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

At a Glance

Metadata	Details
Publication Date	2023-05-12
Journal	Frontiers in Materials
Authors	Jiacheng Song, Zhen Tong, Zhenqiang Yao, Xiangqian Jiang
Institutions	University of Huddersfield, State Key Laboratory of Mechanical System and Vibration
Citations	2
Analysis	Full AI Review Included

Technical Analysis and Documentation: Picosecond Laser Shaping of SCD Micro-Milling Tools

Executive Summary

This documentation analyzes the research demonstrating the fabrication and performance of Single Crystal Diamond (SCD) micro-milling tools shaped using picosecond laser technology for machining fused silica micro-optics.

Core Achievement: Successful fabrication of multi-edge SCD micro-milling tools (minimum rotary diameter 0.4 mm) using picosecond laser ablation.
Methodology Optimization: Implementation of a fractional array machining strategy significantly improved tool concentricity (radial runout reduced to 5.3 µm) and suppressed laser-induced graphitization (I_D/I_G ratio of 1.76).
Material Performance: The SCD tools demonstrated high rigidity and wear resistance, achieving an estimated tool life of 967.6 m during continuous milling.
Optimal Cutting Conditions: Micro-milling of fused silica achieved the best surface finish (Ra = 41.2 nm) using a highly negative rake angle (-30°), confirming the material’s suitability for hard, brittle material processing.
Application Validation: The laser-shaped SCD tool successfully machined high-precision micro-Fresnel lens arrays on fused silica, validating the process for micro-optics manufacturing.
6CCVD Value Proposition: 6CCVD supplies the high-purity MPCVD SCD required for these demanding micro-tooling applications, offering custom dimensions and expert engineering support for laser processing optimization.

Technical Specifications

The following hard data points were extracted from the experimental verification and results sections of the research paper.

Parameter	Value	Unit	Context
Tool Material Blank	1.0	mm	HPHT Single Crystal Diamond (SCD) thickness
Minimum Tool Diameter	0.4	mm	Rotary diameter of multi-edge milling tool
Cutting Section Length	200	µm	Length of the SCD cutting section
Optimal Rake Angle	-30	°	Yielded lowest surface roughness on fused silica
Best Surface Roughness (Ra)	41.2	nm	Achieved on fused silica (5 mm/min feed rate)
Cutting Depth (a_p)	0.05	mm	Micro-milling experiment parameter
Spindle Speed	35,000	rpm	Micro-milling experiment parameter
Optimal Feed Rate	5	mm/min	Corresponds to 0.143 µm/rev feed per tooth
Laser Pulse Width	8	ps	Picosecond laser used for tool fabrication
Laser Average Power	4	W	Used during SCD tool fabrication
Laser Scanning Speed	0.5	m/s	Used during SCD tool fabrication
Radial Runout (Optimized)	5.3	µm	Achieved using fractional array machining strategy
Graphitization Ratio (I_D/I_G)	1.76	Ratio	Indicator of low sp² content after optimized laser processing
Estimated Tool Life	967.6	m	Maximum cutting length before significant wear (22 min continuous milling)

Key Methodologies

The fabrication and testing relied on precise laser control and optimized machining paths to overcome the challenges of processing ultra-hard SCD.

SCD Blank Preparation: A 1 mm thick HPHT SCD sheet was brazed onto a carbide shank. The blank was then pre-cut into a 1 mm diameter cylinder using a picosecond laser.
Laser Machining Strategy: Layered cutting was applied using a picosecond laser (8 ps pulse width) to shape the SCD transition and cutting sections, overcoming the depth-of-field limitations.
Path Optimization for Flatness: An optimal laser path pitch (p_o = 1.56ω) was determined to minimize the fluctuation error of accumulated absorbed laser energy, ensuring a relatively flat surface for subsequent layered ablation.
Fractional Array Machining: This optimized strategy was employed to process each of the six cutting edges sequentially. This method suppressed continuous heating, minimized graphitization, and ensured high concentricity by referencing the processing path center to the shank axis.
Edge Sharpening: The rake face and flank face were processed separately using distinct laser paths to achieve sharp cutting edges (radius approximately 3.2 ± 2.1 µm).
Performance Testing: Micro-milling tests were conducted on fused silica using a 5-axis CNC center (Kern Micro) with varying rake angles (5° to -30°) and feed rates (5 to 15 mm/min) to determine optimal parameters for low-roughness machining.
Micro-Optics Fabrication: The optimized -30° rake angle SCD tool was used to successfully machine micro-Fresnel lens arrays (1.6 mm aperture) on fused silica, verifying the tool’s capability for structured surface generation.

