This article highlights that one of the most accurate industrial cutting blades is a thousandth-of-an-inch supersonic jet of water carrying abrasive particles to a target surface. Waterjets cut simple or complex shapes from steel, glass, plastic, composites, paper, or fabric, without causing the thermal or mechanical distortions associated with mechanical saws. Recovering the abrasive is the mission of the WaterVeyor system developed by Flow International Corp. The WaterVeyor lets waterjet cutters recycle garnet abrasives, thereby reducing waste disposal costs and the cost of purchasing virgin abrasive. Although industrial waterjets are strong enough to shear steel plate, they are also delicate enough to carve decorative glass, where the appearance of the finished product is as important as throughput.
One of the most accurate industrial cutting blades is a thousandth-of-an-inch supersonic jet of water carrying abrasive particles to a target surface. Waterjets cut simple or complex shapes from steel, glass, plastic, composites, paper, or fabric, without causing the thermal or mechanical distortions associated with mechanical saws.
Specialty fabricators such as Nova Classique Glass Industries Inc. of Downsview, Ontario, are using waterjet systems to expand their product lines. What's more, manufacturers of waterjet cutting systems are continually seeking ways to refine them to add to their value. For example, Flow International Corp. of Kent, Wash., has designed an abrasive-recovery system to reduce waterjet operating costs, and a lower-cost unit to reach job shops for which waterjet cutting had been too expensive. ESAB Cutting Systems of Florence, S.C., has combined its waterjet and plasma arc cutting systems to increase productivity in part making.
Modern waterjet cutting was born during the late 1960s, when companies needed to cut the composite materials that were newly developed for aerospace applications, according to George Savanick, a consultant and president of the Waterjet Technology Association in St. Louis. The U.S. government invested research funding in waterjet cutting at that time. Conventional industrial saws created mechanical and thermal stresses that damaged the composites and could render them unusable, so another technology was required to trim the Space Age materials.
In response, engineers adapted high-pressure waterjets, originally used to wash away clay and rock in mining operations, to introduce the first commercial waterjets in 1971. These machines sent a highly focused, supersonic stream of water that cut composites smoothly by eroding them without generating h eat, thereby eliminating the thermal and mechanical distortion caused by saws.
In addition, because a waterjet can be aimed in any direction, it can accommodate angled cuts when needed, and serves as its own machining coolant, carrying away virtually all the dust and particles it produces. Another obvious advantage of waterjets is that they have no cutting blades to grow dull over time.
All waterjet cutting systems share some common design features: they pressurize water from 5,000 to 60,000 pounds per square inch, and focus this high-pressure stream through a small orifice made of a hard material, such as sapphire or diamond. The stream exits at 2,700 feet per second, or 2.5 times the speed of sound.
A booster pump supplies water to the cutting unit, and a filter removes particles that can damage internal components and interfere with a consistent .cutting stream. Where hard water is used, ions are removed from the water as well.
The filtered water enters a hydraulically driven intensifier pump that pressurizes it before delivering it to the cutting nozzle. The cutting nozzles can be stationary so that material can be fed through the waterjet, or integrated with computer-numerical- controlled robots so the waterjet can cut complex shapes.
There are two types of cutting nozzles. For cutting soft materials such as textiles or foodstuffs, water is the sole cutting agent and is sent to a straight-water nozzle designed for that purpose. For harder industrial materials such as steel or glass, an abrasive is added to the stream to accelerate erosion.
The abrasive, typically crushed garnet, olivine sand, aluminum oxides, or corundum, ranges in particle size from 0.2 to 0.5 millimeters. Garnet is widely used because of its relatively low cost and high cutting speed.
There are two types of abrasive cutters-convention-al or dry feed, and slurry feed or direct injection systems. In the dry feed system, the abrasive is held in a pressurized hopper. A pneumatic valve opens the hopper when the watetjet is activated, sending abrasive to a metering assembly, such as a precision disc, that regulates the amount of grit sent to the nozzle to provide a steady flow, to ensure smooth cutting.
