An investigation of effective area in electrorheological fluid-assisted polishing of tungsten carbide

Electrorheological (ER) fluid-assisted polishing is a novel polishing method for the finishing of micro-aspheric lens, dies and mirror. This paper investigates the effective area in the ER fluid-assisted polishing of tungsten carbide, which is used as the die material for the mass production of micro-aspheric glass lens. The effective area is defined as the area in which the abrasive particles concentrated in the vicinity of the tool tip makes the effective material removal from the workpiece. The electric field strength applied between the tool and the workpiece is analysed. The interacting forces between particles suspended in the electrorheological fluid are calculated. An approach is proposed to predict the effective area and the experiments are conducted to confirm the validity of the proposed method.     

Investigation into electrorheological fluid-assisted polishing

Electrorheological fluid (ER fluid) is a functional fluid with the property that its viscosity can vary with the applied electric field strength. This paper investigates a polishing method using the electrorheological fluid, known as ER fluid-assisted polishing, for the finishing of micro dies of tungsten carbide alloy, which are used for the mass production of micro aspheric glass lens. The machining principle of the ER fluid-assisted polishing is introduced. By proper design of experiments based on a Taguchi orthogonal array and by multi-variable linear regression, empirical models are developed for evaluation of the effect of the process parameters on the material removal depth and surface roughness obtained in the ER fluid-assisted polishing. Further experiments are conducted to confirm the validity of the developed statistical model by comparing the model predictions with the experimental results and meanwhile the influences of the process parameters on the polishing performance are revealed.     

Polishing properties of tiny grinding wheel based on Fe3O4 electrorheological fluid

Experiments were conducted to reveal the polishing properties of the Fe₃O₄ electrorheological fluid, which was used to form a dynamical, instantaneous tiny grinding wheel to polish optical glass. The profile of the polished area of the glass surface indicates that the material removal process is dominated by the synergy of the applied pressure and the relative velocity between the abrasives and the workpiece to be polished. It is also found that the rate of material removal is proportional to the intensity of external electric field and decreases with the extension of the machining gap between the workpiece and the needle-like tool.     

硬质合金刀具材料化学机械抛光机理研究

目的研究硬质合金刀具材料化学机械抛光(CMP)机理,为改善硬质合金刀具表面质量提供理论支持。方法分析硬质合金刀具材料在酸性抛光液中的化学反应,研究硬质合金刀具材料CMP的化学反应机理。基于接触力学理论计算抛光垫与工件的实际接触面积和单个磨粒的实际切削面积,在运动学分析的基础上,建立硬质合金刀具材料CMP的材料去除率模型,通过实验验证材料去除率模型的有效性。结果在酸性抛光液中,硬质合金被氧化成Co_3O_4。当工件、抛光垫、磨粒类型、工件安装位置确定时,材料去除率与抛光载荷、磨粒浓度和抛光盘转速有关。常用硬质合金抛光条件下,抛光YG8刀具的修正系数Kcm为8.53,抛光后刀具的最低表面粗糙度能达到48nm,材料去除率为62.381nm/min,材料去除率的理论值和实验值的最大相对误差为13.25%,消除了表面缺陷,获得了较好的镜面效果。结论建立的材料去除率模型具有一定的有效性,对硬质合金刀具材料进行化学机械抛光能消除刀具的表面缺陷,改善表面质量。     

Five-axis grinding of wear-resistant,thermally sprayed coatings on free-formed surfaces

The abrasive wear resistance of tribologically stressed free-formed surfaces can be increased with thermally sprayed tungsten carbide coatings. In order to improve the surface topographies and shape accuracies, the workpieces must be finished prior to industrial application. A suitable machining process is NC grinding on five-axis machining centres using abrasive mounted points. However, the high hardness of the applied coatings and the small diameter of the utilized tools pose a great challenge for the process design. In this paper both, the results of fundamental investigations on the grinding of tungsten carbide coatings as well as a process optimization for the finishing of a coated forming tool are presented. This includes the heat transfer into the coating and the tool wear during the grinding process as well as the wear behaviour of the coating in dependence of the generated surface topography. In order to achieve a smooth surface, elastic-bonded diamond tools were used during polishing in a multi-stage machining process.     

