Input: Both Hewlett Packard and Xerox ‘are investing in 3D printing research and technology development.

Hewlett Packard

Xerox

3D printing

technology


Input: Each AM technologies have manufacturing constraints linked by printing technology, used material and expected functions (aesthetic, mechanical, use, etc).

AM technologies

manufacturing constraints

aesthetic

printing technology

material

mechanical


Input: Areas of interest which have used 3D printing to create objects include aeronautics, architecture, automotive industries, art, dentistry, fashion, food, jewellery, medicine, pharmaceuticals, robotics and toys.

Areas of interest

fashion

jewellery

medicine

3D printing

aeronautics

architecture

automotive industries

art

dentistry

pharmaceuticals

robotics

toys


Input: Automotive manufacturers exploited the technology because of the ability to help new products get quickly to the market and in a predictable manner.

Automotive

technology

predictable


Input: Aerospace companies are interested in these technologies because of the ability to realise highly complex and high-performance products.

Aerospace

technologies


Input: Integrating mechanical functionality, eliminating assembly features and making it possible to create internal functionality (like cooling channels), internal honeycomb style structures, new topological optimisation structure etc.

mechanical functionality

honeycomb

structure

assembly

cooling channels

topological optimisation


Input: combine to create lightweight structures.

lightweight structures


Input: Medical industries are particularly interested in AM technology because of the ease in which 3D medical imaging data can be converted into solid objects.

Medical industries

AM technology

3D medical imaging

be


Input: Thus, each AM technology have advantages and disadvantages for own applications and we propose to review them.

AM technology


Input: Authors have chosen to classify the technologies according to hardening system or melting system which are characterised by a laser, a flashing source, an extrusion or a jetting.

technologies

flashing source

hardening system

melting system

laser

extrusion

jetting


Input: SLA–Stereolithography is the first of the technologies developed originally and simultaneously in France and in the USA to tackle rapid prototyping bottlenecks, as well as faster and better design needs (CAD induced).

SLA

Stereolithography

technologies

bottlenecks

rapid prototyping

CAD

as

as

design


Input: In 1986, 3D Systems was founded by Chuck Hull to commercialise this process.

3D Systems

Chuck

process


Input: Photolithographic systems build shapes using light to selectively solidify photosensitive resins.

Photolithographic systems

build

solidify

photosensitive resins


Input: The laser lithography approach is currently one of the most used AM technologies.

laser lithography

AM technologies


Input: Models are defined by scanning a laser beam over a photopolymer surface.

scanning

laser beam

photopolymer


Input: For a few years, researchers have developed techniques to apply SLA to directly make ceramics.

SLA

ceramics


Input: Ceramic powder (silica and alumina) is dispersed in a fluid UV curable monomer to prepare a ceramic–UV curable monomer suspension.

Ceramic powder

silica

alumina

fluid UV curable monomer

monomer


Input: The building process is the same as conventional SLA and the monomer solution is cured forming a ceramic–polymer composite layer.

building process

as

monomer solution

composite

SLA

cured


Input: The prototypes have higher stiffness than a standard workpiece and their temperature resistance over 200 °C.

prototypes

standard

stiffness

temperature resistance


Input: A higher resolution machine has been developed and called microstereolithography and it can print a layer with thickness of less than 10 μm.

higher resolution

layer

microstereolithography

print


Input: The microstereolithography shares the same principle with its macro scale counterpart, but in different dimensions.

microstereolithography

macro scale

dimensions


Input: In microstereolithography, an UV laser beam is focused to 1–2 μm to solidify a thin layer of 1–10 μm in thickness.

microstereolithography

UV laser beam

solidify

layer


Input: Submicron resolution of the x–y–z translation stages and the fine UV beam spot enable precise fabrication of real 3D complex microstructures.

Submicron resolution

UV beam

precise fabrication

microstructures


Input: SLM–Selective Laser Melting–the system starts by applying a thin layer of the powder material spread by a roller on the building platform.

SLM

Selective Laser Melting

layer

powder material

roller

building platform


Input: A powerful laser beam then fuses the powder at exactly the points defined by the computer-generated component design data.

laser beam

computer-generated

data

fuses

powder

component


Input: The platform is then lowered and another layer of powder is applied.

platform

layer

powder


Input: Once again the material is fused so as to bond with the layer below at the predefined points.

material

as

fused

predefined points

layer


Input: During the process, successive layers of metal powder are fully melted and consolidated on top of each other.

process

melted

metal powder


Input: Today, the 3D printer manufacturers propose machines with powerful double or multi laser technology with layers from 75 to 150 μm in thickness.

3D printer

machines

multi laser technology


Input: The material types that can be processed include steel, stainless steel, cobalt chrome, titanium and aluminium.

material

be

steel

stainless steel

cobalt chrome

titanium

aluminium


Input: Electron Beam Melting is a powder process which distinguishes by its superior accuracy and high-power electron beam (up to 3000 W while maintaining a scan speed) that generates the energy needed for high melting capacity and high productivity.

Electron Beam Melting

powder process

accuracy

electron beam

melting capacity

productivity

scan speed


Input: Selective Laser Sintering (SLS)–use a high-power laser to fuse small particles (polyamide, steel, titanium, alloys, ceramic powders, etc).

Selective Laser Sintering

SLS

fuse

high-power laser

particles

polyamide

steel

titanium

alloys

ceramic powders


Input: As the SLM, the powder bed is lowered by one layer thickness, a new layer of powder is applied on top, and the process is repeated until the model is completed.

As

powder

SLM

powder bed

layer thickness

layer

process

model


Input: But what sets sintering apart from melting is that the sintering processes do not fully melt the powder, but heat it to the point that the powder can fuse together on a molecular level.

sintering

melting

sintering

fuse

processes

melt

heat

powder

powder


Input: The latest SLS machines offer laser powers from 30 W to 200 W in a CO² chamber controlled (in range ProX and sPro).

SLS

machines

chamber controlled

laser powers

range


Input: The porosity of the material can be controlled.

porosity

material

be


Input: This porosity requests a post-treatment by infiltration to harden the final model like the bronze use to the steel.

porosity

post-treatment

infiltration

harden

model

bronze

steel


Input: The SLS prototypes have a greater dimensional accuracy than the PolyJet and 3DP models.

SLS prototypes

PolyJet

dimensional accuracy


Input: Direct Metal Laser Sintering (DMLS)–is similar to SLS with some differences.

Direct Metal Laser Sintering

DMLS

SLS


Input: The technology is a powder bed fusion process by melting the metal powder locally using the focused laser beam.

technology

focused laser beam

powder bed fusion process

melting

metal powder


Input: A product is manufactured layer by layer along the Z axis and the powder is deposited via a scraper moving in the XY plane.

manufactured

layer by layer

powder

scraper


Input: The DMLS process from EOS© is well established for the net shape fabrication of prototype and short series tooling for plastic injection moulding.

DMLS

net shape

fabrication

plastic injection moulding

prototype

short series tooling


Input: The first generation of EOS machine includes a 200-W laser source when the second generation (EOSINT M280) was launched with a 400-W fibre laser.

EOS

laser source

fibre laser


Input: The trend shows an increase in laser power and also an increase in work chamber.

trend

laser power


Input: DMLS often refers to the process that is applied to metal alloys for the manufacturing direct parts in the industry including aerospace, dental, medical and other industry that have small to medium size, highly complex parts and the tooling industry to make direct tooling inserts.

DMLS

manufacturing

process

metal alloys

industry

aerospace

dental

medical

industry

tooling industry

tooling inserts


Input: Today, recent developments in the powders coupled with the durability of the materials are extending its reach to the direct manufacturing of functional prototypes for powder metallurgical and cast components.

powders

durability

materials

direct manufacturing

functional prototypes

powder metallurgical

cast


Input: Support structures are required for most geometry because the powder alone is not sufficient to hold in place the liquid phase created when the laser is scanning the powder.

Support structures

geometry

scanning

powder

powder

liquid phase

laser


Input: The rapid manufacturing of parts by the DMLS process requires the use of a powder, which is composed of two types of particles.

rapid manufacturing

DMLS

powder

particles


Input: One type has a low melting point, and the other a high melting point.

melting point

melting point


Input: The high-melting point particles generate a solid matrix, while the particles with the low melting point bind the matrix after being melted by the laser energy input.

high-melting point

melting point

solid matrix

particles

melted

laser energy

bind


Input: In order to reduce lead time and increase in build speed, a new technology has emerged derivative from SLA.

lead time

build speed

technology

SLA


Input: On the same principle proposed by Pomerantz a photomask system (masking technology) to produce 3D models, the DLP–Digital Light Processing, also known as FTI–Film Transfer Imaging, use the UV photopolymerised materials.

photomask

as

photopolymerised materials

masking

UV

3D models

DLP

Digital Light Processing

Film Transfer Imaging


Input: A film is coated in resin which is then cured by a UV flash of light from a projector for each slice of product.

coated

resin

cured

UV flash

slice

projector


Input: Unlike the 3D laser printer, the DLP projector projects the entire layer, and not only of lines or points.

3D laser printer

DLP

layer


Input: This method allows building much quicker than other methods of rapid prototyping by substituting scanning time of a laser.

rapid prototyping

laser

scanning time


Input: With SLA, the part descends downward into the resin, whereas it is pulled upward out of the resin in a DLP printer.

SLA

DLP printer

resin

resin


Input: SLA process is gentler on the forming implant than the DLP process because, in DLP, the part must attach much more firmly to the build platform to prevent damage when newly formed layers are peeled from the basement plate after each exposure.

