Process control of particle deposition systems using acoustic and electrical response signals

The implementation of statistical quality control methods for monitoring and control of powder abrasion/deposition is of increasing importance in a manufacturing environment. For the wider adoption of both current and new powder coating technologies, quality control systems need to be developed, which are easily installed, non-invasive and work in real time. This study evaluates the use of a dual electro-acoustic and electrostatic surface-charge measurement technique as means of realising real-time process control. Simultaneous changes in the signals were obtained under both powder flow-on and -off conditions and also for edge detection of the substrate. It was discovered that the most important variables which governed changes in the acoustic response signal were due to variations in the deposition pressure and stand-off distance, whilst those for the electrostatic response signal came from changes in particle size and deposition stand-off distance. A phenomenological predictive equation was developed based on a two-level full factorial design with five variables for both response factors. The coefficients of determination, r2, for the models were 93% and 98%, respectively, with respective χ2 probability values of 99% and 99.5%. This enabled the use of specific limits for any variation of variables amongst those tested to be set up, resulting in the apparatus necessary for the development of a sensitive continuous control system. Examining variations in surface roughness with electrostatic signal was observed to show a linear relationship, decreasing at a rate of 0.19 μm per 0.01 eV, as the effective particle size of Al2O3 was increased.