Papers by Author: Hwa Soo Lee

Abstract: In grinding process, the grinding wheel profiles are copied to workpiece surface. Therefore, the finished workpiece surface can be estimated by the grinding wheel surfaces. In this paper, new measuring method of the distribution of cutting edge in grinding wheel surface by two AE sensors is proposed. From experimental results, it is confirmed that the distribution of cutting edges in wheel surface can be measured easily by the proposed method compared to another measuring method.

Abstract: In the grinding operation, grinding wheels are deformed by grinding forces, so that residual stock removal of the workpiece takes place. Since this residual stock removal of the workpiece causes low machining efficiency and deterioration of machining accuracy, high hardness grinding wheels may be selected in order to obtain high machining efficiency and/or high quality machining accuracy. On the other hand, when grinding operations used by low hardness grinding wheels are carried out, it is well known that ground surface roughness is smaller than in case of higher hardness grinding wheels. From such a viewpoint, this study aims to investigate experimentally the effect of the contact stiffness of grinding wheel on the ground surface roughness and the residual stock removal of the workpiece. Grinding operations were carried out using three grinding wheels which are different hardness type, and ground surface roughness and residual stock removal of the workpiece were measured. The contact stiffness of grinding wheel was calculated by a support stiffness of single abrasive grain and a contact area between grinding wheel and workpiece. Comparing the contact stiffness of grinding wheel with the ground surface roughness and the residual stock removal of the workpiece, it was known that ground surface roughness increases and residual stock removal of workpiece decreases with increaseing the contact stiffness of grinding wheel. From these results, since elastic deformation of the grinding wheel changed depending on the suppot stiffness of single abrasive grain, it was clarified that the ground surface roughness and the residual stock removal of the workpiece were changed by the contact stiffness of grinding wheel.

Abstract: A new turning method to control the thrust force to be zero has already been proposed in our laboratory, and it is shown that micro shafts which diameters are less than 1 mm can be generated stably and repeatedly by applying this turning method. As an application of this turning method, a generating method of electrodes of micro electric discharge machining, EDM, for micro holes is proposed. When drilling a micro hole by EDM using an electrode with high aspect ratio, machined chip is difficult to be exhausted. Therefore, machining time has a tendency to be long and the electrode consumption becomes large. Standing in such a viewpoint, a new method to exhaust the chip smoothly by forming the micro electrode geometry is proposed in this paper. As the results of this study, it is confirmed that the machining time of micro holes can be shorted and the consumption of electrode can also be decreased experimentally.

Abstract: It is considered that the contact stiffness between the grinding wheel and the workpiece depends on the number of the abrasive grains in contact with the workpiece and the support stiffness of a single abrasive grain. In this paper, the calculating method of the theoritical contact stiffness of grinding wheel in grinding operation was proposed. Comparing calculated results of the contact stiffness in grinding operation with measured it in the stationary state, the contact stiffness of the grinding wheel in grinding operation was investigated.

Abstract: In order to fabricate micro geometrical shapes by EDM process, micro electrodes as tools are needed. At present, micro electrodes are generated by grinding and/or on-machine EDM operations and then it is well known that efficient productivity of micro electrodes cannot be realized. In this study, a new micro EDM method is proposed, in which, micro electrodes generated in turning operation controlling thrust forces to be zero are utilized. As the results of some experimental evaluations, productivities and availabilities of proposed micro EDM are confirmed.

Abstract: In the case of turning workpieces having high aspect ratios, i.e. length divided by diameter, it is not so easy to obtain high cylindricity because of the elastic deformations due to the thrust forces taking place under operations. In this paper, the generating mechanism of geometrical errors is discussed and its suppressing method is proposed. That is, applying previously established controlling method of thrust forces to turning cylinders with high aspect ratios, it is confirmed that geometrical errors of workpieces due to the action of thrust forces can be suppressed.

Abstract: Usually, the contact stiffness between a grinding wheel and a workpiece has been measured in a stationary state. So, in this study, the contact stiffness under the grinding operation is measured under different table feed rate of the workpiece. From this result, it is known that, while the contact stiffness in the stationary state increases with the increase of the contact force, the contact stiffness under the grinding operation decreases with the increase of the normal grinding force relating the table feed rate. In this paper, since the number of contacting abrasive grain with workpiece is constant irrespective of the table feed rate, and the residual stock removal of workpiece is varied by the table feed rate, it is clarified that the contact stiffness under the grinding operation differs from the contact stiffness measured by the stationary state.

Abstract: Surface geometries of grinding wheels vary due to the wear in grinding process. Since the wheel wear patterns are affected by the grinding process, measuring and investigating these patterns quantitatively, grinding process can be evaluated whether appropriate or not. Utilizing a three-dimensional measuring device for wheel surfaces developed so far, this study aims to evaluate wheel wear patterns quantitatively. As the results, applying developed device, it is clarified that wheel wear pattern can be classified and evaluated quantitatively.

Abstract: In contact areas between grinding wheels and workpieces, elastic deformations of grinding wheel take place due to the act of grinding forces. Since grinding wheels consist of abrasive grains and bonds, it may be regarded that the elastic deformations of grinding wheels in contact areas depend on movements of each abrasive grain. However, plural grains are connected each other complicatedly, and then it is difficult to observe each grain behavior. This study aims to directly observe the behaviors of grains in contact areas with workpieces. A small loading apparatus for grinding wheel is newly developed. Inserting a loaded wheel with this apparatus into SEM, grains behaviors in contact area are directly observed. Furthermore, grains behaviors under loaded condition are analyzed with a wheel model developed previously and observed results are compared with analyzed results.