Manufacturing and Characterization of 3D Miniature Polymer Lattice Structures Using Fused Filament Fabrication

Abstract

The potential of additive manufacturing to produce architected lattice structures is remarkable, but restrictions imposed by manufacturing processes lead to practical limits on the form and dimension of structures that can be produced. In the present work, the capabilities of fused filament fabrication (FFF) to produce miniature lattices were explored, as they represent an inexpensive option for the production of polymer custom-made lattice structures. First, fused filament fabrication design guidelines were tested to assess their validity for miniature unit cells and lattice structures. The predictions were contrasted with the results of printing tests, showing some discrepancies between expected outcomes and resulting printed structures. It was possible to print functional 3D miniature open cell polymer lattice structures without support, even when some FFF guidelines were infringed, i.e., recommended minimum strut thickness and maximum overhang angle. Hence, a broad range of lattice structures with complex topologies are possible, beyond the cubic-type cell arrangements. Nevertheless, there are hard limits in 3D printing of miniature lattice structures. Strut thickness, length and orientation were identified as critical parameters in miniature lattice structures. Printed lattices that did not fully comply with FFF guidelines were capable of bearing compressive loads, even if surface quality and accuracy issues could not be fully resolved. Nevertheless, 3D printed FFF lattice structures could represent an improvement compared to other additive manufacturing processes, as they offer good control of cell geometry, and does not require additional post-processing.

A Comparison of Miniature Lattice Structures Produced by Material Extrusion and Vat Photopolymerization Additive Manufacturing

“…Although the largest relative density and better overall accuracy of the VP-fabricated should lead to better mechanical properties, lattices fabricated by ME have better elastic moduli, with the HPL lattice as the only exception. Differences between ABS and VP resin should be canceled out by using the lattice-to-solid ratios, leaving only geometric parameters as relevant factors that could explain the gap between the stiffness in VP and ME samples: thicker struts in ME lattices leads to stiffer lattices, which is consistent with earlier studies [ 16 , 17 ].…”

“…The failure mechanism that leads to large oscillations in the stress-strain curve of some ME lattices could not be identified in the images captured during the process, revealing the shortcomings of the experimental setup. Nevertheless, a previous study remarked that these oscillations are spaced evenly, coinciding approximately with the cell size of the lattice [ 17 ]. The absence of such oscillations in the VP-fabricated sample suggests that the emergence of this phenomenon depends on both the unit-cell type and the mechanical properties of the solid material.…”

“… Lattice structures (built by ME): ( a ) CVC; ( b ) CD; ( c ) CF; ( d ) TV; ( e ) HPV; ( f ) TOV; ( g ) HPD; ( h ) HPL. Images licensed under the Creative Commons License [ 17 ]. …”

“…During the last decade, special attention has been given to the development of design and optimization methods for lattice structures [ 6 , 9 , 10 , 11 , 12 ]. Moreover, the fabrication and testing for a wide variety of lattices fabricated using different AM processes have been reported, including material extrusion (ME) [ 13 , 14 , 15 , 16 , 17 ], vat photopolymerization (VP) [ 18 , 19 , 20 , 21 , 22 ], jet fusion (JF) [ 23 , 24 , 25 ], and selective laser sintering (SLS) [ 21 , 26 , 27 , 28 ].…”

“…No mechanical testing of the AM-fabricated lattices was carried out. Afterward, Guerra Silva et al [ 17 ] evaluated the capabilities of ME using the same benchmark lattices, demonstrating that it is possible to produce 3D miniature lattice structures with complex topologies using ME, even if accuracy was still low.…”