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Waterjets: Evolving from Macro to Micro

    
Cutting smaller, faster, and deeper

 

By Jim Lorincz
Senior Editor 
       
   

        

Manufacturers of microcomponents are riding a new wave of precision, because one man couldn't produce a number of smaller parts using conventional abrasive waterjet cutting. Walter Maurer, director of Micromachining AG (Aarwangen, Switzerland), co-developed the Womajet abrasive waterjet micromachining center in 2004 with the objective in mind of machining small micro-sized components.Micro parts include a Nitinol medical device (center) that measures 2.03 mm across (surface to surface) with seven separate chambers, each measuring 0.4-mm diam, and a displacement amplifier (right foreground) that is used in high-precision scales and load cells.

"Mechatronics, measuring and control technology, aerospace, and medical, as well as the watch industry, require small components made from special materials or composites," Maurer says. "The accuracy required for these components went beyond the capabilities of conventional processes.until now, that is. Micro-waterjet machining is capable of 10x more accurate positioning than a traditional waterjet," Maurer asserts.

Two Womajet machines delivered to Micro Waterjet LLC (Huntersville, NC) have ±3 µm positioning accuracy, ±0.01-mm cutting accuracy, and a surface quality equivalent of N7 (Ra 1.6 µm), depending on the material type and thickness. The machines are the basis of Micro Waterjet's contract manufacturing service that is creating parts on a micro scale not previously thought possible with conventional abrasive waterjet machining.

One such part is being used as a displacement amplifier in high-precision scales and load cells for the tooling industry. Daniel Leuthardt, Micro Waterjet's development applications engineer, describes it as a part made from spring steel, measuring 7.9 x 5.7 x 0.5-mm thick. Inside the cells and scales, the part is fixed at two 0.33-mm holes with two pins.

"The part works by applying pressure on the long side, compressing and creating a side movement to dictate the actual measurement within the high-precision scales and load cells," Leuthardt explains. "The challenge was to cut the longer openings, or slots, no wider than 0.34 mm with a tolerance of +0.00 -0.03 mm. Multiple part sizes were produced, including larger sizes for crane scales and some prototypes for next-generation development. The process was not only less expensive than previous milling applications, but produced a much higher quality part with a kerf width of just under 0.3 mm."

According to Leuthardt, Micro Waterjet currently provides contract manufacturing services and is building its sales and service support system to offer the Womajet to the general market by the end of 2010. "There will always be a need for conventional waterjet services. We don't feel we are competing with them. In fact, we refer traditional requests to our partners, and vice versa. Our focus is high precision and micro manufacturing, and we will continue to perfect our process to meet new and challenging needs."

The advantages of conventional abrasive waterjet machining, by now, are well known. There are only a handful of material limitations. Steel, stainless, and titanium, and a host of other material workpieces are routinely cut in thicknesses of 6–8" (152–203 mm), and as thick as 18–20" (457–508 mm). The small number of materials that can't be cut by waterjet include tungsten carbide, tempered glass, certain ceramics, and diamond.

Advantages of abrasive waterjet cutting include:

  • Materials can be cut without heat affected zones (HAZ) and heat deformation. Parts have finishes that often eliminate the need for postprocessing operations.
  • Complex 3-D shapes can be machined through the use of sophisticated software and 3-D machining heads.
  • Accuracy of 0.005" (0.13 mm) with repeatability of 0.001" (0.03 mm) is readily achieved.
  • Workplace environmental impact is negligible, with no airborne dust particles, smoke, fumes, or workpiece contamination being produced. Garnet abrasives can be recycled for use or safely disposed of in a landfill.

There are a number of ways in which productivity and cutting speed with abrasive waterjets are being improved. The technology is following several distinct paths, with machine tool builders offering higher pressure pumps, dual-pump systems, single pumps with higher horsepower intensifier pumps, and adding multiple cutting heads to machines.

"Pressure equals productivity," states Tim Fabian of Flow International Corp. (Kent, WA). "The faster the jet travels out of a cutting head, the faster it's going to erode material. Metallurgical advances, and getting pumps and seals to last longer, have been a continuing challenge. Once you hit pressure around 60–70 kpsi [414–483 MPa], a lot more attention has to be given to metallurgical advances. We've used FEA to model components for ultrahigh-pressure pumps to 94 kpsi [648 MPa], which is considered HyperPressure," says Fabian.Machining thicker workpieces, composites for aerospace, medical device components, and military armor plate is growing for abrasive waterjet cutting.

