Polycrystalline Diamond also known as PCD is produced synthetically by sintering together many (Poly) diamond particles, usually in the size of 2 to 30 microns of a meter, with a metal binder (mostly Cobalt) at high temperature and high pressure. The PCD material may contain 90-95% diamond particles and the rest is the binder, PCD is commonly used in cutting tools to cut through composite materials and super hard metals for extended tool life as these materials are very taxing on the milling materials.
Typical characteristics  of PCD:
Hardness – being made from diamond, its hardness is close to pure diamond hardness of 10,000 Hv, however, since it contains metal binder, the hardness will be lower and vary between 6500-7500 Hv.
Wear resistance – it is the second to pure diamond. The hardness of the material allows the ability to withstand wear and long last in any application where abrasive materials are involved. Workpiece material and cutting speed influence on the wear rate. Significant wear rate advantage of PCD vs. Cemented Carbide can be found in machining Composites, MMC, CMC and high silicon Aluminum.
TRS (Transverse Rapture Strength)– PCD is considered a hard material, therefore more brittle and less tough compared to metals. However, PCD materials with different grain sizes, have different TRS. It is evident that PCD material with lower grain size, have higher TRS than PCD with higher grain size.
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To emphasize the difference between various materials, let us look at cutting tool materials in reference to their comparative toughness and hardness.
From this diagram, we can conclude that coated carbide tools have the largest amplitude of usages, therefore they represent the majority of cutting tools in worldwide usage.
In addition, PCD is the hardest cutting tool material, however, has the lowest toughness. This is the reason why PCD tools are being used in applications where workpiece material is relatively abrasive and removed chips are in the form of powder (composites, ceramics etc.) and/or require low shear force (Aluminum, Brass, Copper etc.).
To put things into perspective, let’s discuss about different applications, using PCD tools:
Using Polycrystalline Diamond in Milling:
Milling operations involve interrupted cutting of the material, where each end mill tooth is engaged with the material and exiting it in one tool revolution. Each time the cutting edge enters the material, the “hammering” effect might damage the cutting edge of the tool. PCD tools perform the best in milling of composites, ceramics, and Aluminum. For example, composites parts, such as CFRP and GFRP in the aerospace are trimmed and finished to final dimension by PCD 2 flutes endmills and spiral PCD endmills. PCD end spiral and multi-flute end mills are used to machine ceramics in green stage, such as SiC, BN and C/SiC. PCD reamers and plungers are used in Al-Si materials in the automotive for engine and gear boxes.
Using Polycrystalline Diamond in Drilling and Turning:
In drilling and Turning operations, the tool cutting edge has constant contact with the material, unlike milling, therefore the cutting edge is less likely to chip or fracture. The PCD wear rate is low, compared to carbide, allowing for longer tool life and hole diameter consistency. PCD drills can be found in CNC shops in the aerospace, drilling composites materials, such as CFRP, GFRP and MMC.
PCD drilling and boring tools are used in Al-Si materials in the automotive for engine and gear boxes. PCD turning tools are used in composites in the defense industry for missile parts and in the automotive, machining Al-Si car bearing.
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