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TECHNICAL PAPERS

Elasto-Hydrodynamic Interaction in the Free Abrasive Wafer Slicing Using a Wiresaw: Modeling and Finite Element Analysis

[+] Author and Article Information
M. Bhagavat, V. Prasad, I. Kao

Department of Mechanical Engineering, State University of New York at Stony Brook, Stony Brook, NY 11794-2300

J. Tribol 122(2), 394-404 (Jul 19, 1999) (11 pages) doi:10.1115/1.555375 History: Received May 29, 1998; Revised July 19, 1999
Copyright © 2000 by ASME
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References

Figures

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Schematic of the wiresaw slicing process
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Rolling and indenting of abrasives in FAM, exaggeration of the components of the slicing system
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Typical viscosity variation with shear rate for the slurry (SiC grits with glycol as carrier) 2
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Flowchart for the iterative scheme of the numerical algorithm
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Components of the film thickness, as envisaged by the concept of compliance
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Mapping for the reduction of 3D case to 2D analysis
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Elasto-hydrodynamic pressure profile in the cutting zone for 100 mm ingot length
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Thickness profile for the film in the cutting zone for 100 mm ingot length
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Difference in the compliance of the wire at the center of the contact zone (a) and at the end of the contact zone (b). Large exaggeration to show the effect.
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Variation of minimum film thickness with slurry viscosity and wire velocity for 100 mm ingot length
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Variation of minimum film thickness with slurry viscosity, wire velocity, and wire bow for 50 mm ingot length
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(a) Surface of the as-sliced wafer by the wiresaw shows a uniform distribution of almost equal-sized pits. Such a phenomenon is justifiable only with floating abrasives. (b) The surface of wafer after it is polished at lower speeds shows distinct scratches and sparse pits. This indicates that the abrasives are directly pressed on the ingot by the tool. Only those abrasives of favorable orientation and size will sustain load to cause polishing.
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Mechanism for machining using floating abrasives. The basic tangential driving force is supplied by the shear stress generated by a high velocity gradient slurry film. The elasto-hydrodynamic pressure helps in reducing the rolling tendency of the abrasive under action of shearing stress. Combination of these two forces transmits a force to the ingot. If this force is sufficient then it causes chipping of the brittle ingot.
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The figure on the left shows a schematic of material removal rate verses film thickness, as proposed by Su et al. 8 for elasto-hydrodynamic polishing. As seen, the present wiresaw slicing comes under the iso-visco elastic (IE) regime of lubrication. The figure on the right shows the variation of the representative material removal rate with speed and viscosity for 50 mm length ingot cut by a wire bowed to 2 deg.
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Build-up of pressure head at the inlet to narrow passage
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Pressure profile for cutting 50 mm length ingot
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Thickness profile of the film in the cutting zone for 50 mm ingot length

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