additive manufacturing technologies: an overview...
TRANSCRIPT
Research ArticleAdditive Manufacturing Technologies: An Overview about 3DPrinting Methods and Future Prospects
Mariano Jiménez,1,2 Luis Romero ,1 Iris A. Dom-nguez,1
Mar-a del Mar Espinosa,1 and Manuel Dom-nguez1
1Design Engineering Area, Universidad Nacional de Educacion a Distancia (UNED), Madrid, Spain2Department of Mechanical Engineering, Technical School of Engineering, ICAI, Comillas University, Madrid, Spain
Correspondence should be addressed to Luis Romero; [email protected]
Received 30 November 2018; Accepted 23 January 2019; Published 19 February 2019
Guest Editor: Jorge Luis Garcıa-Alcaraz
Copyright © 2019 Mariano Jimenez et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.
The use of conventional manufacturingmethods is mainly limited by the size of the production run and the geometrical complexityof the component, and as a result we are occasionally forced to use processes and tools that increase the final cost of the elementbeing produced. Additive manufacturing techniques provide major competitive advantages due to the fact that they adapt to thegeometrical complexity and customised design of the part to bemanufactured.The followingmay also be achieved according to fieldof application: lighterweight products,multimaterial products, ergonomic products, efficient short production runs, fewer assemblyerrors and, therefore, lower associated costs, lower tool investment costs, a combination of different manufacturing processes, anoptimised use of materials, and a more sustainable manufacturing process. Additive manufacturing is seen as being one of themajor revolutionary industrial processes of the next few years. Additivemanufacturing has several alternatives ranging from simpleRepRap machines to complex fused metal deposition systems. This paper will expand upon the structural design of the machines,their history, classification, the alternatives existing today, materials used and their characteristics, the technology limitations, andalso the prospects that are opening up for different technologies both in the professional field of innovation and the academic fieldof research. It is important to say that the choice of technology is directly dependent on the particular application being planned:first the application and then the technology.
1. Historical and Current Framework
Many different additive manufacturing (AM) technologiesenable the production of prototypes and fully functionalartefacts. Although very different in solution, principle,and embodiment, significant functional commonality existsamong the technologies.
In order to enter the subject from its origins, beforeproposing a classification or analyzing the different technolo-gies and their advantages and disadvantages, a chronologicalanalysis of facts will be carried out that will allow us tolater base the conclusions.This chronological analysis will bebased ondates of publication ofworks, dates of application forpatents, and dates of acceptance of these patents, being awarethat in any case the dates in which the developments werereached are always prior to those dates of a public nature.
Without a doubt, the milestone that marked the begin-ning of additivemanufacturing took place on 9thMarch 1983,when Charles W. Hull successfully printed a teacup on thefirst additive manufacturing system: the stereolithographyapparatus SLA-1, which he himself built [1].
From then on, there were several advances that pavedthe way for what is today known as additive manufacturing(Table 1). From a chronological point of view, the mostrelevant are as follows [2]:
1986. Carl R. Deckard, at the University of Texas,develops a “method and apparatus for producingparts by selective sintering”, a first step in the develop-ment of additive manufacturing by means of selectivesintering (SS).1988. Michael Feygin and his team at Helisys, Inc.develop a method for “forming integral objects from
HindawiComplexityVolume 2019, Article ID 9656938, 30 pageshttps://doi.org/10.1155/2019/9656938
2 Complexity
Table1:Ke
yinventions
inadditiv
emanufacturin
g(ordered
bypu
blicationof
patent).
Techno
logy
Inventors
Patent
Develo
pmentcentre
Requ
estfor
patent
Publicationof
patent
Principleo
foperatio
n
Stereolitho
graphy
SLCh
arlesW
.Hull
Metho
dandapparatusfor
prod
uctio
nof
three-dimensio
nalobjects
byste
reolith
ograph
y
3DSyste
ms
08.08.1984
12.02.1986
Photop
olym
erizationof
aph
otosensitiver
esin
using
UVlight
SelectiveS
interin
gSS
CarlR
.Deckard
Metho
dandapparatusfor
prod
ucingpartsb
yselective
sinterin
gUniversity
ofTexas
17.10.19
8621.04.1988
Selectives
interin
gof
powder(fusio
n–
solid
ificatio
nusinglaser)
MaterialD
eposition
MD
ScottS
.Crump
Apparatusa
ndmetho
dfor
creatin
gthree-dimensio
nal
objects
Stratasys,Inc.
30.10
.1989
01.05.1991
Deposition
ofmaterial,
usingan
ozzle
,inplastic
state(heatedby
electric
alresistance)
JetP
rototyping
(injection)
JP
EmanuelM
.Sachs;
John
S.Haggerty;
MichaelJ.Cima;
Paul
A.W
illiams
Three-dimensio
nalprin
ting
techniqu
esMassachusettsInst.
Techno
logy
08.12
.1989
09.06.1991
Injectionof
bind
ingagent
andcoloured
inkon
abed
ofpo
wderedmaterial
Laminated
Manufacturin
g(cuttin
g)LM
Feygin,M
ichael;
Pak,Sung
Sik
Form
ingintegralob
jects
from
laminations
-Ap
paratusfor
form
ingan
integralob
jectfro
mlaminations
Helisys,Inc.
05.10
.1988
18.04.1996
Cutting
andgluing
oflaminations
with
the
geom
etry
determ
ined
for
each
layer
Source:W
orld
IntellectualP
ropertyOrganization(W
IPO),https://patentscope.wipo.int.
Complexity 3
laminations”, an automatic lamination cutting system(laminated manufacturing - LM) that produces layerswith the dimensionsmarked out by the electronic file,layers which will then be bonded to form the finalprototype.1989. Scott S. Crump, at the company Stratasys,Inc., develops an “apparatus and method for creatingthree-dimensional objects”, a first step in the devel-opment of additive manufacturing by means of fuseddeposition modelling (FDM).1989. EmanuelM. Sachs andhis team, atMassachusettsInst. Technology, develop “three-dimensional print-ing techniques”, a process of injecting binding agentand coloured ink on a bed of powdered material,using the injectors of a conventional ink-jet printer todo so.
As an evolution of Hull's work based on photopolymeriza-tion, other processes have been developed:
(i) SolidCreation System (SCS).Developed by SonyCor-poration, JSR Corporation and D-MEC Corporationin 1990.
(ii) Solid Object Ultraviolet Laser Printer (SOUP) Devel-oped by CMET Inc. in 1990.
(iii) Solid Ground Curing (SGC) developed by CubitalLtd. in 1991
(iv) Inkjet Rapid Prototyping (IRP), the parts are formedby injecting a photopolymer drop by drop whichis then cured using ultraviolet light. Developed byObject Geometries Ltd. in 2000, under the namePolyjet.
As an evolution of Deckard’s work based on sintering, otherprocesses have been developed [3]:
(i) Direct metal laser sintering (DMLS), where the basematerial is metal powder and the grains are bondedby sintering, without the grains being fully fusedtogether.
