数控车削切屑形态智能预测的动态建模及实时仿真

针对数控加工中切屑形成过程的监控问题,在基于实时工况智能监控平台上,通过研究切屑形态预测的智能动态建模方法（人工神经网络）,建立了切屑形态预测动态模型;并根据切屑空间运动轨迹的数学模型,建立了切屑三维造型模型,并在虚拟现实环境中实现车削过程的切屑实时动态仿真.     

A new material model for 2D numerical simulation of serrated chip formation when machining titanium alloy Ti–6Al–4V

A new material constitutive law is implemented in a 2D finite element model to analyse the chip formation and shear localisation when machining titanium alloys. The numerical simulations use a commercial finite element software (FORGE 2005^®) able to solve complex thermo-mechanical problems. One of the main machining characteristics of titanium alloys is to produce segmented chips for a wide range of cutting speeds and feeds. The present study assumes that the chip segmentation is only induced by adiabatic shear banding, without material failure in the primary shear zone. The new developed model takes into account the influence of strain, strain rate and temperature on the flow stress and also introduces a strain softening effect. The tool chip friction is managed by a combined Coulomb–Tresca friction law. The influence of two different strain softening levels and machining parameters on the cutting forces and chip morphology has been studied. Chip morphology, cutting and feed forces predicted by numerical simulations are compared with experimental results.     

3D Finite Element Modelling of Segmented Chip Formation

This paper presents a 3D coupled thermo-mechanical finite element model for the simulation of segmented chip formation in metal cutting. For modelling, a commercial finite element code is used. The generation of segmentation is achieved either by element erase with respect to damage or by modification of material flow stress data; both being coupled with continuous adaptive remeshing. A normalized Cockroft-Latham model is utilized as the damage criterion for element erase. Flow stress modification is achieved by using Rhim's material model. Fundamental observations from the simulations are concluded and a guideline for further research is proposed.     

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.     

Chip morphology of normalized steel when machining in different atmospheres with ceramic composite tool

Dry cutting tests in air and nitrogen atmospheres with a ceramic cutting tool were carried out on normalized AISI 1045 steel. SEM and EDX techniques are employed to observe the chip morphology and tribological mechanisms are simultaneously discussed. The finite element model of chip formation was created to determine the effective stress and strain distributions in the chip and workpiece. Compared in nitrogen, the friction coefficient in air was reduced when the cutting speed is at 160 m/min and the feed rate is 0.1 mm/r. Experimental data and observation revealed the formation of a lubricating film at the tool-chip interface, which related to the difference chip morphology in air and nitrogen.     

Chip formation during microscale cutting of a medium carbon steel

Microscale orthogonal cutting tests were conducted on normalized AISI 1045 steel and the resulting chips examined using optical and Scanning Electron Microscopy (SEM). As the uncut chip thickness approaches the size of the smallest average grain type in the material, chip formation changes from continuous to a new type of chip called a quasi-shear-extrusion chip. Results indicate that the pearlite and softer ferrite grains play distinct roles in the plastic deformation process. A Finite Element (FE) model was developed to illustrate the behaviour of the chip formation process during microscale cutting of alternating hard and soft layers of material. The FE model is not an optimization tool, but simply an aid in understanding the mechanics of the microcutting process. The resulting chip morphology is compared to the FE model, and discussed. Stick–slip friction observed at the tool–chip interface is found to affect the transition between shearing and ploughing during the cutting process, chip curl, and the plastic deformation process throughout the chip. The ramifications of the results and model predictions are presented.     

Modelling the Effects of Flank Wear Land and Chip Formation on Residual Stresses

The selection of optimum machining parameters and tool geometry for difficult to cut materials used in aerospace applications is usually controlled by the quality and integrity of the surface produced, the burr formation and the part distortion. In this paper, a finite element model is developed to simulate the effects of tool flank wear and chip formation on residual stress when orthogonal cutting Ti-6AI-4V. A crack propagation module is also developed and incorporated into the finite element solver to accurately simulate the segmental chips produced during machining of titanium. The predicted results emphasize the importance of modelling the chip formation mechanism and tool wear correctly because of their effect on the cutting forces and temperature field. This subsequently influences the magnitude and distributions of the residual stress. Good correlation was obtained between measured and predicted residual stress distribution.     

Process simulation using finite element method — prediction of cutting forces, tool stresses and temperatures in high-speed flat end milling

End milling of die/mold steels is a highly demanding operation because of the temperatures and stresses generated on the cutting tool due to high workpiece hardness. Modeling and simulation of cutting processes have the potential for improving cutting tool designs and selecting optimum conditions, especially in advanced applications such as high-speed milling. The main objective of this study was to develop a methodology for simulating the cutting process in flat end milling operation and predicting chip flow, cutting forces, tool stresses and temperatures using finite element analysis (FEA). As an application, machining of P-20 mold steel at 30 HRC hardness using uncoated carbide tooling was investigated. Using the commercially available software DEFORM-2D™, previously developed flow stress data of the workpiece material and friction at the chip–tool contact at high deformation rates and temperatures were used. A modular representation of undeformed chip geometry was used by utilizing plane strain and axisymmetric workpiece deformation models in order to predict chip formation at the primary and secondary cutting edges of the flat end milling insert. Dry machining experiments for slot milling were conducted using single insert flat end mills with a straight cutting edge (i.e. null helix angle). Comparisons of predicted cutting forces with the measured forces showed reasonable agreement and indicate that the tool stresses and temperatures are also predicted with acceptable accuracy. The highest tool temperatures were predicted at the primary cutting edge of the flat end mill insert regardless of cutting conditions. These temperatures increase wear development at the primary cutting edge. However, the highest tool stresses were predicted at the secondary (around corner radius) cutting edge.     

