While it''s easy to relate to a burst of propelled water cutting through and dousing the flames of California''s wildfires, it takes a bit more imagination to visualize water cutting through a 6 in. chunk of steel.
According to Calypso Waterjet Systems, Dallas, TX, the process of waterjet cutting is actually rather simple with its line of Shark waterjet cutters. Exerting a water pressure of 60,000 psi, these waterjet systems provide smooth, precise cutting of a wide range of soft and hard, thin and thick, stacked or non-stacked materials. And, because no heat and no work-induced stress is incurred in the cutting process, almost any material can be cut, including paper, foam, carpet, plastics, ceramics, glass, hardened tool steel, marble, and granite. Just about the only exceptions are carbide and tempered glass.
The water is pressurized to 60,000 psi by hydraulic intensification, and then forced through a small orifice in the cutting head. Inside a mixing tube, abrasive material such as garnet (high-grade sand) is mixed with the high-pressure water, creating an abrasive waterjet stream that exits the nozzle at about 1.5 times the speed of sound.
Through a combination of microerosion or grinding and a shear yielding of the material, a narrow section of material, called the kerf, is removed all the way through the thickness. Since no chemicals, gases, or noxious liquids are used, the operation is environmentally safe and clean.
According to Richard Carey, senior engineer at Calypso, the primary challenge with waterjet cutting systems is that they tend to be flexible tools, making accurate waterjet cutting more difficult to attain when cutting circles and arcs as compared to cutting straight lines. Consequently, there is a need to compensate for this flexibility by adjusting and controlling acceleration and velocities, something that Calypso tried but could not do with G-code controllers.
As a result, Calypso turned to Galil''s 6-axis DMC-2163 Ethernet motion controller with circular interpolation and the ability to compensate for mechanical backlash. With the Galil controller, the Shark waterjet system can traverse over 500 inches per minute and achieve cut accuracies of ±0.003 in. tolerance or better.
Accuracy is further ensured with Calypso''s proprietary, easy-to-use software, which eliminates programming and includes a Feedrate Calculator that automatically determines the compensation required. Operators can simply upload a drawing with the cutting parameters and then click the screen to start or stop the process. They can also choose the material and nozzle size, and then let the software calculate the compensation, making very accurate cuts. This is an exclusive benefit to Calypso''s Shark waterjet cutting systems.
"The Galil controller and its autotuning capability provided the much tighter servo loops and responsiveness necessary to get the quality, crisp circle and arc cuts required," says Carey. "This allows us to run gantries with higher accelerations and velocities."
To accomplish the precise waterjet cuts, Calypso runs a large amount of code through the Galil DMC-2163 Ethernet motion controller, most of which is devoted to a streaming interpreter that allows Calypso to make use of Galil''s powerful trip points. These are needed to perform the coordination of single-axis and vector motion, all of which requires very complex tool sequencing.
"Galil designed the 32-bit microprocessor-based DMC-2163 multiaxis Ethernet controller for such cost- and space-sensitive applications as the Calypso waterjet systems," says Lisa Wade, vp-marketing and sales for Galil Motion Control. "Typically half the price and half the size of box-level Ethernet controllers, the card-level DMC-2163 measures just 4.25 in. x 10.75 in., and can be easily programmed by Calypso for various modes of motion using our simple, two-letter intuitive commands. Plus, the connector option on this controller simplified the interfacing, providing another cost-savings."
Essentially, Calypso''s cutting systems are delivered in two versions -- an integrated cutting table that can be installed quickly and easily without overhead cranes, or a larger area work machine with a separate water table. Their design allows the operator to feed material from all sides, providing more area for cutting. Additionally, material is cut on the surface of the table so that the operator can easily view the process.
"Other machines often have material sitting below table in a pool of water to dampen noise, which makes parts hard to see and decreases productivity," explained Carey.
The Shark systems come in multiple sizes, from the Shark 4 x 4 ft to the Shark LWA 9 x 40 ft table. Most are available in dual- as well as single-head mode. All use the Calypso control system, incorporating Galil''s DMC-2163 Ethernet motion control card.