(ii) Selective laser melting (SLM), where metal powder isfully fused together and so the process is not sinteringbut rather melting.
As an evolution of Crump’s work on fused deposition model-ing, other processes have been developed:
(i) Metal deposition (MD), where a metal filler material(powder jet or wire) is deposited by a nozzle followingthe path marked out by the G-code in the .stl or .amffile [4].
(ii) Fused Filament Fabrication (FFF), name fromthe RepRap community, an open community atRepRap.org, founded by Adrian Bowyer at theUniversity of Bath in 2004 [5].
At this point, hardfacing processes using numerical control(NC) should be mentioned, which are predecessors of fuseddeposition modeling and prior to the work of Crump,
with the difference being that they were not based onelectronic files generated bymeans of solid modeling systems[4]. Although additive manufacturing could date back toautomated welding systems (1970s), where a robotic armcontrolled by numerical control (G-code) deposited materialin welding or hardfacing operations (which may be a similarcase), it was not until 1983 that this G-code was used tocontrol a laser that “solidifies” a resin and builds a part usinga virtual model (solid model and .stl file).
As an evolution of the work of Sachs and his team on theinjection of binding agent or base material, other processeshave been developed:
(i) MultiJet Modeling System (MJM) developed by 3DSystems Inc. in 1999, with multiple heads in parallelthat move along one axis.
(ii) ModelMaker and Pattern Master, by Solidscape, withone single print head that moves along two axes.
(iii) ProMetal, division of Extrude Hone Corporation,process that binds together steel powder and theninfiltratesmolten bronze to produce a part that is 40%steel and 60% bronze [6].
Finally, as an evolution of the work of Feygin and his teambased on cutting laminations, other processes have beendeveloped:
(i) Selective Deposition Lamination (SDL) Invented in2003 by MacCormack. The SDL technique works bydepositing an adhesive in the area required, both themodel and the support, and a blade that cuts theoutline of the layer [7].
It is interesting to point out that there are current processesbased on more than one of the contributions stated or onintegrated processes. This is the case of polyjet modeling(PJM), which is said to be a combination of stereolithographyand injection.
Nowadays, the volume of processes, technologies andinitialisms is so high that there is no extensive classificationsystem in operation. In Table 2 we can see a list of initialismsused in this field, which is by no means exhaustive, whichgives us an idea of how technology is evolving.
In order to highlight the basic pillars of additive man-ufacturing in Table 2, the abbreviations referring to thetechnologies discussed at the beginning of this introductionhave been highlighted in italic.
Given the large number of initiatives and processes thatare developed and patented every day, there is no doubtthat additive manufacturing is a technology that will setthe standards for many productive processes in the shortand medium term. One more proof of this is that theEuropean Union has decided that manufacturing in generaland additive manufacturing in particular shall be one of thekey tools to tackle some of the European challenges and theirsubsequent objectives, above all economic growth and thecreation of added value and high-quality jobs.This decision isgenerating the setting up of research and innovation supportand promotion programmes aimed at achieving a situation in
4 ComplexityTa
ble2:Aseao
finitia
lisms.
3DB
three-dimensio
nalbioplotter
LPD
laserp
owderd
eposition
3DP
three-dimensio
nalprin
ting
LPF
laserp
owderfusion
AF
additiv
efabric
ation
LPS
liquid-ph
ases
interin
gALP
Dautomated
laserp
owderd
eposition
LRF
laserrapid
form
ing
AMadditiv
emanufacturin
gLS
lasersinterin
gBM
biom
anufacturin
gM3D
masklessm
esoscalemateriald
eposition
CAM-LEM
compu
ter-aidedmanufacturin
gof
laminated
engineeringmaterials
MD
metaldepo
sition
DCM
directcompo
sitem
anufacturin
gMD
materialdeposition
DIPC
directinkjetprintin
gof
ceramics
MEM
melted
extrusionmanufacturin
gDLC
directlaserc
astin
gMIM
materialincreasem
anufacturin
gDLF
directed
light
fabrication
MJM
multijetmod
elingsyste
mDLP
digitallight
processin
gMJS
multip
hase
jetsolidificatio
nDMD
directmetaldepo
sition
MS
masksin
terin
gDMLS
directmetallasersinterin
gM-SL
microste
reolith
ograph
yEB
Mele
ctronbeam
melting
PBF
powderb
edfusio
nEB
Wele
ctronbeam
welding
PJM
polyjetm
odeling
EPelectro
photograph
icprintin
gRF
Prapidfre
ezep
rototyping
ERP
electroph
otograph
icrapidprintin
gRM
rapidmanufacturin
gFD
Cfuseddepo
sitionof
ceramics
RPrapidprototyping
FDM
fuseddepo
sitionmod
eling
RPM
rapidprototypingandmanufacturin
gFF
EFfre
eze-form
extrusionfabrication
RTrapidtooling
FFF
fusedfilam
entfabric
ation
RTM
rapidtoolmaker
FLM
fusedlayerm
odeling
SALD
VI
selectivea
realaser
depo
sitionandvapo
rinfi
ltration
FLM
fusedlayerm
anufacturin
gSC
Ssolid
creatio
nsyste
mHSS
high
speedsin
terin
gSD
Lselectived
eposition
lamination
IJP-A
aqueou
sdire
ctinkjetprintin
gSD
Mshaped
eposition
manufacturin
gIJP
-UV
UVdirectinkjetprintin
gSFC
solid
film
curin
gIJP
-Who
t-melt
directinkjetprintin
gSFF
solid
free-form
fabrication
IRP
inkjetrapidprototyping
SGC
solid
grou
ndcurin
gJP
jetprototyping
SHS
selectiveh
eatsinterin
gLA
Mlasera
dditive
manufacturin
gSL
stereolith
ography
LClaserc
ladd
ing
SLA
stereolith
ograph
yapparatus
LCVD
laserc
hemicalvapo
rdeposition
SL-C
stereolith
ograph
yof
ceramics
LDC
laserd
irectcasting
SLM
selectivelaser
melting
LDM
low-te
mperature
depo
sitionmanufacturin
gSLP
solid
laserd
iode
plotter
LENS
lasere
ngineerednetshaping
SLS
selectivelaser
sinterin
gLF
FFlaserfreeform
fabrication
SLSM
selectivelaser
sinterin
gof
metals
LLM
layer
laminated
manufacturin
gSO
UP
solid
objectultra-violetlaserp
rinter
LMlaminated
manufacturin
gSS
selec
tivesinterin
gLM
Dlaserm
ateriald
eposition
SSM-SFF
semiso
lidmetalsolid
freeform
fabrication
LMF
laserm
etalform
ing
SSS
solid
-statesin
terin
gLO
Mlayeredob
jectmanufacturin
gUC
ultrason
icconsolidation
LOM
laminated
objectmanufacturin
gUOC
ultrason
icob
jectconsolidation
Complexity 5
3D model Prototyped model Final model
Figure 1: Ball joint mounted in its housing [8].
which additive manufacturing enables the provision of bothhigh-value products and competitive services.