The abrasive joins the water stream in a special mixing chamber inside the cutting head.
In the slurry feed system, the abrasive is metered into the jetting water before it exits the primary nozzle, by first adding the abrasive to a tank that can be pressurized to the delivery pressure and then connecting this tank to the delivery line.
A water tank beneath the waterjet catches the cut material, or kerf, spent abrasives, and runoff water. This tank also supports the material being cut and dampens noise.
Recovering the abrasive is the mission of the WaterVeyor system developed by Flow International Corp. The WaterVeyor lets waterjet cutters recycle garnet abrasives, thereby reducing waste disposal costs and the cost of purchasing virgin abrasive. Flow International introduced the WaterVeyor system at the International Manufacturing Technology Show in Chicago in September 2000.
“On average, about 66 percent of the operating costs of a waterjet cutting system is incurred by the garnet. A single cutting head waterjet consumes a minimum of 1.4 pounds of garnet per minute, 84 pounds per hour, 672 pounds per eight-hour shift,” said Michael Ruppenthal, director of marketing at Flow International. These figures increase proportionally with multiheaded cutting machines.
Typically, the mixture of spent garnet and kerf are pumped or shoveled out of the catcher tanks and discarded. Although the lighter, pulverized garnet is not cutting-grade material, the heavier garnet particles that withstand impact can be used again.
The WaterVeyor abrasive recovery system includes water eductors in the catcher tank. The eductors set up a venturi effect that removes the water, kerf, and used garnet from the tank and sends it to a hydroclassifier unit. The hydroclassifier, at 12 by 20 to 30 inches, is a scaled- down version of the much larger units used in mining to separate ore and crushed rock or clay.
The hydroclassifier generates air bubbles that cause the lighter, unusable garnet, and most of the kerf, to float to a settling tank. They are disposed of later as waste.
The heavy, reusable garnet sinks to the bottom of the hydroclassifier, and then is pumped to a decanter. Here, water is sucked from the slurry and a blast of compressed air shoots the dewatered clump of garnet into a fluidized airbed where it is dried. The system can recover six pounds of garnet per minute.
A certain percentage of kerf is mixed into the reclaimed garnet and is also used as cutting material.
“We have run tests with 50 percent recycled garnet/50 percent virgin garnet blend, and the mixture demonstrates virtually the same cutting performance as 100 percent virgin abrasive,” said Ruppenthal.
The WaterVeyor system currently works only in conjunction with Flow International’s Waterjet Machining Center cutting machines, which have a 60,000 psi cutting pressure, and are capable of traversing up to 2,000 inches per minute, and cutting contours up to 1,000 inches per minute. End users of machines equipped with WaterVeyor include McKee Foods Corp. of Col- legedale, Tenn., maker of the Little Debbie line of snack foods. McKee uses the waterjet cutting system to fabricate its cake and cookie making equipment. Boeing and other aerospace part makers also use the Water- jet Machining Center.
Flow International’s engineers are adapting the garnet recovery system to be integrated with other of the company’s waterjet systems, and eventually other manufacturers’ abrasive waterjet machines.
An Economy Model
Besides adding value to its waterjet cutting machines by recovering abrasive, Flow International is manufacturing less sophisticated and less costly waterjet systems to make the cutting technology more economical. Its Integrated Flying Bridge waterjet cutting system, introduced in March 1998, costs $165,000 to $220,000. The company’s other cutting machines, depending on their size and equipment, run from $275,000 to $350,000.
The Integrated Flying Bridge is equipped with fewer standard features. The lower-cost system is slightly less accurate, within 0.005 inch versus 0.003 inch, and has a top speed of 500 inches per minute versus 2,000 inches per minute for higher-priced machines.
The pump and xy cutting system are electrically and mechanically integrated into a single unit to save floor space and to let the operator control the pump from the control station. Earlier designs located the pump and xy system separately.
Engineers simplified the high-pressure water tubing of the Integrated Flying Bridge to eliminate swivels and joints, high-maintenance components that cause pressure loss between the pump and nozzle, to provide users with a faster cutting speed.