SLA

forming implant

build platform

basement plate

process

exposure

DLP

DLP

damage


Input: The building platform can be angled upward and the light source down in some masking machines (e.g.

building platform

light source

masking machines

be


Input: Phidias technologies with Prodways 3D printer).

technologies

3D printer


Input: The DLP technology is known for its high resolution, typically able to reach a layer thickness of down to 30 μm.

DLP

high resolution

layer thickness


Input: A new innovation in mask-image-projection based on the stereolithography process has been developed to produce objects with digital materials.

mask-image-projection

process

digital materials

stereolithography


Input: The proposed approach is based on projecting mask images with a new two-channel system design which reduces the separation force between a cured layer and the resin vat.

mask images

two-channel

separation force

cured layer

design

resin vat


Input: The fabrication results demonstrate that the developed dual-material process can successfully produce 3D objects with spatial control over placement of both material and structure.

fabrication

dual-material

spatial control

structure

3D objects

material


Input: Close to DLP principle, the Continuous Liquid Interface Production (CLIP) production is a new type of AM that uses photopolymerisation working in continuous, thanks to a projector and the ability to control oxygen levels throughout an oxygen-permeable membrane.

DLP

Continuous Liquid Interface Production

CLIP

production

AM

photopolymerisation

projector

oxygen

oxygen-permeable membrane


Input: This latter process is 30 times faster than the SLS or the MJM.

process

SLS

MJM


Input: Extrusion technologies- Fused Deposition Modeling (FDM) is a layer AM process that uses a thermoplastic filament by fused depositing.

Extrusion

Fused Deposition Modeling

FDM

AM process

fused depositing

layer

thermoplastic filament


Input: FDM is trademarked by Stratasys Inc in the late 1980s and the equivalent term is Fused Filament Fabrication (FFF).

FDM

Fused Filament Fabrication

FFF

Stratasys


Input: The filament is extruded through a nozzle to print one cross section of an object, then moving up vertically to repeat the process for a new layer.

filament

extruded

print

nozzle

cross section

process

layer


Input: The most used materials in FDM are ABS, PLA and PC (Polycarbonate) but you can find out new blends containing wood and stone as well as filaments with rubbery characteristics.

materials

rubbery characteristics

FDM

ABS

PLA

PC

Polycarbonate

blends

wood

stone

as

as


Input: Compared to ABS, PLA responds differently to moisture, to ageing UV with a discoloration and to withdrawal of material.

ABS

PLA

material

ageing UV

discoloration


Input: To predict the mechanical behaviour of FDM parts, it is critical to understand the material properties of the raw FDM process material, and the effect that FDM build parameters have on anisotropic material properties.

mechanical behaviour

material properties

FDM

FDM

FDM

material

build parameters

anisotropic material properties


Input: The support material is often made of another material and is detachable or soluble from the actual part at the end of the manufacturing process (except for the low-cost solutions, which use the same raw material).

support material

material

raw material

detachable

soluble

manufacturing process


Input: The disadvantages are that the resolution on the z axis is low compared to other AM process (0.25 mm), so if a smooth surface is needed a finishing process is required and it is a slow process sometimes taking days to build large complex parts.

resolution

build

AM process

mm

finishing process

smooth surface

process


Input: FDM technology is the most popular of desktop 3D printers and the less expensive professional printers.

FDM

desktop 3D printers

printers


Input: Directed Energy Deposition (DED)–covers a range of terminology: Laser Engineered Net Shaping (LENS), directed light fabrication (IFF–Ion Fusion Formation), Direct Metal Deposition (DMD), 3D laser cladding.

Directed Energy Deposition

DED

Laser Engineered Net Shaping

LENS

directed light fabrication

IFF

Ion Fusion Formation

Direct Metal Deposition

DMD

3D laser cladding

range


Input: It is a more complex printing process commonly used to repair or add additional material to existing components.

printing process

material

components


Input: LENS is used to melt the surface of the target point while a stream of powdered metal is delivered onto the small targeted point.

LENS

melt

surface

powdered metal


Input: IFF melts a metal wire or powder with a plasma welding torch to form an object.

IFF

metal wire

powder

plasma welding torch


Input: This is a near-net-shape manufacturing process that uses a very hot ionised gas to deposit a metal in small amounts.

near-net-shape manufacturing

ionised gas

metal


Input: DMD melts metal wire by electron beam as feedstock used to form an object within a vacuum chamber.

DMD

metal wire

as

electron beam

vacuum chamber


Input: The objects created in DED can be larger, even up to several feet long.

DED

be


Input: Dough Deposition Modeling (DDM)–groups the marginal processes which file different doughs (Figure 6).

Dough Deposition Modeling

DDM

processes

file

doughs


Input: Some technologies based on FDM printers use a syringe to deposit a dough material like silicone, food dough, chocolate, etc.

technologies

FDM printers

syringe

dough material

silicone

food dough

chocolate


Input: A syringe-based extrusion tool which uses a linear stepper motor to control the syringe plunger position.

syringe-based extrusion tool

linear stepper motor

syringe plunger position


Input: The medical research uses the deposition of biomaterial and cells to realise a tissue structure.

medical

cells

deposition

tissue structure

biomaterial


Input: It presents a novel method for the deposition of biopolymers in high-resolution structures, using a pressure-activated microsyringe.

deposition

biopolymers

high-resolution

pressure-activated microsyringe


Input: Other works show applications to extrude a bio-based material to reconstitute a model and preserve the ecological environment.

extrude

bio-based material

model

ecological environment


Input: Experimentation uses a piston and 3D printer head adapted on a CNC machine to deposit a pulpwood based on wood flour to create a reconstituted wood product.

piston

3D printer head

CNC machine

pulpwood

wood flour

reconstituted wood product


Input: Jet technologies-MJM–Multi Jet Modeling–deposits droplets of photopolymer materials with multi jets on a building platform in ultra-thin layers until the part is completed.

Jet technologies

MJM

Multi Jet Modeling

droplets

ultra-thin layers

photopolymer materials

multi jets

building platform


Input: Two different photopolymer materials are used for building, one for the actual model and another gel like material for supporting.

photopolymer materials

gel

material

model


Input: The photopolymer layers are cured by UV lamps and a gel-like polymer supports the complexity of geometry in wrapping it.

photopolymer layers

gel-like polymer

cured

UV lamps

complexity

geometry

wrapping


Input: The soluble gel-like (support material) is then removed by a water jet.

soluble

gel-like

support material

water jet


Input: The PolyJet technique reproduced details more accurately with a very good surface finish and smoothness.

PolyJet technique

accurately

surface finish

smoothness


Input: The accuracy of a PolyJet machine can reach thickness from 50 to 25 μm, besides the parts have a higher resolution.

accuracy

PolyJet machine

higher resolution


Input: Also known as Thermojet, some systems can produce wax models in jetting tiny droplets of melted liquid material which cool and harden on impact to form the solid object.

as

wax

melted liquid material

jetting

droplets

harden

impact


Input: 3DP–three-dimensional printing, also known as CJP–Colour Jet Printing, combines powders and binders.

three-dimensional printing

Colour Jet Printing

as

powders

binders


Input: 3DP has been developed by the MIT.


Input: Each layer is created by spreading a thin powder layer with a roller and the powder is selectively linked by inkjet printing of a binder.

layer

layer

powder

powder

binder

roller

inkjet printing


Input: The build tray goes down to create the next layer.

build tray

layer


Input: This process has been used to fabricate numerous metal, ceramic, silica and polymeric components of any geometry for a wide array of applications.

process

geometry

fabricate

metal

ceramic

silica

polymeric components


Input: Other powders have been tested to realise green products in wood.

powders

wood

green products


Input: 3DP can print in multicolour directly into the part during the build process from a colour cartridge.

print

build

cartridge


Input: The final model is extracted from the powder bed to realise infiltration with liquid glue.

model

extracted

infiltration

powder bed

liquid glue


Input: The infiltrate improves the colour definition and the mechanical behaviours.

mechanical behaviours


Input: 3DP can provide architects a useful tool to quickly create a realistic model.

tool

model


Input: Prometal is a 3D printing process to build rapid tools and dies.

Prometal

3D printing

build

tools

dies


Input: This is a powder-based process in which stainless steel is used.

process

stainless steel


Input: The printing process occurs when a liquid binder is spurt out in jets to steel powder.

printing process

liquid binder

steel powder


Input: A final treatment is required to solidify the part like sintering, infiltration and finishing processes.

solidify

infiltration

sintering

finishing processes


Input: Liquid Metal Jetting (LMJ) involves the jetting of molten metal in a process similar to inkjet printing, whereby individual molten droplets are ejected and connected to each other.

Liquid Metal Jetting

LMJ

jetting

inkjet printing

molten metal

process

droplets


Input: This process is not commercially available yet.

process


Input: LOM–Laminated Objet Manufacturing–is a rapid prototyping process where a part is sequentially built from layers of paper.

LOM

Manufacturing

rapid prototyping

process


Input: The process consists of the thermal adhesive bonding and laser patterning of uniformly-thick paper layers.

process

adhesive bonding

laser patterning


Input: The system includes an x-y plotter device positioned above a work table vertically movable.

plotter device

work table


Input: The x-y plotter device includes a forming tool to create a layer from a sheet of material positioned on the work table.

plotter device

work table

forming

layer

sheet

material


Input: The layers are bonded to each other with heat-sensitive adhesives provided on one side thereof.

heat-sensitive adhesives


Input: A bonding tool or fuser is mounted to translate across the work table and apply a lamination force and heat to each of the layers.

bonding

heat

fuser

work table

lamination force


Input: The layers are superimposed to give the final object and the layer resolution is defined by the thickness of the paper sheet.

layer resolution

paper sheet


Input: 3D printers can print in full colours (Mcor Technologies).

3D printers

print

Technologies


Input: Stratoconception is a rapid prototyping process with layers of sheets.