All over the world the additive manufacturing industryis beginning to respond to global, national, and regionalstandardisation needs via a series of working groups in whichthe European Union is a key participant: the ISO/TC 261,Additivemanufacturing; theASTMCommittee F42 onAddi-tive Manufacturing Technologies; the CEN/TC 438, additivemanufacturing; or the AEN/CTN 116, Sistemas industrialesautomatizados (https://www.aenor.com/) [9].
The ISO standard (ISO 52900) defines additive fabrica-tion as follows [9, 13]:
“Manufacturing processes which employ anadditive technique whereby successive layers orunits are built up to form a model.”
The terms habitually used in conjunction with additivemanufacturing have been evolving at the same pace as thetechnological developments, and it is convenient to establisha framework of reference that enables an analysis to be carriedout of the developments made and of the standardisationrequired for the future [14]:
(i) “Desktop manufacturing”, perhaps the first name, inlinewith the names at the time (1980s) such as desktopcomputer, desktop design.
(ii) “Rapid Prototyping”. This was the first term usedto describe the creation of 3D objects by way ofthe layer-upon-layer method. The technologies thatcurrently exist enable the manufacture of objects thatcan be considered as being somewhat more than“prototypes”.
(iii) “Rapid tooling”.When it became clear that the additivemanufacturing system not only enabled us to buildprototypes, but also moulds, matrices and tools, thisname began to be used to differentiate it from rapidprototyping.
(iv) “3D Printing”. This is the most commonly usedterm. The term “low-cost 3D printing” is frequentlycoined when we use printers that domestic or semi-professional users can afford.
(v) “Freeform Fabrication”. Is a collection of manufac-turing technologies with which parts can be createdwithout the need for part-specific tooling. A com-puterized model of the part is designed. It is slicedcomputationally, and layer information is sent to afabricator that reproduces the layer in a real material.
(vi) “Additive Manufacturing”. This is the most recentterm applied and it is used to describe the technologyin general. It is commonly used when referringto industrial component manufacturing applicationsand high-performance professional and industrialequipment.
An evolution can be seen in this sequence from obtainingprototypes (with purely aesthetic and geometric goals at thebeginning) to simple functional parts, tools, and moulds,to obtain complex functional parts such as those currentlyobtained via additive manufacturing in the metal industry.
The difference between these techniques is reduced to theapplication for which the additive manufacturing technologyis used.This means that a rapid prototyping technique can beused as a possible technology for the rapid manufacturing ofelements, tools, ormoulds. It answers the following questions:how would it be possible to manufacture a ball joint fullymounted in its housing without having to manufacture theelements separately prior to their assembly? And is the massor individual production of this unit possible at an affordableprice (Figure 1)?
A characteristic common to the different additive man-ufacturing techniques is that of the need for a minimumnumber of phases in the manufacturing process starting withthe development of the “idea” by the designer through toobtaining the finished product [15] (Figure 2).
Obviously, the scheme proposed by Yan and his team isa generalization since not in all AM processes G-Codes arecreated, and preprocessing is not contemplated (necessary insome processes).
In the process described above the designer can performthe entire product manufacturing operation from start tofinish.The involvement of another technician is not necessaryfor carrying out any complementary operations. However, itmust be taken into account that, during the process and priorto manufacture, the designer must know the determining
6 Complexity
Detailed process of a model Conceptual process1. Conceptual development of the idea.2. Design of the model in a 3D CAD application.3. Generation of an .stl or .amf file to enable the
additive manufacturing equipment to interpret the geometrical information (triangulation) modelled in CAD.
4. Orientation within the machine and generationof the NC code (G code) by the additive manufacturing equipment.
5. Manufacturing of the component.6. Cleaning. Removal of the support material (if the
technology uses support material and the component so requires).
7. Post-process phase: (improving the finish and hardening. Some technologies do not require this).
Conceptual development
3D CAD application
Generation the .stl file
Generation the G code
Manufacturing
Cleaning
Post-processing
1
2
3
4
5
6
7
Figure 2: Phases of the additive manufacturing process.
factors of the end product in order to be able to select themost suitable manufacturing technique, make the necessarymodifications to the geometrical data file (stl or amf file), andreview the NC code.The designer must, therefore, have a fulloverview of and the necessary training in all of the phases ofthe process [19, 20].
This article contains a full and up-to-date description ofthe benefits and drawbacks of the most important manu-facturing methodologies and processes that exist within thescope of the additive manufacturing concept, of the char-acteristics of the models manufactured and their associatedcosts, of the functional models, the applications, and thesectors of influence. At the end, there is a reference to theRepRap community and free software due the importancethey acquired last years.
It is important to establish the variables that currentlysupport the implementation of additive manufacturing andits relation to the basic principles of each technology, whichallow detecting the advantages and limitations of each ofthem. In Figure 3, the relationship between themain variablesthat intervene in the development of additive manufacturingis shown: technologies, materials, type of models, associatedcosts, and visual appearance. The current scope of thesevariables and their evolution can be seen in the subdivisionthat is presented in a circular diagram.
2. Processes
2.1. Additive Manufacturing Technologies. Conventionalcomponent manufacturing processes are based on the useof high-capacity resources combined with control elementsto achieve extremely high levels of precision and reliability.The use of computer systems during the design engineering,manufacturing, and simulation phases of a product incombination with other techniques based on mechatronicshave succeeded in making production systems highlyefficient.
However, a number of limitations still plague manu-facturing processes. This is because on occasion we find
ourselves being forced to use processes and tools that increasethe end cost of the element in accordance with the size ofthe production run and the geometrical complexity of thecomponent.
Transformation processes currently exist that enable usto extract, shape, fuse, and bind the base material of ourcomponent, and for the last few years we have also been ableto deposit the material where it is needed; in other words,using a virtual 3D model it is possible to manufacture thecomponent by adding the material in accordance with thesolid volume designed into the model.
Current additive-type technologies are based on thedispersion-accumulation principle (Figure 4). The materialor additives filler processes are those that involve the solidifi-cation of a material the original state of which is solid, liquid,or powder by way of the production of successive layerswithin a predetermined space using electronic processes[21]. These methods are also known by the acronym MIM(Material Increase Manufacturing).
If we focus our attention on the application of the dif-ferent manufacturing technologies used for obtaining rapidprototypes, the current technologies can be classified asadditive (stereolithography, laser sintering, fused depositionmodelling, etc.) andnonadditive (incremental forming, high-speed machining, pressure injection moulding, lost wax,laminating and contouring, etc.).
In Tables 3–8 the most relevant data with respect to themain additive manufacturing technologies are analysed [6, 8,11, 21, 22].
