Influence of grain size and cobalt content on machinability of tungsten carbide with diamond-coated tools
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-01-01 |
| Journal | Materials research proceedings |
| Authors | Marco Diegel |
| Analysis | Full AI Review Included |
Technical Analysis & Documentation: MPCVD Diamond for High-Performance Machining
Section titled âTechnical Analysis & Documentation: MPCVD Diamond for High-Performance MachiningâExecutive Summary
Section titled âExecutive SummaryâThis research validates the critical role of CVD diamond coatings in the high-efficiency orthogonal cutting of Tungsten Carbide (WC), focusing on the self-sharpening mechanism.
- Core Achievement: Demonstrated process-reliable machining of challenging, high-hardness WC (1743 HV30, < 8.5 wt.% Co) using CVD diamond-coated tools, provided the undeformed chip thickness (h) is reduced (3 ”m).
- Self-Sharpening Mechanism: Coating flaking on the rake face acts as a self-sharpening mechanism, reducing the cutting edge radius by approximately 60% and the effective rake angle by 20%, leading to reduced cutting normal force.
- Material Dependence: The timing of the self-sharpening effect is highly dependent on the WC substrate composition. Increasing grain size (0.49 ”m to 1.28 ”m) and Cobalt (Co) content (6 wt.% to 15 wt.%) reduces material hardness and delays the onset of coating flaking (up to 1.5 m cutting path).
- Laser Treatment Efficacy: Pre-treating the rake face by laser removal of the coating stabilizes the cutting process, eliminates the gradual wear-related force increase, and is particularly beneficial for machining low-Co, high-hardness WC.
- Thermal Stability: Measured tool temperatures (100-200 °C) remained far below the 750 °C threshold for diamond graphitization, confirming the thermal stability of the CVD coating under these high-speed cutting conditions.
- 6CCVD Value: 6CCVD specializes in providing the high-quality, microcrystalline Polycrystalline Diamond (PCD) material required for these coatings, offering precise thickness control (down to 0.1 ”m) and custom laser processing to optimize tool geometry.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the orthogonal cutting experiments and material characterization:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| WC Substrate Hardness (CTF12D) | 1743 | HV30 | Fine grain (0.49 ”m), 6 wt.% Co |
| WC Substrate Hardness (CFG-CTM30) | 1138 | HV30 | Medium grain (1.28 ”m), 15 wt.% Co |
| Diamond Coating Thickness | 15 | ”m | Microcrystalline CVD diamond used for optimal tool life |
| Cutting Speed (vc) | 150 | m/min | Constant speed for orthogonal cutting tests |
| Undeformed Chip Thickness (h) | 3 & 5 | ”m | Varied parameter; 3 ”m enabled reliable cutting of 6 wt.% Co WC |
| Maximum Measured Tool Temperature | 100 to 200 | °C | Measured at the cutting edge; well below graphitization limit (750 °C) |
| Coating Flaking Delay (CTF30D) | Approx. 0.5 | m | Cutting path length for fine grain, 15 wt.% Co WC |
| Coating Flaking Delay (CFG-CTM30) | Up to 1.5 | m | Cutting path length for medium grain, 15 wt.% Co WC |
| Cutting Edge Radius Reduction (Flaking) | Approx. 60 | % | Result of the self-sharpening effect |
| Effective Rake Angle Reduction (Flaking) | Approx. 20 | % | Result of the self-sharpening effect |
| Cutting Normal Force Reduction (Flaking) | Approx. 34 | % | Observed when Co content increased from 6 wt.% to 15 wt.% |
Key Methodologies
Section titled âKey MethodologiesâThe study employed highly controlled orthogonal cutting tests using specialized CVD diamond-coated tools to isolate the effects of WC substrate composition and tool geometry.
- Tool Substrate Selection: Carbide tools with submicron grain size (0.5 to 0.8 ”m) and low Cobalt content (6 wt.% Co) were chosen to ensure strong adhesion of the diamond coating.
- Diamond Coating: A microcrystalline CVD diamond coating with a thickness of 15 ”m was applied to the carbide tools.
- Tool Geometry: All tools featured a clearance angle of 12.5° and a rake angle of 0°.
