Input: UC is a single or multiple fibers embedded in the matrix with the volume fraction similar to those of the composite.

fibers

composite

volume fraction


Input: A finite element model of this geometry using two different materials is constructed and various loadings are applied to characterize the behavior of the UC.

finite element model

geometry

materials


Input: In the case of composites with random fiber orientations the composite behavior is approximated by direct averaging over all orientations.

composites

composite

fiber orientations

orientations


Input: Unit cells depend upon the microstructure of the composite; some common types of unite cell are presented in 24.

Unit cells

microstructure

composite

cell


Input: 24 presents a UC for discontinuous short fiber composites with random orientations, 24 and shows UC for continuous fiber reinforced with unidirectional orientation and 3D braided structure, respectively.

short fiber composites

continuous fiber

orientations

unidirectional orientation

3D braided structure


Input: Another commonly used approach is multiscale methods by combining micro level and homogenized macro stress analysis.

micro level

homogenized

stress


Input: Microscopic level analysis can increase the accuracy, but are often too expensive to be used in practice.

Microscopic level analysis

accuracy

be


Input: Multiscale modelling takes advantage of the efficiency of macroscopic models and the accuracy of the microscopic models.

Multiscale modelling

macroscopic

accuracy


Input: The microscope analysis is normally performed at the area of interest with high stress concentration.

microscope

area

stress concentration


Input: 25 shows a multiscale simulation with microscale analysis performed on two different areas of interest and macroscale analysis in the entire domain.

multiscale simulation

microscale analysis

areas of interest

domain

macroscale analysis


Input: 5 Conclusions 3D printing of composite structures can be a turning point for AM technology.

3D printing

turning

AM technology

composite structures

be


Input: The potential of fabricating functional devices, directly from commercial 3D printers with controllable properties, created a huge rush for new developments and research in this field.

fabricating

3D printers

properties

research


Input: The attractive combination of endless possibilities in the range of composite materials and extra customization of AM offers a unique new area in the manufacturing field, for researchers and developers to explore.

range

area

composite materials

AM

manufacturing


Input: AM of composites enables precise control of the physical, electrochemical, thermal, and optical properties; these structures can even transform their shape over time in 4D printing.

AM

4D printing

composites

precise control

electrochemical

optical properties


Input: Fiber reinforcement significantly improves the mechanical properties of 3D printed parts.

Fiber reinforcement

mechanical properties

3D printed parts


Input: It can be implemented in various AM techniques, such as FDM, SLA, SLS, LOM, and extrusion.

be

as

AM techniques

SLS

LOM

extrusion

SLA


Input: Printed CF-ABS composites were even reported with higher specific strength than Aluminum.

composites

Aluminum

specific strength


Input: The alignment of fibers in 3D printing of composites was one of the major challenges in the reviewed literature and its improvement attracted tremendous research interest in almost all of the existing AM methods.

fibers

composites

3D printing

AM

research


Input: Recent advances in FDM printing of continuous fiber reinforced thermoplastics took these improvements one step further to establish AM as a dependable manufacturing method for various industries.

FDM

AM

manufacturing

continuous fiber reinforced thermoplastics

step

industries


Input: In one of the interesting and innovative developments, continuous carbon fiber and PLA were mixed in the printing head before depositing into the printing bed, increasing the fiber/matrix adhesion.

continuous carbon fiber

PLA

printing head

bed

fiber/matrix adhesion


Input: Laser assisted AM for continuous fiber reinforced thermoplastic composites demonstrates superior mechanical properties and at the mean time solves the issue of material waste for LOM.

Laser

AM

LOM

continuous fiber reinforced thermoplastic

composites

material

mechanical properties


Input: Furthermore, developments in 3D printing of fiber reinforced composite structures allowed precise placement of material at micro-scale, to fabricate complex structures in 4D printing of active composites, with ability to transform over time, right after the 3D printing.

3D printing

fabricate

4D printing

3D printing

fiber reinforced composite structures

material

active composites

micro-scale

complex structures


Input: However, most 3D printing methodologies for composite materials still face major challenges, which need to be overcome before becoming a mainstream manufacturing method.

3D printing

manufacturing

composite materials

be

face


Input: Void formation during printing, poor adhesion of fibers and polymer matrix, and challenges in continuous fiber printing are all amongst the existing issues in 3D printing of fiber composites.

Void

adhesion

fibers

polymer

continuous fiber

fiber composites

3D printing


Input: Moreover, most of the commercial 3D printers designed for specific resins and introduction of fillers can lead to blockage, wear, non-adhesion, and increased curing times.

3D printers

resins

lead

wear

curing times


Input: AM of composites is a relatively new technique and there is a lack of research on modelling the structures produced by this process.

AM

composites

research

process

modelling


Input: Existing theories for short and continuous fiber composites can be modified for 3D printed parts.

continuous fiber composites

be

3D printed parts


Input: On the other hand, FEM is a powerful tool to analyze composite structures, and it can be applied for 3D printing with slight modifications of existing finite element models.

FEM

composite structures

finite element models

tool

be

3D printing


Input: In conclusion, AM of fiber reinforced polymer composites is tremendously promising in turning 3D printing from a prototyping method to a robust manufacturing technique.

AM

turning

3D printing

manufacturing

fiber reinforced polymer composites

prototyping


Input: The unique characteristics of 3D printing, such as high customization, combined with extra strength from fiber reinforcement and the ability to produce functional complex 3D structures with total control over material properties, helped AM of fiber-polymer composites gain enormous attention from a broad range of science industries.

3D printing

AM

as

fiber-polymer composites

strength

fiber reinforcement

3D structures

material properties

range

industries


Input: The aerospace industry, automotive industry, biomedical science, electronic industries, and robotics are only a few examples of those attracted by AM of fiber reinforced polymer composites.

aerospace industry

automotive industry

biomedical

industries

robotics

AM

fiber reinforced polymer composites


Input: As the application of additive manufacturing reaches an unprecedented scale in both academia and industry, a reflection upon the state-of-the-art developments in the design for additive manufacturing and structural optimisation, becomes vital for successfully shaping the future AM-landscape.

As

additive manufacturing

shaping

industry

reflection

state-of-the-art

structural optimisation

design for additive manufacturing


Input: A framework, highlighting both the interdependencies between these two central aspects in AM and the necessity for a holistic approach to structural optimization, using lightweight strategies such as topology optimization and/or latticing, was established to summarize the reviewed content.

framework

structural optimization

lightweight

optimization

AM

as


Input: Primarily focusing on isotropic material considerations and basic stiffness-optimal problems, these concepts have already found wide application, bridging the gaps between design and manufacturing as well as academia and industry.

isotropic material

as

as

bridging

design

manufacturing

industry


Input: In pursuit of streamlining the AM-workflow towards digitally print-ready designs, studies are increasingly investigating mathematically-based structural optimization approaches in conjunction with DfAM-specific constraints, providing a portfolio of solutions like generative design, which is gaining traction in industry.

designs

structural optimization

generative design

industry


Input: Besides an overview on economically-driven to performance-driven design optimizations, insight into commercial AM-specific software is provided, elucidating potentials and challenges for the community.

design optimizations

software


Input: Graphical abstract Unlabelled Image Highlights Extensive review, providing a joint perspective on design and structural optimisation in additive manufacturing.

Image

joint

structural optimisation

design

additive manufacturing


Input: Overview on the lightweighting approaches topology optimization and latticing, considering isotropic material assumptions.

lightweighting

topology optimization

isotropic material


Input: Consolidated summary, elucidating the gaps between design and manufacturing as well as academia and industry.

design

manufacturing

as

as

industry


Input: Establishment of a design for AM framework, highlighting the interdependencies between state-of-the art research topics.

design

AM

art


Input: Additive manufacturing, also referred to as 3D-printing, has evolved greatly over the last three decades, emerging from the mere application in prototyping, it has now indisputably established its position as a viable fabrication alternative for end-use parts.

Additive manufacturing

fabrication

as

as

prototyping


Input: This applies to a wide range of industries, including medical engineering, automotive, aerospace and consumer products,.

range

industries

medical engineering

automotive

aerospace

consumer products


Input: lower energy consumption, has driven the research into identifying lightweight and robust designs.

research

lightweight

designs


Input: Topology optimisation and latticing have emerged as the two major lightweighting strategies, best exploiting the design freedoms offered by AM.

Topology optimisation

as

lightweighting

design freedoms

AM


Input: The former represents a rigorous approach, improving the specific stiffness, whereas the latter can be considered as a design approach for weight-reduction in parts that usually have a high safety factor, which has in fact been widely adopted as a common design practice in today's AM-specific software.

specific stiffness

be

as

as

design

safety factor

design

software


Input: multifunctionality and bio-inspired designs, are gaining interest and could help shape the future of structurally advanced AM-parts.

bio-inspired designs


Input: This development is supported by the steady improvements in printer hardware and AM-specific software as well as the enrichment of the available material palette.

printer

software

as

as

material


Input: In fact, AM is attributed a central role in the successful realization of the new industrial revolution, i.e.

AM

industrial revolution


Input: Industry 4.0, affecting both the way we design and fabricate.