2.2. Classification. The classification of the additive man-ufacturing processes has been a controversial issue, evenbordering on obsession, since the appearance of the firstalternatives for obtaining pieces in these technologies. Thefirst classifications took into account whether the startingmaterial was solid, liquid, or powder, posing inconsequentialdoubts that contributed little to the academic community.The same problem was found in the professional field whenthe first commercial solutions began to appear, since the
Complexity 7
History
Mod
el
Material
Visual
appearance
Color
Polymer
Sand
Texture
Woodfill
Metalfill
Rubber-lik
e
TransparentSmooth surface
Finishingpost-proces
MaterialMetals
Metal deposition
Fused filament
fabrication (FFF)
Jet prototyping
(JP)
Laminated
manufacturing(LM
)Selective
Selective
sintering/melting
Selective laser
melting (SLM)
Direct metal
Inkjet rapidprototyping (IRP)
StereolithographySolid groundcuring (SGC)
Solid objetultra-violet laserprinter (SOUP)
Solid creationsystem (SCS)
ThermoplasticThermoset
(resin)Other
(SL)
laser sintering(DMLS)
(SS)
Prometal
ModelM
aker and
Multijet m
odeling
system (M
JM)
pattern master
depositionlam
ination (SDL)
PolymersMoldTo
olin
g
Pres
enta
tion
Form
/Fit
Hig
h str
engt
h
Spec
ial
prop
ertie
sFl
exib
le
Func
tiona
l
Conc
eptu
al
OthersCost
Technology
Material
deposition
(MD)
(MD)
Production
Processinglabour
copyright
Figure 3: Table of contents.
classifications that were proposed had little or no utility [14,23–25].
One of the pioneers in the classification of processes,hierarchizing them based on the startingmaterial, is JP Kruth[26], who proposed an interesting classification in 1991. Inthe literature we can also find other classification alternativesbased on the equipment used [27], to the process itself [28] orto the transformation of materials [29]
The classification proposed by Williams and his team[30] is very academic, but of little use from a practical pointof view. However, the classification proposed by ASTM hassome loopholes and disadvantages, and the same is the casewith the classification proposed by ISO.
ASTM (ASTM F2792) also proposes the followinggroups: binder jetting, directed energy deposition, materialextrusion, material jetting, powder bed fusion, sheet lamina-tion, and vat photopolymerization [31].
Cut layers Fabrication layers
3D model cut
Layer height
Figure 4: The dispersion-accumulation principle [8].
However, for example, it is not very coherent to separatethe photopolymerization processes depending on whetherthey are carried out in a vat or with another alternative, such
8 Complexity
Table3:Stereolitho
graphy
(SL).
Resin
Solid
ificatio
n-S
tereolith
ograph
y
Liqu
id re
sinTr
ay
Plat
form
Mod
elSu
ppor
ts
Mirr
ow
Lase
r
Them
aterialu
ndergoes
point-to-po
intsolidificatio
ndu
etothe
photop
olym
erisa
tionlaserb
eing
directed
onto
a2Dcross-sectionof
them
odel(XY
plane).Th
eplatform
gradually
descends
(Zplane)in
accordance
with
theh
eighto
fthelayer
defin
ed[10].
Layerthicknessvarie
sfrom
between0.1and
0.2mm.Th
eprecisio
nin
SLis+/-0
.2%
(min.+
/-0.2mm).Maxim
ummod
elsiz
e:2100x700x800
mm.
Thefollowingmaterialscanbe
used
(epo
xy-acrylicresin
s:Po
ly1500,P
P,Tu
skXC
2700T/T
usk2700W
,TuskSolid
Grey300
0,Flex70B,
NeX
t,Protogen
White,
Xtreme,WaterClear[11]
.Th
epropertieso
fthe
materialN
eXtare:tensilem
odulus:2370-2490
Mpa;tensile
streng
th:31-3
5Mpa;elong
ationatrupture:8-10%;flexuralmod
ulus:2415-2525
Mpa;
bend
ingstr
ength:68-71M
pa;impactstr
ength:47-52J/m
;deformationun
derload
temperature:48-57∘C.
Advantages
anddisadvantages
Theq
ualityandsurfa
cefin
ishareg
oodor
very
good
.Greatprecision
sand
transparentp
artscanbe
obtained.
Thee
quipmentand
materialsarem
edium-highcost.
They
have
prob
lemstoob
tain
pieces
with
cantileversor
internalho
lesd
ueto
thed
ifficulty
ofremovingthe
supp
orts.
Complexity 9
Table4:Selectives
interin
g/melting(SS).
SelectiveL
aser
Sintering
Exce
ss
Tray
Mat
eria
l
mat
eria
l
Mod
el
Supp
lyca
rtrid
geca
rtrid
ge
Mirr
owLa
ser
Alayero
fpow
derislaiddo
wnandaC
O2lasersintersit
atthep
ointssele
cted
ona2
Dcrosssectio
nof
them
odel
(XYplane).Th
eplatfo
rmgradually
descends
(Zplane)
inaccordance
with
theh
eighto
fthe
layer
defin
ed[12].
Precision
isbetween+/-0
.3%(m
in.+
/-0.3mm).
Them
inim
umlay
erthickn
essis0
.08mm.M
axim
ummod
elsiz
e700x380x580
mm.
Thefollowingmaterialscanbe
used:Polyamide(PA
),Glassfilledpo
lyam
ide(PA
-GF),A
lumide,PA
2241
FR,
TPU92A-
1.Prop
ertie
softhe
PAmaterial:tensile
mod
ulus:1650
Mpa;tensiles
treng
th:22Mpa;elong
ationatrupture:
20%;flexuralmod
ulus:1500Mpa;bending
strength:-
Mpa;impactstreng
th:53J/m
;deformationun
derload
temperature:86∘C.
Advantages
anddisadvantages
Pieces
ofhigh
quality
andprecision
areo
btained.A
largeq
uantity
ofsin
terin
gmaterialsisavailable.Th
eydo
notp
resent
prob
lemstoob
tain
pieces
with
cantileversor
internalho
lesb
ecause
theo
wndu
stmakes
ofsupp
ort.
Thee
quipmentand
materialsarem
edium-highcost.
SelectiveL
aser
Melting
X-Y
defle
ctio
n
Exce
ss
f- ϴ le
ns
cont
aine
r
cont
aine
r
Mod
el
Supp
lypl
atfo
rmC
onstr
uctio
n
bulld
ozer
Pow
der
Mirr
ows
Lase
r
Thep
rintn
ozzle
head
isfittedwith
aCO2laserthatis
directed
viaa
seto
flenseso
ntothep
owderedmaterial.
Thes
uppo
rtstr
ucturesa
remadeo
fthe
samem
aterialas
them
odelandmustu
ndergo
asub
sequ
entfi
nishingor
even
machining
process[3].
Them
inim
umlay
erthickn
essis0
.020
mm.
Them
aterialcan
be:stainlessste
el,Co-Cr,Incon
el625-718,titanium
Ti64
.Prop
ertie
softhe
materialC
o-Cr
:ultimatec
reep
(Rm):
1050
Mpa;elong
ation(E):14%;You
ng’smod
ulus:20
Gpa;H
ardn
ess3
60HV.