焊管成型过程有限元法研究的进展

综述了焊管成型过程分析研究的常用方法（整体分析法、实验研究法、能量分析法、CAD法、有限元法等）;重点介绍了国内外近年来有限元法在焊管成型过程研究中的应用情况。分析认为,有限元法是近年来发展最快的,也是今后研究焊管成型过程的重要手段之一,但焊管变形的数学和力学问题还值得深入探讨,研究模型还需不断完善,尤其是多道次连续成型的全流程仿真尚需深入研究。     

Simultaneous Determination of Flow Stress and Interface Friction by Finite Element Based Inverse Analysis Technique

A finite element based Inverse analysis technique has been developed to determine the flow stress and friction at the tool/workplace interface simultaneously from one set of material tests. The Inverse problem is aimed at minimizing the error between experimental data and predictions made by rigid-plastic finite element simulations. The ring compression test and the modified limiting dome height test (sheet blank with a hole at center stretched with a hemispherical punch) were selected for evaluating the method for bulk forming and for sheet forming, respectively. The determined flow stress data were compared with corresponding data obtained Independently using the well-lubricated cylinder compression test and hydraulic bulge test. Results show that the method discussed In the study is efficient and accurate.     

A new methodology to optimize spiral bevel gear topography

This paper aims to present the new method developed to generate optimized spiral bevel gear surfaces. Thanks to a complex non linear finite element model, the geometrical gear meshing positions under operational loads are first precisely computed. These meshing positions are then used as inputs of a calculation process that seeks to define the best tooth surface topography. So far, this activity was based on sensitivity studies conducted directly by the designer, which led to repeat calculations whose progress was difficult to control.     

螺旋盘管弯曲成形有限元模型的建立

为了得到空间弯曲件成形特点和变形规律,本文对螺旋盘管滚弯成形过程进行了分析研究.在建立的空间弯曲成形的理论模型基础上,依据三维弹塑性大变形动态分析理论,以大型商用有限元软件ANSYS/LS-DYNA为分析工具,对弯曲成形过程中的边界条件进行了合理处理,实现了成形辊轮在空间位置的自由移动和转动,建立了螺旋盘管滚弯成形的有限元模型.     

数值模拟技术在锻造成形中的应用

锻造成形过程是一个非常复杂的弹塑性大变形过程,有限元法是用于锻造成形过程模拟中一种有效的数值计算方法。本文介绍了数值模拟技术在金属锻造成形中应用的基本理论、模拟中的关键技术,阐述了锻造成形数值模拟技术的现状及发展趋势。     

锻件多件拼锻节材的最优化数学模型

本文根据最优化设计原理,推导并建立了大锻件多件拼锻节材的最优化数学模型。该模型可用于先进的大锻件锻压工艺计算机辅助设计(CAD),对大锻件的节材有重要意义。     

Surface defects during microcutting

Surface microdefects such as dimples are always found on machined 1045 steel surfaces as a result of the dual phase microstructure of the workpiece material. Finite element (FE) analysis on dimple and chip formation showed similar trends to those acquired experimentally. The formation of dimples at grain boundaries is explained by considering the plastic dissipation energy inside of individual grains in the material microstructure during microscale cutting. Dimples are shown to occur at a hard-soft grain boundary in the direction of cutting, but never at a soft-hard grain boundary.     

An Analytical Predictive Model and Experimental Validation for Machining with Grooved Tools Incorporating the Effects of Strains, Strain-rates, and Temperatures

By effectively integrating a recently developed universal slip-line model with Oxley's predictive machining theory, a new analytical predictive model for machining with restricted contact grooved tools has been developed and presented in this paper. A computational flow chart is provided to illustrate the method of integration. The cutting forces are predicted for varying flow stress properties to include the effects of strains, strain-rates, and temperatures. Extensive cutting tests involving the use of three groups of chip-grooves have been conducted to validate the new method. An encouraging good agreement has been found between predicted and experimental results.     

ZN—1型粘弹性材料的GHM模型参数确定

将ZN－1粘弹性材料的GHM模型与工程上常用的有限元方法相结合，引入耗散自由度，将由于ZN－1型粘弹性材料导致的非线性微分方程转化为一般的二阶定常线性系统模型，并将GHM模型与最常用的标准线性模型，分数导数模型进行比较，结果表明本研究提出的确定GHM模型参数的方法是正确的。     

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.     

Development of a new and simple quick-stop device for the study on chip formation

After a brief survey in the literature, this paper described how a new, simple and effective quick-stop device was developed for the study of chip formation without employing any explosive charges or breaking any shear pins. A cutoff tool was employed to obtain orthogonal cutting on an engine lathe, imposing the device to collect chip-root sample. Design considerations of the device elements are indicated. Operation of this purely mechanical device is simple and safe. The developed device has been found to give stable and reliable performance. Many photomicrographs of very satisfactory results were obtained, showing that this device successfully served the purpose of providing a research instrument for the study on chip formation. Finally, the formation of a continuous-type chip with a built-up edge is discussed.