It's a paradox. Twin City EDM is both production house and prototype shop. In both capacities, its "core competency" is the wirecut electrical discharge machining process.
That leads to another seeming paradox. For this 40-man shop in Fridley, Minnesota (just outside of Minneapolis), wire EDM makes it possible to successfully mix high volume parts manufacturing with the one-piece, two-piece "impossible" jobs. The process lends itself well to both extremes. At the same time, successful wire EDM requires a mix of the two. Prototype work calls for top notch skills and keeps these skills finely honed. Production work calls for top notch equipment and keeps that equipment busy, generating steady revenue.
The shop has a mix of wire machines from Agie and GFAGIECHilles, including nine Agiecut wire EDMs (150, 170, 270 and 100 Series models), one Robofil 6020, one Robofil 4020, and two Robofil 310 models from GFAGIECHilles. (The shop also owns 25 ram EDMs--60 percent CNC from a variety of builders, as well as two Sodick micro-hole EDMs, making it the largest EDM house in the state and one of the largest in the country.)
Bob Lindell, founder and president of Twin City EDM, puts it this way: "Wire EDM is the solution"--no matter what the challenge, whether it is to produce a half a million locking caps in 6AL-4V titanium (holding two "tenths" tolerances over the entire lot) or the emergency repair of a broken punch and die set that has a customer's production line down.
Wire EDM is the solution. That could be the shop's motto, for sure. It could also be a succinct way to characterize state-of-the-art wire EDM as a manufacturing resource.
What Wire Can Do
Wire EDM is versatile. It can cut virtually any electrically conductive material, from ferrous materials to titanium, platinum, and other exotics to graphite to carbide to a new class of electrically conductive ceramics. Twin City has seen almost all of these materials and has learned how to wirecut all of them.
Wire EDM can cut a single, thick workpiece (Twin City's machines can handle parts up to 14 inches tall and weighing hundreds of pounds) or a stack of very thin, brittle workpieces or banks of workpieces arrayed on clamping fixtures. Twin City has produced gears and surgical instruments with teeth and other details microscopic in size, on one hand, and die blocks or massive extrusion dies on the other hand.
Wire EDM can be used to cut one part feature or detail on workpieces mass produced on screw machines, or it can cut a complete part out of a single blank by indexing and re-orienting the part several times. Twin City sees it both ways on a regular basis.
Hardness of the workpiece material is not a limitation to what a wire machine can cut. It is, however, always a factor when setting machine parameters (discovering and capturing that know-how is a top priority for Twin City whenever it encounters a difficult material). A big plus for wirecutting is the ability to process parts in their hardened or heat-treated condition, thus eliminating the need for additional grinding or machining to correct the distortions or dimensional changes that heat treating can bring on. In fact, using wire EDM to streamline and simplify a manufacturing process is one of Twin City's strengths.
The path followed by the wire electrode in a wirecut machine can be very simple or very complex. It can cut the same shape over and over again or, by moving the upper and lower wire guides independently, it can cut one pattern on the top of a workpiece and another on the bottom, with tapers and various radii in between.
With automatic wire rethreaders (all of Twin City's machines are so equipped), a wire machine can cut a shape, sever the wire, move to a new position, refeed the wire and begin cutting again--to repeat the same path or begin a different one. This potential for "untended" operation is an opportunity for machinists to conduct their own in-line, in-process quality control and prepare for the next job--standard procedures at Twin City.
If versatility is an outstanding characteristic of wire EDM, then versatility is likewise an outstanding characteristic of how Twin City uses the process.
"Our customers are looking for versatility," says Steve Lindell, executive vice president and general manager. "We can do their one-piece jobs and we can do their million-piece jobs. It's usually the one-piece or small-lot jobs that allow us to prove our capability and win their trust. That's one of the main reasons why we need to maintain our prototype and express service shop capability." Now that's versatility.
A Healthy Mix
But there are other reasons why this mix is valuable. In fact, Mr. Lindell is quite adamant about the importance of mixing prototype work with production work, even though most shops are one or the other.