Advantages
anddisadvantages
Pieces
ofhigh
quality
andprecision
areo
btained.Th
ere
isalarge
amou
ntof
metallic
materialsto
besin
tered.
Equipm
entand
materialsaree
xpensiv
e.Th
eyhave
prob
lemstoob
tain
pieces
with
cantileversor
internal
holesd
ueto
ther
elatived
ifficulty
ofremovingthe
supp
orts.
10 Complexity
Table5:Materiald
eposition
(MD).
FusedDeposition
Mod
ellin
g
Mod
el
Mod
el
Hea
d m
achi
ne
Supp
ort
Supp
ort
mat
eria
lco
ilm
ater
ial
coil
Thew
ireisrolledarou
ndac
oiland
depo
sited
usingthe
thermalno
zzlehead
thatmoves
inaccordance
with
the
plane(XY
).Th
eplatfo
rmgradually
descends
(Zplane)
inaccordance
with
theh
eighto
fthe
layer
defin
ed[16].
Thelayer
thickn
essis:0.13
-0.25m
m(fo
rABS
);0.18
-0.25
mm
(forA
BSi);
0.18
-0.25mm
(forP
C);0.25mm
(forP
PSU).Th
emaxim
ummod
elsiz
eis9
14x610x914
mm.
Thefollowingthermop
lasticmaterialscanbe
used:
ABS
,ABS
i,ABS
-M30,A
BS-ESD
7,PC
-ABS
,PC-
ISO
andULT
EM9085.Th
epropertieso
fABS
are:tensile
mod
ulus:1627Mpa;tensiles
treng
th:22Mpa;
elon
gatio
natrupture:6%
;flexuralmod
ulus:1834Mpa;
bend
ingstr
ength:41
Mpa;impactstreng
th:107
J/m;
deform
ationun
derloadtemperature:76-90∘C.
Advantages
anddisadvantages
Lowmedium
costequipm
ent,availablee
venin
domestic
environm
ents.
Possibilityof
elim
inating
supp
ortsby
dissolutionandob
tainingv
eryc
lean
pieces.
Pieces
ofqu
ality
andprecision
canbe
obtained
but
resortingto
high
costequipm
ent.
Complexity 11
Table6:Jetp
rototyping
(JP).
ThreeD
imensio
nalP
rintin
g–GlueInjectio
n
Mod
el
mod
elPo
wde
r
Hea
d m
achi
nem
ater
ial
Tabl
e
Adhe
sive
cart
ridge
Them
odelisbu
ilton
abed
fullof
powderedmod
elmaterial.Ano
zzlehead
injectsa
nagglutinateo
ntothe
surfa
ceof
theb
edandfusesthe
powderinaccordance
with
theg
eometry
ofthe2
Dcross-sectionof
them
odel.
Thep
owderisa
dded
andlevelledusingar
oller.Once
thep
rocesshasb
eencompleted,the
excesspo
wderis
sucked
offtheb
edleavingthem
odelcle
an.Th
emod
elthen
hastobe
cured(hardened)
usingdifferent
coatings
[17].
Minim
umlay
erthickn
essisb
etween0.013and0.076
mm.
Them
aterialu
sedcanbe
ceramic,m
etalandpo
lymers.
Thep
ropertieso
fthe
materialzp150-Z-Bon
dare:tensile
mod
ulus:-
Mpa;tensiles
treng
th:14Mpa;elong
ationat
rupture:0.2%;flexuralmod
ulus:7.2Mpa;bending
streng
th:31M
pa;deformationun
derloadtemperature:
112∘C.
Advantages
anddisadvantages
Pieces
ofcolora
reob
tained,w
ithgreataestheticqu
ality.
Nosupp
ortsaren
eeded.
Itisno
teasyto
obtain
functio
nalpiecesd
ueto
the
fragilityof
thep
ieceso
btained.Th
ecosto
fthe
equipm
entism
edium-high.
12 Complexity
Table7:Laminated
manufacturin
g(LM).
SelectiveD
eposition
Lamination
Plat
form
Lam
inat
ed m
odel
lam
inat
ion
Lam
inat
ed m
odel
Stea
mro
ller
Lase
r
Adhe
sive
Pres
sure
tool
Mac
hine
cut
SDL
Pape
rsu
pply
coil
Pape
rco
llect
ion
coil
Invented
in2003
byMacCormack,
SDLmustn
otbe
confused
with
laminated
objectmanufacturin
g(LOM)techn
olog
y.LO
Muses
alaser,
laminated
papera
ndan
adhesiv
ethat
fixes
them
odelandsupp
ortm
aterial.
TheS
DLtechniqu
eworks
bydepo
sitingan
adhesiv
einthea
rea
requ
ired,bo
thof
them
odelandthe
supp
ort,andab
lade
thatcutsthe
outline
ofthelayer
[7].
LOM:Th
elayer
thickn
essis0
.165mm.
Them
axim
ummod
elsiz
eis
170x220x145mm.
SDL:Layerthicknesscorrespo
ndsto
thethicknessof
thep
aper
used
plus
thatof
thelayer
ofadhesiv
e.Sheetsof
PVCwith
thefollowing
prop
ertie
sare
used:tensiles
treng
th:
40-50Mpa;elong
ationatrupture:
30-100%;flexuralmod
ulus:1200-200
Mpa;deformationun
derload
temperature:45-55∘C.
Advantages
anddisadvantages
Pieces
ofhigh
quality
aesthetic
objectives
areo
btained.Th
estarting
materialsarelow
cost.
Thep
ieces
obtained
canbe
painted.Th
eequipm
entiso
faverage
cost.
No
functio
nalp
artsareo
btained.
Complexity 13
Table8:Injection-po
lymerisa
tion(JP-SL).
Resin
Injection(Projection)
andUltravioletL
ight
Photop
olym
erisa
tion
Mod
el
Hea
d m
achi
ne
Supp
ort
UV
ligh
t
Plat
form
Ahead
with
thou
sand
sofinjectors
depo
sitsd
rops
ofliq
uidresin
thatare
hardened
usingtwoUVraylightsfi
tted
onthes
ides
ofthes
elfsameh
ead.Tw
omaterialscanbe
used
simultaneou
sly(bi-m
aterialpieces)[18].
Them
inim
umlay
erthickn
essis0
.017
mm.
Ther
ange
ofmaterialsisextre
mely
extensivea
ndinclu
destranslucent
resin
s,po
lyprop
ylene,ABS
andelastic
resin
s.Prop
ertie
softhe
SCIW
hite(PolyJet)
material:tensile
mod
ulus:2500Mpa;
tensile
strength:58
Mpa;elong
ationat
rupture:10-25%;flexuralmod
ulus:2700
Mpa;bending
strength:93
Mpa;
deform
ationun
derloadtemperature:
48∘C.
Advantages
anddisadvantages
Theq
ualityandsurfa
cefin
ishareg
oodor
very
good
.Greatprecision
sand
transparentp
artscanbe
obtained.
