Grinding techniques for fabricating micro-lens array mold made of cemented carbide (Polycrystalline diamond tools and mold surface roughness)
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-01-01 |
| Journal | Transactions of the JSME (in Japanese) |
| Authors | Takuya Semba, Yoshifumi Amamoto, Hitoshi Sumiya |
| Institutions | Fukuoka Institute of Technology, Sumitomo Electric Industries (Japan) |
| Citations | 2 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Ultra-Precision MLA Mold Fabrication
Section titled âTechnical Documentation & Analysis: Ultra-Precision MLA Mold FabricationâThis document analyzes the research on fabricating Micro-Lens Array (MLA) molds using Polycrystalline Diamond (PCD) and Nano-Polycrystalline Diamond (NPD) tools, highlighting 6CCVDâs capabilities to support and advance this ultra-precision grinding technology.
Executive Summary
Section titled âExecutive SummaryâThis research successfully demonstrated a grinding-less technique for fabricating high-density Micro-Lens Array (MLA) molds in cemented carbide, achieving critical optical surface quality using advanced CVD diamond tools.
- Ultra-Precision Achievement: Achieved a grinding-less surface roughness of 5 nmRz on cemented carbide MLA dimples (30 ”m diameter, 35 ”m pitch, 1027 lenses).
- Material Superiority: Nano-Polycrystalline Diamond (NPD) tools proved superior to standard PCD, yielding the best roughness (5 nmRz) and lowest diameter expansion rate (2%).
- Mechanism Insight: NPDâs ultra-fine grain structure (approx. 50 nm) provided stable wear characteristics, preventing the exposure of sharp cutting edges that plagued standard PCD tools (which resulted in 15 nmRz).
- Process Control: Success relied heavily on precise tool shaping (nanosecond laser machining + wet lapping) and rigorous thermal management (grinding fluid temperature controlled to 26.1 °C) to limit thermal displacement to < ±25 nm.
- Application Relevance: This technology is crucial for mass-producing high-durability glass MLA molds required for advanced optical devices demanding high heat and wear resistance.
- 6CCVD Value Proposition: 6CCVD supplies the necessary high-purity MPCVD PCD and NPD materials, custom dimensions, and precision finishing services required to replicate and scale this demanding process.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the research detailing the MLA mold fabrication process and results.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Workpiece Material | Ultra-fine Cemented Carbide (CW500) | N/A | MLA Mold Substrate (2620 Hv) |
| Target MLA Dimensions | 30 / 35 / 1027 | ”m / ”m / count | Dimple Diameter / Pitch / Total Dimples |
| Target Surface Roughness (Rz) | < 10 | nm | Grinding-less requirement |
| Achieved Roughness (Rz, NPD) | 5 | nm | Best result (NPD tool) |
| Achieved Roughness (Rz, PCD) | 15 | nm | Standard PCD tool result |
| Diameter Expansion Rate (NPD) | 2 | % | Stability over 1027 dimples |
| NPD Primary Grain Size | ~50 | nm | Nano-Polycrystalline Diamond |
| PCD Primary Grain Size Range | 0.6 - 20 | ”m | Tested range for PCD tools |
| Tool Tip Radius | 0.1 | mm | Hemispherical profile |
| Tool Revolution Speed (St) | 10000 | min-1 | MLA Grinding Condition |
| Z-Axis Thermal Displacement Limit | ±25 | nm | Required for < ±1% diameter error |
| Grinding Fluid Temperature (Tw) | 26.1 | °C | Optimized for thermal stability |
Key Methodologies
Section titled âKey MethodologiesâThe fabrication process relied on specialized preparation of the diamond tools and stringent environmental control during plunge grinding.
- Diamond Tool Material Preparation:
- Tools were fabricated from sintered PCD (0.6-20 ”m grain size) and NPD (approx. 50 nm grain size).
- The NPD material, lacking sintering aids, provided superior stability compared to standard PCD.
- Tool Shaping (Pre-forming):
- A nanosecond pulse laser was used to pre-form the diamond tool tip to a hemispherical radius of 0.1 mm.
- Wet Lapping (Working Surface Flattening):
- Tools were wet lapped using a CVD diamond disk (15 mm diameter) and diamond slurry (0.05-1.2 ”m grain size, 0.1 wt%).
- Lapping was performed to ensure a flat working surface and remove defects, with slurry size selection being critical (e.g., 0.6 ”m slurry was required for NPD to remove lap marks).
- Thermal Management:
- The machining environment was controlled to ±0.1 °C.
- The grinding fluid (water-soluble) temperature (Tw) was set to 26.1 °C to minimize thermal displacement of the workpiece in the Z-direction to < ±25 nm over the 4-hour machining period.