Development of Ultrasonic Vibration Assisted Polishing Machine for Micro Aspheric Die and Mold

Demands are increasing for micro axis-symmetric aspherical lenses to be installed in various optical devices. The micro glass lenses are generally molded by glass press process with micro aspheric ceramic molding dies or molds made of tungsten carbide or silicon carbide. These dies and molds are mostly ground with micro diamond wheels, but require additional finishing process as the size of the dies and molds become smaller and the required accuracy becomes higher. In order to finish micro aspheric dies and molds with diameter less than 3mm, an ultrasonic vibration assisted polishing machine is developed. A small polishing tool is mounted on a 3-axis controlled table, and vibrated at an ultrasonic frequency with piezo-electric actuators. The polishing pressure can be controlled with a resolution of 2 mN. Some micro aspheric molding dies made of binder-less tungsten carbide were polished, and the form accuracy below 70 nmP-V and surface roughness of 7 nmRy were obtained with the developed machine.     

Elliptical Vibration Cutting of Tungsten Alloy Molds for Optical Glass Parts

Elliptical vibration cutting is applied to ultra-precision machining of tungsten alloy molds for optical glass parts in the present research. The tungsten alloy is expected as a new mold material instead of conventional ones such as sintered tungsten carbide and CVD-silicon carbide. However, it cannot be finished precisely by ordinary cutting because of rapid tool wear, brittle fracture and adhesion to the tool. Therefore, the ultrasonic elliptical vibration cutting is applied to the ultra-precision machining of tungsten alloy. Practical ultra-precision molds are obtained by the elliptical vibration cutting, and they are applied to glass molding successfully.     

Study on magnetic polishing of free-form surfaces

Magnetic polishing technology applicable to free-form surfaces such as the die/mold manufacturing field, has been studied using two types of magnetic polishing tool. Finishing efficiency and final surface roughness can be satisfactorily achieved at the same time by magnetic polishing using two types of magnetic polishing tool. One is an abrasive wheel type and the other is a magnetic brush type. The possibility of free-form surface polishing has been confirmed by use of the magnetic polishing technology because it has flexibility of profiling and does not need any complex tool-path control, with respect to workpiece surfaces. Magnetic force was estimated and measured. A two-stage magnetic polishing experiment has been executed using the magnetic polishing tools and mini CNC milling machine without tool-path control. A realization of efficient polishing of curved surfaces is possible using the two-stage magnetic polishing method, and it was also confirmed that automation of free-form surface polishing is possible by this method.     

面向大平面光学玻璃的射流抛光喷嘴设计

射流抛光是应用于先进光学制造业的一种新的加工方法,喷嘴是射流抛光设备的重要元件。传统的针形喷嘴加工效率较低,不能满足大平面光学玻璃的加工需求。为此,设计了新型喷嘴以提高射流抛光效率,对不同结构参数的喷嘴进行了数值模拟。模拟结果表明:新型喷嘴可满足大平面光学玻璃的加工需求;选择较小的喷嘴出口宽度、较大的喷嘴收缩角度和收缩段长度可有效地提高射流抛光的加工效率。     

High-speed five-axis milling of hardened tool steel

This paper investigates critical issues related to high-speed five-axis milling of hardened D2 tool steel (hardness HRc 63). A forging die cavity was designed to represent the typical features in dies and molds and to simulate several effects resulting from complex tool path generation. Cutting tool materials used were coated carbide for the roughing and semi-finishing processes and polycrystalline cubic boron nitride (PCBN) for the finishing process. The effects of complex tool paths on several critical machining issues such as chip morphology, cutting forces, tool wear mechanisms, tool life and surface integrity were also investigated. The main tool failure mode was chipping due to the machine tool dynamics. A five-axis analytical force model that includes the cutter location (CL) data file for computing the chip load has been developed. The effect of instantaneous tilt angle variation on the forces was also included. Verification of the force model has been performed and adopted as a basis for explaining the difficulties involved with high-speed five-axis milling of D2 tool steel.     

