Experimental Analysis of Ductile Cutting Regime in Face Milling of Sintered Silicon Carbide

At a Glance

Metadata	Details
Publication Date	2022-03-24
Journal	Materials
Authors	Marvin Groeb, Lorenz Hagelüken, Johann Groeb, Wolfgang Ensinger
Institutions	Facility for Antiproton and Ion Research, Technical University of Darmstadt
Citations	4
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for Ultra-Precision Machining of SiC

Executive Summary

This documentation analyzes the successful achievement of a ductile cutting regime in sintered Silicon Carbide (SiC) using Polycrystalline Diamond (PCD) tooling, directly correlating the research requirements with 6CCVD’s advanced MPCVD diamond capabilities.

Ductile Cutting Achieved: Researchers successfully demonstrated a ductile material removal regime in sintered 6H-SiC via high-speed face milling, a significant advancement over conventional grinding.
PCD Tooling Validation: The critical role of high-quality Polycrystalline Diamond (PCD) tools was confirmed, enabling ultra-precision material removal at nanometric chip thicknesses.
Critical Threshold Identified: The brittle-to-ductile transition occurred at a critical chip thickness (H_m) between 46 nm and 55 nm, requiring exceptional tool edge sharpness and material stability.
Superior Surface Quality: Ductile-milled surfaces achieved low roughness (Sa 0.1 to 0.2 µm) and exhibited significantly reduced sub-surface damage (SSD) compared to conventional diamond grinding.
Material Integrity Maintained: Compositional analysis (XRD, RLS) confirmed that the high-pressure phase transformation during ductile cutting was metastable, resulting in no detectable machining-induced amorphization or chemical change in the SiC.
6CCVD Value Proposition: 6CCVD provides the high-purity, low-defect MPCVD PCD material necessary to fabricate the next generation of ultra-precision cutting tools required for replicating and advancing this high-speed ductile machining technique.

Technical Specifications

The following hard data points were extracted from the experimental results, highlighting the precision required for ductile regime machining of SiC:

Parameter	Value	Unit	Context
Critical Chip Thickness (Scratch Test)	55	nm	Brittle-to-Ductile Transition Depth
Critical Chip Thickness (Drag Test)	46	nm	Brittle-to-Ductile Transition Depth
Achieved Surface Roughness (Sa)	0.1 to 0.2	µm	Ductile Cutting Regime
Median Chip Thickness (Hm) for Ductile Indication	< 80	nm	Required for spontaneous Smr improvement
Best Ductile Parameter Set (Hm)	56	nm	Parameter Set 17
Best Ductile Parameter Set (Cutting Speed)	250	m/min	Parameter Set 17
Tool Material Used	Polycrystalline Diamond (PCD)	N/A	2 mm diameter endmill
SiC Polytype	Hexagonal (6H)	N/A	Sintered SiC used
Maximum Spindle Speed	42,000	min^-1	Machining Center Capability
SiC Flexural Strength	450	MPa	Material Property

Key Methodologies

The successful achievement of the ductile cutting regime relied on a highly controlled ultra-precision machining environment and advanced metrology:

Ultra-Precision Machining: Experiments were conducted on a vertical CNC machining center (Kern Micro HD) featuring friction-free microgap hydrostatics and closed-loop linear drives, achieving positioning errors in the sub-micrometer range.
Tooling and Kinematics: 2 mm PCD endmills were used in a face milling setup (interrupted cut). The cutting process utilized chip thinning in a climb direction, inducing high hydrostatic pressure necessary for the brittle-to-ductile phase transformation.
In-Process Monitoring: Acoustic Emission (AE) signals (600 kHz sensor) were recorded and analyzed via Power Spectral Density (PSD) sums. A sharp increase in the AE PSD sum correlated with the transition to the ductile cutting regime, offering potential for in-process optimization.
Quantitative Surface Metrology: Confocal Laser Scanning Microscopy (CLSM) was used to measure ISO 25178 areal surface quality parameters (Sa, Sq, and the critical surface bearing parameter Smr).
Microstructural Analysis:
- Scanning Electron Microscopy (SEM) provided qualitative surface characterization (grooves, breakouts, pitting).
- Raman Laser Spectroscopy (RLS, 532 nm) and Grazing Incidence X-ray Diffraction (XRD) confirmed the stability of the 6H-SiC crystal structure and the absence of amorphization.
Sub-surface Damage (SSD) Assessment: Scanning Acoustic Microscopy (SAM) was performed at 80 kHz and 400 kHz, demonstrating a significantly reduced amount of SSD in the ductile-milled samples compared to brittle-milled or ground samples.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to support and advance research into ultra-precision machining of hard ceramics like SiC by supplying the highest quality MPCVD diamond materials required for advanced tooling.

