Grinding Accuracy Research Articles

An Accurate Digital Grinding Method on Inner Surface of Thin-Walled Rotary Part

The physics performance of thin-walled rotary parts made of hard brittle material on high-speed aerocraft cannot meet the technical requirements after semi-finished processing, in order to compensate the physics performance, the wall thickness should be properly grinded based on the inner surface reference in the finish machining. A processing method consisted of measuring, calculating and grinding functions is investigated. The data of complex surface is obtained with trigger measuring technology, and the reconstructed profile is calculated with cubic polynomial approaching algorithm, which has fast and stable merits in suit with efficient machining. The grinding G program is generated according to the concrete construction of machining tool. This method has been verified by experiments.

Key Technologies of Image Measurement for Curve Accurate Grinding

Image analysis was used to evaluate the curve grinding process. The measurement system organization and its principle of operation were introduced. Some key technologies that influence the system precision were also studied in details. Real-time image of work piece and wheel grinding can be gathered while using CCD camera. For image de-noising, a kind of wavelet threshold function was presented to calculate the new wavelet coefficients. Local threshold algorithm was used to compute different scale threshold, another threshold is suggested when MSE is minimum. Image signals are reconstructed through invert discrete wavelet transformation with the new wavelet coefficients. For the purpose of increasing the measurement precision, a closed mathematical model of sub-pixel edge detection operator was founded according to the gray moment operator’s invariant characteristics and Tabatabai’s first three sample gray moments. An application of system validity and the comparison results of work piece were also given. From experiments it can be said that the proposed method in this paper is effective, and its detection precision and results are reasonable.

A new digital measurement method for accurate curve grinding process

In this paper, an online measurement and error compensation system for curve grinding based on pattern recognition was presented and verified by experiments. The measurement system organization and its principle of operation were introduced in detail. The work piece and grinding wheel image were sampled at certain positions to avoid spark influence. In order to increase system resolution, images were sampled only at local areas of the work piece and grinding wheel. A discrimination technology based on a circular tolerance zone was proposed which can solve the problem of local image edge comparison. For image de-noising, a local threshold algorithm was applied to determine new wavelet coefficients. Furthermore, a two-step edge detection method was used to realize sub-pixel precision. Finally, a series of experiments were carried out to examine the detection precision of the image measurement system and its influencing factors. From experiments, it can be said that the proposed method in this paper is effective, and its detection precision is much better than traditional methods.

Analysis and Application of Acoustic Emission Signals in Accurate Grinding Machining

This paper analyzes Acoustic Emission (AE) signals in accurate-grinding machining, and influencing factors related in the process. It is indicated that there is favorable corresponding relationship between AE signals with different characteristic parameters and accurate-grinding status, which can be used to monitor the accurate-grinding machining and grinding quality.

The Use of Mechatronics for the Improvement of Grinding Accuracy

Various aspects of the improvement of the functioning of grinding accuracy are considered. Active methods of the control of grinding systems are proposed to ensure the quality required for finishing. It is pointed out that the quality of finishing is closely connected with the mutual position of the tool and the work piece in the grinding process. This position is appreciated by permissible state areas of the axis of the tool and the work piece. Analytical expression of this interaction is described by non-traditional mathematical model’s dependences. Mathematical models presented evaluate eccentricity between the tool and the work piece or between other elements of the system and enable one to better understand the appearance of the second and higher harmonics on the work piece processed or on the tool. They allow one to simulate the finishing not only of the cylindrical, but also of non-round profile work pieces, such as cams, eccentrics, etc. The mathematical dependences worked out allow one to build various modifications of the grinding systems and to evaluate the quality of their functioning. A circuit for the active control of the tool position is proposed, with the goal of quality improvement of finishing. For this purpose the usage of the adaptive spindle with tilting-pad journal bearings is suggested.

Analysis of Chatter Marks in Accurate Grinding on Optical Curve Grinder

Chatter marks that limit ground surface finish have been observed in accurate grinding by using optical curve grinder. To reveal the mechanism of chatter marks, the relationships between grinding parameters and chatter marks are experimentally studied. The profile of the ground surface is analyzed through microscope as well as FFT method. It is found the dynamic characteristics of grinder and the vibration test are efficient tools for this study. Modeling of grinding chatter marks is proved effective for the result of simulation showing consistent with that of experiments. The results of study point out the way to eliminate chatter marks and establish the basis for detection and prediction of the marks.

