Eddy current non-destructive testing of metallic 3D printed specimens
Quek, Swee Kiong
Date of Issue2015
School of Mechanical and Aerospace Engineering
The recent boom in three-dimensional printing or addictive manufacturing was mainly due to expired patents and improvement in technologies. This interest many industries, in particular the aerospace industry, as the advantages of addictive manufacturing processes outweigh the advantages of conventional manufacturing processes with cost and time savings as the main push factors. In additional, near full density final products could be created by addictive manufacturing (selective laser melting). Inspection of porosity content present in addictive manufactured product became the utmost importance as this would serve a health indicator for addictive manufacturing processes. Although many researches had been done on both addictive manufacturing and non-destructive testing, none had been conducted on the usage of current non-destructive testing techniques on addictive manufactured products. This report served a stepping stone for porosity inspection by eddy current nondestructive testing technique in addictive manufactured parts. In addition, comparison would be made with X-ray and ultrasonic non-destructive testing techniques to evaluate on the robustness of eddy current non-destructive testing. Furthermore, standard operating procedure for profiling defects by eddy current would be included in this report since there were no established procedures in the industries. Nine specimens were created, using selective laser melting, with different porosity content. The relative densities were measured using density measure kit as an initial step in determining the porosity contents. These specimens were then subjected to conductivity, ultrasonic and X-ray test. The results would be normalised and plotted to determine the reliability of the non-destructive testing techniques. For eddy current, the results obtained were plotted against the conductivity curve in order to derive the conductivity values for the specimens. The results would then be normalised to serve as a comparison between different non-destructive testing techniques. On the other hand, eddy current cone radius and half power analysis would also be conducted to facilitate the formulation of operating procedure for defect profiling. Post-test analyses initially suggested that eddy current topped the porosity level measurement. However, on closer inspection in the delta between different nondestructive testing techniques normalised values and the total weighed sum values; ultrasonic testing produced the best results. Hence, it can be concluded that eddy current testing would ranked second behind ultrasonic testing. This anomaly was due to the depth of penetration between eddy current (limited to skin depth) and ultrasonic (entire height of specimen). The novel discovery of SK sensing zone radius and SK half power procedures could possibly brought about a change in the current eddy current NDT inspection. Current application of eddy current NDT is limited to defect finding. However, with the inclusion of SK procedures, exact profiling could be obtained by using the very same technology. Hence, analogous to ultrasonic codes, the SK procedures could fundamentally enhance the usage of eddy current technique in industrial applications. Since limitations were observed in the conduct of the experiment, it is recommended that further eddy current testing to be conducted on a regular shaped specimens. This would allow the sensing zone to penetrate the entire specimen as opposed to the current setup. Moreover, with entire specimen being properly scanned, the results obtained could be better than those of ultrasonic testing.
Final Year Project (FYP)
Nanyang Technological University