The Scale Effect of Roughness on Hydrodynamic Contact Friction

Multistage abrasive finishing processes (grinding, polishing, honing, etc.) are commonly used to produce the geometrical properties of a surface to meet its technical functionalities in the operating characteristics of contacting parts in friction, relating to their durability and reliability (running-in performance, wear resistance, load-carrying capacity, etc.). Coarse abrasive grits followed progressively finer ones are used, which leads to a multiscale stratified surface texture.

In this article, a numerical model of elastohydrodynamic (EHD) contact coupled to a multiscale surface texture model was developed that allows tracking the scale effect of surface features and their interactions on friction performance and lubricant flow under hydrodynamic lubrication conditions. Because the simulation model has as an input the surface topography and to overcome the variability in surface finish formation, textured surfaces at different stages of the finishing process were simulated (virtual texturing method). Surface topography can be decomposed into two principal components: superficial roughness and valleys. Superficial roughness was modeled using a fractal model and a scaling factor was introduced to model valley patterns. The results show the relationship between friction and surface scales.     

The characterization of internal combustion engine bores

In recent years the production of cylinder bores has received much attention by manufacturers. The finishing processes used include boring, honing and plateau honing. A feature of the surface changes which occur during running is related to the wearing action caused by the piston ring on the bore. This action very rapidly causes a “transitional topography” where the surface generated exhibits the influence of the piston ring which modifies the machined surface. The transitional surface although modified still retains significant characteristics of its initially machined state.Plateau honing is a finishing process which attempts to impart a transitional topography which may be considered partially “run in” and hence provides a condition which is part way towards the fully run-in state.In this paper the methods of producing engine bores are considered, the surface profiles obtained by these methods are examined and attempts to characterize their surface topography are made. The effects of wear are studied and from a consideration of the surface topography of the initial machining process a characterization technique is proposed.It is shown in the paper that the assessment of R_a, or preferably R_q, is sufficient to monitor final machining and functional wear on a cylinder bore provided that the general shape of the initial surface is known.     

电化学光整加工中表面毛化的应用

基于对电化学光整加工之后表面微观几何形貌变化的分析,认为“高原”型表面微观几何形貌的存在对电化学光整加工的整平能力及其效果的提高有一定的影响,提出将表面毛化技术应用于电化学光整加工的设想,并实验验证了适度的表面毛化对光整加工是有利的;同时将此方法应用于无缝碳钢钢管内孔的表面光整加工中,在表面粗糙度Ra达0.2μm以下的同时,生产效率也得到提高。     

Modeling and controlling of surface micro-topography feature in micro-ball-end milling

The machined surface micro-topography has a great influence on the surface quality and the surface function. A simulation algorithm of machined surface topography is present in this paper, in which the influence of the tool vibration is considered. From the overall surface texture formation, surface texture interval, surface texture height, and surface texture direction, the geometric characteristics of surface micro-topography in micro-milling was defined and investigated. The influence of process parameters, especially the initial phase angle of cutter and the tool vibration, on the geometric characteristics of surface micro-topography is investigated, and the method to control the process parameter is proposed. Especially, this paper presents a novel method, through the planning of noncutting tool path, to control the initial phase angle of cutter which has significant effect on surface topography. The experiments shows that the control deviation of the surface texture direction is less than 2°, and the machined surface topography consistent with the simulation result, which means that the modeling and controlling of surface topography is feasible and effective.     