The one-of-a-kind jobs tend to be the most technically challenging, he says. "That keeps our skills sharpon the shop floor, in engineering, in programming, in tooling, in scheduling--everything."
These jobs expose the shop to the widest range of workpiece materials, as well as the most complex geometries. "We've seen literally thousands of combinations and have learned how to wirecut them," says Ron Henderson, the wire EDM lead person.
Twin City's reputation for taking on the difficult jobs has opened doors and helped the company build a stable customer base that returns again and again. It has also helped the shop get involved with customers early in the design and engineering phase, when the advantages of wire EDM can be best planned for and exploited.
"We can work with designers, manufacturing engineers or production managers to find ways of solving problems or creating efficiencies," explains LeRoy Peltier, Twin City's chief engineer. "And it's not just for new products. Cost reduction or product enhancement programs can also benefit from using wire EDM to reduce production steps or eliminate secondary operations."
Getting involved with customers early can't be over-emphasized, Mr. Lindell believes. "That gives us the best chance to help customers increase profits, reduce time to market, or meet a unique requirement. When that happens, we're more successful because we can make our customers more successful."
Working on prototypes gives Twin City an opportunity to get a head start on strategies for high volume production if that is where the part is ultimately headed.
For the machine operators, prototype work means variety and a change of pace, as well as a chance to learn new techniques. It keeps things interesting.
All this said, Twin City's emphasis remains squarely on high volume production. About 85 percent of its revenue comes from production jobs, and the goal is to boost that to 90 percent next year. Because of the company's growth curve, prototyping is expected to increase by 25 percent next year also.
Versatility Requires Flexibility
Being able to mix production with prototypes not only reflects the versatility of wire EDM, but it also reflects the flexibility of the shop. This shop goes to remarkable lengths to cultivate its flexibility. It focuses on flexible people. Likewise, it focuses on a flexible shop infrastructure to back them up.
"Our workforce is flexible because individuals have a range of skills. Training and development are the keys," says Mr. Lindell. "The same guy who runs the machine knows how to set up the job, handle inspection, and get the parts shipped. Routine maintenance is also part of his or her responsibilities."
Training sessions are regular and frequent. The shop has a program underway to have all shop personnel certified at the master machinist level.
However, training isn't pursued simply to make employees more valuable to the company. Each employee's personal goals and career objectives are considered.
"We want them to be more valuable to themselves," says Lynn Keefer, a consultant working with Twin City. Mr. Keefer conducts or coordinates many of the shop's training and development activities. For example, the development process helps employees understand production management, capacity planning and finance (not only business accounting principles but also topics pertaining to personal money matters and household budgeting).
"Training works in the other direction, too," Mr. Lindell points out. "We want to learn from our employees. They're smart and have good ideas. That's the real payback to our investment in training and development, so we can't afford to miss out on their insights and know-how."
One way the shop captures this input is on the job sheet. There is a place for notes from the operator, where setup tips, improvement opportunities and the best machining parameters can be reported. These notes are fed into the continuous improvement process and then become a part of the permanent job file.
Organizing flexible people for "nimbleness" is the other key. Scheduling is the critical issue here.
Twin City has a full-time master scheduler, who works with the enterprise-wide scheduling and material resource planning system.
The scheduler directs the manufacturing flow for all departments and shifts (the shop operates 24 hours a day). Initially, a certain amount of "float" goes into a week's schedule. This allows the shop to take on emergency rush jobs which inevitably pop up, without creating serious bottlenecks. Even so, operators are automatically granted four hours of discretionary overtime, to accommodate these contingencies, ensure the workmanship, or finish a setup to maximize productivity in the next shift.
Also worth noting is that preventive maintenance is scheduled right along with work activity, ensuring that there will be time for taking care of the equipment. Every wire machine has a maintenance log outlining what maintenance item must be addressed daily, twice a week, weekly, every so many hours of operation, and so on, to six levels, with a space for the operator's signature to show at a glance that machine's maintenance record.
