Influence of wheel speed on surface finish and chip geometry in precision contour grinding

A geometric computer model of a precision grinding operation was developed to calculate the surface features generated during contour grinding with a radiused wheel. This simulation includes the influence of the wheel (rotational speed, diameter, and nose radius), the workpiece (radius at cutting point, rotational speed), and the feedrate of the grinding wheel over the part. The model indicates that small changes in the wheel speed relative to the workpiece can have a dramatic effect on the surface finish over a specific area. Analysis of ground surfaces reveals uniform surface profiles and easily distinguished features that could only be produced by a constant wheel speed. This occurs for an air-bearing, air-turbude grinding spindle that has limited torque and is driven under open-loop control. The effects of the relative speeds are analyzed and an energy-based “phase locking” mechanism is proposed that can provide feedback to the grinding spindle from the material removal operation. By monitoring the spindle speeds during the grinding process and evaluating the resulting surface features, the phase effect has been experimentally verified.     

Theoretical and experimental analysis on super precision grinding of monocrystal silicon

Through investigating the diamond-silicon grinding system, the grinding mechanism, including chip removal and subsurface damage, is discussed with the aid of the molecular dynamics (MD) approach and grinding experiments. Based on MD simulation, nanometric-grinding mechanism is analyzed from the viewpoint of instantaneous distribution of atoms, grinding force, and the potential energy between atoms and the profile of the groove. The simulation results show that some silicon atoms are deformed and piled up in front and on two sides of the abrasive surface because of the extrusion and cutting. When the energy in silicon lattice reaches its maximum value, the bonds of silicon atoms are broken and the material is removed. With the advancement of the abrasive, the silicon lattice under the abrasive surface is fractured, and then the amorphous layers are formed and propagated, which causes the subsurface damage. At the same time, some amorphous atoms are reconstructed and the degenerating layer of the machined surface is formed. Besides, the recovery of elatstic deformation occurs in the machined surface of the workpiece. In addition, the grinding experiment and profile detection with the aid of the measurement for 3D profiling are performed to verify the simulation results. The good agreement in the profile of the groove between the experimental value and the simulating value shows that MD simulation is very effective and reliable, and successful to fulfill the investigation on nanometric machining mechanism.     

Surface integrity of silicon wafers in ultra precision machining

Silicon wafers are the most extensively used material for integrated circuit (IC) substrates. Before taking the form of a wafer, a single crystal silicon ingot must go through a series of machining processes, including slicing, lapping, surface grinding, edge profiling, and polishing. A key requirement of the processes is to produce extremely flat surfaces on work pieces up to 350 mm in diameter. A total thickness variation (TTV) of less than 15 μm is strictly demanded by the industry for an 0.18 μm IC process. Furthermore, the surfaces should be smooth (R_a<10 nm) and have minimum subsurface damage (<10 μm) before the final etching and polishing. The end product should have crack-free mirror surfaces with a micro-roughness less than 1.8 Å. In this paper, experiments are conducted to investigate the effects of various parameters on the subsurface damage of ground silicon wafers.     

A precision grinding method for screw rotors using CBN grinding wheel

Aiming at the high precision machining of screw rotors, a new grinding method for screw rotors using cubic boron nitride (CBN) grinding wheel is presented in this paper. Small electroplated CBN grinding wheel is firstly used to grind screw rotors. The mathematical model for the axial profiles of CBN grinding wheel is developed based on gear engagement theory. Taking the backlash of screw rotors and the coating thickness of CBN layer into consideration, the modification of the base body of the wheel shape is introduced into the design of the CBN grinding wheel. Wire cut electrical discharge machining low speed (WEDM-LS) was used to machine the base body of the CBN grinding wheel. The formed turning tools of the base body of CBN grinding wheel using WEDM-LS and the wheel shapes of CBN grinding wheel using the formed turning tool were performed. The CBN grinding wheels for the screw rotors were made to verify the validity and effectiveness of the presented method. The electroplated CBN grinding wheels were used to machine the screw rotors, and the machining experiments were performed. The data obtained in the experiments reach the fifth class of Chinese Standard GB10095-88.     

碳化硅陶瓷的超声振动辅助磨削

采用普通磨削方式和超声振动辅助磨削方式对无压烧结SiC材料进行了磨削工艺实验,对不同磨削方式下磨削参数对磨削力比、表面损伤及亚表面损伤的影响进行了对比研究,并分析了超声振动磨削作用机制。实验结果显示,该实验中SiC材料去除主要以脆性去除为主,砂轮磨削力比随着磨削深度和进给速度的增加缓慢增加,随着主轴转速的增加略有减小;普通磨削时SiC工件亚表面损伤深度随着磨削深度、进给速度增加逐渐增加,而超声振动辅助磨削变化较小。与普通磨削相比,在相同的磨削参数下,超声振动辅助磨削的高频冲击使材料破碎断裂情况得到改善,且磨削力比减小近1/3,表面裂纹、SiC晶粒脱落、剥落等表面损伤较少,表面损伤层较浅,亚表面裂纹数量及深度都有较大程度降低,可以获得较为理想的表面质量。     

