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“Always
Searching for a Better Way”
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It starts on the computer screen at OAR Moldworks, where the designer gives the item a form that can be manipulated, studied, altered, and finally sent to the Graphite Machining Center - where it is brought to life in the form of an EDM electrode. OAR's Graphite Machining Center has taken over the bulk of the Electrode making, and has proven that it can out-produce traditional methods - with time to spare. It easily supplies their CNC EDMs with a steady stream of electrodes, to keep them running around the clock. All this, without any graphite dust escaping its efficient collection system. The electrode contains, virtually, the entire shape. This means it's all accomplished in a single set-up. This mold was EDMed with a rougher and a finisher, both made from Poco 200 on the Graphite Machining center. After a thorough inspection of the electrode, it became a set-it-and-forget-it job. After EDMing, a minor amount of polishing was done on the cavity. The holes you see in the electrode were not for flushing. They were to allow the dielectric oil to escape as the electrode descended, and also to prevent gas build-up.
When we step back and take a good look at what today's EDM Machines are accomplishing, the EDM industry, and everyone related to it, has a right to feel very proud. This includes all the machine builders, the designers, R & D Departments, and countless others whose job involves improving the EDM process. However, there is another group within the EDM industry that should receive their fair share of credit for bringing EDM to the level it has reached today - and they are the countless number of EDM users throughout the world.
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It as the users, with a pioneer spirit, that had enough faith in the early EDM machines, to first invest in them, and with very little technical information, make them productive! They did this through continuous on-the-job experimentation, while attempting to run a successful business. The experimented with all the facets of the EDM process - electrode materials, dielectric fluids, tooling & accessories, flushing techniques, power supply settings, and even mysterious "black boxes" that were supposed to perform EDM miracles. Many users became true EDM experts, educating the EDM manufacturers on what their machines were capable of, and suggesting improvements. And when the next generation of EDM Machines came out, they were quick to acquire one, and continue their experimentation. You might say they had become addicted to the EDM process, and were a major force in the continual improvement and growth of the EDM industry. Ozzie Rosenholm, whose whole working career has been producing three-dimensional shapes, is still hard at work sharing his experience. OAR's second generation - Mark Rosenholm enjoys the "hand-on" work, and chose to follow the Moldmaking end of the business - while his Brother Andy, chose the administrative path. Ozzie is a lucky man indeed. Ray Enos, OAR's EDM specialist, is shown at one of the three CNC EDMs, and explains how he gets great finishes, along with low electrode wear, from electrode material that was designed for roughing cuts. Ray has been using EDM, as far back as the early Tube-type machines, and there's no doubt about it, in the EDM industry, experience is the best teacher. |
OAR Moldworks - One of the Pioneers
We recently visited OAR Moldworks of Providence, RI, a moldmaking Company that has been using EDM Machines since the early '70s, and we spoke with Ozzie Rosenholm, their President. He explained that his entire working career involved producing three-dimensional shapes, and it started when he attended the Rhode Island School of Design in the early '50s. It was there that he learned the art of hob cutting, which involved hand sculpting three-dimensional shapes into tool steel hobs. The hob would then be hardened and polished, and used in a special hobbing press to force the shape into steel mold cavities. The steel used for the mold cavities was a special variety that could be easily hobbed, and then case hardened. This was how most of the plastic injection molds were produced during that era.
A Better Way
Ozzie recalls working as a hob-cutter, and having as many as 80 hobs backed up on his workbench, with many of them requiring intricate detail work. Each hob required certain traditional steps, such as rough milling, chiseling, engraving, riffling, heat treating, and final polishing - before they could be used for hobbing the mold cavities. Ozzie admits that he took certain liberties with hob-cutting tradition, and often used small grinding wheels to help speed up the process. Thereby, completing the batch of 80 hobs in just three weeks. It was this desire to always find a better way to accomplish a job, that would eventually become the driving force behind Ozzie forming his own company, and the manner in which it would be run.
Ozzie explained that a new method of cutting hops was becoming popular, and that was by using a pantograph. His employer showed no interest in this new technology,so Ozzie decided it was time to go into business for himself. He ordered two pantographs form Germany, and in June of 1966, he started OAR Tool & Die, and learned how to produce hobs using this mixture of art and metal cutting technology. His business prospered with no major changes in moldmaking technology.