6CCVD Solutions & Capabilities

This research validates the critical role of high-quality Single Crystal Diamond (SCD) in advanced micro-tooling, particularly when combined with precision laser shaping techniques. 6CCVD is uniquely positioned to supply the foundational materials and engineering support necessary to replicate and advance this work.

Applicable Materials

To replicate or extend this research, high-purity, low-defect SCD material is essential for minimizing graphitization and maximizing tool life.

Research Requirement	6CCVD Material Solution	Technical Rationale
High-Purity SCD Blanks	Optical Grade Single Crystal Diamond (SCD)	Our MPCVD SCD offers superior crystal quality and low defect density compared to standard HPHT, ensuring better thermal stability and reduced sp² conversion during picosecond laser ablation.
Thick Substrates for Tooling	SCD Substrates (up to 10 mm)	We provide SCD substrates up to 10 mm thick, offering greater design flexibility for robust micro-milling tools and shanks requiring high stiffness.
Alternative Tooling	Polycrystalline Diamond (PCD) Plates	For applications requiring larger tool diameters or where cost is a factor, 6CCVD offers PCD plates up to 125 mm, suitable for larger micro-tooling or abrasive applications.

Customization Potential

The paper highlights the need for specific dimensions (0.4 mm diameter) and precise geometry control. 6CCVD’s in-house capabilities directly address these customization needs.

Custom Dimensions: 6CCVD supplies SCD and PCD wafers/plates in custom dimensions up to 125 mm. We can provide the exact 1.0 mm thick SCD blanks or thicker substrates (up to 10 mm) required for micro-tool fabrication.
Precision Laser Cutting: We offer advanced laser cutting services to pre-shape diamond blanks, ensuring high dimensional accuracy prior to final picosecond laser shaping, minimizing material waste and processing time.
Ultra-Low Roughness Polishing: While the paper focused on laser shaping, the quality of the starting material is paramount. 6CCVD provides ultra-precision polishing services, achieving surface roughness Ra < 1 nm on SCD, ideal for preparing the highest quality tool blanks.
Metalization Services: Although not the focus of this paper, 6CCVD offers internal metalization capabilities (Au, Pt, Pd, Ti, W, Cu) for brazing or electrical contact applications, crucial for integrating diamond tools onto shanks or for BDD electrodes.

Engineering Support

The successful outcome of this research hinged on optimizing the laser processing path to manage graphitization and runout. 6CCVD’s in-house PhD team provides critical support for such advanced manufacturing challenges.

Material Selection Consultation: Our experts assist engineers in selecting the optimal SCD crystal orientation and quality to maximize performance and minimize defects during high-energy processing (like picosecond laser ablation).
Process Optimization for Micro-Tooling: We offer consultation on integrating MPCVD diamond into complex manufacturing workflows, including strategies to manage thermal effects and achieve the required geometric precision for micro-milling tools used in fused silica micro-optics projects.
Global Logistics: We ensure reliable, global shipping (DDU default, DDP available) of high-value diamond materials, supporting international research and production schedules.

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

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

Original Source

DOI: https://doi.org/10.3389/fmats.2023.1176545

References

2012 - Manufacture and application of ultra-small micro end mills [Crossref]
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2006 - Investigation of micro cutting operations [Crossref]
2022 - Understand anisotropy dependence of damage evolution and material removal during nanoscratch of MgF2 single crystals [Crossref]
2015 - Laser fabrication of diamond micro-cutting tool-related geometries using a high-numerical aperture micro-scanning system [Crossref]
2022 - Micro-grooving of brittle materials using textured diamond grinding wheels shaped by an integrated nanosecond lasersystem [Crossref]
2014 - 3-D micro and nano technologies for improvements in electrochemical power devices [Crossref]
2011 - Microscopic investigation of single-crystal diamond following ultrafast laser irradiation [Crossref]
2014 - Micro-cutting with diamond tool micro-patterned by femtosecond laser [Crossref]
2012 - Laser in micro and nanoprocessing of diamond materials [Crossref]