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。     

Implementation of a process and structure model for turning operations

The consideration of the dynamic interaction between the machine tool structure and the cutting process is a prerequisite for the simulative prediction and optimization of machining tasks. However, existing cutting force models are either dedicated to already examined manufacturing operations or require extensive measurements for the determination of cutting coefficients. In this context this paper outlines a modular, analytical cutting force model applicable to common turning processes. It takes into account the dynamic material behavior, nonlinear friction ratios on the rake face as well as heat transfer phenomena in the deformation zones. On the part of the machine tool structure a parametric model based on the Finite Element Method (FEM) is implemented. Both models are coupled for the simulation of process and structure interactions, whereas the influence of the control system is considered as well. The simulation results were verified experimentally on a turning center.     

Identification of a friction model for modelling of orthogonal cutting

Numerical approaches to high-speed machining are necessary to increase the productivity and to optimise the tool wear and the residual stresses. In order to apply such approaches, rheological behaviour of the antagonists and friction model of interfaces have to be correctly determined. The existing numerical approaches that are used with the current friction models do not lead to good correlations of the process variables, such as the cutting forces or the tool–chip contact length. This paper proposes a new approach for characterizing the friction behaviour at the tool–chip interface in the zone near the cutting edge. An experimental device is designed to simulate the friction behaviour at the tool–chip interface. During this upsetting-sliding test, an indenter rubs in a specimen with a constant speed, generating a residual friction track. Contact pressure and friction coefficient are determined from the test’s numerical model and are then used to identify the friction data according to the interface temperature and the sliding velocity. These initial findings can be further developed for implementation in FEA machining models in order to increase the productivity.     

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.     

Modeling of chip–tool interface friction to predict cutting forces in machining of Al/SiCp composites

In Al/SiCp metal matrix composites, in addition to machine, tool and process-related parameters, a change in composition (size and volume fraction of reinforcement) has a influence on machining force components. In the analytical models in the literature, the effect of abrasive reinforcement particles, which affects the coefficient of friction and consequently the friction angle, has not been considered while predicting cutting forces in machining of MMCs. In this paper, chip–tool interface friction in machining of Al/SiCp composites has been considered to involve two-body abrasion and three-body rolling caused due to presence of reinforcements in composites. The model evaluates resulting coefficient of friction to predict the cutting forces during machining of Al/SiCp composites using theory of oblique cutting. Further, the model considers various frictional forces on the wiper geometry on the cutting edge that has been found to improve the integrity of machined surface on composites. The predicted cutting force values were found to agree well with the corresponding experimental values for finer reinforcements composites with the assumption that 40% of the reinforcement particles contribute to the abrasion at chip–tool interface. However, for the coarser reinforcement composites, assumption that the 60% of the particles contribute to the abrasion yields better results.     

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.     

Analysis of an equivalent tool face for the cutting speed range prediction of complex grooved tools

Manufacturers need to obtain optimal operating parameters with a minimum set of experiments as well as minimizing the simulations in order to reduce machining set up costs. The cutting speed, V_c, is one of the most important cutting parameter to evaluate; it clearly most influences, on one hand, tool life, tool stability, and cutting process quality, and on the other hand controls production flow. In addition, in today's applications, complex groove geometries have made more difficult the assessment of cutting models for the prediction of tool-material–work-material combination behaviour. In this paper, an original approach based on the experimental estimation of the friction coefficient and enabling to simplify the complex groove geometry in a flat rake face is presented. A model for cutting force prediction is also proposed. Four different complex grooved inserts and three different cutting tool material grades for each insert are studied for the modelling approach. Orthogonal cutting simulations using the Thirdwave Systems’ AdvantEdge code package are compared with experimental measurement. Results show good agreement and that this approach may reduce both number of experiments and simulation times to determine the cutting speed range. Finally, the paper ends with discussions and concluding remarks.     

A More Realistic Cutting Force Model at Uncut Chip Thickness Close to Zero

The relevance of the results of many machining simulations depends on the quality of the cutting force model used. Most of the cutting force models raise problems for uncut chip thickness close to zero. It is mainly due to the management of strong discontinuity and the infinitive limit of the cutting stiffness when the uncut chip thickness goes to zero. Furthermore, the correlation of these models with the experimental results is not very good at low and high uncut chip thickness. To resolve these difficulties, a new model of cutting force is proposed. It gets the advantage to be a continuous law with a finished limit of cutting stiffness when the uncut chip thickness goes to zero. The validation of this model with experimental results in milling and drilling shows a good correlation for a large variation of uncut chip thickness.     

