超高速点磨削相关机理研究

结合超高速磨削技术和点磨削工艺,给出对点磨削及其相关技术的理解.建立砂轮磨损和承载等模型,研究发现,与传统外圆磨削相比,点磨削砂轮承载更均匀,寿命更长,磨削性能更佳.由点磨削参数条件下的单颗磨粒成屑试验发现,磨粒的实际切深要比理论切深小,并由单颗磨粒成屑机理给出合理解释.由砂轮连续成屑机理和砂轮相对工件运动轨迹的分析发现,工件轴向进给速度应低于保证良好磨削表面的最小旋切圈数的临界值.点磨削是一种优质的旋切工艺,能够实现较大切深的磨削加工,兼具高材料去除率和高表面质量的优点.由于主轴偏摆,砂轮和工件接触无闭合磨削区,经湿磨试验发现,点磨削接触区内有更大流量的磨削液通过.     

工件旋转法磨削硅片的磨粒切削深度模型

半导体器件制造中,工件旋转法磨削是大尺寸硅片正面平坦化加工和背面薄化加工最广泛应用的加工方法。磨粒切削深度是反映磨削条件综合作用的磨削参量,其大小直接影响磨削工件的表面/亚表面质量,研究工件旋转法磨削的磨粒切削深度模型对于实现硅片高效率高质量磨削加工具有重要的指导意义。通过分析工件旋转法磨削过程中砂轮、磨粒和硅片之间的相对运动,建立磨粒切削深度模型,得到磨粒切削深度与砂轮直径和齿宽、加工参数以及工件表面作用位置间的数学关系。根据推导的磨粒切削深度公式,进一步研究工件旋转法磨削硅片时产生的亚表面损伤沿工件半径方向的变化趋势以及加工条件对磨削硅片亚表面损伤的影响规律,并进行试验验证。结果表明,工件旋转法磨削硅片的亚表面损伤深度沿硅片半径方向从边缘到中心逐渐减小,随着砂轮磨粒粒径、砂轮进给速度、工件转速的增大和砂轮转速的减小,加工硅片的亚表面损伤也随之变大,试验结果与模型分析结果一致。     

磨削热的产生及减小措施

磨削热会引起工件烧伤、变形、裂纹,因此,如何减少磨削热是提高磨削质量的重要课题之一。 1.磨削热的产生砂轮在对工件表面进行磨削加工时,由于磨粒微刃对被加工件表面的切削、刻划、摩擦和抛光作用,使金属在短时间内经历挤压、滑移、挤裂和切离四个阶段。而磨粒与工件的摩擦及金属的塑性变形能量则全部转化为热量,在磨削区域局部表层的     

高速磨削合成切削液的研制

当砂轮线速度高于50ｍ/ｓ时,单位时间内通过磨削区的磨粒增加,砂轮与工件的摩擦加剧,发热量增大,引起合成切削液(以下简称磨削液)温度升高[1]。在高速磨削产生的高接触压力下,如果磨削液的清洗性差,则切屑容易粘附在砂轮表面,造成砂轮气孔堵塞、变钝,使用寿命缩短;如果磨削液的润滑性和冷却性差,易造成工件表面烧伤、拉毛和划伤。目前,一些厂的高速磨床仍用普通磨削液,其结果是工件表面粗糙,砂轮耐用度下降,磨削液使用周期变短。针对高速磨削的特点,研制了一种用于轴承加工的高速磨削液,并已应用于工业生产中。1　组成与制备高速磨削液应具…     

有序化砂轮磨削表面粗糙度仿真

为改善砂轮的磨削性能,将有序排布理论引入到电镀砂轮磨粒排布中。分别探讨了叶序、错位、无序排布砂轮在不同磨削参数下对工件表面粗糙度的影响,同时建立叶序、错位、无序排布电镀砂轮磨削表面粗糙度数学模型,并利用MATLAB软件进行仿真。在砂轮缓进给磨削过程中,叶序排布砂轮所获得的工件表面粗糙度值低于其他排布方式的砂轮。且工件表面的粗糙度值随着磨削速度比的增大而减小,随着磨削厚度的增大而增大。这为实际磨削工件表面粗糙度分析提供了很好的辅助和验证方法。     

