Papers by Author: Shinya Tsukamoto

Abstract: Fluid dynamic bearings, which have an advantage in high-accuracy revolutions, are employed for spindle motors of hard disk drive, cooling fans for central processing unit, spindles of machine tool, etc. Micro herring-bone grooves are manufactured on cylindrical surface of the shafts in the bearing units, and they generate dynamic pressure during spins. Although the depth of the herring-bone grooves is generally constant, the shafts of which groove depth decreases from the ends of the groove array to its center improve the performance of bearing. The micro grooves are mainly manufactured by chemical etching, electrochemical machining, cutting and form rolling. However, the chemical etching and the electrochemical machining are difficult to control 3D machining profiles with high accuracy. The cutting and the form rolling have problems in tool lives and manufacturing costs. On the other hand, blasting is expected as one of micro fabrication methods. Therefore, we focused on blasting, and have investigated its material removal capabilities by fundamental tests. The purpose of this study is to control machining profiles in cylindrical blasting. The machining profiles of cylindrical workpieces in blasting were simulated based on the material removal capabilities obtained by the fundamental blasting tests. Then, the simulated profiles agreed well with the experimental ones by blasting under the same experimental condition.

Abstract: While grinding with CNC cylindrical grinding machines, there are many factors that determine the precision and accuracy of the finished product. These may include dimensional accuracy, surface roughness, circularity (roundness), cylindricity, etc. But all these factors pertain to the work. The condition of the tool, in this case, the cutting edges of the grinding wheel, also greatly influence the profile and precision of the work. So, in order to maintain the precision of the work, there is a need to repeatedly and regularly maintain the cutting edges in a good cutting condition, by the process of dressing. In other words, when the swarf gets adhered to the grinding wheel, the abrasive particles can no longer perform machining with the same efficiency, due to increase in contact surface area between the abrasive particles and the work. This dissertation describes a technique that can be adopted to continuously monitor the grinding forces generated during the grinding operation, by using an in-process 2-dimensional piezoelectric force sensor, which can simultaneously measure the force and break it down into its two force components. The force sensor not only calculates the force generated, but also quantifies the force variation. By analyzing the variation in the radial and tangential force components individually, and by conducting Fourier analysis on the observed data, it is found that deterioration of the grinding wheel and the dress pattern can be continuously monitored and controlled.

Abstract: In surface grinding of a large workpiece used for a sliding surface of the machine tool, high shape accuracy is required for the ground surface. Therefore, it is important to investigate the causes of the shape error observed in a large workpiece machined by surface grinding. In this study, we focused on the thermal deformation and residual stress as the causes of shape error. The in-process measurement of the workpiece temperature distribution was carried out to estimate the effect of the thermal deformation to the shape error. The estimated value of the shape error calculated from the measured temperature distribution was much less than the actual measured shape error. Therefore, the residual stress on the ground surface was measured with a portable X-ray stress measurement device. The residual stress was changed from compressed state to tensile state as the grinding pass increased. The ground shape was also deformed to concave shape as the grinding pass increased. The value of the shape error was finally reached to the constant value in several grinding conditions. From these experimental results, it is suggested that the shape error of the large workpiece is caused by the residual stress applied to the ground surface.

Abstract: Superfinishing is widely used as a final finishing method for sliding surfaces of bearings. In superfinishing, a fine finished surface can be obtained by transiting the machining states from the cutting action to the finishing one as the tool loading is encouraged. To obtain good machining conditions, it is necessary to judge the transition of the machining state reliably. However, it is difficult to judge the transition of the machining states. In this study, we focused on the change of the dynamic component of the machining force, which was applied to the oscillation direction of the superfinishing stone, during machining process. With machining experiments, the relationship between the declination of the dynamic machining force and the transition of the machining state was confirmed.

Abstract: In dry grinding of hard carbon parts, the grinding performance of wheel is remarkably lost by carbon chips loading on wheel surface. The deterioration in grinding performance of wheel affects the grinding accuracy and efficiency. Generally, the grinding performance of loading wheel recovers by dressing. However, the dressing is not suitable from a viewpoint of the wheel life and the production cost because many abrasive grains having sharp edges under loading carbon chips on wheel surfaces are lost by dressing. In this study, we propose the application of dry ice blasting as a removal method of loading carbon chips. The dry ice is little influence on the working environment because of the quick sublimation of dry ice particles to carbon dioxide. In addition, the dry ice blasting might be suitable for the chip removal method because the dry ice doesn’t remain on wheel surfaces after blasting without the damage of wheel surfaces. The dry ice blasting tests of resinoid bond diamond wheel surface with no grinding performance by loading carbon chips are carried out, and the effects of dry ice blasting on removal of loading carbon chips are investigated, analyzing the protrusion height of abrasive grains, the impact pressure in the dry ice blasting and so on.

