The extreme hardness, wear resistance, and thermal conductivity of diamond make it an ideal cutting tool material. However, individual diamond crystals cleave quite easily when struck parallel to certain planes (the process used to facet diamond gemstones takes advantage of these relatively weak planes). As a result, individual diamond crystals do not make good cutting tools—unless they are meticulously oriented.

Diamond sintering overcomes the problem of weak planes in diamond gemstones by bonding a mass of small diamond particles onto a larger, coherent structure. Sintered diamond provides greater toughness and durability than single crystals because the individual crystals in a sintered body are randomly oriented. This prevents cracks from propagating along the weak planes where traditional diamond crystals cleave most easily. Sintered diamonds also provide more uniform wear than a single crystal, while maintaining similar thermal conductivity and hardness properties. All of these factors combine to make sintered diamond the preferred material for cutting rock.

At US Synthetic, the sintering process begins with premium saw-grade diamond crystals. These crystals are sintered together at temperatures of approximately 1400°C and pressures of around 60 kbar in the presence of a liquid metal catalyst. Typically, the diamond is bonded to a tungsten carbide substrate during the same high-temperature, high-pressure process. This sintered diamond and tungsten carbide composite is known in the industry as a polycrystalline diamond cutter (PDC).

The extreme hardness of diamonds presents obvious machining and finishing challenges. In typical machining situations, the finishing tool is harder than the work piece. With diamond inserts, this isn’t possible, since diamond is the hardest known substance. This makes machining diamond analogous to cutting through a wooden beam with a wooden saw. As a result, US Synthetic uses millions of carats of industrial diamond each year to machine and finish PDCs to their final dimensions. Over the years, we have developed specialized techniques and machines for lapping, grinding, polishing, brazing, and cutting PDC inserts. These techniques make it possible for us to finish PDCs to exacting specifications, despite the inherent challenges of machining sintered diamond.