Date of Award

Spring 2022

Project Type

Dissertation

Program or Major

Mechanical Engineering

Degree Name

Doctor of Philosophy

First Advisor

Brad BLK Kinsey

Second Advisor

Joseph JCK Klewicki

Third Advisor

Jinjin JH Ha

Abstract

Water Droplet Machining (WDM) is a new manufacturing process, which uses a series of high-velocity, pure-water droplets to impact and erode metal 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 stream. 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. Furthermore, the erosion mechanisms involved in droplet-solid interactions are not well-understood. Therefore, this research aims to elucidate the capabilities of WDM, and uncover the mechanics involved in droplet impact. This is done by investigating the force imparted by liquid droplets across a wide range of impact parameters, where a novel force model is developed for inertial-dominated impacts. A force comparison is made between continuous jet and droplet train impacts, where the findings show that a droplet train has a higher erosive potential than its continuous jet counterpart, owing to the higher forces exerted by individual droplets. In addition, the stress state inside of a material subject to a Hertzian contact, which is connected to this research as it emulates the axisymmetric nature of a droplet-like loading, is explored using integrated photoelasticity. Finally, the process parameters and erosion characteristics of WDM are investigated using a custom-fabricated machine, where a range of waterjet-types (and droplet trains) are produced. The industrial efficacy of this process is evaluated by manufacturing a diverse array of engineering materials.

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