Investigation of the Effect of End Mill-Geometry on Roughness and Surface Strain-Hardening of Aluminum Alloy AA6082

At a Glance

Metadata	Details
Publication Date	2020-07-10
Journal	Materials
Authors	P. G. Filippov, Michael Kaufeld, Martin Ebner, Ursula Koch
Institutions	Technische Hochschule Ulm, Ludwig-Maximilians-Universität München
Citations	4
Analysis	Full AI Review Included

Technical Documentation & Analysis: Ultra-Precision Micro-Milling with Monocrystalline Diamond

Executive Summary

This research validates the critical role of Monocrystalline Diamond (MD) tool geometry in achieving superior surface integrity during micro-milling of aluminum alloy AA6082, a finding highly relevant for high-frequency component manufacturing.

MD Superiority: Monocrystalline Diamond (MD) end-mills achieved significantly lower surface roughness ($R_q = 26 \text{ nm}$) compared to Solid Carbide (SC) tools ($R_q = 119 \text{ nm}$).
Geometry is Key: The MD tool’s extremely sharp cutting edge radius ($r = 17 \text{ nm}$) was identified as the main factor influencing surface roughness, demonstrating that tool material quality dictates final component quality.
Minimal Strain Hardening: The MD tool operated in a “pure cutting regime,” resulting in a minimal strain-hardened zone (max. $60 \text{ nm}$ depth) and lower maximum hardness increase (125%) compared to the SC tool ($> 200 \text{ nm}$ depth, 160% increase).
Process Parameter Insensitivity: Within the tested range ($f_z = 3 \text{ µm}$ to $14 \text{ µm}$), the feed per tooth had no significant influence on horizontal surface roughness or strain hardening, emphasizing the dominance of tool edge quality.
Application Relevance: These results are crucial for the high-precision manufacturing of Terahertz (THz) measurement technology modules, where low surface roughness is essential for minimizing transmission loss.
6CCVD Value Proposition: 6CCVD provides the high-purity Single Crystal Diamond (SCD) material necessary to fabricate these ultra-sharp, low-defect MD micro-milling tools.

Technical Specifications

Parameter	Value	Unit	Context
MD Tool Cutting Edge Radius ($r$)	17	nm	Monocrystalline Diamond (MD)
SC Tool Cutting Edge Radius ($r$)	670	nm	Solid Carbide (SC)
MD Machined Surface Roughness ($R_q$)	26	nm	Average horizontal roughness on AA6082
SC Machined Surface Roughness ($R_q$)	119	nm	Average horizontal roughness on AA6082
MD Tool Cutting Edge Roughness ($R_q$)	90 ± 48	nm	Measured optically
SC Tool Cutting Edge Roughness ($R_q$)	2355 ± 1551	nm	Measured optically
MD Strain-Hardened Zone Depth	Max. 60	nm	Hardness increased up to 125%
SC Strain-Hardened Zone Depth	> 200	nm	Hardness increased up to 160%
Bulk Hardness ($H_{IT}$) AA6082	1195 ± 46	MPa	Electropolished reference sample
Cutting Velocity ($v_c$)	28.3	m/min	Micro-milling parameter
Rotational Speed ($n$)	18,000	min^-1	Micro-milling parameter
Tool Diameter ($D$)	500	µm	Nominal cutter diameter
Axial Cutting Depth ($a_e$)	15	µm	Fixed parameter

Key Methodologies

The experiment compared the performance of two micro end-mills (SC and MD) on AA6082 aluminum alloy using a high-precision CNC machining center.

Workpiece Preparation: AA6082-T651 aluminum alloy plates were used. Reference samples were electropolished to achieve a non-strain-hardened surface.
Tool Inspection: New, unused Solid Carbide (SC) and Monocrystalline Diamond (MD) single-tooth end-mills (nominal $D = 500 \text{ µm}$) were microscopically inspected to determine actual cutting edge radius ($r$) and roughness ($R_q, R_t$).
Milling Parameters: Samples were produced on a KERN Pyramid Nano CNC machine using fixed parameters:
- Cutting velocity ($v_c$): $28.3 \text{ m/min}$
- Rotational speed ($n$): $18,000 \text{ min}^{-1}$
- Axial cutting depth ($a_e$): $15 \text{ µm}$
- Radial cutting depth ($a_p$): $500 \text{ µm}$
Variable Feed: The single tooth feed ($f_z$) was varied at $3 \text{ µm}$, $8 \text{ µm}$, and $14 \text{ µm}$.
Roughness Measurement: Confocal microscopy was used to measure one-dimensional roughness parameters ($R_q, R_t$) perpendicular (horizontal) and parallel (vertical) to the milling direction.
Hardness Measurement: Instrumented Indentation via the Enhanced Stiffness Procedure (ESP) was performed using a Berkovich indenter (tip radius $153 \text{ nm}$) to generate depth-dependent hardness curves ($H_{IT}$).
Strain-Hardening Analysis: The Korsunsky film-substrate model was numerically fitted to the hardness-depth data to estimate the thickness and hardness of the strain-hardened layer.

