The cutting edge geometry and final dimensions of the tool are usually ground on a CNC tool grinder. However, superhard tools with polycrystalline diamond (PCD) cutting edges pose a challenge to the ground. In fact, grinding PCD tools with the hardest diamond grinding wheel known takes a lot of time and many grinding wheels, making them cost-prohibitive.
One way to control costs is to remove PCD materials by EDM, either through EDG or wire-EDM, using a tungsten-copper disk electrode. The cobalt binder in PCD materials can act as an electrical conductor for EDM. The main benefit of EDM or wire-cutting processes for PCD tool blade shapes is the reduction in machining costs. Ries points out that “the removal of PCD material by contactless EDM processing does not require expensive diamond grinding wheels.”
Ries has been using the EDM process for PCD tools since the early 1980s. Thermal damage to diamond materials, up to a depth of 0.2mm, had been a problem with the process, he said.” We try to use other electrical components to change the charge-discharge performance, or to control the rate of charge-discharge.”
Ries points out that the poor controllability of the discharge pulse has been a problem in the past. In order to ensure the reliability of the cutting edge, it is necessary to remove the damaged PCD material layer due to the thermal damage of the PCD cutting edge, which can lead to tool breakage and failure during use.
The main advantage of EDM processing and fine grinding is that the life of the PCD tool can be extended. Ries said the need for fine milling after EDM processing often depends on economic considerations.”It depends on how much time you’re going to spend. It is important to consider how much longer the tool will last in processing if time is spent on fine grinding it.”
In 2000, Ries compared the service life of a precision milling and EDM-machined PCD tool for cutting high si alloys. The results show that the PCD tool life of EDM is 85% of that of the grinding PCD tool.”Based on the continuous improvement in EDM performance since then, I estimate that today’s tool life is 90 to 95 percent. How long does the fine grinding take? What is the cost of the grinding wheel? What are the increased labor cost and the time spent on the machine?”