aj garcia honors thesis sample
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- 1. Finishing of Individual Sapphire Wafers University of Florida Center for Manufacturing Innovation A.J Garcia November 24, 2014
- 2. Sapphire (Al203) Background Hexagonal structure 9 mohs scale hardness Chemically and biologically inert Non-thrombogenic 2040 C melting point Low thermal expansion coeff. Wide transmission range 0.18 m 5.5 m Stretches from IR to UV Birefringent Electrical insulator Anisotropic 2 (http://www.cyberphysics.co.uk/topics/light/emspec t.htm)
- 3. Applications Electronics Epitaxial growth of semiconductors Gallium nitride LED manufacturing Silicon-on-sapphire integrated circuits Radiation hardened devices Scratch resistant screens Corrosion resistant components Nozzles, crucibles Optical windows and lenses in extreme environments
- 4. Motivation Applications demand precision surfaces Electrical industry Uniform semiconductor growth Precision form requirements Optical industry Image distortion Incomplete transmission
- 5. Effect of magnet arrangements Guide magnet arrangement investigation Workpiece 10 mm x 10 mm x 1 mm rectangular sapphire Slurry 50-70 m diamond abrasive mixed with lubricant Abrasive surface P120 grit abrasive paper Guide magnet arrangement 1, 2, 3 Set guide magnet rotation speed 350 rpm Finishing time 20 min 0.85 0.9 1.75 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 1 2 3 Ave.ThicknessReductionm/min Guide magnet arrangement Aim to improve tool motion Eliminating sticking Arrangement 3 enabled ideal motion Motion produced greater thickness reduction across surface
- 6. Surface roughness 6 measurements along diagonal 2.02 mm spacing Abrasive: 0-0.5 m diamond abrasive slurry Average initial roughness: 937 nm Sa d 0 y x 10 mm 10 mm Measurement locations (equally spaced)
- 7. WOT roughness reduction: Results Average roughness after finishing: 700 nm Sa Partial finishing of surface Smooth plateaus amid rough valleys 0-0.5 m abrasive does not penetrate valleys 0 200 400 600 800 1000 1200 2.02 4.04 6.06 8.08 10.1 12.12 SurfaceRoughnessRa[nm] Diagonal Distance From Corner [mm] Before After
- 8. Results
- 9. Surface Roughness with Flooded Basin 0 0.5 1 1.5 2 2.5 3 3.5 4 0 6.3 12.6 18.9 25.2 31.5 RoughnessSa[nm] Radial distance from center [mm] Before finishing After finishing
- 10. Radial Distance [mm] 0 6.3 12.6 Unpolished surface Polished surface Radial Distance [mm] 18.9 25.2 31.5 Unpolished surface Polished surface Sa = 1.77 nm Sa = 3.24 nm Sa = 1.40 nm Sa = 1.55 nm Sa = 1.68 nm Sa = 1.68 nm Sa = 0.67 nm Sa = 0.77 nm Sa = 1.52 nm Sa = 1.67 nm Sa = 1.35 nm Sa = 1.99 nm
- 11. Tool magnet sticking Evidence of excessive magnetic flux High magnetic force High normal reaction force High friction Exclusion of lubricant and diamond particles N S N S Magnetic force Guide magnet Tool magnet Workpiece Iron particle Abrasive particle Normal force Jig
- 12. Magnetic field density -10 10 30 50 70 90 110 130 0 5 10 15 20 25 30 Magneticfluxdensity[mT] Radial distance from center, r [mm] 3mm 6mm 9mm 12mm 15mm 12.7 mm r Tool magnet Guide magnet 3 mm jig height Steep drop in magnetic flux density Maximum of 121 mT 9 mm jig height 71 mT Consistent across tool magnet Jig height 0 16 mm + jig height
- 13. Surface roughness with 9 mm jig height Average before: 6.0 nm Sa Average after: 0.9 nm Sa 0 1 2 3 4 5 6 7 8 9 10 0 6.3 12.6 18.9 25.2 31.5 SurfaceRoughnessSa[nm] Radial Distance from Center of Polishing [mm] Before Finishing After finishing
- 14. Abrasive path simulation End goal: Develop method for predicting material removal Plan: Design mathematical model of ideal particle motion Observe correlation between surface changes and number of particle passes Observe changes caused by parameter variation Introduce corrective terms
- 15. Simulation Plot Example parameters: R = 3, r = 1, h = 0.5, = 6.28, t = 1, res = 2 xmin = -5, xmax = -4, ymin = -1, ymax = 1
- 16. Simulation inaccuracies Inaccuracies noticed when h = 0 = + cos() cos + = + sin() sin + = + cos() = + sin() Becomes parametric equations of a circle Simulation generates an annulus
- 17. Simulation inaccuracies Generate circle using parametric circle equations = cos() = sin() A = 10, = 21 rad/s t = 0 s : 900 s Also generates an annulus Thickness increases with t res too low
- 18. High res circle Same parameters to generate circle res increased from 4 to 6 Correctly represents a circle Lower res limit set to 6
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