Drop-on-Demand additive manufacturing could offer a facile solution for scalable on-site manufacturing. With an increasing number of functional materials available for this technology, there are growing opportunities for applications, such as electronics. Here we report on a novel printing strategy, Off-the-Grid (OtG), which enables refined positioning of individual droplets and enhanced resolution compared to the traditional printing strategy. We demonstrate successful printing of structures with feature position control smaller than a single droplet size, and hence enhanced shape fidelity for intricate designs. This strategy is extended to filled patterns, enabling improved layer coverage and customisable inter-layer droplet positioning to control surface morphology. The OtG strategy is applied to produce functional designs, such as conformable circuitry and miniaturized antennae, and is transferable to different materials, from metal nanoparticle and polymeric inks on inkjet platforms, to molten metals on a MetalJet printer. These results could advance exploitation of AM in electronics, wearable electronics, medical devices, and metamaterials.

This work discusses the implementation of a novel technique for simultaneous 3D particle tracking velocimetry and dual-wavelength pyrometry of spatter particles ejected during the Laser-Powder Bed Fusion (L-PBF) process using a single high-speed spectral plenoptic camera. In this methodology, particle tracking uses the Light-Field Ray Bundling algorithm paired with a four-frame best estimate track initiation with 3D Kalman filter for tracking to generate high-resolution, time-resolved 3D tracks of spatter particles. Utilizing the same light-field image data, spatter particle temperature is measured using dual-wavelength pyrometry that calculates temperature from the ratio of two narrow-band wavelength intensities. Preliminary results demonstrate the viability and potential of this technique for the L-PBF processes on the example of a turnaround laser scan. The temperature measurements indicate that the detected particles are in the liquid phase, with temperatures greater than 1950 °C. The simultaneous measurements demonstrate an overall deceleration and cooling of particles during their flight.

3D hybrid additive manufacturing describes the combined application of different additive manufacturing processes in order to manufacture a component with almost unlimited design freedom and free choice of materials. One challenge in the hybrid additive manufacturing lies in the different conditions of individual additive manufacturing processes. For example, in the combined application of the laser powder bed fusion (PBF-LB) of metals with the fused filament fabrication (FFF) of polymers, damage can occur in the plastic due to the higher processing temperatures of PBF-LB. Therefore, in this work a process strategy for the buildup of metallic structures in the PBF-LB process on polymer base structures was developed. By reducing the laser energy density in combination with increasing the height of the first layer, a processing window could be identified. The built hybrid components were investigated with micro-computed tomography and the effects of different processing parameters on the interface between the polymer and metal part are discussed. Finally, a strategy to increase the strength of the interface is presented.

Keyhole pore formation is one of the most detrimental subsurface defects in the laser metal additive manufacturing process. However, effective ways to mitigate keyhole pore formation beyond tuning laser processing conditions during keyhole mode laser melting are still lacking. Here we report a novel approach to mitigate keyhole pore formation during laser powder bed fusion (LPBF) process by using stable nanoparticles. The critical keyhole depth for keyhole pore generation (i.e., the largest keyhole depth without keyhole pore formation) during LPBF of Al6061 increases from 246 µm to 454 µm (85% increase) after adding TiC nanoparticles. In-depth x-ray imaging studies and thermo-fluid dynamics simulation enable us to identify that two mechanisms work together to mitigate keyhole pore generation: (1) adding nanoparticles prevents the keyhole from collapsing by increasing the liquid viscosity to impede the protrusion development; (2) adding nanoparticles slows down the keyhole pore movement by increasing the liquid viscosity, resulting in the recapturing of the pore by the keyhole. We further demonstrate that adding TiC nanoparticles can also eliminate the keyhole fluctuation induced keyhole pore during LPBF of Al6061. Our research provides a potential way to mitigate keyhole pore formation for defect lean metal additive manufacturing.