Influence of tool inclination on chip formation process and roughness response in ball-end milling of freeform surfaces on Ti-6Al-4V alloy

An experimental test part, which was made up of flat, concave, and convex surfaces of variable curvatures, was designed to be fabricated in a four-axis machining center. Aluminum alloy 7075 and titanium alloy Ti-6Al-4V were used for the fabrication. Within the finishing process, smeared/adhered material was found in some areas of the concave and convex surfaces of the titanium alloy. On the other hand, smeared/adhered material was not found in the aluminum alloy. To characterize the type of defects, the 3D roughness parameters of the surfaces were measured by confocal microscopy, and surface morphology was observed using optical microscopy and scanning electron microscopy. The kinematics of the ball-end milling process was modeled and it was found that the lead and tilt angles between the tool axis and surface normal vector vary continuously, producing transitions between oblique-plunge-push-up milling and oblique-reverse-push-up milling. This causes variation in the thickness behavior during the chip formation process. It was found that the lead angle has a moderate influence, while the tilt angle has a strong effect on the quality of the surfaces of the titanium alloy, with negative tilt angles producing the worst surfaces when there was the oblique-plunge-push-up milling process.     

Analysis on formation mechanism of ultra-smooth surfaces in atmospheric pressure plasma polishing

Atmospheric pressure plasma polishing (APPP) is developed for the final finishing of high quality ultra-smooth surfaces. To improve surface quality, formation mechanism of ultra-smooth surfaces in APPP is studied. Quantum chemistry simulation is used to investigate the interaction between atoms. Simulation of single Si-F bonding process indicates 0.2 eV difference of binding energy between convex and concave models, which reflects the reaction probability of convex structure is higher than that of concave structure. By comparing the spatial atomic configuration and species diffusion path, it is also demonstrated convex topography should be removed faster than concave topography. So roughness of optical surfaces can be reduced further to form ultrasmooth surfaces. And experimental results accord well with theoretical analysis. Detected by atomic force microscopy every 40 s, the average maximum height of surface is testified to decrease faster than the maximum depth obviously, which makes the whole surface going toward a new equilibrium status with lower roughness. Another experiment proves the average surface roughness decreases from Ra 4.529 to 0.926 nm after 100 s continuous machining. And the stereo images also indicate obvious improvement of surface topography. Moreover, free outmost electron is proved to be helpful to promote chemical reaction by simulation, so fresh surfaces may be more favorable for APPP which makes sample preparation more purposeful.     

Using rotary contact method for 5-axis convex sculptured surfaces machining

The 5-axis tool positioning strategy named rotary contact method (RCM) for sculptured surfaces machining has been developed in our previous paper (Wengang Fan et al., J Manuf Sci E-T ASME 134(2):021004.1-021004.6, 2012). The RCM finds the optimal tool positions by rotating the tool backward based on the offset surface instead of the design surface, and can generate big machined strip width without gouging. However, the RCM only deals with concave sculptured surfaces machining well at present, and the special property of convex sculptured surfaces machining has not been fully exploited. To resolve this problem, the general convex sculptured surfaces machining using the RCM is implemented in this paper. Firstly, the tool position error distribution for different tool feed directions is deeply investigated. It is concluded that the best tool feed direction is collinear with the maximum direction of curvature, which is completely opposite to the case for concave sculptured surfaces machining. Then the relationship between the key parameters in the RCM and the tool position error distribution as well as the tool path generation is totally discussed. Finally, machining simulation and cutting experiment of a convex sculptured surface example are performed. The results show that the RCM can apparently raise the efficiency of manufacturing process by contrast with the algorithm in the software UG for convex sculptured surfaces machining.     

