Haruhisa Sakamoto

Effects of Megasonic Coolant on Cylindrical Grinding Performance

The effects of the coolant activated by ultrasonic waves, which a re in the order of MHz frequency, on performances of cylindrical grinding were examined expe rimentally. The coolant is also termed as megasonic coolant. From the experiments, the followi ng results are obtained. The activation of the coolant by ultrasonic waves increases the spouting s tre th of the coolant. The ultrasonic vibration is maintained to have a spouted distance of 160 mm. This makes the coolant to twine around the wheel and the workpiece surface, and ensures that the c oolant infiltrates into the grinding point. In the grinding for hardened steels, the megasonic coolant suppresses dulling and wheel wear. On the other hand, in the grinding for hard to grind materia ls, such as stainless steels and aluminum alloys, the megasonic coolant suppresses depositing and welding of chips on working surface, which would improve surface finish.

Change in Dynamic Characteristics of Spindle for Machining Centers Caused by Chucking Mechanism of Clamped Toolholders

In this study, the effects of clamping toolholders on the dynamic characteristics of spindle systems are evaluated experimentally. In the experiments, the transfer functions are obtained by the impulse response method, and then, the dynamic characteristic parameters are identified based on the vibration model of single-degree of freedom. Two types of machining center spindles and four types of toolholders are evaluated. From the experimental results, the following are revealed: (1) the clamping toolholder enhances the vibration amplitude markedly compared with that of the spindle not clamping toolholder. (2) The different chucking mechanisms clearly change the dynamic stiffness of the spindle systems. (3) The order of magnitude of the dynamic stiffness of the spindle systems agrees well with that of the isolated toolholders. It is confirmed experimentally that clamping of the appropriate toolholder improves the dynamics stiffness of the spindle systems for machining centers.

Estimation Method of Grain-Height Distribution Based on the Working Surface Profile of Grinding Wheels

To manage and control grinding process theoretically, the cutting-edge density should be quantified. In this study, the estimation method of the grain-height distribution, which is necessary to quantify the cutting-edge density, has been examined. From the results of simulation by modeling the grain distribution of a grinding wheel, the close correlation has been confirmed between the grain-height distribution and the peak-height distribution of the working surface profile. Based on this, the grain-height distribution can be estimated from the peak-height distribution by narrowing the width accompanied maintaining the total frequency. Since the estimated grain-height distribution agreed well to the distribution determined from the measured 3D-topography, the validity of the method has been confirmed.

Critical Feed/Tooth Value Providing Finest Machined Roughness by Peripheral Cutting with Micro Endmills

This study concerns the rational determination of machining conditions for micro endmills that are less than 1.0mm in diameter. The characteristics of machined surface roughness are measured according to machining conditions, especially the feed per tooth Sz. The machined surfaces conditions are also observed with SEM. From the experiments, the following are made clear: (1) The feed per tooth Sz at the critical value Szc makes machined surface roughness the finest. (2) The conditions of Sz larger than Szc make cutting marks regular, that is, stable cutting can be done under those conditions, and then, the roughness improves according to decreasing Sz. (3) The conditions of Sz smaller than Szc cause irregular machined surfaces including pileups and diggings, that is, cutting becomes unstable conditions. The excessively thin chip-thickness prevents from stably engaging edge on workpiece surface. (4) Although the values of Szc are independent from the type of machine tools and cutting speeds, the values decrease according to decrease in tool diameter. (5) The value of Szc increases when tool has worn over its limit. Therefore, in order to determine machining conditions rationally, the changing behavior of Szc should be understood according to tool wear.

Development of On-Machine Measurement System for Axis Motion Behavior of Rotational Tools with Various Shapes (Consideration of Measurement Principle and Error Factors)

Many researches on measurement and evaluation method of rotational accuracy of machine tools’ spindles has been carried out, since it greatly affects machining accuracy. However, major factor influencing directly on the machining accuracy is behavior of rotational motion of the tool axis and then it can be said that the on-machine measurement and evaluation of the behavior is very important. In this study, therefore, the measurement principle and error factors are considered in design of the device for measuring the axis motion behavior of the rotational tool with various shapes. The results obtained here are as follows. (1) Measurement principle of behavior of the rotational axis motion of the tools with various shapes could be proposed. (2) The proposed principle is applicable to various types of rotary tool such as end mills and drills. (3) It is also applicable to the measurement of tool wear. (4) The allowable range of error factors in designing and making of the device was made clear.