抛光垫特性对硬质合金刀片CMP加工效果的影响

目的研究不同种类的抛光垫对硬质合金刀片表面化学机械抛光(Chemical Mechanical Polishing/Planarization,CMP)加工过程的影响,为实现硬质合金刀片高效精密CMP加工提供有效参考。方法利用Nanopoli-100智能抛光机,通过自制的Al2O3抛光液,分别采用9种不同种类的抛光垫对牌号为YG8的硬质合金刀片进行CMP实验,将0~40、40~80、80~120 min三个加工阶段获得的材料去除率和表面粗糙度进行对比,同时观察最佳的表面形貌,分析抛光垫特性对CMP加工效果的影响。结果在抛光转速60 r/min,抛光压力177.8 k Pa的实验条件下,9种不同类型的抛光垫中仅有5种适合用于YG8硬质合金CMP加工。而且抛光垫的表面粗糙度在YG8刀片CMP加工过程中的影响最为显著,抛光垫表面粗糙度越高,CMP加工的材料去除率越高。此外,抛光垫的使用时间对CMP过程也有影响,抛光垫使用时间越长,CMP的材料去除率越小。结论 YG8硬质合金刀片经5种不同类型抛光垫CMP加工后,其表面的烧伤、裂纹等缺陷均得到了极大改善。当使用细帆布加工40 min时,材料去除率最高,为47.105 nm/min;当使用细帆布加工80min时,表面粗糙度最低,为0.039μm。     

Material removal mechanisms of cemented carbides machined by ultrasonic vibration assisted EDM in gas medium

A new electrical discharge machining (EDM) technology named tool electrode ultrasonic vibration assisted electrical discharge machining in gas medium (UEDM in gas) is proposed and its principle is introduced. Relevant experimental equipment was designed by which a series of machining experiments of cemented carbide material were carried out. The mechanisms of cemented carbide material removal are discussed in detail through observing and analyzing the microstructures of machined surface. Five material removal mechanisms of cemented carbides machined by UEDM in gas were proposed, which are melting and evaporation, oxidation and decomposition, spalling, the force of high-pressure gas and the affection of ultrasonic vibration.     

基于碳化硅纤维丝束不规则运动的多孔薄板类零件表面抛光理论与实验研究

汽车空调压缩机用多孔类阀板表面多采用硬研磨工艺进行光整加工,存在表面粗糙度大、孔边有毛刺、阀片与阀板配合表面密封不严等问题。为解决以上问题,提出利用碳化硅纤维丝束抛光替代传统的研磨。完成应用碳化硅纤维丝束进行抛光的运动轨迹的理论分析,采用MATLAB软件对运动参数进行优化仿真,对比分析了毛刷头和工件不同速度对运动轨迹的影响规律。设计制作了双面智能抛光机,并通过实验对运动参数和抛光效果进行验证。结果表明:此种方法将阀板表面的抛光轨迹变成小的均匀曲线交叉网格,消除孔边毛刺并对孔边进行了倒小圆角,提高了阀板表面质量。     

玻璃材料高速抛光用固着磨料磨具试验研究

目的实现玻璃材料的高效高质量低成本抛光。方法选择不同添加剂作为辅料制作固着磨料抛光磨具,阐明制作工艺流程、添加剂辅料配方及比例、固着磨料磨具对材料硬度、剪切强度等性能的影响。以工件材料去除率、表面质量以及磨耗比等作为评价指标分析不同添加剂辅料对加工效果的影响,并通过等效系数优化方法确定添加剂辅料的最优配方。结果碳化硅与钼酸铵可增加磨具的硬度和剪切强度,磨具中加入适量氧化铝可有效提高工件表面质量。结论固着磨料抛光磨具的添加剂辅料最优配方为:10.6%(质量分数)4000#Al2O3和2%(质量分数)10000#SiC。     

