ITIL: Interlaced Topologically Interlocking Lattice for continuous dual-material extrusion

Tim Kuipers,Charlie C.L. Wang,Jun Wu,Renbo Su

doi:10.1016/j.addma.2021.102495

Tim Kuipers, Charlie C.L. Wang + Show 2 more

Open Access

https://doi.org/10.1016/j.addma.2021.102495

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Abstract

Material Extrusion (MEX) systems with dual-material capability can unlock interesting applications where flexible and rigid materials are combined. When chemically incompatible materials are concerned the adhesion between the two might be insufficient. Therefore researchers typically rely on dovetail type interlocking geometries in order to affix two bodies mechanically. However, dovetail type interlocking introduces extrusion discontinuities and relies on the material’s resistance to deformation, which is difficult to model. We propose a simple and effective 3D lattice consisting of interlaced horizontal beams in vertically alternating directions which interlock topologically: the interlaced topologically interlocking lattice (ITIL). It ensures continuous extrusion and ensures an interlock even for highly flexible materials. We develop analytical models for optimizing the ultimate tensile strength of the ITIL lattice in two different orientations relative to the interface: straight and diagonal. The analytical models are applied to polypropylene (PP) and polylactic acid (PLA) and verified by finite elements method (FEM) simulations and physical tensile experiments. In the diagonal orientation ITIL can obtain 82% of the theoretical upper bound of 8 . 6 MPa . ITIL seems to perform comparably to dovetail interlocking designs, while it lends itself to application to non-vertical interfaces. Optimizing the lattice for non-vertical interfaces, however, remains future work. • Topological interlocking does not rely on the material’s tendency to deform. • Topological interlocking can satisfy extrusion continuity constraints. • Which lattice is strongest depends on the space available for interlocking. • The tensile strength of any interlock cannot exceed a theoretical upper bound. • Tensile properties of our lattice can are well approximated by analytical models.

Highlights

Multi-material extrusion 3D printers unlock a plethora of applications through combining the unique material properties of various materials
We propose a simple and effective 3D lattice consisting of interlaced horizontal beams in vertically alternating directions which interlock topologically: the interlaced topologically interlocking lattice (ITIL)
Given that the simulations make use of the same material properties which were acquired from tensile tests performed by Ultimaker, the simulations can teach us about the validity of the homogeneity assumptions in the analytical models

Summary

Introduction

Multi-material extrusion 3D printers unlock a plethora of applications through combining the unique material properties of various materials. Depending on the combination of materials the adhesion between the materials can be excessively weak. While only a small number of all possible 3D printing material combinations may exhibit any incompatibility issues, it is often precisely those incompatible combinations where the different chemical make-up produces interesting applications. PP is often used for living hinges, which consist of a single part rather than moving components. In such cases it is necessary to rely on mechanical interlocking to prevent the materials from breaking apart from each other

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