TCI Precision Metals of Gardena, Calif., uses the Integrated Flying Bridge. Craftsmen at TCI grind, saw, machine, flatten, and otherwise provide blanks and finished parts of stainless steel, brass, copper, plastic, ceramic, and other materials for markets that include aerospace, medicine, and semiconductors. TCI had a Flow International xy gantry waterjet, before installing the Integrated Flying Bridge cutting system in 1998.
“The whole point of purchasing the waterjet was to cut certain materials, such as Inconel, titanium, tool steel, and others that we couldn’t cut before,” said John Beizer, president of TCI. The method also eliminated machining of hard edges, caused by metallurgical changes wrought by laser or plasma arc cutting.
Operators load wide or long parts onto the machine’s 4×8- or 6×l2-foot cutting tables.
A Windows-based FlowMaster control system directs the flying bridge and cutting head.
Water and Plasma Mix
ESAB Cutting Systems of Florence, S.C., has designed both waterjet and plasma arc cutting systems for years. In January of this year, the twain met in a combination cutting system. Parts manufacturers use waterjet cutting to make the intricate cuts of internal geometry, then use plasma arc cutting to make high-speed perimeter cuts. For example, waterjets cut bolt holes in stainless steel flanges whose edges are plasma cut. Motor housings and components in off-road vehicles and construction equipment are also often waterjet and plasma cut.
“Because the two cutting processes are traditionally performed at different locations, there is always the chance of losing some cutting accuracy,” said Jeff De- Falco, product manager at ESAB.
“This is compounded when the part is inkjet or plasma marked for bin storage or further processing at other locations. ESAB’s combination system performs all these functions with the part at a single position.”
The hybrid cutting system is built on ESAB’s Hydrocut gantry-style waterjet systems. A rail runs along both sides of the cutting table, providing the longitudinal axis. A beam spanning the rail gauge, serving as the latitudinal axis, carries a cross carriage upon which the waterjet and plasma cutting heads are mounted. Thus, the Hydrocut is an xyz axis machine.
The rails are about 8 inches from the floor, so wide or large workpieces can be placed on the cutting tables, which range from 8 to 20 feet wide, and up to 75 feet long. First, the waterjet makes internal cuts, and then the plasma arc system makes perimeter cuts. If needed, inkjet and plasma marking heads do their job after that.
Laser sensors pinpoint the position of a workpiece, and height control sensors make adjustments in the case of uneven plates.
A planetary drive system powered by ac brushless motors moves the cutting heads to within 0.007 inch accuracy and 0.003 inch repeatability, at cutting speeds ranging from 0.01 to 750 inches per minute.
Computer numerical controls direct the cutting and marking processes. “We make our own CNC hardware and write our own software for waterjet and plasma cutting," said Joe Blackmon, ESAB marketing manager.
Axial piston pumps, ranging from 30 to 200 hp and using variable displacement, generate a waterjet pressurized up to 60,000 psi. The stream travels through nozzles ranging from 0.020 to 0.065 inch, and emerge from the cutting head’s diamond orifice, available in sizes from 0.003 to 0.022 inch. The larger orifice and nozzle sizes can accommodate the greater water and abrasive flows needed to make thicker cuts. A pre-aligned cartridge body, orifice, and focusing tube provide a tightly focused waterjet to cut faster while consuming less abrasive.
The Etch-Delete plasma cutting torch charges the cutting gases, either oxygen, nitrogen, argon/hydrogen, or air itself, with 100 to 1,000 amps, depending on the material being cut. For plasma marking, the CNC’s software varies the current sent to the plasma arc torch to ramp up or ramp down when the torch is started, stopped, or makes a curve in the material. “This makes marks cut into the metal more legible,” Blackmon said.
One of the first installations of the waterjet/plasma cutting system was made in early March at Metals and Services Co. in Addison, 111. Metals and Services is a stainless steel service center that processes plate, sheet, and bar that are used to make equipment for the oil and gas, paper, chemical, and food processing industries.
