麻花钻加工20Cr的断屑仿真分析

利用有限元软件DEFORM-3D,对麻花钻钻削20Cr的断屑过程进行了仿真分析。根据塑性材料断裂强度理论,以切屑卷曲变形为断屑判据。通过模拟分析,得出了工件的等效应力、应变及其分布,以及工件上P点最大等效应变的变化规律,阐释了该点最大等效应变与切屑卷曲变形的正相关性。提出并验证了P点最大等效应变的峰值可作为麻花钻加工20Cr的断屑判据。     

基于计算机数值模拟的刀具断屑槽磨损研究

采用ABAQUS有限元分析软件进行切削分析试验,研究刀具断屑槽磨损对切屑成型的影响。模拟了两种槽型的带断屑槽刀具在相同磨损参数和切削条件下的切削应力,并比较了不同槽型在相同磨损程度下对切屑成型的影响。试验结果表明:断屑槽磨损会增大刀—屑接触长度和切屑的卷曲半径,并且会引起切削应力的波动;梯形断屑槽刀具相比于弧形断屑槽刀具更适合加工。     

硬质合金刀片断屑槽槽型对其切削性能的影响

采用具有多种断屑槽槽型的同种基体材质的刀片进行车削实验,应用高速摄影机捕捉切削区域切屑产生、流出、卷曲和折断过程。通过磨损测量仪观测断屑槽,并结合切屑形态分析,明确断屑槽合理几何形状;通过三维受力分析仪采集切削过程中的振动和切削力信号,揭示断屑槽对切削力的影响规律;综合切削参数、断屑槽几何结构和切削力三方面的因素,最终确立断屑槽槽型与进给量对切屑折断的作用机制。研究数据以期为断屑槽设计与车削刀具的应用提供数据支撑。     

高压冷却下PCBN刀具切削高温合金切屑卷曲折断机理及试验研究

高温合金广泛应用于航空航天领域,是一种典型的难加工材料,切削过程中切屑缠绕工件及刀具、不易折断,从而降低刀具寿命和已加工表面质量。PCBN是超硬刀具材料,加工高温合金等高温高强度钢性能优异,但由于刀具材料特性通常采用平前刀面,因此切削过程中断屑比较困难。高压冷却是金属高效切削加工中一种新型加工技术,可以有效改善断屑性能、提升断屑能力、提高刀具寿命和加工表面质量。目前对高压冷却断屑机理研究较少,且高压冷却切削仿真不易实现,为充分研究高压冷却下高温合金切削加工中的切屑折断机理,通过建立切屑卷曲半径预测模型和断屑模型,进行高压冷却下切屑折断机理研究,主要通过在高压冷却下,对PCBN刀具切削镍基高温合金进行试验研究,研究不同冷却液压力下切屑卷曲半径变化规律,对理论分析结果进行验证。研究结果表明:在高压冷却加工中由于高压冷却液的存在,切屑受到附加冷却液压力影响,使弯矩发生变化,造成切屑卷曲半径减小,最终导致切屑应变增大、切屑易于折断;且由于卷曲半径的改变使极限进给量和极限背吃刀量降低,使高压冷却加工改善断屑性能的效果非常明显。上述研究成果为实现高温合金高压冷却条件下的切削加工奠定了理论基础。     

数控车削刀具圆弧半径对切削过程影响的数值分析

数控车削加工中刀具的圆弧半径对切削力,切屑的断屑,切屑的形状,加工表面质量、加工变形以及已切削表面的残余应力的大小,状态,分布有着很大的影响.本文采用有限元分析方法,利用有限元增量理论,建立了二维金属切削仿真模型,分析中采用网格自适应准则,模拟了典型零件车削二维切削过程中切屑的形成,得到了加工后已加工表面的残余应力的大小,状态以及分布状况,对于工程中的实际应用具有重要的意义.     

铝合金高速铣削机理三维仿真建模与分析

为了研究铝合金7050-T7451高速铣削机理,建立了能反应实际铣削状态的斜角切削有限元模型.该模型采用双刃螺旋立铣刀进行模拟,模拟过程考虑刀具的进给运动和旋转运动,工件材料模型通过高温拉伸实验与高速压缩实验得到,刀-屑接触摩擦采用可自动识别滑动摩擦区和粘结摩擦区的修正库仑定律,切削温度模型等效为窄带热源.采用建立的有限元仿真模型模拟了铣削过程中的切屑成形状态,分析了应力、应变和温度分布情况以及铣削力值.研究结果表明,铝合金高速铣削加工形成连续带状切屑,最大应力发生在第一变形区,切屑形成时应变最大,最高温度出现在刀、屑接触部位,模拟得到的铣削力可以接受.     

