Key Engineering Materials Vols. 523-524

Abstract: Diamond wires are widely used in cutting hard and brittle materials such as silicon, sapphire, etc. However, present low production efficiency of diamond wires causes their high cost. To solve the problem, a drum-type manufacturing method for electroplated diamond wire tools was developed. Multi diamond wire tools could be manufactured simultaneously at high speed with a single machine. Electroplating characteristics of developed method were evaluated. Additionally, composite electroplating experiments were carried out to find optimal conditions for manufacturing diamond wire tools.

Abstract: 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.

Abstract: Demands for high speed and high precision machining technologies have recently increased in a variety of industries. In general, a high speed spindle system can realize such high performance machining, however it generates a large amount of heat that causes thermal deformation. However, few research papers on thermal deformation-minimized spindle systems have been published so far. This paper presents a newly developed spindle system driven by a built-in air turbine. The developed spindle system has a self-cooling function with the air turbine. In addition, the spindle system has a compact and simple structure compared to the conventional spindle cooling systems. The air turbine was designed to improve the cooling and torque performances. Actual spindle rotational experiments were performed in order to evaluate rotating accuracy and thermal characteristics of the spindle system during rotating at a high speed. Experimental results confirmed that the spindle system can minimize thermal deformation of the spindle by the self-cooling function.

Abstract: Hydrostatic bearing systems are used in machine tools due to the high damping capacity, the high stiffness, and the smooth motion. Demands for higher stiff bearing system have recently increased in various industrial sectors. In order to achieve higher stiffness of the bearing system, working fluid with lower compressibility should be used. High bulk modulus fluid with very low compressibility has been recently developed. This paper presents a hydrostatic bearing system using high bulk modulus fluid. The basic characteristics of the bearing are evaluated with an experimental setup for evaluating the bearing system and then compared the degassed oil with the conventional oil. Furthermore, static and dynamic characteristics of the bearing system were evaluated and compared with that of a conventional hydrostatic bearing. Experimental results confirmed that the high bulk modulus fluid enhances the performance of the hydrostatic bearing.

Abstract: An air bearing lead screw, whose nuts are levitated from the screw threads, has a great advantage of accurately transforming rotational motion to linear motion due to no friction, no backlash and no hysteresis. Therefor precise linear motion can be provided by precise rotational motion which can be obtained by a precise rotary encoder and a motor controller. We developed a positioning controller with servo sampling rate of 10 kHz that employed FPGA (Field Programmable Gate Array) and applied it to positioning of an air bearing stage. The stage consists of an air bearing lead screw and an air bearing linear guide. A rotary encoder, whose resolution has 225000 pulses per rotation, was directly mounted on an axis of the lead screw. This paper describes the positioning performance of the stage by the use of this semi-closed loop control, such as the resolution of less than 10 nm, the linearity over the long stroke.

Abstract: High performance milling spindles, which have high rigidity and high speed, are required for high productive machining. In order to evaluate the rigidity change of the spindle, authors has been developed a magnetic loading device. This device provides attractive force in radial direction to a dummy tool attached to a spindle. By using this device, the static stiffness of the rotating spindle has been successfully evaluated. However the loading rate could not be controlled due to the electric response lag caused by the magnetic field. To solve this problem, electric response of the coil-tool system with the air gap is analyzed and the dynamic response is estimated. The air-gap's influence on the load was also evaluated. Based on the analysis, a dynamic loading test is designed carried out for the measurement of the rigidity of a machine tool spindle.

Abstract: A valveless MEMS pump utilizing a multi-layer thin film NdFeB/Ta permanent magnet (TFPM) has been presented. The MEMS pump consists of a diaphragm actuator utilizing 6μm in thickness and 3 mm in diameter TFPM which is bonded on a membrane made of polydimethylsiloxane (PDMS) of about 80μm thickness, a pump chamber and a pair of diffuser elements. TFPM is sputtered on a 50μm thick Nb sheet. The diffuser elements are used to generate a one-way fluid flow. The chamber is made of acryl plates. UV negative film resist is used to bond different layers. Applying amplitude of ±7.5V square wave voltage, the pump flow rate reaches to 130μL/min at frequency of 15Hz.

Abstract: A MEMS actuator using a magnetic fluid enclosed with polyimide (PI) diaphragms is proposed. The actuator produces a large displacement and force thanks to its structure in which a magnetic fluid is confined between two thin-film PI diaphragms (diameter: 5 mm) fabricated on two silicon substrates. The two substrates with diaphragms are glued together by sandwiching a polyester sheet to form a diaphragm unit. The thickness of the diaphragms is 8.5 µm so that they can deflect greatly. The magnetic fluid inserted between the two diaphragms is composed of magnetite and isoparaffin. The diaphragm unit (containing the magnetic fluid) is deflected by applying an external magnetic field to it with a magnet coil. Response times and displacements of the diaphragms were measured when a magnetic field was applied. Under an applied voltage of 10 V, the diaphragm unit could produce displacements of 4 µm at the diaphragm center. Response time to reach 90% of the maximum diaphragm displacement was about 2 s. Under an applied voltage of 80 V, force generated by the diaphragm unit was 0.065N. It is concluded from these experimental results that the proposed actuator is applicable to MEMS devices such as micro pumps and give another example here.

Abstract: A thin-film polyimide diaphragm for a MEMS actuator was fabricated and its process and mechanical characteristics were investigated. Owing to its low elastic modulus and the thin-film process, a thin-film polyimide diaphragm has a merit in terms of producing a large displacement. Given that merit, spin coating was used for forming a thin film of polyamide, and deep-RIE (Bosch process) was used for fabricating the diaphragm section of the actuator. Thin-film polyimide diaphragms with micrometer-order thickness were fabricated. To drive the diaphragm as an actuator, the following two methods were applied: heat expansion by applying an electric current and volume expansion of a gas-liquid phase-change material confined in a cavity between polyimide diaphragms. As for the former method, an aluminum thin film is deposited on the diaphragm. As for the latter, paraffin (vaporized by heating) is used as the phase-change material. Displacement characteristics for each method were revealed by the experiments. In the case of both methods, displacements of tens of micrometers were outputted. Experiments of driving actuator confirmed that the proposed systems work as actuators. The actuators developed in this research are applicable to micro-pumps for medical and other uses.

Abstract: In order to realize a smart nano-machining and measurement system based on atomic force microscope (AFM), we have been developing diamond probes with a high-aspect-ratio, sharpened diamond tip. In this paper, we described the most important micromachining techniques for the fabrication of the diamond probes. The high-aspect-ratio diamond microstructures were successfully fabricated by employing our proposed two-step reactive ion etching (RIE) processes. A novel bonding technique of diamond to Si at wafer level was also developed by using an inorganic-organic hybrid sol-gel film (MeSiO_3/2) as an adhesive layer to prepare a diamond/SOI wafer as the starting material. Moreover, we demonstrated the applicability of a fabricated diamond probe not only to AFM measurements but also to a tool for nanomachining.