Mathematical modelling of abrasive waterjet footprints for arbitrarily moving jets: Part II - Overlapped single and multiple straight paths

Controlled-depth abrasive waterjet machining (milling) is considered as a niche technology, capable of generating complex geometries in any material regardless of its properties. The key enabler of waterjet milling is the development of a model for predicting the jet footprint. The authors' previous work reported on a geometrical model for a single footprint of a free-moving jet for various impingement angles upon the target surface. Firstly, the present work identifies ways to make the single jet footprint models accurate for low jet impingement angles that are likely to occur when footprints are overlapped. Then, the paper presents for the first time a validated model that predicts the surface micro-geometry for overlapped footprints (jet with step-over movement), and an analysis of error propagation for predicting the material removed in successive layers. The modelling approach has proved its validity by being able to predict the surfaces obtained from single and multiple (i.e. layered) overlapped footprints with low errors, i.e. <6% and <9% respectively. The importance of the development of the model (dependent on feed velocity, tilt angle and stepover of the jet) for surface micro-geometry resulting from overlapped jet footprints research resides in (i) ability to simulate real controlled-depth waterjet machining when jet kinematics follows a raster path; (ii) it opens up the possibility of generating complex part geometries by adjusting the trajectory and velocity of the jet and thus the development of accurate and flexible CAM software for waterjet milling to support this technology.