Study on deformation of titanium thin-walled part in milling process

Machining of thin-walled parts is a key process in aerospace industry. The part deflection caused by the cutting force is difficult to predict and control. In order to predict the cutting deformation of a titanium alloy Ti6Al4V thin-walled part in milling process, in this paper, the three-dimensional finite element models of a helical tool and a thin-walled part with a cantilever are established. In the simulation process, milling chips are formed along with the introduction of the friction model between cutter and chip and the chip separation method. Using the established three finite element models, milling process is simulated. With the simulation cutting parameters, milling experiment is carried out. Consequently, a comparison of the results between the simulated and experimental cutting deformation are obtained. The results show that the established finite element models are accurate and can be used to predict cutting deformation.     

Upper bound analysis of oblique cutting: improved method of calculating the friction area

This paper describes further development of the upper bound analysis of oblique cutting with nose radius tools described previously by Adibi-Sedeh et al. [[1]] by incorporation of an improved method for calculating the friction area at the chip-tool interface. Previously, the friction area was obtained from the shear surface area assuming that the ratio of these areas is the same as in orthogonal machining. Our results showed that this led to overestimation of the effect of friction on the chip flow angle, thereby resulting in smaller changes in the chip flow angle with inclination angle as compared to experimental data. In the new approach, the chip-tool contact length is obtained from the length of the shear surface assuming that the ratio of the lengths is the same as in orthogonal machining and the friction area is calculated using this length. The chip flow angle predicted using the new approach shows much better agreement with experimental data. In particular, the dependence of the chip flow angle on the inclination angle is accurately reproduced. Upper bound analysis of oblique cutting using this new model for the friction area provides an elegant explanation for the relative influence of the normal and equivalent rake angles on the cutting force.     

A study of the tool-chip interface contact problem under low cutting velocity with an elastic cutting tool

To understand the effects of elastic deformation of the tool and the crater phenomenon generated by the cutting force and high pressure during metal cutting processing on the cutting process, an iterative mathematical model for calculating the tool-chip contact is developed in this paper under the assumption of elastic cutting tools. In this model, the finite-element method is used to simulate the cutting of mild steel by a cutting tool of three different materials. The results obtained in the simulation are found to match experimental data reported by related studies. The simulation results also indicate that tools with a smaller stiffness produce greater elastic deformation. Further, decrease of the rake angle due to elastic deformation of the tool can result in greater difficulty in internal deformation of the material and an increase in cutting force. The micro-crater phenomenon on the tool face generated by high pressure at the tool-chip interface is the preliminary symptom of crater wear on the tool face. Therefore, under some machining conditions, such as in precision machining or in automation processing where tool compensation is required, the phenomenon of elastic deformation of the tool must be considered carefully to ensure product precision.     

Modeling of 3D temperature fields for oblique machining

Fast and accurate temperature prediction for oblique cutting processes is still one of the most complex problems and challenges in the machining research community. For the first time in this article, a novel 3D temperature prediction model based on the finite difference approach for oblique cutting processes is presented. An elliptic structural grid generation method is implemented. Representing different oblique cutting geometries is straightforward now. Moreover, since the resulting equation system is algebraic, the model allows much faster calculations compared to available finite element method based machining temperature models. 3D oblique simulation results verify that temperatures are in good agreement with experimental results.     

Deformation prediction and error compensation in multilayer milling processes for thin-walled parts

Deformation prediction and error compensation are effective approaches to improve machining accuracy in milling thin-walled parts. In this paper, it is considered that the machining deformation of the previous layer will influence the nominal cutting depth of the current layer. Therefore, a dynamical model is established to predict the deformation in multilayer machining a thin-walled part. The coupling relation between cutting force and machining deformation is taken into account using iterative computation. The dynamical model is validated by comparing the simulation result with the experimental one. A new approach of active error compensation is proposed, in which the machining error is compensated at each layer. By comparing the simulation results of compensation at the last layer with the results of compensation at per-layer, a conclusion is drawn that compensation at per-layer makes smaller machining errors and the errors are more uniform.     

A finite element analysis for the characteristics of temperature and stress in micro-machining considering the size effect

In this paper, a finite element method for predicting the temperature and the stress distributions in micro-machining is presented. The work material is oxygen-free-high-conductivity copper (OFHC copper) and its flow stress is taken as a function of strain, strain rate and temperature in order to reflect realistic behavior in machining process. From the simulation, a lot of information on the micro-machining process can be obtained; cutting force, cutting temperature, chip shape, distributions of temperature and stress, etc. The calculated cutting force is found to agree with the experiment result with the consideration of friction characteristics on the chip–tool contact surface. Because of considering the tool edge radius, this cutting model using the finite element method can analyze micro-machining with a very small depth of cut, almost the same size of tool edge radius, and can observe the ‘size effect' characteristic. Also, the effects of temperature and friction on micro-machining are investigated.     

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.     

