While graphite electrodes have been the mainstay of the moldmaking industry, a new trend is emerging in the form of copper/tungsten electrodes. Not only do they have double the life of graphite electrodes, but they also provide a better finish, according to Brad Fox, president of St. Paul, MN-based Rapid Tooling Technologies, LLC - a company that focuses on rapid tooling solutions by offering production grade inserts, tungsten/copper electrodes and production tooling design assistance. And outsourcing them will keep the headache, hassle and dirt out of the shop.
The process that makes these electrodes faster was invented by the 3M Co. (St. Paul, MN) - a diversified technology company - notes Fox. "At the time, they called it Tartan Tooling," he says. "It started commercialization by 3M in the early 1980s and was primarily directed toward the production of electrodes. In the early '80s, CNC programming and CNC in general was not nearly as sophisticated as it is today - which is why the Tartan process took off. In the later '80s they also started making steel inserts."
Fox explains that the basic process involves making a master pattern of the electrode - oversized by 0.1 percent (isotropic) to account for the tungsten shrink. Then, a "transfer mold" is poured over it. The pattern is removed, leaving its impression in the transfer mold. Then, a special blend of tungsten is mixed together with a binder. This mixture is put into the transfer mold, taking the exact shape of the electrode geometry. After it hardens, the "green" electrode is demolded and put into a hydrogen reduction furnace to burn off the binder and sinter the tungsten particles together. After sintering, a last step of infiltration fills the area evacuated by the binder with a pure copper.
The advantages of using these electrodes rather than producing electrodes in-house are numerous, says Fox. "The benefits will apply primarily to work that has a good amount of complex detail," he notes. "Anything that will involve time-consuming programming and tricky CNC machining would be a good candidate for this technology. Also, deep burns will be good because of their long life." Another viewpoint is to look at your shop's manpower and equipment utilization. "Tooling shops see outsourcing electrodes as an extension of their company; utilizing electrode providers for the difficult geometry while their in-house capabilities complete the rest of the work," Fox elaborates. "This way, the entire job comes together at the same time - resulting in an overall reduction in time and cost."
- Speed/cost: for complex geometry, this process is faster and cheaper.
- When you need multiple electrodes, this "batch-driven" process can produce many electrodes at the same time.
- Good surface finish (close to what you would get with copper electrodes).
- Long life (copper/tungsten electrodes will last about two to three times longer than graphite).
- Robust electrodes that cannot be damaged easily - with graphite (and even copper to a degree) you can nick or chip them easily.
- Replication of "artistic" hand-carved objects (impossible to program) into electrodes.
Peter Cridge, president of Cridge Custom Porcelain (Fallsington, PA) - a decorative ceramic manufacturer - has been using the electrodes for the past 10 years. "We use the electrodes to add surface detail to the wire cut punch blanks used in ceramic powder compaction," he notes. "The advantage is that the material holds its edge throughout the burn and can be reused several times to reburn detail as it is worn away from the steel in the compaction process. Using graphite usually requires more than one electrode unless you burn very slowly. This increases the cost of the tool.
"Another major advantage is that hand-sculpted art from a model maker can be exactly duplicated using copper/tungsten electrodes," Cridge continues. "This is almost impossible and very expensive using electrodes made by other methods." He adds that by casting the electrode, he does lose the ability to easily scale or change part of the image - which is possible if the electrode was digitized and machine cut.
In conclusion, Fox notes that sintered electrodes are simply another "tool" that moldmakers can utilize to help them produce molds faster and cheaper. "By streamlining the work - utilizing both in-house and outsourcing capabilities - a company can approach the project strategically and therefore meet cost and leadtime objectives.