硅片低损伤磨削砂轮及其磨削性能

针对传统金刚石砂轮磨削硅片存在的表面/亚表面损伤问题,研制了一种用于硅片化学机械磨削加工的新型常温固化结合剂软磨料砂轮。根据化学机械磨削加工原理和单晶硅的材料特性,设计的软磨料砂轮以氧化铈为磨料,二氧化硅为添加剂,氯氧镁为结合剂。研究了软磨料砂轮的制备工艺,分析了软磨料砂轮的微观组织结构和成分。通过测量加工硅片的表面粗糙度、表面微观形貌和表面/亚表面损伤,进一步研究了软磨料砂轮的磨削性能。最后,与同粒度金刚石砂轮磨削和化学机械抛光(CMP)加工的硅片进行了对比分析。结果表明,采用软磨料砂轮磨削的硅片其表面粗糙度Ra1nm,亚表面损伤仅为深度30nm的非晶层,远好于金刚石砂轮磨削硅片,接近于CMP的加工水平,实现了硅片的低损伤磨削加工。     

Intelligent control of precision thread grinding

This paper presents an intelligent control method for obtaining a leadscrew of higher lead accuracy in thread grinding. Leadscrews are important for machine tools or length measuring machines. With the development of CNC machine tools, leadscrews are required to have high-level precision. This paper describes an improved control method for closed-loop compensation in the thread grinding and analyses of instantaneous drive chain errors. To reduce such errors, a newly designed intelligent control system is constructed. As a result, a leadscrew with high pitch accuracy can be obtained.     

Surface finish measurement using microwaves

This paper describes a method of measuring the surface finish using microwaves and contains the results of measurements made on surfaces produced by some machining processes     

精密电火花磨削加工的切向进给法

采用块状工具电极的精密电火花磨削加工法是低刚度轴和微细轴类零件电火花加工的主要方法之一,该方法过去采用的是径向进给方式。文章提出一种新的块状工具电极的进给方式－切向进给方式,阐述了这种进给方式的优点和应用前景,并进行了初步的验证试验。     

钽合金精密镜面研磨工艺的实验研究

采用传统的精密机械研磨方法,对钽钨铪合金进行了精密研磨实验研究.通过大量实验,优化出了适合此类材料的研磨工艺,得到Ra25nm左右的光滑表面.该研磨方法成本低、污染小、操作简便.实验表明,磨料特性、研磨压力和研磨液的成分配比等参数对研磨效果的影响较大.     

精化普通磨床适应精密磨削加工

对普通万能外圆磨床进行精化并采取一系列工艺措施,成功地对T4680主轴进行精密磨削加工,表面粗糙度达到Ra0.02μm,圆柱度在0.002mm以内。     

Monitoring force in precision cylindrical grinding

Aerostatic spindles are used in precision grinding applications requiring high stiffness and very low error motions (5–25 nm). Forces generated during precision grinding are small and present challenges for accurate and reliable process monitoring. These challenges are met by incorporating non-contact displacement sensors into an aerostatic spindle that are calibrated to measure grinding forces from changes in the gap between the rotor and stator. Four experiments demonstrate the results of the force-sensing approach in detecting workpiece contact, process monitoring with small depths of cut, detecting workpiece defects, and evaluating abrasive wheel wear/loading. Results indicate that force measurements are capable of providing useful feedback in precision grinding with excellent contact sensitivity, resolution, and detection of events occurring within a single revolution of the grinding wheel.     

Peripheral electrochemical grinding of sintered carbides — Effect on surface finish

Peripheral electrochemical grinding was studied on eight typical commercially available sintered carbide tool grades, with emphasis on surface integrity. The different wheel-workpiece regions — the “contact” region, characterized by a simultaneous electrochemical and abrasive action, and the “after-wheel” region in which only the electrochemical aspect is present — were examined with a microscope. A wide range of practical working conditions was covered for additional data. Geometrical surface parameters such as overcut and surface roughness were related to those of the main process. Electrochemical surface parameters such as selective etching, oxide layer formation and local activation were evaluated by optical and scanning electron microscopy. An appropriate process mechanism was suggested on the basis of the results.     

A knowledge based feed-back control system for precision ELID grinding

Newer materials with excellent properties are of recent interest in the optical, electrical and electronics industries. Finishing of new materials for the required stringent specification stated by those industrial applications emerges the innovation of new techniques and processes in the field of manufacturing. Electrolytic in-process dressing (ELID) is one of those new manufacturing techniques which may produce mirror surface finish on various optical and non-optical materials. The easy implementation and the efficiency of the ELID technique have been drawing the attention of the optical manufacturing industries in the recent years. However, further improvements are essential in order to minimize the difficulties experienced during implementation and to extend its suitability for future applications. The authors propose a knowledge based feed-back control system for ELID grinding to eliminate the application difficulties and to improve the effectiveness of the process. This study aims to experiment and to analyze the various features of the developed feed-back control system. The main objective is to examine the effectiveness of the system for precision finishing of optical and non-optical harder materials. The possibilities to reduce the geometrical inaccuracies of the workpiece have been examined in this study. The results show that application of the feed-back control system minimizes the number of correction cycles necessary for precision finishing of hard materials, such as, quartz.     