The effect of tool geometry on regenerative instability in ultrasonic vibration cutting

Ultrasonic vibration cutting as a cutting process has been widely used in the precision machining of difficult-to-cut materials due to an enhanced cutting stability and increased productivity. The authors' previous researches have shown that chatter vibration prediction is made possible by the suggested cutting model. This paper is an attempt to determine cutting parameters based on regenerative chatter prediction in order to facilitate the machining objectives of high accuracy, high efficiency and low cost in ultrasonic vibration cutting. The machinability of SCM440 steel, called typical hardened steel, is investigated theoretically and experimentally. The cutting model is developed by introducing an experimental cutting database of SCM440 steel. The simulation and experimental results show that the workpiece material parameter has a direct influence on the occurrence of regenerative chatter. In order to achieve the chatter-suppressing dynamics in hard ultrasonic vibration cutting, a stability diagram is predicted based on the simulated work displacement for tool geometry changing. The stability diagram indicates that the regions of the chatter-suppressing dynamics expand with increasing tool rake angle and decreasing tool clearance angle. It is also found from the predictive results that regenerative chatter can be suppressed by a change of tool geometry. The determined tool geometry with the aid of the computer simulation is demonstrated through actual data of ultrasonic vibration cutting. By the use of the designed tool geometry, a good experimental result is achieved.     

钛合金TC4切削过程流动应力模型研究

运用有限元技术对切削过程进行仿真可以预测切削力、切削温度、应力分布,优化刀具参数和切削条件。建立适合于切削条件中大应变、高应变率条件下材料的流动应力模型,是切削过程有限元仿真的关键技术。文章通过正交切削实验和有限元迭代的方法,修正了难加工材料TC4在大应变、高应变率条件下的J-C流动应力模型,使修正模型能够适应切削仿真中的大应变、高应变率要求。计算结果表明,采用新的J-C流动应力模型进行计算,所得主切削力值与实验测量值的平均误差从36.28%降为12.06%,进给力的平均误差由原来的61.03%降为现在的25.57%。该修正的流动应力模型比用霍普金森实验所得到的流动应力模型更适合于切削过程的有限元仿真,可以提高切削仿真的计算精度。     

Experimental verification of the mist generation mechanism in turning

The mechanism of aerosol generation generally consists of spin-off, splash, and evaporation/condensation. Previous researchers have shown some theoretical models and experimental results for predicting the particulate size and generation rate without real cutting in turning operation. These models seem to describe aerosol generation accurately due to the spin-off mechanism. However, in real machining, the cutting tool or cutting chips destroy the spin-off mechanism, and the majority of the mist is due to a splash phenomenon. In this paper, experimental results show that the aerosol generation mechanism in real machining should be mainly explained with both a splash model and spin-off model.     

涡轮叶片切削参数研究与仿真

为解决涡轮叶片可选加工参数较多、加工质量与效率难以保证的难题,提出一种涡轮叶片的五轴加工工艺。利用解析分析的方法建立切削力理论模型,对比验证切削力经验公式的模型精度。结合工件受力变形有限元模型,选取优化后的切削参数,并利用可视化软件实现对叶片无偏摆点铣与侧铣程序的编制与仿真。可视化仿真结果表明：该加工工艺及参数下,可获得加工精度较高的叶片表面;点铣法加工精度较高,通用性强,与侧铣法相比效率较低。铣削试验结果表明：仿真表面结果与试验表面在变化规律上吻合良好,证明了所提工艺与参数的有效性,提升了涡轮叶片的制造精度与效率。     

Heat generation and temperature prediction in metal cutting: A review and implications for high speed machining

Determination of the maximum temperature and temperature distribution along the rake face of the cutting tool is of particular importance because of its controlling influence on tool life, as well as, the quality of the machined part. Numerous attempts have been made to approach the problem with different methods including experimental, analytical and numerical analysis. Although considerable research effort has been made on the thermal problem in metal cutting, there is hardly a consensus on the basics principles. The unique tribological contact phenomenon, which occur in metal cutting is highly localized and non-linear, and occurs at high temperatures, high pressures and high strains. This has made it extremely difficult to predict in a precise manner or even assess the performance of various models developed for modelling the machining process. Accurate and repeatable heat and temperature prediction remains challenging due to the complexity of the contact phenomena in the cutting process. In this paper, previous research on heat generation and heat dissipation in the orthogonal machining process is critically reviewed. In addition, temperature measurement techniques applied in metal cutting are briefly reviewed. The emphasis is on the comparability of test results, as well as, the relevance of temperature measurement method to high speed cutting. New temperature measurement results obtained by a thermal imaging camera in high speed cutting of high strength alloys are also presented. Finally, the latest work on estimation of heat generation, heat partition and temperature distribution in metal machining is reviewed. This includes an exploration of the different simplifying assumptions related to the geometry of the process components, material properties, boundary conditions and heat partition. The paper then proposes some modelling requirements for computer simulation of high speed machining processes.