CUTTING: PLASMA/ WATERJET/ OXY FUEL

Abrasivejet Machining 
Is 75% Faster, Cheaper
Than Wire EDM

Today, state-of-the-art abrasivejet technology has grown into a full-scale production process with precise, consistent results; and job shops that use abrasivejet are seeing their profit margins grow as well.

After starting with wire EDM (electrical discharge machining) as his primary vocation, Steve Miller, president of Milco Wire EDM, Inc., and owner of Milco Waterjet, LLC, is one operator who has become an abrasivejet believer. "It really got started when I was asked to run a wire EDM room for two weeks while the regular foreman was on vacation," Miller recalls. "When that guy left to start his own company, I took over running the room full time." Later, Miller became a partner in a downtown Los Angeles wire EDM company; and in 1990, Miller started Milco Wire EDM.

"Business at Milco was always steady," says Miller. "But even with stack ups (stacking materials to cut multiple parts) there were times when it was too expensive to cut precision parts in the quantities the client required. And, we had to pass on cutting other parts because of materials being non-conductive. So when a local distributor told me that I could do all these jobs quickly and economically using an abrasivejet, naturally I was interested." Soon after, Miller installed an OMAX 2652 JetMachining Center, with full-scale production beginning in January 1996.

Miller immediately noticed a similarity between wire EDM and abrasivejet machines: both cut complex contours with a kerf. One uses a wire to penetrate, while the other uses water. "The water is three times as thick as the wire," says Miller, "but it fits right into jobs that don’t require the same tolerances as wire. What’s more, it typically does those jobs more economically." Abrasivejet machining usually is not so much a replacement for, but a natural addition to, wire EDM. "Just last week we used the OMAX to cut dropouts from ½" thick hot rolled steel, then used wire EDM to cut very precise dowel holes in the same parts," Miller says.

For many applications, abrasivejet machining costs only one quarter of wire EDM. "It also can be more forgiving," Miller points out. "Hot rolled steel is particularly difficult to cut on a wire EDM because of surface impurities that reduce cutting speeds and may cause the wire to break. In the past, we’d have to remove surface impurities with a disk sander; then make sure no tape or other non-conductive materials got between the stack up. The OMAX is able to ‘ignore’ many material aberrations that would cause wire EDM to lose flushing. That cuts down on prep time [and makes the job more profitable]."

The abrasivejet has enabled Milco to cur non-conductive and reflective materials as well. "One of the many things we do is cut quartz wafer carriers for the semiconductor industry," Miller explains. "The quartz is delivered to us in ¼" thick sheets of varying size, at a cost of about $8 per square inch. That kind of cost leaves no room for error. Quartz can be especially difficult to cut because of a tendency to fracture. The abrasivejet cuts various part configurations — many of them with holes — without any problems. It also helps us minimize material waste by allowing us to cut the maximum number of parts per sheet."

Milco often uses the OMAX as a CNC (computer numerical control) mill, speeding part preparation time by creating holes for wire insertion later. "A mill could certainly do the job, but only after spotting the hole, changing tools to drill a pilot, then changing tools again to drill out the hole. We’ve created backup plates using the abrasivejet to cut all the clearance holes for Allen cap screws, all the start holes for the wire and all the internal shapes that the slugs would fall through. We even used it to cut holes that were counter-bored or tapped afterwards. Then, after heat treating the plates, we used wire EDM to cut holes requiring a tighter tolerance."

Abrasivejet Cuts Steel Plate More Accurately

Abrasivejet machining is often more economical than wire EDM for creating prototypes. One good example is the quick-release binder Milco cut for a nationally-known snowboard manufacturer to replace conventional snowboard straps. "The abrasivejet made it really easy for us to do this job," recalls Miller. "We found out that it took the contracting company all day to create a stack of prototypes on a wire EDM that we cut in only two hours on the abrasivejet."

That kind of speed enables Milco to be very competitive, even against shops who own laser equipment. Not only does the abrasivejet cost only a fraction of a full-blown laser system; but the average hourly rate for their OMAX equipment is about half that of laser services. According to Miller, "I actually get a lot of abrasivejet work from laser companies: small quantity jobs they don’t want; reflective materials they can’t cut; materials that are too thick for them to handle; and general overflow.

Milco also capitalizes on the economy of their abrasivejet equipment by using it to create compound dies. "The average cost for making a shoebox-sized compound die (using traditional methods) is from $2,000 to $4,000. Even a ‘pancake’ tool and die house would charge $1,000 to $2,000. That makes it incredibly expensive to make limited runs of prototype parts, especially when the tooling probably will be modified or changed down the line. In many instances, the abrasivejet can create the same part, in less time, for about $5 to $20.

"Plasma, flame and laser cutting don’t achieve the accuracy on ½" plate that the abrasivejet can," he adds. "What’s more, they all leave behind a heavy crust that’s extremely hard to mill."

The OMAX controller automates most programming and tool set-up work, practically eliminating the need for special operator skills or prior experience. "I have to say that the OMAX controller is probably one of the simplest programming systems I’ve ever seen," says Miller. "Every machine has its own idiosyncrasies, but if you know anything about programming or writing up a tool path, operating the JetMachining Center is something you can pick up in about an hour. There are four people here who use it — two of them apprentices . . .. All were able to pick up the basics in short order."

Miller says that his company’s recent growth owes a lot to their OMAX equipment. "We don’t work in just one area; our clients now come from a variety of industries including food, medical, aerospace, tool and die, and injection molding. After all, the JetMachining Center can cut virtually any kind of geometry you can program, through almost any kind of material you can find."

Milco traded in their first OMAX eight months ago for the larger model 55100. "We started doing a lot of work with larger parts," Miller explains. "Some of the plates we used were so big we needed a fork truck to lift them into place. OMAX made it [the 2652] for tooling, small fixtures, prototypes, and things like that; we needed something bigger."

Milco also purchased an OMAX P2040 pump to upgrade their larger abrasivejet machine. "The new pump is about 75% quieter than our old one. The replacement parts for it are less expensive than the old pump. And, it has an additional 4,000 psi over the old pump offered," Miller says. "In July we’re moving to a facility that’s twice the size of our present location, and I’m already making provisions for a second abrasivejet."