Industry 4.0

design

fabricate


Input: This is clearly reflected by the prediction of a threefold increase in the industry's market value as stated in the Wohlers report.

prediction

industry

as


Input: Jiang envisage among others intensified manufacturing of both critical and non-critical spare parts as well as increased customization of products with AM, which will require improvements in the structural performance and adequate design practices, respectively.

manufacturing

AM

as

as

structural performance

design


Input: From a design and structural standpoint, reviews in AM have so far focused on either the development of design rules and frameworks in the context of DfAM or the role of e.g.

design

AM

design rules


Input: TO, latticing, processing parameters, materials and bio-inspired approaches, respectively.

parameters

materials

bio-inspired


Input: Herein, a joint scope including a much wider consideration for DfAM in structural optimization for AM is captured, reviewing two key lightweighting strategies in AM, namely TO and latticing and providing insight into the academic versus the commercial landscape.

joint

structural optimization

AM

AM

lightweighting


Input: 1 introduces a framework, relating key intrinsic and extrinsic DfAM aspects that were identified in the field of design and structural optimisation for AM.

framework

structural optimisation

design

AM


Input: An intrinsic aspect is, therefore, representing the primary drivers when designing for AM, whereas the extrinsic factors can be regarded as current research topics in design and structural optimization for AM.

AM

AM

extrinsic factors

research

design and structural optimization

be

as


Input: The remit of this paper, however, goes beyond this framework, highlighting the underlying dependencies between the individual extrinsic factors in the state-of-the-art research today.

framework

extrinsic factors

state-of-the-art research


Input: Three interrelated themes referred to as entail process- and material-induced aspects, lightweighting strategies as well as broader DfAM-factors and are arranged analogously to the chronological order of headings in this paper.

as

as

as

lightweighting


Input: This review focuses on structural optimisation in AM with particular emphasis on DfAM.

structural optimisation

AM


Input: As most works on lightweighting strategies are based on isotropic material assumptions, reinforced-materials and the process-induced anisotropy caused by the fabrication in a layer-by-layer fashion or infill pattern, are not assessed.

As

isotropic material

reinforced-materials

lightweighting

anisotropy

fabrication

layer-by-layer fashion

infill


Input: As the role of anisotropy for topology optimisation in AM was discussed in, elucidating that this research is still in its infancy and requiring more fundamental investigations for a critical review, this paper summarizes the more consolidated knowledge in this field.

As

anisotropy

topology optimisation

AM

research


Input: A DfAM framework, encapsulating intrinsic and extrinsic aspects of the cutting-edge research on AM-friendly structural optimisation, preludes the main part of this work and provides context and structure to the reviewed studies.

framework

research

structural optimisation

structure


Input: The joint focus on structural optimisation in AM using TO and latticing with incorporation of DfAM aspects constitutes the remit of this paper.

joint

structural optimisation

AM


Input: Secondly, the synergistic and expertise-dominated application of cellular structures, as design approach to lightweighting, will be addressed.

cellular structures

as

be

lightweighting


Input: Hereby, focus is put on their application and significance in standard engineering problems rather than the medical field, as reviewed elsewhere.

standard

engineering

medical

as


Input: Moreover, it is important to note that the reviewed works are primarily looking into basic structural problems, concentrating on improved stiffness under volume constraints.

stiffness

volume constraints


Input: 2 Structural optimisation with isotropic material in AM The role of structural optimisation in AM is increasing across industries with lightweighting strategies that can broadly be differentiated into mathematically-driven and expertise-driven, with recent studies seeing increased utilization of both.

Structural optimisation

structural optimisation

isotropic material

be

AM

AM

industries

lightweighting


Input: Here, TO is frequently adopted for the design of structurally-sound AM-parts and has meanwhile surpassed the use of shape and size optimization in isolation.

design

structurally-sound AM-parts

optimization


Input: However, it has become a general practice in commercial software to post-process TO-solutions by optimizing the size or shape of the final structure to adhere e.g.

software

post-process

structure


Input: to minimum feature sizes that match the resolution of the printer.

minimum feature sizes

resolution

printer


Input: In contrast, expertise-driven structural optimisation such as latticing is not a lightweighting strategy per se, as stiffness is greatly compromised in exchange for e.g.

structural optimisation

as

se

as

lightweighting


Input: A good example of this is the latticing of a part for weight reductions and enhanced functionality in areas where stiffness can be sacrificed.

weight

areas

stiffness

be


Input: Generative design formally merges these two schemes through a parallel implementation to provide a portfolio of solutions i.e.

Generative design


Input: 1 Topology optimisation in AM Bendsand Kikuchi's as well as Sigmund's landmark work, introducing the concept of shape and TO centred on the homogenization approach and the MATLAB implementation of a density-based TO, respectively, laid the foundation for today's TO-methods.

Topology optimisation

AM

homogenization

as

as


Input: The most prominent TO approaches can be summarized as follows: Density-based; Level Set; Evolutionary/Genetic Algorithms; Topological Derivatives and Phase Field.

be

as

Set

Algorithms

Phase


Input: Discrete TO can be described as a method that explores the optimal connection of the elements, whereas continuum TO determines the optimal spatial distribution of material within a domain.

be

as

elements

material

continuum

domain

spatial distribution


Input: At the core of each structural TO problem lies an objective function that needs to be minimized or maximized while being subjected to a set of constraints such as volume, displacement or frequency.

core

be

as

set


Input: As part of an iterative process, in methods utilizing density as a design variable, Finite Element Analysis, sensitivity analysis, regularizations and optimisation steps are repeated in this order until convergence is achieved.

As

as

process

Finite Element Analysis

sensitivity analysis

regularizations

density

design


Input: In the context of DfAM, research today is geared towards print-ready TO designs bridging challenges of design and fabrication.

research

bridging

designs

design

fabrication


Input: This refers to methods that change the numerically optimal solution either intrinsically through the imposition of manufacturing constraints or in subsequent post-processing steps which alter the geometrical layout.

solution

manufacturing constraints

post-processing

layout


Input: Support-free designs and strategies to reduce the support volume are facilitators for a time- and cost-efficient fabrication.

designs

support

fabrication


Input: In pursuit of both physically and digitally print-ready designs, smooth boundary representations have drawn great attention in recent years.

designs

smooth boundary


Input: In this review, this refers to mesh-refinements, ensuring a better surface representation or CAD-friendly geometries.

surface

geometries


Input: In this context, correct digitalizing of TO-solutions will be pivotal for future CAD/CAM software, including an automated design procedure that integrates DfAM considerations and requires less AM-expertise.

be

CAD/CAM software

design


Input: Emerging TO methods with DfAM consideration for smooth boundary representation include the Development Method and the Morphable Method.

smooth boundary


Input: Herein, basic geometric shapes and polygons, capturing the geometrical layouts, have served as simple design primitives for representing topologies.

geometric shapes

design

as

topologies


Input: 1 SIMP-based designs for AM Density-based TO methods are most prevalent in academia and follow the general procedure.

designs

AM


Input: A well-established continuum method often referred to as the SIMP approach, first introduced by Bends, relates the elements relative densities to the effective material moduli using the power law.

continuum

as

elements

material

power


Input: As most works use linear elastic assumptions with the standard density-based TO approaches, they lack the ability to solve problems with large deformations accurately.

As

elastic

standard

deformations

accurately


Input: However, regarding DfAM, designs with elastoplastic print consumables, as commonly used, could particularly benefit from more realistic material considerations.

designs

print

as

material


Input: Major findings in studies on non-linear TO include: 1) the difference between linear and non-linear modelling of large deformations is particularly evident in buckling and snap-through scenarios; 2) a non-linear analysis made insignificant changes to the stiffness/compliance of a linear elastic structure but altered the topology significantly; 3) non-linearity assumptions are beneficial for realizing compliant mechanisms; 4) issues with excessive distortions or convergence of the numerical model can be solved.

non-linear modelling

deformations

non-linear analysis

topology

compliant mechanisms

model

buckling

linear elastic structure

be


Input: 1 Academic approaches to structurally optimized AM-friendly parts With the maturation of TO-codes in recent years towards greater computational efficiency and complexity, the inclusion of DfAM aspects is on the rise.

computational efficiency

complexity

inclusion


Input: Most of today's research on TO for AM is economically-driven and deals with support volume reduction, their complete elimination or simplified removal.

research

reduction

AM

support


Input: Support-free structures with reasonably good quality can generally be expected for an inclination angle in the realm of 45, which has been widely adopted for structural optimization problems anything lower is associated with additional fabrication cost motivating efforts in achieving conformity between design and print.

quality

structural optimization

be

inclination angle

design

fabrication

print


Input: However, it should be noted that fine-tuning of process parameters in polymer FDM has shown to allow even lower print-angles.

be

polymer

process parameters

FDM


Input: Performance is inevitably compromised by imposing manufacturing constraints but opposed to accounting for support volume, performance-driven factors in TO methods, including e.g.

Performance

manufacturing constraints

support


Input: In, the performance and printability of a structure derived from a coupled truss and SIMP-based optimisation approach were investigated.

performance

structure

printability

coupled truss


Input: By projecting a truss framework onto the corresponding TO-solution, the material was re-distributed, promoting adherence to overhang angle limits.

truss

framework

material

overhang angle limits


Input: As a result, a topology that does require less support but has reasonably high performance was created.

As

topology

performance

support


Input: Additionally, it was found that the printing direction is a key control parameter between manufacturability and performance.

parameter

manufacturability

performance


Input: An efficient DfAM filter for TO, avoiding support structures, has also been the subject of research in the works of Langelaar, in which a projection method was proposed for 2D and 3D cases.

filter

support structures

research


Input: More recently, Langelaar has extended this AM-filter approach to a method for optimizing topology, support layout and build orientation simultaneously, providing designers and engineers with a portfolio of results with the corresponding fabrication cost and part performance.

topology

layout

performance

support

build orientation

fabrication


Input: The support-filter itself is based on the premise of a layer-wise AM fabrication, whereby it is examined whether the base elements in the underlying layer offer support considering the critical support-free inclination angle of 45Together with a sensitivity filter based on the adjoint method, the AM-filter formulation is integrated into the code of Andreassen, making it an easily accessible tool for print-ready AM-parts with improved structural performance.