Profile Grinding of Superalloys with Ultrafine-Crystalline cBN Wheels

This paper deals with the grinding characteristics of newly developed polycrystalline cBN (cBN-U) abrasives in creep feed profile grinding of nickel-based superalloys. Experiments for producing a V-shaped groove on a flat surface in one pass by creep feed grinding have been carried out using the new polycrystalline cBN-U and representative conventional cBN (cBN-B) grits. When grinding with cBN-U abrasives, both radial wear and profile wear are less, and hence the grinding ratio is around 10 times higher than that with the conventional cBN-B abrasives. Grinding forces in grinding with cBN-U abrasives are reduced by 20-30% compared with those in Grinding with cBN-B abrasives. The cBN-U abrasive is suitable for the applications with a high dimensional accuracy in creep feed profile grinding for nickel-based superalloys, because it gives less profile wear, and hence better form retention, than conventional cBN abrasive.

Effect of Ultrasonic Elliptic Vibration on Friction between Shoe and Workpiece in Ultrasonic Elliptic-Vibration Shoe Centerless Grinding

This paper describes an experimental investigation of the effect of ultrasonic elliptic vibration of the shoe on the friction between the shoe and the workpiece in ultrasonic elliptic-vibration shoe centerless grinding, a new centerless grinding technique proposed previously by the present authors. In the new technique, an ultrasonic elliptic-vibration shoe is employed to control the workpiece rotational speed as a regulating wheel does in conventional centerless grinding. The grinding accuracy is affected significantly by the workpiece rotation stability, which is dependent on the frictional force between the workpiece and the ultrasonic elliptic-vibration shoe. The issue relating to the friction between the workpiece and the shoe is therefore very important in the complete establishment of the new centerless grinding technique. In the present work, in order to clarify the effect of ultrasonic elliptic vibration of the shoe on the frictional coefficient and to determine the appropriate ultrasonic elliptic vibration conditions, a measurement apparatus was built up in-house and used to measure the frictional coefficient under the presence and absence of the ultrasonic elliptic vibration. The measurement results indicated that the frictional coefficient decreases with increase in the size of the ultrasonic elliptic motion, and a shape of the elliptic motion, in which the frictional coefficient reaches maximum, exists.

천체망원경용 비구면 반사경 표면조도 향상을 위한 최적연삭변수 수치결정모델

지상 및 우주 천체 망원경용 비구면 반사경면 초기 제작공정에는 고정입자 휠을 사용하는 연삭이 있다. 본 연구에서는 매 연삭 가공 이전에 설정한 목표 표면조도를 달성할 수 있도록 입력 연삭변수들을 결정하고, 표면 가공오차를 추적하며 , 가공 경과시간을 최소화하는 새로운 연삭공정을 개발하였다. 특별히 이 공정 기법은 이전 연삭 가공 작업시 까지 수집된 입력 변수 및 가공 결과 표면조도 자료를 다 변수 회귀분석 방법에 대입하여 목표 표면조도에 따른 최적 연삭가공 입력변수를 매 가공 작업 시 진화적으로 제시하는 지능형 공정 조절 능력을 갖추고 있다. 개발된 공정기법과 초정밀 컴퓨터 수치제어 연삭기를 사용하여 <TEX>$96.1\~65.0nm(Ra)$</TEX> 범위 의 목표 표면조도를 갖는 제로듀어 소재에 대하여 10회 가공 실험을 수행 한 결과 <TEX>$<ETC>=-0.906{\pm}3.38(\sigma)nm(Ra)$</TEX>의 가공 정밀도를 달성하여, 지능형 연삭공정의 효율을 입증하였다. 이러한 연구결과는 천체망원경용 반사경면 연삭 가공 시 정성적 경험에 의존하여 가공하는 기존 기술을 극복하고 정량적 수치 모형에 의하여 가공소요시간 최소화 및 나노미터 급 표면조도를 달성하는 진화형 공정 최적화 기술의 확립이라는 의의를 가지고 있다. Bound abrasive grinding is used for the initial fabrication phase of the precision aspheric mirrors for both space and ground based astronomical telescopes. We developed a new grinding optimization process that determines the input grinding variables for the target surface roughness, checks the grinding error magnitude in resulting surface roughnesses, and minimizes the required machining time. Using the machining data collected from the previous grinding runs and subsequently fed into the multivariable regression engine, the process has the evolving controllability that suggests the optimum set of grinding variables for each target surface roughness. The process model was then used for ten grinding experiments that resulted in the grinding accuracy of <TEX>$<E_{TC}>=-0.906{\pm}3.38(\sigma)\;nm(Ra)$</TEX> for the target surface roughnesses of Zerodur substrate ranging from 96.1 nm (Ra) to 65.0 nm (Ra) The results imply that the quantitative process optimization technique developed in this study minimizes the machining time and offers the nanometric surface roughness controllability superior to the traditional, qualitative, craftsman based grinding process for the astronomical optical surfaces.

