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Crenshaw Die & Mfg. Corp.

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Waterjet Cutting: Solving Today's Cutting Problems

Waterjet Cutting

Cutting with water, alone or with abrasives, is an emerging technology with superior shape-cutting ability.

Has this ever happened to you? You get a panicked call from a company you've never heard from before. They're holding up a multimillion dollar production run because their design engineer specified a two-bit part in a shape or material no one can cut to specification in time to meet the deadline. Now they are frantically calling every job shop they can think of in the hope of finding someone to get them out of a jam.

If you have waterjet cutting capabilities in house, the chances are good that you can do the job, meeting both the specs and the deadline, and earn a healthy profit for you and gratitude from the company, which could lead to increased business in the future.

One of the best new shape cutting methods, waterjet tools can produce precise shapes from nearly any material to net or near-net dimensions without burrs, slag, heat-distortion, or delimitation. Waterjet systems routinely cut complex openings, contours, and patterns from even hard-to-cut materials in shapes that are impossible to produce using traditional tools.

Process Description

Waterjet cutting and drilling was made possible in the early 1970s with the development of a commercially viable pump that could deliver ultrahigh-pressure water. The principle of cutting with water is fairly simple. Designed and manufactured by Flow Systems, Inc., in Kent, WA, an intensifier pump pressurizes water up to 55,000 psi and forces it through a nozzle as small as 0.004" in diameter, generating a high-velocity waterjet traveling at speeds up to three times the speed of sound. This waterjet by itself can cut a variety of non-metallic materials, such as acrylics, felt, foam, Mylar, plastic, polyethylene, polyimide, and rubber. Waterjet cutting was first used extensively in disposable diaper, cardboard, printed circuit board, and food applications.

In 1984, Flow Systems patented a method that entrains abrasives (typically garnet) in the waterjet where a portion of the water's momentum is transferred to the particles. This high-velocity abrasivejet, called PASER (from Particle Stream Erosion), cuts virtually any material-metals, composites, stone or glass. The first industries to benefit from this new cutting technology were manufacturers in the aerospace, primary metals, foundry, glass, and heavy equipment industries.

Process Advantages

Several unique properties make waterjets or abrasivejets a superior choice for cutting in a variety of applications. The waterjet/abrasivejet cuts in any direction. Integrated with a multi-axis computer-controlled gantry, the system combines this omni directional cutting capability with the flexibility and repeatability of computerized cutting programs.

The hair-thin stream of water produces minimal kerf, which maximizes material use and gives you unmatched precision for cutting small holes, narrow slots, and closely spaced patterns. Smaller parts can be nested within larger ones. Unlike a saw's rough cut, which leaves material that must be machined away to achieve final dimensions, the waterjet/ abrasivejet cut is so precise, the first cut is often the final cut.

The operation's low operating temperature doesn't produce the slag created by laser and plasma-arc systems, so there is no need for expensive grinding, annealing, or machining of heat-affected surfaces to obtain final dimensions.

The waterjet/abrasivejet cuts with minimal lateral or vertical force, which eliminates the need for costly part-support structures. Even when cutting thin or unstable workpieces, the gantry's support table holds the parent and cut materials stationary. The table is also a catcher tank that collects the spent water, abrasive, and kerf material. The low thrust makes it possible to use the power of waterjet cutting in a hand-held tool. And waterjet/abrasivejet cutting is often faster than traditional methods, depending upon the thickness of the material and the surface quality you want.

A basic waterjet cutting system consists of a water pressure booster and filtration system, the intensifier pump, and a nozzle. The booster increases incoming water pressure to the level required by the intensifier. The three-stage filtration system extends the operating time of pump seals, system check valves, and cutting orifices. Abrasivejet cutting systems require the addition of an abrasive hopper, an abrasive metering valve, and a specially designed focusing nozzle with a mixing chamber.

Economics

The initial investment for a waterjet cutting system ranges from $60,000 to integrate the required waterjet/abrasivejet cutting equipment with an existing X-Y table, to $200,000 for a turnkey system that includes the table/catcher, gantry, and CNC unit.

Operating costs are relatively low when compared with most traditional cutting systems. Waterjet orifices, abrasive focusing nozzles, and pump seals and valves require occasional replacement. But even where waterjet/abrasivejet cutting is more expensive, the additional cost is usually more than offset by the higher quality of the finished part.

Payback results from the time and dollars you save over more labor-intensive methods, the higher quality of finished products, and the potential for increased sales in new and existing markets. As more people learn what waterjets can do, demand for products that use the technology will increase.

A significant, if less obvious, investment is the time it takes to gain the expertise you need to operate these sophisticated systems economically. If you have experience with CNC controllers, the learning time will be shorter than it would be otherwise. Nevertheless, the simple principles of waterjet/abrasivejet cutting technology are clearly not simple in practice.

Conclusion

Is there anything the waterjet/abrasivejet cannot cut? Well, it won't cut tempered glass. It also does a poor job on wood. The process darkens the surface around the cut, which requires additional sanding to remove the discoloration. But because there are so many other economical ways to cut wood in all its varieties, this doesn't seem to be an important reason to reject this cutting system.

Waterjet/abrasivejet cutting is still an emerging technology with almost unlimited potential for growth. A waterjet system, when added to the traditional cutting, machining and milling capabilities found in most job shops, can open markets with new demands for unusual shapes in hard-to-cut materials and increase the profitability of existing markets by producing higher-quality parts at lower cost.

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This technical information has been contributed by
Crenshaw Die & Mfg. Corp.

Click on Company Name for a Detailed Profile

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