锯齿形切屑成形机理分析与计算机模拟

基于ABAQUS分析了高速切削过程中锯齿形切屑的形成机理和影响切屑锯齿化程度的主要因素,选取不同切削速度和刀具前角进行切屑形成过程模拟和测试。结果表明,随着切削速度的增加以及刀具前角的减小,切屑的锯齿化程度随之增大。     

淬硬45钢斜角切削锯齿形切屑的有限元模拟

目前大多数对高速切削锯齿形切屑的仿真模拟都是针对二维直角切削,三维仿真模拟极少。实际切削加工是一个三维变形过程,为了更准确地揭示高速切削机理,亟需开展三维切削加工过程中锯齿形切屑的仿真研究。本文针对淬硬45钢(45HRC)斜角高速切削过程中锯齿形切屑的三维有限元建模及分析,基于ABAQUS通用有限元软件,采用Johnson-Cook材料模型和失效应变分离准则,模拟淬硬45钢(45HRC)斜角高速切削过程中锯齿形切屑的形成过程,并对不同刀具前角和切削厚度下的切屑锯齿化程度、流屑角和宽度变形系数进行分析。结果表明:随着刀具前角的减小和切削厚度的增大,切屑的锯齿化程度越来越明显;切屑的流屑角基本不受刀具前角的影响,近似等于刃倾角,但随着切削厚度的增大而逐渐增大;宽度变形系数随刀具前角的减小和切削厚度的增大而增大。     

基于ABAQUS的Ti6Al4V切削仿真研究

以刀具前角作为变量,采用单因素变量法建立了基于ABAQUS的Ti6Al4V正交切削有限元模型。模拟了锯齿形切屑形成过程,深入分析了锯齿形切屑形成机理。研究了不同刀具前角对切屑锯齿化程度和切削力的影响。研究结果表明:刀具前角变化对锯齿形切屑形成有着重要影响;随着刀具前角增大,锯齿化程度逐渐减小,切削力也会逐渐减小。     

高压冷却下锯齿形切屑几何表征试验

理论分析了锯齿化程度、锯齿化频率与锯齿化步距等几何表征模型;在高压冷却条件下进行了聚晶立方氮化硼（PCBN）刀具切削GH4169镍基高温合金试验,并对不同切削用量与冷却液压力下的切屑进行试样制备及抛磨,以分析锯齿形切屑的形貌及表征;分析了不同切削参数下锯齿形切屑几何表征的变化规律。试验结果表明：随着切削速度、进给量和背吃刀量的增大,切屑的锯齿化程度和锯齿化步距增大,而锯齿化频率减小;随着冷却液压力的增大,切屑的锯齿化程度降低,锯齿化频率增大,锯齿化步距先增大后减小;在高压冷却条件下切屑的断屑能力得到了提高,且随着冷却液压力的增大,断屑效果进一步提高。     

切削工艺对Ti6Al4V合金锯齿形切屑的影响研究

通过实验研究了切削速度和切削厚度对Ti6Al4V合金锯齿形切屑、齿距和锯齿化程度以及绝热剪切带微观组织转变的影响,并对锯齿形切屑的形成过程及机理进行了分析。结果表明:随着切削速度的增加,锯齿形切屑单元的尺寸和切屑的锯齿化程度不断增加,切屑锯齿的剪切带更容易形成转变带,在切削速度为550 r/min时剪切带中基本都由转变带组成。随着切削厚度的增加,齿距不断增大,当切削厚度0.3 mm后锯齿化程度变化幅度减小;当切削厚度从0.2 mm增加至1.0 mm时,剪切带组织逐渐从形变带转变为形变带+转变带,并在切削厚度为1.0 mm时完全形成转变带。     

基于黏结-滑移摩擦模型的304不锈钢切削力仿真研究*

通过预测加工304不锈钢时产生的切削力,从而对切削参数和刀具几何参数进行优化,是提高304不锈钢的加工精度、切屑控制及保障刀具寿命的基础。建立304不锈钢切削仿真模型,为提高模型的精确性,选择Johnson-Cook本构方程和黏结-滑移摩擦模型。结果表明：采用黏结-滑移摩擦模型的切削力预测结果更为准确,表明相对于纯剪切摩擦与库仑摩擦模型,黏结-滑移摩擦模型能更准确地描述刀-屑摩擦特性。展开不同参数下的切削力研究,研究发现：切削力随着刀具前角、后角和切削速度的增大而减小,随切削刃钝圆半径和切削厚度、宽度的增大而增大,其中切削宽度、厚度及前角对切削力大小影响较大。研究结果为304不锈钢切削效率的提高和切削机制的研究提供了理论依据。     

