Study of the Transcription Effects of Pressing Dies with Ultrasonic Polishing on Glass Molding

At a Glance

Metadata	Details
Publication Date	2021-11-21
Journal	Processes
Authors	Ken-Chuan Cheng, Chien-Yao Huang, Jung-Chou Hung, A-Cheng Wang, Yan-Cherng Lin
Institutions	National Applied Research Laboratories, Chien Hsin University of Science and Technology
Citations	3
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for Precision Glass Molding Dies

This document analyzes the research on ultrasonic polishing of pressing dies for Micro Lens Array (MLA) fabrication and outlines how 6CCVD’s specialized MPCVD diamond materials (SCD and PCD) provide superior solutions for replicating and advancing this high-precision glass molding (PGM) technology.

Executive Summary

Application Focus: Fabrication of high-precision Micro Lens Arrays (MLAs) via Precision Glass Molding (PGM) to transform Gauss-distributed light into a uniform straight line.
Critical Achievement: Demonstrated that achieving an ultra-smooth die surface roughness (Ra) of 0.023 µm (23 nm) is necessary to ensure high transparency and functional transcription of the sine-wave profile.
Transcription Success: An excellent Transcription Ratio (Tr) of 99% was achieved between the pressing die topography and the molded glass surface at optimized PGM parameters.
Methodology: The pressing die (SKD-11 steel) was initially cut by Wire Electrical Discharge Machining (WEDM) and subsequently polished using high-frequency (30 kHz) Ultrasonic Polishing (UP) with diamond abrasives.
Parameter Optimization: Key PGM process parameters were established at a working temperature of 690 °C and a pressing force of 250 N.
Material Limitation: The reliance on polishing soft steel dies requires complex, time-consuming steps and limits the ultimate surface quality and die lifetime, presenting a clear opportunity for direct diamond die replacement.

Technical Specifications

Parameter	Value	Unit	Context
Optimal Die Surface Roughness (Ra)	0.023	µm	Required for high-transparency MLA production
Required Transcription Ratio (Tr)	99	%	Achieved at optimal T and F
Critical Pressing Force (F)	250	N	Optimal force to prevent rupture (F < 270 N)
Critical Working Temperature (T)	690	°C	Optimal temperature for PGM (T < 690 °C causes poor Tr)
Roughness Improvement Ratio (RIR)	90	%	Achieved using #8000 diamond abrasive mesh
Ultrasonic Polishing Frequency	30	kHz	Applied to the polishing rod
Die Material Used	SKD-11	Mold Steel	Initial die material (15 mm x 15 mm x 15 mm)
Glass Transition Temperature (T_g)	564	°C	Soda lime glass
Glass Molding Temperature	680 - 690	°C	Operating range for PGM

Key Methodologies

The experiment focused on optimizing the die surface finish and PGM parameters to maximize the transcription effect for sine-wave MLAs.

Initial Die Fabrication: Sine-wave profiles were designed using CAD and cut into SKD-11 mold steel using Wire Electrical Discharge Machining (WEDM), resulting in an initial surface roughness of 0.20 µm Ra.
Ultrasonic Polishing (UP) Setup: A high-frequency (30 kHz) ultrasonic apparatus was used with a polymer polishing rod and diamond slurries to finish the die surface.
Polishing Optimization: The polishing path utilized circular and reciprocating motions. Diamond abrasive mesh sizes were tested, confirming that #8000 mesh achieved the highest Roughness Improvement Ratio (RIR) of 90% in 25 minutes, reducing Ra to 0.023 µm.
Precision Glass Molding (PGM): Soda lime glass discs (10 mm diameter) were placed in a vacuum chamber. The mold core and glass were heated and stabilized at 690 °C.
Molding and Cooling: A pressing force of 250 N was applied to press the glass into the sine-wave shape. The MLA was then cooled by nitrogen before removal.
Performance Verification: The resulting MLAs were verified by measuring surface roughness and testing the optical function using a laser to confirm the transformation of a Gauss spotlight into a uniform straight line.

6CCVD Solutions & Capabilities

The research highlights the extreme difficulty and time required (25 minutes of specialized ultrasonic polishing) to achieve the necessary surface roughness (Ra = 0.023 µm) on metal dies. 6CCVD specializes in providing diamond materials that inherently possess superior hardness, thermal stability, and surface quality, making them the ideal choice for high-volume, high-precision PGM applications like MLA fabrication.

