the rake face of the tool. Ductile damage begins to accumulate, eventually leading to separation at the tool tip. This marks the onset of a second stage during which further displacement of material along the rake face is accompanied by separation of material at the tool tip (i.e. cracking), which now continues in all subsequent deformation. The displaced material, although not yet attaining its fullest extent, now begins to take on the appearance of a continuous chip. A third stage begins when the material, which up till now has been in intimate contact with the rake face, develops curvature and leaves the tool. This does not, however, mark the beginning of steady-state cutting, because chip curl continues to increase until a steady value is attained. During this period, the contact length with the tool then reduces somewhat, before settling down to a steady value. The thrust force is a maximum at the point of greatest chip contact length. The paper demonstrates that material separation is caused by shearing rather than tension. The specific distortional energy is an appropriate criterion for evaluating ductile damage in shear and the onset of separation ahead of the cutting edge. In turn this determines the value of the fracture toughness in shear.     

An analytical finite element model for predicting three-dimensional tool forces and chip flow

A model of three-dimensional cutting is developed for predicting tool forces and the chip flow angle. The approach consists of coupling an orthogonal finite element cutting model with an analytical model of three-dimensional cutting. The finite element model is based on an Eulerian approach, which gives excellent agreement with measured tool forces and chip geometries. The analytical model was developed by Usui et al. [ASME J. Engng Indust. 100(1978) 222; 229], in which a minimum energy approach was used to determine the chip flow direction. The model developed by Usui required orthogonal cutting test data to determine the tool forces and chip flow angle. In this paper, a finite element model is used to supply the orthogonal cutting data for Usui's model. With this approach, a predictive model of three-dimensional cutting can be developed that does not require measured data as input. Cutting experiments are described in which good agreement was found between measured and predicted tool forces and chip flow angles for machining of AISI 1020 steel.     

An application of the finite element method to the prediction of cutting tool performance

In metal cutting tools the are close to the tool point is the single most important region and conditions at the tool point must be carefully examined if improvements in tool performance, through changes in tool design and material, are to be achieved. The paper describes an analysis of cutting tool performance through a determination of the stress distribution within, and at the boundaries of, the tool wedge. The stressanalysis was based on a two-dimensional model as encountered in orthogonal cutting, using a range of cutting geometries including tools with double rake angles. A finite element technique was employed which can be effectively utilised in the solution of metal cutting problems once the boundary conditions have been established. The results presented demonstrate the significance of the chosen boundary conditions to the analysis of metal cutting. Finally it is argued that the deformation of the cutting edge, especially at the clearance face under the stress field set up in the tool, may well be a determining factor in establishing tool life as based on the flank wear criterion.     

Finite element modeling of segmental chip formation in high-speed orthogonal cutting

An explicit, Lagrangian, elastic-plastic, finite element code has been modified to accommodate chip separation, segmentation, and interaction in modeling of continuous and segmented chip formation in highspeed orthogonal metal cutting process. A fracture algorithm has been implemented that simulates the separation of the chip from the workpiece and the simultaneous breakage of the chip into multiple segments. The path of chip separation and breakage is not assigned in advance but rather is controlled by the state of stress and strain induced by tool penetration. A special contact algorithm has been developed that automatically updates newly created surfaces as a result of chip separation and breakage and flags them as contact surfaces. This allows for simulation of contact between tool and newly created surfaces as well as contact between simulated chip segments. The work material is modeled as elastic/perfectly plastic, and the entire cutting process from initial tool workpiece contact to final separation of chip from workpiece is simulated. In this paper, the results of the numerical simulation of continuous and segmented chip formation in orthogonal metal cutting of material are presented in the form of chip geometry, stress, and strain contours in the critical regions.     