Stratoconception

process

rapid prototyping

sheets


Input: It consists in the decomposition of a model by calculating a set of elementary layers called ‘strata’ and by placing reinforcing pieces and inserts in strata.

decomposition

model

strata

strata

set

reinforcing pieces

inserts


Input: The elementary layer are displayed and manufactured by rapid milling or laser-cutting.

layer

manufactured

milling

laser-cutting


Input: The strata are assembled with inserts to rebuild the final object.

strata

inserts


Input: This process is useful thanks to milling of a low-cost sheet in raw material (wood, MDF, PVC, aluminium, etc).

process

milling

sheet

raw material

wood

MDF

PVC

aluminium


Input: When you find out the AM technologies and you can use some of them, experts know that several manufacturing constraints and mechanical behaviours bring complications.

AM technologies

manufacturing constraints

mechanical behaviours


Input: For example, the powder technology leads to extract the final product outside of a power bed before cleaning it and often to applying a post-treatment.

powder technology

power

bed

cleaning

post-treatment


Input: Moreover, the manufacturing orientation of the model influences the quality of geometry because of material gradient and the manufacturing direction.

manufacturing

manufacturing

model

quality

geometry

material gradient


Input: The part orientation can deeply modify the planarity, the circularity and the surface accuracy.

orientation

planarity

circularity

surface accuracy


Input: You have the same constraints with other technologies as the 3DP or DED.

technologies

as

DED


Input: The internal structure of product due to the material orientation, the manufacturing technology and its manufacturing by layers generates use constraints which need to be integrated.

internal structure

material orientation

manufacturing technology

manufacturing

be


Input: We can quote in a non-exhaustive list the anisotropy for the part made by FDM, the crack propagation for powdered parts and the ageing UV for the models in photopolymers.

anisotropy

FDM

crack propagation

ageing UV

photopolymers


Input: You can find out the accuracy of some AM machines from manufacturer sources on the Table 1.

accuracy

AM machines

manufacturer


Input: From a 3D printer to another, designer does not answer to the same need and accuracy is often decisive to get a reliable product or a functional mechanism.

3D printer

accuracy

functional mechanism


Input: Furthermore, the post-treatment, post-machining or post-finishing are often required to get a finished product.

post-treatment

post-machining

post-finishing


Input: The recycling and the raw material cost have to be taken into account too.

recycling

raw material

be


Input: To sum up, a set of stages are to define in upstream to assess the AM technology implications.

set

AM technology


Input: The incrementation of experience greatly improves the engineering and manufacturing process.

engineering

manufacturing process


Input: The expiring patents open the market for others manufacturers proposing of new machines.

patents

machines


Input: Since February 2014, a major patent related to SLS expired (Apparatus for producing parts by selective sintering n.d.).

patent

SLS

selective sintering


Input: New technologies resulting from expiring patents appear with the solutions proposed by the companies DWS Systems (Italy) or Formlabs (USA).

technologies

patents

companies


Input: 3D printing applied to medical has appeared for some years through different applications.

3D printing

medical


Input: The organ transplantation sector has difficulties and the organ printing by jet based on 3d tissue engineering offers a possible solution.

organ transplantation

solution

organ printing

3d tissue engineering


Input: Some research define organ printing as a rapid prototyping computer-aided 3D printing technology based on using layer-by-layer deposition of cell and/or cell aggregates into a 3D gel with sequential maturation of the printed construct into perfused and vascularised living tissue or organ.

research

layer-by-layer deposition

printed construct

organ printing

as

aggregates

3D gel

rapid prototyping

3D printing technology

cell

cell


Input: The success of an implantation depends on compatible materials.

implantation

materials


Input: We can find a variety of biomaterials such as curable synthetic polymers, synthetic gels and naturally derived hydrogels.

biomaterials

as

polymers

synthetic gels

naturally derived hydrogels


Input: Prosthetic is the first biomedical area which has used the 3D printing and it presents several successes.

Prosthetic

biomedical

area

3D printing


Input: We can quote a patient’ s skull anatomy reproduced via 3D printing for pre-surgical use in manual implant design and production and the enhancement of the fixation stability of the custom made total hip prostheses and restore the original biomechanical characteristics of the joint.

s

3D printing

production

implant

biomechanical

design

stability

hip prostheses

joint


Input: Several applications combine some degradable or allogeneic scaffolding with cellular bioprinting to create customised biologic prosthetics that have the great potential to serve as transplantable replacement tissue.

allogeneic scaffolding

cellular bioprinting

prosthetics

as


Input: New articles showed that the medical 3D Printing market might reach 983.2 million $by the year 2020.

medical

3D Printing


Input: Projects for home construction through 3D printing are emerging such as the Shanghai WinSun Decoration Engineering Company.

construction

Engineering

Company

3D printing

as


Input: This company can print the basic components separately before assembling them on site.

company

print

components


Input: These concrete houses are built in one day by 3D printing and their construction costs about 3800 $.

concrete

3D printing

construction


Input: The 3D printer developed by the Chinese group is much larger than a conventional system and uses the same DDM technology.

3D printer

conventional system

DDM technology


Input: The building industry introduced a vocabulary such as rapid construction or rapid building.

building industry

construction

as


Input: The use of the STL format limits the exchange of trades data.

STL format

limits

data


Input: If the STL format allows exporting from a surfacing model towards the specific software, the designer needs to insert rules in upstream work in CAD.

STL format

model

software

insert

CAD


Input: The emergence of more enriched new exchange format appears such as the Additive Manufacturing file Format (AMF) with important parameters (< material >, < composite >, < metadata >, etc.

exchange format

AMF

parameters

as

material

composite

Additive Manufacturing file Format

metadata


Input: ) or the STL 2.0.

STL


Input: Alternative file format exports are also required to support depiction of complex organic geometry, whilst allowing multiple-material and mono/multicolour capabilities; the development of STL 2.0 or Additive Manufacturing file Format (AMF) is promising, particularly for the composition of complex geometries and multiple-material.

file

STL

Additive Manufacturing file Format

support

geometry

multiple-material

mono/multicolour

AMF

composition

complex geometries

multiple-material


Input: The article shows that we need to transfer more trades data to the additive manufacturing machine through an enriched exchange format.

data

exchange format

additive manufacturing machine


Input: The standard ISO/ASTM 52915:2013 Standard specification for additive manufacturing file format (AMF) Version 1.15 describes a framework for an interchange format to address the current and future needs of additive manufacturing technology.

standard

Standard

AMF

framework

ISO/ASTM

additive manufacturing file format

specification

additive manufacturing


Input: The manufacturing units and the small size of AM build tray complicate the production line.

manufacturing

production line

AM build tray


Input: Industrials seek to reduce the lead time and increase in build speed but a lot of additive manufacturing technologies are not adapted.

lead time

build speed

additive manufacturing


Input: The interoperability is little studied by 3D printer manufacturers.

interoperability

3D printer


Input: Reflecting the strategy of some companies like ExOne or Voxeljet, the professional 3D printers can be combined to the production line and offer the largest printers on the world market for 3D printing of sand and metal materials.

companies

3D printers

printers

be

sand

metal materials

production line

3D printing


Input: Announced as a new industrial revolution, the additive manufacturing technologies will make the difference when it will be interoperable with the set of manufacturing process.

as

be

industrial revolution

additive manufacturing

manufacturing process

set


Input: Development orientations show that the new 3D printers will be more integrated inside the production line with the automation and the connectivity with the digital chain.

orientations

automation

3D printers

be

production line

digital chain


Input: A recent example is the emergence of hybrid system combining the 3D printing by laser deposition of metals (DMD) and the CNC machining through the LASERTEC AdditiveManufacturing6 solution proposed by DMG MORI© which accelerates the realisation of the finished product.

hybrid system

3D printing

laser deposition of metals

DMD

CNC machining

solution


Input: In order to reduce the time and cost of moulds fabrication, additive manufacturing is used to develop and manufacture systems of rapid tooling.

moulds fabrication

additive manufacturing

rapid tooling

manufacture


Input: Powder-based sintering processes are now able to produce metal moulds that can withstand a few thousand cycles of injection moulding.

Powder-based sintering

injection moulding

metal


Input: AM technologies propose to manufacture of sand moulds for the casting.

AM technologies

casting

manufacture

sand moulds


Input: A method to produce a lost mould for casting is used with the thermojet technology by wax.

lost mould

casting

thermojet technology

wax


Input: We saw that some powder technologies could realise sand moulds for casting (Voxeljet, ExOne).

saw

casting

powder technologies

sand moulds


Input: Other approaches ally the additive manufacturing technology and the topological optimisation to realise a rapid tooling and to use less material while keeping its properties.

additive manufacturing

rapid tooling

topological optimisation

material

properties


Input: The layers manufacturing is able to improve a product or a tooling by inserting new methods as cooling channels or sensors.

layers manufacturing

tooling

as

sensors


Input: For example, an injection mould manufactured by a Stratoconception and after assembly of strata, cooling channels are provided in the various inter-stratum planes for allowing a fluid to pass through the part.

injection mould

cooling channels

Stratoconception

strata

assembly

fluid


Input: You must perceive that this type of method can improve the behaviour of a moulded part by adjusting the location of the cooling channels to a specific geometry.

moulded

cooling channels

geometry


Input: Another challenge is to reduce weight and decrease the material used while keeping the product functions (mechanical, use…).

weight

material

mechanical


Input: Moreover, the main and support material can be expensive in the AM technology.

support material

be

AM technology


Input: Topology optimisation is a mathematical approach that optimises material layout within a given design space, for a given set of loads and boundary conditions so that the resulting layout meets a prescribed set of performance targets.