Equipm
entand
materialsaree
xpensiv
e.Th
eyhave
prob
lemstoob
tain
pieces
with
cantileversor
internalho
lesd
ueto
the
difficulty
ofremovingthes
uppo
rts.
14 Complexity
as injection. A difference is made between directed energydeposition and material extrusion when both are, without adoubt, deposition processes.
Moreover, it is not justifiable to distinguish betweeninjection processes when an “adhesive” or a “material” isinjected, since, at the end of the day, both materials will endup forming part of the prototype or final part, as is the case ofthe ProMetal system.
It is also interesting to see that there are two types ofinjection: (a) when an adhesive is injected (which ends upforming a “material” part of the product) and (b) when a“material” is injected.
Lastly, there are different processes, some very important,that do not fall into any of the groups in this classification,such as in the case of mask sintering or digital light process-ing, for example.
ISO proposed, in its 2010 working draft, the followingten processes: stereolithography, laser sintering, laser melt-ing, fused layer modeling/manufacturing, multijet modeling,polyjet modeling, 3D printing, layer laminated manufactur-ing, mask sintering, and digital light processing [32].
There is no doubt that for the simple fact of definingten processes, other important processes are left out. Inthis classification, it can be seen that the manufacturers’considerations have more of an influence than logic. In2015 ISO assumes the ASTM classification with its standardISO/ASTM 52900:2015 (ASTM F2792).
An additive manufacturing system is in itself a produc-tion system and, therefore, for the purposes of classification,the systematics of manufacturing processes should be used.In every manufacturing system, there must be four elementspresent [4]:
(i) Material
(ii) Energy
(iii) Machine and tool
(iv) Technology (know-how)
From the point of view of the material, we could opt forthe classic classification of solids, liquids, powder, etc. [14];however, for both the engineer who wishes to manufacturethe product and their customer, it is more important toexpand upon the technical qualities of the material and, thus,we need to begin to classify the processes according to theirability to workwithmetalmaterials (with highmelting pointsand which, therefore, require more energy in the process) orwith other materials. And it is these technical qualities thatwe are going to focus on in this article.
From the point of view of energy, it is important toanalyse what type of energy is required and how this energyis transmitted. With regards what type of energy is required,this may be as follows:
(i) Heat (electrical resistance, electron beam, etc.)
(ii) UV light (visible or laser)
(iii) Chemical energy (for adhesion processes, chemicalreactions, etc.)
With regard to how this energy reaches the material forsuccessful transformation, this may be via the following:
(i) Laser (valid to provide UV light and heat)(ii) Electrical resistance(iii) Electron beam
From the point of view of the machine, it is important toanalyse the alternatives of smaller machines, suitable foroffices, compared to industrial machines and as regards thetools, these shall include the following:
(i) Vats and containers for photosensitive liquids orpowder
(ii) Deposition or extrusion nozzles(iii) Injectors
With regard to technology, the most important variable, it isnecessary to know if it is available commercially or if it is onlyan option available in research centres, as in this case therewill likely be a wait involved, although fortunately not long ifthe technology is valid.
In conclusion to all of this, Table 9 shows the classificationsystem that takes these variables into account: material,energy, machine and tool, and technology.
To specify this classification, which can cover all additivemanufacturing processes with simple approaches and thatcan evolve as technology evolves, we present the classificationchain of the five processes analyzed in the introduction, thebasic pillars of additive manufacturing (Table 10).
For example, stereolithography (SL) is a process that usesresins as material (2); uses laser as energy (f); is a professionalmachine (3); uses vats and containers for photosensitiveliquids as tools (a); and is available commercially (4). For thisreason, stereolithography will have a classification: 2f3a4.
2.3. Analysis of the Environment. In order to carry outthis study, we worked with leading additive manufacturingcompanies, both ones that are developing new processes andones that are part of the market providing service. Contactwas also established with researchers in technology centresand universities and their contribution has proved to behighly valuable.
Unsurprisingly, this study entails an exhaustive analysisof the most important literature in the field of additivemanufacturing, a study thatwe cannot include in this paper infull due to the obvious space constraints. Nonetheless, a seriesof papers must be listed which, due to their special interest inthe subject, provide information that has proved fundamentalin producing this paper.
In the field of metal additive manufacturing, an analysishas been performed on processes using powder, whetherpowder injected, powder deposited in layers, or processesusing wire [22, 33–35].
As has been discussed, this paper has been approachedfrom both a professional perspective (expanding upon themost interesting innovations in this field) and a researchperspective. Therefore, papers that take into account thesocial impact of additive manufacturing have been analysed
Complexity 15
Table9:Classifi
catio
nmatrix
ofthep
rocesses
inadditiv
emanufacturin
g.
Material
Materialswith
alow
meltingpo
int(1)
Resin
s,transparent
materials(2)
Flexiblematerials(3)
Ceram
ics(4)
Powder(5)
Sheets(6)
Metalsa
nddifficult
materials(7)
Energy
Heat
Chem
icalenergy
UVlight
(visibleo
rlaser)
Mechanicalenergy
Electricalresistance(
a)Electro
nbeam
(b)
Highpo
wer
laser(c)
Adhesiv
es(d)
Reagents(e)
Laser(f)or
visib
lelight
(g)
Cutting
tool(h)
Machine
and
tools
Lowcost(suchas
RepR
ap)(1)
Office
(2)
Professio
nal(3)
Indu
stria
l(4)
Vatsandcontainersforp
hotosensitive
liquids
orpo
wder(a)
Deposition
orextrusion
nozzles(b)
Injectors(c)
Cutting
tool(d)
Techno
logy
Inconceptualanddevelopm
entp
hase
(1)
Inexperim
entalphase
(2)
Availablea
tresearchcentre
(3)
Available
commercially(4)
16 Complexity
Error in the conversion of the 3D model into STL format
Error in the decomposition in layers of the 3D model
Stepping effect error Model infill error
Ideal surface
Figure 5: Technology limitations in the rapid prototyping process.
Table 10: Classification of the original processes in additive manu-facturing.
Stereolithography (SL) 2 – f – 3 – a – 4Selective Sintering (SS) 1 – c – 3 – a – 4Material Deposition (MD) 1 – a – 3 – b – 4Jet Prototyping (JP) 5 – d – 3 – c – 4Laminated Manufacturing (LM) 6 – h – 3 – d – 4
[20, 35–37]. Papers focusing onmedical issues have also beenanalysed [38–40] and papers have been locatedwhich expandupon design methodologies for additive manufacturing [6],the involvement of concurrent engineering [41], and the studyof nonrigid materials [42]. The fields of architecture [23, 43–45] and the automotive industry have also been addressed [6].
References have also been found relating to functionalprototypes [46], which show the use that additive manu-facturing still has in this regard, along with papers on verycontrasting environments, such as the food industry [47]. Inthe field of research, papers relating to studies of the processes[48] or medical studies with living cells [36, 38, 49–51] areworth mentioning.
Naturally, this study also considers the RepRap move-ment [5, 21, 52], as although technologically speaking it doesnot contribute much, it has undoubtedly played an essentialrole from both a social perspective and one of technologydisseminations, and so it cannot be omitted in any seriousstudy on additive manufacturing.
