For a metals fabrication shop looking to achieve greater accuracy and improved production flow, the ability of waterjet machining to help minimize additional processing to a single operation can be a boon. One company that learned that recently for itself is Petersen Inc. of Ogden, Utah.

The operation carries out fabrication, machining, assembly, and engineering services for customers in the nuclear, aerospace, petrochemical, mining, and general industrial areas. "We are a job shop,” says Bart Anderson, manufacturing engineer. “Most projects are low to medium volume and every job is different in size and quantity."

Petersen now uses waterjet machining on massive workpieces many feet in length.Petersen now uses waterjet machining on massive workpieces many feet in length.Part sizes vary from a few inches in length up to mining industry components that measure 60-80 feet. Individual workpieces typically weigh from a few hundred to more than 5,000 pounds.

But a consistent recent trend has been increasingly stringent tolerance demands. As such a contributor to greater accuracy and improved production flow has been abrasive waterjet machining technology. The company uses waterjet cutting as a bridge between traditional plate cutting methods and precision machining operations.

"We use waterjets in all the industries we service to minimize the amount of additional processing," says Anderson. "Where parts cut on other equipment often require further processing, such as grinding or machining, to reach final tolerance, waterjetting often enables us to achieve that tolerance in a single operation."

The company's initial foray into the use of the technology came when it acquired a preowned OMAX 55100 JetMachining Center with a 4ft7in by 8ft4in cutting envelope. Previously, the shop conducted plate and shape cutting via a CNC burn table with oxyacetylene torch and plasma cutting capabilities. But Petersen's experience with the machine led it to buy two further machines directly from OMAX – a 120X JetMachining Center and most recently an OMAX 160X JetMachining Center.

That first machine was initially used only for smaller parts, but that changed with a job that involved fabricating a storage cask for spent nuclear fuel. The workpiece material was high-strength ASTM A537 carbon steel and the finished plate was 14-feet long, 0.312in thick and weighed 150lbs.

Customer requirements called for the plate to be bent 90 degrees after having slots cut in it, but the plasma process created a heat-affected zone along the edge of the cut line, leading to problems. Machining the slots after the bending operation would have required additional set-ups and transfers. So Petersen opted to try waterjet cutting.

"We improved our results drastically, almost an order of magnitude for cutting accuracy,” says Anderson. “We achieved tolerances between 0.010-0.020in - close to a normal machining tolerance on a fabricated 14ft long part."

The increased accuracy enabled the shop to eliminate post-cutting operations and to cut features in the flat pattern that plasma cutting was unable to accurately produce. Waterjet cutting has now replaced the plasma process on approximately 25% of the shop's other projects.

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