Surface roughness measurements in finish turning

A new approach is proposed for the on-line measurement of the maximum peak-to-valley roughness,R _max, of a finished-turned surface in the feed direction. The method is based on solving the inverse problem of light scattering by using a linear least-square estimate of the angular scattered light pattern reflected from a surface. A laser system has been developed to capture the light reflected under different cutting conditions. The effects of the ambient room light as well as the workpiece's rotational speed and methods for thier compensation are also discussed. Good correlation was found between the optical and stylus-measuredR _max.Nomenclature R _max maximum peak-to-valley roughness within the sampling length - R _q RMS surface roughness within the sampling length - R _a arithmetically averaged roughness within the sampling length - _z r.m.s. surface height within the sampling length - u r.m.s. slope of the surface within the sampling length - T correlation distance of the surface, defined as the distance in which the correlation coefficient,C(), equals e^–1 - I(₁,) intensity of reflected light - I _m(₁,₂,) measured intensity of reflected light at instant - ₁ angle of incidence of laser beam - ₂ scattering angle defining a CCD pixel location (₁ and ₂ are measured with respect to the normal of the surface of the workpiece coincident with the centre of the laser beam) - v scattering vector of reflected light - _x,_z components ofv in thex andz direction, respectively - L sampling length associated with the laser spot on the surface of the workpiece - j representative location of a CCD pixel - j CCD pixel location corresponding to the mean light level - p _j density function of the light intensity of thejth pixel - wavelength of laser light - nose radius of the cutting tool - ASLP angular scattered light pattern - K correction factor for the measured light intensity - S _m standard deviation of the measured ASLP - S _c standard deviation of the ASLP calculated from an estimatedR _max - K control step size ofK - computational error, defined as =|S _m–S_c|/S _m - K _a,K_b starting and ending point, respectively, within the search range forK - K _c,K_d two points within (K _a,K_b), determined by the golden section search method - V cutting speed (m/min) - f feed rate (mm/rev) - d depth of cut (mm) - H hardness of workpiece (found on Rockwell scale C) - CCD charge-coupled device     

精密球体研磨机压力控制系统设计

为解决传统自适应压力控制和PID压力控制下精密磨球机在磨球时出现的诸如响应时间长,控制精度不够高、机械振动过大等问题,将模糊控制技术应用到磨球机的压力控制中.开展了系统输入变量E,EC和输出变量SV模糊化分析,建立了3个模糊变量之间的关系,提出了基于DSP芯片的压力模糊控制方法,在Matlab软件的Simulink平台...     

In-process force measurement for diameter control in precision cylindrical grinding

This article shows the theory and implementation of a force measurement-based approach to controlling workpiece diameter in cylindrical grinding. A simple model proposed is used to relate infeed velocity to grinding force. The model is extended to accurately control the amount of material removed in outer diameter plunge grinding given the normal force, which may be monitored in real-time. The model incorporates the key parameters, including the structural loop stiffness, the plunge infeed velocity, and the wheel and workpiece properties. However, only the infeed velocity must be explicitly known. The contribution of this work is experimental validation that the lag between infeed and stock removal can be predicted using force feedback without a priori knowledge of the grinding system. This allows very accurate diameter control (0.25 μm of nominal), even in the presence of thermal drift, wheel wear, and machine error.     

Development of a model for precision contour grinding of brittle materials

A graphical computer model of the chip geometry resulting from a three-dimensional grinding operation was developed for use in relating the critical depth data obtained from the one-dimensional plunge-grinding technique. This model predicts the resulting surface finish and calculates the theoretical roughness and the final chip geometry for a precision grinding operation. The model is based on euclidean geometry at the intersection of the surfaces of two solid objects. This model was programmed to calculate the remaining surface height as the wheel progresses across the part. The output of the surface profile for successive cuts can be subtracted to illustrate the shape of the chip removed for each revolution of the grinding wheel. Chip geometry as influenced by depth of cut, feed rate, and tool shape was shown to be an important parameter in diamond turning of brittle materials. Similar relationships are developed for the additional geometric complexities of a precision grinding operation. The theoretical surface features are then compared with the actual features generated by grinding brittle materials.     

Wheel speed equilibria in precision contour grinding

In grinding operations, wheel speed significantly affects surface finish and chip thickness. The grinding wheel speed represents an equilibrium condition based upon the energy input by the grinding motor and the energy removed by the grinding process. An analysis of these energy relationships allows prediction of wheel speed and shows how it changes during grinding because of changes in chip geometry. The analysis also reveals that some wheel speeds are energetically preferred. Wheel speed measurements and images of ground surfaces corroborate the analytical predictions. The presence of narrow ranges of preferred wheel speed has implications for selection of grinding conditions and adoption of wheel speed control.