Molding Machines Get Bigger and More Powerful
As the molding machines got bigger and pressures increased, case hardened mold cavities didn't always stand up under the higher pressures, especially if a part failed to eject properly and got caught. It could sink into the case hardened steel cavity because of its softer interior, thus requiring a time consuming repair job. Since injection molding relies on automatic operation, often without an operator, the mold should be able to withstand an occasional misfeed without damage. The only way possible with the higher pressures, was to construct the mold components from tool-steel.
This increased the difficulties in building molds, since it was not possible to hob tool-steels effectively. Several processes were devised to combine hobbing and machining, however, they were rather complicated and expensive to employ. Splitting the mold into several sections to facilitate machining was an option, however, it complicated the design, and increased the possibility of errors. A better way to build tool-steel mold cavities was needed, and the timing was perfect for a new metalworking process - EDM.
The Wire EDMs at OAR are kept busy on many different jobs. One of them, is producing electrodes that would be very difficult to grind. Narrow, thin, blade-style electrodes are always a candidate for Wire cutting in Copper at OAR. Especially when the cavities are made of Beryllium Copper, a popular material for mold cavities, because it rapidly transfers heat. This picture shows a perfect example.
EDM - The Better Way
OAR had already investigated EDM, and since they had pantographs to produce the electrodes, they decided to acquire and EDM Machine - and shortly thereafter, a second one. As with any technology OAR uses, they work hard to get the most out of it, and are quick to take advantage of new developments. For instance, when orbiters first came on the EDM scene, they acquired a new EDM Machine equipped with one, and quickly learned the orbiting techniques. This resulted in highly accurate mold cavities with improved finishes, produced faster.
A tooling system was then adapted to each of their EDMs and electrode making machines, to insure accuracy, along with speed and convenience when changing electrodes. With the increased EDM productivity from all the improvements, more electrodes were necessary, and computer designing and CNC machining for producing them made a big difference. Even though OAR had increased the throughput of their EDM operation, they were searching for a method of taking advantage of the nighttime and weekend hours.
CNC EDM - OAR's Next Step
CNC EDM was the next step for them, and their machine, fully equipped with an automatic electrode changer, was an instant success. Over time, manual EDM equipment was sold off to provide room and capital for several more machines, and productivity increased with each new CNC Machine. However, there was a limit.
When their EDM line-up consisted of four CNC machines, each one equipped with the latest automatic controls and electrode changers, it was difficult to keep all four running constantly. They always had ample work, however, due to the quantity of electrodes necessary, at least one EDM out of the four always seemed to be idle while waiting for electrodes.
At the time, OAR had six men constantly machining electrodes by various methods - grinding, milling, CNC machining, and upon occasion, pantograph. With so much graphite being machined all over the shop, it was very difficult to control the dust generated, in spite of the high capacity vacuum system they had installed. It seemed that a percentage of the dust always escaped capture by the vacuum system.
A Better Way To Produce Electrodes
The problem of producing an adequate supply of electrodes to the latest generation of high-efficiency CNC EDMs, has recently caught the attention of several machine tool builders, and new offerings are currently available. OAR was attempting to accomplish several goals by purchasing a Graphite Machining Center.
First and foremost, was the high-speed machining of accurate, three dimensional graphite electrodes - many of them being highly detailed. Second, was to reduce the cutter wear caused by machining graphite, and to completely control the dust problem. They envisioned a set-it-and-forget-it - load & unload operation, that could run untended. They also wanted to position the machine close to the EDM's, without any danger of extraneous graphite dust infiltrating the electronics.
OAR decided on an Electrode Making machine, and they also decided to sell one of their CNC EDMs to help pay for it. Their thinking was, that three CNC EDMs being supplied with a steady stream of electrodes and operating around the clock, could easily do the job of four EDMs that were idle some of the time.
The Graphite Machining Center was the Better Way
Today, OAR easily supplies their 3 EDMs with enough electrodes to keep them running around the clock, and has solved their graphite dust problem. Most of the skilled people that formerly produced electrodes, are now utilized on other jobs. And the surprising thing is, that since the electrodes are completes so fast, the Graphite Machining Center is idle a good portion of time. They view this as a good sign for future expansion.
