An analytical force model for orthogonal elliptical vibration cutting technique

The elliptical vibration cutting (EVC) technique has been found to be a promising technique for ultraprecision machining of various materials. In each overlapping EVC cycle, the thickness of cut (TOC) of work material, and the tool velocity get continuously varied. These two inherent phenomena, in fact, introduce transient characteristics into its cutting mechanics, which are considered to be different from the one applied for conventional cutting technique. Recently, a few theoretical models have been developed to understand the material removal mechanism with the EVC technique; however, in those studies, the transient phenomena were not considered. In the present research, an analytical force model for the orthogonal EVC process was developed in order to fully understand the EVC mechanism, and to more accurately predict the transient cutting force values. Three important factors: (i) transient TOC, (ii) transient shear angle, and (iii) transition characteristic of friction reversal were investigated and analyzed mainly based on geometric modeling and the Lee and Shaffer's slip-line solution. Mathematical evaluation shows that they may have significant influence on EVC process, and thus on its output performance. In order to validate the proposed force model, a series of low-frequency orthogonal EVC tests were conducted. The experimental transient cutting force values were compared with the predicted values calculated using the proposed model, and they are found to be in a good agreement with each other.     

An Approach to Theoretical Modeling and Simulation of Face Milling Forces

A new approach to theoretical modeling and simulation of face milling forces is presented. The present approach is based on a predictive machining theory in which machining characteristic factors in continuous cutting with a single-point cutting tool can be predicted from the workpiece material properties, tool geometry, and cutting conditions. The action of a milling cutter is considered as the simultaneous work of a number of single-point cutting tools, and the milling forces are predicted from input data of workpiece material properties, cutter parameters and tooth geometry, cutting condition, cutter and workpiece vibration structure parameters, and types of milling. A predictive force model for face milling is developed using this approach. In the model, the workpiece material properties are considered as functions of strain, strain rate, and temperature. The ratio of cutter tooth engagement over milling is taken into account for the determination of temperature in the cutting region. Cutter runout is included in the modeling for the chip load. The relative displacement between the cutter and workpiece due to the cutter and workpiece vibration is also included in the modeling to consider the effect on the undeformed chip thickness. A milling force simulation system has been developed using the model, and face milling experimental tests have been conducted to verify the simulation system. It is shown that the simulation results agree well with experimental results.     

Process capability study of laser assisted micro milling of a hard-to-machine material

Laser assisted micro milling (LAMM) is capable of generating three-dimensional micro scale features in hard-to-machine materials. This paper compares the process capability of LAMM with conventional micro milling of a hardened tool steel. In particular, the potential advantages of LAMM over micro milling with respect to cutting forces, tool wear, material removal rate, burr formation and surface roughness are investigated when micro milling hardened A2 tool steel (62 HRC). The results show that LAMM has significant advantages over micro milling, especially in terms of cutting forces, material removal rate and tool wear. The average reduction in the resultant cutting force is found to be up to 69% with laser assist. In addition, tool wear is found to be substantially less with laser assist even when the material removal rates are increased by a factor of six over the tool manufacturer recommended cutting conditions.     

论疏水作用力的特性及影响因素

疏水絮凝是天然水中经常发生的现象,也是水处理中常被利用的原理.而疏水作用力则是引起疏水絮凝的最主要原因,具有重要的科学意义和应用价值.在过去30多年里,科学家们从实验测定、数值模拟及理论研究3个方面做了大量的研究,使人们对疏水作用力有了一定的认识,但由于问题的复杂性及研究所具有的高难度,目前疏水作用力的理论仍不够完善.为有助于进一步研究,本文综述了疏水作用力的一些特性及影响因素,如疏水作用力的实验规律、疏水作用的距离范围、疏水作用力的粒度界限、表面接触角对疏水作用力的影响、电解质对疏水作用力的影响及温度对疏水作用力的影响等.对大量文献的分析归纳表明,实验规律有单指数函数模型、双指数函数模型及幂函数模型,作用距离范围分为短程作用力及长程作用力,微粒半径大于临界半径时才可产生疏水作用力,疏水作用力随接触角的增大而增大,电解质对疏水作用力基本无影响,关于温度的影响,迄今尚有不同的看法和争论,还需更进一步的研究.     

