Once considered a novelty, ultra high-pressure waterjets are becoming the machine tool of choice for greater efficiency and productivity.

Since abrasive waterjet technology was first invented by Kent, WA-based Flow International Corporation in the early 1980s, the technology has been evolving rapidly. Compared with a growth rate of 9.5% for machining centers and the total machine tool market, waterjets during the same period grew at a rate of 20.5%, according to the Market Intelligence Research Corporation’s (M.I.R.C.) World Standard and Special Machine Tools Market Report. 

The reason for this increase in popularity? Waterjets require fewer secondary operations and produce net-shaped parts without heat-affected zones (HAZ), heat distortion or mechanical stresses caused by other cutting methods. They cut with a narrow kerf, which enables parts to be tightly nested and provide better material usage. Also, waterjets cut virtually any material, leaving a satin-smooth edge. These benefits add up to significant savings per part in an industry that has traditionally defined productivity by processing cost per hour.

"Waterjets are a very versatile technology," explains Chip Burnham, Flow International’s Vice President of Marketing. "The versatility stems from the fact that material is removed by a supersonic erosion process; almost any material can be eroded, regardless of thermal properties or electrical conductivity. The waterjets also can cut material of any thickness with a minimum of fixturing and setup time. With PC-based controllers like FlowMaster®, the operator does not need to be a master craftsman to produce parts; very little skill or expertise is required."

Having waterjets expands a job shop’s capabilities beyond what is possible using only laser, EDM or milling processes. While other cutting applications may have limitations, waterjets are ideal for cutting tough, costly materials, such as titanium, Inconel, brass, any steel, aluminum, glass, stone and composites. "Although waterjets can cut up to 8" thick, most cutting done is between 1/16" and 3" thick, with a finished part accuracy of ±0.003" to ±0.010"," says Burnham.

Waterjet Complements Laser Applications

Used with lasers, waterjets provide a significant advantage. When cutting single layers of thin sheet metal, lasers can cut at high speed with tolerances of ±0.001" to ±0.006". Since lasers must focus on what is being cut, they are limited in the thickness of material they can cut. Waterjets, however, can cut thicker materials with accuracies of ±0.003" to ±0.010".

Unlike lasers, waterjets cut using cold supersonic erosion and are not dependent on the material’s thermal properties. When cutting different materials with lasers, various optical and gas parameters must be adjusted. With waterjets the only parameter that needs to be changed is the cutting speed, which is handled automatically by the machine’s PC (personal computer)-based controller. Finally, lasers emit toxic vapors when cutting some materials, while waterjets produce no toxic byproducts. 

When Edmonton, Alberta-based Laser Ray set out to diversify its operations, owners Ian Brooker and his father, Elmer, investigated a variety of cutting methods. Once they discovered the power and versatility of abrasive waterjets, the Brookers elected to install Flow International’s Flying Bridge system with its PASER™ 3 cutting head and FlowMaster® PC-based software. Using the waterjet with the shop’s flatbed laser system, Laser Ray has applied the machine to a variety of projects, including 3" thick metal plates, glass and in-laid marble floors.

"Waterjets are very complementary to lasers and give us an advantage when cutting thicker materials," says Ian Brooker. "We can cut materials with the waterjets that we can’t process on the lasers, such as aluminum and glass. Using the waterjets to cut parts out of thicker materials, we get a quality cut and smooth edge, often eliminating the need for secondary handling."

To illustrate the point: when the Brookers needed to cut thick pipe for a mining company, they found the pipe was too thick for the lasers. According to Ian Brooker, the job took 20 minutes to cut using a mechanical hacksaw. "Using the waterjets to cut the pipe," he adds, "cutting time dropped from 20 minutes to 15 seconds."

Abrasive Waterjet Faster Than Traditional Machining

Although wire EDM (electrical discharge machining) can cut very thick materials to more precise tolerances — ±0.0015" to ±0.0005" — than waterjets, it cuts very slowly. Waterjets can cut through very thick materials much faster than wire EDM with tolerances of ±0.003" to ±0.015". Unlike wire EDM, waterjets are not dependent on the electrical conductivity of the material being cut. Since wire EDM cuts with heat, this also limits the materials that it can cut.

Connelly Machine Works in Santa Ana, CA had been cutting parts to near-net with a saw and machining to finished tolerance on a CNC (computer numerical control) mill. However, this often required multiple passes, or wire EDM. "Time was a big disadvantage to this approach," says Ray Connelly, one of the shop’s principals. "It tied up our milling machines, and EDM was too expensive and slow."

While investigating the purchase of a wire EDM, Ray and John Connelly changed their minds and decided to install a Bengal® abrasive waterjet machining center from Flow International. The Connellys were sold on the Bengal when they discovered that it would cut net and near net parts to ±0.006" accuracy from virtually any flat material up to 4" thick. The fully integrated system is equipped with Windows™-based FlowMaster, the PASER 3 cutting head, an X-Y motion system, a 40,000 psi pump and a 39" by 19.6" worktable.

