Erosion characteristics of water droplet machining

Abstract

Water Droplet Machining (WDM) is a new manufacturing process, which uses a series of high-velocity, pure-water droplets to impact and erode solid workpieces, for the purpose of through-cutting, milling and surface profiling. The process is conducted within a vacuum environment to suppress aerodynamic drag and atomization of the waterjet and droplet train. This preserves droplet momentum and allows for a more efficient transfer of energy between the water and workpiece, than in standard atmospheric pressure. As a new manufacturing technique, parameter-specific details and characteristics of this process are absent from the scientific literature. Therefore, this study aims to elucidate the capabilities of WDM, and uncover its erosion characteristics. Experiments are performed using a custom-fabricated machine, where a range of waterjet-types (and droplet trains) are produced. The experiments are performed on two industrial-relevant metals: stainless steel SS 316 L and aluminum AA 6022-T4. The target shape is a partial-cut through the material, i.e., a trench. A parametric study investigates the effects of stand-off distance, orifice diameter, and feed-rate on the trench shape, material-removal-rate, and reveals the conditions which render WDM an effective machining process. It was found that, for orifice diameters of 100 μm, an effective stand-off distance is between 457 and 686 mm; below that, no material removal is observed. In this configuration, accurate through-cuts are produced and can be used for manufacturing purposes. For large orifice diameters, e.g., 250 μm, an atomized spray is produced, which features a comparatively large material removal rate, and can be used for surface profiling and milling.