In-situ monitoring for liquid metal jetting using a millimeter-wave impedance diagnostic.

This article presents a millimeter-wave diagnostic for the in-situ monitoring of liquid metal jetting additive manufacturing systems. The diagnostic leverages a T-junction waveguide device to monitor impedance changes due to jetted metal droplets in real time. An analytical formulation for the time-domain T-junction operation is presented and supported with a quasi-static full-wave electromagnetic simulation model. The approach is evaluated experimentally with metallic spheres of known diameters ranging from 0.79 to 3.18 mm. It is then demonstrated in a custom drop-on-demand liquid metal jetting system where effective droplet diameters ranging from 0.8 to 1.6 mm are detected. Experimental results demonstrate that this approach can provide information about droplet size, timing, and motion by monitoring a single parameter, the reflection coefficient amplitude at the input port. These results show the promise of the impedance diagnostic as a reliable in-situ characterization method for metal droplets in an advanced manufacturing system.

Inspection of plate weldments through an interposed layer of viscoelastic material using an elastic-electromagnetic scanning method.

In this article, an elastic-microwave based non-destructive evaluation method is presented to inspect for cracks in weldments and thinning of coated steel plates. The approach uses a microwave interferometer operating at 94 GHz to record the total surface displacement of a coated steel plated as it is driven by an incident elastic field. These spatiotemporal data coupled with wavefield processing algorithms provide powerful detection and localization capabilities. From these wavefield data sets, a plate thickness mapping capability has been demonstrated that can detect thickness changes on the order of 0.79 mm (1/32 in.). It is also shown that a topological energy analysis of the wavefield data can detect and locate small flaws on the order of 5-10 mm (0.19-0.40 in.) in the welded joint. Note, all of these results are obtained through a 50.8 mm (2 in.) thick viscoelastic coating without disturbing the coating or the coating bond. At present the algorithm cannot resolve individual flaws within a grid space, just their cumulative effect. Even with the current limitations, this detection approach appears to be a promising alternative to traditional phased array imaging methods where the coating layer must be removed prior to inspection.