Characteristic Vibrational Modes of Piezoceramic Plates with Variable Thicknesses

The paper considers characteristic oscillations of finite round piezoceramic plates of variable thicknesses, with convex and concave surfaces. Characteristic oscillation spectra of these plates were studied in the regimes of resonance and antiresonance, and the dynamic coefficient of electro-mechanical coupling was calculated as a function of plate dimensions and displacement distribution over the surface. Improvements in the characteristics of thickness oscillations in the plates (the possibility of increasing the coefficient of electro-mechanical coupling and smoothing the distribution of the normal displacement component over the plate surface) owing to variable thicknesses of piezoceramic plates have been analyzed. This can be achieved only in plates with convex conical surfaces, whereas concave conical surfaces of plates lead to inferior characteristics of thickness oscillations. Improvements in characteristics of thickness oscillations in piezoelectric plates fabricated from ceramics with various compositions will be discussed.     

非均匀C-C细分曲面的曲率分析

分析了非均匀C-C细分的特点,为细分网格上正则部分的曲率计算给出了两种方法:基于网格顶点的曲率计算和基于网格面的曲率计算。这两种方法都能精确计算出网格的正则点在极限位置的曲率。对于以面为基础的方法,还能精确计算出网格的正则面在极限曲面上对应区域的任意参数位置的曲率。这两种曲率计算的方法也能够精确计算出网格正则部分的其它几何属性,如法矢量、主方向、主曲率等。对于奇异点附近区域的曲率,本文给出的算例用局部逐层细分的方式进行逼近。细分曲面任意位置的几何属性都可能需要计算时,本文的方法可以作为解析法的补充。     

圆弧齿轮齿面沿接触线是滚动与滑动并存的证明

经严格的数学与运动学论证,否定了圆弧齿轮经典著作中的一个基本观点：凸齿廓与凹齿廓之间沿接触线是纯滚动.并得出了正确结论：两齿面之间沿接触线的运动形式是滚动与滑动并存.通过对凸凹齿廓上两螺旋接触线的分析可知,齿轮副的两条接触线长度不相等,进而得到啮合点在接触线上的速度大小亦不相等,因而得出上述结论.依此定量之结论,便可合理解释圆弧齿轮传动中的一些物理现象：如油膜厚度大,齿面磨损均匀,跑合性良好等.     

Side milling of ruled surfaces: Optimum positioning of the milling cutter and calculation of interference

Side milling is a process that enables machining time and thus costs, to be reduced. This type of machining is particularly well suited to ruled surfaces and all surfaces where one of the principal curvatures is very small compared to the tool radius and changes little over the entire surface. These surfaces must be treated with great care, as they are often on parts with high added value such as turbine blades, aircraft wings or helicoidal parts as used in fluid dynamics.We then need to calculate and minimise interference that may arise if the ruled surface cannot be developed. Whereas machining is usually carried out by setting the tool according to a rule, we suggest a new setting of the tool allowing interference to be reduced considerably. The computation algorithms for this setting were developed so as to be used in real-time by CAD/CAM software.A comparative study of errors made with each type of setting is also presented. This shows a considerable reduction in errors when the setting we suggest is implemented.     

Role of Head Parameters on Head-Disc Interface

The effect of a nanoslider's crown, camber, twist and suspension load are parametrically studied and compared from a tribological standpoint. In this paper, stiction, friction, and contact start-slop (hereafter CSS) were performed on a modified disc drive equipped with a special strain gauge. For convex (positive crowned and cambered) sliders, up to five to six times reduction in rest stiction can be easily attained compared to flat sliders. This also applies to drives which have been turned off and turned on after one week.

Flat sliders with much of the air bearing surfaces etched away are, also studied. The patterned sliders did not reduce stiction when tested on a lightly textured disc coated with a lube system consisting of mobile and bonded phases.

The normal suspension force and weight of the slider when bonded together determine the apparent slider contact between the disc surface asperities. The reduction in contact area from six to four grams suspension load on the asperities is about 24 percent.

The effect of convex slider improves the disc durability during CSS. It is believed the geometry allows the convex-shaped magnetic slider to take off from the disc surface sooner than flat ones. That was observed by Lee and Bolasna. The concave slider will reduce stiction also because of smaller contact area. However, its inability to take off early results in catastrophic disc wear. Once in flight, the sliders are insensitive to the convex or concave effect.     

