Laser Induced Phased Arrays (LIPA) to detect nested features in additively manufactured components

Don Pieris,Theodosia Stratoudaki,Yashar Javadi,Peter Lukacs,Sam Catchpole-Smith,Paul D Wilcox,Adam Clare,Matt Clark

doi:10.1016/j.matdes.2019.108412

Don Pieris, Theodosia Stratoudaki + Show 6 more

Open Access

https://doi.org/10.1016/j.matdes.2019.108412

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Abstract

Additive manufacturing (AM) has the capability to build complex parts with internal features, which have many advantages over conventionally manufactured parts. This makes AM an alternative for advanced manufacturing sectors. AM components suffer from defects due to the lack of understanding in the build process. This makes the adaptation of AM in safety-critical industries, such as aerospace, problematic. The current AM work flow calls for costly off-line inspections to qualify components as defect-free. The layer by layer nature of the AM provides an opportunity for an on-line inspection to take place. This can provide early detection of defects as well as information for optimization and repair of the build. Laser Induced Phased Arrays (LIPA) present themselves as a viable remote, non-destructive, ultrasonic technique capable of being implemented as part of an on-line inspection of AM. Lasers are used to generate and detect ultrasound and a phased array is synthesized in post-processing. This paper demonstrates the capability of LIPA to successfully detect and locate features within AM components off-line. Cylindrical features as small as 0.2 mm in diameter and 26 mm above the inspection surface were detected using LIPA and verified using X-ray computed tomography (XCT).

Highlights

IntroductionEt al / Materials and Design 187 (2020) 108412 nested features and complex external geometry
Prior to the application of the total focusing method (TFM) imaging algorithm, a digital band-pass filter was applied in the frequency domain in order to maximize the signal to noise ratio (SNR) and for the case shown in Fig. 5, a band-pass filter centered at 3 MHz with 100% bandwidth, at −40 dB was used
Since D6 and D4 are of similar size and internal structure and the same is true for D5 and D3, it is an indication that the low sensitivity of the shear wave in the region where D4 and D5 are located, is more significant reason for the low ultrasonic signal observed in Fig. 5 than the internal roughness and backfilling of these features

Summary

Introduction

Et al / Materials and Design 187 (2020) 108412 nested features and complex external geometry. The strength, stiffness and density of these parts can be tailored to the application using various infill patterns. AM processes such as powder bed fusion (PBF) have the capability to manufacture components which could not be produced using conventional methods such as milling and casting [2] and in-process repair of defects found on or close to the built surface may be possible [3]

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