- Plunge Grinding:
- MLA dimples were fabricated by transferring the hemispherical tool profile onto the cemented carbide workpiece (2620 Hv).
- Grinding parameters included a tool speed of 10000 min-1 and a Z-feed rate of 0.1 mm/min.
- Total machining time for 1027 dimples was 104 minutes.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials and precision engineering services required to replicate and scale this ultra-precision MLA mold fabrication technology. Our capabilities directly address the material and dimensional requirements of this research.
Applicable Materials
Section titled âApplicable MaterialsâTo achieve the superior 5 nmRz surface finish and tool stability demonstrated by the researchers, the highest quality diamond material is essential.
- Ultra-Fine Grain Polycrystalline Diamond (PCD): Required to replicate the performance of the NPD tool. 6CCVD offers specialized ultra-fine grain PCD wafers, ensuring the consistent, high-density diamond structure necessary for stable wear and minimal self-dressing effects.
- Standard Polycrystalline Diamond (PCD): Available in various grain sizes (0.6 ”m to 20 ”m range used in the paper) for initial tool prototyping and optimization studies.
- Single Crystal Diamond (SCD): While not used in this study, high-purity SCD (Ra < 1 nm polishing capability) can be supplied for alternative ultra-precision turning or milling applications where zero grain boundary effects are desired.
Customization Potential
Section titled âCustomization PotentialâThe research utilized specific tool geometries (0.1 mm hemispherical tip) and workpiece dimensions (20 mm diameter). 6CCVD excels in providing custom material solutions:
| Requirement from Paper | 6CCVD Solution & Capability | Technical Advantage |
|---|---|---|
| Custom Tool Dimensions | Plates/Wafers up to 125 mm (PCD). We supply diamond material in custom dimensions and thicknesses (0.1 ”m - 500 ”m) suitable for complex tool fabrication. | Enables scaling of MLA molds beyond the 20 mm diameter used in the study. |
| Tool Pre-forming | Advanced Laser Cutting Services. We offer high-precision laser cutting to pre-form complex geometries, significantly reducing the time and cost associated with mechanical shaping of the 0.1 mm hemispherical tip. | Ensures high initial profile accuracy before final wet lapping. |
| Surface Finishing | Ultra-Precision Polishing. We guarantee polishing down to Ra < 5 nm on inch-size PCD, confirming our capability to meet or exceed the 5 nmRz requirement achieved by the NPD tool. | Provides a high-quality starting surface for the diamond tool, optimizing the lapping process. |
| Tool Mounting & Bonding | Internal Metalization Capabilities. We offer custom metal layers (Ti/Pt/Au, W, Cu, Pd) for robust bonding of the diamond tool to the high-speed spindle assembly (10000 min-1), ensuring thermal and mechanical stability. | Critical for maintaining tool integrity and minimizing thermal runout during high-speed grinding. |
Engineering Support
Section titled âEngineering SupportâThe success of this research hinges on optimizing the interaction between the diamond toolâs grain size, the lapping slurry, and the grinding parameters (e.g., controlling the cutting ratio âaâ).
- Material Selection Consultation: 6CCVDâs in-house PhD team specializes in CVD diamond material science and can assist researchers and engineers in selecting the optimal diamond grain size and material grade for similar Ultra-Precision Grinding and Glass Molding projects.
- Process Optimization: We provide technical support to help clients define the optimal material specifications to manage tool wear, control the cutting ratio âaâ, and achieve stable sub-10 nm Rz surface finishes.
- Global Supply Chain: We offer reliable global shipping (DDU default, DDP available) to ensure timely delivery of custom diamond materials worldwide.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
A grinding technique was developed to fabricate a micro-lens array (MLA) mold made of cemented carbide with a diameter of 30 ÎŒm, a pitch of 35 ÎŒm, a diameter expansion rate of 0%, a surface roughness of less than 10 nmRz and 1027 lenses. Grinding tools made of polycrystalline diamond (PCD) and nano-polycrystalline diamond (NPD) with a tip radius of 0.1 mm and formed by laser machining and wet lapping were employed. Grinding was performed by transferring the hemispherical tool profile to the cemented carbide with a hardness of 2650 Hv. When NPD was employed, the tips of diamond particles, which were not aligned in height on the working surface, were worn down and the particles of the lower layer were exposed. A huge number of diamond particles with a size of 50 nm were engaged in the grinding operation. This phenomenon made it possible to fabricate lenses with a surface roughness of less than 10 nmRz and a diameter expansion rate of 2%. In contrast to NPD, removed chips contributed to dressing the working surface of PCD. The sharp cutting edge newly exposed on the working surface caused a negative effect on creating a fine surface and contributed to increasing the actual depth of cut. Accordingly, the formable surface roughness and diameter expansion rate were 15 nmRz and 3%, respectively.