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Abrasive water-jet cuts metal without heat.

A recently introduced water/abrasive cutting system from Flow Systems Inc, Kent, WA, shows some real advantages over other forms of cutting in a variety of applications. Known as the PASER.sup.TM (acronym for PArticle Stream Errosion), the system uses a high-pressure water stream and commercially available abrasive materials such as garnet or silica. The Paser can cut metals up to 7" thick--as well as many nonmetals--without heat, leaving a relatively smooth-cut surface finish (typically in the range of 75 to 125 rms).

Cutting speeds vary with abrasive and work material. Typical are 6 to 8 ipm in 0.5"-thick mild steel, 2 to 3 ipm for 2"-thick mild steel. In general, aluminum alloys, at a given thickness, cut twice as fast as steel; titanium and superalloys cut 10 to 20 percent slower. Because it cuts without heat, there is no chance of thermal distortion, localized structural changes, or thermally induced oxidation.

Safety is another system feature, and problems normally associated with heat buildup are eliminated. There is no radiation emission, nor danger of flying particles. The system produces virtually no airborne dust, which is important when cutting materials such as lead, asbestos, and fiberglass.

Abrasive-jet cutting can save time and money in applications normally requiring secondary grinding or finishing. It cuts through most sections of heavyweight materials in a single pass, leaving a clean, finished edge. Because it cuts in any direction, it can contour shapes and bevels. It is designed for easy integration into CNC systems, including optical tracers and full-scale robotics.

A Paser abrasive jet has a reactive load that typically is less than 30 lb. Many industrial robots can handle this load with no difficulty. With a wide selection of swivels, fittings, tubing, and coils available, high-pressure water can be delivered to the end of a robot arm without hampering or inhibiting its range of movement. In fact, the equipment has been integrated with 5-, 6-, and even 7-axis robots. It is lightweight, flexible, and can be adapted to pedestal or gantry systems.

How it works

The system consists of an intensifier pump capable of producing water pressures of 30,000 psi. High-pressure water is piped form the pump to the abrasive nozzle in stainless-steel tubing. A sapphire nozzle orifice, called the water jewel, measuring between 0.003" and 0.018"-dia is used to form the high-pressure water into a thin stream.

After the jet is formed, abrasive particles are added. The particles are focused around the jet by a 0.062"- to 0.092"-ID tungsten-carbide tube with lengths of 2" to 6". The combined water and abrasive stream can approach velocities of 3000 fps.

Kerf material is entrained within the stream, directed into a receiver, and transported to a disposal system. Minimal kerf is created (width ranges from 0.047" to 0.062"), depending on material and nozzle parameters.

Water consumption is about 1 gpm. Abrasives are typically consumed at the rate of 0.5 lb/min for an average hourly cost of $2.50

At work in a foundry

A series of test on the suitability of the Paser to remove burn-in and core sand, and to cut gates, risers, and flash from gray-iron sand castings, was conducted at John Deere's Component Works Foundry, Waterloo, IA. The results were interpreted by David Malm, a Deere foundry engineer. Here's what he reported.

"Objectives of the program were to determine capabilities of the abrasive-jet equipment. Testing was pursued in two areas--use of a hand-held wand-mounted Paser gun and use of a similar unit mounted on a Cincinnati Milacron HT.sup.3 robot.

"Ability of the jet to cut metal or remove burn-in was varied by changing abrasive-jet system components. To determine the best combination to perform a given job, each component variable had to be isolated, e.g., water pressure, water-jet size, abrasive type and size, rate of abrasive consumption, and focus-nozzle size and length.

"The hand-held unit that we used consisted of a 6-ft wand with an abrasive-jet nozzle mounted at one end. All work was performed in an enclosed booth over a work table that captured water and spent abrasive for disposal.

"The robot-mounted unit jet was similar except that the gun was mounted at the end of the robot arm, and the on/off control for the water and abrasive was handled by the robot controller.

"To remove burn-in sand," Malm continues, "the wand was used to take advantage of freedom of movement. Castings with varying degrees of contamination were used. The jet was applied by directing the wand at the work surface. Stand-off distance was 4" to 6". Applying the abrasive jet too close removed parent metal. The wand was easy to direct and control. Forces created by the jet nozzle were small--15 lb or less--creating no operator control problems.

"Several abrasives were tried, in both fine (40 to 60 mesh) and coarse (36 mesh) sizes, including garnet, aluminum oxide, silicon carbide, and foundry sand. The harder abrasives worked better, but were only about 30 percent faster than foundry sand. When we compared the cost of the harder abrasives (30^ to 55^/lb) to the cost of foundry sand (1^/lb), we decided to use sand and accept lower performance in return for substantial material-cost savings. Feed rates varied from 1 to 3 lb/min."

Water jet nozzle jewels varied from 0.10" to 0.18" dia. Water consumption varied between 1.0 and 1.5 gph, depending on nozzle-jewel size. Focus-nozzle ID varied from 0.062" to 0.092". Nozzle tube length varied from 3" to 6".

"Trials with focus nozzles showed that larger IDs were more effective for removing burn-in," notes Malm. "Focus-nozzle length didn't appear to be a factor. Nozzle life varied from 4 hr to 10 hr.

"Ability to remove burn-in proved superior to current methods and provided a higher-quality part. Two factors in operating this equipment became apparent: Castings processed by the abrasive jet, when not dried within a short period of time, rust, and operating this equipment creates a high noise level (80 to 100 dBA). We overcame the latter by requiring the operator to wear hearing protection equipment.

"In the metal-cutting portion of our tests, trials indicated that an operator couldn't apply the abrasive jet with the wand at a uniform rate and hold it steady enough to obtain a good cut. Tests conducted using the robot-mounted gun revealed that the finer mesh sizes worked best. Again the harder abrasives cut more effectively (up to 30 percent faster than foundry sand); however, the cost differential favored sand for production applications.

"Testing with varying focus-nozzle types and sizes showed that nozzles with smaller IDs made deeper and higher-quality cuts than nozzles with larger IDs. Nozzle length also impacted cutting ability, with longer ones providing increased cutting depths. But, the added cost of a longer nozzle more than offset the 10-percent increase in cutting ability.

"Nozzle life varied between 4 hr and 8 hr. And, cut quality was greatly influenced by nozzle wear. Typical cutting performance in gray iron was 1/16" deep at 36 ipm; 7/8" deep at 4 ipm.

"We believe, for metal cutting, the Paser must be used with automation, such as a robot, NC machine, or tracing table, because of the inability to manually manipulate the abrasive water jet accurately at a steady feed rate. Also, for this system to be more competitive with current metal-cutting methods, cutting rate must be increased. Cutting in lighter metals, such as aluminum, does show substantial increases in cutting rates, however."

For more information about the abrasive water-jet process, circle E15.
COPYRIGHT 1985 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1985 Gale, Cengage Learning. All rights reserved.

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Title Annotation:Flow Systems Inc.'s innovation
Publication:Tooling & Production
Date:May 1, 1985
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