Abstract: The grinding performance of wheel remarkably decreases by the wheel loading in dry grinding of precision hard carbon parts. When the wheel loading occurs, the dressing is carried out to remove loading chips for generation of the grinding performance. However, many abrasive grains, which have enough cutting ability under loading chips, are removed in dressing. We therefore have developed the wheel surface cleaning using adhesive films without dressing to remove loading carbon chips on wheel surfaces in our previous reports, and the cleaning could achieve the lean regeneration of grinding performance of fine grade diamond wheels. The removing ability of loading chips is improved by increasing the peeling speed of adhesive film, the pressing time of adhesive films or the number of pressing time. However the optimum cleaning condition has not been investigated. In this report, from the viewpoint of efficiency in the treatment, we therefore investigate the optimum rolling press process of adhesive film on loading disc wheel surfaces in dry grinding of carbon. The optimum treatment processes are experimentally made clear, analyzing SPa of cleaned wheel surfaces, which is one of surface roughness parameters having the correlation with the protrusion height of abrasive grains. Furthermore, the effect of the treatment on regeneration of grinding performance is experimentally verified by grinding tests of hard carbons.

Abstract: In surface grinding, the shape error is occurred by the thermal deformation of a ground workpiece. To finish the workpiece with high accuracy, it is necessary to understand the temperature distribution of the workpiece during grinding process. However there is no study to analyze the temperature distribution of a large workpiece during surface grinding process. In this study, an advanced simulation analysis method of the temperature distribution for a large workpiece was developed. In the developed simulation analysis method, the temperature distribution was calculated from the power consumption of the wheel motor. The power consumption can be obtained easily without any specialized equipment. To evaluate the developed simulation analysis method, in-process measurement of the temperature distribution of a large workpiece was also carried out. A large workpiece ground in this study weights about 1.3 tons. The temperature distribution was measured with thermistors mounted in many places of the ground workpiece. At the area close to the grinding surface, it was found that temperature rises immediately after the passage of grinding wheel with measuring the developed in-process measurement system. On the other hand, at the area far from the grinding point, temperature does not change quickly. The in-process measured temperature distribution agreed well with the simulated results.

Abstract: In the NC machine tools for automatic mass production processing lines, it is demanded that high stable machining accuracy is maintained for a long time. The main factor of deterioration in machining accuracy depends on the thermal deformation of machine tool, and the measures are one of the most important issues in the machine tool design. The thermal deformation is practically estimated by the temperature changing state of machine tools based on obtained data of their thermal deformation chracteristics. The estimation accuracy of thermal deformation depends on the thermometry points of machine tool greatly. This study describes an approach to the most suitable thermometry points in machine tool to determine the effective thermal deformation measures experimentally. As a result, the existence of points where the temperature of components changed with relation to thermal deformation very closely was confirmed.

Abstract: Currently, the machining fluid includes several chemicals such as cutting oil and grinding oil is used for the machining. However, such the machining fluid that is caused enormous disposal cost and environmental load, should reduce using. Therefore, in this investigation, electric rust preventive machining method which uses only water for machining fluid is developed. Because using only water without extreme pressure agents, oil and so on, this method decreases disposal of waste machining fluid. In this paper, the system to remove impurities from a used machining fluid, and to reuse machining fluid is designed. To reproduce water efficiently, the order of arranging the filter is changed. In consequence, it has been efficient when the filtration filter is set up first, and the activated carbon filter is set up in the second. In addition, the reproduction of the water when the supply pressure is 0.75 MPa is verified by using this system. As a result, the water which passed a water recycle system, the impurities such as iron, conductivity, turbidity, colour decreased, and purification of the water is possible for this system. And, 5.2 L/min refined water recycle is achieved.

Abstract: Micro patterning on cylindrical surface, e.g. dynamic pressure bearings, is mainly carried out by chemical etching. However, there exist environmental problems in the waste etchant processing and safety ones in works using toxic chemical liquids. On the other hands, blasting is expected as one of micro patterning methods and comes into use for not only surface modification but also machining of hard and brittle materials. The purpose of this study is to develop the micro blasting technique for cylindrical parts. Therefore, machining characteristics in blasting of rotating workpieces are experimentally investigated, analyzing the stock removal and the surface roughness. In addition, the patterning of micro herringbone grooves are carried out on spindle surfaces based on the obtained characteristics.