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Precision Replication of Micro-Optics Through Injection Molding

Precision Replication of Micro-Optics Through Injection Molding. David Gill -- Dr. Thomas Dow -- Alex Sohn. Precision Engineering Center -North Carolina State University. Project Goals. Accurately Replicate Micro-Optics Using the Injection Molding Process

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Precision Replication of Micro-Optics Through Injection Molding

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  1. Precision Replication of Micro-Optics Through Injection Molding David Gill -- Dr. Thomas Dow -- Alex Sohn Precision Engineering Center -North Carolina State University

  2. Project Goals • Accurately Replicate Micro-Optics Using the Injection Molding Process • Find The Injection Molding Factors That Have the Greatest Effect on the Replication of Micro-Optics Blaze Grating Dimensions in nm

  3. Presentation Outline • Injection Molding Process Factors • Design of Experiment Process Factors ==> Replication Fidelity • Micro-Optics Features • Research Results

  4. Nissei HM-7 • Machine Characteristics • 6.2 cm3 Shot Size • 102 mm Tie Bar Spacing • 7 Ton Clamping Force • Hydraulic Actuation • Water Based Mold Temperature Control

  5. Mold Barrel Screw Injection Hold Injection Molding Process Factors

  6. 28x4 = 1024 Tests 32 Tests DOE Design of Experiment • Selected a High and Low Value for Each Factor • Both Values Must Create a Measurable Part (More Than 3000 Parts) Assumptions - Linear Response Between Factor Values - No Interaction Between Factors

  7. Micro-Optic Features Depth Aspect Ratio = Width

  8. Feature Measurements Astigmatism Coma Spherical Aberration Residual RMS Residual PV Grating Step Height Wedding Cake Step Height Phase Interferometer White Light Interferometer Stylus Profilometer

  9. Blaze Grating: Step Height Error 112 nm (7%) 127 nm Replication Fidelity Achieved Fresnel: Residual RMS Error 76 nm Sphere: Residual RMS Error Wedding Cake: Step Height Error 1.8µm (0.9%)

  10. Fresnel Replication 1mm Mold PMMA Lens

  11. Mold 2500x Mold 1000x PMMA 2500x PMMA 1000x Blaze Grating 50µm 20µm

  12. 1/p

  13. Sphere Fresnel Grating Optimization of DOE Results

  14. Summary • Injection Molding Process and Factors in Molding • Design of Experiment • Micro-Optical Features and Measurement Methods • Results of the DOE • Confirmation of the Results

  15. Conclusions • Repeatable Replication of Micro-Optics is Possible Using Injection Molding • Molding Factors Influence the Replicated Shape of Micro-Optics • Mold Temperature and Screw Rotation Speed Have the Greatest Impact on Replication Fidelity The authors wish to acknowledge the support of this research by the National Science Foundation (grant #9908223, Dr. K. P. Rajurkar, Program Director)

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