6CCVD Solutions & Capabilities

The research conclusively demonstrates that the use of Monocrystalline Diamond (MD) tools with extremely sharp, low-roughness cutting edges is essential for achieving the surface quality required in advanced micro-manufacturing, such as Terahertz components. 6CCVD specializes in providing the foundational diamond materials and processing capabilities necessary to meet these stringent requirements.

Applicable Materials

The MD tool used in this study relies on the intrinsic perfection of Single Crystal Diamond (SCD).

Optical Grade SCD: 6CCVD supplies high-purity, low-defect SCD wafers and plates, which are the ideal starting material for manufacturing ultra-precision micro-milling tools. The low defect density of our SCD ensures the mechanical stability and ultra-sharpness required to achieve cutting edge radii as low as $17 \text{ nm}$.
Custom Thickness: We offer SCD material in thicknesses ranging from $0.1 \text{ µm}$ up to $500 \text{ µm}$, providing tool manufacturers with the necessary bulk material for robust tool design.

Customization Potential

The success of the MD tool is directly linked to its ultra-low cutting edge roughness ($R_q \approx 90 \text{ nm}$). 6CCVD’s polishing capabilities are critical for replicating and exceeding this performance.

Requirement from Paper	6CCVD Capability	Technical Advantage
Ultra-Sharp Edge Radius ($r = 17 \text{ nm}$)	High-Purity SCD Substrates	Ensures material integrity for atomic-scale edge finishing.
Low Tool Roughness ($R_q \approx 90 \text{ nm}$)	Proprietary Polishing Services	We guarantee $R_a < 1 \text{ nm}$ on SCD, enabling tool manufacturers to achieve sub-20 nm edge radii consistently.
Tool Dimensions ($D = 500 \text{ µm}$)	Custom Dimensions & Laser Cutting	We supply SCD plates up to $125 \text{ mm}$ (PCD) and offer precise laser cutting to prepare blanks for micro-tool fabrication.
Potential Metalization	In-House Metalization	If future tool designs require bonding layers, 6CCVD offers custom metalization (Au, Pt, Pd, Ti, W, Cu) directly on the diamond substrate.

Engineering Support

The findings regarding minimal strain hardening (max. $60 \text{ nm}$ depth) are vital for applications where surface mechanical properties must remain close to the bulk material, such as high-frequency components.

Application Expertise: 6CCVD’s in-house PhD team specializes in material selection and optimization for similar RF/Terahertz (THz) Waveguide projects, where surface integrity directly correlates with signal transmission efficiency.
Material Optimization: We assist engineers in selecting the optimal diamond grade (e.g., SCD for ultimate sharpness or PCD for large-area coverage) to ensure the tool material minimizes the ploughing effect and subsequent strain hardening, maximizing component performance.
Global Supply Chain: We offer global shipping (DDU default, DDP available) to ensure rapid delivery of custom diamond materials worldwide.

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

View Original Abstract

Micro-milling is a promising technology for micro-manufacturing of high-tech components. A deep understanding of the micro-milling process is necessary since a simple downscaling from conventional milling is impossible. In this study, the effect of the mill geometry and feed per tooth on roughness and indentation hardness of micro-machined AA6082 surfaces is analyzed. A solid carbide (SC) single-tooth end-mill (cutting edge radius 670 nm) is compared to a monocrystalline diamond (MD) end-mill (cutting edge radius 17 nm). Feed per tooth was varied by 3 μm, 8 μm and 14 μm. The machined surface roughness was analyzed microscopically, while surface strain-hardening was determined using an indentation procedure with multiple partial unload cycles. No significant feed per tooth influence on surface roughness or mechanical properties was observed within the chosen range. Tools’ cutting edge roughness is demonstrated to be the main factor influencing the surface roughness. The SC-tool machined surfaces had an average Rq = 119 nm, while the MD-tool machined surfaces reached Rq = 26 nm. Surface strain-hardening is influenced mainly by the cutting edge radius (size-effect). For surfaces produced with the SC-tool, depth of the strain-hardened zone is higher than 200 nm and the hardness increases up to 160% compared to bulk. MD-tool produced a thinner strain-hardened zone of max. 60 nm while the hardness increased up to 125% at the surface. These findings are especially important for the high-precision manufacturing of measurement technology modules for the terahertz range.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma13143078

References

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