The Science and Technology of Thermal Spray Coatings
Monday, April 30, 2001 10:30 AM in Room Sunrise
T1-1-1 Diagnostics and Control in the Thermal Spray Process
J.R. Fincke, W.D. Swank, D.C. Haggard, R.L. Bewley (Idaho National Engineering and Environmental Laboratory)
Plasma spraying has been a successful enabling technology in many applications. However, the plasma-spray process features complex plasma-particle interactions that often result in significant process variation that limit process repeatability. This is primarily due to the variations in the particle state that occur run-to-run and during long continuous depositions for large parts. The limited ability to maintain a narrow operating window precludes applications requiring tight control of resulting coating structure, and increases the complexity in developing new process recipes to achieve specific set of coating materials objectives. This paper reports our work on developing real-time diagnostics and control for the plasma spray process that can improve yield and enable the ability to engineer new coating structures with reduced time and cost to market. The strategy is to directly monitor and control those degrees of freedom of the process that determine the resulting coating properties. This includes monitoring of particle velocity and temperature as well as the shape and trajectory of the spray pattern. Diagnostics that have been developed specifically for this purpose are described along with the implementation of closed loop process controllers based on these measurements.
T1-1-3 Two Methodologies for Controlling Thermal Spray Processes
R.A. Neiser, R.C. Dykhuizen, F.W. Spencer (Sandia National Laboratories)
Thermal spray processing is used to fabricate deposits of a wide range of metals, ceramics, polymers, and composites. One of the great advantages of thermal spray technology is its flexibility. For most thermal spray processes a significant number of operating parameters can be adjusted in the search for high-quality deposits. Quickly and efficiently locating a set of spray conditions that yield high-quality deposits in this multi-dimensional parameter space is a challenging problem. Once a set of conditions has been identified, holding the process constant can be difficult. For example, thermal spray devices have a number of hardware components such as nozzles, power leads, and electrodes that are treated as consumables. As they age their performance will drift, ultimately requiring the hardware to be exchanged. Of course, the feedstock materials may differ somewhat from lot to lot, introducing further drifts from the original "optimized" spray conditions. Two approaches have been developed at Sandia to address parameter optimization and process stability. Both methods use sensors to monitor process outputs, namely particle temperature and velocity. The first uses process maps to locate inherently stable regions of parameter space that are forgiving in terms of slight variations in input conditions. The second approach is more complicated. It dynamically adjusts process inputs on a real-time basis to keep a process output constant. As compared to other feedback control schemes, this second method is very general and does not require a significant amount of pre-existing data to work.