Effect of nose radius on surface roughness of diamond turned germaniumlenses

At a Glance

Metadata	Details
Publication Date	2023-01-01
Authors	Adeniyi Adeleke, Peter Babatunde Odedeyi, Khaled Abou-El-Hossein
Institutions	Nelson Mandela University, University of North Carolina at Charlotte
Citations	2
Analysis	Full AI Review Included

Technical Documentation & Analysis: Diamond Turning of Germanium Lenses

Executive Summary

This research highlights the critical role of diamond tool geometry in achieving optical-grade surface finishes on brittle materials via Single-Point Diamond Turning (SPDT). The findings directly underscore the necessity of utilizing the highest quality Single Crystal Diamond (SCD) material for tool fabrication.

Application Focus: Ultra-precision machining of Single Crystal Germanium (Ge) for high-quality infrared (IR) lenses.
Core Finding: Increasing the diamond tool nose radius significantly reduces surface roughness (Ra), leading to improved ductile efficiency during machining.
Methodology: Experiments utilized a Box-Behnken design on a Precitech Nanoform 250 ultra-precision diamond turning lathe.
Material Requirement: Achieving the required optical excellence demands diamond tools fabricated from defect-free, high-purity SCD material.
6CCVD Value Proposition: 6CCVD specializes in providing the necessary high-grade MPCVD SCD material, polished to Ra < 1nm, which serves as the foundation for the world’s most precise SPDT tools.
Future Research Alignment: The study identifies tool wear and crack formation as key future research areas, both of which are intrinsically linked to the crystallographic quality and mounting stability of the SCD tool insert.

Technical Specifications

The following table summarizes the key parameters and outcomes extracted from the research abstract concerning the diamond turning process.

Parameter	Value	Unit	Context
Workpiece Material	Single Crystal Germanium (Ge)	N/A	Target material for infrared lenses
Machining Process	Single-Point Diamond Turning (SPDT)	N/A	Required for achieving high surface finish on brittle materials
Key Input Variable	Tool Nose Radius	N/A	Two different parameters studied
Optimized Parameters	Feed, Speed, Depth of Cut	N/A	Optimized using Box-Behnken design
Machining Equipment	Nanoform 250	N/A	Precitech ultra grind precision diamond turning lathe
Metrology Equipment	PGI Dimension XL	N/A	Taylor Hobson surface Profilometer
Key Outcome	Surface Roughness (Ra)	N/A	Decreased with increased nose radius
Performance Metric	Ductile Efficiency	N/A	Improved by optimized nose radius selection

Key Methodologies

The experimental approach focused on optimizing cutting parameters to minimize surface roughness during the diamond turning of single crystal germanium.

Experimental Design: A Box-Behnken design was implemented to create an optimal combination of cutting parameters (feed, speed, and depth of cut).
Tool Parameter Variation: The effect of two distinct diamond tool nose radius parameters was systematically studied and analyzed.
Machining Execution: All turning operations were performed on a Precitech Nanoform 250 ultra grind precision diamond turning lathe.
Surface Metrology: Surface roughness measurements were taken after each run using a Taylor Hobson PGI Dimension XL surface Profilometer.
Performance Analysis: Results were evaluated based on surface roughness reduction and improvement in ductile efficiency, confirming that appropriate nose radius selection is critical for optical excellence.

6CCVD Solutions & Capabilities

This research validates the necessity of ultra-high-quality diamond tooling for advanced manufacturing processes like SPDT. 6CCVD is the premier supplier of the MPCVD diamond materials required to manufacture these precision tools.

Applicable Materials

To replicate or advance this research, tool manufacturers require the highest purity, lowest defect density diamond material.

Material Recommendation: Optical Grade Single Crystal Diamond (SCD)
- Application: Fabrication of the Single-Point Diamond Turning (SPDT) inserts used to machine the Germanium lenses.
- Justification: SCD offers unparalleled hardness, thermal stability, and wear resistance, which are essential for maintaining the critical nose radius geometry and minimizing tool wear—a key factor identified for future research.

Customization Potential for Tool Manufacturers

6CCVD provides the foundational material and engineering services necessary for producing next-generation SPDT tools.

Requirement	6CCVD Capability	Specification Range
Tool Insert Substrate	Custom SCD Plates/Wafers	Thickness: 0.1 µm to 500 µm
Surface Finish	Ultra-Precision Polishing	Ra < 1nm (Essential for minimizing initial tool defects)
Tool Mounting Stability	Custom Metalization Services	Au, Pt, Pd, Ti, W, Cu (Internal capability for secure tool bonding)
Large Format Tooling	Polycrystalline Diamond (PCD)	Plates/wafers up to 125mm (for large-scale tool holders or specialized applications)

Engineering Support

The study emphasizes the need to understand complex interactions like tool wear, cutting force, and crack formation. These phenomena are highly dependent on the quality and orientation of the diamond tool material.

Expert Consultation: 6CCVD’s in-house PhD team provides specialized material consultation to tool manufacturers, assisting with optimal crystallographic orientation and material selection for similar Ultra-Precision Diamond Turning projects.
Quality Assurance: We ensure the highest material quality, providing the stable foundation required to achieve the sub-nanometer surface roughness targets demonstrated in this research.

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

View Original Abstract

Abstract: The desire for quality infrared lenses with better surface finish has brought about the usage of brittle materials like germanium to be machined via a single-point diamond turning machining process. However, achieving the required surface finish is complex if special machining techniques and approaches are not employed. In this paper, the effect of two different tool nose radius parameters on the surface roughness of single point diamond turned germanium workpiece were studied and analyzed. The machining parameters selected for this experiment were feed, speed, and depth of cut. Box-Behnken design was adopted to optimally create a combination of cutting parameters. The machining operations were carried out on a Precitech Nanoform 250 ultra grind precision diamond turning lathe. Measurement of surface roughness after each run in both experiments was achieved using a Taylor Hobson PGI Dimension XL surface Profilometer. The resulting outcomes show that at most experimental runs, the surface roughness value decreased with an increase in nose radius, leading to improved ductile efficiency. Mean absolute error was also used to compare the accuracy validation of the two models. The study examines the machining of single crystal germanium to optical excellence and highlights how the selection of appropriate nose radius is critical to achieving the desired lens quality at reduced production cost and meeting specific applications. Future research directions will be carried out to understand the complex interaction between cutting tool nose radius and other factors like tool wear and cutting force, the crack formation in surfaces of diamond-turned brittle materials, and the use of machine learning to develop models that will allow manufacturers to provide an accept/fail answer for a given set of parameters for surface generation.

Tech Support

Original Source

DOI: https://doi.org/10.17118/11143/21048