“We shipped our first part made by the ESAB hybrid cutting system in the second week of March,” said Joe Baessler, vice president and co-owner of the company. “It was a storage tank flange.
We used the waterjet to cut the intricate interiors, and the plasma arc to make exterior cuts at high speeds. Ordinarily, we would use one cutting process, stop, then either change the tooling or move the part to another workstation. By cutting the part faster with the combined waterjet/plasma system, we were able to reduce the cost to our client.” Baessler said that his company would use the ESAB hybrid cutting machine to make large parts on a cutting table measuring 10×25 feet, one of the largest in the industry, that will not require further finishing.
“Our latest version of the combination waterjet/plasma cutting system, the VapoJet, is designed specifically for the HVAC industry,” DeFalco said. “It uses waterjet to cut insulation and plasma arc to cut sheet metal in ducting.”
Although industrial waterjets are strong enough to shear steel plate, they are also delicate enough to carve decorative glass, where the appearance of the finished product is as important as throughput. This was the experience of Nova Classique Glass Industries, which designs and manufactures custom glass components used in curved staircases, store fronts and fixtures, coffee and dining room tables, shower doors, furniture, and tiles.
Nova relied solely upon craftsmen wielding diamond knives to cut its glass parts, which are later sandblasted and finished. The company still has many of its products cut by hand, but about three years ago, it decided to purchase a waterjet cutting system in order to carve more complex shapes, such as sculptures of an ice skater or hockey player in motion, with greater precision in more varied types of glass, including laminated glass, which is virtually impossible to cut manually.
The Ontario glass sculpting firm selected the JA510-A CNC abrasive waterjet cutting system made by Technicut of Carrollton, Texas. This system was equipped with an Ingersoll-Rand Streamline SL-IV 50-hp intensifier, and an abrasive delivery and metering assembly.
The intensifier is a self-contained unit that has a plunger pump. The pump uses a variable-displacement, pressure-compensated hydraulic technology to raise the water pressure of the machine to the needed 55,000 psi. The Streamline has a 25 percent longer stroke than its predecessors, so it can pump more water volume per stroke.
The SL-IV is self-diagnostic and has a transparent top cover, so operators can watch its performance and catch problems quickly. Engineers replaced the tie-rod design of past generation intensifiers with a bolted assembly, enabling maintenance workers to service individual parts without totally disassembling the top of the unit. In addition, the intensifier pump’s ring-shaped plunger snaps into and out of place to facilitate repair of the plunger and hydraulic seals.
Nova stores up to 200 pounds of garnet abrasive. The 30-psi internal air pressure locks the filling port until the internal vessel pressure is discharged, and when the vessel is activated, propels abrasive through a flexible supply hose directly into the metering system near the cutting head. The meter system sends abrasive into the cutting head’s mixing chamber. The abrasive waterjet stream exits a 0.012-inch-diameter diamond orifice.
Because Nova had never used waterjet cutters before, there was a learning curve involved. For example, the company discovered that piercing a start hole in glass requires lower pressure than cutting the glass to prevent cracking or breaking. The original nozzles on the Technicut had difficulty creating the pressure needed to pierce the start hole, according to Goran Vujcic, chief programming specialist at Nova. The company replaced these nozzles with Ingersoll-Rand’s Autoline abrasive cutting nozzle assemblies.
Like ES AB’s waterjet nozzle, the Autoline has a pre-aligned cartridge body, diamond orifice, and focusing tube to produce a sharply defined stream that will cut faster, consume less abrasive, and minimize wear.
Nova Classique cuts glass with the waterjet at speeds ranging from 0.1 inch per minute, to a maximum speed of 40 inches per minute. At each speed the accuracy is 0.004 inch per axis, and repeatability within 0.0005 inch per axis. Spent water, abrasives, and kerf are captured in an 80×130-inch tank.
Vujcic said the real value of the CNC system is that “we can make multiple copies easily and scale them up or down just as easily.”