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6CCVD Research

Micro milling of fused silica using picosecond laser shaped single crystal diamond tools

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2023-05-12
JournalFrontiers in Materials
AuthorsJiacheng Song, Zhen Tong, Zhenqiang Yao, Xiangqian Jiang
InstitutionsUniversity of Huddersfield, Shanghai Jiao Tong University
Citations2
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research details the development and performance validation of multi-edge Single Crystal Diamond (SCD) micro milling tools fabricated using an optimized picosecond laser technique for machining fused silica.

  • Tool Fabrication Innovation: A “fractional array machining strategy” was proposed, significantly reducing the total radial runout of the cutting edges (down to 5.3 ”m) and inhibiting diamond graphitization (ID/IG ratio of 1.76).
  • Tool Geometry: Multi-edge SCD milling tools were successfully fabricated with a minimum rotary diameter of 0.4 mm, designed for high material removal rates in hard, brittle materials.
  • Optimal Cutting Performance: Micro milling tests on fused silica confirmed that tools with a negative rake angle (-30°) minimize brittle damage and yield the best surface quality.
  • Surface Integrity: The optimal cutting condition (rake angle -30°, feed rate 5 mm/min) achieved a best surface roughness of Ra = 41.2 nm on fused silica.
  • Application Success: The laser-shaped SCD tool successfully machined arrays of micro Fresnel lenses (1.6 mm aperture) on a fused silica sheet, verifying its capability for optical microstructure fabrication.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Laser TypePicosecond-Used for SCD tool shaping
Laser Pulse Width8psLaser system specification
Max Average Laser Power40WLaser system specification
Optimal Laser Pitch (po)1.56ω-Based on minimum energy fluctuation
SCD Sheet Thickness1.0mmTool blank material (HPHT)
Cutting Section Diameter0.4mmMinimum rotary diameter of tool
Cutting Section Length0.2mmWorking depth of tool
Spindle Speed (Milling)35,000rpmFused silica micro milling test
Cutting Depth (ap)0.05mmFused silica micro milling test
Best Surface Roughness (Ra)41.2nmAchieved with -30° rake angle tool
Optimal Rake Angle-30°For lowest roughness on fused silica
Optimized Radial Runout5.3 to 9.4”mUsing fractional array machining strategy
Graphitization Ratio (ID/IG)1.76-Optimized tool (higher ratio indicates less graphitization)
Diamond Raman Peak (ID)1333cm-1sp3 carbon hybridization
Graphite Raman Peak (IG)1580cm-1sp2 carbon hybridization
Estimated Tool Tip Cutting Length967.6mTool life estimate (at 0.143 ”m/rev feed)

Key Methodologies

Section titled “Key Methodologies”

The research involved two primary phases: SCD micro tool fabrication using a picosecond laser system, and subsequent micro milling performance testing on fused silica.

I. Picosecond Laser Tool Fabrication

Section titled “I. Picosecond Laser Tool Fabrication”
  1. Tool Blank Preparation: A 1.0 mm thick HPHT SCD sheet was brazed onto a carbide shank and initially cut into a 1 mm diameter cylinder using the picosecond laser.
  2. Layered Ablation: Layered cutting was employed to achieve the required depth (200 ”m) for the cutting and transition sections, compensating for the laser’s limited depth of field.
  3. Path Optimization (Fractional Array Machining):
    • This strategy was used to process the multi-edge cutting section.
    • Only one cutting edge was processed per ablation step, and the shank was rotated (indexed) before processing the next edge.
    • This method ensured the processing path center aligned with the shank axis, suppressing cutting-edge radial runout caused by shank positioning errors.
  4. Edge Sharpening: The rake face and flank face were processed separately using distinct laser paths to avoid long laser dwell times at abrupt change points, thereby achieving a fine, sharp cutting-edge profile (radius 3.2 ± 2.1 ”m).
  5. Graphitization Control: The optimized fractional array strategy reduced thermal defects, resulting in a higher ID/IG ratio (1.76) compared to the direct processing strategy (1.32).
  6. Tool Geometries: Tools were fabricated with a 10° clearance angle and theoretical rake angles of 5°, 0°, -15°, and -30°.

