Macro-, meso- and microstructural characterization of metallic lattice structures manufactured by additive manufacturing assisted investment casting

Abstract

Cellular materials are recognized for their high specific mechanical properties, making them desirable in ultra-lightweight applications. Periodic lattices have tunable properties and may be manufactured by metallic additive manufacturing (AM) techniques. However, AM can lead to issues with un-melted powder, macro/micro porosity, dimensional control and heterogeneous microstructures. This study overcomes these problems through a novel technique, combining additive manufacturing and investment casting to produce detailed investment cast lattice structures. Fused filament fabrication is used to fabricate a pattern used as the mold for the investment casting of aluminium A356 alloy into high-conformity thin-ribbed (~ 0.6 mm thickness) scaffolds. X-ray micro-computed tomography (CT) is used to characterize macro- and meso-scale defects. Optical and scanning electron (SEM) microscopies are used to characterize the microstructure of the cast structures. Slight dimensional (macroscale) variations originate from the 3D printing of the pattern. At the mesoscale, the casting process introduces very fine (~ 3 µm) porosity, along with small numbers of (~ 25 µm) gas entrapment defects in the horizontal struts. At a microstructural level, both the (~ 70 μm) globular/dendritic grains and secondary phases show no significant variations across the lattices. This method is a promising alternative means for producing highly detailed non-stochastic metallic cellular lattices and offers scope for further improvement through refinement of filament fabrication.

Vibration Damping and Acoustic Behavior of PU-Filled Non-Stochastic Aluminum Cellular Solids

“…The final shape of the cast and heat-treated (T6) samples may be visualized in Figure 1b. Overall, this process yields fine and detailed ribs/struts with a high-quality microstructure (globular 73 ± 39 µm α-Al grains, modified/refined eutectic Si and absence of significant defects) with good fabrication repeatability and anisotropic behavior [13]. This implies that fabrication-related variations in the tested samples (e.g., dimensional and microstructural changes) do not significantly affect the results of this study.…”

“…Given that this variable is also predominantly affected by the ratio of pore volume and superficial area (Equation ( 11)) [44] and recurring to Figure 15a, it may be observed that as the value of this variable increases, there may be an elevation in the sound absorption coefficient. The frequency-dependent dynamic thermal permeability (𝑘 𝜔 ) may be calculated using Equation (13), being dependent on the differentials of pressure and time (𝜕𝑃/𝜕𝑡), porosity (Ф), air thermal conductivity (k) and excess of the temperature inside the cellular The frequency-dependent dynamic thermal permeability (k (ω)) may be calculated using Equation (13), being dependent on the differentials of pressure and time (∂P/∂t), porosity (Φ), air thermal conductivity (k) and excess of the temperature inside the cellular solid (τ) [40,42]. The static thermal permeability (k 0 ) relates thermal effects between the rigid frame and the fluid at low frequencies actuating in the boundary layer, according to Equation ( 13) [45].…”

Investigation of a Template‐Based Process Chain for Investment Casting of Open‐Cell Metal Foams

“…This effect cannot be detected in investment cast open-cell metal foams, where reticulated polymer foams or additively manufactured optimized lattice structures have been used as sacrificial templates, as a much lower node-to-strut thickness ratio is given. [28,39,40] The solidification and following quenching of the cast foams resulted in a variation of the grain size of the microstructure of α-Al along the melt flow direction (Figure 4). Different cooling rates in the foam after casting, due to high heat capacities of the investment material and mass accumulation of molten metal in the feeding system, are the reasons for this behavior.…”

“…additive manufacturing. [27,28] In the case of additively manufactured sacrificial structures, the problem of high-volume scalability remains. In terms of reticulated foams, PU or PE foams are commonly used.…”

Aluminum metal composites primed by fused deposition modeling-assisted investment casting: Hardness, surface, wear, and dimensional properties

“…Investment casting (IC) is becoming increasingly popular among materials scientists to create near-net-shape products with enhanced surface finish and dimensional stability. 5 Another advantage of using the IC process is composite materials with intricate shapes with poor machinability and workability. 6 Recent studies have reported using the fused deposition modeling (FDM) process to fabricate sacrificial patterns required for the IC process.…”