The diamond cutting tools that are used in woodworking begin as individual diamond crystals sintered along with a carbide backing in a high-pressure, high-temperature environment. From the joining or sintering of these crystals, we derive the term polycrystalline (many crystals) diamond, also referred to as PCD. After the material is cooled, it is finished in a disc form before being cut into the various shapes required for tips on cutting tools and saw blades.
The tips consist of a diamond layer that is approximately 0.5mm in thickness supported by the carbide so that total thickness is generally 1.6mm. This tip is then brazed to the tool body for finishing.
The major causes of concern for the diamond material are chipping, leaching and overheating, all of which can lead to premature failure of individual tips, and ultimately the entire tool. Leaching results when the cobalt material is exposed to acidic chemicals used in cleaning or processing of the tool as well as during the final machining operations. Ultimately, the leached surface provides less support for the diamond materials, which results in premature failure due to chipping.
The diamond edge is especially prone to chipping. It is so brittle that care is taken to not use micrometers when checking dimensions of the tool during processing to avoid chipping the cutting edge. Chipped surfaces quickly deteriorate, causing problems with finish and tool life.
Overheating is another major cause of tool failure. Typically, overheating takes place during the brazing operation, when re-tipping a tool that is being serviced. The PCD material begins back-converting to its natural carbon state with temperatures of approximately 700C. If exposed to high heat for longer periods of time at slightly lower temperatures, we can also see this degradation occur. Cracking of the material also can result from overheating as stresses relieve in both the carbide and diamond layers at different rates.
By educating everyone on the proper care and handling of these materials, it is easy to realize 20 to 100 times the life of carbide tools (depending on application). Clean with mineral spirits instead of highly acidic detergents to decrease the opportunity for cobalt leaching. Handle the tools carefully, making sure to avoid contact with items before and after operation. And utilize induction brazing instead of torch brazing or utilize pyrometers to avoid overheating. Diamond is the hardest substance known to man, but still requires proper care to maximize its benefits.
Source: Scott A. Ries is the PCD Division manager, Vollmer of America Corp.
For information visit Vollmer-US.com or call (412) 278-0655.