AM

elements

layer

sensitivity

support

filter

inclination angle

tool

structural performance


Input: Numerical examples provided in illustrated the printability of TO-structures as a function of printing orientation.

printability

as

orientation


Input: a half MBB beam, Langelaar highlighted not only the effectiveness of the filter to avoid shallow angles and its effect on the final topology compared to the unconstrained model, but also the variation in compliance with the building orientation.

half MBB beam

effectiveness

topology

model

variation

filter

building orientation


Input: An extension of this method could potentially be promising for multidirectional slicing in robotic AM.

be

multidirectional slicing

AM


Input: Gaynor and co-workers as well as Qian, showed that the Heaviside Projection offered an alternative means to constraining the overhang angles in TO-solutions.

as

as

overhang angles


Input: In this scheme was employed to enforce a binary solution from the greyscale SIMP-solution by controlling the minimum radial length scale.

binary

radial length


Input: determine the minimum self-supporting angle in 2D.

self-supporting angle


Input: Gaynor and Guest found major changes in the topology and deterioration in performance with increasing self-supporting angles.

topology

performance

self-supporting angles


Input: In the Heaviside Projection was employed both on the density and the density gradient to obtain well-defined boundaries and constrain the perimeter length in undercuts and overhangs for 3D cases.

density

density gradient

boundaries

undercuts

overhangs


Input: improved convergence to a discrete solution.

discrete solution


Input: As an example, a cantilever beam was optimized for individual minimum overhang angles, illustrating that overhang angle and gradient constraint need to be concurrently changed and that the compliance is significantly increased over the unconstrained pendant, especially for increased overhang angles.

As

be

cantilever beam

minimum overhang angles

overhang angle

overhang angles


Input: Leary proposed an approach in which infeasible inclination angles are initially identified, followed by a layout transmission into a support-free design and the determination of the optimal building orientation.

inclination angles

design

layout

building orientation


Input: Firstly, a binary topology was obtained through thresholding of the gradient values to identify the perimeters and its local gradients.

binary topology

local gradients


Input: Subsequently, smoothing of the boundary was performed using the rolling average method.

boundary

rolling average


Input: The actual novelties are the iterative internal and external boundary modifications centred on a recursive subdivision of domains to ensure the final design complies with the allowable inclination angle.

boundary

design

inclination angle


Input: The change in the geometrical layout increased the volume fraction of the part, however, due to the avoidance of support, experimental results showed a reduction in fabrication time.

layout

experimental

reduction

volume fraction

fabrication time

support


Input: Benchmarking against standard TO result, numerical analyses showcased: a) different stress distributions while the maximum von Mises stress stayed constant and b) the heat transfer is increased, which is of particular interest for e.g.

standard

heat transfer

stress distributions

von Mises stress

b


Input: metal-AM, as entrapment of excessive temperature, leads to microstructural changes over time as shown by.

as

as

temperature

microstructural


Input: It is important to note, however, that a weight increase is associated with this method, which should be carefully weighed against the material savings achieved by avoiding the supports or the ease in manufacturing.

weight

be

material

supports

manufacturing


Input: In contrast, a more recent paper by Thore investigates the abovementioned factor of stresses in support-free TO-solutions, while adhering to the volume constraint, linking economy and fabrication.

investigates

volume constraint

fabrication


Input: Contrary to the above works, digitally print-ready designs, accounting for research that highlight efforts to facilitate the transition between design and print such as methods that require minimal post-processing to be manufacture-ready are gaining interest.

designs

design

research

transition

post-processing

print

as

be


Input: Interpreting density-based TO solutions, even when they are discrete, poses a bottleneck for post-processes such as shape optimisation or the use of CAD programs for the conversion into AM-compatible file formats.

bottleneck

as

CAD

file


Input: A smooth boundary representation is, therefore, an aspect of particular attention in the context of TO.

smooth boundary


Input: An approach which is post-processing the layout of a TO-solution was recently presented by Liu.

post-processing

layout


Input: Here, a multi-step transformation method from a greyscale SIMP-based solution into STL and IGES formats has been presented.

solution

STL

IGES


Input: It is comprised of: 1) density thresholding and mesh refinement; 2) skeletonisation; 3) identify small features and increase their elemental density; 4) density filtering; 5) density thresholding while preserving volume fraction; 6) create STL file utilizing; 7) boundary interpretation using spline fitting; 8) obtain IGES file from an in-build MATLAB function.

density

density

density

density

mesh refinement

boundary interpretation

skeletonisation

spline fitting

volume fraction

STL

file

IGES file


Input: Shape optimisations procedures using a CAD model were shown to be suitable with designs obtained from the adaptive boundary fitting method due to its smooth boundaries.

CAD model

be

designs

boundary

smooth boundaries


Input: Studies like this represent a key element in today's research from DfAM, namely the transformation of complex AM-designs into CAD/CAM environments.

element

research

CAD/CAM environments


Input: 2 Commercial software implementations for lightweight structures Promoted by the greater application of TO in industry, an increased range of software providers have emerged, maturing and facilitating access to ready-to-use tools.

software

software

ready-to-use

lightweight structures

industry

range


Input: Particularly TO software providing greater freedom in utilizing subroutines, as recently demonstrated in, present a promising platform for further innovations in this field.

software

as

platform


Input: on automotive components like an upright.

automotive


Input: In, significant weight savings of one to two-thirds were achieved while ensuring the same structural performance as the original parts.

weight

structural performance

as


Input: In, shape controls ensured control over the member size, accounting for the minimum resolution of the electron beam melting process for a successful print.

resolution

electron beam melting

print


Input: It was observed, that all considered factors were closely related to the amount of support material used, as it increased the fabrication time and cost.

support material

as

fabrication time


Input: From the above study, it can be concluded that the layout of the final design for the industrial sector will be the result of multi-objective considerations, specifically drawing attention to the performance-economy relation with the utilized print materials.

be

be

layout

industrial sector

materials

design

drawing

print


Input: This highlights the importance of a DfAM framework that assures correct weighting of the relevant parameters and provides similar to the generative design a portfolio of quantifiable geometrical solutions.

framework

parameters

generative design


Input: The optimisation of a heat sink design displayed the software's capabilities to deal with multi-objective optimisation, as the design variables included friction force, thermal conductivity and out-of-plane heat transfer, besides the density of the elements.

heat sink

design

design

software

friction force

heat transfer

as

elements

thermal conductivity

density


Input: Despite showcasing the theoretical capabilities of today's TO-software, the above-mentioned studies commonly lack experimental verification.

theoretical

experimental


Input: Generally, numerical examples in TO involve either cantilever, half MBB or full MBB beams, but there is no explicit agreement by the scientific community on their aspect ratio, making comparisons difficult.

cantilever

half MBB

MBB beams

aspect ratio


Input: From a practical standpoint, standardised flexure tests would be better suited for experimental verification and therefore aid the comparison between both the TO-models and their physical counterparts.

flexure tests

be

experimental


Input: 3 Advanced applications TO-designs are increasingly adopted in technologically advanced industries as AM hardware and software are maturing, making complexity and scalability of AM-parts more tangible.

industries

as

AM

software

complexity


Input: Recent case-studies on topologically optimized engine pistons or car chassis indeed showed a promising development for increased uptake of TO in the automotive sector.

topologically

car

automotive sector


Input: As an example, Aage looked into optimizing the wing structure of a Boeing 777 using high-performance computing to overcome current limitations regarding the number of resolvable voxels and representable feature size.

As

structure

voxels

Boeing

high-performance computing

feature size


Input: However, this should not distract from the more pressing challenge the AM-community is currently faced to further exploit AM capabilities, namely the reduction of the computational cost and improvement of the resolution for standard engineering problems.

pressing

faced

AM

reduction

standard

resolution

engineering


Input: In case of small- and mid-sized companies these are commonly solved with standard desktop machines rather than employing high-performance computing.

companies

standard

machines

high-performance computing


Input: the fruition of compliant mechanisms, realized by means of multi-material printers and the use of materials with greatly varying Poisson's ratios.

compliant mechanisms

multi-material

materials


Input: 2 AM-designs derived from evolutionary TO Evolutionary algorithms have been used and constantly improved for structural optimisation over the last two decades.

algorithms

structural optimisation


Input: The most prominent representative is BESO, introduced by Yang as an extension to the Evolutionary Structural Optimisation method put forward by Xie and Stevens.

BESO

Structural Optimisation method

as


Input: However, issues related to stepped contours i.e.

contours


Input: smooth boundaries remain.

smooth boundaries


Input: 1 Digitally print-ready designs In light of DfAM, achieving a smooth boundary representation, especially for discrete TO-solutions, is currently a subject of intense study.

designs

smooth boundary


Input: Capitalizing on the shape functions, a smoother boundary, accounting for discontinuous material distributions within single FEs, was realized.

boundary

material

distributions


Input: Despite revealing the same overall topology, the Iso-XFEM method provided a superior structural stiffness as compared to the BESO implementation for the same amount of iterations and identical mesh-size.

topology

BESO implementation

Iso-XFEM method

stiffness

as


Input: BESO with a finer initial fixed mesh matched the performance but at a computational expense.

BESO

performance

fixed mesh


Input: As the mesh manipulation is outweighing the computational benefit of BESO, the AM-friendly Iso-XFEM method was regarded as the preferential TO method, streamlining the design process towards digitally-print-ready models and effectively tying in aspects of lightweighting and boundary representation.

As

as

mesh manipulation

BESO

design process

boundary representation

Iso-XFEM method

lightweighting


Input: In a more recent study, Iso-XFEM was applied as a design-procedure to obtain a lightweight brake pedal.