3. Analysis
3.1. Characteristics of the Models Manufactured Using theAddition ofMaterial Technique. When the three-dimensionalmodel is obtained using a reverse engineering process and theprecision of the final model is determined by the scanning
process, the virtual 3D modelling, and the additive manufac-turing process. If an inverse engineering process has not beenused, the models manufactured are determined by the virtual3D modelling and the manufacturing process used [53].
We have already seen that during the manufacturingprocess the model is built by way of the depositing of layerson the x-y plane resulting in solid volume being acquired inthe direction of the Z axis. This process is characterised by avolume error between the volume of the virtual 3Dmodel andthe volume of material obtained in the model and, therefore,the manufacturing precision is the result of superimposingdifferent errors in the production of the model which affectthe surface quality, the dimensional accuracy, and the finalweight of the model.
The technology limitations that occur in this process areas follows: an error in the conversion of the 3D model intoSTL format (triangulation of the geometry), an error in thedecomposition in layers of the 3Dmodel (exact division of thethickness), stepping effect error (orthogonal deposition of thematerial by layers), and, finally, model infill error (Figure 5).
There are studies which show that the models obtainedusing rapid prototyping techniques have an average error inthe majority of the 0.05 mm dimensions with respect to theoriginal model or of modelling control in 3D [42].
The additivemanufacturing of three-dimensional modelswith an aesthetic (visual) or assembly objective is achievedusing techniques that involve the layer-upon-layer additionof plastic materials, while functional models or those capableof withstanding mechanical testing must be manufacturedmainly in metal and, in some cases, in a polymeric materialthat is subjected to a postproduction hardening process.
Studies undertaken by different research institutes showthat those products manufactured in metal using addi-tive technologies provide the same or better mechanicalperformances than the same products manufactured usingconventional processes [22]. The resistance to corrosion of
Complexity 17
Model made for aesthetic (visual) purposes Model made for hydraulic testing purposes
Figure 6: Function prototypes for testing.
products manufactured using additive technologies is similarwhere the same level of surface finish is involved.
One objective during research is that of obtainingfunctional prototypes using polymeric materials capable ofwithstanding mechanical testing using rapid prototypingtechnologies. The advances made in the field of depositionmaterials and the subsequent finishing of the model maylead to functional prototypes that do not require the useof techniques based on rapid manufacturing (RM), therebyavoiding tooling costs (see Figure 6) [23, 46].
3.2. Technologies and Decision Variables. Some of the tech-nologies described above require the use of amaterial, knownby the name of support material, the purpose of which is tohold any overhanging designed parts in place. Once the depo-sition process has been completed, the support material mustbe removed during an operation carried out subsequentlyto manufacture (postprocessing), and the technique used toremove it shall depend on the support material in questionand, therefore, on the additive manufacturing technologyemployed. In some additive technologies there is no supportmaterial as the support function that is performed by thematerial that has not hardened [18].
With respect to the mechanical properties of the pro-totypes obtained via the addition of material, these aredetermined by the quality of the result of the fusion betweenlayers and the properties of the material. The followingparameters (DIN EN ISO 178/179/180/527/2039) must beestablished in order to analyse the mechanical properties ofthe materials used in the different additive manufacturingmethods: elastic modulus, breaking stress, elongation, flex-ural modulus, impact strength, compressive strength, andmelting point (Table 11) [11, 54–56].
The choice of the most suitable technique for each typeof prototype is based on the definition of the objectivebehind the production of the prototype: aesthetic, func-tional, investigational, or visual if the purpose is only tocheck the external appearance of the item designed [19,39, 42, 57–60]. When it comes to making this choice ananalysis may be planned based on a study of the possiblevariables: technology, resolution and precision, materials,software, the mechanical properties of the material (traction,compression, impact, softening, and density), surface finish,production time, cost, maximum dimensions of the itemor model, posthardening requirements, guarantee, noise, CEcertification, operational temperature, electrical connections
and consumption, interface (network, hardware, softwareand exchange formats), weight, and spares and consumables(Table 12) [23].
Of all the aforementioned study variables, those habitu-ally taken into account when choosing the prototyping tech-nology are resolution-precision, the mechanical and thermalproperties of the material, surface finish, production time, andthe cost of the prototype.
With respect to the evaluation of the different prototypingtechnologies in accordance with the cost of the prototype,the fact that the comparison of technologies is restricted bythe type of machine used must be taken into account. It iscommonly thought that those prototyping machines basedon stereolithography (SL) and selective laser sintering (SS)can be applied to the industrial production of prototypes,while all the others are seen as being machines that can beused professionally, but not in situations where the mainobjective is production. The manufacturers are currentlyoffering domestic or desktop, professional, and industrialrapid prototyping machines, and therefore the costs incurredby using these machines must be offset by the performancelevels shown above and by the production levels that can beobtained [39].
However, to calculate the price of an element manufac-tured using additive technologies the following generalmodelcan be followed in which the final manufacturing cost ofthe prototype (Cp) of the 3D model has been calculated inaccordance with the following equation [8]:
Cp = Ce + Cm + Ct + Ca (1)
where
Ce is production cost (machine depreciation data)Cm is cost of materialCt is the processing cost of the 3D model and labourcostCa is finishing (post-processing) cost
If this calculation model is transferred to a specific case,observe the following example of the cost of a prototypegenerated using the MD technique in a professional grademachine that can be easily adapted to any additive technol-ogy. In this case, as can be seen, there is no finishing cost(Table 13).
18 Complexity
Table11:Th
eprin
cipalm
echanicaland
thermalprop
ertie
softhe
functio
nalm
aterialsused
inAM.
PROPE
RTY
STANDARD
PROTO
TYPINGTE
CHNOLO
GIES–HABITU
ALMAT
ERIALS
SLSS
MD
JPSL-JP
Next
PA12
ABS
ABS
+VisiJetM3X
zp150-Z-
bond
Digita
lABS
PolyJetW
hite
Tensile
mod
ulus
(MPa)
AST
MD638M
22370-2490
1650
1627
1915
2168
-2600-300
02500
DIN
ENISO527
Tensile
strength(M
Pa)
AST
MD638M
31-35
4822
3749
1455-60
58DIN
ENISO527
Elon
gatio
natrupture(%)
AST
MD638M
8-10
206
4,4
8.3
0.2
25-40
10-25
DIN
ENISO527
Flexuralmod
ulus
(MPa)
AST
MD790M
2415-2525
1500
1834
1917
-7.2
1700-2200
2700
DIN
ENISO178
Bend
ingstr
ength(M
Pa)
AST
MD790M
68-71
-41
6265
3165-75
93DIN
ENISO178
Impactstr
ength(J/m
)AST
MD256
47-52
53107
96.4
--
65-80
-DIN
ENISO180
Deformationun
derload
temperature
(∘ C)
AST
MD64
848-57
8676-90
73-86
88112
58-90
48
Complexity 19
Table 12: Decision variables when choosing a prototyping technology.