II. Fused Silica Micro Milling Tests

Section titled “II. Fused Silica Micro Milling Tests”
  1. Equipment: Tests were conducted on a Kern Micro 5-axis machining center equipped with a high-speed spindle (35,000 rpm) and a force-measuring device.
  2. Workpiece: 1 mm thick fused silica sheet (Mohs hardness 7).
  3. Cutting Parameters:
    • Spindle Speed: 35,000 rpm (fixed).
    • Cutting Depth (ap): 0.05 mm (fixed).
    • Feed Rates: 5, 10, and 15 mm/min (variable).
  4. Performance Analysis:
    • Cutting force amplitude was monitored, showing proportionality to the feed rate.
    • Surface roughness (Ra) was measured, confirming that the -30° negative rake angle tool yielded the lowest roughness (41.2 nm).
  5. Application Demonstration: A micro Fresnel lens array (1.6 mm aperture, 8 mm focal length) was successfully machined on fused silica using the optimal -30° rake angle tool.

Commercial Applications

Section titled “Commercial Applications”

The technology developed for high-precision SCD tool fabrication and micro milling is critical for industries requiring high-quality micro-structured surfaces on hard and brittle materials.

  • Micro-Optics and Photonics:
    • Mass production of high-precision micro Fresnel lenses, diffractive optical elements (DOEs), and micro-lens arrays on glass and fused silica substrates.
    • Fabrication of complex optical components for sensors and communication systems.
  • Advanced Tooling and Manufacturing:
    • Supply of high-performance, multi-edge SCD micro milling tools with superior concentricity and extended service life for ultra-precision machining centers.
    • Enabling high material removal rate machining of ultrahard materials (e.g., ceramics, silicon carbide, sapphire) where conventional methods are inefficient.
  • Biomedical and Microfluidics:
    • Creation of micro-channels and structured surfaces on hard materials for bioengineering applications and lab-on-a-chip devices.
  • Tribology:
    • Fabrication of micro-textured surfaces on hard components to improve friction and wear characteristics.
View Original Abstract

Fused silica is widely used as a material for optical lenses owing to its excellent optical properties and low thermal expansion coefficient. However, as a hard and brittle material, there is very limited option of processing technologies to machining fused silica with surface structures. In this paper, a picosecond laser based single crystal diamond tool fabrication technology is proposed to generate micro milling tools with different geometrical designs, and the tool cutting performance is experimentally tested through micro-milling of fused silica under different cutting conditions. An optimal picosecond laser processing path is proposed to inhibit the graphitization of diamond tool and improve the concentricity of tool blades, and a multi-edge milling tool with a minimum rotary diameter of 0.4 mm can be obtained. The effects of rake angle on cutting force and the degree of brittle damage on the subsurface of fused silica are studied by micro milling tests of fused silica using the laser-shaped tools. The results show that the fused silica machined by diamond milling tool with a rake angle of −30° has the best surface finish (Ra = 41.2 nm). Using this laser-machined milling tool, a plurality of micro Fresnel lenses with aperture of 1.6 mm were successfully machined on a fused silica sheet.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2012 - Manufacture and application of ultra-small micro end mills [Crossref]
  2. 2012 - Biomedical production of implants by additive electro-chemical and physical processes [Crossref]
  3. 2006 - Investigation of micro cutting operations [Crossref]
  4. 2022 - Understand anisotropy dependence of damage evolution and material removal during nanoscratch of MgF2 single crystals [Crossref]
  5. 2015 - Laser fabrication of diamond micro-cutting tool-related geometries using a high-numerical aperture micro-scanning system [Crossref]
  6. 2022 - Micro-grooving of brittle materials using textured diamond grinding wheels shaped by an integrated nanosecond lasersystem [Crossref]
  7. 2014 - 3-D micro and nano technologies for improvements in electrochemical power devices [Crossref]
  8. 2011 - Microscopic investigation of single-crystal diamond following ultrafast laser irradiation [Crossref]
  9. 2014 - Micro-cutting with diamond tool micro-patterned by femtosecond laser [Crossref]
  10. 2012 - Laser in micro and nanoprocessing of diamond materials [Crossref]

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