钛合金切削性能及绝热剪切带微观形态研究

采用正交试验方法对钛合金进行切削试验,研究了切削用量和刀具前角对切削力和锯齿化程度的影响规律,并采用金相显微镜对锯齿形切屑的切屑形貌和绝热剪切带内材料特征进行观察和分析。结果表明:进给量和背吃刀量对切削力的影响高度显著,刀具前角对进给力的影响高度显著而对主切削力的影响显著;刀具前角、进给量、切削速度对锯齿化程度的影响显著性依次减小;随着锯齿形切屑变形程度增加,绝热剪切带内组织特征由形变带向转变带转化;锯齿形切屑裂纹形成于绝热剪切带与下一个梯形基块的交界处,并沿绝热剪切带方向扩展;刀具前角对裂纹影响较显著,当刀具前角为10°时,裂纹更加明显。     

高速切削过程绝热剪切局部化断裂预测

基于高速切削过程绝热剪切饱和极限理论,结合锯齿形切屑绝热剪切带的变形和受力条件,以及材料的动态塑性本构关系,建立以切削速度、切削厚度和刀具前角为预测变量的高速切削过程绝热剪切局部化断裂的预测模型,并以淬硬45钢和FV520(B)不锈钢为例,预测其发生绝热剪切局部化断裂的临界切削条件。通过高速切削试验和金相试验,讨论了切削条件对绝热剪切局部化断裂过程的影响规律和敏感程度,验证了绝热剪切局部化断裂的预测结果。结果表明:较大切削厚度和较小刀具前角会降低绝热剪切局部化断裂的临界切削速度,建立的绝热剪切局部化断裂预测模型能有效预测切屑发生绝热剪切局部化断裂的临界切削条件。     

基于ABAQUS的钛合金高速切削有限元模拟

基于有限元分析软件ABAQUS建立了高速切削Ti6Al4V的二维正交切削有限元模型,仿真研究了高速切削加工时切削速度、切削深度对切削力大小、切削力波动频率以及锯齿形切屑形态的影响。结果表明:平均切削力在90m/min~360m/min的切削速度范围内趋于平稳,随着切削深度的增大而增大;切削力波动频率随切削深度的增加而减小,随切削速度的增大而增大;切屑锯齿化程度及锯齿化步距都随切削速度及切削深度的增大而增大。     

CBN刀具正交切削钛合金温度场的有限元分析

应用ABAQUS/Explicit软件建立了钛合金Ti6Al4V的二维正交切削模型,采用温度—位移耦合分析步,研究了CBN刀具二维正交切削Ti6Al4V时切削参数及刀具前角对切削温度的影响。研究结果表明,切削速度、切削厚度的增大均会使切削温度升高,其中切削速度对切削温度的影响最大,切削厚度次之;切削温度随着刀具前角的增大而降低,但当前角继续增大至20°后,切削温度略有上升。切削区高温分布区域随切削速度的增加而有所减小,随着切削厚度的增加,切削区高温分布区域增加。     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

ANGULAR DISTORTION ALLOWABLE VALUE AND ASSESS METHOD OF WELD ON COKE TOWER

A graph as the new engineering method for estimate the safety of bulging deformation of coke tower is proposed. Through stresses analysis of circumferential weld of coke tower and comparing the stresses produced by pressure with heat stress of steady state, residual stress, bending stress produced by both itself weight and wind loads, it showed that the stresses produced by pressure on the angle distortion are the main factor of equivalent stress of the combined stress. After comparing four kinds of stress controlling conditions, the relation to stress with depth of angular distortion, grade of curvature of angular distortion and half of region of angular distortion has been inferred. Graph of deformation allowable value of coke tower for different condition by angular distortion and half of region of angular distortion has been plotted. The five steps for its engineering use have been explained. The lighter the grade of curvature is, the larger of bulge allowance, may be, and the bigger of depth of angular distortion may pose too. For the coke tower with a popular structure of Dg 5 400 mm×28 mm, the result by graph is nearly more than the result of two formulas formed by other research, the error is less than 7.0%. But, the graph can be easily applied to different size of angular distortion.