电化学机械复合光整加工及表面特性研究

很多先进制造设备对其零部件的表面质量提出了越来越高的要求,而大多数常用的光整加工方法,很难在高效和高质量两方面满足工件的加工需要,因此目前很多精密零件都采用了复合加工的方法,以使工件的表面形貌与其功能相匹配。本文对电化学机械复合光整加工方法进行了研究,自行研制了加工设备,进行了光整加工实验,对加工后工件表面特性进行了研究。     

Surface topography analysis in high speed finish milling inclined hardened steel

The surface texture of a milled surface is an inherently important process response in finish milling. It is one of the most commonly used criteria to determine the machinability of a particular workpiece material. However, literature survey on the study of the surface topography analysis relating to the cutter path orientations when high speed finish inclined milling is scant. Previous works were either involved in conventional milling of easy-to-cut workpiece materials or machining at different workpiece inclination angles. Furthermore, none of the previous work has detailed the true surface topography of the machined surface with regards to the cutter condition. Instead, the works provided quantitative values in terms of the Ra value. This article is concerned with evaluating cutter path orientations on an inclined workpiece angle of 75° to simulate finish milling of free form moulds and dies. Surface topography effects are assessed with regards to different cutter path orientations on its surface. The aims of this study are to provide an in-depth understanding on the surface texture produced by various cutter path orientations when high speed finish inclined milling hardened steel at a workpiece inclination angle of 75° using surface topography analysis and determine the best cutter path orientation with respect to the best surface texture achieved. 3D topography maps together with 2D surface profiles are used to assess the experimental results. The conclusion is that milling in a single direction vertical upward orientation gave the best workpiece surface texture.     

New criterion of grain size choice for optimal surface texture and tolerance in belt finishing production

The basics of the belt finishing process are not well understood yet because it is difficult to define the relationships between process variables and surface characteristics particularly from the point of view of surface roughness and tolerance. For this reason, the optimal working variables of the belt finishing process are not yet predictable.This work is devoted to track the effect of the abrasives grains size. The optimal abrasives grains size is firstly identified by comparing the initial and the finished surface topographic signature on a wide range of surface wavelengths. The analysis method is based on a multi-scale characterization using the continuous wavelets transform. It makes it possible to define a criterion as for the choices of the optimal abrasive grains size of the belt finishing process for a given workpiece surface.     

Measurement and control of surface finish in manufacture

The topography of technical surfaces and the reasons for their assessment in the fields of process control and precision engineering are reviewed. Alternative approaches to surface characterization and the range of instrumentation currently available for measuring surface texture are discussed. Particular reference is made to digital profiling instruments based on microprocessors and to the extended range of parameters these instruments can provide. Throughout, discussion is linked to the contents of Australian Standard AS2536     

基于形态变换的三维表面形貌方向特性研究

针对面向功能的三维表面形貌表征存在的问题,基于灰值形态学的基本运算构造了边缘检测形态算法,有效地提取了三维形貌的形态学边缘,实现了三维形貌的纹理方向特征的提取,获得了表征纹理方向特性的表征参数.该方法不仅适用于直线纹理,而且也适用于曲线纹理,为分析表征三维形貌的各向异性特征提供了一个新的方法.把它引入到粗糙表面的润滑分析中,能够更确切地揭示出各向异性表面的纹理方向特性对润滑性能的影响规律.     

电化学机械精准光整加工技术研究

介绍了该研究组近年来在电化学机械精准光整加工技术研究方面的工作进展情况,包括：光整过程中同时完成形状成形的光整与成形复合加工技术;同时改善零件精密度和表面形貌的跨尺度精确成形加工技术;保证精密度条件下改善表面形貌的自由曲面零件手持式工具光整加工技术。研究工作表明：通过合理优化电化学机械加工工艺系统结构和参数,对于齿轮、轴承等规则表面零件,可以实现同时改善零件精度和表面几何形貌;对于非规则表面零件,可以在保证零件精密度条件下改善零件表面几何形貌。     

The development of the modified Hurst orientation transform for the characterization of surface topography of wear particles