Topology optimisation

mathematical

layout

design space

boundary conditions

layout

performance

material

set

set


Input: Using topology optimization, engineers can find the best concept design that meets the design requirements.

topology optimization

design

concept design


Input: Any complex geometry is feasible in additive manufacturing, the topological optimisation implementation of a model leads to a new internal structure while maintaining conditions (mechanical, design shape, functions, etc).

complex geometry

model

additive manufacturing

topological optimisation

design

internal structure

mechanical


Input: Topologically, optimised parts have been created with internal geometry, using a narrow-waited structure that avoids the need for building supports.

Topologically

structure

internal geometry

supports


Input: Additive manufacturing technology standards are intended to endorse the knowledge of the industry, help stimulate research and encourage the implementation of technology.

Additive manufacturing

standards

research

technology

industry


Input: The standards define terminology, measure the performance of different production processes, ensure the quality of the end products, and specify procedures for the calibration of additive manufacturing machines.

standards

performance

processes

quality

calibration

production

additive manufacturing machines


Input: Several major standards were created very recently by the International Organisation for Standardisation (ISO); we can mention the main ones: ISO 17296-2:2015: Overview of process categories and feedstock.

standards

process

International Organisation for Standardisation

ISO

ISO 17296-2:2015

feedstock


Input: It describes the process fundamentals of AM with the existing processes and the different types of materials used.

process

processes

materials

AM


Input: ISO 17296-3:2014: Main characteristics and corresponding test methods: It covers the principal requirements applied to testing with the main quality characteristics of parts, the appropriate test procedures, and the recommendations.

ISO 17296-3:2014

testing

quality


Input: ISO/ASTM DIS 2019: Standard Practice–Guide for Design for AM: It is being developed since 2015 and will bring together good practices in design for getting a reliable product.

ISO/ASTM

Standard

Design

design

AM


Input: You can also find other standards specifying the terminology in AM or the requirements for purchased AM parts.

standards

AM

AM parts


Input: In recent decades additive manufacturing has evolved from a prototyping to a production technology.

additive manufacturing

production

prototyping


Input: It is used to produce end-use-parts for medical, aerospace, automotive and other industrial applications from small series up to 100,000 of commercially successful products.

medical

aerospace

automotive

industrial


Input: Metal additive manufacturing processes are relatively slow, require complex preparation and post-processing treatment while using expensive machinery, resulting in high production costs per product.

Metal additive manufacturing

post-processing treatment

production costs


Input: Design for Additive Manufacturing aims at optimizing the product design to deal with the complexity of the production processes, while also defining decisive benefits of the AM based product in the usage stages of its life cycle.

Design for Additive Manufacturing

product design

complexity

processes

life cycle

production

AM


Input: Recent investigations have shown that the lack of knowledge on DfAM tools and techniques are seen as one of the barriers for the further implementation of AM.

tools

as

AM


Input: This paper presents a framework for DfAM methods and tools, subdivided into three distinct stages of product development: AM process selection, product redesign for functionality enhancement, and product optimization for the AM process chosen.

framework

product development

product optimization

tools

AM process

AM process


Input: It will illustrate the applicability of the design framework using examples from both research and industry.

design

research

industry


Input: Additive manufacturing was first developed in the late 1980 with increasing quality and market penetration ever since.

Additive manufacturing

quality

penetration


Input: Starting as prototyping technology it has developed into a technology that allows for mass production of end use parts.

as

technology

technology

mass production


Input: In 2018 BMW has reported on 3D printing of its one millionth component in series production.

3D printing

production

component


Input: Major AM markets that include aerospace, automotive, consumer products, medical, and general industries report simular success stories.

AM

aerospace

automotive

consumer products

medical

industries


Input: According to a study by Deloitte AM is implemented within industry to increase the perceived value in any of three area's: profit, risk and time.

Deloitte AM

industry

area


Input: Next to that the tactical path along which these industries have incorporated AM implementation can be characterized by product and/or supply chain change.

industries

AM

be

supply chain


Input: Four different paths have been identified: Path 1 describes companies that do not seek radical modification of their products and supply chain, but look at AM to improve their value proposition to the customer.

companies

supply chain

AM


Input: Typical examples of the use of AM for path 1 are printed prototypes and tools and fixtures.

AM

prototypes

tools


Input: Path 2 looks at AM as a means to define new business cases in which the production of end user products can be realized beneficially.

AM

production

business cases

be


Input: Examples include for example the production of spare parts and production on problematic production locations like space, war zones and the oil & gas industry.

production

production

production

oil

gas


Input: Path 3 describes strategies being enabled by AM based new product performance.

AM

performance


Input: Examples are the fuel nozzle by GE, embedded electronics and lightweight structures.

fuel nozzle

lightweight structures

GE

embedded electronics


Input: Path 4 describes companies that base their new business models on changes in both the supply chains and the products.

companies

business models

supply chains


Input: An example for this path is the 3D scanning and printing of custom shoes in retail stores.

3D scanning


Input: All tactical development paths described above deal with product design within an AM-based supply chain.

product design

supply chain


Input: It is required both for the realization of AM-based enhanced product performance as well as when printing more standard product designs; these designs also have to be optimized for specific AM process opportunities and constraints so they are produced reliably, on time and cost efficiently.

performance

standard

as

as

be

product designs

designs

AM process


Input: Design for Additive Manufacturing describes methodologies used to optimize the product design with the goal of improving performance in all lifecycle stages.

Design for Additive Manufacturing

product design

performance


Input: The lack of knowledge on DfAM has been identified as one of the barriers that holds back further adoption of AM in industry.

as

AM

industry


Input: This can be attributed to the attention given to AM as a production technology, which only blossomed over the last decade.

be

AM

production


Input: Attention to design for AM trailed behind and only grew in importance when interest in commercial production of end user goods increased.

design

AM

production


Input: The CIRP community has published papers related to AM processes, AM materials, specific AM application areas and AM geometrical aspects.

AM processes

AM

AM

AM materials

areas


Input: The CIRP keynote paper by Thompson focused on DfAM and disclosed the width and complexity of the DfAM theme, and addressed many of the themes that should be considered as part of product development for AM.

complexity

product development

be

as

AM


Input: These topics ranged from design strategies and artefact design up to economic and strategic considerations on the implementation of AM within industrial product development processes.

design

design

AM

industrial

processes


Input: The paper focussed on design considerations that should be addressed when deciding on the transition from classical production processes to additive manufacturing.

design considerations

transition

processes

be

production

additive manufacturing


Input: This keynote paper focuses on the state of the art on methods and tools related to the design of geometry or functional AM artefacts within an industrial setting.

art

industrial

tools

design

geometry

AM


Input: A general introduction to AM processes and process steps will be presented 2.

AM processes

process

be


Input: Section 3 will present a framework for the selection and application of DfAM methods and tools.

framework

tools


Input: In Sections 4the DfAM framework will be discussed in more detail; lightweighting, internal topology, surface topolgy, material complexity and part integration.

framework

internal topology

surface

complexity

be

material

lightweighting


Input: When required, methods and examples of application will focus on AM based production of metal parts in an industrial setting.

AM

production

metal

industrial


Input: The applicability of the design framework is however not limited to the examples given but can, at a generic level, be apllied to the majority of the known AM processes.

design

be

AM processes


Input: 2 Additive manufacturing AM is defined by the ISO/ASTM joint standard 52900:2018 as the process of joining materials to make parts from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing and formative manufacturing methodologies.

Additive manufacturing

joining

subtractive manufacturing

manufacturing

ISO/ASTM

standard

process

as

as

3D model

layer

layer


Input: Note that this definition is very general and can be applied to a wide range of technologies.

be

range

technologies


Input: Hybrid technologies that for example use additive plus subtractive processes within a single machine may therefore not be considered as AM machines in the strict definition of the term.

Hybrid technologies

additive

be

as

subtractive processes

machine

AM machines


Input: For the near future it is foreseen that fully automated manufacturing lines, combining AM in tight and repetitive sequences alongside other fully automated production and handling processes, will become the standard for the modern factory.

manufacturing

AM

production

processes

standard


Input: 2.1 AM processes According to ISO/ASTM there are currently seven AM process categories that result in a 3D CAD model being formed into a solid, integrated part: Binder jetting: droplet printing of a liquid used to bind powder particles together; Directed energy deposition: material is simultaneously fed into a moving focused energy region; Material extrusion: material is fed through a nozzle in a liquid state after which solidifies; Material jetting: material is jetted in liquid droplet form after which it solidifies; Powder bed fusion: powder material is selectively heated so that the particles partially or fully melt to form a solid matrix; Sheet lamination: sheets of material are bonded together either before or after the part outline is separated from the sheets; Vat photopolymerisation: a platform is dropped through or raised above a vat of liquid resin where light is used to selectively solidify it.

AM processes

AM process

Binder jetting

bind

Directed energy deposition

Material extrusion

Material jetting

Powder bed fusion

Sheet lamination

Vat photopolymerisation

ISO/ASTM

model

droplet

particles

liquid state

liquid droplet form

particles

melt

solid matrix

solidify

material

material

material

powder material

sheets

material

sheets

resin

nozzle

platform

vat


Input: Most of these categories have so far resulted mainly in machines that are designed for one-off prototypes or for production that heavily employs manual work.

machines

designed

prototypes

production


Input: Whilst the AM technology itself is largely automated, the design process, machine setup and finishing stages may require a significant amount of knowledge and skills to perform.

