Waterjet Cutting Produces Superior Quality, Significant Cost Savings

Waterjet Cutting

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By Mark Shortt
Editor, Design-2-Part Magazine

Minimal tooling is required with a process that, when used with abrasives, can cut materials more than 10 inches thick without a heat-affected zone. New technology has helped reduce or eliminate taper and associated secondary machining.

When maintaining integrity of the material is essential in a machining application, abrasive waterjet machining often warrants serious consideration as the right process for the job. By concentrating a high-pressure stream of cool or ambient water (often mixed with abrasives) to cut narrow grooves in nearly any material, the fluid jet process produces no heat that can change or distort the cut edge. And because the process requires minimal or no tooling, it also merits a second look in cases where additional machining is required and tool wear becomes an issue.

"Applications are growing due to the tighter tolerances capable of being achieved," says Rodie Woodard, president, Maximum Industries, Inc., Dallas, Texas. "Manufacturers who evaluated waterjet as recently as five years ago should revisit the technology to determine justification. Speeds are faster, edge quality better, and tolerances are much tighter."

The versatility of the process is evident, Woodard says, from its ability to cut materials ranging from thin foams and rubbers to thick stainless steel and titanium. Ken Piel, president of MicroJet, a 20-person job shop in Monroe, Washington, agrees. "Abrasive waterjet can cut almost all materials," says Piel. "Because of its benefit of cutting with cold or ambient-temperature water, job shops have the ability to pursue virtually all industry segments. One day, we may produce parts out of foam rubber to be used as toys, and the next day, we may produce parts from titanium to be used in the aerospace industry."

Waterjet (or fluid jet) technology actually encompasses two types of cutting processes: waterjet machining and abrasive waterjet machining. Whereas waterjet systems use only water as the cutting medium, abrasive waterjet machines mix water with abrasive particles, such as garnet, to form a highly potent cutting force. Although it is technically correct to distinguish the two processes, the term "waterjet" is often used as a shorthand way of referring to the more versatile and widely used abrasive waterjet process. Both technologies apply extremely high pressures to water, directing it through a small orifice to cut materials with a considerable amount of highly concentrated energy. The force of the cutting stream is great enough that a catch tank often filled with ceramic balls is positioned under the system to prevent the stream from cutting through the shop floor.

In waterjet machining, a narrow jet of water acts as a highly concentrated force to cut, drill, or deburr parts made from a variety of materials. Powered by a considerable amount of pressure, water jets emanate from nozzles ranging from 0.002 inch to 0.040 inch in diameter to cut narrow grooves in materials up to one inch thick, according to Manufacturing Engineering and Technology (S. Kalpakjian, 4th ed., 2001). Materials such as plastics, rubber, wood, fabrics, and composites can be cut, along with paper, leather, brick, and insulating materials. Known as an environmentally safe, comparatively efficient, and clean cutting process, waterjet machining is used in the food processing industry to cut and slice food products. It is also employed to cut vinyl and foam coverings for automobile dashboards and body panels. Advantages of the process include the fact that no heat is produced, and predrilled holes are not required before cutting, according to the reference.

Abrasive waterjet machining can be used to cut nonmetallic and advanced composite materials of various thicknesses, as well as metals up to a foot thick. The process incorporates abrasive particles, such as silicon carbide, aluminum oxide, or most commonly garnet, in the high-pressure cutting stream to increase the rate of material removal. It is particularly suited for heat-sensitive materials that cannot be machined by heat-producing processes, such as flame cutting or plasma cutting. However, because cutting speeds are not as high for metals as they are for reinforced plastics, the process is not always suited to jobs requiring high production rates, according to the reference.

Intense Pressures

In a typical waterjet cutting system, an intensifiera high-pressure pumping mechanism that uses hydraulics to create water pressures of up to 60,000 psidetermines the force of the cutting stream. As the pressurized water is pumped through a nozzle (mixing tube), it is combined with particles of abrasive material, usually garnet, and focused into a coherent cutting beam. Acting as a highly concentrated force, the water/abrasive jet is directed through a small orifice, or jewel, typically made of ruby, sapphire, or diamond. The abrasive waterjet exits the jewel as a narrow cutting stream, which, at up to three times the speed of sound, is capable of cutting through virtually any hard material.

The fact that most waterjet cutting is accomplished with the use of water and abrasive has implications for the diameter of the cutting stream, which typically measures approximately 0.030 inch to 0.050 inch, according to Piel. Because the kerf is also approximately that width, it is often outside the specifications of a part. Abrasive waterjet, he says, would not be able to comply with a requirement for an inside radius of 0.005 inch or a slot 0.015-inch wide.