Quality inspection of metal surfaces by diffractive optical element-based glossmeter

Planar, convex and concave metal surfaces were produced by utilizing finishing processes that are exploited in the production of tools for plastics injection molding. A novel glossmeter, the so-called diffractive optical element-based glossmeter (DOG), was used for the inspection of the gloss of the surfaces. The Society of the Plastics Industry (SPI) A1 standard, which has the lowest surface roughness of such standards, served as a reference for the success of the finishing process. The results show that by using DOG we can gain local microscopic and macroscopic information on the gloss and its variation. The DOG is sufficiently sensitive to detect small gloss variation as well as the texture of the surface, e.g. anisotropy in surface marks. Some of the surfaces in this study have a higher surface quality than the A1 surface.     

Hierarchical roughness optimization for biomimetic superhydrophobic surfaces

Superhydrophobic surfaces should have high contact angles (CA) with water and low contact angle hysteresis (CAH). High CA may be achieved by increasing surface roughness, while in order to have low CAH, superhydrophobic surfaces should be able to form a stable composite interface with air pockets between solid and liquid. Capillary waves, nanodroplets condensation, hydrophilic spots due to chemical surface inhomogeneity, and liquid pressure can destroy the composite interface. These destabilizing factors have different characteristic length scales, so a hierarchical roughness is required to resist them. It is shown that convex rather than concave profile enhances stability, so nanoscale convex bumps should be superimposed over microasperities, in order to pin the liquid-air interface. In addition, the nanoroughness is required to support nanodroplets. The ability of the interface to support high pressure requires high asperity density and size, so it is in conflict with the requirement of low fractional solid-liquid contact area for low CAH and slip length. The new parameter, spacing factor for asperities, is proposed, and requirements for optimum design, which combines conflicting conditions, are formulated and discussed. Remarkably, biological superhydrophobic surfaces satisfy these requirements.     

Analysis of a flexible web on a grooved concave surface under softEHL

This article describes characteristics of a flexible web moving through a grooved, concave, and soft surface in an elastohydrodynamic lubrication. Both trapezoidal and semi-elliptical grooved surfaces have been investigated under air lubrication. The modified Reynolds equation based on the first-order boundary slip and permeability of a soft bearing material has been formulated and solved numerically to obtain a traction characteristics between a polypropylene web and a grooved concave surface in the contact region. The concave shape was mainly considered under varying depths of grooves, flexible web velocities, normal loads, equivalent Young’s moduli, curvatures and material permeability values. The simulation results are compared between friction coefficient for a trapezoidal grooved concave surface and a semi-elliptical grooved surface.     

A numerical study on the transient impulsive pressure of a water jet impacting nonplanar solid surfaces

This paper presents an in-depth investigation into the transient impulsive pressure of an arc-curved water jet impacting a solid surface. The emphasis of this study is on the variations of the surface shape, which are classified into four types: The flat surface, the concave surface, the convex surface and the inclined surface. The numerical tool of arbitrary Lagrangian-Eulerian formulations is used to model the arc-curved jet impacting these different solid surface types. Elaborately designed experiments were conducted to test the impulsive pressure profile; the experimental results are found to be in approximate agreement with the numerical results. The impulsive pressure profiles of water jet impacting the flat and inclined solid surface are observed to exhibit two quintessential stages, in line with the traditional pressure profile; however, a double/multiple-peaked pressure structure is observed for the cases of the water jet impacting the concave and convex solid surfaces. Additionally, the value of the peak pressure is found to be a quadratic representation with the jet velocity, and the duration of the peak pressure is found to be an exponential representation with the jet velocity. The compression degrees of the liquid jet impacting the different surfaces are validated to be the root cause for the discrepancy of the impulsive pressure.     