Applicable Materials

The research confirms the necessity of high-quality PCD for achieving the critical nanometric chip thickness required for ductile regime machining.

Research Requirement	6CCVD Solution	Material Specification
High-Performance Tooling	Polycrystalline Diamond (PCD)	High-purity MPCVD PCD wafers (0.1µm - 500µm thickness) for superior tool blank fabrication.
Extreme Edge Sharpness	Ultra-Low Defect PCD	Our MPCVD process ensures highly uniform grain structure and low defect density, crucial for maintaining the 1-2 µm edge sharpness required to induce hydrostatic pressure at the 50 nm chip thickness level.
Future SCD Tooling	Optical Grade Single Crystal Diamond (SCD)	For research extending into Single Point Diamond Turning (SPDT) of SiC, our SCD material (Ra < 1 nm) offers the ultimate in edge fidelity and thermal stability.

Customization Potential

The success of this research hinges on precise tool geometry and material properties. 6CCVD offers comprehensive customization services to meet these exacting standards:

Custom Dimensions: We supply PCD plates and wafers up to 125 mm in diameter, allowing tool manufacturers to design larger, more complex tool geometries than the 2 mm endmills used in this study.
Precision Polishing: To ensure the nanometric edge quality essential for ductile cutting, 6CCVD offers ultra-precision polishing services, achieving roughness values of Ra < 5 nm on inch-size PCD wafers.
Advanced Metalization: While not explicitly detailed for the cutting edge, future tool designs may require integrated sensors or complex mounting. We offer in-house metalization capabilities including Ti, W, Pt, Au, Pd, and Cu deposition.
Substrate Thickness: We provide custom diamond substrates up to 10 mm thick, ideal for robust tool bodies or specialized mounting fixtures required for high-speed, high-force milling operations (up to 42,000 min^-1).

Engineering Support

The transition from brittle to ductile cutting in ceramics is a complex material science challenge. 6CCVD’s in-house PhD team specializes in diamond material optimization for Ultra-Precision Machining (UPM) applications.

Material Selection: We assist engineers in selecting the optimal diamond type (PCD grain size, SCD orientation, BDD conductivity) to maximize tool life and performance in high-speed SiC milling projects.
Process Optimization: Our experts can consult on how diamond material properties influence the critical chip thickness threshold and acoustic emission signatures, aiding in the development of robust in-process monitoring systems.
Global Supply Chain: We ensure reliable, global shipping (DDU default, DDP available) of high-value diamond materials, minimizing lead times for critical research and production cycles.

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

View Original Abstract

In this study, sintered silicon carbide is machined on a high-precision milling machine with a high-speed spindle, closed-loop linear drives and friction-free micro gap hydrostatics. A series of experiments was undertaken varying the relevant process parameters such as feedrate, cutting speed and chip thickness. For this, the milled surfaces are characterized in a process via an acoustic emission sensor. The milled surfaces were analyzed via confocal laser scanning microscopy and the ISO 25178 areal surface quality parameters such as Sa, Sq and Smr are determined. Moreover, scanning electron microscopy was used to qualitatively characterize the surfaces, but also to identify sub-surface damages such as grooves, breakouts and pitting. Raman laser spectroscopy is used to identify possible amorphization and changes to crystal structure. We used grazing incidence XRD to analyze the crystallographic structure and scanning acoustic microscopy to analyze sub-surface damages. A polycrystalline diamond tool was able to produce superior surfaces compared to diamond grinding with an areal surface roughness Sa of below 100 nm in a very competitive time frame. The finished surface exhibits a high gloss and reflectance. It can be seen that chip thickness and cutting speed have a major influence on the resulting surface quality. The undamaged surface in combination with a small median chip thickness is indicative of a ductile cutting regime.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma15072409

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