Piel says that waterjet is increasingly being used to "hog out" parts from expensive or difficult materials. "Machining large amounts of material away from the finished part dimension is time consuming, hard on tools, and turns potentially usable materials into chips," he says. "Our ability to nest parts closely together often can equate to a 20% or 30% saving in materials."

Competing Processes

By wetting the workpiece, waterjet cutting has the potential for damaging certain materials if precautions are not taken, says Leo Denlea of Advanced Laser Dies (ALD), Pico Rivera, California. For example, some steels rust very quickly, and occasionally, laminates will delaminate. "Some softer materials tear or stretch while being waterjet cut," says Denlea. "Tapered cut edges are an issue, though some new technology is addressing this.

"Tolerances cannot be as tight as, say, EDM, though 0.010 inch is easily done and 0.005 inch can be achieved in many applications," adds Denlea. "The material itself, the machine setup, and the age and condition of the water/abrasive nozzle components determine edge quality."

Lasers can cut at faster speeds, with tolerances of 0.001 to 0.006 when cutting single layers of thin sheet metal. Their effectiveness, however, is limited by the thickness of the material. Waterjets can cut thicker materials, with accuracies of 0.003 to 0.010. And unlike lasers, their suitability for a particular application does not depend on the material's thermal properties because they cut by means of cold, supersonic erosion rather than heat.

Also, cutting different materials with lasers requires the adjustment of various parameters, such as optics and gases. With waterjets, however, the only real parameter that needs to be changed is the cutting speed, according to Jack Budd, owner of Precision Waterjet, Orange, California. "With a PC-based controller, this parameter is automatically taken care of by the machine," Budd notes. "Waterjets are very easy to use and maintain."

Plasma cutting is another process that cuts through materials faster than waterjets. Unlike lasers, plasma cutters can cut through very thick materials. But because plasma cuts with heat, it leaves a significant heat-affected zone that requires secondary finishing in many cases. Waterjets leave a better finish because they do not cut with heat and cause no metallurgical changes in the material being cut. They also usually cut with higher precision than plasma ( 0.003 to 0.010, versus 0.005 to 0.030), Budd says.

A process that frequently competes head to head with waterjet cutting is wire electrical discharge machining (wire EDM), an extremely accurate process that can be used to cut a range of materials (including steels, Inconel, carbide, graphite, aluminum, copper, brass, and titanium) up to 6 inches thick. Wire EDM leaves no burr, little heat-affected zone, and an excellent surface finish. However, it is a much slower process than waterjet cutting.

Higher-Quality Parts

One of the ways to achieve higher edge quality on waterjet-cut parts is to reduce or eliminate taper by adjusting machining parameters, such as cutting speed and type or amount of abrasive used. Another way to eliminate taper is by using taper control technologysuch as the recently introduced Dynamic WaterjetTM from Flow International Corporation, Kent, Washingtonthat automatically adjusts cutting angles to cut parts with high accuracy and speed. Unlike other systems that remain fixed at a 90-degree angle to the plane of a flat plate, the Flow Dynamic Waterjet automatically tilts a small, articulated "wrist" cutting head as required, depending on the material and the part. The technology employs patented software models to control the angle of the cutting head for specific accuracy and part tolerance requirements.

Precision Waterjet is one of the many job shops that have begun using the Flow Dynamic Waterjet, reported to be capable of cutting metal or composite parts from 0.050-inch thick to more than 6 inches thick. Besides eliminating taper, the technology is also said to cut parts up to four times faster than traditional waterjet cutting processes and produce higher-quality parts with significantly greater accuracy in flat-stock materials.

"Using Dynamic Waterjet, we're able to cut to spec right off the machine," Budd says. "We recently cut 1/4-inch and 3/8-inch-thick titanium bicycle parts to finished precision, where the conventional waterjet would have left taper and the need for additional machining. We're now soliciting gear work since we've found that we can accurately cut gears out of special composite materials, aluminum, and steel, with a very fast turnaround."

Budd also says that the machine allows the company to "stack cut 3 to 4 pieces high and hold tolerance" while substantially reducing cost. Using the Dynamic Waterjet to cut and stack 1/16-inch aluminum four sheets high, he says, reduces the cost per part to two-thirds that of the conventional waterjet.

An Alternative for Specialized Hole-Drilling

Although used more often for precision cutting and trimming, waterjet processing continues to win acceptance as an alternative method for specialized hole-drilling applications. According to Matt Kalina, marketing director, LAI Companies (Phoenix, Arizona), the drilling of angled and shaped holes are applications for which the process is increasingly gaining favor.