Iso-XFEM

as

lightweight


Input: The structure was effectively enhanced for AM, using a manual post-processing step, in which a partial cellular infill based on Body Centred Cubic unit cells was included to improve the performance under arbitrary loading and to reduce warpage arising from residual stresses in SLM.

structure

post-processing

Body Centred Cubic

performance

warpage

AM

SLM

infill

cells

residual stresses


Input: In, a modified BESO method was used to optimize the strut thickness of lattices used in an engine bracket, to improve the compliance over a homogenous design.

BESO method

lattices

strut thickness

bracket

homogenous design


Input: The material allocation is conducted based on the ratio between the local and global stress magnitude i.e.

material

stress

magnitude


Input: the stress distribution as well as the predefined strut diameter bounds.

stress distribution

as

as

strut diameter


Input: compliant mechanisms, a modified BESO with local displacement constraints was employed by Zuo and Xie.

compliant mechanisms

BESO

displacement constraints


Input: Here, the standard penalization factor was introduced for the material interpolation and to ensure convergence, however, for the FEA several critical nodes were assigned to local displacement functions based on the individual virtual loads to fine-tune the topology for a specific load case.

standard

material interpolation

displacement functions

topology


Input: Numerical examples displayed dissimilar topologies compared to the conventional compliance-driven approach and a significant reduction in the maximum vertical deflection.

topologies

reduction

vertical deflection


Input: As outlined by the authors, this method lends itself for lightweight structures such as an aircraft wing, for which awareness and control over the deformed shape are required.

As

as

lightweight structures

aircraft wing

deformed shape


Input: For the most part, TO procedures employ fixed meshes for the FEA.

fixed meshes


Input: A mesh refinement captures the material behaviour more accurately, however at higher computational cost due to more degrees of freedom.

mesh refinement

degrees of freedom

material

accurately


Input: A fine mesh for updating design variable and a hierarchical system for the FEA.

fine mesh

design


Input: This resulted in a relatively-smooth topology, due to the finer resolution representing the boundaries of the structure, whereas the size of the internal elements remained coarse.

topology

structure

finer resolution

boundaries

elements


Input: It is of note that caution must be taken in choosing an appropriate value for the maximum element size to obtain accurate FEA results.

be

element size

accurate


Input: 3 Level set TO for AM Level set method centre around the structural boundaries i.e.

set

set

AM

boundaries


Input: interfaces and their implicit representation via iso-contours of the corresponding level set function.

via iso-contours

level set function


Input: The inherently smooth and well-defined boundaries obtained lend themselves for parameterization into geometric shapes, potentially linking aspects of manufacturing and digitalization.

boundaries

geometric shapes

manufacturing


Input: However, for analysis, the geometrical model is mostly discretized and mapped onto a fixed mesh, following the density-based methods.

geometrical model

fixed mesh


Input: For instance, by embracing both economic and performance-driven DfAM considerations, Liu and co-workers have developed a feature-based approach as well as algorithms that take into account the deposition path/building direction and support-free manufacturing.

as

as

algorithms

deposition

manufacturing


Input: Regarding DfAM studies have shown that gaps between paths due to sharp angle changes can be avoided and as the paths follow the principal stress trajectories, the overall performance can be increased.

sharp angle

be

as

be

principal stress

performance


Input: In, the contour offset method and the structural skeleton based method, including a support structure constraint, were investigated.

contour offset method

structural skeleton

support structure


Input: It was found that the structural performance was comparable between both methods, whereas, the skeleton-based method was favourable as it avoided manufacturing irregularities.

structural performance

as

manufacturing


Input: The authors optimized a cantilever beam for self-supported AM, using a multi-LS interpolation approach, to illustrate their method.

cantilever beam

AM

interpolation


Input: Similarly, the skeletonisation of 2D LS topologies was utilized in to constrain the minimum hole size and control the number of holes in the topology to ensure better manufacturability.

skeletonisation

topologies

topology

manufacturability

hole size


Input: In, it was applied to avoid small struts by controlling the minimum or maximum length scale of the features i.e.

struts

length scale


Input: the distance between skeleton and boundary.

boundary


Input: 8b illustrates the difference in topology between constraint and unconstraint LS TO of a cantilever beam.

topology

cantilever beam


Input: In the study of Allaire, the aspect of the overhang constraint was considered from two perspectives.

overhang constraint


Input: The latter has been developed in and centres on the intermediate AM stages, resulting in the continuous change in shape and boundary conditions with each consecutive layer.

AM

boundary conditions

layer


Input: the cooling rate as another fabrication constraint for this minimum compliance problem.

cooling rate

minimum compliance problem

as

fabrication


Input: Likewise, in, Mart accounted for process-induced effects, such as porosity in parts created from electron beam melting.

as

electron beam melting


Input: Considering fabrication-stages and -flaws for different AM-processes is certainly representing a more interconnected and realistic application of DfAM, encompassing intrinsic and extrinsic factors, shared in the upper and middle band, and contributing to higher quality AM-parts in the future.

intrinsic and extrinsic factors

quality


Input: Certain design requirements like fixed passive elements or other functional affiliations often do not allow support-free angles.

design

elements


Input: Mirzendehdel and Suresh reduced the support volume of topologically optimized structures using an LS based Pareto TO, considering both support structure and topological sensitivities through dynamic weighting.

support

topologically

Pareto

topological sensitivities

dynamic

support structure


Input: Similar attempts to reduce support volume include tree-like and topologically optimized supports.

support

supports

topologically


Input: 2 Cellular structures in AM Cellular structures represent an important structural design feature in AM, commonly used for lightweighting.

Cellular structures

structural design

feature

AM

AM

lightweighting


Input: Characterized by slender/thin members, such as struts/bars or sheets/plates, these formations are increasingly utilized as an integral feature in AM-designs primarily due to material and time-/energy-saving in fabrication as well as improvements in strength-to-weight ratio, as summarized in.

as

as

material

as

as

as

feature

fabrication


Input: Besides the specific strength, their ability to dissipate energy, heat and vibration add value to the design.

specific strength

heat

design


Input: Recently, a significant increase in buckling load and buckling strength have been recorded by using triangular lattice-infills or topology optimized hierarchical microstructures, respectively.

buckling load

buckling strength

topology

microstructures


Input: In metal-AM, they can also help mitigate warpage, arising from process-induced residual stresses, however, some lattice types must be altered to accommodate for e.g.

warpage

lattice

residual stresses

be


Input: The use of lattices, contrary to the common misconception, is therefore not a lightweighting approach from a pure stiffness standpoint, which needs to be considered in the design process.

lattices

design process

lightweighting

stiffness

be


Input: An overview from design to analysis of cellular structures for AM can be extracted from.

design

cellular structures

AM

be


Input: Unit cells represent the building blocks of a lattice, which is generated either from sweeping, meshing/mapping, tessellation to obtain a regular pattern or stochastically yielding unstructured formations, which is often achieved via techniques such as dithering.

Unit cells

lattice

pattern

tessellation

as


Input: Unit cells are generally classified into truss based and surface-based.

Unit cells

truss


Input: Numerous cell topologies were generatively developed over the years, leading to the emergence of unit cell libraries/families for AM.

cell topologies

unit cell

AM


Input: Ground trusses, often resembling lattice-like configurations, are characterized by a freeform frame-network with locally varying strut diameters which also lends themselves well for AM.

freeform

strut diameters

AM


Input: It is however of note, that isotropic open-cell truss-like structures have an up to threefold inferior stiffness performance compared to their closed-cell lattice counterparts of the same relative density.

isotropic

stiffness

relative density

performance

lattice


Input: On this account, considering that lattices are not stiffness-optimal and given the choice, surface-based unit cells should be favoured for lightweight designs.

lattices

unit cells

lightweight

be

designs


Input: Unit cell tessellation approaches often give rise to non-conformity as loose-hanging members are formed when a lattice is created, impairing the structural performance.

Unit cell

lattice

tessellation

as

structural performance


Input: Lattices derived from tessellated surface-based unit cells are less affected by this phenomenon.

Lattices

unit cells


Input: On the contrary, conformal lattices were found to yield greater structural performance.

conformal lattices

structural performance


Input: Works on graded lattices most generally focus on piecewise variation in volume fractions that change from one unit cell to another.

lattices

variation

unit cell

volume fractions


Input: However, due to the implicit definition of triply periodic minimal surface lattices, true functional grading is achievable with ease.

triply periodic minimal surface

lattices


Input: Together with the advancement in hardware technology, capable of fine- and multi-scale structures, these new lightweight lattice structures with locally changing material properties represent a unique offering of AM.

technology

lightweight lattice

material properties

multi-scale structures

AM


Input: Discrepancies between the ideal and the actual performance of lattices, reviewed in, is owed to irregularities introduced during manufacturing, which include micro-voids or the change in surface roughness, making the prediction of the mechanical performance based on the relative density and linear elastic assumptions difficult.

performance

lattices

prediction

manufacturing

micro-voids

surface roughness

relative density

elastic

mechanical


Input: A comparison between the experimental and numerical analyses of lattices and a summary of simulation methods are summarized in.

experimental

lattices

simulation


Input: Latticing tools are increasingly provided in today's CAD software and are commonly used to substitute low-stress areas for weight reduction.

tools

CAD

areas

weight

reduction


Input: Particularly the ability to achieve a balance between robustness and compliance in tailored lattices was recently stressed.

robustness

lattices


Input: Another emerging research field in AM, aiming-among others-at combing high strength and stiffness, is biomimicry.

research

biomimicry

AM

strength

stiffness


Input: Moreover, it is of note, that some software providers like ELiSE are already incorporating bionic templates into designs geared towards AM.

software

bionic templates

designs

AM


Input: 1 Topologically optimized lattices based on academic codes Promising academic approaches dealing with structural optimisation of lattices for AM are on the uprise.