一种玻璃抛光用新型抛光盘的研究

研究了一种用于玻璃抛光的新型抛光盘。该抛光盘用不饱和聚酯树脂做结合剂,用环烷酸钴和过氧化甲乙酮组成促进引发体系,以氧化铝-氧化铈新型核壳复合磨粒作磨料,以硫酸镁做造孔剂,以铜粉、碳化硅作为导热填料,以钼酸铵作为活性抛光剂。其成品成本较低,磨削效率高,抛光面平整度好,没有裂纹、亮丝、划痕,可以达到稀土抛光盘的抛光效果。     

模具曲面的C1连续刀具路径加工

模具曲面加工时,一种方法是采用C0连续刀具路径加工;本文论述了另一种方法即采用C1连续刀具路径加工。后一种方法得到的G代码NC文件更小,加工出来的曲面几何尺寸更精确,表面粗糙度更低,加工和抛光时间更少。     

Smooth trajectory generation for five-axis machine tools

This paper presents a smooth spline interpolation technique for five-axis machining of sculptured surfaces. The tool tip and orientation locations generated by the CAM system are first fitted to quintic splines independently to achieve geometric jerk continuity while decoupling the relative changes in position and orientation of the cutter along the curved path. The non-linear relationship between spline parameters and displacements along the path is approximated with ninth order and seventh order feed correction splines for position and orientation, respectively. The high order feed correction splines allow minimum deviation from the reference axis commands while preserving continuous jerk on three translational and two rotary drives. The proposed method has been experimentally demonstrated to show improvements in reducing the excitation of inertial vibrations while improving tracking accuracy in five-axis machining of curved paths found in dies, molds and aerospace parts.     

Prediction of cutting forces in three and five-axis ball-end milling with tool indentation effect

Simulation of multi-axis ball-end milling of dies, molds and aerospace parts with free-form surfaces is highly desirable in order to optimize the machining processes in virtual environment ahead of costly trials. This paper presents a mechanics model that predicts the cutting forces in feed (x), normal (y) and axial (z) directions by modeling the chip thickness distribution, and cutting and indentation mechanics. The shearing forces are based on commonly known cutting mechanics models. The indentation of the cutting edge into the work material is modeled analytically by considering elasto-plastic deformation of the work material pressed by a rigid cutting tool edge with a positive or negative rake angle. The distribution of chip thickness and geometry of indentation zone are evaluated by considering five-axis motion of the tool along the toolpath. The proposed model has been experimentally validated in plunge indentation, as well as in three and five-axis ball-end milling of free-form surfaces. The prediction of axial (z) cutting forces is shown to be improved significantly when the proposed indentation model is integrated into the mechanics of ball-end milling.     

数控机床五轴变换系统设计与研究

为实现数控机床五轴联动加工,基于国内蓝天系列数控系统提出了控制系统结构的改进方法。数控系统分为任务层和运动层,五轴变换单元集成在运动层。在对五轴机床进行分类并分析其几何信息的基础上,设计了机床的五轴运动库。以CA摆头机床为例,推导了其正向和反向运动变换。基于改进系统及五轴运动库,设计并分析了机床旋转刀具中心控制和三维半径补偿端铣。改进系统具有较好的可移植性,可在数控加工中直接执行刀具位置和方向指令。     

A new method of automatic polishing on curved aluminium alloy surfaces at constant pressure

This paper presents original research results of automatic polishing on curved surfaces of aluminium alloy moulds at constant pressure. The automatic polishing of aluminium alloy material is achieved. A parameter S is defined, which can express the comprehensive influential factors in the automatic polishing process and give a relationship among the polishing quality and the various machining variables. Based on this, a new method for comprehensive control of polishing quality is suggested.