AM technology

finishing

design process

machine setup


Input: All the above processes were initially developed to create parts from different polymeric materials, with the exception of sheet lamination.

processes

polymeric materials

sheet lamination


Input: Some of these technologies have now been developed to a level where they have been incorporated into large batch production.

technologies

batch production


Input: Some of these batches can be considered to be part of a continuous production line.

be

be

continuous production line


Input: The most well-known of these would be AM machines used in production of teeth aligners and hearing aids.

be

AM machines

production

hearing aids


Input: These examples show that when the additional complexity of form and/or the individual part cost allows it, AM can be used for final part production of parts.

complexity

AM

production

be


Input: The impact of AM on process chain towards final production is however most heavily felt when producing metal parts.

impact

AM

production

process chain

metal


Input: All of the above process categories have a means in which to arrive at a metal part.

process

metal


Input: The first approach is by mixing metal particles with the material joining mechanism.

mixing

metal

material joining


Input: For example, metal particles can be added to photopolymers in vat photopolymerisation or mixed with polymer powder in powder bed fusion or with filament in material extrusion.

metal

be

photopolymers

polymer

filament

vat photopolymerisation

powder bed fusion

material extrusion


Input: In general this will end in a blended part that exhibits some of the properties of the metal like improved surface hardness or heat deflection.

properties

surface

heat deflection

metal

hardness


Input: The second approach is where the parts above are used in a secondary furnace cycle to burn off the polymer and cause the metal particles to sinter together.

furnace

polymer

metal

sinter


Input: This process therefore requires an additional programmable furnace to achieve this effect.

process

furnace


Input: In addition to the process categories mentioned in the previous paragraph, binder jetting is also widely used in this manner.

process

binder jetting


Input: It should be noted in particular that part shrinkage will occur using this approach.

be

shrinkage


Input: This shrinkage can be minimised if an infiltrant is used to fill in voids prior to densification.

shrinkage

voids

be

densification


Input: For example 420 stainless steel parts can be infiltrated with bronze at 1100.

420 stainless steel

be

bronze


Input: Many technologies have been refined to a level where geometric tolerances are highly predictable and achieving up to 97% final density values.

technologies

predictable

geometric tolerances

density


Input: Conventional polymer AM materials can often be used in casting processes to achieve metal parts.

polymer

AM materials

be

metal

casting


Input: Some of the original processes were developed around waxes as a means to integrate with conventional investment casting.

processes

waxes

as

conventional investment casting


Input: It was found later that other, stronger polymers could be used in this way provided the casting shells were strengthened and the burnout conditions were modified.

polymers

be

casting shells

burnout conditions


Input: Four of the above process categories can directly produce metal parts; powder bed fusion, directed energy deposition, material jetting, and sheet lamination.

process

metal

powder bed fusion

directed energy deposition

material jetting

sheet lamination


Input: It is interesting to note that sheet lamination is largely a hybrid process.

sheet lamination

process


Input: In sheet lamination there can be a large amount of material, often much more than is used for the part itself, that is separated from the part in a subtractive manner during the AM process.

sheet lamination

subtractive

AM process

be

material


Input: These sheets can be metal and bonded together using ultrasonic bonding.

sheets

be

ultrasonic bonding


Input: This is a low temperature welding process for joining dissimular metals and can for example allow embedding of electronics in the structure without damaging it.

temperature

process

electronics

structure

joining

metals


Input: It is a niche AM route towards metal parts.

AM

metal


Input: By far the most widely used AM approach for metal parts is powder bed fusion.

AM

powder bed fusion

metal


Input: This is largely because of the basic simplicity of the process combined with the fact that a range metals is readily available and suitable for mainstream applications.

process

range

metals


Input: A beam of energy is used to selectively melt the powders to form the solid part.

beam

melt

powders


Input: Electron beam melting is available but most systems use laser energy, normally in a sealed chamber, in an inert gas environment or a vacuum.

Electron beam melting

laser energy

inert gas


Input: This sealed chamber may be at an elevated temperature but still considerably below the melting point of the metal.

be

metal

temperature

melting point


Input: Since this means very large thermal gradients, it is normal to connect the parts to a solid substrate in a similar way to processes that require support structures.

thermal gradients

solid substrate

processes

support structures


Input: These supports have a different purpose in that they anchor the part to prevent internal stress warpage during build.

supports

internal stress

build


Input: Directed energy deposition is a process that almost entirely focuses on metal parts.

Directed energy deposition

process

metal


Input: A high energy source is used to melt metals that are delivered in either powder or wire form.

source

melt

powder


Input: The energy focal point is also where the material is delivered and so there is a periodic melting followed by rapid solidification.

energy focal point

material

melting

rapid solidification


Input: Similar issues to powder bed fusion exist regarding residual stresses with the additional complexity of a significantly varying thermal environment.

powder bed fusion

residual stresses

complexity


Input: Since there is no surrounding powder to help stabilise the heat transfer, the directed energy deposition process will have differing cooling profiles dependent on the mass of surrounding material at the energy delivery point.

powder

material

heat transfer

directed energy deposition process

cooling


Input: Material jetting for the production of metal parts is hampered by the high temperatures needed to get the metals in the proper liquid state.

Material jetting

production

metal

metals

temperatures

liquid state


Input: As a result this technology, when used to directly fabricate metal parts, is still in the development stage.

As

technology

fabricate


Input: 2.2 AM process steps The process of creating an additively manufactured product can be subdevided into seven steps.

AM process

additively manufactured product

process

be


Input: 1 Model design.

Model

design


Input: 3D CAD software can be used to create a solid or surface model or scan data is used to create the 3D geometry; 2 STL file creation.

software

data

be

surface model

3D geometry

STL

file


Input: The 3D model is converted into a file format that is understood by AM machines.

3D model

file

AM machines


Input: The STL file format is widely used and approximates the 3D model by a surface that is constructed using triangles.

STL

file

3D model

surface


Input: Other file formats exist that are better suited to advanced AM features like multi material parts; 3 Build preperation.

file

AM

material

Build


Input: The STL file is transferred to the build preparation software, where the location and orientation of the part in the build envelope are defined.

STL

file

build preparation

build envelope

orientation


Input: The software slices the geometry into individual layers.

software slices

geometry


Input: For each layer the geometric data of that layer, in combination with the machine parameters, like laser power, layer thickness and scan patterns, is translated into build instructions for the AM machine; 4 The build process.

layer

layer

machine parameters

laser power

layer thickness

scan patterns

build

build

data

AM machine


Input: After the build process the part is removed from the build plate/envelope and excess material is removed.

build

build plate/envelope

material


Input: Additional post-processing steps might be needed to improve the functional characteristics of the part.

post-processing

be


Input: 6 Quality and inspection.

Quality

inspection


Input: Often quality and inspection methods are applied that are based on other production technologies like casting and forging.

quality

inspection

production

casting

forging


Input: But the complexity of the geometry can induce unique inspection problems like inaccesable surfaces or the absence of measuring datum planes; 7 Application.

complexity

geometry

surfaces

inspection

datum planes


Input: For most industrial parts produced by additive manufacturing the expected benefits in the use phase are the reason for designing parts to be created by additive manufacturing.

industrial

additive manufacturing

additive manufacturing

phase

be


Input: 2.3 AM design stages As mentioned in Thompson, the AM design process has to take into account a lot of aspects related to several key performance indicators.

AM

AM

As

process

performance


Input: Globally, as defined in the standard ISO/ASTM 52910:2018 the AM design steps can be structured into three global stages.

as

be

standard

ISO/ASTM

AM


Input: The first stage relates to go/no-go evaluations concerning the part, tool or product to be considered.

tool

be


Input: Manufacturability issues will have to be checked at this stage even before defining any geometry.

Manufacturability

geometry

be


Input: Before that, however, crucial decisions must be made with respect to functional decomposition and functional integration.

be

decomposition


Input: One later decision will be to define the complete manufacturing for each feature as well as the scheduling of the individual manufacturing operations, with possible use of different manufacturing technologies.

be

as

as

manufacturing

manufacturing

manufacturing technologies

feature


Input: The material and its characteristics will also have to be defined for each voxel of the part.

material

be

voxel


Input: The definition of the material characteristics must be fixed as well as the definition of transitions between different materials in different regions of the objects.

material

be

as

as

materials


Input: These possibilities are limited to AM technologies that allow assembly of different materials or grading material characteristics in a given part.

AM technologies

assembly

materials

material


Input: The third stage corresponds to the final check and optimization of process characteristics with respect to the best possible properties of the manufactured objects.

optimization

process

properties

manufactured


Input: For example, the number of parts produced is dependent on the choice of orientation of the part and consequently on the support structures that are minimized with respect to an optimum part geometry.

orientation

geometry

support structures


Input: These three global design stages serve to minimize the technical and economic risks before going to manufacturing.

design

manufacturing


Input: Design does not therefore just rely on a simple set of design guidelines.

Design

design

simple

set


Input: A global and systemic vision of the complete value chain has to be considered with respect to global indicators like in particular lead time, cost and quality, in order to evaluate feasibility, suitability and stability of AM-based value chain performances.

be

lead time

quality

feasibility

stability


Input: 3 A DfAM framework Design for manufacturing and assembly has been around for many years and deals with the design of products while focussing on both the manufacturing and assembly process.

framework

Design

design

manufacturing

assembly

manufacturing

assembly


Input: The goal of DfMA is to include manufacturing and assembly knowledge early in the design proces to increase chances of success and shorten the development cycle.

manufacturing

assembly

design


Input: Many variants exist, focussed for example on specific production technologies like injection molding or casting.

production

injection molding

casting


Input: DfAM focusses on AM processes but differs from other DfX processes.

AM processes

processes


Input: It deals with many different AM process variants and needs to take the whole process chain into account to be successful while research has shown that the number of interacting aspects that define successful production is large.

AM process

production

process chain

be

research


Input: Finally, AM is a new group of processes that provides other opportunities and constraints to traditional forming and subtractive processes which implies non-traditional approaches to product design are required.

