Abrasive waterjets now a viable 3D cutting option

Abrasive waterjet systems have always provided some advantages for parts manufacturers. For one, the high-pressure stream of water and abrasive grit, usually garnet, that is delivered to the workpiece surface can cut through pretty much any material. For another, being a cold process, abrasive waterjetting (AWJ) doesn’t create a heat-affected zone.

But in its initial incarnation, AWJ was no threat to most other cutting methods because it was largely limited to 2D cutting. Ask someone to draw a picture of a waterjet system and chances are he’ll sketch something with a nozzle pointing down at a wide table to cut a flat sheet.

Image courtesy Flow International.

While that’s still the most common setup, waterjet cutting heads are also found on articulated robot arms and gantries for trimming the contours of airplane wings. There are enclosed 5-axis, and even 6-axis, AWJ systems. And even on a traditional setup of a cutting head over a table, that head can cut 60° angles with no taper. AWJ has become a versatile 3D cutting technology.

The Move to Z

A number of technological advancements had to be made in order for AWJ to become a dependable cutting method in the Z-axis, as well as in X and Y. “Out of the gate, getting the needed positional accuracy was the first necessity for the evolution from 1D to 3D cutting,” according to Stephen Bruner, vice president of marketing at OMAX Corp., Kent, Wash. New hardware developments, from the drive systems to the cutting head, were necessary, he noted.

Advancements in controls and software were key in the development of 3D cutting at Jet Edge Inc., St. Michael, Minn., according to Engineering Manager Michael Wheeler. The more axes that need to be coordinated to achieve a cut, the more complex the system becomes, he said. In a 1D cut—typically slitting applications—only one motor is
controlled. In a 2D system, two or three motors, depending on system configuration, need to be coordinated. “However, 5-axis cutting requires coordinating six motors. Our AquaVision Di motion controller has continuously evolved to meet the demands of adding additional axes of motion.”

Advances in cutting head technology were also necessary. One advancement was designing the head so it could automatically and accurately change its angle to cut up to 60°. For example, OMAX’s A-Jet, which was introduced in 2009, is completely programmable and automatic. “Rather than having to manually adjust, cut, adjust again, cut and so on, the user can program and impart more dynamic angling to the cuts,” Bruner said.

WARDJet’s InfiniWinder cutting head has positioning accuracies of ±0.0166°.

Another advancement was making a cutting head that could compensate for taper in the cut, said Brian Sherick, vice president of sales at Flow International Corp., Kent, Wash. As the waterjet cuts, its energy is dissipated, he explained. “It imparts a V-shape to the cut—the top of the cut is thicker than the bottom. The faster one moves the jet, the less time the stream has to remove material.”

About 12 years ago, Flow patented its Dynamic Waterjet XD system, wherein the head compensates for taper by adjusting the angle “in such a way that all of the taper is on the scrap side. The side of the part, the side that matters, has a consistent, clean cut.” The company’s Dynamic Waterjet XD is the 5-axis version of this taper-compensation technology.

The advantages of 3D AWJ are many. Jet Edge’s Wheeler said the biggest benefit is versatility. “With a traditional 2D abrasive waterjet, every part cut is a flat shape out of flat stock. With 3D abrasive waterjet, parts can be cut from
variable-thickness stock and be given diverse geometry.” Wheeler added that chamfers, countersinks and other features traditionally created by a secondary process can often be cut with a 3D waterjet.

Jeff Day, senior applications engineer at WARDJet, Tallmadge, Ohio, said applications benefitting from 3D AWJ include general fabrication tasks, such as weld preps and countersinks, and tube and pipe cutting—achieved with systems that have a rotary axis. “Aerospace suppliers also use it to minimize the machining of expensive materials,” he noted. “Scrap material in the form of chunks are more valuable than chips.”

Continuous Improvement

The advancements that make 3D AWJ possible have all been in place for years. If you haven’t taken a look at a 3D waterjet system recently, however, you’ll be surprised at how much and in how many ways the systems have improved.

“If someone last looked at waterjet 10 years ago and came in for a demonstration today, they would see a much more refined, proven, reliable and predictable process,” asserted Flow’s Sherick.

WARDJet’s Day said the accuracy and repeatability of 5-axis cutting has improved over the past decade because of improvements in motion controls—including their higher data-processing speeds—and software that compensates for inaccuracies. “Programming 5-axis parts has become easier because of the ability to program paths from imported 3D models,” he said.

Wheeler concurred. “Early 3D waterjet cutting was more 2.5D. It was used mostly for adding chamfers or controlling taper. As software has improved, complex paths have become significantly easier to program.”