Simulation of the ductile machining mode of silicon

At a Glance

Metadata	Details
Publication Date	2021-05-13
Journal	The International Journal of Advanced Manufacturing Technology
Authors	Hagen Klippel, Stefan Süssmaier, Matthias Röthlin, Mohamadreza Afrasiabi, Uygar Pala
Institutions	Inspire, ETH Zurich
Citations	11
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for Ductile Machining Simulation

This document analyzes the research paper, “Simulation of the ductile machining mode of silicon,” focusing on the requirements for high-performance diamond tooling and simulation materials. It connects the experimental and numerical needs directly to the advanced capabilities of 6CCVD’s MPCVD diamond products.

Executive Summary

The research successfully simulated single-grain diamond cutting of monocrystalline silicon using advanced mesh-free methods (SPH) to optimize the ductile-to-brittle transition in diamond wire sawing (DWS).

Core Achievement: Validation of numerical models (Johnson-Cook flow stress) against experimental scratch tests using a real, non-idealized diamond grain geometry.
Material Stress: Simulations predicted extremely high localized hydrostatic pressures (> 60 GPa) under the diamond tool, confirming the occurrence of phase transformations in silicon during cutting.
Process Insight: The study concluded that tool forces in ductile-mode cutting are primarily induced by the ductility and plastic deformation of the silicon, rather than brittle fracture energy.
Tooling Requirement: The wide variation in critical depth of cut ($h_{cu,crit}$) (0.112 µm to 1.270 µm) highlights the critical need for highly controlled, precise diamond cutting edges.
6CCVD Value Proposition: 6CCVD provides the necessary high-purity Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) materials, along with ultra-precise polishing (Ra < 1 nm) and custom geometry services, essential for replicating and extending this high-precision micro-machining research.
Future Research Need: The paper identified limitations in temperature prediction and constitutive modeling, requiring better experimental data on diamond-silicon friction and thermal properties—data 6CCVD can help supply.

Technical Specifications

The following hard data points were extracted from the experimental and simulation results, focusing on parameters relevant to material science and tooling.

Parameter	Value	Unit	Context
Workpiece Material	Monocrystalline Silicon	-	(100) direction assumed
Cutting Speed (v_c)	10	m/s	High-speed DWS simulation
Simulated Cut Depths (h_cu)	200, 500, 1000, 1500	nm	Range studied (0.2 µm to 1.5 µm)
Experimental Residual Depth (h_res)	0.55 to 2.65	µm	Ductile (0.55 µm) to Brittle (2.65 µm)
Critical Depth of Cut (h_cu,crit)	0.112 - 1.270	µm	Highly sensitive to crystallographic orientation
Diamond Grain Protrusion	Approx. 10	µm	Used for 3D meshing and simulation
Cutting Edge Radius (r)	1.4 - 6.7	µm	Varies over the cutting edge of the real grain
Maximum Simulated Temperature (T_max)	Up to 1700	K	Reaching Si melting point (1688.15 K)
Maximum Hydrostatic Pressure	> 60	GPa	Localized compression leading to phase transformation
Assumed Friction Coefficient ($\mu$)	0.3	-	Coulomb friction model used for simulation
Silicon Young’s Modulus (E)	129.09e⁹ Pa (at 300 K)	Pa	Temperature dependent model used

Key Methodologies

The experiment combined advanced computational physics with high-precision micro-machining tests to analyze material removal mechanisms.

Numerical Simulation: Utilized an in-house developed, GPU-accelerated code (mfree_iwf) based on the Smoothed Particle Hydrodynamics (SPH) mesh-free method. This approach handles the large deformations inherent in cutting brittle materials without intensive remeshing required by classic Finite Element Methods (FEM).
Material Constitutive Model: The Johnson-Cook flow stress model was implemented to describe the isotropic, ductile material behavior of silicon in the transition zone.
Tool Geometry Acquisition: A non-idealized diamond grain, isolated from a commercial diamond wire, was measured using optical microscopy to generate a precise point cloud, which was then triangulated into a 3D mesh (4426 tetrahedron elements) for simulation.
Experimental Setup: Cutting tests were performed on a Fehlmann Picomax Versa 825 5-axis milling machine. A polished silicon surface was rotated while the stationary diamond grain was fed vertically and horizontally.
Data Acquisition: Process forces (Cutting Force $F_c$ and Normal Force $F_N$) were measured using a Kistler 9256C dynamometer (eigenfrequency $f \approx 6$ kHz). Flash temperatures were measured using a Fire-3 two-color fiber optic pyrometer.
Surface Analysis: Residual scratch depth ($h_{res}$) and surface topography were optically evaluated at the center of the scratch path.