AM

forming

subtractive processes

processes

product design


Input: Many papers exist on individual aspects of the design process while for a succesful design process all relevant aspects should be taken into account.

design process

design process

be


Input: The framework defines a structured method to link design challenges to specific design goals and focusses on the 3 stages presented 2.3.

framework

design

design


Input: Examples used will focus on AM-based manufacturing of metal products although the framework is generic in nature and can also be applied for other material/process combinations.

manufacturing

metal

be

framework


Input: 3.1 AM suitability Additive manufacturing is a relatively new group of production processes, of which integration in industry is just starting to gain momentum.

AM

Additive manufacturing

production

processes

industry

gain


Input: This momentum might be attributed to the claims of a future where AM will realize low cost efficient production of any shape in any material.

be

material

AM

production


Input: Current industrial additive manufacturing practice shows that this bright future is yet to be.

industrial

additive manufacturing

be


Input: Timely identification of the match between design task, product requirements and AM capabilities is needed.

design

AM


Input: proposes to base this evaluation on the following criteria: Do available AM materials match the product application? Does the product design fit the build envelope of AM hardware? Can the product functionality improve when applying the following product design modifications or product opportunities?-Part customization-Lightweighting-Use of internal channels or structures-Functional integration-The use of designed surface structures-The use of multi-material or gradient material parts.

AM materials

material

product design

product design

designed

fit

multi-material

build envelope

AM

product functionality

Lightweighting


Input: This is to evaluate the balance between the expected economic benefits of product design opportunities against, in most cases, the increased manufacturing costs.

product design

manufacturing costs


Input: The dominant objectives established in that last paper are improved part performance, manufacturing and reduction of lead time.

performance

reduction

manufacturing

lead time


Input: 3.2 AM material, process and machine selection If AM potential has been established then AM resources should be identified, as these affect downstream design choices.

AM material

be

as

process

machine selection

AM

AM

design


Input: This includes the decision between direct AM-based production, indirect AM-based production or hybrid approaches.

production

production


Input: Also post-processing steps, needed to reach the required product characteristics, could be identified in this stage.

post-processing

be


Input: For reasons of process chain selection, hybrid production processes can be subdivided based on the method used to generate the bulk of the geometry.

process chain selection

processes

geometry

production

be


Input: From an industrial perspective some hybrid technologies use conventional technologies to create the bulk of the part and use AM as a subsequent production method to add detailing features.

industrial

hybrid technologies

technologies

AM

production


Input: This sequencing of processes can have economic benefits or can result in parts that exceed the standard build chamber dimensions.

processes

standard

build chamber


Input: An AM process that produces the bulk of the part using AM technologies and integrates subtractive technologies during the build process can be seen as the second group of hybrid processes.

AM process

AM technologies

subtractive

build

be

as

processes


Input: For metal parts this sub-group typically consists of DED-based metal additive manufacturing technologies and with milling to post-process functional, internal or hard to reach surfaces.

metal

DED-based metal additive manufacturing technologies

milling

post-process

surfaces


Input: Based on interdependencies and sequencing of process steps, alternative processing chains can be generated and evaluated.

process

be


Input: Based on the design requirements and selections already made, Bikas proposes to use screening and selection for AM processes based on criteria related to machine, material, process and part constraints.

design

AM processes

machine

material

process


Input: The Senvol database links AM processes to available materials and build envelops of industrial AM machines.

Senvol database

AM processes

materials

build

industrial

AM machines


Input: Also the screening and ranking method proposed by Ashby can be applied for AM material and process selection.

be

AM material

process selection


Input: 3.3 Initial cost estimation The decision to apply additive manufacturing for functional parts involves balancing the cost of additive manufacturing against the expected benefits during the design, production and use phase.

cost estimation

phase

additive manufacturing

additive manufacturing

production

design


Input: Although the cost/benefits analysis during the early design stage is important, information required for detailed cost estimation is often missing.

cost/benefits analysis

design

cost estimation


Input: Knowledge on the expected product volume, production technology and required post-processing steps can give insight into the expected costs.

volume

post-processing

production


Input: For the early cost estimation of the production of the part, the costs are often expressed as cost per cm3 of the printed part.

cost estimation

production

as


Input: Most cost estimations found in literature only take the process related post-processing steps into consideration and additional costs must be taken into account when the functionality of the printed part has to be improved also.

cost estimations

process

post-processing

be

be


Input: Most cost estimation calculations are based on the assumption of in-house production and an idealized representation of the AM process investigated.

cost estimation

production

AM process


Input: It is assumed that one AM machine is used for one product the whole life time of the machine, resulting in a high machine load.

AM machine

machine

machine


Input: For example, Baumers presents a cost breakdown for metal powder bed based production of a stainless steel 304L product with wire erosion support removal and de-powdering as post processing steps.

metal powder

stainless steel 304L

as

bed

production

wire erosion

support

de-powdering


Input: Based on that analysis four major cost aspects were identified: Indirect cost, material costs, labor costs, and risk associated costs.

material

labor costs


Input: Risk related costs include build failures and accounts for 26% of the AM unit cost.

build failures

AM


Input: In the production of laser based powder bed fusion system was compared to an electron beam variant.

production

powder bed fusion

laser

electron beam variant


Input: The AM deposition rates are relatively slow and are identified as the major driver for the manufacturing costs.

AM

as

manufacturing costs


Input: An alternative cost estimation study was presented by Baldinger and focusses on buy scenarios for AM parts.

cost estimation

AM parts


Input: The cost estimations are based on reviews of the cost price for obtaining an AM part through commercial service providers and focused on both plastic and metallic parts.

cost estimations

AM part

plastic and metallic parts


Input: This research compared twenty-one AM service providers worldwide and found that the main cost drivers for this scenario are total volume of the order, packing density in the build envelope and the number of parts ordered.

research

volume

AM

density

build envelope


Input: It seems that two strategies are applied by the companies; group A and B.

companies

B


Input: Companies in group A use cost estimation strategies where part cost is almost independent of the number of parts ordered.

Companies

cost estimation


Input: These companies focus on optimizing the utilization of the build volume and have a slightly longer lead time.

companies

build volume

lead time


Input: Companies in group B estimate cost for each order separately, have a large difference in cost per cm3 for order sizes one and one-hundred, but have a slightly shorter lead time.

Companies

B

lead time


Input: 2 Post-processing can add considerably to the cost of AM parts.

Post-processing

AM parts


Input: In many cost models only the costs of the post-processing steps directly related to the AM process are considered.

cost models

post-processing

AM process


Input: For example, Lindeman calculated the post-processing costs for metal parts produced by L-PBF to be between 4 and 14%.

post-processing

metal

be

L-PBF


Input: Simpson gives a more generic overview of post-processing cost for metal AM.

post-processing

metal AM


Input: 3.4 Build job considerations Build jobs are usually considered during the phase of process planning.

Build

Build

phase

process planning


Input: Process planning is one of the most important activities in manufacturing planning and is a pivotal link between design and manufacturing.

Process planning

manufacturing

manufacturing

design


Input: Compared to traditional processing, the context changes for Additive Manufacturing, but it is still within the manufacturing scope.

Additive Manufacturing

manufacturing


Input: Although AM machines are highly integrated and automatic, before enabling the building process for a machine, there are also some preparation tasks that should be done after receiving a design model and its related production requirements.

AM machines

machine

building process

be

design

production


Input: In this chain, optimization of the number of parts and their relative positioning in 2D or in 3D, is required when building multiple parts.

optimization


Input: Support generation could be achieved before or after the nesting stage.

Support generation

be

nesting


Input: Layer building can then be normally achieved by slicing the 3D set of nested or packed parts with their support structures.

Layer

be

slicing

support structures


Input: In some cases this stage is very different because the orientation of the part during the process changes.

orientation

process


Input: In such cases, the generation of the material deposition trajectory has to be achieved by taking into account non-planar layers.

material

be

deposition


Input: Alternative operations of adding and subtracting material and functions are sometimes considered to improve manufacturing efficiency, as an alternative solution to conventional methods like welding and machining.

material

as

manufacturing

welding

machining

solution


Input: This approach, usually named hybrid manufacturing, needs specific AM process planning solutions in order to process from feature decomposition to a complete part recomposition, taking into account sequencing aspects and material excess regions for machining depending on expected dimensional and surface qualities.

hybrid manufacturing

process

AM process

machining

feature decomposition

material

surface qualities


Input: However, orientation and placement have to be validated with respect to global thermal conditions of manufacturing.

orientation

be

manufacturing


Input: As material and geometry are obtained at the same time, it is mandatory to validate the material quality induced by the input of energy during the material transformation and the consequences on the metallurgical properties of the part.

As

material

material

geometry

metallurgical


Input: Consequently, potential deformations are also calculated and some modifications of strategy are also possible in order to compromise between production performance parameters and part material properties.

deformations

performance parameters

material properties

production


Input: Some simulation tools exist starting from the nested or packed global model integrating support structures.

simulation

model

support structures


Input: For some specific applications, process planning for AM may also generate assembly instructions.

process planning

AM

assembly


Input: This occurs when a part's size exceeds the build volume of a machine and it can be decomposed into several small sections to be made separately.

build volume

machine

be

be


Input: 3.5 AM process constraints Like with all technologies, there are many constraints to AM.

AM process

AM

technologies


Input: This section will focus on four primary constraints that are common to all AM process categories and particularly relevant to the AM of metals: Speed of build, materials, build envelope, and accuracy.

AM process

AM

metals

build

build envelope

materials

accuracy


Input: Although AM used to be called Rapid Prototyping, one is now quite accustomed to having prototypes built quickly, but this is difficult to scale up.

