Origami-Based Design for 4D Printing of 3D Support-Free Hollow Structures

The integration of additive manufacturing(AM)in design and engineering has prompted a wide spectrum of research efforts,involving topologically optimized solid/lattice structures,multimaterial structures,bioinspired organic structures,and multiscale structures,to name a few.However,except for obvious cases,very little attention has been given to the design and printing of more complex three-dimensional(3D)hollow structures or folded/creased structures.One of the main reasons is that such complex open or closed 3D cavities and regular/freeform folds generally lead to printing difficulties from support-structure-related issues.To address this barrier,this paper aims to investigate four-dimensional(4D)printing as well as origami-based design as an original research direction to design and build 3D support-free hollow structures.This work consists of describing the rough 3D hollow structures in terms of two-dimensional(2D)printed origami precursor layouts without any support structure.Such origami-based definitions are then embodied with folding functions that can be actuated and fulfilled by 3D printed smart materials.The desired 3D shape is then built once an external stimulus is applied to the active materials,therefore ensuring the transformation of the 2D origami layout to 3D structures.To demonstrate the relevance of the proposal,some illustrative cases are introduced.

A Direct Toolpath Constructive Design Method for Controllable Porous Structure Configuration with a TSP-based Sequence Planning Determination

The inherent capabilities of additive manufacturing(AM)to fabricate porous lattice structures with controllable structural and functional properties have raised interest in the design methods for the production of extremely in-tricate internal geometries.Current popular methods of porous lattice structure design still follow the traditional flow,which mainly consists of computer-aided design(CAD)model construction,STereoLithography(STL)model conversion,slicing model acquisition,and toolpath configuration,which causes a loss of accuracy and manufac-turability uncertainty in AM preparation stages.Moreover,toolpath configuration relies on a knowledge-based approach summarized by expert systems.In this process,geometrical construction information is always ignored when a CAD model is created or constructed.To fully use this geometrical information,avoid accuracy loss and ensure qualified manufacturability of porous lattice structures,this paper proposes a novel toolpath-based con-structive design method to directly generate toolpath printing file of parametric and controllable porous lattice structures to facilitate model data exchange during the AM preparation stages.To optimize the laser jumping route between lattice cells,we use a hybrid travelling salesman problem(TSP)solver to determine the laser jumping points on contour scans.Four kinds of laser jumping orders are calculated and compared to select a minimal laser jumping route for sequence planning inside lattice cells.Hence,the proposed method can achieve high-precision lattice printing and avoid computational consumption in model conversion stages from a geomet-rical view.The optical metallographic images show that the shape accuracy of lattice patterns can be guaranteed.The existence of“grain boundaries”brought about by the multi-contour scanning strategy may lead to different mechanical properties.

Laser Additive Manufacturing of Bio-inspired Metallic Structures

High-performance/multifunctional metallic components primarily determine the service performance of equip-ment applied in the aerospace,aviation,and automobile industries.Organisms have developed structures with specific properties over millions of years of natural evolution,thereby providing inspiration for the design of high-performance structures to satisfy the increasing demands of modern industries.From the perspective of manufacturing,the ability of conventional processing technologies is inadequate for fabricating these complex structural configurations.By contrast,laser additive manufacturing(AM)is an effective method for fabricating complex metallic bio-inspired structures owing to its layer-by-layer deposition advantage.Herein,recent devel-opments in the laser AM of bio-inspired cellular,plate,and truss structures,as well as the materials used in laser AM for bio-inspired printing are briefly reviewed.The organisms being imitated include butterfly,Norway spruce,mantis shrimp,beetle,and water spider,which expand the diversity of multifunctional structures for laser AM.The mechanical properties and functions of laser-AM-processed bio-inspired structures are discussed.Additionally,the challenges,possible outcomes,and directions of utilizing laser AM technology to fabricate high-performance/multifunctional metallic bio-inspired structures in the future are outlined.

Interfacial Characteristics and Formation Mechanisms of Copper–steel Multimaterial Structures Fabricated via Laser Powder Bed Fusion Using Different Building Strategies

Laser powder bed fusion(LPBF)is an innovative method for manufacturing multimaterial components with high geometrical resolution.The LPBF-printing sequences of materials may be diverse in the actual design and application of multimaterial components.In this study,multimaterial copper(CuSn10)–steel(316 L)structures are printed using different building strategies(printing 316 L on CuSn10 and printing CuSn10 on 316 L)via LPBF,and the characteristics of two interfaces(the 316 L/CuSn10 or“L/C”and CuSn10/316 L or“C/L”interfaces)are investigated.Subsequently,the interfacial melting mode and formation mechanisms are discussed.At the L/C interface,the keyhole melting mode induced by the high volumetric energy density(EL/C=319.4 J/mm3)results in a large penetration depth in the pre-solidified layer and enhances laser energy absorption,thus promoting the extensive migration of materials and intense intermixing of elements to form a wide diffusion zone(∼400μm).At the C/L interface,the conduction mode induced by the low volumetric energy density(EC/L=74.1 J/mm3)results in a narrow diffusion zone(∼160μm).The interfacial defects observed are primarily cracks and pores.More cracks appeared at the C/L interface,which is attributable to the weak bonding strength of the narrow diffusion zone.This study provides guidance and reference for the design and manufacturing of multimaterial components via LPBF using different building strategies.