Page 30 - MetalForming January 2013

More than Metals—
Waterjet Technology
BY DR. DAVID A. SUMMERS
Wandering the aisles at the recent IMTS and FABTECH trade shows, the booths exhibiting waterjet-cutting technology always seemed to attract quite a crowd. The process creates relatively little noise, so show attendees can still com- municate, and cutting demonstrations often produce the type of show trinkets that attendees enjoy keeping and show- ing off. And, these souvenirs serve as perfect reminders of the capabilities of the waterjet-cutting process.
The introduction of high-pressure waterjet into the metalworking industry was not quite so high tech. Early cutting machines operated at a pressure of around 5000 PSI, effective only for remov- ing the burrs left behind from machin- ing. Compared to using mechanical probes, the waterjet stream could reach into part corners and other difficult-to- clear areas. Modern waterjet-cutting machines, in fact, often can eliminate deburring altogether, by combining water- jet cutting with conventional machining.
The deburring example showcases one of the advantages of high-pressure waterjet cutting: The highly focused force of the jet, when properly placed on the target, cuts without significant damage along either edge of the cut surfaces. An early example of this capa- bility, and a noted commercial success, was the cutting of cardboard. Here, a
Dr. Summers is a Curators’ Professor Emeritus at the Missouri University of Science & Technology, Rolla, MO; 573/341-4111.
Opens Doors
Fig. 1—This test block cut at the Missouri University of Science & Technology shows how waterjet cutting and conventional milling can work together to achieve remarkable results in thick plate. An abrasive jet outlined the final shape of the milled pocket, before a mechanical tool removed the central material. In this way, a very narrow rib (less than 3 mm) around the pocket can be left undistorted by the stresses imposed by the mechanical tool.
waterjet will cut across the sheet with- out crimping the edges, maintaining the strength of the box edge, in contrast to mechanical cutting processes.
Adding abrasive to the waterjet stream allows it to cut through metal- lic workpieces as well as glass and other ceramic materials, leaving cut surfaces unchanged by the cutting process. Compared to thermal- and mechani- cal-cutting processes, waterjet cutting leaves no heat-affected zone, and min- imizes the local stresses induced in thicker material. This minimizes dis- tortion around the cutting path and in the narrow ribs of material left either in
the part or the web. Fabricators partic- ularly appreciate this capability when cutting thicker parts, where an abrasive jet can be used to outline the final shape of a milled pocket, for example, before a mechanical tool removes the central material (Fig. 1). In this way, a very narrow rib around the pocket can be left undistorted by the stresses imposed by the mechanical tool.
Lastly, when cutting parts that will later be fastened, a fabricator can locate and fixture the parts together in their final alignment, and accurately cut fas- tener holes—all in one setup. This avoids the residual burrs that would
28 MetalForming/January 2013
www.metalformingmagazine.com