Method of accurate grinding for single envelop-ing TI worm

TI worm drive consists of involute helical gear and its enveloping Hourglass worm. Accurate grinding for TI worm is the key manufacture technology for TI worm gearing being popularized and applied. According to the theory of gear mesh, the equations of tooth surface of worm drive are gained, and the equation of the axial section profile of grinding wheel that can accurately grind TI worm is extracted. Simultaneously, the relation of position and motion between TI worm and grinding wheel are expounded. The method for precisely grinding single enveloping TI worm is obtained.

Effects of minimizing hydrodynamic pressure in ultra-precision mirror grinding

This paper describes an investigation about the fluid delivery method that minimizes the generation of hydrodynamic pressure and that improves grinding accuracy. Traditionally, grinding fluid is delivered for the purpose of cooling, chip flushing and lubrication. Hence, numbers of conventional investigations are focused on the delivery method to maximize fluid flux into the contact arc between grinding wheel and workpiece. It is already known that hydrodynamic pressure generates due to this fluid flux, and that it affects overall grinding resistance and machining accuracy. Especially in the ultra-precision mirror grinding process that requires extremely small amount of cut per each pass, its influence on the machining accuracy becomes more significant. Therefore, in this paper, a new delivery method of grinding fluid is proposed on the point of minimizing hydrodynamic pressure effect. Experimental data indicate that the proposed method is effective not only to minimize the hydrodynamic pressure but also to improve machining accuracy.

Effects of minimizing hydrodynamic pressure in ultra-precision mirror grinding

This paper describes an investigation about the fluid delivery method that minimizes the generation of hydrodynamic pressure and that improves grinding accuracy. Traditionally, grinding fluid is delivered for the purpose of cooling, chip flushing and lubrication. Hence, numbers of conventional investigations are focused on the delivery method to maximize fluid flux into the contact arc between grinding wheel and workpiece. It is already known that hydrodynamic pressure generates due to this fluid flux, and that it affects overall grinding resistance and machining accuracy. Especially in the ultra-precision mirror grinding process that requires extremely small amount of cut per each pass, its influence on the machining accuracy becomes more significant. Therefore, in this paper, a new delivery method of grinding fluid is proposed on the point of minimizing hydrodynamic pressure effect. Experimental data indicate that the proposed method is effective not only to minimize the hydrodynamic pressure but also to improve machining accuracy.

Investigation for Estimating Grinding Accuracy and Power Machined by Generating Mechanism

A rotor housing of a Wankel engine has a peri-trochoidal form that is machined by internal grinder, which is operated upon generating mechanism. This mechanism is elastically deformed by inertia force, torque and grinding force that are caused in grinding process. Therefore, some gaps arise in positional relation between a workpiece and a grinding wheel. Besides, grinding parameters, such as radius of curvature, work speed, the contact length and interference anele at the grinding point, vary considerably while the workpiece rotates in a revolution. In this case, it is necessary to estimate the accuracy of ground form and grinding power to design and to manufacture a form generating mechanism or to grind the trochoidal form. The authors show how to estimate the accuracy of ground form and grinding power by the grinding process simulation. Some results are presented in graphs and tables. Good agreement is found between analytical results and measured values.

The effect of high pressure air jet on form accuracy in slot grinding

Slot grinding used for slot machining of high hardness materials needs high form accuracy and high surface integrity, such as ceramics that are difficult to do cutting and electric discharged machining, and non-conducting materials like high-polymer materials. Generally, the end of a slot grinding wheel has a “V” shape, so the end step is broken by the increase of a grinding resistance such as the clogging. To solve this problem, a high pressure air jet was put in the opposite position of grinding point and form accuracy and wheel wear by the various grinding parameters were measured. The object of this study is to analyze the effects of high pressure air jet to improve form accuracy when the brittle materials were slot grind with a V-shaped cast iron-bonded diamond wheel. High pressure air jet seems to result in the reductions of the wheel wear and enhancement of form accuracy. It is because high pressure air jet blows out the chips between the grains and so the clogging is decreased. The wheel wear becomes reduced by the decrease of the grinding resistance followed by the decrease of clogging. From the above results, we can show the grinding mechanism in slot grinding process.

METHOD OF COMPENSATING INPUT FEED FORWARD CONTROL AND ITS APPLICATION IN THE GRINDING OF BALL LEADSCREW

In order to improve the accuracy of ball lead-screw grinding, a new method of compensating input feedforward control is used in the system of laser feedback error compensation for lead-screw grinder. Theoretical analyses shows that this input-revising algorithm can improve the accuracy and the transient response of the system. When this method is used in the ball lead-screw grinding error compensation system, the maximum error is effectively decreased.