磨削烧伤和磨削裂纹产生的原因及预防

磨削加工在机械加工中占有相当重要位置,淬火后工件表面的加工,及较高的尺寸精度和表面粗糙度,主要是靠磨削来保证。磨削加工所用的砂轮表面,是由无数磨粒组成的,每个磨粒相当一把刀具,所不同的是,大部分磨粒具有负前角和小后角。由于磨粒在砂轮表面的分布有高有低,很不规则,在磨削过程中,有些磨粒切削工件形成切屑,有些磨粒仅在工件表面上刻划出痕迹,还有一些磨粒即不切削也不刻划工件,而只是与工件表面产生滑擦,因为磨削速度很高(为车、铣床速度的20倍),这种刻划和滑擦将产生高达1000℃左右的温度,会引起被磨工件表层金相组织的变化。磨削所消耗的能量也是比较大的。因此,磨削过程比其他金属切削加工过程更为复杂。 1.磨削烧伤和磨削裂文产生的原因     

钎焊金刚石砂轮高速磨削氧化铝的磨削比能研究

采用自制的钎焊金刚石砂轮对氧化铝陶瓷进行高速磨削试验研究,重点探讨不同磨削参数对磨削比能的影响。结果表明:磨削比能随砂轮线速度的增大而增大,而随磨削深度、工件速度和材料去除率的增大而减小;磨削比能与单颗磨粒最大切削厚度有直接的关系;在磨削过程中,大部分磨削能量消耗于金刚石磨粒对陶瓷工件的滑擦与塑性耕犁。     

切点跟踪磨削法磨削力计算模型分析

在切点跟踪磨削过程中,结合磨削切点在工件和砂轮表面的运动方程,通过对砂轮与工件之间弹性变形的分析得到其接触弧长,同时通过对单颗磨粒的受力分析得到了砂轮与工件之间的磨削力的计算模型,并通过磨削实验对磨削力计算模型的可靠性进行了验证。MATLAB计算结果表明,切点跟踪磨削中磨削力角的变化呈现出周期性,随磨削深度的变化呈现出非线性。不同磨削深度下的磨削实验验证了切点跟踪磨削法磨削力计算模型的可靠性和正确性。     

新型点磨削砂轮磨削力模型及试验研究

点磨削砂轮轴线与工件轴线之间存在倾斜角α,磨削过程中磨粒的运动轨迹改变,点磨削力及理论模型也随之变化。以传统磨削力理论为基础,利用点磨削模型的转换,建立点磨削力理论模型,通过试验验证理论模型的正确性。试验结果表明:模型的计算值与试验结果的趋势一致,数值相近。点磨削力模型为实际加工提供一种辅助和验证方法。同时提出一种带有粗磨区倾角θ的新型点磨削砂轮,在点磨削力模型的基础上,做了进一步研究,建立新型砂轮的磨削力分配模型。通过点磨削试验对该模型进行试验验证,用不同θ角的砂轮在一系列磨削参数条件下磨削阶梯轴。试验表明:模型分析结果与试验结果一致,在相同磨削参数下,带有粗磨区倾角θ的新型点磨削砂轮的磨削力要小于θ=0°的传统点磨削砂轮磨削力,磨削力随着θ角的增大而减小。此外,还可以得出磨削参数倾斜角α、磨削深度ap和砂轮速度vs对点磨削力的影响规律。     

基于磨削痕迹仿真的磨削纹理生成机理

针对球面和非球面垂直磨削法加工中出现的磨削纹理，开展了基于磨削痕迹轨迹仿真的磨削纹理生成机理研究，建立了磨削痕迹运动分布方程，仿真分析了磨削痕迹在垂直磨削表面的生成和分布机制，揭示了磨削加工参数变化引起的磨削纹理生成机理。通过仿真结果可以看出，垂直磨削后的工件表面残留磨削痕迹分布为中心区域密集、外缘区域稀疏，并具备周期性、放射分布的特征；砂轮圆周上参与磨削的磨粒残留在工件表面的磨削痕迹长度、形状和分布规律几乎完全相同，磨削痕迹间仅存在一定的相位偏差；砂轮与工件的转速比为整数时，相邻螺旋周期的破碎磨削痕迹首尾相接，使得磨削痕迹交接处发生了破碎的耦合与扩展，加剧了工件表面的破碎，并将破碎的磨削痕迹连接在一起，形成磨削纹理。     

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.