AM

be

Rapid Prototyping

prototypes


Input: Furthermore, there is increasing demand for AM to be used in mainstream production, which requires much faster throughput.

AM

production

be

throughput


Input: AM has the benefits of geometric freedom, no minimum batch constraint and rapid change between batches, which meets many of the demands of modern manufacturing industry.

AM

manufacturing

geometric freedom

industry


Input: The hunt is therefore on for faster AM technology.

AM technology


Input: Many metal AM systems use lasers due to the demand for large amounts of focussed energy.

metal AM


Input: The ideal situation would be to provide the required energy over an entire layer simultaneously but so far this has not been demonstrated to be possible.

be

be

layer


Input: A compromise is the supply of multiple laser beams controlled simultaneously.

laser beams


Input: Different lasers can be used to process different regions with finer spots being used for more detailed parts and wider beams to process bulk regions.

be

process

process

finer spots

bulk regions


Input: Careful attention must be given to beam control so that they don't affect each other, including the vapour trails from the molten metal regions.

be

molten metal

beam control


Input: A contrasting approach to increasing throughput for batch production of metal parts is the use of binder jetting methods or material extrusion with metal-filled binder materials.

throughput

batch production

metal

binder

binder jetting methods

material extrusion


Input: Such methods can achieve faster AM throughput and can be more easily scaled to create larger parts.

AM

be


Input: The downsides relate to increases in post-processing times during heat treatment and during machine finishing, if required.

post-processing

heat treatment

finishing

machine


Input: These requirements are also driving the development of open-architecture, robot-based metal AM systems, like Wire Arc AM and Laser Metal Deposition.

metal AM

AM

Laser Metal Deposition

Arc


Input: There is a huge and increasing number of metals and other materials used to make products.

metals

materials


Input: Most of these metals are carefully chosen to suit product requirements in strength, chemical resistance, thermal properties, processability, cost, etc.

metals

strength

chemical resistance

thermal properties


Input: In comparison, there are a very few materials available in AM.

materials

AM


Input: All AM processes are suited to a subset of materials, the requirements for which can be very specific, like the need for photo-curable resins.

AM processes

materials

be

photo-curable resins


Input: Many materials can be formed by AM using thermal energy, but the amounts of energy vary considerably.

materials

thermal energy

be

AM


Input: It is not easy to melt metals in an AM process chamber specifically built for polymers for example.

melt

AM process

polymers


Input: In addition, raw materials often need to be presented with well-defined morphology, like in filament or carefully-graded powder distributions.

raw materials

be

filament

powder

morphology

distributions


Input: However, even within a smaller range of materials the processing requirements can still be difficult to specify.

range

materials

be


Input: Metals within L-PBF systems for example will absorb laser energy in different proportions.

Metals

L-PBF systems

laser energy


Input: The physics around phase change behaviour and effects in the molten state can all be quite different, significantly affecting the final material microstructure.

physics

phase

be

material


Input: Furthermore, much of this is significantly different from other manufacturing processes like casting and forging.

manufacturing processes

casting

forging


Input: All these need to be carefully studied before AM materials can be released to the market.

be

AM materials

be


Input: As, AM becomes more widespread, one can expect more materials to become available but it is widely accepted that range of materials needs to be increased.

As

be

AM

materials

materials

range


Input: Having said that, current AM materials like Ti-6Al-4V, 316 stainless steel and CoCr alloys, etc.

AM materials

stainless steel

CoCr alloys


Input: Many products are made from metals because of the needs for strength and accuracy.

metals

strength

accuracy


Input: In AM, part strength is often acceptable but part accuracy is very often not.

AM

strength

accuracy


Input: Metal parts are often mated with others and so the joining surfaces must align with each other.

Metal

joining


Input: Most metal AM processes create parts with poor surface finish, usually no better than 15 Rz and very often considerably worse.

metal AM

surface finish


Input: Machine finishing is therefore a common requirement as a post-process.

Machine

finishing

as

post-process


Input: Thermally induced distortion due to large temperature gradients during builds and corresponding residual stresses is also a common phenomenon for metal AM.

distortion

temperature gradients

builds

residual stresses

metal AM


Input: Features may therefore be imprecisely located and it may be better to provide a machining allowance in the initial AM part design.

be

be

machining allowance

AM part


Input: The introduction of hybrid machines that combine AM with subtractive and other manufacturing processes that operate in a sequential manner aim to overcome issues around part accuracy.

machines

AM

subtractive

manufacturing processes

accuracy


Input: This is particularly useful where the requirement is internal to the part geometry and difficult to achieve as a post-process.

geometry

post-process

as


Input: 3.6 AM post-processing constraints For much of the time that AM technology has been under development, post-processing has been something that you would rather not do and eliminate if possible.

AM

AM technology

post-processing


Input: AM is now considered as something that can shorten process chains, not eliminate them entirely.

AM

as

process chains


Input: Sometimes it may be appropriate to include a design feature in the post-process rather than in the AM build itself.

be

design

post-process

AM


Input: Post-processing tasks can be broadly divided in terms of those that can require significant manual intervention and those that can be carried out in a largely automated fashion.

Post-processing

fashion

be

be


Input: Of course this depends on the available technology to achieve these tasks as well as the level of investment, quality issues, volume of production, etc.

technology

quality

volume

as

as

production


Input: Post-processing can also be considered in terms of those that need to be carried out due to the characteristics of the AM process used and those that are more aimed at enhancement of the AM parts.

Post-processing

be

be

AM process

AM parts


Input: Like with the previous classification, there are overlaps or grey areas, around where exactly surface finish fits for example.

classification

fits

areas

surface finish


Input: This can also form part of the decision making in the process design The AM technology specific processes mainly refer to the chosen build process and are aimed at providing a consistent quality of output suited to the general application.

process

processes

quality

design

AM technology

build


Input: Many processes use support structures which have to be removed somehow, often requiring further finishing of regions where the supports connected with the part.

processes

support structures

be

finishing

supports


Input: Build strategies often revolve around minimising the amount of supports or avoiding key surfaces for aesthetic or accuracy reasons.

Build strategies

surfaces

aesthetic

supports

accuracy


Input: For many machines, flat and curved surfaces can appear different due to the stair-stepping phenomena.

machines

curved surfaces


Input: Abrasive or chemical finishing can be used to make these surfaces appear more uniform.

Abrasive

be

finishing

surfaces


Input: A further post-processing task can revolve around excess material that may be adhering to the part surfaces.

post-processing

surfaces

material

be


Input: This may be a surrounding material that protects these surfaces or they may be residual material due to inconsistencies in the process, similar to flash in moulding operations.

be

material

be

material

flash

surfaces

process

moulding


Input: Although specific to powder-based AM technology, pore-filling and densification can also be application specific in terms of the material chosen to create a fully dense part.

AM technology

densification

be

material

fully dense


Input: Densification can also be in the form of a furnace cycle, perhaps using hot isostatic pressing.

Densification

hot isostatic pressing

be

furnace


Input: Since some processes can be slightly heterogeneous in nature, accounting for shrinkage may require careful preparation and difficult to precisely control.

processes

heterogeneous

shrinkage

be


Input: Metal AM parts in particular are commonly used as fully functional parts.

Metal AM

as


Input: Choice of metal as a part material often relates to part strength and while precision can represent a problem.

metal

as

material

strength

precision


Input: Finish machining of key surfaces is often required, much in the same way as we would treat a casting.

Finish machining

casting

surfaces

as


Input: In these specific regions it may be appropriate to grow some of these surfaces in the design phase to provide sufficient machining allowance to ensure high quality, accurate results.

be

surfaces

quality

design

machining allowance

accurate


Input: It can be argued that there will be fewer of these surfaces to finish since it is common thinking that AM allows for part consolidation due to the ability to create internalised features.

be

be

surfaces

part consolidation

AM


Input: Although it is quite possible to print features like holes and screw-threads using AM, the precision demands on such features can be very stringent and beyond the capacity of the AM technology used.

print

AM

AM technology

precision

be

capacity


Input: It may be possible to save material by printing a hole but the time taken to finish a partially-made hole may be the same, or even longer, than to drill a complete hole in a blank space.

be

material

be

blank

drill


Input: This may be even more relevant if the hole contained a screw thread.

be

screw thread


Input: Again, it can be argued that this adds complexity to the process decision-making, but it is pertinent when relating to heavily industrial applications.

be

complexity

process

industrial


Input: Coatings can go from simple paint jobs to improve aesthetics and seal against corrosive atmospheres through to providing significant functional properties, including bioactive features.

Coatings

go

simple

corrosive

properties

bioactive features


Input: These tasks may require significantly specialised facilities to those used in other production steps and as such may be outsourced.

production

as

be


Input: This could also be the case with other forms of chemical and heat treatment.

be

heat treatment


Input: Many AM parts can include complex internal or difficult to reach features.

AM parts


Input: Should these features require finishing, it may be somewhat difficult to achieve a stable quality, even when using automated techniques.

finishing

be

quality


Input: Some methods are under development to address these issues but more effort could be made and in fact most methods for surface finishing are highly manual in nature.

be

surface finishing


Input: 3.7 AM quality, inspection and certification Many AM applications can be found in highly regulated industries, like aerospace and medicine.

AM

AM

inspection

be

industries

aerospace

medicine


Input: This is even the case within the medical industry where one might expect such parts to be customised to suit a patient's needs and anatomy.

medical industry

be


Input: Quality control, inspection and certification would therefore be conducted in a similar fashion to conventionally manufactured parts.

Quality control

fashion

manufactured

inspection

be


Input: Validation in these cases is as much about ensuring consistency in the manufacturing process and traceability of the supply chain as it is about the functionality of the part.