原子力显微镜在环境样品研究与表征中的应用与展望

简要阐述了原子力显微镜仪器操作原理及最新成像技术发展情况;结合作者近期的研究工作,从环境微生物界面观察与表征、腐殖酸在微界面上的聚集行为观测、无机高分子絮凝剂的界面形貌及行为观察以及膜材料表面结构观测与表征等4个方面对原子力显微镜在环境领域内的应用情况作了概括介绍．最后,对原子力显微镜在环境微界面研究与表征中的应用前景进行了展望。     

Application of FEM simulation of chip formation to stability analysis in orthogonal cutting process

Models for chatter prediction in machining often use a mechanistic force model that calculate the force as the product of a material dependent cutting constant and chip area. However, in reality, the forces are the result of complex interaction between the tool and the chip, and are affected by many factors. The effects of these complex, and often nonlinear, factors on the machining dynamics may only be included in chatter prediction if the chip formation process is simulated concurrently with simulation of the machining dynamics. In this paper, finite element simulation of the chip formation process is combined with simulation of chatter dynamics and the inter-relationship between the chip formation process and the chatter phenomenon is investigated. Mesh adaptation technique is used to simulate the chip formation within an FEM elastoplastic analysis with dynamic effects and frictional contact. The combined modeling predicts the occurrence of process damping at low cutting speeds, which other models are generally unable to predict.     

Orthogonal machining of single-crystal and coarse-grained aluminum

Orthogonal machining of single-crystal and coarse-grained (i.e., grain size considerably larger than the uncut chip thickness) materials has been a subject to many studies in the literature. The first part of this paper presents background on machining single-crystal materials, including experimental and modeling attempts. The second part briefly describes more recent modeling results from the authors, and presents new experimental results on planing and plunge-turning of single-crystal and coarse-grained aluminum using diamond tools. The experiments indicate that (1) cutting across grains of a coarse-grained aluminum workpiece produces distinctly varying forces and surface roughness from one grain to another, (2) plunge-turning and planing of single crystal aluminum provide equivalent force data for large rake angles, (3) forces alter between two distinct levels while cutting single crystals with small rake angles, and (4) with small rake angles, subsurface damage on single-crystal aluminum is extensive, reaching depths comparable to the uncut chip thickness.     

微滤过程中腐殖酸与膜表面黏附特性的试验研究

为了进一步研究微滤过程中腐殖酸对微滤膜的污染机制,通过运用原子力显微镜(AFM),结合自制的PVDF胶体探针考察了不同的pH、离子强度以及钙离子浓度等水质条件下膜-腐殖酸与腐殖酸-腐殖酸之间微观黏附力的变化趋势以及与膜的通量衰减幅度之间的相关性.结果发现,微观黏附力是膜面污染产生的根本原因.由于pH的电性中和以及离子强度的电性屏蔽作用,膜-腐殖酸以及腐殖酸-腐殖酸之间黏附力随着pH的减小或离子强度的增大都呈增大趋势;而随着钙离子浓度的增大,由于少量钙离子的"架桥"作用以及过量时的电性中和作用,两种黏附力先增大后减小.各条件下,膜-腐殖酸与腐殖酸-腐殖酸之间黏附力都呈相同的变化趋势,且与对应污染膜的通量衰减幅度具有正相关性,为更加深入了解膜污染的形成机制提供了一定的理论支持.     

Evaluation of vegetable based cutting fluids with extreme pressure and cutting parameters in turning of AISI 304L by Taguchi method

Many problems such as health and environment issues are identified with the use of cutting fluids (CFs). There has been a high demand for developing new environmentally friendly CFs such as vegetable based cutting fluids (VBCFs) to reduce these harmful effects. In this study, performances of six CFs, four different VBCFs from sunflower and canola oils with different ratios of extreme pressure (EP) additives, and two commercial types of CFs (semi-synthetic and mineral) are evaluated for reducing of surface roughness, and cutting and feed forces during turning of AISI 304L austenitic stainless steel with carbide insert tool. Taguchi’s mixed level parameter design (L₁₈) is used for the experimental design. Cutting fluid, spindle speed, feed rate and depth of cut are considered as machining parameters. Regression analyses are applied to predict surface roughness, and cutting and feed forces. ANOVA is used to determine effects of the machining parameters and CFs on surface roughness, cutting and feed forces. In turning of AISI 304L, effects of feed rate and depth of cut are found to be more effective than CFs and spindle speed on reducing forces and improving the surface finish. Performances of VBCFs and commercial CFs are also compared and results generally show that sunflower and canola based CFs perform better than the others.     

