It would be easy to overlook the "hole popper" at Blanda, Inc., in Eagan, Minnesota, a suburb of Minneapolis. A visitor to this wire EDM shop might not even realize when he's entered the shop area, which is right off the main entrance. The shop looks more like a modern business office with that trendy "open look."
Sleek, fabric-covered partitions set off a computer area in the middle of this spacious, well-lit shop. Large potted plants stand decoratively in corners or hide building columns. Everything is clean and tidy--indeed, most business offices have more clutter and clatter than this place.
Yet it is very much a working shop. Lined up around the central computer area are various makes and models of electrical discharge machines and related equipment--eight wire EDM units, a CNC (computer numerical control) ram EDM (die sinker), and a small-hole EDM. In the background are additional machine tools, including a four-axis CNC horizontal machining center, a large vertical machining center and various pieces of conventional production equipment.
In this remarkable setting, Blanda Inc.'s "hole popper"--a small-hole EDM machine from Current EDM (Mountain View, California)--is rather inconspicuous. It is not a very large machine. Nevertheless, it is a very important piece of equipment that frequently plays a critical role in what this shop does best, that is, using wire EDM for some remarkably inventive, creative and strategic process plans.
Bob Blanda, owner and founder of this shop (which bears his name), is especially good at planning mold work to maximize the flexibility and accuracy of the wire EDM process. Small-hole EDM makes many of these strategies possible or more efficient. Making start holes in exactly the right places is one of the keys that allows Mr. Blanda to unlock the creative potential of wire EDM.
One Of The First
Bob Blanda started his shop approximately 17 years ago in nearby Bloomington, but three years ago he moved into a brand new 15,000-square-foot building at its present location. In the early days, Mr. Blanda's shop was one of the first shops in the area with wire EDM.
Trained as a tool and die maker, Mr. Blanda spent several years working for a metal stamping firm. Then he started his shop to build stamping dies on his own, with the idea that wire EDM would provide many opportunities for improving the design and construction of those dies. Over the years, the shop moved into tools for injection molding, extrusion dies and special machine components.
Looking back, Mr. Blanda recalls how limited and slow the wirecut EDM process was in the first few years on his own. In those days, you were lucky to cut an inch and a half an hour in a one-inch thick piece of steel. Most cuts were straight up and down. Tapers were tricky at best. There were few options for making start holes, which are the openings through a workpiece that give the wire electrode a place to start if the cut can't be made from the side.
However, being a pioneer user of wire EDM had one great advantage. Bob Blanda worked with some of the most forward looking customers, the kind of customers who were searching for better ways to do things, or ways to do that which hadn't been done before. He learned a lot about mold and die design from them. They, in turn, expected him to be creative and resourceful.
As the EDM process, both wire and ram, changed over the years and became more versatile, more accurate and much faster, Mr. Blanda's shop changed and grew with it. When EDM units especially designed to quickly make small holes appeared on the market, it is not surprising that Blanda Inc. was one of the first shops to acquire one. That was approximately six years ago.
The company is now on its second EDM "hole popper," a model EdmDrill CT300. Besides making start holes for wire EDM, it is also quite useful for production work and prototyping.
Blanda Inc.'s small-hole EDM unit is representative of this class of machine tools. In some ways, these machines look like hybrids between wire and ram EDM. The electrode feeds into the workpiece on a programmable Z axis much like a ram or die sinker EDM. However, the electrode is not a block of copper or graphite but a rod-like tube. This tube may range in diameter from 0.004 to 0.250 inch. De-ionized and filtered water serves as the dielectric fluid and is pumped through the hollow center of the tube at very high pressure to provide flushing. The tube is rotated for concentricity and even wear as it sinks into the workpiece.
As in all EDM, the tube electrode is energized, causing electrical sparks to jump from the electrode to the workpiece. Each spark creates an intensely hot but extremely localized spot on the workpiece that literally boils off a microscopic bit of material. Sparking occurs continuously between the electrode and the workpiece thousands and thousands of times per second. The net result is a rapid erosion of the workpiece material in a shape slightly larger than that of the electrode, the difference representing the "spark gap" that must exist between the electrode and surface.
The chief benefits of small-hole EDM are speed, accuracy, the ability to drill very hard materials, the ability to leave virtually no burr, and a very high depth-to-diameter ratio. Moreover, because the electrode does not contact the workpiece, holes can be started on rounded, contoured, tapered, or uneven workpiece surfaces that would probably cause a conventional drill to wander. In short, if you want to make very deep, very small holes in hardened material like die steel or high carbon alloys quickly and accurately, small-hole EDM is an option for almost any shop.
Small-hole EDM, however, is indispensable at Blanda Inc. According to Mr. Blanda, this unit is in almost constant use. The majority of electrodes used on this machine range from 0.020 to 0.060 inch in diameter. Approximately five percent of the time, smaller electrodes down to 0.004 inch are used; a similar percentage of the time, larger electrodes up to 0.250 inch are used. Most work involves through-holes in workpieces from one to two inches thick. Typical workpiece materials are A2, D2, S7 and all grades of stainless.
The electrodes used in small-hole EDMs, regardless of make or model, are rather remarkable. All are precision-made brass or copper tubes that come in lengths up to 16 inches. Smaller electrodes (under 0.040 inch) feature a single cavity down the hollow center, but larger sizes (0.040 to 0.250 inch) are available in a "coreless" style. These electrodes feature an internal webbing that divides the hollow center. As the electrode rotates during operation, this webbing erodes material that would otherwise be left behind as a solid core rising from the bottom of a blind hole.