振荡断屑研究

在切削加工中,切屑的形状直接影响着正常生产和操作工人的安全。在自动机床及自动生产线上断屑、卷屑及切屑的处理问题往往成为生产的关键。生产上控制切屑的卷曲及折断的方法很多。主要的有:采用卷屑槽或断屑台;改变主切削刃的形     

精车半精车时新型三维断屑槽型的研究

对断屑机理及屑形控制方法进行了较深入的研究。提出了判断切屑的基本应变和卷曲应变大小的切屑应变系数K_e的表达式,以及控制K_e来形成短螺旋形类切屑的良好断屑方法和设计三维断屑槽结构的计算公式。应用本文的理论,成功地研制了一种新型三维断屑糟刀片。     

整硬麻花钻容屑槽与法向前角对钛合金钻削性能的影响

采用UG NX11.0软件建立了三种不同卷屑角的容屑槽,以锥面刃磨的方式构建钻尖三维模型。测量主切削刃的法向前角并绘制法向前角的分布曲线,分析三种曲线之间的关系。利用AdvantEdge有限元仿真软件模拟钻削过程中的切削力、切削形貌、切削温度和应力分布,并通过切削试验验证了有限元模拟的可靠性。结果表明：容屑槽卷曲角直接影响主切削刃法向刀具前角的分布,且主切削刃的法向刀具前角越大,切削越锋利,切削力越小;在一定范围内,随着容屑槽卷曲角α增大,轴向切削力减小,且切屑卷曲直径也越小,有利于排屑和提高刀具寿命。     

精密切削过程三维有限元分析

采用有限元方法模拟三维精密切削过程,包括三维正交切削和三维斜角切削。切屑和刀具的摩擦应力采用修正库仑摩擦方程来计算,工件的流动应力是应力、应变、应变率和温度的函数,采用局部网格重划分技术。通过三维切削模拟可以获得在不同刃倾角精密切削过程的条件下切屑形状、切削力和切削温度场的分布情况。仿真结果表明:刃倾角对主切削力和切深抗力影响不大,但对切屑形状、进给抗力和切削温度场分布影响较大。     

Stress analysis of lead-free solders with under bump metallurgy in a wafer level chip scale package

The wafer level chip scale assembly (WLCSP) has increasingly become popular due to its compact, wafer scale assembly. In a WLCSP assembly, the under bump metallurgy (UBM) connecting the solder joints and the chip is crucial for the assembly reliability. This study focuses on a WLCSP with 96.5Sn3.5Ag/95.5Sn3.8Ag0.7Cu solder joints and Ti/Cu/Ni UBM on a 2–layer microvia build-up electric board. Furthermore, the Garofalo-Arrhenius creep model in finite element analysis ANSYS 6.0 is used for simulations on the WLCSP assembly under thermal cycling to investigate the deformations of the assembly with different thickness of nickel layer, the maximum equivalent strain and maximum equivalent stress of microvias/joints. Finally, the Coffin-Manson equation is applied to predict the fatigue lives of four combinations of solder joints with different eutectic alloy and thickness of nickel layer.     

The mechanism of ductile chip formation in cutting of brittle materials

A theoretical analysis for the mechanism of ductile chip formation in the cutting of brittle materials is presented in this paper. The coexisting crack propagation and dislocation in the chip formation zone in the cutting of ductile materials are examined based on an analysis of the geometry and forces in the cutting region, both on Taylor’s dislocation hardening theory and the strain gradient plasticity theory. It was found that the ductile chip formation was a result of large compressive stress and shear stress in the chip formation zone, which shields the growth of pre-existing flaws by suppressing the stress intensity factor K _I . Additionally, ductile chip formation in the cutting of brittle materials can result from the enhancement of material yield strength in the chip formation zone. The large compressive stress can be generated in the chip formation zone with two conditions. The first condition is associated with a small, undeformed chip thickness, while the second is related to the undeformed chip thickness being smaller than the radius of the tool cutting edge. The analysis also shows that the thrust force F _t is much larger than the cutting force F _c . This indicates that large compressive stress is generated in the chip formation zone. This also confirms that the ductile chip formation is a result of large compressive stress in the chip formation zone, which shields the growth of pre-existing flaws in the material by suppressing the stress intensity factor K _I . The enhancement of material yield strength can be provided by dislocation hardening and strain gradient at the mesoscale, such that the workpiece material can undertake the large cutting stresses in the chip formation zone without fracture. Experiments for ductile cutting of tungsten carbide are conducted. The results show that ductile chip formation can be achieved as the undeformed chip thickness is small enough, as well as the undeformed chip thickness is smaller than the tool cutting edge radius.     