- Laser Treatment: Half of the tools underwent laser-treatment to precisely remove the diamond coating from the rake face, simulating the beneficial self-sharpening effect caused by coating flaking.
- Experimental Setup: Orthogonal cutting tests were conducted on a CNC vertical broaching machine (Forst RASX 2200x800x600 M) at a constant cutting speed of 150 m/min, without cutting fluid.
- Data Acquisition:
- Cutting forces (Fc and FN) were measured using a Kistler 9257B dynamometer.
- Tool temperature was monitored using a FLIR SC7500 thermography camera (emission coefficient set to 1).
- Chip formation was recorded using a Vision Research Phantom v7.3 high-speed camera.
- Test Criteria: Each tool was used until a predetermined cutting path of 10 m was reached (corresponding to 100 cuts), or until tool failure occurred.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research confirms the necessity of high-quality, precisely controlled CVD diamond materials for advanced tooling applications, particularly where controlled wear (self-sharpening) is desired. 6CCVD is uniquely positioned to supply the required diamond materials and customization services to replicate and advance this research.
| Research Requirement | 6CCVD Material & Service | Technical Advantage |
|---|---|---|
| High-Purity CVD Diamond Material | Polycrystalline Diamond (PCD) Plates/Wafers. We supply high-quality MPCVD PCD material, ideal for brazing onto carbide inserts or for use as standalone tools. | Ensures consistent mechanical properties and optimal adhesion characteristics required for predictable coating flaking and self-sharpening. |
| Precise Coating Thickness (15 ”m) | PCD Thickness Control (0.1 ”m - 500 ”m). 6CCVD guarantees precise thickness control, enabling engineers to tune the diamond layer to match specific WC substrate compositions and desired flaking rates. | Allows for experimental optimization of tool life and self-sharpening timing based on the material being machined. |
| Custom Tool Geometry & Rake Face Preparation | Advanced Laser Cutting & Etching Services. We offer in-house laser processing to create complex tool geometries and replicate the beneficial âlaser-treatedâ condition (removed coating on the rake face) identified in the study. | Facilitates rapid prototyping and production of optimized tool inserts with precise microgeometry (e.g., cutting edge radius rÎČ). |
| Need for Ultra-Hard Machining Material | Single Crystal Diamond (SCD) Plates. For applications requiring the highest possible wear resistance beyond PCD coatings, 6CCVD offers SCD plates up to 500 ”m thick with superior hardness and thermal conductivity. | Extends the application range to even harder materials or higher cutting speeds where PCD coatings may fail prematurely. |
| Surface Finish Requirements (Ra < 1nm) | Precision Polishing Services. We provide polishing down to Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, ensuring minimal friction and improved chip flow, especially critical for the laser-treated tools. | Reduces initial cutting forces and thermal load, maximizing the efficiency of the cutting process. |
| Global Supply Chain & Logistics | Global Shipping (DDU Default, DDP Available). We ensure reliable, fast delivery of custom diamond materials worldwide. | Supports international research and manufacturing schedules without logistical delays. |
Engineering Support
Section titled âEngineering SupportâThe successful outcome of this research hinges on correlating diamond material properties (e.g., microcrystalline structure, thickness) with specific substrate compositions (WC grain size and Co content). 6CCVDâs in-house PhD team specializes in material science and can assist engineers and researchers in selecting the optimal diamond grade and processing parameters for similar High-Precision Machining and Tooling projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract. Tungsten carbide is an important material for manufacturing cutting tools, molds and dies due to its combination of high hardness and high resistance to mechanical loads and wear. The primary restriction associated with utilizing this material pertains to the time-consuming and costly machining process, which is attributed to its low machinability. As an alternative to conventional electro discharge machining, milling with diamond-coated carbide tools has shown promising results. Due to a lack of knowledge about the interactions between the tungsten carbide to be machined, the tool and the process parameters, the economic advantages of the milling process are currently not fully utilized. In application of the cutting tools, a self-sharpening effect due to flaking of the coating on the rake face occurs, which results in improved cutting conditions. The present study addressed the prevailing knowledge cap regarding the interaction between material composition, parameter selection and tool design. Tungsten carbides with different compositions were machined in orthogonal cutting tests. In the investigations, increasing grain size and cobalt content caused a reduced thermomechanical process load and therefore delayed a favorable self-sharpening effect.