EDM machining and EDG electro-erosion processes for PCD cutting tool manufacturing

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Cutting tools made from polycrystalline diamond (PCD) are increasingly adopted in aerospace manufacturing because of their ability to machine composite materials and metals. Electrical discharge machining (EDM) and electrical discharge grinding (EDG) are two processes offered by some CNC grinding machine builders for producing ultra-hard cutting tools.

Here are some key distinctions between laser machining and electrical discharge methods (EDM and EDG) as they pertain to PCD cutting tools.

EDM and EDG rely on electrical conductivity to erode material. PCD is composed of diamond grains sintered with a metallic binder – typically cobalt – providing the necessary conductivity. During machining, each spark generates a plasma channel rapidly heating the workpiece surface to temperatures exceeding 2,800°C. Under this intense heat, the cobalt binder melts, expands, and transfers localized thermal stress into the surrounding diamond crystals.

As a result, EDM and EDG can produce micro-cracks and heat-affected zones on PCD surfaces, whereas laser machining minimizes thermal damage and delivers a cleaner finish. Lasers also enable the formation of sharper edges free from micro-cracking. Unlike electrical discharge methods, laser machining is a thermal-photonic process that doesn’t rely on electrical conductivity.

EDM operates with two electrodes – a tool electrode and the PCD workpiece – submerged in a dielectric fluid. When voltage is applied, a spark discharges across the gap, generating intense heat melting and vaporizing a minute portion of the workpiece material. Among the different EDM methods, the cutting tool industry uses wire erosion. In this process, a continuously fed wire electrode, unwound from a reel to counter its rapid wear when machining PCD, performs the cutting. Wire EDM is particularly well-suited for machining tipped or inserted PCD cutting tools, such as woodworking tools and PCD-tipped saw blades.

EDG, also referred to as disc erosion, is a non-traditional machining process removing material from electrically conductive workpieces – such as PCD – using electrical sparks generated by a rotating conductive wheel. Like EDM, the process relies on the thermal energy of sparks, but the machine configuration resembles a conventional grinding machine. Here, the electrode takes the form of a rotating metal wheel, and instead of coolant oil, dielectric fluid is used to sustain spark formation. EDG wheels are typically non-abrasive and fabricated from conductive materials such as copper, brass, graphite, or composites thereof.

Some manufacturers offer hybrid machines integrating EDG and conventional grinding with diamond wheels. These versatile platforms are equipped with dual spindles – one dedicated to erosion and the other to grinding – providing greater flexibility for machining PCD tools. The dielectric fluids used in hybrid machines are specially formulated to support erosion (EDG) and conventional grinding, ensuring consistent performance across both functions. In addition to cooling the workpiece and the EDG wheel, the dielectric fluid serves as an insulating medium enabling controlled electrical discharges.

MyGrinding Inc.
https://www.mygrinding.com