From large-scale to micromachining: A review of force prediction models

In this paper, a review of work performed in the area of force modelling in metal cutting processes is presented. Past and present trends are described and criticised to compare their relevance with current requirements. Several approaches are reviewed, such as empirical, mechanistic and analytical models. The models’ ability to predict forces, from rough machining to finish machining, is analysed.     

Interfacial forces between silica surfaces measured by atomic force microscopy

Colloidal particle stability and some other interfacial phenomena are governed by interfacial force interactions. The two well known forces are van der Waals force and electrostatic force, as documented by the classical Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory. Moreover, advances in modern instrumentation and colloid science suggested that some short-ranged forces or structure forces are important for relevant colloidal systems. The interfacial and/or molecular forces can be measured as a resultant force as function of separation distance by atomic force microscopy (AFM) colloid probe. This article presents a discussion on AFM colloid probe measurement of silica particle and silica wafer surfaces in solutions with some technical notifications in measurement and data convolution mechanisms. The measured forces are then analyzed and discussed based on the ‘constant charge’ and ‘constant potential’ models of DLVO theory. The di erence between the prediction of DLVO theory and the measured results indicates that there is a strong short-range structure force between the two hydrophilic surfaces, even at extremely low ionic concentration, such as Milli-Q water purity solution.     

Ball end milling mechanistic model based on a voxel-based geometric representation and a ray casting technique

Prediction of machining forces involved in complex geometry can be valuable information for machine shops. This paper presents a mechanistic cutting force simulation model for ball end milling processes, using ray casting and voxel representation methods used in 3D computer graphics field. Using this method, instantaneous uncut chip cross sectional areas can be extracted, which can be used in cutting pressure coefficient extraction and machining simulation including machining forces and geometry of the workpiece. The major advantage of the proposed scheme is that it can simulate milling processes with arbitrary cutting tool geometry on a workpiece with complex geometry, using an algorithm with constant time complexity. A series of cutting experiments were carried out to validate the model.     

水质条件对膜-羧基官能团之间微观作用力的影响特征

为了探讨pH值、离子强度及膜材料对膜-污染物间相互作用力的影响特征,利用自制的典型膜污染物羧基官能团胶体探针,结合原子力显微镜定量考察了羧基官能团与PVDF及EVOH超滤膜间的相互作用力随pH值及离子强度的变化特征.结果表明:带有羧基基体的污染物与PVDF及EVOH超滤膜之间的相互作用力皆随着pH值的增大而减小;但是上述作用力随着离子强度的增加呈现特殊的变化趋势:在离子强度为0~10mmol/L时,膜-带有羧基基体的污染物之间相互作用力随着离子强度的增加而增大;在离子强度为10~500mmol/L时,膜-羧基之间相互作用力随着离子强度的增大而减小.在特定的水质条件下,EVOH-羧基间的作用力远小于PVDF-羧基之间的作用力.     

辉光放电等离子体降解模拟染料废水的研究

用辉光放电等离子体技术对伊红B模拟染料废水降解进行了研究.借助紫外光谱和荧光光谱分析其降解过程,用酸度计测定了降解液pH的变化,用原子力显微镜观察了降解过程中伊红B的形貌并初步探讨了降解机理.结果表明,伊红B被降解为CO2、H2O和简单无机盐;在波长为513 nm时,降解110 min后,脱色率达到95%;反应后降解液pH降低,说明反应过程中有羧酸类物质生成.通过吸光度值计算得到了动力学常数k=0.0206 min-1,降解过程符合一级反应动力学特征.     

pH值对有机物(BSA)膜污染的影响

选用BSA(牛血清蛋白)代表有机污染物,使用QCM-D技术考察了BSA在PVDF膜面的吸附行为及吸附层结构随pH值的变化特征,并采用原子力显微镜定量测定了相应pH值条件下PVDF-BSA及BSA-BSA之间作用力,结合膜污染试验,解析pH值对有机物污染膜行为的影响机理.结果发现,在BSA的等电点,PVDF-BSA及BSA-BSA之间的静电排斥力最小,导致BSA迅速吸附累积于膜面,形成密实的BSA污染层,引起超滤膜通量大幅度衰减.当pH值偏离BSA等电点后,BSA间静电排斥力的增强有效削弱了BSA在膜面的吸附量,相应BSA污染层松散度增大,膜污染减弱.在实际的水处理中,通过适当的pH值调节,针对性将超滤膜及污染物调整至带有相同电性、并增大二者所带净电荷量,是减缓超滤膜污染的有效手段.     

