Hwa Soo Lee

Grinding Chatter – Origin and Suppression

Abstract Grinding chatter is one of the most critical errors in grinding operations and one that has a strong impact on the ultimate geometrical workpiece accuracy. In the paper the origin of chatter that is particularly due to regenerative effects during inner and outer diameter as well as surface grinding is explained. After the discussion on its influence on surface quality, the possibilities related to process monitoring for the detection of chatter during grinding are presented. Special attention is paid to the suppression of chatter e.g. by employing active or passive damping methods. Furthermore, information on a suitable procedure to conduct a stability assessment for grinding machines is provided.

Surface grinding with ultra high speed CBN wheel

Abstract Effectiveness and problems of surface grinding machine with a ultra high speed CBN wheel were experimentally investigated. Diameter of the CBN wheel expands depending on the wheel speed. The value of the wheel expansion is able to be compensated by calculation. Higher surface speed of the wheel results in lower grinding forces. This tendency is more remarkable when stock removal rate is higher. There exist optimum conditions in the grinding with ultra high speed CBN wheel. Utilizing these results, surface grinding machines with ultra high speed CBN wheel was newly commercialized.

Application of Superfinishing to Curved Surfaces

It is well known that the superfinishing is a high efficient surface finishing method to cylindrical workpieces. In this method, grinding stones are pressed to the outside of cylindrical surfaces. Rotating cylindrical workpieces and making relative vibrations between grinding stones and ground surfaces in the directions of the center lines of workpiece rotations, the cylindrical surfaces are ground and mirror surfaces are realized relatively in short time. Therefore, this finishing method is widely applied to the finishing of precise machine elements. However, this method cannot be applied in case of that the workpiece which is not simple cylindrical geometries so far. In this study, a new application method of superfinishing to the cylindrical workpieces having curved parts is proposed and its performance is discussed experimentally.

Quantitative damage assessment of concrete structures based on 3D laser scanning

Recently scaling damages of concrete structures have become apparent and it is now investigated to develop a method for quantitatively assessing the damages. In this paper, we propose a beneficial method for this purpose based on long-distance 3D laser scanning. In our proposed method, original shapes of the concrete structures before to be damaged are estimated on their laser scanned data by region growing, the distances to the estimated shapes are computed at each scanned point, and then their surface concavity and convexity are quantitatively evaluated based on the computed distance. We demonstrate the effectiveness of our proposed method from various experiments on real scanned data of concrete structures with scaling damages.

Contact Stiffness of Grinding Wheels due to the Difference of Table Feed Rate

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.

A Study on the Contact Stiffness of Grinding Wheels

Abstract. The contact stiffness between grinding wheels and workpieces has been numerically analyzed by applying the theory of Hertzian contact, in which a wheel is considered to be uniform continuous body. It is well known, however, that the grinding wheels are not actually uniform continuous bodies. Consequently, when analyzing the elastic deformation of grinding wheels, the theory of Hertzian contact should not be applied in a simple way. In this study, a mathematical model of grinding wheels consisting of rigid bodies and spring elements had been proposed. By utilizing this model, elastic deformations of the grinding wheels with resinoid bonds in the contact area with workpieces are considered. The analyzed elastic deformations of grinding wheels coincide with the experimental results.

Effect of Static Stiffness of Grinding Systems on a Generating Mechanism of Workpiece Geometrical Accuracy

In grinding operation, static stiffness between grinding wheel and workpiece affects on the generating process of workpiece geometrical forms. In this study, the effect of the stiffness on the center generating process of eccentric workpiece in cylindrical grinding is theoretically analyzed. And designing a grinding simulator which can set the stiffness of grinding system, theoretical analysis is experimentally confirmed. Depending on these results, a predicting method to estimate the grinding time required to complete the process is proposed.

Generation of Uniform Diameter Micro-Bubbles Using a Piezo-Vibration Assisted Capillary Nozzle

In this study, we generated the uniform diameter micro-bubbles using a piezo-vibration assisted capillary nozzle for apply the nano/micro bubbles device use. The capillary nozzle (diameter: 35 μm) was fabricated by FIB technique, and attached with piezo-device as micro bubbles generator. The fabricated piezo-nozzle showed inflective movement, whose displacement amount was about 3 μm. Micro bubbles were not able to generate from capillary nozzle without piezo-vibration, while micro bubbles, whose diameter was in the range of 20 μm to 21 μm, could be generated from the capillary nozzle with piezo-vibration.

Effect of Contact Stiffness of Grinding Wheel on Ground Surface Roughness and Residual Stock Removal of Workpiece

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.

Generation of Microelectrodes for Micro EDM

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.