Monitoring of Argon plasma in a coating manufacturing process by utilising IR imaging techniques: Thermal spray monitoring

Atmospheric plasma spray is a complex multivariable manufacturing process used in a wide range of industries. Deviations in the process parameters have been shown to affect the coating quality. Currently, the quality analysis is performed at the end of the process rather than checking for defects during the process. However, monitoring for these deviations during a coating process is difficult due to environmental hazards such as UV radiation, dusty environment, and excessive noise generation. A commercially available thermal imaging camera was integrated into this space to directly monitor the atmospheric plasma heat distribution and its influence on the in-flight particle trajectories during spraying. A novel metric called asymmetric angle is proposed to monitor the asymmetry of the plasma heat distribution. This is an important metric as a symmetric heat distribution is required to heat all the particles adequately to form a good quality coating. Further metrics of Gaussian Aspect Ratio (GAR) and contour area were found to have a relationship with the plasma gas flow rate and are discussed. The spray angle of the material is also tracked by fitting a 1D line to the regional Shannon entropy of the thermal image. The limitations of these metrics are discussed with possible avenues of further investigation.