Topologically

lattices

structural optimisation

lattices

AM


Input: The digitalisation of these intricate structures is a prerequisite to ensure optimisation, bridge the gap to manufacturing and ultimately improve the structural performance of lightweight AM-parts.

bridge

manufacturing

structural performance

lightweight


Input: Computationally efficient representation of lattices is as challenging as it is important for the analysis and manufacturing steps.

lattices

as

as

manufacturing


Input: As a consequence, research is actively looking into ways to reduce the computational expense, aiding streamline the design process and enabling geometrical layouts, such as functionally graded lattices.

As

as

research

design process

lattices


Input: 1 Structurally optimized lattices using the homogenization method To capture the heterogeneous nature of lattices, unit cells are commonly homogenized into representative volume elements.

lattices

heterogeneous

lattices

unit cells

volume

homogenization method

homogenized

elements


Input: Homogenization-based methods have recently been integrated into a lattice mesostructural optimisation framework for AM.

lattice

framework

AM


Input: In, Messner presented the inverse homogenization, in which the macrostructural material properties of a periodic lattice consisting of simple unit cells are combined with a subsequent parameterization to obtain a 3D truss-like lattice structure with struts of round cross-sections and isotropic material behaviour.

homogenization

simple

macrostructural material properties

lattice

cross-sections

cells

lattice structure

struts

isotropic material


Input: In the context of digital AM, it is worth mentioning, that such a parameterization of the design space is beneficial for better control over the geometrical layout using CAD-like environments and therefore bridging the gap between important intrinsic DfAM aspects.

AM

design space

layout

bridging

CAD-like environments


Input: 2 Graded lattices derived from mapping combined with density-based TO Various studies have utilized a mapping approach to update a cellular structure based on the density values obtained from unpenalized TO.

lattices

cellular structure

density


Input: Some of these use the abovementioned homogenization approach to map the unit cells achieving a more accurate mechanical response.

homogenization

unit cells

accurate


Input: In, a SIMP-solution provides the density distribution, which is mapped onto the explicit cellular structure, leading to the newly density-adjusted structure.

density distribution

cellular structure

structure


Input: In an FEA of a beam under three-point bending it was determined that the stiffness of the explicit cellular model increased with greater gradient density and lower cell size, approaching the implicit i.e.

beam

three-point bending

stiffness

density

cell size

model


Input: Great reliability of the numerical model was concluded after negligible differences in performance were obtained in comparison with the specimens created from SLA.

reliability

model

performance

SLA


Input: An increase in stiffness by more than a third over the uniform lattice was revealed in the experiment, highlighting a viable design approach for structurally enhanced AM-parts.

stiffness

lattice

experiment

design


Input: The dependence between cell size and performance elucidates the need for high-precision, fine-scale manufacturing in future work.

cell size

performance

fine-scale manufacturing


Input: Manufacturing of extruded 2D lattices is straightforward for most printing technologies, however, 3D cellular structures can pose a challenge for e.g.

Manufacturing

extruded

printing technologies

3D cellular structures


Input: powder-based processes, as unconsolidated material is easily encapsulated in cavities.

processes

encapsulated

as

material


Input: This was taken into consideration by Jin through manufacturing constraints such as the minimum section thickness, the minimum hole diameter and the uniformity of the section thickness i.e.

manufacturing constraints

diameter

as


Input: The authors mapped the lattice of square cell honeycombs onto the density matrix of the TO-solution.

lattice

cell

density matrix


Input: The FEA reveals superior compressive performance of the developed graded lattice even with the manufacturing constraints over the uniform lattice.

performance

lattice

manufacturing constraints

lattice


Input: Similar to, the authors found that a decreasing cell size and an increasing gradient density has a positive effect on the structural performance.

cell size

density

structural performance


Input: Song expanded the concept to irregularly shaped cells for AM.

cells

AM


Input: Here, a triangular mesh, obtained from a domain of unit tangent circles, is the basis for the formation of the cellular structure with predetermined cell/circle ratios.

triangular mesh

domain

cellular structure


Input: This irregular lattice is then mapped onto the density field obtained from unpenalized SIMP.

lattice

density field


Input: Experimental tests showed that the irregular cell structure obtained from the unpenalized SIMP outperformed those using penalization.

Experimental

cell


Input: Mapping strut-based unit cells with different densities into a hexahedral mesh of a topologically optimized structure enabled Robbins to create structures with an external topology based on the penalized SIMP-result filled with a conformal lattice with properties determined from the homogenization method.

strut-based

conformal lattice

cells

topologically

structure

topology

properties

homogenization method


Input: The meshing was done with the Sandia's Sculpt tool, allowing for the adaption and smoothing of the mesh at the boundaries, aiding the creation of a flawless and print-ready STL files.

tool

boundaries

STL

files


Input: To guarantee the same weight of structures with various unit cell densities, the external topology was adapted accordingly, revealing an improved performance for less dense lattices.

weight

unit cell

topology

performance

lattices


Input: Even though the structure was printed using laser power bed fusion of stainless steel, no experimental verification was conducted, which is a recurring shortcoming in many of the reviewed studies on structural optimisation using either TO or lattices.

structure

experimental

structural optimisation

lattices

laser power bed fusion

stainless steel


Input: While all the aforementioned studies solely focused on the performance aspects of the mapped structures, Panesar took also aspects of design and manufacturability into account.

performance

manufacturability

design


Input: Hereby investigating intersected, scaled and graded lattices with strut- and surface-based self-supporting unit cells for design aspect like structural optimality, design effort, support requirements, robustness i.e.

lattices

self-supporting

design

design

cells

support

robustness


Input: resilience to variation in loading and design-to-manufacturing discrepancy.

variation


Input: The authors used a voxel paradigm, rather than the traditional volume boundary representation via B-rep, to represent lattices and employed an iso-value matrix, similar to, for functional grading.

voxel

volume

boundary representation

lattices

B-rep


Input: purely topologically optimized result.

topologically


Input: Authors highlighted the superiority of the proposed lattice types in terms of specific stiffness over the uniform lattice and the robustness of the graded lattice making it the most well-rounded performing lattice.

lattice

lattice

lattice

lattice

specific stiffness

robustness


Input: Particularly, the lattices comprised of surface-based unit cells were found to result in more resilient structures.

lattices

unit cells


Input: However, from a performance i.e.

performance


Input: stiffness perspective, all lattices perform inferior compared to the solid pendant.

stiffness

lattices


Input: Moreover, the cellular structures reduced the support structure requirements compared to the solid design.

cellular structures

support structure

design


Input: Similar to, the voxel-based method of Aremeu employs a net-skin approach, ensuring conformal lattices despite tessellation, through re-connecting strut-members at the boundary.

conformal lattices

tessellation

boundary


Input: The authors believe, that due to the limited resolvable resolution of AM machines, this method would satisfy the level of detail required for the model without high computational cost and geometrical complexity, however, no numerical nor experimental verification was conducted in this study.

resolution

AM machines

model

experimental

geometrical complexity


Input: More recently Wang have topologically optimized a strut-based Kagome lattice structure based on the SIMP method with direct AM considerations.

topologically

strut-based

lattice structure

AM


Input: The novelty is that it represents a structure-based rather than a boundary-based TO and constitutes a method to increase the specific stiffness of the primitive unit cell.

specific stiffness

unit cell


Input: In an attempt to fine-tune the structural response of lattices, Maskery have recently observed a sequential failure of piece-wise graded BCC lattices in compression promoting increased energy absorption in comparison to the ungraded lattice.

lattices

failure

BCC

compression

energy absorption

ungraded lattice


Input: Furthermore, the results indicated non-homogeneous bulk properties, making the use of Gibson-Ashby models inadequate, as they are developed for uniform density lattices.

non-homogeneous bulk properties

density

Gibson-Ashby models

as


Input: It is important to note however, that this model is still useful for obtaining ballpark values for lattices through simple calculations.

model

lattices

simple


Input: Due to the very specific failure mechanisms in graded lattices, future work ought to put more emphasis on the experimental verification in order to make more reliable predictions for their performance.

failure mechanisms

lattices

experimental

predictions

performance


Input: 3 Variable-density infills derived from density-based TO An emerging topic in structural optimization with a promising application for AM are TO-based compliance-driven infill strategies for porous material, which account for the principal stress directions imposed by the loading condition.

structural optimization

AM

infill

porous material

principal stress


Input: Infills derived from homogenization-based TO, using projection-based methods, was subject under investigation in, making designs potentially more feasible for AM through the incorporation of a minimum length scale constraint for the microstructural features matching the print-resolution.

designs

AM

length scale

microstructural

print-resolution


Input: In, this method was experimentally underpinned, demonstrating how self-supporting variable-density lattices can be generated.

self-supporting

lattices

be


Input: Work by Wu centres on SIMP, whereby in, solely the infills of 3D structures were optimized and the shell was represented by passive elements, whereas the approach in demonstrated a concurrent optimisation of shell and infill for 2D structures.