"Materials can be processed in less than half the time that alternative production methods take, while eliminating heat-affected zones, offering a significant savings to customers," says Kalina. "Care has to be taken to properly shield non-cut surfaces during waterjet drilling and to prevent the most common defects with angled hole drillingdivoting and worm-holing."

Laser machining and electrical-discharge machining (EDM) have long been the established production methods for precision hole drilling, and for good reason. However, EDM hole-drilling may be too slow and costly for certain projects, and laser drilling sometimes produces an undesirable heat-affected zone in the area around the hole. In situations where the benefits of waterjet drilling outweigh the costs of the more established methods, waterjets are making inroads.

According to Kalina, holes can be waterjet drilled at angles ranging from 15 to 90 degrees to the surface. A typical waterjet application, he says, involves drilling 0.040-inch-diameter holes in stainless steel 0.125-inch thick. Ovals, squares, and diamonds are among the typical non-traditional drilling shapes.

"A diameter of 0.020 inch is typically the lower limit in size for abrasive waterjet-drilled holes, although smaller holes can be drilled in specialized abrasive waterjet processes and with water-only drilling," says Kalina.

Waterjet Problem Solvers

Abundant technological resources and three strategically located production facilities enable LAI Companies to provide advanced waterjet and laser contract manufacturing services throughout the United States. The firm offers five-axis laser and five-axis waterjet machining, and High-Definition Waterjet Cutting and DrillingTM of a wide range of materials. Its 19 waterjet workstations include three five-axis waterjet stations and five with rotary capabilities. According to Kalina, the company has used waterjet processing to drill "tens of millions" of holes in materials such as titanium, steel, and composites.

Successful projects include the manufacturing of titanium screen panels with 27,000 diamond-shaped holes, holding tolerances to 0.0015 inch. Another case involved the drilling of approximately 4,400 turbine cooling holes in plates made from Hastelloy. LAI Companies operates production facilities in Phoenix, Arizona (LAI Southwest, Inc.), Westminster, Maryland (LAI East/Laser Applications, Inc.), and Minneapolis, Minnesota (LAI Midwest, Inc.).

American Wire EDM, Inc., which recently moved to a new 11,000-sq-ft facility in Placentia, California, provides water jet cutting for customers in the automotive, aircraft, military, and commercial sectors. The company's variety of manufacturing capabilities allows the firm to offer "simple to complex parts from start to finish," according to John Carson, president. "We are capable of acquiring material for the job, doing the secondary CNC machining or wire EDM after water jet machining, and also grinding, etching, plating, anodizing, or powder coating," says Carson.

In a recent job, American Wire EDM cut deck plates for a customer out of Tread Bright (aluminum diamond plate). The parts had to be cut out of full sheets (4 feet x 8 feet) without damaging the mirror-like finish that was already on the material, Carson noted. "With the waterjet process, we were able to cut parts at a very competitive price while maintaining the finish on the material," Carson said. "In addition, through nesting of parts, we were able to increase the yield of parts per sheet due to the small cutting kerf of the waterjet. These factors gave us an obvious advantage over conventional machining, which would have been costly, and stamping, which would have damaged the material."

The firm's water jet is also capable of cutting tough-to-machine materials, such as titanium and Inconel. Often, the company is able to rough machine partsout of sheet stockto within 0.010 of finish. As a result, Carson says, customers spend less money on material and increase their throughput in their own shop. They also save time and money by purchasing fewer roughing cutters.

"In one case, the customer decided not to purchase another CNC mill because we provided him with a semi-finished part," said Carson. "Another way that the CNC shops win is that their machines last longer and become more profitable. Roughing tough materials wears out the machine faster when you compare it to just finishing a part that is pre-machined or roughed out on a waterjet machine."

As a contract waterjet cutter, Advanced Laser Dies (ALD) specializes in rapid turnarounds for short run and prototype work. Many of the company's customers in the rubber and foam industries fabricate flat parts with molds or steel rule die-cutting operations. Typical parts include gaskets, insulators, flat panels, nameplates, labels, and pads. For one customer, ALD solved several problems related to the cutting of three-inch-thick, white foam pads.

"First, the foam discolors if touched by a bare hand," said ALD's Leo Denlea. "We solved that by putting clean rubber gloves on the machine operators. Secondly, the edge was quite rough. That took a lot of experimentation with feed rates and orifices to solve. Finally, splash-back from the water stream was damaging the back of the parts. After a lot of experimentation, we came up with a custom fixture and a series of sacrificial sheets to protect the parts. Ultimately, we came up with a clean, accurate, and cost-effective part that could not be easily die cut, molded, laser cut, or wire cut."

