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Variations of Waterjet: Robotic and Abrasive

 Ellen Kehoe








By Ellen Kehoe
Senior Editor

No sooner had waterjet cutting gone mainstream did someone think of adding an abrasive to the water flow and integrating a robot into the system. From SME Technical PaperTP85PUB248: "High pressure waterjet machines capable of cutting relatively soft materials such as paper, cloth, wood, and fiberglass can now cut ceramics, metal composites, and tough metals such as Inconel and titanium because of a recent design innovation which induces abrasive grit into the water jet." 

The first commercially operational abrasive waterjet (hydrobrasive) application was in the mid-1980s at a Rockwell International plant for cutting titanium parts for the B1-B bomber. "Compared with conventional techniques, it is estimated that 50% cost savings were realized. The operation ran 24 hour days, accumulating 8000 hours in a year and a half." Diameter turning by abrasive waterjet (M. Hashish, TP04PUB277).

For cutting everything from baby diapers to granola bars, among the variety of abrasive waterjet nozzles are single jet, multiple jet and annular jet. The abrasive can be introduced by external mixing, an abrasive layer or a direct pump. The hydrobrasive process also involves hydraulic, abrasive, mixing and cutting parameters and cutting results. 

One tutorial-style paper compares abrasive waterjet (AWJ) to other commonly used techniques for the machining of advanced materials in linear cutting, turning, milling, drilling or wafer cutting. Although solid tool machining, laser cutting, ultrasonic machining, electrical discharge machining and waterjet are often complementary and have advantages for certain materials and applications, AWJ offers unique combined features. AWJ is suitable for many operations, can machine very soft and very hard materials, can machine multimaterial composites selectively, can cut stacks of different materials, has high material removal rates, can machine omnidirectionally, requires no heavy clamping for workpieces and no direct hard contact with the workpiece, and is ideal for automation, robotics and remote control.


A Deeper Dive

Other papers examine AWJ cutting hardware components and optimization of parameters. As techniques matured, the need for nozzle wear sensing, velocity control and machine vision component monitoring emerged. 

Water usage and water treatment, including filtration, softening, deionization and reverse osmosis, are topics covered in a paper by a real "Culligan man." "All water is not alike.… Every water supply has something in it besides two parts hydrogen and one part oxygen.… The two major types of contaminants that cause problems for waterjet cutting are particulate matter (sediment) and the total dissolved solids, primarily calcium and magnesium." Particulate matter causes rapid orifice wear; dissolved solids clog orifices, making them inefficient. 

A study on deep hole metal boring with abrasive waterjets was presented at the 1996 North American Manufacturing Research Conference (NAMRC), with experimental simulation and drilling tests to validate the selected concepts and determine specific parameters, strategies and techniques to incorporate in a drill head design.Abrasive waterjet mixing chamber and nozzle (C.L. Holland, TP85PUB248).

Another NAMRC paper introduced a hybrid laser/waterjet cutting process for brittle materials. The proposed mechanism offered potential benefits such as reduced energy, increasing cutting speed, improved accuracy and finish and controlled depth and shape. The same Iowa State University authors presented CO2 laser/waterjet cutting of polycrystalline cubic boron nitride a later NAMRC. Waterjet-guided laser cutting is described by Synova SA authors as a powerful hybrid technology for fine cutting and grooving

Several papers from SME's peer-reviewed journals discuss waterjet techniques. Among the topics are surface texture in abrasive waterjet cutting, the effect of abrasive-cut edges on formability and fatigue performance of high-strength steels, micromachining fine features with waterjet and aggregate notch cavity formation on abrasive-cut surfaces.


Robotic Systems

Many of the installations mentioned in the above papers incorporate robots. The combination of CAD programming, computer-aided scheduling and a multiaxis robotic gantry with an ultra high pressure waterjet cutting system greatly broadened the definition of "flexible." 

In several additional papers, the practical aspects of robotic waterjet processes are discussed for: large machining cells, a waterjet/hydrobrasive near-net shaping system, flexible systems, CAD/CAM programming for cutting insulation and gasket material for air handling products, a pierce-trim-stack operation for truck gas tank shields and cutting composite
aerostructure components

Published Date : 2/12/2015

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