Powder Bed Fusion (PBF) metal 3D printing has matured from a prototyping technology to become an option when producing functional, lightweight, or highly complex parts e.g., in the aerospace and biomedical industry. In this process, energy from an electron beam or a laser beam selectively melts metallic powder layers while consolidating the part. Powder (tiny particles between 15 μm to 60 μm) is confined within a working bed, once a layer is consolidated, the build platform sinks, a new powder layer is recoated, and the process is repeated. The challenge has now shifted to the process qualification and the required Quality Control (QC). QC has been tried during production with different sensing approaches, to gather layer-wise process signatures allowing the indirect assessment of defective conditions.
Taking advantage of the electrical conductivity difference between powder and consolidated metal, Eddy Current Testing (ECT) has been proposed for the direct assessment of relevant PBF defective conditions. Contactless layer-by-layer imaging was demonstrated with ECT sensor array probes installed on the machinery recoater. This experimentally demonstrated ability brings important benefits, potentially shared with other Electromagnetic (EM) methods. Other EM methods and operations at different Radio‑Frequency (RF) spectrum may provide potentially relevant and complementary data to ECT. In parallel, Deep Learning (DL) has brought new possibilities to the inversion of EM multi-method data.
EMLAYERING is an exploratory R&D project running at the Instrumentation and Measurement Group at Instituto de Telecomunicações, Lisbon. This project aims at revealing the full potential of EM testing for the PBF layer-wise QC by: exploring different contactless EM methods to complement ECT; proposing EM multi-method array probes with high spatial resolution; leveraging DL for detection and characterization of defective conditions. The goal is to attain the scientific knowledge on EM multi-method NDT needed to demonstrate high-resolution EM multi-method array probes and DL combined potential for the PBF layer‑wise QC.
This research initiative counts with the expertise in Materials and Mechanical Engineering from the Non‑Destructive Testing Laboratory of the Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa (https://sites.fct.unl.pt/labndt-demi) and in Physics Engineering and Microfabrication from the Instituto de Engenharia de Sistemas e Computadores - Microsistemas e Nanotecnologias (https://sites.google.com/site/inescmn/home).
Recently, we have been working on the scalability of ECT array probes to increase the number of sensors and therefore the achieved spatial resolution. Different approaches explored commercially available surface-mounted technology coils as sensor elements and minimalist electronic signal generation and demodulation profiting from microcontrollers' advanced mixed-signal peripherals. An array probe with 16 sensor coils with 5 mm pitch was materialized together with the full digital readout electronics within an 80 mm by 40 mm printed circuit board area. Preliminary results in PBF samples are being gathered.
More info about this project: https://www.it.pt/AutomaticPage?id=3486