Validation

consistency

supply chain

as

as

manufacturing process


Input: The US Federal Food and Drug Administration is widely regarded as a key standards organisation around the world and many other countries base their own medical standards on the FDA.

as

standards

medical

FDA


Input: In 2017 the FDA published guidelines related to technical use of AM in medical devices.

FDA

AM

medical devices


Input: These guidelines cover aspects related to AM-based design of medical devices as well as how they are manufactured and validated.

design

medical devices

as

as

manufactured


Input: Certification of medical devices is required if there is a medium to high risk potential to the user.

medical devices


Input: All implantable devices would be Class II or Class III, whilst AM produced foot orthotics are class I, requiring no premarket notification to prove they have been clinically tested certification).

implantable devices

foot orthotics

be

AM


Input: The medical device manufacturer Stryker released their Spine Tritanium PL Cage around 2016.

medical device

manufacturer

PL Cage


Input: AM is used to create a complex porous geometry of titanium that aims to promote bone ingrowth in a lumbar spine fusion process.

AM

porous

geometry

bone ingrowth

lumbar spine fusion process

titanium


Input: It is possible that introduction of this device may have been premature as it is believed that more experimental work is needed to establish the boundaries for fatigue in AM lattice structures.

as

experimental

boundaries

fatigue

AM


Input: It should be noted that similar porous and irregular lattice structures have been used in 100,000s of successful acetabular hip implant cases.

be

porous

lattice structures

hip implant


Input: This issue of possible failure will be even more important should the device have a customisable geometry.

failure

geometry

be


Input: The FDA refers to these as Customised or Humanitarian-use devices.

FDA

as


Input: These must also be limited in number and subject to significant medical board scrutiny.

be

medical


Input: Medical authorities are currently at a significant cross-road as to how to provide custom implants for more widespread use.

Medical

custom implants

as


Input: Aerospace certification, through the Federal Aviation Authority, also appears to be at a similar cross-road.

Aerospace

be


Input: However, it is noted that many parts already in use could be repaired when damaged using AM techniques, most specifically using Directed Energy Deposition.

be

AM techniques

Directed Energy Deposition


Input: Many safety critical parts, like turbine blades, could be repaired in this way.

safety

turbine blades

be


Input: Emphasis must therefore be on the AM process to ensure that functionality is maintained to a suitable standard.

be

AM process

standard


Input: For example Air New Zealand are saving significant repair costs by making their own replacement seat tray-tables using materials like the flame-retardant ULTEM 9085 polymer material from Stratasys.

repair costs

materials

polymer material

Stratasys


Input: This is just part of a much wider push to demonstrate a sustainable industry for AM in aerospace.

sustainable

industry

aerospace

AM


Input: Many of the above issues for medical and aerospace are reflected in a more general form within the standards under development by ISO Technical Committee 261 in conjunction with the ASTM F42 Group.

medical

aerospace

standards

ISO


Input: Numerous techniques, like the printing of test coupons alongside critical components, machine calibration and material storage, etc.

components

machine calibration

material


Input: This has led to significant improvements in process monitoring within industrial scale AM machines.

led

industrial

process monitoring

AM machines


Input: Many polymer-based systems have camera monitoring that allow determining the build status and remote intervention if problems can be seen.

camera

build status

be


Input: Many metal L-PBF systems also have optional laser power and melt-pool sensing to determine the state of part with the possibility of detecting a failure before it damages the machine.

metal

L-PBF systems

machine

laser power

sensing

failure


Input: 4 Tools and methods for designing lightweight parts Lightweight design always has been a hot topic in structural engineering.

Tools

lightweight

Lightweight

structural engineering

design


Input: AM processes can produce highly complex structures, constructed using both internally and externally very complex surfaces.

AM processes

complex structures

surfaces


Input: More importantly, there is no clear relationship between the complexity of the part and the associated production cost, providing more freedom to explore the design space to its full extent.

complexity

production cost

design space


Input: As a result, not only conventional lightweighting design tools are used for AM, but also some new methods have emerged to fully grasp the benefits of AM.

As

lightweighting

design

AM

AM


Input: In relation to lightweight design for AM, four groups of methods and tools can be identified: topology optimization, generative design, lattice structure filling, and bio-inspired design.

lightweight

design

topology optimization

lattice structure

bio-inspired design

AM

tools

be

generative design


Input: 4.1 Topology optimization Topology optimization was originally used for mechanical design problems to answer a layout optimization question: how to put the right material in the right place of a pre-defined design space? The objective was to obtain the expected mechanical properties at minimum material use.

Topology optimization

design

Topology

optimization

layout

design space

mechanical properties

mechanical

material

material


Input: The method uses numerical analysis and design solution update steps in an iterative way, mostly guided by gradient computation or non-gradient discrete approaches.

design

computation

non-gradient discrete approaches


Input: Traditionally, TO is driven by an objective function, minimizing or maximizing while being subjected to a set of predefined constraints, such as mass, deformation, vibration frequency, etc.

set

as

deformation

vibration frequency


Input: Usually, continuous design variables are used to solve the TO problem in a discretized way.

continuous design variables


Input: During this optimization iteration process, segments of the predefined initial design space are step by step removed so as to arrive at the minimal part volume/mass.

optimization

process

design space

step

step

as


Input: Initial methods developed remove materials bit by bit using a strain energy distribution and a preset threshold value.

materials

distribution

strain


Input: More advanced methods use genetic algorithms that both add and remove materials.

genetic algorithms

materials


Input: porous structures and lattice structures, but with relaxed mathematical constraints.

porous

lattice structures

mathematical


Input: As stated in, even current pure TO studies still face problems, such as efficiency, general applicability, ease of use, etc.

As

as

face


Input: Many of them only use relatively simple boundary conditions with limited constraints, e.g.

simple

boundary conditions


Input: When introducing extra AM related constraints such as support structures/overhangs, minimum printable features, anisotropic material properties, heat-transfer, thermal strain/stress into TO, this would result in more complex constraints or boundary conditions.

AM

as

anisotropic material properties

boundary conditions


Input: This again would result in more difficulties for the TO process to find the solutionwith an effective and fast converging simulation process.

process

process

simulation


Input: Attracted by the great potential of AM, researchers investigated TO with AM constraints, focussing on generating an optimal topologically lightweight material layout, to be printed without any manufacturing problems.

AM

AM

manufacturing

topologically lightweight

layout

material

be


Input: Therefore, recent researches on TO for DfAM are geared towards print-ready designs bridging challenges in design and printing.

designs

design

bridging


Input: One is to represent AM constraints with mathematical models and embed them into the TO iteration process.

AM

mathematical

process


Input: The other is to use TO to generate one or a set of finite reference design solutions and apply design rules or experience to adapt these solutions manually or automatically to the AM constraints.

set

design

design rules

AM


Input: This last category thus applies AM constraints in the post-processing stage of a given TO result.

AM

post-processing


Input: For ease of practice, most of the earliest works directly tried to use existing traditional TO, or other similar structure optimization methods, for lightweight design in DfAM, without considering any AM constraints.

structure optimization

lightweight

design

AM


Input: The main reason for this was the assumption that AM can overcome manufacturing problems of TO generated structure as these structures would encounter in conventional manufacturing processes.

AM

manufacturing

conventional manufacturing

structure

as


Input: Although the 2D or 3D TO produced structures could be printed by polymer AM processes, the direct application of the existing non-tailored TO may have difficulty using metallic AM.

be

polymer

AM processes

metallic AM


Input: This is more complicated due to the multi-physical phenomena which can not be handled by relatively simple macro mechanic and geometric based calculations.

be

simple

macro


Input: A large number of researchers began to associate specific AM constraints with their TO process, either as a TO process driver or a TO post-processor.

AM

process

process

as


Input: However, their efforts are mainly focusing at 2D problems with consideration of only one simple or limited subset of AM constraints, e.g.

simple

AM


Input: support volume or overhang area.

support

overhang area


Input: For example Leary, describes a variant where traditional TO is conducted and a boundary decomposition algorithm is applied to detect and decompose the internal or external boundary areas needing support structures.

boundary decomposition algorithm

boundary

support structures

areas


Input: Then, the detected and decomposed relatively large cavities are filled with a set of smaller generated boundaries so as to avoid the appearance of overhang as shown in 7.

set

boundaries

as

as

overhang


Input: In that example even though a sophisticated decomposition algorithm was designed and the use of support structure in printing was mostly avoided, the result is still far from optimal.

decomposition

algorithm

designed

support structure


Input: 2D results sometimes are quite useless in practice since the broadened design freedom exists in 3D, not 2D.

design freedom


Input: Taking the TO example in 7, we can easily rotate the 2D result around the X-axis in the 3D and then we will find that there is no need of support structures.

support structures


Input: This means all the optimization steps are useless if we simply change the build orientation.

optimization

build orientation


Input: The dilemma may be caused by two factors: the TO researcher has a lack of knowledge on the AM processes or the direct embedding of AM constraints with mathematical models in the 2D or 3D TO processes is quite tough.

be

AM processes

AM

mathematical

processes


Input: Readers may find more representative research on 2D TO for AM lightweight design in.

research

AM

design


Input: To extend beyond 2D, researchers adopted the decomposition method as proposed in and tried to extend it to 3D TO for AM.

decomposition

as

AM


Input: However, like the 2D cases presented above, reducing support structures is based on the compromise of adding more volume in the structure itself, which will decrease the global optimality.

volume

structure

support structures


Input: In addition, it is still not a real 3D TO for AM design since the decomposition and overhang angle control with volume filling still uses 2D operations.

volume

AM

decomposition

overhang angle

2D operations


Input: `For these investigations discussed above, the 2D TO process is relatively easy to realize when only considering overhang or support structure AM constraint.

process

overhang

support structure

AM