**1. Introduction**

Recent years have seen the rapid increase in the demand for microscale components smaller than 100μm in diameter, such as micro machine parts, micromachining tools, micro pin gauges, medical catheters, and probes used in scanning tunneling microscope (STM) and semiconductor inspection. To meet this demand, many researchers have actively engaged in the development of new technology for fabricating such devices precisely and efficiently by non-traditional or mechanical machining methods.

Non-traditional machining has employed laser beam lithography and the focused ion beam method. Maruo and Ikuta [1], Yamaguchi et al. [2], and Nakai and Marutani [3] utilized laser beam lithography to fabricate 3D microscale photopolymer components including microscale cylindrical parts. Vasile et al.[4] developed a processing method for the sharpening of STM probes with a focused ion beam. Furthermore, electric discharge machining (EDM) technology is quite effective in micromachining, as seen, for example, in studies on wire EDM of minute electrodes by Heeren et al. [5] and Masuzawa et al. [6,7]. However, these non-traditional methods can only be applied to a limited set of materials, and problems involving machining efficiency and accuracy have not been resolved.

On the other hand, traditional mechanical machining methods, such as cutting and grinding, have also been employed in microscale fabrication. For example, Uehara et al. [8] studied electrolytic in-process dressing (ELID) cylindrical grinding of a micro-shaft, and Okano et al. [9] researched cylindrical grinding of a micro-cylinder. Yamagata and Higuchi [10] developed a four-axis controlled ultra-precision machine and conducted precision turning experiments on a stepped shaft. In these traditional mechanical methods, however, the workpiece is held at its end by a chuck or at both ends by two centers during machining operation. Consequently, it is difficult to perform high-efficiency, high-accuracy machining,

© 2012 Fan, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

especially on microscale cylindrical workpieces with a large aspect ratio because of the low stiffness of the workpiece support mechanism. Fortunately, these problems can be solved if a centerless grinding technique is employed since the workpiece can then be supported along its entire length on a regulating wheel and blade. However, in microscale machining by conventional centerless grinding, an extremely thin blade is required because the blade thickness must be smaller than the workpiece diameter so that the regulating wheel does not interfere with the blade. This necessitates the installation of a costly blade and significantly reduces the stiffness of the workpiece support mechanism. In addition, because of the extremely low weight, the microscale workpiece springs from the blade easily during grinding due to the surface tension of the grinding fluid adhering to the lifting regulating wheel circumference surface. This phenomenon is called "spinning" [11], and causes the grinding operation to fail. However, as will be explained below, these problems would be overcome by employing the ultrasonic-shoe centerless grinding technique developed by the present authors [12–15] in microscale fabrication.

Fabrication of Microscale Tungsten Carbide Workpiece by New Centerless Grinding Method 123

The Fig.2 shows the detail principle of ultrasonic vibration shoe centerless grinding. The workpiece is supported by an ultrasonic elliptic-vibration shoe together with a blade, and it is fed towards the grinding wheel by the shoe. When two alternative current (AC) signals (over 20kHz) with a phase difference of *Ψ*, generated by a wave function generator, are applied to the PZT after being amplified by means of power amplifiers, the bending and longitudinal ultrasonic vibrations are excited simultaneously. The synthesis of vibration displacements in the two directions creates an elliptic motion on the end face of the metal

Consequently, the rotation of workpiece is controlled by the friction force between the workpiece and the shoe so that the peripheral speed of the workpiece is the same as the bending vibration speed on the shoe end face. The speed varies with the variation of the voltage. In addition, the geometrical arrangements of workpiece such as the shoe tilt angle , the workpiece center height angle over the grinding wheel center, and the blade angle can be adjusted to get the optimum geometrical arrangement in order to achieve the least

Based on the processing principle described above (see Fig.2), a grinding apparatus was built as illustrated in Fig.3. The cylindrical workpiece is constrained between the ultrasonic shoe, the blade, and the grinding wheel. The shoe and the blade are xed on their holders by using bolts. A ne feed mechanism consisting of a linear motion way, a ball screw, and the

Motion forward and backward on to the grinding wheel during grinding. The rotational speed of the workpiece is controlled by the elliptic motion of the shoe. Once the clockwise rotating workpiece interferes with the grinding wheel that is rotating counterclockwise at high speed, the workpiece is fed forward and grinding commences. As can be seen in Fig.1 (a), the gap between the lower right edge of the shoe and the top face of the blade should be smaller than the workpiece diameter; otherwise the workpiece would fall through the gap, causing the grinding operation to fail. Therefore, when grinding a microscale workpiece less than100μm in diameter, the vertical position of the shoe must be adjusted carefully so that

shoe holder is driven by a stepping motor to give the shoe a ne

**Figure 2.** The detail principle of ultrasonic vibration shoe centerless grinding

elastic plate.

roundness error.