"This attention to maintenance has paid off handsomely," says John Curtis, director of sales. "Our very first EDM--37 years old--is still producing high quality parts that go directly to our customer's production line."
Scheduling is more than a systematic method for loading available machine hours. It has strategic as well as tactical value. The goal is get everything for a job to the machine operator at the right time, to maximize flexibility and productivity at the same time.
What's interesting is how Twin City defines "everything" in this context. It not only includes a proven CNC program, clamping and fixturing components, inspection routines, but also the operator's understanding of how to do the job properly. In other words, the "know-how" part of the formula is taken into account when planning and scheduling the job. Sometimes this means special instructions or training and sometimes it means having a setup reviewed or extra assistance provided.
Scheduling has its technical implications, too. Nearly all of this shop's wire machines are equipped for submerged cutting, that is, the entire work tank fills up with dielectric fluid to immerse the workpiece under the surface during cutting. Submerged cutting promotes better flushing and minimizes wire breakage, especially in applications with interrupted cuts and other difficult cutting situations. Submerged cutting simplifies setup because flushing fixtures are unnecessary or need not be elaborate. Because all of the machines have submerged cutting capability, the kinds of jobs that require it can be scheduled on any available machine.
Scheduling also impacts the three main "support teams" that serve the shopfloor personnel. These are engineering, programming and the toolroom.
"To do what we're doing with wire EDM, you have to be strong in all three of these areas," notes Mr. Lindell.
- Engineering Strength. Chief engineer Peltier knows wire EDM inside and out. With a background that includes experience as a wire EDM operator and former shop owner, Mr. Peltier understands how an energized wire (in some cases thinner than a human hair) will behave inside the cut and what is happening in the spark gap.
Strength in the production engineering area is vital because this is precisely where the design and manufacturing engineers in many customer companies are the weakest. They often do not understand what is feasible with wire EDM. Twin City's engineering capability fills that gap. Feasibility, however, is not merely a technical issue. It's a matter of knowing what you can do with smart fixturing design, smart programming, smart setup and smart operation. Twin City's engineers know how to fully exploit wire EDM as achieved in their own shop with its unique parts-cutting capabilities.
- Programming Strength. Scheduling a job has to take into consideration the amount of programming required and its complexity. It's not unusual for programming of complex prototype work to exceed the actual time that is required on the wire machine. At Twin City, three programmers and one machine operator who can act as backup, handle programming for the entire shop. Programming is done with Agie's Mechanic programming system or with the EDM module in MasterCAM. Programs are checked out carefully with simulation before being released to the shop floor. Also, an extensive and detailed "cover sheet" of notes and instructions is attached to the wire path data. This minimizes the chances for any misunderstandings in setup or process plans. "In many cases, we help our customers verify their design geometries through this process," says Bryan Nordstrom, lead programmer at Twin City.
- Toolroom Strength. The third key support group that bolsters the flexibility and productivity of the shop floor is the toolroom. Here, the critical issue is fixturing design for high volume production, because getting as many parts into the machine at one time and using cutting time as efficiently as possible determines production time and cost. Part loading and unloading and quick clamping also come into play. For example, getting parts in and out of the machine efficiently has to be balanced with precise location and proper, "foolproof" orientation. Fixturing strategies are often how Twin City manages to hit cost targets that customers propose as they explore product re-engineering and cost reduction campaigns. Fixture design is also a quality issue. Often, the challenge on a simple part is holding extremely tight tolerances--0.0002 inch is not uncommon. In these cases, a well designed fixture provides repeatable location and orientation but avoids cumulative errors in multiple arrays of parts.
Think Wire EDM
Not many shops have exploited the versatility of wire EDM as thoroughly as Twin City. The range of applications routinely performed in this shop is remarkable. If you want to see what wire EDM can do, Twin City EDM is one of the best places to visit.
The phrase "only limited by the imagination" comes to mind when looking at the many ways this shop uses wire EDM. In fact, helping its customers think imaginatively and productively with the wire EDM process in mind, may be what Twin City does best.