Key Engineering Materials Vols. 291-292

Abstract: This paper describes an experimental investigation of the effects of ultrasonic vibration in the truing and dressing of the small CBN grinding wheel used for the internal ultrasonic grinding of small holes. In the precision machining of small holes measuring several millimeters in diameter, improvement in the wheel truing accuracy is significantly levels off when using a single diamond dresser or a rotary GC wheel dresser. In the present work, a new truing and dressing technique was proposed, by which the grinding wheel is ultrasonically vibrated in its axial direction during the truing operation using a rotary GC cup dresser. In order to validate the proposed new technique, experiments were carried out. During experimental operations, the GC cup wheel was traversed along the vitrified CBN grinding wheel axis with an in-feed motion toward the grinding wheel in the wheel radial direction. The influences of the truing parameters on the truing force, the run-out of grinding wheel and the grinding wheel surface properties were investigated. As a result, it was found that applying ultrasonic vibration to the grinding wheel decreased the truing force by more than 22%, and the run-out of grinding wheel decreased from an original value of 150µm to a final one of less than 0.8µm, while that obtained without ultrasonic vibration was more than 1.1µm. As well, better surface properties of the grinding wheel were obtained by the application of ultrasonic vibration.

Abstract: The optimum condition selection of rotary dressing operations using Hall and AE sensor is presented. The acquired current signals from a hall sensor were studied as one of the method to obtain the optimum condition of dressing and the correlations between dressing condition and AE signals were also evaluated with the root mean square (RMS). Dressing operation was performed to investigate the effects of depth of cut, rotating speed and coolant. In order to verify the optimum condition of dressing, AE and hall sensor signals were compared in RMS with the surface micrograph of grinding wheel. This verification experiment demonstrates the effective dressing condition selection for centerless grinding.

Abstract: In modern grinding processes the field of application for vitrified bonded wheels is constantly increasing. Regarding the grinding itself, the advantages of these wheels are obvious. But their ability to be dressed offers further benefits as well. Usually in-machine dressing is favorable. Nevertheless, in-machine dressing causes non-productive-times during which no part production is possible. To reduce this disadvantage, a powerful monitoring is needed in order to minimize the number of needed dressing strokes and to verify the created grinding wheel geometry. The approach applicable for industry is to use an acoustic emission sensor for monitoring, which is usually integrated in modern grinding machines to minimize the air grinding time. This article also provides basic knowledge about Acoustic Emission.

Abstract: Grinding is a final step in the production chain of gears and therefore determines the quality of the product. In the industrial practice gears are cut - generally by means of a hobbing process - and their surface is hardened through a heat treatment, which has the target of increasing the wear resistance of the tooth flanks. Grinding is therefore necessary to remove the material distortions originating during the heat treatment and to fulfill dimensional and quality requirements. Usually only gears with high quality requirements are ground. Otherwise grinding is not carried out to reduce the production costs. In the recent years however the percentage of ground gears has been growing continuously due to the rising demands on load capacity, quiet running and life time as well as the increasing performance offered by the grinding processes. Generating grinding by means of cylindrical grinding worms shows the highest potential among the existing processes for gear grinding due to the high material removal performance that can be achieved. In order to use dressable worms efficiently the dressing technology has to be optimized. The present contribution describes the technology for dressing vitreous bonded grinding worms. This process is based on the use of form dressing rollers by means of which the grinding worm geometry and topography are generated. The investigations are aimed at analyzing the influence of the dressing parameters, in particular the speed ratio between dressing and grinding tool, and the attainable gear quality and surface properties. The results show significant dependencies between the dressing strategy and the grinding results.

Abstract: Metal bonded diamond grinding wheels are widely used in the grinding process, especial in ELID grinding. However, truing is difficult owing to the high toughness of metal bond materials and high hardness of diamond abrasives. To realize high precision and high-efficiency truing, we propose a new micro-truing method consisting of electro-discharge truing and electrolysis-assisted mechanical truing in this paper. The process principle and fundamental experimental results are introduced, and the truing performance is discussed. Research results show that the proposed new method is effective for truing metal bonded diamond grinding wheels.

Abstract: In V-groove ELID grinding process, to achieve optimal grinding performance and satisfactory surface quality and profile accuracy, metal bonded diamond grinding wheels need to be carefully sharpened. In this paper, we applied the proposed new micro-truing method consisting of electro-discharge truing and electrolysis-assisted mechanical truing to sharpen the edge of large grinding wheels. The minimum wheel tip radiuses of 6.3 and 8.5µm were achieved for the #4000 and #20000 grinding wheels. The truing mechanisms and sharpening performance are also discussed.

Abstract: We observed that the lubrication effect is greater than the cooling effect for decreasing the friction heat in face grinding. It was clarified that cool-air grinding is difficult to apply to face grinding under the present grinding conditions. We could obtain the minimum ground surface roughness (hereafter noted as surface roughness) at a mist suppｌy volume of 15 to 30ml/h in mist grinding. The largest stock removal rate (hereafter noted as grinding efficiency) is obtained in mist grinding. However, grinding efficient was small in cool-air mist grinding, by which a large cooling effect of cool air was expected. Though mist and cool-air mist grinding perform similar to wet grinding in few grinding passes, wet grinding is properly applied by large chip removal action in many grinding passes.

Abstract: To improve the characteristic of the floating nozzle method, a new coolant supply method using a coolant flow guided flexible sheet was developed. In this method, all the coolant supplied from the nozzle outlet can surely be directed immediately to the grinding point, because the coolant flow guided flexible sheet made of a thin sheet material is attracted to the wheel surface automatically, and confines the coolant between the wheel surface and the sheet. Therefore, the coolant can be completely prevented from deviating away from the grinding point. In fact, when the coolant flow rate of 4 l/min was supplied from the upper part of the wheel by using this method, the amount of coolant that reached the grinding point was 18 times higher than the case of only the floating nozzle method. It was clarified that this method had the effect to improve the grinding performance. Furthermore, this new method has a possibility of the wide application such as in profile grinding and cam grinding.

Abstract: To solve the problem associated with the cryogenic cooling approach and the one with the chilled air approach, an actively cooled coolant approach is proposed and examined. The proposed cooling system is also able to reduce the time period to reach the equilibrium state to enhance productivity. An active cooling prototype was developed that utilizes a compact air conditioner design, which is easy to use, movable, and can be easily fitted into different type of machine designs with relatively low costs. The system is based on the use of forced convection of the heat generated during the machining process. Experimental and computational studies of the effects of actively cooled coolant for grinding brittle materials are carried out. The experimental results show that the use of actively cooled coolant is able to improve surface quality for up to 13.1% on average in terms of surface roughness Ra. The results of optical and SEM examinations confirmed that the proposed approach is advantageous. Computational testing results show that the heat can be taken away more effectively by using the proposed approach.

Abstract: Grinding, like other abrasive processes, may generate high local temperatures along the arc of cut. These can cause various forms of surface damage in the most sensitive finishing phase of the manufacturing cycle. Traditional cooling methods based on large amounts of water-oil emulsions can be both ineffective and environmentally unacceptable. A new approach to this problem has been devised utilizing the high penetrative power of fast air jets combined with a water/soap mist to greatly improve convective cooling and lubrication along the arc of cut. The results obtained offer striking improvements compared to traditional liquid coolants especially if the relative simplicity of the method is considered.