Applicable Materials for PGM Dies

To replicate or extend this research with superior performance and lifetime, 6CCVD recommends the following materials for direct use as pressing dies:

Optical Grade Single Crystal Diamond (SCD): Ideal for achieving the highest possible surface quality and transcription precision.
- Advantage: 6CCVD guarantees polished SCD surfaces with Ra < 1 nm, offering a 23x improvement in surface smoothness compared to the 0.023 µm Ra achieved on the polished steel die. This ensures perfect transcription and superior optical performance.
High-Purity Polycrystalline Diamond (PCD): Recommended for large-area dies or applications requiring maximum durability and thermal uniformity.
- Advantage: PCD offers exceptional wear resistance, eliminating the sticking and rupture issues observed with steel dies at high temperatures (690 °C), thereby maximizing die lifetime in production environments.

Customization Potential for Advanced PGM

6CCVD’s manufacturing capabilities directly address the needs of high-precision molding engineers:

Research Requirement	6CCVD Capability	Benefit to Client
Die Size (15 mm x 15 mm)	Custom Dimensions up to 125 mm	We supply custom-cut SCD and large-area PCD wafers up to 125 mm, supporting scaling from R&D prototypes to mass production.
Ultra-Low Roughness (Ra < 0.023 µm)	Precision Polishing Services	We offer standard polishing to Ra < 1 nm (SCD) and Ra < 5 nm (Inch-size PCD), providing a ready-to-use die surface that surpasses the required specification.
Complex Sine-Wave Profile	Laser Cutting and Shaping	6CCVD offers advanced laser cutting and shaping services to create complex geometries directly in the diamond material, reducing reliance on post-processing steps like WEDM and ultrasonic polishing.
Potential for Integrated Sensors	Custom Metalization	We offer in-house metalization (Au, Pt, Pd, Ti, W, Cu) for integrating heating elements or temperature sensors directly onto the diamond substrate, enhancing process control (e.g., monitoring the critical 690 °C temperature).

Engineering Support

6CCVD’s in-house PhD team specializes in the material science of diamond for extreme environments. We can assist engineers and scientists in selecting the optimal diamond grade (SCD vs. PCD) and thickness (0.1 µm to 500 µm) for similar Micro Lens Array (MLA) and Precision Glass Molding (PGM) projects, ensuring maximum transcription fidelity and die longevity.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

The micro lens array (MLA) has played an important role in optical systems for the past few years, and the precision of pressing dies has dominated the quality of MLAs in glass molding. Few studies have covered the transcription effects on surface roughness of pressing dies for this technology. Therefore, this research utilized pressing dies to produce a sine-wave lens array on glass molding, to transform the Gauss-distributed spotlight into a uniform straight one and then characterize the transcription effects of these lenses. Pressing dies with a sine-wave shape were firstly cut by wire electrical discharge machining (WEDM), and then ultrasonic polishing using diamond abrasives was applied to finish the sine-wave surface with an original roughness of 0.2 μm Ra. Next, the sine-wave lens arrays were pressed by glass molding at the appropriate pressure and temperature, before evaluating the transcription effects of transforming the Gauss-distributed spotlight into a uniform straight one. The result showed that the sine-wave lens array stuck easily to the pressing die and then ruptured during glass molding due to the poor surface roughness of pressing tool. However, the diamond abrasive with appropriate sizes could establish good surface roughness on pressing dies via ultrasonic polishing, and the pressing die with a low surface roughness of 0.08 μm Ra was able to successfully perform MLA in the glass molding. However, only pressing dies with a surface roughness smaller than 0.023 μm Ra could produce precision glass lenses to transform the Gauss-distributed spotlight into a uniform straight one.

Tech Support

Original Source

DOI: https://doi.org/10.3390/pr9112083

References

2007 - Homogenized LED-illumination using microlens arrays for a pocket-sized projector [Crossref]
2020 - Thermo-viscoelastic Modeling of Nonequilibrium Material Behavior of Glass in Nonisothermal Glass Molding [Crossref]
2020 - Analyzing sustainable performance on high-precision molding process of 3D ultra-thin glass for smart phone [Crossref]
2002 - Use of micro ultrasonic vibration lapping to enhance the precision of microholes drilled by micro electro-discharge machining [Crossref]
2002 - Study of precision micro-holes in borosilicate glass using micro EDM combined with micro ultrasonic vibration machining [Crossref]
2008 - Precision treatment of silicon wafer edge utilizing ultrasonically assisted polishing technique [Crossref]
2012 - Combined ultrasonic vibration and chemical mechanical polishing of copper substrates [Crossref]