Copper (C1220T) vs. Oxygen-free Copper (C10200T)
Our copper electrodes and oxygen-free copper (OFHC/OFCu) electrodes differ in one respect: purity. Whereas our copper electrodes are made at 99% purity, oxygen-free electrodes are made to a purity approaching 99.97% copper. Impurities can have an adverse effect on the expected properties of copper, leading to lower conductivity, lower impact strength, and poorer ductility, among other things. The great purity of oxygen-free copper means that it very closely approximates the properties of elemental copper. Of these properties, it is copper’s great electrical conductivity that has the greatest relevance to EDM precision hole drilling.
Electrical Conductivity’s Importance to EDM
Electrical discharge is by its very nature dependent on electrical conductivity. The more resistance a material has, the more energy is required to conduct electricity through that material. This extra energy is dissipated as heat. So an electrode with greater resistance is not only less energy efficient—it can also suffer from the effects of being heated. Heat causes thermal expansion and can warp an electrode due to weakening of the material. These can both lead to defects in the workpiece and shorten the lifespan of the electrode. An oxygen-free electrode minimizes these problems due to its higher conductivity. Operators don’t have to change out electrodes as often, reducing cycle time. In addition to its greater longevity, oxygen-free copper also has a faster burn-rate, reducing the time to machine a part. Oxygen-free copper’s durability and speed act in concert to greatly increase working efficiency.
Is Oxygen-free Copper for Everyone?
The short answer is no. The primary benefit of oxygen-free copper is efficiency, so those benefiting most are going to be high-yield machine shops with very predictable production schedules. For these kinds of manufacturing facilities, the time and cost saving benefits of oxygen-free copper’s greater life span and consistency over thousands of manufactured parts become readily apparent. For those making prototypes or parts at smaller yields, it is not necessarily beneficial to use oxygen-free copper over regular copper.
In January, 2016, an aerospace company approached us about fulfilling a contract after hitting a production plateau with their copper electrodes. They were drilling holes into a rocket motor component, and needed to produce it more efficiently due to budgetary constraints. They were also reluctant to modify their production method, as the part was being produced exactly to contract specifications. Changing power settings on machines or altering the dimensional characteristics of electrodes to increase production speed would have resulted in a part in violation of contractual specifications. With all these factors in consideration, we suggested that they use oxygen-free copper electrodes. This way, they could use electrodes with the exact same dimensions as before, made of the same material. Switching to oxygen-free electrodes gave them the expected hole drilling characteristics, but with the extra efficiency they needed.