Maximum Industries, Inc., provides waterjet cutting services for OEM customers in a variety of sectors, including aerospace, food, architectural, and general industrial. "We coordinate the complete manufacture of parts," says Rodie Woodard. This includes everything from purchase of materials to cutting, forming, and machine shop services. Recently, the company used waterjet to cut 5-inch-thick foam rollers for a client that was replacing the inking rollers on its equipment. In this case, waterjet was preferable to die cutting, Woodard said. Because of the compressible nature of the foam, a perpendicular side could not be achieved if the rollers were die cut, he explained. Non-contact waterjet cutting, however, provided a smooth, straight edge that required no secondary operations.

Hydro-Abrasive Machining, Inc., Los Angeles, California provides abrasive waterjet cutting services to manufacturers of civilian and military aircraft, electronics, and communication satellites, as well as companies in the film and amusement park industries. Using precision multi-axis (five-axis and two-axis) machines with multiple cutting heads, the company reportedly can achieve surface finishes of up to 63 RC on materials such as Inconel, Kevlar, titanium, and graphite/epoxy laminates.

MicroJet has published a waterjet edge-quality standard that allows customers to select the type of edge required, and, in turn, hold the supplier accountable to produce that standard. The edge-quality standard helps fill a need created by what the company sees as the lack of industry standardization or definition regarding parameters for waterjet-cut parts. "We frequently hear horror stories from companies displeased with what they received from their supplier," says Ken Piel. "Often, they are disappointed in dimensional tolerances, the draft, and the edge quality supplied by their vendor. We've attempted to eliminate this problem by always including these parameters in our response to the RFQ." By specifying "up front" the essential parameters of what a customer should expect from a waterjet-cut part, the company helps prevent misunderstandings regarding precision and quality of the work performed.

"Past the early stages of the product life cycle, job shops are separated by their ability to differentiate themselves by things other than their machines or technology," says Piel. "While our company has some of the most accurate and powerful equipment on the market, we separate ourselves from the others by how we conduct business. We have a high propensity for detail, an extremely high level of customer service, and are fanatical about quality." MicroJet conducts its operations in an 11,500-sq-ft facility.

Precision Waterjet, based in Orange, California, provides "ultra high-pressure waterjet cutting services" to customers in industries such as aerospace, architecture, construction, flooring, and design, according to Jack Budd. Incorporating the Flow Dynamic Waterjet into its operations has enabled the firm to increase the quality on finished parts with no secondary operations, thus saving customers time and money.

"Using conventional waterjets, I would rough cut titanium and nickel alloy parts, which required dome milling to finish the parts," says Budd. "With the new machine, the outside periphery can be cut to a finished edge and dimensional tolerance. Waterjet drilling of holes can be done without taper, meaning no secondary operation is required. This is a tremendous saving to our customers."

The company performs waterjet cutting on parts that include aluminum panels measuring 78 inches by 148 inches; intricate titanium parts for the aerospace industry; 1/4-inch and 3/8-inch-thick titanium parts for bicycles; steel gears; and side frames and base plates for assembly machines. Additional items include aluminum, brass, and bronze sign inlays, marble and granite medallions, and 1-inch-thick Inconel parts.

"Most customers require us to hold 0.020" on all features with 250/125 RMS, but more of our customers are requesting tighter tolerances," says Budd. "We are currently cutting some aerospace parts to 0.003" with < 125 RMS."

One of the company's projects entailed cutting brass, copper, and stainless steel flooring pieces for the RA Nightclub in the Luxor Hotel in Las Vegas. The project required a smooth edge, and the 3/8-inch-thick stainless steel around the "Eye of RA" required more than 2,000 small oval slots through which fiber optic lighting would shine. Cutting the slots with other methods, such as laser or flame cutting, would have left ragged edges, Budd explained. They also would have warped the material, making the parts totally unacceptable. "Using waterjets, the job was completed much more quickly than by using traditional cutting methods, since the waterjets left satin-smooth edges that required no secondary processing," Budd said.

The company has three Flow waterjets, including one with the Flow Dynamic Taper Control. All are equipped with multiple heads. The company also has a 5000-Watt CO2 laser.

Reference

Kalpakjian, Serope. 2001. Manufacturing Engineering and Technology, 4th edition, pp. 761-763. Reading, Massachusetts: Addison-Wesley Publishing Co.

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