A modified Hurst orientation transform (HOT) method for characterization of wear particle surfaces is proposed and described in this paper. The method involves the calculation of self-affine Hurst coefficients in all directions and displays the calculated coefficient values in a form of rose plot. The calculation of individual Hurst coefficients, H, is based on the rescale range (r/s) analysis (r(d)/s∼ d ^H ). The rose plot is then used to obtain three texture surface parameters, i.e.: texture aspect ratio, texture minor axis and texture direction. The effectiveness of this modified HOT and resulting surface texture parameters was evaluated. The method was first applied to computer-generated images of isotropic and anisotropic particle fractal surfaces and then to field emission scanning electron microscope images of wear particles found in synovial joints. The ability of the surface parameters to reveal surface isotropy or anisotropy, measure roughness and determine the dominant direction of surface texture was assessed. The effects of measurement conditions such as noise, gain variations and focusing on the surface parameters were also investigated. The results demonstrate that the HOT and surface texture parameters developed can successfully be used in the characterization of wear particle surface topography. This revised version was published online in August 2006 with corrections to the Cover Date.     

Analysis of magnetorheological abrasive flow finishing (MRAFF) process

A new precision finishing process called magnetorheological abrasive flow finishing (MRAFF), which is basically a combination of abrasive flow machining (AFM) and magnetorheological finishing (MRF), has been developed for nano-finishing of parts even with complicated geometry for a wide range of industrial applications. In this paper microstructure of the mixture of magnetic and abrasive particles in magnetorheological polishing fluid (MRPF) has been proposed, and normal force on the abrasive particles is calculated from the applied magnetic field. A model for the prediction of material removal and surface roughness achieved has also been presented. And, finally theoretical results are compared with the experimental data available in the literature, and they are found to agree well.     

超声振动光整的EDEM数值模拟与实验研究

采用EDEM离散元分析软件对普通钝化光整实验及带有超声振动辅助光整实验进行数值模拟，仿真结果为超声振动光整加工系统的提出提供了依据。使用超声振动光整设备对平头铣刀进行钝化实验，进行了不同钝化条件下的实验研究。通过扫描电镜观察了钝化前后铣刀的表面形貌及钝圆半径的变化，分析了超声振动光整对钝化效率及效果的影响。实验结果表明，增加了超声振动钝化后的钝化效率提高了约26%，表面形貌得到较大改善。     

样条小波在表面方向特征提取中的应用

表面形貌是影响表面功能的主要因素,其中包含形状误差、波纹度、粗糙度等多种成分。方向特征是机械加工表面中的常见特征,如何有效的将其分离出来直接关系到表面质量的评定。基于Radon变换对方向特征的敏感性,结合样条小波对方向特征的提取和对噪声的抑制作用,在拟合表面和实测表面分别实验,得到表面线性方向特征的有效提取。     

三维表面形貌的逾渗特性表征

为了建立表面形貌微观结构与其功能特性之间的关系,基于逾渗理论建立了表面形貌的逾渗模型,用逾渗概率、空体集团平均大小和空体集团分布系数对三维表面形貌的逾渗特性进行了量化表征。采用数字滤波技术生成具有给定自相关函数和纹理取向的数字化粗糙表面,分析了具有相同均方根粗糙度而结构不同的三维表面形貌的逾渗特性,给出了表面纹理方向参数和自相关长度对表面逾渗特性的影响,并借助部分三维形貌参数(ISO25178)建立了表面形貌与逾渗特性参数间的量化关系。结果表明:对于各向异性表面,沿横向搜索跨越空体集团,表面逾渗发生时的表面高度、逾渗阈值和逾渗体积均随着表面纹理方向参数的增大呈减小趋势,而空体集团分布系数呈增大趋势;沿纵向搜索时,其变化规律与横向相反。对于各向同性表面,逾渗发生时的表面高度和逾渗阈值随着表面自相关长度的增大呈先减小后小幅增大趋势,而逾渗体积和空体集团平均大小呈逐渐减小趋势。研究结果为面向功能的表面形貌设计提供了理论基础。     