揺動速度制御型連続研削・研磨装置の開発 第１報 装置構造と基本研磨特性

ULSI devices, which consist of fine patterns of less than 0.1 μm, require a large silicon wafer having a site flatness better than 0.1 μm/30mm. We have developed an oscillation-speed-control-type sequential grinding and polishing machine, which can accurately polish a 12-inch wafer to less than 0.3 μm in flatness by measuring wafer profile on machine after highly accurate grinding. This paper describes the structure and motion accuracies of the machine, the basic polishing characteristics, and the polishing profiles at uniform oscillation speed. Pressure and stock removal increase in the periphery of a wafer when the tool overhangs from the wafer. They agreed with the theoretical results. Super-high flatness of less than 0.2 μm over the entire surface was achieved by adjusting the oscillation range at a uniform oscillation speed. This result is consistent with a simulation corrected on the basis of an experimental result that shows that stock removal saturates with the increase of relative velocity.

In-Process Error Compensation for Tooth Form Grinding Works. Robust Error Estimation Algorithm against the Measuring Error and Experimental Result of the In-Process Grinding Error Compensation.

Robust error compensation algorithm for tooth form grinding works of an involute spur gear is proposed. The proposed algorithm is insensitive for the measurement error of the tooth form profile data. Relationship between indirect measurement quantity ; the grinding error and direct measurement quantity ; the tooth profile data are expressed by an implicit function. Error propagation analysis for the implicit model is derived using implicit derivative of the model function. Error ellipsoid of the indirect measurement quantity, which expresses the projection of the error hyper sphere of the direct measurement quantity, is defined. By taking the structural restrictions of the grinding error model into the least square calculation of the error estimation, the primary axis length of the error ellipsoid became smaller, which means the algorithm became more insensitive for the measuring error. Proposed algorithm was implemented on an in-process measuring system with personal computer. Accurate grinding error compensation was confirmed by experimental results.

In-Process Error Compensation for Tooth Form Grinding Works. 2nd Report. Robust Error Estimation Algorithm against the Measuring Error and Experimental Result of the In-Process Grinding Error Compensation.

Robust error compensation algorithm for tooth form grinding works of an involute spur gear is proposed. The proposed algorithm is insensitive for the measuring error of the tooth form profiie data. Relationship between indirect measuring quantity ; the grinding error and direct measuring quantity ; the tooth profiie data are expressed by an implicit function. Error propagation analysis for the implicit model is derived using implicit derivative of the model function. Error ellipsoid of the indirect measuring quantity which express the projection of the error hyper sphere of the direct measuring quantity is defined. By taking the structural restrictions of the grinding error model into the least square calculation of the error estimation, the primary axis length of the error ellipsoid became smaller, which means the algorithm became more insensitive for the measuring error. Proposed algorithm was implemented on a in-process measuring system with personal computer. Accurate grinding error compensation was confirmed by experimental results.

Automatic dwell control in computer numerical control plunge grinding

Accuracy in precision grinding is strongly affected by variations in the normal grinding force. The force gives rise to deflections of the machine, grinding wheel and workpiece. To allow relaxation of the deflection a dwell period is included at the end of the grinding cycle. Estimation of the time constant during grinding allows the automatic selection of the correct dwell time for the individual workpiece and current force level. A new strategy has been developed for the estimation of the time constant based on power measurement during dwell. The strategy employs the weighted least mean squares technique together with weightings based on classification of the power level into bands. The power bands are designed so as to employ lower weightings to be applied to power samples in the regions of the power curve most prone to causing an inaccurate estimate of the time constant. The complete system was implemented on an adaptive system comprising a PC and an Allen Bradley 8200 CNC (computer numerical controller). The time constant identification and dwell control algorithms were executed within the PC and synchronized to the grinding cycle executed under the control of the CNC. The system was successfully tested under laboratory and industrial conditions. It was shown to produce a reliable and accurate estimate of the time constant with workpieces exhibiting time constants in a range from 0.7 to 55 s. The system was shown to cope with this wide range of time constants without user intervention and to be tolerant of the high signal noise levels typically encountered in an industrial environment.

GRINDING PRECISION AND ACCURACY OF FIT OF CEREC 2 CAD-CIM INLAYS

The authors conducted research to determine the grinding precision and accuracy of fit of ceramic inlays generated with the completely redesigned CEREC 2 computer-assisted design/computer-integrated manufacturing, or CAD-CIM, unit. They found that the grinding precision of the CEREC 2 unit was 2.4 times greater than that of CEREC 1. With CEREC 2, the mean (+/-standard deviation) luting interfaces were 56 +/- 27 micrometers, which is a 30 percent improvement in the accuracy of fit compared with that of CEREC 1.