"Composites for aerospace applications, medical device components, and military armor plate have been recent growth areas," says Fabian, noting that Flow's machines for Boeing and Airbus have served as important R&D platforms for developing full five-axis 3-D-capable waterjet machining. "We're seeing a lot more requests for cutting thick workpieces. We have some end users who are cutting 16–18" [406–457-mm] titanium and alloys in 4 x 2' [1.2 x 0.6-m] lengths. The HyperPressure technology allows this type of work to be performed at far greater speeds and lower costs."

High-pressure jetstreams are produced and focused by orifices from 0.003 to 0.030" (0.08–0.76-mm) diam. For materials that can delaminate—such as composites—prepiercing is often required to ensure a clean cut.

A proponent of UHP single-pump waterjet technology, Flow has introduced its Mach series of products with ultrahigh pressure intensifiers rated to 94 kpsi (648 MPa) in the Mach 4, 60 kpsi (414 MPa) HyPlex Hybrid directdrive pump in the Mach 3, and 55 kpsi (379 MPa) JetPlex direct-drive pump in the Mach 2. "What we have done is create very distinct lines with the Mach series, with a pump and package tailored to the customer's production and budget requirements.

"Advanced manufacturers are asking for increases in cutting speed, and we are evolving toward full five-axis 3-D cutting," says Fabian. "We have developed software functionality that enables us to import programs and manipulate 3-D solids right at the machine. The real trick, however, was to keep this system very simple to operate. Part of the reason we have evolved into the 3-D world is because of composites and the aerospace industry's extensive use of these materials. We are able to download a file from CATIA right into the machine," Fabian says.

Jet Edge (St. Michael, MN) offers a wide range of electric and diesel (for mobile applications) waterjet intensifier pumps rated from 30 to 280 hp (22–209 kW) in 36, 60, and 90 k psi (248, 414, and 621-MPa) models. Jet Edge's most recent product introduction is the iP60-100 100- hp (75 - kW), 60- k psi (414-MPa) waterjet intensifier pump for precision cutting, water blasting, cleaning, and surface preparation applications using orifices up to 0.021" (0.53 mm), and delivering 2.0 gpm (7.6 L/min) of ultra-high pressure.

"The iP60-100 is offered with a dual-intensifier. With digital control, the user can turn one off and or turn them both on to use the whole capacity of the pump," says Jet Edge's Bradley Schwartz. "We mostly sell multiple-head machines today, giving users a decided advantage, especially when bidding cutting metals like 6" [152.4-mm] thick titanium. It's an advantage to have more horsepower per head, and then cut with more than one head."

For cutting complex parts, Jet Edge offers the Mid Rail Gantry Waterjet System that features work envelopes from 5 x 5' (1.5 x 1.5 m) to 21 x 13' (6.4 x 4 m). The Mid Rail Gantry is equipped with one abrasivejet cutting head with the option of adding a second cutting head. Ballscrew-driven for higher accuracy, the Mid Rail Gantry uses an industrial PC controller and can be configured so that all three axes are fully programmable, with Z axis optional.

Jacquet Mid Atlantic (Pottstown, PA) recently installed a 21 x 13' (6.4 x 4-m) large-format Mid Rail Gantry Waterjet System. The machine is equipped with two Jet Edge Permalign II abrasivejet cutting heads, a 100-hp (75-kW) intensifier pump, an optional mirroring package, independent programmable Z carriages, programmable height sensing, closed-loop water filtration system, and a garnet-removal system.

"We are improving the quality and competitiveness of our customers in two ways," says John Cheung, chairman and CEO of Omax Corp. (Kent, WA). "We view software as the strength of our company. We always strive to give the user higher cutting speed and better quality of finished product through improvements in software. We've had two releases of software in the last several years that have significantly improved performance. The first release several years ago increased cutting speed by about 30%. The second release a year or two ago, produced a 20% increase in cutting speed."

To meet an expected demand for more affordable entrylevel products, Omax introduced its Maxiem brand waterjet line for manufacturers who desire speed, flexibility, and efficiency in waterjet cutting, but don't need the precision of its Omax products. Due to differing specifications, Maxiem does not compete with current Omax offerings, and is designed instead to broaden the market for waterjets.