Fluid-Like Properties of Chip Flow in High-Speed Metal Cutting Process

Strain rate in high-speed metal cutting is high, and properties of chip flow under high strain rate conditions are different under low cutting speed conditions. Shear stress and shear strain rate have a linear relationship; hence, the behavior of chip flow during high-speed metal cutting is more similar to fluid than to solid. Therefore, metal cutting should be analyzed by using fluid analytical method. This article investigated the fluid-like properties of chip flow during high-speed metal cutting and determined velocity, pressure, and strain rate distributions on rake face and shear plane. A speed stagnation point is located some distance from the tool tip on the rake face. The location of this point influences the life of the cutting tool and the quality of the finished surface. The pressure peaks, decreases along the rake face, and then reaches zero at some point away from the tool tip. This point represents the separation of the chip from the tool. The total stress on the shear plane is the sum of tensile stress, pressure stress, and shear stress. The strain rate is related to velocity; its value rapidly increases at the tool tip and the free surface corner and then decreases.     

高速切削钛合金Ti6Al4V切屑的形成及其数值模拟

应用Hopkinson压杆实验装置,确定了航空用钛合金Ti6Al4V高应变和高温条件下的应力-应变关系,结合Ti6Al4V合金准静态试验数据,建立了适合高速切削仿真的Johnson-Cook本构模型;通过有限元数值模拟,仿真了高速切削Ti6Al4V合金的锯齿状切屑形成过程,分析了整个锯齿状切屑形成过程的切削力、切削温度、等效塑性应变的变化,深入探讨了锯齿状切屑的形成机理;将模拟计算得到的切削力和切削温度与试验结果进行了比较,两者具有较好的一致性。
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航空铝合金7075-T7451三维铣削过程有限元仿真

采用有限元分析软件AdvantEdge建立反映金属切削过程高温、大应变及高应变率状态的切削模型,模拟了航空铝合金7075-T7451铣削加工过程,获得了两个铣削周期内的铣削力变化曲线,并预测了工件及刀具上的温度分布;模拟了铣削过程中切屑的形成,获得了与实际切屑相似的切屑形状。通过铣削力实验获得了相同铣削条件下的铣削力值,与模拟铣削力值比较,发现两者具有较好的一致性,从而证明了有限元模型的正确性。     

An experimental study on influences of material brittleness on chip morphology

Though several material properties such as hardness, thermal conductivity, specific heat, strain hardening, and thermal softening ability have been studied in terms of influencing segmental or serrated chip formation process, rare study about material brittleness affecting the chip formation process has been carried out. In this paper, an orthogonal cutting experiment with four steels with different brittleness was carried out. The effect of workpiece material brittleness on segmental chip formation and consequent chip morphology was investigated. The experimental results show that the material brittleness heavily affects chip formation process and chip shape. A novel chip formation model was developed to explain the mechanism of material brittleness working on the chip formation process. The mechanism is that material brittleness lowers the value of failure strain and thus makes the maximum stress in flow stress curve occur earlier, which leads to the catastrophic shear instability in primary shear zone and consequent segmented chip.     

2-D discontinuous chip cutting model by using strain energy density theory and elastic-plastic finite element method

The formation of discontinuous chip is investigated in this paper. The cutting simulation was conducted on 60–40 brass (60% Cu, 40% Zn) under an extremely low cutting speed. The region of the maximum strain energy density (SED) distribution value relative to the minimum value, i.e. (dw/dv)_min^max, was used as the criterion to predict the initial breakage location under the presumption that the curvature direction of the maximum SED was the direction of crack growth. The shape and cutting force of discontinuous chip crack, the stress and strain distribution of the workpiece and chip, and the variation of various nodal force on the chip–tool interface were derived.     

Finite element analysis of the effect of sequential cuts and tool–chip friction on residual stresses in a machined layer

A thermo-elastic–viscoplastic model using explicit finite element code Abaqus was developed to investigate the effect of sequential cuts and tool–chip friction on residual stresses in a machined layer. Chip formation, cutting forces and temperature were also examined in the sequential cuts. The affected layer from the first cut slightly changes the chip thickness, cutting forces, residual strain and temperature of the machined layer, but significantly affects the residual stress distribution produced by the second cut. Residual stress is sensitive to friction condition of the tool–chip interface. Simulation results offer an insight into residual stresses induced in sequential cuts. Based on simulation results, characteristics of residual stress distribution can be controlled by optimizing the second cut.     

基于统一强度理论的复合型裂纹断裂准则

提出一个复合型裂纹等效应力断裂准则，用以解决工程上普遍存在的复合型裂纹的断裂问题。该准则通过借鉴强度理论对复杂应力状态的处理方法，将等效应力作为度量复合型裂纹开裂的基本物理量。该准则在预测发生临界扩展时提出两个基本假设，(1)裂纹沿着等效应力最小的方向开始扩展。(2)等效应力达到临界值时裂纹开始扩展。根据选取的等效应力计算公式的不同，等效应力准则有不同的形式，当等效应力的计算采用总应变能理论时，等效应力准则等价于应变能密度准则；当等效应力采用σr时，等效应力准则可近似逼近最大周向应力理论。采用统一强度理论计算等效应力。最后通过与实验结果及其他理论的计算结果对比，验证基于统一强度理论的复合型裂纹断裂准则满足工程精度要求，且适用性好。