3D structures

shell

shell

elements

infill

2D structures


Input: In these structures were separated through multiple successive smoothing and projection steps combined with interpolations of intermediate densities to obtain discrete topologies with checkerboard-free domains and well-defined boundaries.

discrete topologies

boundaries


Input: In contrast to the standard objective function, a local rather than a global volume constraint was employed in both studies, meaning the density of the neighbouring elements was limited in a predefined radius, controlling the porosity locally.

standard

volume constraint

density

porosity

elements


Input: It was found, that higher radii result in topologies with coarser pores and greater stiffness as the local volume constraint becomes less influencing.

topologies

pores

stiffness

as

volume constraint


Input: Furthermore, Wu emphasized that these control parameters are beneficial for the manufacturability of parts intended for powder-based AM-processes, as closed walls cause entrapments.

parameters

manufacturability

as


Input: To avoid slender struts without infill, a length scale constraint is introduced in, which was implemented by an erosion and dilation projection before a final sensitivity analysis was conducted.

slender struts

infill

length scale

sensitivity analysis


Input: Conversely, in, the authors introduce an anisotropic filter, forcing the material to accumulate in preferred i.e.

anisotropic filter

material


Input: a prescribed direction in order to resemble bone-inspired infills, resulting in truss-like formations.

bone-inspired infills


Input: The filter, in particular, helped improve the uniaxial buckling stability.

filter

buckling


Input: Recently, Wu have presented a computationally more efficient extension to their work that is using a simultaneous optimization of the shape and the distribution of the lattice, demonstrating a twofold increase in buckling load over the equivalent TO-solution.

optimization

distribution

lattice

buckling load


Input: Besides weight reductions, improvements in damage tolerance and robustness generally illustrate greater functionality, mechanical capability and versatility of lattices, potentially outweighing the losses in stiffness for certain engineering problems compared to a solid solution.

weight

damage tolerance

robustness

mechanical capability

stiffness

lattices

engineering

solid solution


Input: Another emerging topic for AM within topologically optimized and variable-density lattices, which will not be further discussed, are both multi-scale and multi-material structures.

AM

topologically

lattices

be

multi-material structures


Input: Primary investigations into a concurrent optimization of both macroscale and a micro-scale lattices, using two different materials, show great promise for the design-potential of AM.

optimization

macroscale

materials

micro-scale lattices

AM


Input: 4 Strut-sizing and -scaling for structurally optimized truss-like structures Emerged from the idea to drastically decrease the computational complexity and processing time, the size matching and scaling method for mesoscale lattices, represents an alternative approach for structural optimisation.

complexity

structural optimisation

mesoscale lattices


Input: Besides the modification of the topology as certain struts that have a minor contribution to the structural performance are eliminated, the method mainly centres on the size optimisation of the struts.

topology

as

struts

struts

structural performance


Input: An average stress distribution of the solid body serves as the basis upon which the unit cell topology with geometrical features is determined prior to the mapping onto the initial geometry.

average

distribution

unit cell topology

geometry

as

geometrical features


Input: Choosing the exact node size and thresholds for the upper and lower bounds of the strut diameter were deemed to be vital for the assurance of manufacturability with AM.

strut diameter

be

manufacturability

AM


Input: Overall this does not take away from its feasibility for application in large structures as shown on the basis of a light-weight micro air vehicle fuselage and is, therefore, a viable alternative to pure TO.

feasibility

as

light-weight

fuselage


Input: This method represents a lattice generation tool integrated into Siemens NX CAD software.

lattice generation

CAD


Input: In light of the multifunctional performance of lattices, Seepersad have demonstrated how a post-processing steps can be used to obtain lattice topologies with e.g.

performance

lattices

post-processing

lattice

be


Input: improved heat transfer, by effectively identifying lattice members that can be sacrificed, based on a hybrid FEA and finite difference approach.

heat transfer

lattice

be


Input: A more recent study has demonstrated a solution for a similar multifunctional optimization for a heterogeneous cellular structures using a decision support problem formulation.

solution

optimization

heterogeneous cellular structures

support


Input: 5 Evolutionary algorithms for structurally enhanced lattices Tang made use of a BESO-based approach to design a latticed engine bracket with optimal strut thicknesses, using a kernel-based algorithm.

algorithms

lattices

design

bracket

strut thicknesses

kernel-based algorithm


Input: Points of the boundary and internal elements are subsequently separated, and the initial wireframe is mapped onto the boundary kernel points, followed by a trimming procedure used to remove wires outside the functional volume.

boundary

elements

boundary kernel points

volume

trimming


Input: Finally, these two sets of frames are merged together forming the final conformal lattice, which undergoes the BESO algorithm to modify the strut thickness based on the von Mises stresses obtained from the FEA of the homogenized functional volume and predetermined geometrical limits.

forming

homogenized

conformal lattice

geometrical limits

BESO algorithm

volume

strut thickness

von Mises stresses


Input: The structural performance was improved in contrast to a homogeneous lattice and the weight reduced by up to 75% over the original solid design.

structural performance

homogeneous lattice

design

weight


Input: A recent study by Tang dealt with DfAM in the context of lattices and used BESO to locally improve the size of truss-like members, creating a heterogeneous lattice.

lattices

BESO

heterogeneous lattice


Input: In this study, a meta-model was created, which was comprised of the geometrical manufacturing constraints regarding the deflection of horizontal struts and the thickness of struts with reference to the inclination angle.

geometrical manufacturing constraints

horizontal struts

inclination angle

struts


Input: Additionally, the optimized lattice structure led to an increase in stiffness over the traditional homogeneous pendant.

lattice structure

stiffness

homogeneous


Input: Besides, the abovementioned more favourable examples for the use of evolutionary algorithms for the optimisation of lattices, Chu have conversely demonstrated eminent drawbacks of the PSO over the non-evolutionary LMO optimisation, due to the stochastic nature of such algorithms.

algorithms

lattices

non-evolutionary LMO optimisation

stochastic

algorithms


Input: Based on ground truss structures which were optimized for a given volume fraction and a set allowable deflection, the optimal strut dimensions were obtained with both algorithms.

truss

strut

volume fraction

set

dimensions

algorithms


Input: Results showed comparable structural performance but the superior computational efficiency and convergence of the LMO method.

structural performance

computational efficiency


Input: The integration of DfAM constraints into the optimisation algorithms remains a bottleneck for a streamlined design procedure, calling for benchmarking studies helping to identify more efficient approaches in digital AM in future work.

algorithms

bottleneck

design

AM


Input: 2 Topologically optimized lattices employing commercial software As the role of AM in the industry is slowly shifting towards production, ready-to-use design software capitalizing on now amenable features like lattices, are becoming more readily accessible.

Topologically

lattices

software

ready-to-use

lattices

As

AM

production

industry

design


Input: 3DXpert for Solidworks, nTopology or ANSYS which is providing a AM-specific design platforms.

ANSYS

design


Input: 1 Modelling structurally optimized lattices for printing In the context of trusses, Gorguluarslan developed a two-phase lattice optimisation framework, specifically tackling the issue of the minimum manufacturable cross-section.

Modelling

lattices

lattice

framework

manufacturable


Input: Here a primary ground structure optimisation is followed by a rectification process in which elements falling below a certain minimum cross-sections threshold are eliminated, before a final optimisation step is conducted, for which the method of Feasible Directions is employed.

structure

process

cross-sections

step

elements


Input: Altair's OptiStruct and HyperMesh were utilized for structural optimisation.

HyperMesh

structural optimisation


Input: Among others, the typical cantilever beam example was used to compare the effectiveness of the framework and the MFD algorithm with Chang and Rosen's SMS method and the Relative Density Mapping of Alzahrani, respectively.

cantilever beam

effectiveness

framework

MFD algorithm

Relative Density


Input: Under restriction of the minimum feature size, MFD was identified to outperform SMS and RDM in terms of stiffness but required more computational effort.

minimum feature size

RDM

stiffness


Input: However, it was also found that designs obtained from genetic algorithms and PSO have an even superior structural performance.

designs

genetic algorithms

structural performance


Input: In Abaqus served as a tool for the TO within the RDM method.

Abaqus

as

tool

RDM


Input: Compared to the SMS method, the density values of the TO are used to map the struts into the domain, making RDM less dependent on the FEA analysis.

density

struts

domain

RDM


Input: Arisoy developed a framework for the substitution of solid parts of a CAD model with lattices, which served as the basis for a plugin in Siemens's NX CAD software.

framework

lattices

CAD model

CAD

as


Input: boundary surface defining the layout of the lattice.

boundary

layout

lattice


Input: During the FEA of the solid part, meshed with tetrahedral elements, a remeshing process including trimming is conducted ensuring that the elements are part of the lattice.

tetrahedral elements

remeshing process

lattice

trimming

elements


Input: Besides an improved and efficient workflow for AM, the authors concluded to have improved the boundary smoothness of the lattices with the implicit volume representation, so that the manufacturability for AM is improved.

workflow

lattices

manufacturability

AM

AM

boundary

implicit volume representation


Input: In terms of digitalization and streamlining the design process, this study demonstrated great promise, as the lattices were modelled within the same CAD environment.

design process

lattices

as

CAD


Input: Based on the design optimisation of a missile launcher beam on a macro- and mesoscale, H exemplarily demonstrated the potential of multi-scale optimisation.

design

macro- and mesoscale

missile launcher beam


Input: They have effectively combined TO with partial substitution of solids with lattices, to design a lightweight beam using the commercial software Altair Inspire and Materialise Magics.

lattices

lightweight

software

design

beam


Input: 2 Experimental benchmarking of 3D-printed lattices In contrast to the previous studies, Beyer and Figueroa tested different unit cell structures experimentally and Harl even determined the performance of optimized lattice structures by comparing them to numerical results.

Experimental

unit cell

performance

lattice structures


Input: The experimental verification is vital as structural optimisation and DfAM aspects are mutually dependent.

experimental

as


Input: This stems from the individual characteristics and limitations of different AM processes affecting the properties.

AM processes

properties


Input: As outlined by Gibson, this is related to common meso- and microstructural features of cellular structures, affecting the structural performance, including: 1) material properties; 2) cell topology and shape; 3) relative density of structure.

As

microstructural

material properties

cell topology

structure

cellular structures

structural performance

relative density


Input: As the process-parameters influence the microstructure and consequently the performance, verification with the numerical model becomes vital for estimating the actual properties and improving future models.

