High-Precision Cutting Edge Radius Measurement of Single Point Diamond Tools Using an Atomic Force Microscope and a Reverse Cutting Edge Artifact

At a Glance

Metadata	Details
Publication Date	2020-07-13
Journal	Applied Sciences
Authors	Kai Zhang, Yindi Cai, Yuki Shimizu, Hiraku Matsukuma, Wei Gao
Institutions	Dalian University of Technology, Tohoku University
Citations	12
Analysis	Full AI Review Included

Executive Summary

This research presents a high-precision metrology method for measuring the cutting edge radius ($R_{tool}$) of Single Point Diamond Tools (SPDTs), overcoming limitations imposed by Atomic Force Microscope (AFM) tip convolution.

Core Value Proposition: The proposed Edge Reversal Method accurately evaluates $R_{tool}$ by measuring both the actual cutting edge and a replicated Reverse Cutting Edge Artifact (RCEA), effectively eliminating the convolution effect of the AFM tip radius ($R_{tip}$).
System Innovation: A newly designed nanoindentation system is utilized to fabricate the RCEA on a soft copper workpiece with high-precision control over the indentation depth.
Precision Control: The system operation was optimized to control indentation depth ($d_{depth}$) within the critical range of 20 nm to 200 nm, ensuring high accuracy.
Elastic Recovery Validation: Experimental results confirmed that the elastic recovery of the copper workpiece is negligible within the optimized indentation depth range, maintaining measurement accuracy.
Achieved Accuracy: The method successfully measured $R_{tool}$ for two different diamond tools (nose radii 1 mm and 2 mm) in the 30 nm to 41 nm range, achieving a low measurement uncertainty of 1.97 nm (k=2).
Tip Independence: The measurement accuracy was verified to be independent of the AFM cantilever tip radius, demonstrating the robustness of the reversal technique.

Technical Specifications

Parameter	Value	Unit	Context
Target $R_{tool}$ Range	10 to 100	nm	Requirement for ultra-precision diamond cutting
Optimized Indentation Depth Range	20 to 200	nm	Range where elastic recovery effect is minimized
Measured $R_{tool}$ (Tool 1, Avg.)	30.38 ± 0.31	nm	Diamond tool with 1 mm nose radius
Measured $R_{tool}$ (Tool 2, Avg.)	41.29 ± 0.66	nm	Diamond tool with 2 mm nose radius
Measurement Uncertainty (k=2)	1.97	nm	Coverage factor k=2 (95% confidence)
Standard Deviation of Uncertainty	0.005	nm	Calculated across various indentation depths (Tool 1)
Workpiece Material	Copper	N/A	Prepolished, 10 x 10 x 2 mm³ size
AFM Cantilever 1 ($R_{tip}$, Nominal)	7	nm	Olympus OMCL-AC240TS
AFM Cantilever 2 ($R_{tip}$, Nominal)	12	nm	Bruker MPP-11100-10 (Used for verification)
AFM Scan Range (X x Y)	2 x 2	µm	Used for both actual and reverse edge scans
Cantilever Spring Constant (RCEA)	155	N/m	Aluminum cantilever used in nanoindentation system
Indentation Force Sensor	Capacitive Sensor	N/A	Used to detect cantilever deflection

Key Methodologies

The measurement process relies on three primary steps: RCEA fabrication, AFM measurement of the actual tool edge, and AFM measurement of the RCEA, followed by calculation using the edge reversal formula.

