The Prediction of Fluid Flow, Particle In-Flight and Coating Characteristics in Atmospheric Plasma Spraying

Doctoral thesis, 1999

The aim of this thesis is to make a contribution to the development and application of models for the simulation and optimisation of plasma spray processes in production engineering. In particular, focus is placed on the development, combination and application of models for coating deposition and robot motion optimisation, the prediction of coating temperatures during deposit, the simulation of the plasma flow field, and in-flight characteristics of injected particles. Two deposit models to predict coating thickness on complex geometries are presented. These models make it possible to optimise the robot motion with respect to the layer thickness. Plasma jet flow field and plasma-particle interactions are predicted using two different models: by use of an in-house computational fluid dynamic (CFD) code in combination with a model for particle injection, and also by use of a commercial CFD code, the latter which has been adapted to plasma spraying by application programming. The heat transfer between the plasma jet and the workpiece has been predicted using a commercial finite element method (FEM) system. By using various combinations of these models, a number of investigations have been performed to establish connections between spray process parameters, particle in-flight characteristics and coating properties. The model predictions have, whenever possible, been compared with experimental results, and reasonable correlations were obtained, albeit that many effects have not been fully considered in the models. An ultimate goal for research in this field is to produce an off-line simulation tool by which coating properties can be optimised during the design stage and in production. The results of the present work add some pieces to this puzzle, indicating that the models developed may be combined into powerful and cost-effective tools for the evaluation and optimisation of the plasma spray process.