While graphite materials can be used to machine carbide materials, it is not the best method. One of the reasons is the extremely high electrode wear rate. Burning with a fine-grain graphite, such as DS4 or POCO-3, will lead to 50-60% electrode wear when used to machine carbide. Changing to a copper-impregnated graphite such as DS4C POCO-C3 will improve the wear rate slightly, to about 40-50%.
Carbide is a sensitive material to EDM and can be damaged if too high a power setting is used. Carbide and its typical cobalt binder material are prone to micro-cracking when excessive machining power is applied. To preserve the material’s metallurgical integrity and provide good component life, power settings for carbide materials are less aggressive than those of steel materials.
When burning tungsten-carbide with graphite or copper-graphite electrodes, it is generally recommended to use the machine’s copper-tungsten or tungsten-carbide conditions. Depending on the shape and size of the electrode, some minor cutting condition parameters may need adjusted to achieve stable machining. Be sure to increase the off-time and jump settings to allow for more cleaning of debris from the spark gap. This is important because the high electrode wear generates much more debris than low electrode wear applications.
Using graphite-based electrode materials to machine tungsten-carbide often means utilizing lower-cost materials to lower manufacturing costs.
Copper-tungsten is the best to efficiently machine tungsten-carbide, but its cost is very high—1.5-2 times higher than a high-quality fine-grain graphite, and copper-tungsten materials are upwards of 5-8 times higher than fine-grain graphite materials.
Copper-tungsten is still the best electrode material of choice for finishing operations, as this will provide the best part accuracy and surface finish. Graphite-based electrode materials can be used for roughing or semi-finishing, and more electrodes will need to be machined compared to processing with all copper-tungsten electrodes. It’s logical to use graphite-based electrode materials for cost savings when machining carbide, but it might not be for everyone. Carefully evaluate the entire process to determine if the material cost savings, additional electrode manufacturing time, and additional machine setup time justify using graphite-based electrodes for roughing and semi-finish operations.