多孔介质内H2S贫氧燃烧制氢数值模拟

为探索H2S在多孔介质内超绝热缺氧燃烧裂解制氢的机理,采用流体力学数值模拟与化学动力学研究相结合的方法,使用一个17组分、57步的复杂化学反应机理,模拟了H2S在直径为3 mm的Al2O3圆球堆积的多孔燃烧反应器内的缺氧燃烧制氢过程,模拟结果与试验数据基本吻合.模拟结果显示:富燃条件下,多孔介质内H2S的燃烧温度超过了绝热燃烧温度,为H2S的裂解制硫、制氢提供了高温环境,H2S部分裂解生成单质硫和氢气,从而实现了对硫化氢中的硫和氢同时利用的目的.     

Simultaneous measurement of tool torque,traverse force and axial force in friction stir welding

Simultaneous measurement of the tool torque, traverse force and axial force during friction stir welding process is of great significance to the understanding of the underlying process mechanism and the optimizing of the process parameters. Different from the traditional measurement methods using load cell or rotating component dynamometer, an indirect but economical methodology is used in this study for the simultaneous measurement of the traverse force, axial force and tool torque by monitoring the output torques of the servo motors and main spindle three-phase AC induction motor inside the FSW machine. The values of the traverse force, axial force and tool torque are determined under different welding conditions, and the influencing factors are examined. The measured results in friction stir welding of AA2024-T4 aluminum alloys at different combinations of tool rotation speed and welding speed lay foundation for process optimization.     

原子荧光法测定硒的不确定度评定

在环境样品的理化分析过程中,一切测量结果都不可避免地带来一定的不确定度,有很多因素都会影响到监测的最终结果,如：基准物质的称量、纯度、所用玻璃器皿、取样体积、实验温度等等。以测定水中硒的含量为例,分析和评价影响水中硒的测量的不确定度,建立数学模型,对在分析过程中产生的不确定度进行识别和计算,从而对原子荧光法测量硒的不确定度分析评定。掌握水中硒测量不确定度评定方法,能帮助分析人员确定测定结果的可靠程度,确保测定结果的准确、可靠。     

纳米TiO2薄膜在不同基质表面的负载及光催化性能

以釉面陶瓷和普通钠钙玻璃为载体,用溶胶凝胶法在其表面进行了纳米TiO2薄膜的负载.采用X射线衍射法(XRD)、扫描电子显微镜(SEM)和X射线光电子能谱仪(XPS)对薄膜进行了表征与分析.结果表明,TiO2为完全的锐钛矿型,平均粒径约为15nm;TiO2薄膜在2种载体上分布均匀,膜厚约为300nm;TiO2薄膜在釉面陶瓷表面呈连续分布,而在玻璃表面上出现了破裂现象;2种载体中的一些基质离子在TiO2薄膜均有渗透.光降解实验表明,2种载体上的TiO2薄膜对亚甲基蓝的降解均符合一级反应动力学.TiO2/釉面陶瓷催化活性大于TiO2/玻璃,该薄膜对实际生产多菌灵废水具有催化降解作用.2种载体上的TiO2薄膜重复使用20次,对亚甲基蓝的去除率降低约2%.     

Micro dimple milling on cylinder surfaces

The paper presents a micro dimple machining on a cylinder surface with a two-flutes ball end mill. When the cutter axis is inclined and the depth of cut is less than the tool radius, non-cutting time, during which neither of the two cutting edges contacts the workpiece, appears in a rotation of the cutter. The rotation of the workpiece and the feed of the tool are controlled so that the cutting areas do not overlap each other. In order to incline the tool with respect to the tangential direction on the cylinder surface, the tool is located at a position oriented at 45° from the top of the cylinder. An analytical model is presented to control the shapes of the dimples with the cutting parameters. The presented machining is verified in cutting tests with measuring the shape and the profile of the dimples. Pre-machining operations are conducted to have a high cylindricity of the workpiece in longitudinal turning and polishing. The cutter runout of the tool is also eliminated by adjusting the orientation and the position of the tool in the collet chuck with measuring the cutting force. The micro dimples are machined accurately as they are simulated.