曲面圆弧包络磨削表面粗糙度特性研究

对曲面磨削表面粗糙度成型原理进行了分析,得出曲面磨削时其表面粗糙度由磨粒划痕和砂轮两步距间的残留高度构成。探讨了其分布均匀性的原理,揭示了各参数对其均匀性的影响。通过砂轮进给速度的变速控制,可以降低约60%的表面粗糙度波动率。根据理论分析可知,在加工凹曲面时,其理论残留高度值约为凸曲面的两倍。实际加工时,采用较小的砂轮进给步距或砂轮圆弧半径可达到凸曲面的表面粗糙度效果。     

基于宏程序的凹凸椭圆模块化编程研究

为了使编制的宏程序既能适合不同的非圆曲面加工需要,又能满足编程时编程坐标原点的设置及直径编程的习惯,以椭圆为例,从基本方程分析、变量设置到程序设计,完成了凹凸椭圆模块化宏程序编制的研究。     

A new light microscopic method for the synchronous bidirectional illumination and viewing of living cells in different contrast modes, and/or at different focal levels or magnifications.

A new method of light microscopy for the analysis of the behaviour of living cells in vitro exploits two objects for simultaneous image formation, each serving the other as a condenser. Simultaneous viewing from opposite sides allows the specimen to be examined at: (a) two different magnifications, permitting the locomotion of whole cell (groups) to be studied at a low magnification and details of interaction of colliding surfaces at a high magnification; (b) two different focal levels, permitting, for example, details near the substrate surface to be recorded at the same time as information concerning the behaviour of the free, dorsal surface; and (c) two different contrast modes, such as negative and positive phase contrast, and dark and bright field illuminations. These possibilities can be combined, for example, to contrast a high magnification view in negative phase contrast at one focal level with a low magnification image in ordinary brightfield at another focal level in the same living cells.     

基于三坐标测量臂的大尺寸模板精度测量

本文重点研究工件尺寸大于其测量范围的零件测量方法,巧妙应用蛙跳算法实现了大尺寸凹凸模定位销、型腔孔柱定位尺寸及各型腔孔柱圆柱度、分形面的平面度等精度的综合测量。通过对凹凸模的测量结果进行形状和重合精度对比表明:凹凸模的定位销直径一致性较高,凹模的型腔孔直径较凸模柱的直径均匀,部分孔柱的重合精度较差,对中性最大偏差达到3.039mm。因此,需要改善该凸模的加工方法和夹具定位设计方案,提高其与凹模的重合精度。     

二维轮廓嵌套加工刀轨生成算法

提出一种新的刀轨生成算法,成功解决了由通用等距方法的刀轨加工而成的凸台和凹槽在嵌套时产生干涉的问题。该算法只需要三次等距即可计算出凸台和凹槽加工刀轨,并且能够处理包含自由曲线的轮廓。最后给出的算例验证了该算法的有效性。     

TOOTH CONTACT ANALYSIS OF CONICAL INVOLUTE GEARS

The mathematical model of conical involute gears is developed based on the theory of gearing and the generating mechanism. Tooth contact analysis (TCA) is performed to examine the meshing and bearing contact of the conical involute gear pairs with intersected and crossed axes. In addition, the principal directions and curvatures of the gear surfaces are investigated and the contact ellipses of the mating tooth surfaces are also studied. Finally, the numerical illustrative examples are provided to demonstrate the computational results, test gears are made for tooth-bearing tests, and the conclusion is verified that the theory has the applicability.     

基于数据点正投影和曲面法矢的自由曲面造型

提出用控制自由曲面形状的数据点投影和曲面在数据点的法矢进行自由曲面造型的新思想。利用数据点的正投影 (二维坐标 )和曲面法线方向计算出数据点的三维坐标后 ,即可采用现有的自由曲面造型方法 ,如采用参数双三次样条曲面等自由曲面造型方法构造自由曲面。这种给定自由曲面数据的方法具有易于控制自由曲面形状、几何意义明显等优点