Nanoindentation System Design:
- The system uses a Fast Tool Servo (FTS) unit for precise vertical displacement and a linear stage for coarse approach.
- Indentation depth ($d_{depth}$) is monitored using two capacitive sensors: an “inside sensor” measuring tool displacement ($d_{in}$) and an “outside sensor” measuring cantilever deflection ($d_{out}$). $d_{depth} = d_{in} - d_{out}$.
RCEA Fabrication (Optimized 3-Step Process):
- Step 1 (Coarse Approach): The linear stage moves the diamond tool close to the copper workpiece until the gap equals the FTS stroke.
- Step 2 (Contact Establishment): The FTS actuates the tool in small steps (5 nm) until the outside sensor output changes, indicating tool-workpiece contact. This generates a negligible indentation (less than 5 nm).
- Step 3 (Controlled Indentation): The tool is indented to the command depth (20 nm to 200 nm range). The bisector of the tool’s rake and clearance faces is aligned perpendicular to the workpiece surface.
AFM Measurement of Actual Cutting Edge:
- The diamond tool is positioned under the AFM (e.g., using Cantilever 1, $R_{tip}$ = 7 nm).
- The AFM scans the actual cutting edge topography (2 µm x 2 µm).
- The measured radius ($R_{tool_m}$) is obtained by fitting an arc to the apex of the cross-sectional profile. This value includes the AFM tip convolution: $R_{tool_m} = R_{tool} + R_{tip}$.
AFM Measurement of Reverse Cutting Edge Artifact (RCEA):
- The RCEA is scanned using the same AFM cantilever.
- The measured radius of the reverse edge ($R_{mark_m}$) is obtained by fitting an arc to the apex of the profile. This measurement is also a convolution: $R_{mark_m} = R_{mark} - R_{tip}$.
Final Calculation (Edge Reversal Method):
- The true cutting edge radius ($R_{tool}$) is calculated using the combined measured values ($R_{tool_m}$ and $R_{mark_m}$) and accounting for the elastic recovery coefficient ($\xi$): $$R_{tool} = \frac{1}{2 - \xi} \times (R_{tool_m} + R_{mark_m})$$
- Since $\xi$ is verified to be very small (0.012 at 20 nm depth), the convolution effect of $R_{tip}$ is effectively cancelled, yielding the high-precision $R_{tool}$.

Commercial Applications

The high-precision metrology developed in this research is critical for industries requiring nanometric control over surface finish and feature geometry.

Precision Optics Manufacturing: Essential for quality control of SPDTs used in diamond turning ultra-precision lathes to fabricate complex optical elements, including:
- Microlens arrays.
- Compound eye freeform surfaces.
- Sinusoidal grids and surface encoders.
Advanced Tooling and Metrology: Provides a reliable, traceable method for characterizing the geometry of cutting tools, which directly impacts the minimum achievable depth of cut and surface roughness in nanometric machining.
Semiconductor and Wafer Fabrication: Applicable to measuring tool edge radii used in processes requiring extreme surface integrity and nanometric tolerances.
Tool Wear Monitoring: Establishes a highly accurate baseline measurement, enabling precise tracking and quantitative evaluation of tool wear progression during ultra-precision machining operations.
Nanoindentation System Development: The optimized nanoindentation system design provides a robust platform for high-precision replication of nano-scale features for metrology standards and artifacts.

View Original Abstract

This paper presents a measurement method for high-precision cutting edge radius of single point diamond tools using an atomic force microscope (AFM) and a reverse cutting edge artifact based on the edge reversal method. Reverse cutting edge artifact is fabricated by indenting a diamond tool into a soft metal workpiece with the bisector of the included angle between the tool’s rake face and clearance face perpendicular to the workpiece surface on a newly designed nanoindentation system. An AFM is applied to measure the topographies of the actual and the reverse diamond tool cutting edges. With the proposed edge reversal method, a cutting edge radius can be accurately evaluated based on two AFM topographies, from which the convolution effect of the AFM tip can be reduced. The accuracy of the measurement of cutting edge radius is significantly influenced by the geometric accuracy of reverse cutting edge artifact in the proposed measurement method. In the nanoindentation system, the system operation is optimized for achieving high-precision control of the indentation depth of reverse cutting edFigurege artifact. The influence of elastic recovery and the AFM cantilever tip radius on the accuracy of cutting edge radius measurement are investigated. Diamond tools with different nose radii are also measured. The reliability and capability of the proposed measurement method for cutting edge radius and the designed nanoindentation system are demonstrated through a series of experiments.

Tech Support

Original Source

DOI: https://doi.org/10.3390/app10144799

References

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