As

microstructure

performance

verification

model

properties


Input: In, Netfabb's Selective Space Structures tool was utilized to create lattices from rectangular prisms and hexagonal geometries, which were subsequently manufactured using the PolyJet and SLM process for polymers and aluminium, respectively.

tool

lattices

geometries

manufactured

PolyJet

process

hexagonal

SLM

polymers

aluminium


Input: The compression and flexure tests of unit cells composed of a polymer revealed that the hexagonal unit cells show greater yield strengths and that comparable properties with the solid pendant can most likely be achieved with vertical trusses in the cell.

compression

yield strengths

flexure tests

unit cells

properties

vertical

polymer

be

hexagonal unit cells

cell


Input: Within the scaled lattices fabricated from polymer and aluminium, it was found that the kagome structure displayed the best performance-to-mass ratio.

lattices fabricated

polymer

aluminium

kagome structure


Input: Moreover, it was reported that the aluminium lattice was superior to the polymer counterpart with respect to the solid structures, possibly stressing differences in manufacturing and therefore highlighting the role of DfAM.

aluminium lattice

polymer

manufacturing


Input: A connection between relative cell density, unit cell structure and structural performance, was established, giving designers and engineers helpful indications for the selection of the adequate lattice configuration.

cell density

unit cell

structure

lattice configuration

structural performance


Input: Similarly, Harl employed the CAESS ProTOp software for both the lattice generation and the subsequent TO of the lattice.

software

lattice

lattice generation


Input: The latter was conducted to improve the structural performance by lowering the local stress concentration to which cellular structures are prone to.

structural performance

local stress concentration

cellular structures


Input: Using selective laser sintering with polyamide, the designs were tested in flexure and the results clearly highlight the potential of using TO lattices in terms of weight-reduction, robustness and stiffness as well as its superiority over uniform lattices.

selective laser sintering

polyamide

as

as

designs

flexure

lattices

lattices

robustness

stiffness


Input: The next paragraphs build on this idea of TO cellular structures by locally changing the cell density with the use of commercial software.

build

cellular structures

cell density

software


Input: In a study by Rezaie a beam under three-point bending was topologically optimized using Abaqus and subsequently manufactured in ABS using FDM.

beam

three-point bending

topologically

manufactured

Abaqus

ABS

FDM


Input: Here, the external boundaries of the bounding box were preserved, and the lattice composed of hollow cubic unit cells was mapped onto a SIMP-result.

boundaries

bounding box

lattice

unit cells


Input: Additionally, manufacturability was taken into consideration by tailoring the hole-size to match the printer's resolution.

manufacturability

printer

resolution


Input: In comparison with the standard topologically optimized beam, the loss in performance turned out to be very minor.

standard

performance

beam

be


Input: Especially when considering the more fabrication-friendly design of the cellular lattice, this method can be a viable alternative for lightweight structures.

design

lattice

be

lightweight structures


Input: The significance of the results, however, must be reviewed critically, due to insufficient batch size and the well-known and inherent quality fluctuations in AM.

be

quality

AM


Input: Improved quality control measures are therefore needed form a manufacturing standpoint while an extensive data library will ease the choice in adequate lattice configurations from a design perspective.

quality control

data

lattice configurations

manufacturing

design


Input: These aspects constitute -among others-a necessity with the increasing uptake of AM across industries.

AM

industries


Input: With the combination of the density-gradients from TO with a size optimisation, Daynes derived functionally graded truss-structures that align with the isostatic lines i.e.

functionally graded truss-structures

isostatic lines


Input: the principal stresses during loading.

principal stresses


Input: By making use of the Altair OptiStruct software, a topologically optimized design is automatically obtained, substituted by pre-selected unit cells before a size optimisation ensures that the overall target density is achieved.

software

topologically

unit cells

design

density


Input: Upon the information on in-plane stresses and orientation extracted from the software, the authors developed a MATLAB subroutine to create a functionally graded mesh, which was fed back into the software for analysis.

orientation extracted

software

software

functionally graded mesh


Input: The substitution of the domain with BCC unit cells conformal with the isostatic lines resulted in a graded lattice with improved structural performance.

domain

BCC

isostatic lines

lattice

cells

structural performance


Input: Twice the stiffness and about 75 times greater strength were demonstrated in the experimental three-point bending tests compared to the uniform lattice design.

stiffness

strength

experimental

bending tests

lattice design


Input: These study highlights how much potential is still untapped in commercial software regarding the utilization of tailored, functionally graded lattices for enhanced specific structural performance.

software

functionally graded lattices

structural performance


Input: 3 Commercial and academic software solutions for TO and the generation of cellular structures AM-specific design tools, incorporating TO or the implementation of lattices, are central to the greater adoption of AM.

software

lattices

cellular structures

design

AM


Input: Today's software landscape for AM-specific design provides a range of features that have been summarized in the supplementary information of this review.

software

design

range


Input: It is important to note, that the majority of commercial software to-date solve specific problems that are common for a wide range of industrial applications.

software

range

industrial


Input: 14a illustrates the proportionate distribution of underlying TO-methods/approaches in commercial software to-date.

distribution

software


Input: 14b constitutes the predominant file formats available in current lattice generation software.

file

lattice generation


Input: Analogously, lattice generation software is dominated by STL file formats, however, with the emerging complexity in e.g.

lattice generation

STL

file

complexity


Input: multi-material prints we see the adoption and market share increase of 3MF and AMF file formats.

multi-material

AMF


Input: To evaluate the effectiveness of the different software, more benchmarking research will be needed.

effectiveness

software

research

be


Input: A first attempt, recently published by Saadlaoui compared the performance of a topologically optimized cube under compression loading using Optistruct and Abaqus.

performance

topologically

cube

compression

Abaqus


Input: A stress-constrained optimisation and a discrete-compliance optimisation were conducted in Abaqus as well as a continuous compliance optimisation in Optistruct.

stress-constrained

Abaqus

as

continuous compliance


Input: Both numerical and experimental results were obtained for the three approaches, whereby SLM was adopted for the fabrication of the specimens.

experimental

SLM

fabrication


Input: This was explained by the consideration of internal material behaviour for the numerical model rather than the external criteria in the experiment.

material

model

experiment


Input: This aspect also includes local plastic deformations in the actual specimen, which do not necessarily affect the global elastic properties or mechanical strength and which are not accounted for in the commonly employed linear-elastic computational models, as stated by Saadlaoui.

local plastic deformations

elastic

mechanical strength

computational models

as


Input: In terms of the computational procedures, the study revealed that the stress-constrained optimisation approach has the highest computational cost, but the corresponding specimen demonstrated the best mechanical performance with respect to the ratio of strength to weight.

stress-constrained

mechanical

ratio of strength

weight


Input: Computational efficiency and power are particularly important in continuum structural optimisations and will be key for viable design procedures in large-scale, multifunctional, multiscale and cellular-based TO.

Computational efficiency

continuum

power

be

design


Input: Recent efforts made to improve the feasibility of TO codes for machines with standard computational performance are equally important as the more salient examples, exploiting immense resources to explore what is ultimately possible.

feasibility

standard

performance

machines

as


Input: General conclusions, drawn from this review, can be summarized as: Superior solutions/designs for AM-parts can be obtained using structural optimization methods such as TO if DfAM considerations are included.

be

as

be

as

structural optimization methods


Input: This elucidates the need for a holistic design approach, paving way for how we design for AM in the future.

design

design

AM


Input: Aspects of digitalization are still somewhat underrepresented and pose a bottleneck between design and manufacturing, including computationally inexpensive models and an entirely self-contained process from CAD file to Gcode.

bottleneck

process

design

manufacturing

CAD file


Input: To bridge the gap to manufacturing, CAD/CAM software needs to be further improved, pathing among others the way for greater efficiency and compatibility when post-processing digital designs.

bridge

manufacturing

CAD/CAM software

be

post-processing

designs


Input: Both multifunctional TO-based designs, considering multiple objectives and part-integration as well as latticing were considered particularly promising for lightweight high-performance parts.

designs

as

as

lightweight


Input: Functionally graded structures, specifically those that are optimized to better conform to the load trajectories, are inciting increased research interest.

Functionally graded structures

research


Input: The most prominent TO method, both in academia and industry, is the density-based approach assuming isotropic material property.

industry

isotropic material


Input: Level set methods seem to establish themselves increasingly in the market, due to the intrinsic smooth boundary representation, which is of great benefit for a streamlined design procedure.

set

smooth boundary

design


Input: The sheer amount of software available for both TO and latticing that includes AM-specific design constraints, clearly demonstrates the industry is gravitating towards a wide application of AM.

software

design

industry

AM


Input: This is supported by the intensified interest in the academic community to make optimisation process more computationally efficient which is a necessity to make AM more accessible for a range of industries.

process

AM

range

industries


Input: As reviewed, the majority of studies concentrate on structural optimisation with the inclusion of inclination angle constraints as opposed to fabrication, materials or digitalization.

As

inclusion

as

structural optimisation

materials

inclination angle

fabrication


Input: Aspects deemed important for future work on the design and structural optimisation in AM, are as follows: Consistency through benchmarking mathematically-driven models and confidence via experimental verification will be important as industries are on the verge of adopting AM as means of production.

design

structural optimisation

Consistency

experimental

AM

AM

production

as

be

as


Input: Structural analyses accommodating path planning i.e.

