Fast Tool Servo Diamond Turning of micro-structured surfaces

    Fast Tool Servo (FTS) Diamond Turning is increasingly becoming an important technique for fabrication of micro-structured surfaces (or free-form surface, non-axisymmetrical surfaces, etc). It differs from the conventional diamond turning in that an additional axis, which is named Fast Tool Servo (FTS) or Slow Slide Servo (SSS), is integrated into the conventional diamond turning machine. The newly integrated axis is able to move the cutting tool in and out of the workpiece rapidly within one spindle rotation. The mainly difference between FTS and SSS is the their bandwidth. The bandwidth for SSS is normally below 100 Hz [1], while the bandwidth for FTS can go up to 10 kHz (the normal bandwidth is serveral kHz) [2-5] depending on the types of actuators used and the structural design.In addition, the stroke for the FTS is normally very small within micrometer range, while the stroke for the SSS is in millimeter range.Therefore, FTS diamond turning is limited to machine surfaces with feature height below 1 mm.

    A FTS diamond turning machined is developed at the Advanced Manufacturing Lab at National University of Singapore as shown in Fig. 1. Fig. 2 is a closer view of the machine. A piezoelectric type FTS was developed and integrated into a miniature lathe [6] to realized the function of machining micro-structured surfaces.  

  

Fig.1 A photo for the self-developed FTS Diamond Turning machine at Advanced Manufacturing Lab, National University of Singapore.

Fig.2 A closer view of the FTS Diamond Turning machine.

    Some typical examples of the fabricated micro-structured surfaces are micro-lens array, aspheric lens, Fresnel lenses, sinusoidal grid, etc. Fig. 3 shows a photo of a fabricated micro-lens array. It was measured by whitelight interferometer and an example of the measured result is shown in Fig. 4. It can be seen that the micro-lens array was successfully fabricated with good surface fidelity. 

Fig.3 Photo of a fabricated micro-lens array

Fig. 4 Measurement of portion of the micro-lens array

    To explore the capability of the FTS diamond turning machine, my photo as shown in Fig. 5 is used to generate motion command for fabrication. The machined surface was once again measured by Vecco White-light Interferometer. 2D and 3D view of the measured surface are shown in Fig. 6 and Fig. 7 respectively.

Fig. 5 My photo used for machining.

Fig. 6 2D view of the machined surface measured by Veeco Whitelight interferometer.

Fig. 7 3D view of the machined surface.

References:

[1]http://www.tlatla.net/Res11/4/images/PDFs/Slow%20Slide%20Servo%20Applications%20-%20Y.%20Tohme%2005.05.pdf

[2]Lu, X.-. and D.L. Trumper, Ultrafast Tool Servos for Diamond Turning. CIRP Annals - Manufacturing Technology, 2005. 54(1): p. 383-388.

[3] Trumper, D. and X. Lu, Fast Tool Servos: Advances in Precision, Acceleration, and Bandwidth. Towards Synthesis of Micro-/Nano-systems, 2007: p. 11-19.

[4] Yu D.P., Gan S.W., Wong Y.S., Rahman M., and Hong G.S., "Design of a Fast tool servo based Diamond Turning Machine for Fabricating Micro-structured Surfaces," Key Engineering Materials, 443, pp. 669-674, 2010.

[5] Yu D.P., Gan S.W., Wong Y.S., Rahman M., and Hong G.S., "An Optimization Approach for Tool Path Generation of Micro-structured Surfaces in FTS-based Diamond Turning," The 3rd international conference of Asian Society for precision engineering and nanotechnology, Kitakyushu, Japan, 2009.

[6] Gan S.W., Rahman M., and Lim H.S., "Development of a fine tool servo with force monitoring system for nanomachining applications," J. Vac. Sci. Technol. B, 27-3, pp. 1272-1277, 2009.