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