Waterjet cutting is an erosive process that uses high-pressure water to cut through various materials to create 2D shapes such as foam and rubber gaskets and to cut products such as foods, textiles, etc. Combined with an abrasive, waterjet cutting is used to cut hard materials such as steel, aluminum, laminated glass, stone, ceramic, etc. The machines offer alternatives to other methods such as EDM (another erosive process), plasma or laser cutting, as well as traditional techniques such as milling and punching. A primary advantage of waterjet cutting over some other operations is that it adds no heat to the material during the process, minimizing the need for post-cutting heat treatment. This makes it especially useful for aircraft parts. For information about other manufacturing processes please refer to our Types of Manufacturing article.
Fundamentals
Most waterjet systems use a computer-controlled X-Y traversing system to move the waterjet nozzle over the workpiece according to CNC instructions. The head can be attached with an articulating arm to allow for bevel cuts. Fixed heads can be used too for slitting operations where the workpiece itself moves. The workpiece is sometimes immersed in a water pool to reduce noise and mess. Systems are available that combine water and abrasive cutting (for hard materials) and as water-only systems (for soft goods). For abrasive cutting, a jeweled orifice reduces wear of the nozzle.
Waterjet cutting can produce high-quality cuts with inch tolerances in the half-a-thousandth range possible. Stainless steel thicknesses of as much as 10 in. are reportedly cuttable. The key to water jet cutting is the existence of high-pressure pumps, either hydraulic intensifiers or motor-driven triplex pumps, to deliver pressures in the 60,000 psi range. For hard materials, typically round or sharp-edged abrasives are used, which are mixed with the waterjet through a venturi. A typical system will consume about 100 lb. of abrasive during a two-hour cutting period.
Applications
Water-only cutting has many applications in cutting soft materials. It provides a clean, wear-free method for cutting food products from meats to vegetables. In cutting other soft materials such as foam and rubber, the process lends itself to stacking of multiple sheets and single-line cutting. It is useful for a single item and low-volume prototyping of gaskets and the like. The method can be used for cutting Styrofoam, laminations, leather, cardboard, vinyl, etc. It is used in converting operations as a method of minimizing dust.
Harder materials rely on abrasives in the waterjet – usually garnet, which is available in various mesh sizes. For thin sections under 3mm or so, the water-abrasive mix produces a straight-walled cut and edges turn out perpendicular with faces. As sections become thicker, part edges begin to undercut due to the fanning out of the water stream. This can be controlled somewhat by tilting the cutter so that the fanning edge is biased toward the scrap side of the cut. Single-line cutting is possible, especially with the absence of any heat-affected zones, and particularly for thin sections.
Although the waterjet leaves a small kerf, the stream still has a radius to it, making sharp inside corners unobtainable. For piercing, the water jet starts with an initial higher-pressure punch which produces a slight crater or indentation at the surface. Waterjet cutting is foremost a through-cut process, and though it can be used for etching there is not as much ability to control for the depth of cut as there is with milling.
Waterjet cutting is considered a clean process as there is no burning. It is also clean in the sense that it produces no swarth along the cut edges. It does carry the concern of consumables and their disposal when abrasives are used. Abrasives can be reclaimed and reused to an extent. Water quality plays a part in the proper functioning of a waterjet system as well. Unlike plasma cutting, which works only for electrically conductive materials, waterjet cutting can process many material types. Also unlike plasma cutting, it is not available as a handheld, portable device, making it a better fit for in-shop production rather than for field work. Although waterjet cutting is capable of making high definition cuts, it is an order of magnitude less accurate than EDM, albeit ten times faster. Waterjet and laser cutting are about equal in their abilities to produce fine detail, with plasma cutting less so but reportedly making progress in this area. As thicknesses grow much beyond 2 in., waterjet cutting is the most effective of the non-traditional metal cutting processes.
Waterjet machines are available in a variety of sizes from small-format cutters in the typically 2 x 4 ft. cutting area range to large-format machines with widths as great as 10 ft. and lengths up to 50 ft.
Operation
CNC programming for waterjet cutting is claimed to be straightforward and many manufacturers offer systems that import CAD files into manufacturing software which, in turn, creates G-code for the cutter. Feed rates for many standard materials and thicknesses are generated automatically. Although most systems rely on X-Y motion and vertical adjustment of the waterjet nozzle, 5-axis systems are available.
Services
Many job shops and fabrication facilities select waterjet cutting as a primary tool for its ability to handle a wide range of materials. Likewise, cutting services providers often have access to all non-traditional cutting forms and so can offer the technology most advantageous to any given job. Some equipment vendors sell waterjet, plasma, and laser cutting equipment with the idea that these are somewhat complementary, and not necessarily competing, technologies.
Summary
This article presented a brief discussion of waterjet cutting services including the fundamentals of the operation and how it compares to similar cutting technologies. For more information on other products.
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