Prediction of tool and chip temperature in continuous and interrupted machining

In this paper, a numerical model based on the finite difference method is presented to predict tool and chip temperature fields in continuous machining and time varying milling processes. Continuous or steady state machining operations like orthogonal cutting are studied by modeling the heat transfer between the tool and chip at the tool—rake face contact zone. The shear energy created in the primary zone, the friction energy produced at the rake face—chip contact zone and the heat balance between the moving chip and stationary tool are considered. The temperature distribution is solved using the finite difference method. Later, the model is extended to milling where the cutting is interrupted and the chip thickness varies with time. The time varying chip is digitized into small elements with differential cutter rotation angles which are defined by the product of spindle speed and discrete time intervals. The temperature field in each differential element is modeled as a first-order dynamic system, whose time constant is identified based on the thermal properties of the tool and work material, and the initial temperature at the previous chip segment. The transient temperature variation is evaluated by recursively solving the first order heat transfer problem at successive chip elements. The proposed model combines the steady-state temperature prediction in continuous machining with transient temperature evaluation in interrupted cutting operations where the chip and the process change in a discontinuous manner. The mathematical models and simulation results are in satisfactory agreement with experimental temperature measurements reported in the literature.     

The influence of friction models on finite element simulations of machining

In the analysis of orthogonal cutting process using finite element (FE) simulations, predictions are greatly influenced by two major factors; a) flow stress characteristics of work material at cutting regimes and b) friction characteristics mainly at the tool-chip interface. The uncertainty of work material flow stress upon FE simulations may be low when there is a constitutive model for work material that is obtained empirically from high-strain rate and temperature deformation tests. However, the difficulty arises when one needs to implement accurate friction models for cutting simulations using a particular FE formulation. In this study, an updated Lagrangian finite element formulation is used to simulate continuous chip formation process in orthogonal cutting of low carbon free-cutting steel. Experimentally measured stress distributions on the tool rake face are utilized in developing several different friction models. The effects of tool-chip interfacial friction models on the FE simulations are investigated. The comparison results depict that the friction modeling at the tool-chip interface has significant influence on the FE simulations of machining. Specifically, variable friction models that are developed from the experimentally measured normal and frictional stresses at the tool rake face resulted in most favorable predictions. Predictions presented in this work also justify that the FE simulation technique used for orthogonal cutting process can be an accurate and viable analysis as long as flow stress behavior of the work material is valid at the machining regimes and the friction characteristics at the tool-chip interface is modeled properly.     

An FEM study on residual stresses induced by high-speed end-milling of hardened steel SKD11

Milling of Hardened steel SKD11 is usually a finishing process, therefore stable cutting process must be guaranteed at first. Residual stresses (RS) were studied in this paper with the help of finite element method (FEM) for its significant influence on the quality of machined part. A two-dimension (2D) fully thermo-mechanical coupled finite element (FE) model was employed to evaluate RS remaining in a machined component. The model was developed based on the effective rake angle and the variable undeformed chip layer. Johnson–Cook plasticity model was introduced to model the workpiece material. Coulomb friction was assumed at the tool–chip interface. Two same cutting tools were employed to model continuous feed milling process. RS profiles were obtained after the cutting and stress relaxation stages. The predicted RS profiles were in reasonable agreement with the experimental results.     

A new experimental methodology to analyse the friction behaviour at the tool-chip interface in metal cutting

This paper investigates a new test to analyse the friction behaviour of the tool-chip interface under conditions that usually appear in metal cutting. The developed test is basically an orthogonal cutting process, that was modified to a high speed forming and friction process by using an extreme negative rake angle and a very high feed. The negative rake angle suppresses chip formation and results in plastic metal flow on the tool rake face. Through the modified kinematics and in combination with a feed velocity that is five to ten times higher than in conventional metal cutting, the shear and normal stresses are only acting in a simple inclined plane, allowing to calculate the mean friction coefficient analytically. In addition, the test setup allows to obtain the coefficient of friction for different temperatures, forces and sliding velocities. Experiments showed, that the coefficient of friction is strongly dependent on the sliding velocity for the example workpiece/tool material combination of C45E+N (AISI 1045) and uncoated cemented carbide.