Machining 6.5" (165-mm) titanium billets for Boeing is done with a Jet Edge waterjet leaving 0.25" (6.3-mm) excess, and machined to final shape. Productivity is doubled by using two cutting heads.The Maxiem line is well-suited for shops that are currently subcontracting their cutting or making parts by other processes that require subsequent operations to achieve the same high precision and surface quality of a waterjet. "The targets are the many fab shops and job shops that cut metal, maybe occasionally, do welding, but don't generally require the 0.001" [0.03-mm] accuracy of our Omax Jetmachining Centers," says Cheung.

The Maxiem is an abrasive waterjet cutting system with an X-Y table containing Intelli-TRAX traction drive technology and a motorized Z axis. The high-pressure 50 k psi (345 MPa) direct-drive pump is available in 20 and 30-hp (15 and 22-kW) versions. The Maxiem waterjets feature Intelli-MAX Basic, a control containing the core functionality of Omax's software. The Maxiem machines are slated to be available in these table sizes: Maxiem 1530 at 5 x 10' (1.5 x 3.0 m), Maxiem 1515 at 5 x 5' (1.5 x 1.5 m), the Maxiem 2040 at 6 x 12' (2.0 x 4 m), and Maziem 2030 at 6 x 10' (2 x 3 m).

Omax subscribes to the dual-pump approach to delivering hydraulic horsepower to the cutting jet nozzle. "Horsepower is pressure times flow rate, so we increase the flow rate at the nozzle by using two pumps together," Cheung explains. "Maintenance is much more predictable and manageable, and our software gives us an edge in processing capability."

 

The Maxiem entry-level line of waterjets is wellsuited for the many fab shops and job shops that cut metal, maybe occasionally, do welding, but don't generally require the 0.001" (0.03-mm) accuracy of Omax Jetmachining Centers.

"Waterjet machining today is like EDM machining back in the 1970s when EDM was relatively new," says Steve Szczesniak of MC Machinery Systems Inc. (Wood Dale, IL). "People didn't know a lot about it, but once they saw its capabilities they loved it. That's exactly what is happening with waterjet machining. It's becoming more versatile in cutting complex parts and doing it faster and with greater accuracy," says Szczesniak.

MC Machinery Systems has introduced its new Mitsubishi DX series waterjet, which features 40-mmdiam NSK ballscrews, a stainless side wall tank that is completely separate from the machine frame, crash protection in the X,Y,Z axes, the Mitsubishi 700 Series CNC control, and a redesigned ITC (Intelligent Taper Control) that analyzes the cut and provides taper control without the need for reducing speed. "We want the part to end up with a straight cut. The ITC does a one or two-degree mechanical/pneumatic displacement of the head. The C axis turns to point the jet, depending on the material and thickness of material being cut so that the taper ends up in the scrap, and the part is cut straight," Szcsesniak explains.

"The new five-axis head allows us to turn the C axis 360° and the A axis ±90° for tapering and beveling with some limitations. Obviously when tipping a waterjet more than 45° there is a safety issue that must be taken into consideration," says Szczesniak. "Fixuring is of critical importance in dissipating the energy of the waterjet once the cut process is done and through the material. We offer an indexing/lathe option so that we can do tubing with the five-axis or conventional machine by inserting a sacrificial piece of material on the inside of the tube, so that you don't cut all the way through the tubing."

 

Proactive and Reactive Pump Maintenance

Reliability of pumps has continued to improve across the board. According to Flow International's Tim Fabian, there are two kinds of pumps, crankshaft (direct-drive) and intensifier, each with its own maintenance requirements.   

"These are very different kinds of pumps," Fabian explains. "The crankshaft pump requires proactive maintenance; the intensifier pump requires reactive maintenance. The crankshaft pump runs at much higher rpms. If you let it run too long, it can damage itself. The 60 k psi (414-MPa) crankshaft pump needs rebuild at 500–600 hr. Rebuild time, however, is 2–3 hr.

"Intensifier pumps can run between 600–1500 hr between maintenance cycles and rebuilds. We have sensors built into our machines, heat sensors and temperature sensors in our check valves that let the operator know when the seals are beginning to wear out. With an intensifier pump, you typically have a month or two to react to that alert before it becomes an issue. Rebuild time for the higher-pressure pumps is 1–2 hr."

   

This article was first published in the November 2009 edition of Manufacturing Engineering magazine.


Published Date : 12/1/2009

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