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The new method of making electrodes has changed their thinking in several additional ways. In the past, they would always make a few extra electrodes and store them away, "just in case". Today, they make only the quantity they need, and if they ever require more, it's easy enough to call up the program, load electrode blanks, and just push the start program and walk away. The graphite blanks are mounted to the tooling by the apprentices, and all the machining is accomplished by the Graphite Machining center. It can even machine internal sharp corners. Another change at OAR is the ability to machine larger, more complex electrodes, with the entire shape on them if possible. After machining, they are inspected and used to EDM the entire mold cavity, eliminating the chance of any possible errors when segmenting a complex shape. According to Ozzie, with every new job, they try to do as much on the Electrode Maker as possible, and they are still learning. One area they plan to use the machine for is cutting mold cores, that in many cases, are traditionally machined and hand finished. By EDMing them, the thickness of the plastic part will be more uniform, and much of the hand finishing can be eliminated. If this is economically successful, it can be significant in how molds will be built in the future. |
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The Wire EDM - Electrode Making and More
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OAR was quick to recognize the value of the Wire EDM for machining inserts and insert pockets for molds. Once they has Wire cutting capability, they started to use it for many other things, and one of them was for electrodes. Ray Enos, OAR's EDM Specialist, explained the problems of EDMing deep, narrow slots into mold cavities for reinforcing ribs. Grinding the thin tapered Graphite electrodes was always difficult, and they didn't stand up well when EDMing Beryllium Copper. He was also aware that copper electrodes would have less wear in that situation, however, they were almost impossible to grind effectively. Fortunately, when the Wire EDM came on the scene, any shape they required could be easily cut into copper. Today, it's routine for electrodes to be produced on the Wire EDMs. Another problem solved by the Wire EDM is drilling knock-out holes through Beryllium Copper cavities. Due to the variation in the consistency of the material, drilling a hole precisely to size could be a problem. If the material is hard, the hole can be undersize, and too soft a part can cause an oversize hole. How OAR solves this problem, is to drill a small start-hole on location, and then Wire EDM the finished hole to size. In that way they never have a problem. |
Laminating Electrodes
Ray Enos, OAR's EDM Specialist, explained that today, they only use two different grade of Graphite, Poco 200 for general EDM work, and Poco 3 for fine finishing. He mentioned that even though the 200 is intended for roughing and semi-finishing, he has managed to attain some very nice finished using it. By carefully calculating and programming the orbiting steps along with gradual power reductions, especially when getting close to the final size, finished can be attained, that are much better than you might expect. It takes a bit of experience to know just how much material to leave for clean up between finishes, but it's worth the effort to get the most from electrode material, that was only intended for roughing and semi-finishing.
Ray also told us he save on electrode cost by laminating a layer of Poco 3 onto the main body of an electrode made from Poco 200. He explained that in many cases, the face of the electrode contains most of the detail, but also has to do most of the work - while the main body contains relatively smoother shapes. By laminating a layer of finishing grade graphite to maintain the detail, they get much more out of the electrode, white reducing graphite costs. Of course this is only practical on larger electrodes, where the cost savings are substantial, because of the extra work involved.
Surface Finish Specialists
OAR Moldworks is the company that produces the EDM Today Surface Finish System. Ray Enos is in charge of the production, and told us an interesting story. It seems that a customer wanted a textured finish on their molded parts, and Ray showed them the molded sample patches on the cover of the case to select one. The one they selected called for a 73 Rmax finish in the mold. Ray produced the mold to that finish, and when the customer saw it, he said it was way too rough a finish. However, when Ray molded the parts, they were precisely what the customer wanted. This proves that most of the time, the mold is EDMed to a finer finish than necessary, which translates into a more expensive job. It's nice to have a system that tells the whole story - the molded finish, and exactly how to arrive at it.
The Future for OAR Moldworks
If the past is any indication, the future looks very bright for OAR Moldworks. The company is already second generation, since two of Ozzie's Sons have joined him. Mark works in the hands-on Moldmaking part of the company, while Andy is in the Administrative area. Ozzie is still full of ideas and going strong, and that seems to be contagious since we sensed that same attitude through out the entire shop. OAR's future is tightly linked to the Molding industry, which is one of the healthiest in the nation. With every visit, we see and hear exciting things about the use of new equipment and technology in the world of moldmaking, and our most recent visit was no exception, Space constraints prevent us from writing about all that's new, but you can be sure we will visit OAR Moldworks again.