PRECISION MATERIAL REMOVAL USING THE ELECTROKINETIC PHENOMENON C. S. Leo 1 , T. L. Blackburn 3 , S. H. Ng 2 , C. Yang 1 , D. L. Butler 1,2,* and S. Danyluk 3 1 School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore, 639798 2 Singapore Institute of Manufacturing Technology, 71 Nanyang Drive, Singapore, 638075 3 George W. Woodruff, School of Mechanical Engineering, Georgia Institute of Technology, 801 Ferst Drive, Atlanta, Georgia, USA, 30332-0405 INTRODUCTION Non-contact material removal processes offer numerous advantages over traditional machining approaches and no where is this more apparent than in the fabrication of micro devices. Current micromachining techniques such as microgrinding and micromilling have limitations with respect to their positioning accuracy and tool deflections. Electro thermal processes such as microEDM and laser machining usually result in a heat affected zone being produced. Other approaches such as etching and non-contact ultraprecision polishing are either costly or are not suitable for high throughput. In order to address these limitations, alternative micromachining techniques are required. In this paper, a non-contact material removal technique based on the electrokinetic phenomenon is proposed for precise material removal at rates in the order of nanometers/min. The aim of this research is to have a better understanding of the electrokinetic material removal technique by studying the trajectory of the particles and the influence of the frequency of the electric field on the material removal rate. CONCEPT OF PROPOSED TECHNIQUE The two primary mechanisms that are involved in the material removal technique are the electrokinetic and hydrodynamic effects. Electrokinetic effect on the particles is based on the movement of suspended colloids under an electric field while the hydrodynamic effect is based on the movement of the particles under a fluidic flow. When a particle is submerged in an aqueous solution, it is charged as the solid interfaces of the particles carry electrostatic charges where a difference in potential is developed across the interface between the two phases. The charged interface of the particle will attract counter-ions and repel co-ions to form an electric double layer. The surface charge of the particles is related to the particles’ zeta potential, size and dielectric constant which can be determined by [1]: 4 E o Q a π εε ς = (1) where Q E is the surface charge of the particle, a is the radius of the particle, ε is the dielectric constant, ε o is the permittivity of vacuum, and ς is the zeta potential of the particle. As mentioned earlier, one of the primary forces that acts on the particles (normal to surface of the workpiece) to cause surface wear is the electrokinetic force which is mainly governed by electrostatics, given by equation (2) [1]. _ sin(2 ) 4 E E AC DC Bias DC Bias AC o F QE V V ft a d d π π εε ς + = ⎡ ⎤ ⎛ ⎞ = + ⎢ ⎥ ⎜ ⎟ ⎝ ⎠ ⎣ ⎦ (2) where V AC is the AC voltage of the electric field, V DC-Bias is the DC voltage of the electric field, d is the distance between the two electrodes through which an AC electric field with DC bias is applied and f is the frequency of the AC electric field. Besides the influence of the electrokinetic effect on the material removal, the other determining factor that acts on the particles (along the surface of the workpiece) to cause surface wear is the hydrodynamic effect of the fluidic flow that is mainly given by the expression: 2 ' 1 6 4 y u U H ⎡ ⎤ ⎛ ⎞ ⎢ ⎥ = − ⎜ ⎟ ⎢ ⎥ ⎝ ⎠ ⎣ ⎦ (3) where u is the localized fluid velocity, U is the general fluid velocity, y ’ is the height of the localised element of the fluid at the centre of the channel and H is the height of the microchannel. In addition, the horizontal component of the particle motion exerted by the flowing fluid was