How to choose the right PCD, solid CVD Crystal and MCD materials for diamond tools
- ToolingBox
- May 19
- 4 min read
Attract: Diamond tools are indispensable in the precision machining of non-ferrous materials, composites, and advanced ceramics due to their exceptional hardness, wear resistance, and thermal conductivity. However, selecting the optimal diamond tool material—polycrystalline diamond (PCD), solid chemical vapor deposition (CVD) diamond crystal, or monocrystalline diamond (MCD)—remains a critical challenge for manufacturing engineers.
This paper provides a systematic decision framework for matching diamond tool materials to specific machining scenarios. A simplified logic flowchart and a quick-reference summary table further aid material selection. Practical considerations regarding tool geometry, edge preparation, cooling strategies, and cost optimization are also discussed, and machinists make informed, technically sound, and economically viable decisions when deploying diamond tools in production environments.
I. First, confirm whether diamond tools are suitable.
Diamond tools cannot machine ferrous metals (such as steel, cast iron, stainless steel, etc.) because diamond will react chemically with iron under high-temperature cutting conditions, causing rapid tool wear.
✅ Applicable workpiece materials:
High-silicon aluminum alloys (Si content > 8%~12%)
Copper, brass, oxygen-free copper
Metal matrix composites (MMC, such as SiC/Al)
Carbon fiber/glass fiber composites (CFRP/GFRP)
Graphite, carbon, ceramics
Hard plastics, rubber
II. Comparison of Machining Properties of Three Types of Diamond Materials (Key Selection Dimensions)
Comparison | PCD | Solid CVD Crystal Diamond | MCD |
Sharpness of cutting edge | Medium (due to coarser grains, the minimum cutting edge radius is larger) | High (fine grains, can be ground into sharp cutting edges) | Extremely high (capable of achieving atomically sharp cutting edges) |
Toughness / Impact Resistance | Ideally (metal binder cushioning, resists intermittent cutting) | Good (no binder, but uniform polycrystalline structure) | Poor quality (has cleavage surfaces, is brittle, and is susceptible to impact). |
Wear Resistance | Excellent | Excellent (highest hardness) | Good (but anisotropic, uneven wear). |
Surface roughness (Ra) of the machined surface | 0.2~0.4 μm (standard) | 0.05~0.2 μm (mirror finish) | <0.02 μm (super mirror finish) |
Heat resistance | Medium (adhesive softening limit, approximately 700°C) | High (purity diamond, stable above approximately 900°C.) | Medium (graphitization begins at approximately 650℃) |
Available geometry | can be welded into complex shapes (turning tools, milling cutters, drill bits). | can be used to manufacture large-size blades | Small size (typically <8×8 mm), shape restricted |
Typical Appearance | Black | white or Transparent | Pale yellow |
Cost | Low to Medium | Medium to high | Tall (especially large sizes) |
❌ Not suitable for: Carbon steel, alloy steel, cast iron, titanium alloys (some special coating CVD may be attempted, but generally not recommended).
III. Specific Recommendations for Selection Based on Machining Scenarios
1. Roughing, Large Allowance Cutting, Intermittent Cutting (e.g., Milling, Drilling)
A. PCD is the First Choice
Reason: Highest toughness, strong impact resistance, and less prone to chipping.
Typical Applications:
a. Roughing of high-silicon aluminum alloy pistons and housings
b. Roughing of metal matrix composites
c. CFRP drilling (PCD drill bits)
d. Rough milling of graphite electrodes
B. Second Choice:
If the workpiece has extremely high hardness (e.g., high-grain MMC), CVD polycrystalline diamond thick-film tools can be considered, but impact should be considered.
2. Semi-finishing and Finishing (requiring high surface quality and dimensional accuracy)
A. CVD polycrystalline diamond is the First Choice
Reason: High hardness, good wear resistance, sharp cutting edge, can achieve a near-mirror surface, and does not have the anisotropy problems of single crystals.
Typical Applications:
a. Precision turning and milling of high-silicon aluminum alloys (Si≥12%)
b. Finishing of CFRP composite materials (CVD tool life can reach 2~4 times that of PCD)
c. Mirror turning of copper alloys
d. Semi-finishing of ceramic materials
B. Alternative: For higher toughness requirements (with slight discontinuity), fine-grained PCD can be selected.
3. Ultra-precision machining (nanoscale surface roughness, optical-grade mirror finish)
A. The only choice: MCD (single-crystal diamond)
Reason: It can grind extremely sharp and smooth cutting edges (edge radius can reach tens of nanometers), producing mirror finishes with Ra<0.02 μm or even Rz<0.1 μm.
Typical Applications:
a. Optical lens molds (copper, oxygen-free copper)
b. Laser reflectors, infrared optical components
c. Precision rollers, air bearing spindles
d. Medical surgical instruments (such as tools for processing artificial lenses)
Note: Continuous cutting must be ensured; impact is strictly prohibited; precise control of cutting depth and feed rate is required; high tool cost, suitable for high value-added parts.
4. Continuous cutting, high-speed cutting (high surface velocity, e.g., >1000 m/min)
CVD or PCD are preferred (depending on surface requirements).
a. CVD is more heat-resistant and suitable for finishing at higher speeds;
b. PCD has good toughness and is suitable for light impact conditions at high speeds.
5. Machining of thin-walled parts, slender shafts, and miniature parts (sensitive to cutting forces)
MCD (extremely sharp, minimum cutting force) or CVD are preferred.
Avoid using blunt PCD, as it may cause workpiece deformation.
IV. Simple Decision Flowchart (Logic Chain)
V. Additional Practical Suggestions
Tool Geometry and Edge Treatment
PCD tools are often treated with negative chamfering or passivation to improve chipping resistance.
MCD tools require orientation (to ensure the cleavage planes and the main cutting force direction avoid easily splitting angles), generally done by specialized tool manufacturers.
CVD Crystal Diamond tools can be made with sharp edges or slight chamfering, suitable for finishing.
2. Cost Trade-offs
For mass production of aluminum alloy parts: PCD offers the best cost-performance ratio.
High-precision, small-batch optical molds: MCD is a worthwhile investment.
Composite material machining: CVD's long lifespan offsets its higher unit price.
3.Cooling methods:
Diamond tools are generally dry-cut or micro-lubricated (MQL) to avoid thermal shock caused by excessive water-based cutting fluids.
When cutting high-silicon aluminum alloys, MQL helps with chip removal and temperature reduction.
4.Acceptance inspection:
For high surface quality requirements, it is recommended to perform edge microscopy inspection of the tool (MCD requires confirmation of crystal orientation).
The weld strength of PCD/CVD inserts should be confirmed (especially for high-feed milling).
VI.Summary Table (Quick Reference)
Machining requirements | Recommended Diamond Materials | Reasons |
Rough milling, drilling, high feed, intermittent cutting | Optimal toughness and impact resistance | |
Precision machining of aluminum alloys, CFRP, and copper alloys (Ra≤0.2) | High hardness + high sharpness + uniform wear | |
Mirror-finish ultra-precision machining (Ra<0.02 μm) | Atomic-level sharp edge | |
High-speed continuous cutting | Solid CVD Crystal Diamond or Fine-grained PCD | High temperature resistance, low friction |
Thin-walled/micro parts | MCD or Solid CVD Crystal diamond | slight cutting force |
Cost priority, large removal volume | PCD | Lowest unit cost |
In actual selection, it is recommended to verify through trial cutting, especially for new materials or high-requirement parts. Tool suppliers can usually also recommend specific grades and cutting edge designs based on your machine tool, workpiece drawings, and process parameters.
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