6CCVD Solutions & Capabilities

The simulation and experimental work presented in this paper underscore the critical role of high-quality, precisely engineered diamond materials in achieving controlled ductile-mode machining of brittle substrates like silicon. 6CCVD is uniquely positioned to supply the materials and customization required to advance this research.

Applicable Materials

To replicate or extend this research, particularly in developing more accurate constitutive models or testing new tooling geometries, researchers require diamond materials with known, consistent properties.

Research Requirement	6CCVD Material Solution	Technical Advantage
High-Purity Tooling	Optical Grade SCD (Single Crystal Diamond)	Ideal for single-grain scratch tests, offering maximum hardness, thermal stability, and low defect density for consistent results.
Large-Area Tooling/Wafers	High-Quality PCD (Polycrystalline Diamond)	Available in plates/wafers up to 125 mm, suitable for large-scale DWS tool development or testing complex tool arrays.
Thermal/Electrical Testing	BDD (Boron-Doped Diamond)	Customizable doping levels for experiments requiring specific electrical conductivity or thermal management properties (e.g., studying tool heat transfer, which the paper noted as a limitation).

Customization Potential

The paper emphasizes that the critical depth of cut and resulting forces are highly sensitive to the grain geometry, particularly the cutting edge radius (1.4 µm to 6.7 µm). 6CCVD’s advanced fabrication capabilities ensure precise control over these critical parameters, moving beyond the “non-idealised” grains used in DWS.

Precision Polishing: We offer ultra-low roughness polishing (Ra < 1 nm for SCD, Ra < 5 nm for inch-size PCD), allowing researchers to define and maintain specific cutting edge radii with sub-micron precision for controlled experiments.
Custom Dimensions and Substrates: We provide SCD and PCD plates/wafers in custom dimensions and thicknesses (SCD/PCD up to 500 µm thick, Substrates up to 10 mm), enabling the creation of custom tool inserts or large-scale test platforms.
Advanced Metalization: For integrating diamond tools into complex force dynamometers or thermal management systems, 6CCVD offers in-house metalization services (Au, Pt, Pd, Ti, W, Cu). This ensures robust, low-resistance electrical and thermal contacts required for accurate force and temperature measurement (as used in the paper’s setup).
Laser Cutting and Shaping: We provide custom laser cutting and shaping to create precise, defined tool geometries (e.g., cone, wedge, or specific rake angles) that are superior to the fractured grains used in DWS, allowing for focused study of crystallographic effects.

Engineering Support

The authors concluded that the Johnson-Cook model is insufficient and that more elaborated constitutive models, including fracture criteria and anisotropic behavior, are needed.

6CCVD’s in-house PhD team, specializing in CVD diamond growth and material properties, can provide expert consultation on:

Accurate Material Parameters: Supplying precise thermal diffusivity ($\alpha$), specific heat ($C_p$), and Young’s modulus data for our specific SCD and PCD grades, crucial for improving the accuracy of thermal predictions (a noted weakness in the paper).
Constitutive Model Development: Collaborating on projects requiring advanced material modeling for high-pressure, high-strain-rate applications, ensuring that the diamond tool properties are accurately represented in SPH or FEM simulations.
Tool Design Optimization: Assisting engineers in selecting the optimal diamond material (SCD vs. PCD) and crystallographic orientation for specific micro-machining projects, such as high-speed silicon wafer processing.

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

Tech Support

Original Source

DOI: https://doi.org/10.1007/s00170-021-07167-3