Using the Bengal, Connelly cuts a variety of parts out of stainless and carbon steel, Inconel, titanium and brass. "When we saw what the Bengal could do, how fast it could cut and how easy it was to operate, we were convinced it was the machine for us," says John Connelly. "We now hog parts out in one pass with the Bengal and machine them to finish tolerance in a single pass with our CNC mills," says Ray Connelly. "We also can use the same program on both the Bengal and the CNC mill. All we do is change the offsets."

Since the Bengal leaves a finished edge free of an HAZ, the Connellys also improved material utilization and reduced secondary operations. "We previously consumed a lot of tooling trying to penetrate edges hardened by HAZ," said Ray Connelly. "An edge machined with abrasive waterjets is very easy on inserts and bits. The Bengal consumes much less material than saw cutting. We nest parts pretty tight and definitely get more parts from a piece of material."

Waterjet Saves Big on Consumables

Like laser processing, plasma cuts through materials faster than waterjets; however, unlike laser, plasma can cut through very thick materials. Since plasma cuts with heat, there is a significant HAZ on materials, so some sort of secondary finishing is usually required. Since they do not cut with heat, waterjets leave a better finish on cut materials, with no HAZ and no metallurgical changes. Also, waterjets usually cut with far greater precision than plasma: ±0.003" to ±0.010" vs. ±0.005" to ±0.030". 

R.F. Chapmans of Pacoima, CA has used plasma for cutting since 1984. The company found that consumable costs associated with plasma cutting were becoming too high, and they were determined to find a way to reduce them. In evaluating several different technologies, waterjets seemed to be the ideal solution.

"Waterjets don’t have the same consumable costs that plasma cutters require," explains Mark Wymer, the company’s manager. "When piercing a hole with the plasma cutter, there is a fixed cost involved every time you make a strike — whether you’re making a 3/8" hole or 30" to 40" of cuts. The waterjets have lower operating costs and are much more cost effective."

R.F. Chapmans installed Flow International’s Flying Bridge with 20X pump in June 1997. Since then, they’ve realized significant cost savings and greater flexibility by using both plasma and waterjets for jobs. "Both cutting methods have their own applications that they work best for, and we definitely take advantage of both (waterjets and plasma) for projects," says Wymer. "The waterjets are more versatile because they cut with no heat, can cut smaller parts with greater precision, and are ideal to cut aluminum, stainless steel and titanium."

Abrasive Waterjet: How It Works

A basic waterjet cutting system consists of a filtration system, high pressure pump, nozzle and catcher. Standard filters remove particles of greater than 0.5 micron, preventing damage to pump seals, check valves and orifices.

Hydraulically driven intensifier pumps pressurize water to 60,000 psi or more. Although water is usually not viewed as compressible, under normal operating conditions it is compressed by about 12%. This means that no high-pressure water is discharged from the intensifier until the piston has traveled one-eighth of its total stroke. As the piston reaches the end of the stroke, a shuttle valve reverses oil flow, and the intensifier generates high-pressure water in the opposite direction.

Water then travels to the shock attenuator, a pressure vessel that maintains output pressure to ±3% for a constant, even water flow. It is then transferred from this reservoir via stainless steel tubing to the nozzle and finally exits through a diamond, ruby or sapphire orifice (0.004" to 0.022" in diameter), traveling at three times the speed of sound.

Operating at 60,000 psi or higher requires precision components, attention to detail and the proper materials. For example, a typical installation uses special stainless-steel tubing to connect the pump to the cutting head, which prevents premature fatigue failure. Other parts are machined to tolerances of ±0.0001". The basic ultra high-pressure water-generating system includes an abrasive hopper, abrasive metering valve, and a specially designed mixing chamber and focusing nozzle — usually called a mixing tube.

The metering valve attached to the hopper serves three functions: turning the flow of abrasive on and off; metering abrasive flow; and purging the abrasive feed line of water when the waterjet is not in use. Abrasive is metered through a precision disk that works like an hourglass to ensure a consistent, even flow.

The abrasive cutting head consists of a high-pressure valve actuator, valve body, nozzle body, waterjet orifice and mixing tube. The cutting head operates pneumatically with the abrasive-metering valve; when the cutting head is activated, the metering valve opens to allow abrasive flow.

When the cutting system is actuated, high-pressure water flows through the orifice, into the cutting head and out through the mixing tube. A venturi effect is created as the water enters the cutting head, pulling the metered abrasive particles through the feed line and into the head. Abrasive combines with the ultrasonic waterjet stream to create the high-energy cutting stream, which then exits the cutting head through the mixing tube.

The subject material is cut by supersonic erosion, usually with cutting forces of less than 2 lb. The temporary vertical force during start-hole piercing is slightly greater, but overall fixturing requirements for waterjets are minimal. After cutting, a water-filled catcher tank collects the abrasive/kerf/water mixture. The tank also acts to support the material and reduce noise. New catcher systems are designed with water level control for quiet, clean underwater cutting. A series of 4" thick sheet metal slats hold up the material, using simple clamps and tooling.

Buckley Owens Machinery Corp. 6416 Fly Road | East Syracuse, New York 13057 Telephone 315.432.0708 Fax 315.432.0736 Email: info@buckleyowens.com