Proposal of Finishing Method of MLA Mold Applied Sphere Indentation

In this study, the novel finishing method of the Micro Lens Array mold is proposed. This method combines the cutting by a ball-endmill and the finishing by sphere indentation. In the previous step, U-shape grooves intersected at right angle are machined by a ball-endmill. In the following step, the ball tool indents at the intersection between U-shape grooves, consequently, the aiming lens form and the aiming surface roughness are obtained. From the results of the manufacturing experiments of the MLA mold by this method, the following are made clear : The proposed method is effective to suppress the deformation of neighboring lens forms caused by following indentation. The improvement effect of sphere indentation on the finished surface roughness is remarkable in the early stage of indentation. The transcribing deviations are 12μm or less in comparison between the radius of lens form and the ideal value regardless of radii in grooves previously cut. In case of the indentation of neighboring four (2 × 2) lenses, the deviation reduces down to 3μm.

Method of Improvement in Identification Accuracy of the Dynamic Characteristics of Joints in Jointed Structure

In this study, we examined influencing factors on the identification accuracy and improving method of the identification accuracy. As a result, the influence of the condition of the dynamic characteristic values is large and these values should correspond to the tangential and vertical directions. The influence of treating dynamic characteristic parameters of the same plural joints is also large, and then the parameters of the same plural joints should have the same value. In addition, the tangential dynamic characteristics should be identified from the vibration mode which has large tangential relative displacement between the joint interfaces. Similarly, the vertical one should be identified from the vibration mode which has large vertical relative displacement between the joint interfaces. Finally, the identification accuracy can be improved greatly by considering these influences.

Proposal of Purification Method of Grinding Coolant by Dissolution of Micro-Bubbles

In this study, the purification method of coolant by the micro-bubble dissolution is proposed. The micro-bubble dissolving device with the simple configuration is incorporated within the coolant supply system of an external grinding machine, and then, the effect of the purification method is examined experimentally on the ground surface roughness. From the results, the following are clarified: The dissolved micro-bubbles can rise up grinding debris by electrical adsorption, and then, the debris is concentrated on the coolant surface in the coolant tank. By this effect, the grinding debris, especially the grain fragments of the grinding-wheel, can be removed from the coolant. The coolant purification by the enough dissolved micro-bubbles reduces the density of grinding debris down to a fourth of the initial condition. This purification effect improves the ground surface roughness. The longer the dissolving duration is, the more the ground surface roughness is improved. Eventually, the improvement of the surface roughness reaches down to a half of that without the micro-bubble dissolution.

Development of Measurement Device for Thermal Displacement in Cylindrical Grinding Machines (Study on Measurement Method for Thermal Displacement with Rotation of Wheel Spindle)

Cylindrical grinding machines are typical machine tools for the final finishing process which produce high accurate and value-added products. However the universal method of measurement and evaluation for their thermal displacement has not been established. Therefore, in this study, we propose a measurement and evaluation method for the thermal displacement of the cylindrical grinding machines with rotation of the wheel spindle and make a device on an experimental basis based on the proposition and examine their validity. As the result of this study, it is made clear that the method proposed by us can measure and evaluate effectively and simultaneously 5 thermal displacements of the cylindrical grinding machines, that is, 3 translational deviations and 2 angular deviations.

Analysis of Effective Cutting-Edge Distribution of Grinding Wheel Based on Topography of Working and Ground Surfaces

In this study, the determination method of the number of the effective cutting-edges had been proposed based on the measurements of working surface topography and the grinding force. Furthermore, its validity is made clear based on the topographical analysis of the ground surface roughness of pure copper, which is excellent in transcribing the working surface. From the results, the following are found out: The ground surface topography contains the periodical component, which is originated in the grinding and dressing conditions, on the fractal noise component. The cutting traces by each cutting-edge can be countable from the ground surface profile, and then, the number of the effective cutting-edges is identified at one line within the working surface. On the other hand, the number of the effective cutting-edges also can be identified based on the working surface, but, this method requires the determination of the typical grain shape. From the experiment, it is confirmed that the grain shape should be almost spherical for making the numbers of the effective cutting-edge identified from the working and ground surfaces equal.