Freeform waterjetting

In contrast to cutting through materials with abrasive waterjets, abrasive waterjet milling uses high-energy fluid jets to produce complex, freeform surface features on parts by controlling the jet penetration depth. However, waterjet milling relies on craftsmanship, or a trial-and-error approach, in which users need to do significant development work to identify optimal operating parameters followed by extensive part-quality analysis, according to Dragos Axinte, a professor of manufacturing engineering at the U.K.-based University of Nottingham. 

Images courtesy of University of Nottingham

Using the ConforM²-Jet control, a freeform surface on a Ti6Al4V workpiece is efficiently abrasive waterjet milled without human intervention.

To improve process capability, the university’s Machining and Condition Monitoring Research Team is leading a European project to develop a self-learning control system, called ConforM²-Jet. “Self-learning methodologies are increasingly used to search for optimal solutions of complex systems when experimental data is available,” Axinte said. “The self-learning ability of the ConforM²-Jet controller will increase the robustness and efficiency of high-energy, fluid-jet milling production systems. At the end of the project, we will have produced the software and a control system to completely automate abrasive waterjet milling and hence take it out of the craftsmanship remit.”

Axinte explained that the controller is highly accurate because it uses calibrated mathematical models of the material-removal and process-monitoring techniques that allow corrections during waterjet milling without human intervention. The models are used to develop the predictive controller, which is supported with CAM software developed to generate the theoretical jet-plume path for a particular part. 

The jet path is then transferred to the self-adaptive model, which also receives real-time sensorial information that indicates the status of the abraded footprint, or depth of removed material. An acoustic emission sensor mounted on the workpiece monitors the input jet energy that erodes the surface to help calculate the area of the abraded waterjet footprint, Axinte added.

“Based on this information, the self-adaptive module makes the necessary adjustments to key process variables, such as jet feed speed,” he said, “thus, bringing the abrasive waterjet milling process to the required performance level.”

The researchers have only applied garnet abrasive in the waterjet, but Axinte noted the “universal” system allows the use of other abrasives, such as aluminum oxide and silicon oxide, when processing harder materials, such as engineered ceramics.

The ConforM²-Jet consortium plans to license or commercialize the system.

For more information, contact the University of Nottingham at +44 115-951-4013 or www.nottingham.ac.uk.