夹心式复合加工表面形貌特征

对夹心式电化学机械复合光整加工设备进行了改进，通过工艺试验广泛地搜集了大量试验数据，确定了较合理的工艺参数。依据试验数据，多角度地研究了电化学机械复合光整加工的表面形貌特点，并从理论上深入讨论了电化学机械复合光整加工表面形貌对工件工作性能的影响，最后得出的结论为：电化学机械复合光整加工对工件原始表面的低频成分有较大程度的降低，而对高频成分影响较小，有明显的阳极整平作用，被加工工件表面的尖峰状凸起被去除，工件表面呈现出微观“高原型”，表面轮廓不平度高度特性参数大幅度降低，工件表面轮廓分布集中，且呈负偏态，轮廓偏斜度为负值，轮廓支承长度率曲线陡峭，工件的表面质量得到综合改善，这对提高零件的抗接触变形能力、改善摩擦、磨损性能、降低工件的磨合时间、提高工件的精度保持性、延长工件的寿命均有利。     

表面微凹坑和纹理方向对界面摩擦的耦合影响

选取三种不同纹理的铝合金试样,并在试样上加工不同面积占有率的规则圆形微凹坑,利用自制的摩擦试验装置,在油润滑条件下以不同接触压力进行摩擦试验,试验过程中滑动方向与表面纹理方向的夹角分别为0°、45°、90°。利用非接触式三维轮廓仪测量试验前后试样的三维表面形貌,并选取Sa、Str、Vvv、Vvc等表面表征参数来分析滑动接触界面表面形貌的变化。结果表明：表面纹理方向的差异导致铝合金表面在滑动接触摩擦过程中表现出各向异性,而在其表面加工不同面积占有率的微凹坑,减弱了铝合金表面纹理方向性对界面摩擦的影响,反映出表面微凹坑和纹理对界面摩擦的耦合作用。同时界面摩擦对试件的表面形貌也有明显的影响,Str、Vvv、Vvc在试验后发生了规律性的变化。     

Nanofinishing of freeform surfaces (knee joint implant) by rotational-magnetorheological abrasive flow finishing (R-MRAFF) process

Freeform complex surfaces have become an inevitable part of many devices to perform specific functions. Some of these components require nanolevel surface roughness value to meet the desired requirements in their applications. Finishing of freeform surfaces to nanometer surface roughness value is always difficult for any process. Rotational-magnetorheological abrasive flow finishing (R-MRAFF) process has been applied so far for finishing internal surfaces of relatively simple geometry. In this work, an attempt has been made to improve external topography of freeform surfaces using this process. Large hydrodynamic pressure coupled with magnetic fluid is the principal idea behind these experiments. A smooth mirror like finished surface is achieved with improved finishing rate (nanometer/min) by controlling two motions (axial and rotational) simultaneously on stainless steel workpiece similar to knee joint implant. Magnetorheological polishing fluid with different mesh sizes of abrasive particles and at different extrusion pressures is used to reduce final surface roughness value, to increase uniformity of surface finish on the freeform surface and to enhance finishing rate. Surface roughness ranging from 35 to 78 nm is achieved at various locations as compared to larger variation in Ra value obtained in the earlier research work.     

Developing A Surface Roughness Model for End-Milling of Micro-Channel

Micro-milling operations are one of the common manufacturing processes that are used primarily to produce miniaturized components within the range of less than a millimeter. The surface roughness of the channel plays an important role in the motion of fluid in the channel. Since most traditional finishing operations cannot be performed easily on micro-channels, the study of relationship between micro-milling parameters and surface roughness is of extreme importance. In this work, the geometrical features of cutting edge, along with the concept of minimum chip thickness, are taken into consideration for constructing the micro-channel surface texture using kinematic rules and transformation operators. ACIS, a 3D B-rep geometric kernel, is used as a geometric engine for simulation of surface texture produced in the micro-milling process. In addition, the relationship between cutting conditions and surface roughness is investigated using DOE method and a regression model. All micro-channel experiments were performed on stainless steel 316. Finally, simulation and regression results are compared with measured surface roughness and the validity of these two models is approved. Depending on the available data, one of these two approaches can be used to predict the surface roughness of the channel's floor.