Laser Ultrasonic inspection of a Wire + Arc Additive Manufactured (WAAM) sample with artificial defects

Certain defects like pores, incomplete fusion and micro cracks are sometimes inevitable in Wire + Arc Additive Manufactured (WAAM) components. However, these defects cannot be detected easily by conventional ultrasonic testing due to the rough surface and high temperature of WAAM components. In this paper, a Laser Ultrasonic (LU) system, consist of a pulsed laser and a laser interferometer, is employed to achieve non-contact inspection of artificial defects (crack, flat bottom hole and through hole) in a WAAM sample without surface machining. First, several WAAM samples with different welding parameters are manufactured by a robotic Gas Metal Arc Manufacture (GMAW) system. The 2D profiles of these samples are measured and reconstructed by a geometric optical measuring instrument for Finite Element (FE) analysis. Then, the multi-physics (Heat Transfer, Solid Mechanics, Pressure Acoustics) coupled FE model is established to simulate LU inspection of defects in the WAAM sample. The propagation of laser ultrasonic waves in the WAAM sample, as well as the mechanism of interaction between ultrasonic waves and defects is investigated numerically. In addition, LU inspection experiments are designed and conducted to obtain the A- and B-scan plots of different defects in the WAAM sample. Finally, quantitative inspection of the artificial defects is realized by analyzing the A- and B-scan plots. This paper verifies the feasibility of LU inspection of WAAM components without surface machining.