Abrasive Waterjet offers manufacturers a cost-effective, productive alternative to high-def plasma and wire EDM. PHOTO courtesy OMAX.
By Kip Hanson
It was dirty, sediment-filled rushing water that carved the Grand Canyon from what was once an ancient seafloor in the southwestern United States. Closer to home, there’s Niagara Falls, Fraser Canyon, and the majestic Gros Morne National Park, all of which formed over millions of years thanks to the unstoppable force called erosion.
Of course, you’re not making geological wonders. You’re making parts, and only have two weeks to deliver plasma-cut blanks from that chunk of plate steel sitting out back, or to wire EDM that big extrusion die. Why should you care about erosion and dirty water?
The answer is simple. Abrasive Waterjet (AWJ) offers manufacturers a cost-effective, productive alternative to high-def plasma and wire EDM. It’s faster than the latter, though not as accurate. And although it can’t compete with plasma in the speed race, it’s the hands-down winner in precision. It also leaves no heat-affected zone (HAZ) like plasma and can cut cleanly through almost any material, even glass. For some applications, AWJ rocks.
Like Mother Nature, AWJ relies on erosion to do its work. The typical machine comes equipped with a pump (or sometimes multiple pumps) boasting pressures of 50,000 PSI or more. These pumps force tiny bits of garnet through an equally tiny nozzle that concentrates their energy, allowing them to rip away small bits of metal, glass, and composite as they pass.
That garnet is the magic behind AWJ and its erosive capabilities and is what gives AWJ its “abrasive” moniker. Water is only the fast-moving vehicle—the jet—that carries these compact cutting tools, much like the glue that holds bits of silicon carbide or aluminum oxide to sandpaper.
The latter of these abrasives can also be used in AWJ, although it may present certain health risks like pulmonary aluminosis, and lead to increased wear on machine components. Garnet, which is either mined from various deposits or collected and sieved from river and beach sand, offers several advantages. These include its ability to fracture—or friability—to create sharp cutting edges, making it very effective in a wide range of materials.
Cutting materials aside, shop owners often overlook AWJ in favor of the more traditional processes mentioned earlier. And that’s a shame. AWJ is a low-maintenance, easy-to-use machining technology that cuts everything from hardened steel to aluminum, glass, rubber, plastic, foam, ceramic, and composite materials. Like I said earlier, it cuts through pretty much anything.
I also noted that it can cut through even very thick metals—up to 10 inches is not unusual. And some AWJ machine builders offer five-axis heads, making them suitable for tapered parts like stamping punches and many aerospace components. Shops use AWJ for unattended production of machinable blanks, delicate composite parts, gears and sprockets, and much more, all without concerns over tool wear or undesirable heat effects.
Bring your earplugs, though. Propelling tiny bits of garnet to supersonic speeds is a noisy process. Most experts will also recommend you don’t cheap out on the garnet—alluvial (from rivers and beaches) is roughly half the price of mined materials but is less sharp, so cuts more slowly. And if you find yourself loving AWJ and using loads of garnet, you might consider investing in a recycling unit. Either way, happy eroding! SMT
TECHNICAL EDITOR KIP HANSON has more than 40 years experience in the manufacturing industry. He is the author of Machining for Dummies and Fabricating for Dummies and has written over 1500 articles on a diverse range of metal manufacturing topics.