Additive Manufacturing (AM) is quickly moving from rapid prototyping to production of highly complex, low volume components. However, AM approaches introduce new challenges related to quality assurance of the mechanical properties and homogeneity of the manufactured parts. A slight variation of the process parameters while manufacturing might lead to the formation of microscale defects and heterogeneities that affect the reliability of the part. Moreover, due to the layer-by-layer building associated with AM, defects may arise during printing that are undetectable without the use of NDT techniques. X-ray Computed Tomography (CT) is commonly used to generate high resolution images to identify defects in AM parts. This approach is useful for accurately studying the internal structure of the part; however, it is expensive when used for ongoing quality control purposes and requires elevated safety precautions. Additionally, thick parts made of heavy metal alloys such as Inconel are difficult to inspect using CT scanning due to their large attenuation of X-rays. To address these issues, ultrasonic NDT is a cost effective and safe alternative for defect detection in additively manufactured parts. Even though the resolution of ultrasonic imaging cannot match that obtained by CT, it is sufficient for detecting flaws for quality control purposes. In this work, we investigate using ultrasonic phased arrays for inspection of parts manufactured by the Selective Laser Melting (SLM) AM technique. SLM involves melting powdered material layer by layer using a laser power source to construct the desired part geometry. We study the defects that can be generated during SLM if the laser power fluctuates from preset values. The nature, size, and distribution of the expected defects were identified by deliberately varying the laser power at specified locations of the AM samples and imaging their internal cross sections using metallurgy techniques. The Finite Element Method (FEM) was used to simulate the propagation of elastic waves in the AM samples and their interaction with the generated defects. The Full Matrix Capture (FMC) method was used to generate the phased array raw time domain signal through FEM simulations. In FMC, each array element is excited separately and the signals from all the array elements are recorded to provide all the possible information about the sample. Several post processing algorithms were implemented to generate images of the defects present in the AM part, and the image quality of each algorithm was compared. The effect of the flaw size, location, distribution and material properties on the constructed image and the detectability of the defect are outlined from FEM simulation results. The results show that ultrasonic imaging could be used to detect common flaws generated in the presence of laser power fluctuation during SLM processing.


Ultrasonic Inspection of Additive Manufactured Components

No proceedings papers in 2020. Video only.

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