Laser photothermal non-destructive inspection method for hairline crack detection in unsintered automotive parts: A statistical approach

A statistical non-contacting and non-intrusive method for revealing the presence of cracks in unsintered (green) parts manufactured by powder metallurgy (PM) technology was developed based on photothermal radiometry (PTR). The technique relies on the interaction of a modulated laser-generated thermal wave with the crack resulting in change of amplitude and phase of the detected signal. The crack existence at points in high stress regions of a group of green sprockets was evaluated through the proposed method. The results were validated by an independent destructive technique—microscope observation of the tested green sprockets following sintering, sectioning, and polishing at the locations where signal changes were observed in the green state. Statistical analysis confirmed the excellent sensitivity (91%) of the method in detecting the presence of hairline (∼5–10 μm) cracks. This PTR diagnostic technique may lead to a simple and reliable on-line inspection methodology in high-stress locations of PM manufactured industrial steel products. Ultimately, the method can be developed for non-destructive quality and feedback control of the metal forming process of green automotive parts.