Structural analyses

path planning


Input: tailored infills and a simultaneous optimization of process and design will constitute a central aspect to improved structural performance in the future.

optimization

process

design

structural performance


Input: In conjunction with a growing interest in fibre-reinforced AM, a key challenge will be to develop TO methods that account for anisotropic material considerations, paving the way for next-generation lightweight structures.

fibre-reinforced AM

be

anisotropic

lightweight structures


Input: The digital AM-workflow for print-ready designs would immensely benefit from smooth boundary representations.

designs

smooth boundary


Input: post-processing procedures for discrete solutions and more recently the intensified use of the level set method were observed.

post-processing

discrete solutions

set


Input: Their uptake by the industry into upcoming software could potentially constitute a boost for the future of AM.

industry

software

AM


Input: In light of both increasing complexity through the inclusion of DfAM constraints and multi-objective optimization as well as the orientation towards large-scale designs, generating high-resolution designs efficiently, will become a key challenge across all TO methods in the future.

complexity

optimization

orientation

inclusion

as

as

designs

high-resolution designs


Input: Contrary to previous developments, the industry pulls academia with regard to generative design, rather than taking solutions up.

industry

generative design


Input: Due to the feasibility of economically producing large-scale metal components with relatively high deposition rates, significant progress has been made in the understanding of the Wire Arc Additive Manufacturing process, as well as the microstructure and mechanical properties of the fabricated components.

feasibility

process

microstructure

mechanical properties

fabricated

metal

as

as

components

components

high deposition rates

Wire Arc Additive Manufacturing


Input: As WAAM has evolved, a wide range of materials have become associated with the process and its applications.

As

range

materials

process


Input: This article reviews the emerging research on WAAM techniques and the commonly used metallic feedstock materials, and also provides a comprehensive over view of the metallurgical and material properties of the deposited parts.

research

material properties

WAAM

metallic

feedstock materials

metallurgical


Input: Common defects produced in WAAM components using different alloys are described, including deformation, porosity, and cracking.

defects

deformation

cracking

WAAM

components

alloys

porosity


Input: Methods for improving the fabrication quality of the additively manufactured components are discussed, taking into account the requirements of the various alloys.

fabrication

additively manufactured

alloys


Input: The integration of materials and manufacturing process to produce defect-free and structurally-sound deposited parts remains a crucial effort into the future.

materials

manufacturing process


Input: In recent years, wire arc additive manufacturing has increasingly attracted attention from the industrial manufacturing sector due to its ability to create large metal components with high deposition rate, low equipment cost, high material utilization, and consequent environmental friendliness.

wire arc additive manufacturing

industrial

metal

components

equipment

high deposition rate

material utilization


Input: The origin of the WAAM process can be traced back to the 1925s when Baker proposed to use an electric arc as the heat source with filler wires as feedstock materials to deposit metal ornaments.

WAAM

process

heat source

materials

be

as

as

metal

electric arc


Input: The WAAM technique bears various nomenclatures by different research institutions worldwide, as shown in 1.

WAAM

research

as


Input: Today, WAAM has become a promising fabrication process for various engineering materials such as titanium, aluminium, nickel alloy and steel.

WAAM

fabrication

engineering materials

as

aluminium

nickel alloy

steel


Input: Compared to traditional subtractive manufacturing, the WAAM system can reduce fabrication time by 40and post-machining time by 15depending on the component size.

traditional subtractive manufacturing

post-machining

WAAM system

component

fabrication time


Input: For instance, recent breakthroughs in WAAM technology have made it possible to fabricate aircraft landing gear ribs with a saving of approximately 78% in raw material when compared with the traditional subtractive machining process.

WAAM

fabricate

traditional subtractive machining process

technology

gear

raw material


Input: Due to the highly complex nature of WAAM, many different aspects of the process need to be studied, including process development, material quality and performance, path design and programming, process modelling, process monitoring and online control.

WAAM

process

process

performance

process

process monitoring

be

material

design

modelling


Input: Several WAAM review papers have been published by leaders in the field, covering state-of-the-art systems, design, usage, in-situ process monitoring, in-situ metrology and in-process control and sensing.

WAAM

state-of-the-art

in-situ

in-situ

design

sensing


Input: Nevertheless, there is still a need for a systematic review of the properties of various WAAM-processed materials, the defects associated with different alloys, and a summary of current and future research directions that are aimed at quality improvements for the alloy classes of interest.

properties

materials

defects

research

quality

alloys

alloy


Input: This paper reviews the microstructure and mechanical properties of various metals, including titanium and its alloys, aluminum and its alloys, Ni-based alloy, steel and other intermetallic materials fabricated by the various WAAM processes.

microstructure

mechanical properties

fabricated

processes

metals

titanium

alloys

aluminum

alloys

Ni-based alloy

steel

intermetallic

WAAM


Input: The common defects that have been found to occur for different materials are also summarized.

defects

materials


Input: The current methods for both in-process and post-process quality improvement and defect reduction are introduced.

post-process

defect


Input: Finally, a discussion is given on improving quality of WAAM fabricated parts through process selection, feedstock optimization, process monitoring and control and post-process, including proposals for future research directions.

quality

fabricated

process selection

process monitoring

post-process

research

WAAM

feedstock optimization


Input: 2 Wire arc additive manufacturing systems 2.1 Classification of WAAM process Depending on the nature of the heat source, there are commonly three types of WAAM processes: Gas Metal Arc Welding -based, Gas Tungsten Arc Welding -based and Plasma Arc Welding -based.

Wire arc additive manufacturing

WAAM

WAAM

Gas Metal Arc Welding

Gas Tungsten Arc Welding

Plasma Arc Welding

Classification

process

heat source

processes


Input: As listed in 1, specific class of WAAM techniques exhibit specific features.

As

WAAM


Input: The deposition rate of GMAW-based WAAM is 2times higher than that of GTAW-based or PAW-based methods.

deposition rate

GMAW-based WAAM


Input: However, the GMAW-based WAAM is less stable and generates more weld fume and spatter due to the electric current acting directly on the feedstock.

GMAW-based WAAM

weld fume

spatter

feedstock


Input: The choice of WAAM technique directly influences the processing conditions and production rate for a target component.

WAAM

production

component


Input: 2.2 Robotic WAAM system Most WAAM systems use an articulated industrial robot as the motion mechanism.

WAAM system

WAAM systems

articulated industrial robot

mechanism


Input: Two different system designs are available.

designs


Input: The first design uses an enclosed chamber to provide a good inert gas shielding environment, similar to laser Power-Bed Fusion systems.

design

inert gas

Fusion

laser


Input: The second design uses existing or specially designed local gas shielding mechanisms, with the robot positioned on a linear rail to increase the overall working envelop.

design

designed

gas

robot


Input: It is capable of fabricating very large metal structures up to several a meters in dimension.

fabricating

metal

dimension


Input: 2 shows an example of this design of WAAM system, used for the research and development at the University of Wollongong.

design

WAAM system

research


Input: Fabricating a part using WAAM involves three main steps: process planning, deposition, and post processing.

Fabricating

WAAM

process planning

deposition

post processing


Input: For a given CAD model, 3D slicing and programming software generates the desired robot motions and welding parameters for the deposition process, aimed at producing defect-free fabrication with high geometrical accuracy.

CAD model

3D slicing

software

parameters

robot

welding

deposition process

fabrication

accuracy


Input: Based on the welding deposition model for the specific material being used to fabricate the component, the 3D slicing and programming software offer automated path planning and process optimization to avoid potential process-induced defects.

welding

fabricate

deposition

software

process optimization

defects

specific material

component

3D slicing

automated path planning


Input: During fabrication, the robot and external axis provide accurate motion for the welding torch to build up the component in a layer-by-layer fashion.

fabrication

robot

welding torch

component

accurate

build

layer-by-layer fashion


Input: Advanced WAAM systems can be equipped with various sensors to measure welding signals, deposited bead geometry, metal transfer behaviour and interpass temperature, thereby supporting in-process monitoring and control to achieve higher product quality.

WAAM systems

sensors

be

metal

welding

deposited bead geometry

interpass temperature

product quality


Input: This is an area of current and future research interest, with the potential for significantly improving WAAM process performance.

area

research

process performance

WAAM


Input: 3 Metals used in WAAM process WAAM processes use commercially available wires which are produced for the welding industry and available in spooled form and in a wide range of alloys as feedstock materials.

Metals

alloys

feedstock materials

WAAM

process

processes

welding industry

range


Input: 2 indicates the commonly used alloys and their various applications in WAAM.

alloys

WAAM


Input: Manufacture of a structurally sound, defect free, reliable part requires an understanding of the available process options, their underlying physical processes, feedstock materials, process control methods and an appreciation of the causes of the various common defects and their remedies.

Manufacture

defect

process

physical processes

process control

defects

feedstock materials


Input: This section reviews the metals that are commonly used in WAAM, with a particular emphasis on the microstructure and mechanical properties of the additively manufactured alloys.

metals

WAAM

additively manufactured

microstructure

mechanical properties


Input: 3.1 Titanium alloys Titanium alloys have been widely studied for application of additive manufacturing in aerospace components due to their high strength-to-weight ratio and inherently high material cost.

Titanium alloys

Titanium

alloys

material

additive manufacturing

aerospace components


Input: There are increasing demands for more efficient and lower cost alternatives to the conventional subtractive manufacturing methods, which suffer very low fly-to-buy ratios for many component designs.

conventional subtractive manufacturing methods

component


Input: There exists many business opportunities for the WAAM process, particularly for large-sized titanium components with complex structures.

WAAM

process

complex structures

titanium

components


Input: The distinctive WAAM thermal cycle, which involves repeated heating and cooling, produces meta-stable microstructures and inhomogeneous compositions in the fabricated part.

WAAM

heating

cooling

thermal cycle

meta-stable microstructures

fabricated


Input: For example, Baufeld investigated the microstructures of Ti6Al4V fabricated using a GTAW-based WAAM system, and found two distinctive regions on the as-built wall.

microstructures

fabricated

WAAM system


Input: In the bottom region, where alternating bands are perpendicular to the build direction, a basketwave Widmanststructure with phase lamellae is present, while in the top region, where no such bands appear, needle-like precipitate is the main structure.

build direction

phase

structure

lamellae

precipitate


Input: Similar microstructural evolution has also been observed in the PAW-based process.

microstructural evolution

process