In the past 25 years, we have seen thermal spray processes such as Atmospheric Plasma Spray (APS), High Velocity Oxygen Fuel Spray (HVOF) and Suspension Plasma Spraying (SPS) transition from research and development towards mainstream production technology. Since thermal spraying is a multi-parameter and multi-response process, it is susceptible to process instabilities. Consistency and repeatability are of utmost importance in production lines that spray high volumes of coatings. Since process parameters such as feed rate, particle velocity, temperature, electrode wear and nozzle blockages can dramatically affect the coating properties, monitoring and controlling these parameters can significantly improve the process repeatability. This study presents an improvement in the online process monitoring sensor, the Accuraspray 4.0, to achieve repeatable coatings. The Accuraspray 4.0 introduces a new process stability measurement in order to quantify and control the variability in thermal spray processes and to make process monitoring more production friendly. The sensor includes a stability analysis tool which compares the real-time standard deviations of nominal plume parameters against bench-marked values found using statistical principles. This study details the theory behind the process stability measurement and presents a case study conducted in collaboration with an automotive production facility employing this new feature. It was found that monitoring the standard deviations of parameters being measured can allow the user to control stability in their thermal spray process to spray large volumes with higher confidence in the consistency of their coatings. This upgrade brings the Accuraspray 4.0 one step closer to becoming the industry standard for thermal spray production facilities.

Numerous efforts have been carried out over the years to improve process control in the thermal spray industry. Among those, the need for online monitoring of the thickness of the coating is unquestionable as it leads directly to better uniformity, less powder usage and increased productivity. In 2006, a new technology based on 3D profiling has been adapted to the thermal spraying environment and has shown conclusive results for online real-time monitoring of the thickness of single layers as they were being sprayed. A micron level resolution was achieved independently of the process, the powder and the thermal effects related to thermal spraying. In this paper, we present the latest results from early industrial implementations. New applications of this technology for substrate geometries with increased complexity are also investigated.

In the past ten years, significant progress has been made in the field of advanced sensors for particle and spray plume characterization. However, there are very few commercially available technologies for online characterization of the as-deposited coatings. In particular, coating thickness is one of the most important parameter to monitor and control. Current methods such as destructive tests or direct mechanical measurements can cause significant production downtime. This paper presents a novel approach that enables online, real-time and non-contact measurement of individual spray pass thickness during deposition. Micron-level resolution was achieved on various coatings and substrate materials. The precision has been shown to be independent from surface roughness or thermal expansion. Results obtained on typical HVOF and plasma sprayed coatings are presented. Finally, current fields of application, technical limitations and future developments are discussed.