Quality Control for Advanced Residual Stress Inducing Surface Treatment Processes

Since the inception of production processing of parts for improved fatigue life using laser peening, increasing emphasis has been placed on methods and techniques to assure that the correct stress wave was applied to the part to impart the desired residual compressive stress. There are no reliable NDE techniques which are generally applicable to monitor surface enhancement processes, so it is critical for high value parts to have a high level of real-time process controls and monitors in place. Currently, for laser peening there are several quality control measures in place to ensure the correct laser pulse energy, temporal pulse width, and fluence spatial profile are delivered to the process cell for each location on each part. A higher level of quality assurance can be obtained by employing sensors which detect physical phenomena associated with the actual delivery of the laser peen stress wave. By adding advanced sensors which monitor the laser beam interaction or stress wave generated, the probability of a substandard processed area would be greatly reduced. Several technical approaches to the quality control sensor problem have been investigated in the past and recently some new sensor concepts have been identified for further evaluation in this program.