Hole-making speed is difficult to state because it varies depending on the material and electrode size, so Mr. Blanda falls back on the figures given by the Current EDM spec sheet for this model: 0.040-inch hole through 1-inch thick tool steel in under 35 seconds.
Small-hole EDM is accurate. According to Mr. Blanda, hole size can be maintained routinely to ±0.001 inch. Accuracy on location is even more important to him, however. Examples of where locational accuracy really counts are start holes for very thin slots, ejector pins or interconnecting cooling lines in core blocks.
The EdmDrill CT300 positions the electrode in the X and Y axes under programmed command of the CNC unit. Hole depth is programmable. When making multiple holes, it can be programmed to compensate for electrode wear by automatically zeroing off the surface of the workpiece. Other automatic routines further facilitate operation.
One type of mold design, which Mr. Blanda is especially proud of, uses no ejector pins to remove the finished part after cooling. Such molds use wire EDM to cut the parting lines and holes for core blocks so that the entire B side moves to strip the finished part. Some slide blocks are H-shaped pieces, spring loaded so that when the mold opens, the sliding action clears the molded part so that it can be ejected.
Eliminating ejector pins makes the mold simpler to maintain, with fewer parts to wear and create unacceptable flashing in the molded part. The sliding B-plate, in contrast, can be cleaned and lubricated in one piece. Without ejector pins, this design allows faster cycle times. The mold heats faster and cools faster.
The extensive use of wire EDM in this type of mold design is highly practical because much of it can be set up for untended operation. In most cases, all start holes for the various wire cuts will be drilled on the small-hole EDM at one time. At the wire EDM, automatic rethreading allows features to be wirecut one after the other. After completing one programmed wire path, the wire is severed, the machine moves to the position of the next start hole, rethreads the wire and resumes cutting.
Any Way You Slice It
It is Mr. Blanda's policy to use EDM wherever and whenever possible. It is not unusual for his shop to use wire, ram and small-hole EDM, all on the same mold. The goal is to use the various EDM processes to complement one another and produce a mold with fewer components and to speed overall mold production time. For example, he looks for ways to cut an electrode for ram EDM with wire EDM rather than by milling, turning or grinding. Likewise, he looks for ways to use wire EDM to produce mold cavities rather than use a ram EDM or a machining center.
One technique that is particularly handy for forming electrodes, Mr. Blanda has found, is to "slice" a block of copper or graphite on several planes with wire EDM. First, the block electrode material is attached to a standard 20-mm round holder. Then, strategically located start holes, which are all produced on the small-hole machine at one time in several successive setups, are drilled. (These start holes are key to the simplicity and effectiveness of this technique.)
Next, on the wire EDM, the electrode may be rotated 180 degrees or turned on its side several times to complete all the wirecut "slices" to yield the required shape. Mounted in an indexing head, the block can be positioned at any angle for a variety of cuts to get a wide range of complex and intricate shapes.
This technique can be used to create double-sided electrodes that have identical front and back "faces" for roughing and finishing with a single electrode on a CNC ram EDM. The electrode sinks the cavity by cutting sideways on a mold block mounted horizontally. First the roughing cut is finished, then the electrode is turned completely around for the finish settings.
Holes To Go
Small-hole EDM also plays a role in prototyping and production jobs at Blanda Inc.
Wire EDMing a stack of sheet metal parts to simulate the output of a stamping press is one of the more useful applications to emerge in the last several years. These prototype "stamped" parts can be produced quickly and inexpensively because the only tooling required is a programmed wire path to cut the part profile. Stacking the sheet metal blanks makes the process very productive.
Pierced holes and other openings can be wirecut as well. Start holes for these features are produced on the small-hole machine. The stack of sheets is then transferred to a wire EDM, such as Blanda Inc.'s Mitsubishi DWC90SZ, where automatic rethreading allows for untended machining. When the wire EDM completes one feature, it cuts the wire, moves to the position of the next start hole, rethreads the wire and resumes cutting. Precise location of the start hole is essential.
For fast drilling of deep, accurate holes in small workpieces, EDM is also a winner. These high volume production jobs are hardly foreign to Blanda Inc. Spray nozzles for automatic dispensing equipment are a typical example.
The nozzles are supplied as screw-machined parts approximately five-eighths inch long in stainless. A 0.012-inch hole through the length of the part is drilled on the small-hole machine, one part at a time in a simple fixture wirecut (of course) to size. This operation takes approximately six minutes. Each part is then moved to a wire EDM to wirecut the diameter of the through-hole to 0.020 inch, with a tolerance of ±0.0001 inch on the diameter. This step takes approximately one minute per part.
Although the many and important uses that Blanda Inc. has for small-hole EDM say a lot about the value of this technology, the real issue is how this shop uses this resource in its synergistic approach to solving problems for customers. Bob Blanda is at his best when he can start with the customer's part drawings and can design the corresponding mold to take advantage of every productive resource at his disposal. That small-hole EDM helps him get more out of wire EDM and that wire EDM helps him get more out of ram EDM is just one example of using different processes strategically and creatively to build a better mold.
Building better molds, however, is the ultimate goal. Outstanding applications for small-hole EDM, or for any process for that matter, count only if they deliver outstanding results to customers. And doing that is what makes Blanda Inc. stand out. MMSblog comments powered by Disqus