CHARACTERISTICS SPECIFICATIONS TO BE CONSIDERED
COSTS
Price of the machine (including post-production and maintenance)Unitary model cost
Cost of training qualified operatorsControl and modelling software
Annual maintenance cost
DIMENSIONS
WorkspaceDimensions of the machineWeight of the machine
Noise levelMandatory accessories
WORKMATERIAL
Colour or number of colours, transparencyPossibility of recycling material
Technical characteristics of the materialWorking temperature
PRECISION
PrecisionHeight/Thickness of layerMinimum detail size
ResolutionMinimum wall thickness
OTHERS
Vertical working speedNetwork/On-line connection
Files supported, scope of the software associated with the machineAdaptability to accessories
User friendliness (ease of handling and maintenance)
3.3. The Benefits and Disadvantages of Additive Manufactur-ing. The processes used to manufacture conventional partsand components are influenced by a series of limitationsrelated to the obtaining of certain shapes, such as curvedholes, mould release angles, or preventing tools from cominginto contact with geometrically complex pieces. And thenthere is the fact that some manufacturing processes donot comply with a company’s commitment to a sustainableproduction process by involving the residues related with theuse of cooling liquids.
Two characteristics comprise the main differencebetween the additive manufacturing techniques andtheir conventional counterparts. These not only providesignificant competitive advantages, but also do not make themanufacturing process more expensive:
(1) The geometrical complexity of the part to be manu-factured. Elegant geometrical forms, hollow interi-ors, internal channels, variable thicknesses, irregularshapes, etc. can easily be reproduced based on thegeometrical template obtained from a 3D CAD.
(2) The customisation of the part to be manufactured.Products that are exactly identical or completely dif-ferent can be obtained without any notable influenceon the process and without additional costs. Thiscustomisation represents one of the main current
trends in the development of products with a highadded value, and the mass application thereof is oneof the paradigms pursued by the industrial sectors indeveloped countries, which see it as being the key totheir sustainability.
These two characteristics can provide massive benefits indifferent industrial sectors:
(i) Lightweight Products.They enable the manufacture ofproducts designed for a specific function and withmade-to-measure features, e.g.: lighter for reasons ofweight savings, strength or costs. Some of the additivemanufacturing techniques are capable of filling amodel with different degrees of porosity without achange of material.
(ii) Multimaterial Products. They make it possible tomanufacture a product using several materials simul-taneously in the same solid. This means that thetechnique overcomes one of the current limitationswith respect to the weight/mechanical strength ratioby the introduction of new functionalities or thelowering of production costs [61, 62].
(iii) Ergonomic Products. The design of the componentscan achieve a greater degree of interaction with the
20 Complexity
Table13:C
alculationof
thep
rototyping
costusingmateriald
eposition
(MD)techn
ique.
COST
SANALY
SISFO
RTH
EPR
OTO
TYPINGOFITEM
SIN
A3D
PRIN
TER
MAC
HIN
EDEP
RECIAT
IONDAT
ACe
Priceo
fMachine
(€)
25,000
Yearlymaintenance
cost(€)
2,900
Yearso
fdepreciation
4Depreciation(h/year)-2
23days-year/
8ho
urs-day
1,784
Machine-depreciationpricep
erho
ur(€/h)
4.72
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Complexity 21
user by adapting to the exact anthropometric char-acteristics of each individual (prostheses) withoutnecessarily affecting the manufacturing costs.
(iv) Integrated Mechanisms. They make it possible tomanufacture a mechanism that is totally embeddedin the finished item without the need for subsequentassembly and adjustments, e.g., a journal bearing, aroller bearing, a spring and its support, and a screwed-on worm gear.
As far as the production of industrial components is con-cerned, the followingmust be highlighted as obvious benefits:
(i) A reduction of the time it takes new designs to reachthe market: when additive manufacturing is usedas a manufacturing technique of the end productand not only in the production of prototypes, manyof the current launch and validation phases can bedrastically shortened. Another advantage is that itprovides great flexibility when it comes to respondingto the continuous changes in market demand.
(ii) Short production runs: the size of the production runcan be minimal to the extent of being on a per unitbasis while hardly influencing manufacturing costs(if and when the depreciation of the equipment isnot considered). One of the characteristics that makethis possible is the lack of a need for tooling, whichrepresents a considerable advantage with respect tothe conventional manufacturing methods.
(iii) A reduction of assembly errors and their associatedcosts: ready assembled components can be obtainedwith the only subsequent operation being the qualitycontrol inspection.
(iv) A reduction of tool investment costs: tools do not formpart of the additive manufacturing process. This rep-resents a great deal of flexibility as regards adaptingto the market and a reduction, or even elimination,of the associated costs (toolmaking, stoppages due toreferred changes, maintenance, and inspection).
(v) Hybrid processes: it is always possible to combinedifferent manufacturing processes. In this case com-bining additive manufacturing processes with con-ventional processes might be interesting to makethe most of the advantages offered by both. Forexample, it might be extremely beneficial to combineadditive manufacturing technology with mechanisedmaterial removal in order to improve surface qualityvia a reduction of the “stepping effect” produced bythe additive manufacturing technologies. Hybridis-ation can also occur in the opposite direction, inother words manufacturing using subtractive meth-ods starting with a block before adding, by way ofadditive manufacturing, those especially complicatedcharacteristics which generate high value.
(vi) Optimum usage of materials: material wastage isreduced to a minimum. Any waste material can beeasily recycled.
(vii) A more sustainable manufacturing process: toxicchemical products are not directly used in appreciablequantities.
However, additive manufacturing technologies do have anumber of drawbacks which must be borne in mind whenchoosing the technology best adapted to the requirements ofthe product to be manufactured.
(i) Additive layer manufacturing produces what isknown as the stepping effect. The disadvantages ofthis phenomenon include complicating the shapingof geometrical curves and an extremely rough surfacefinish. This effect means that shafts and holes musttypically be manufactured with their circular cross-section in plan. If they are not, the roundness of thepiece would not be acceptable. On the other hand,and putting roundness to one side, positioning thepiece in another way might be useful depending onthe application in question; it would be interesting tomanufacture an overturned sliding axis in such a waythat no ‘interlocking’ occurs.
(ii) With respect to some technologies, the manufactur-ing operation itself can be slow, thereby making itparticularly suitable for small production runs.Whenthe production run reaches a certain size it maywell be appropriate to use a conventional technologydespite the fact that, as has been seen above, thesetechnologies have a number of limitations, especiallygeometrically speaking.
(iii) The materials used in some of the technologies mightnot be suitable for the product to be manufactured.
(iv) The depositing of layers produces anisotropic materi-als. Given the fact that many industrial componentsare subjected to forces that put the material understress and that they are so sized as to use theminimumamount ofmaterial, it is possible that the performanceof the components with respect to the forces theymust withstand while in service results inadequate.
(v) The tolerances obtained using the majority of theadditive manufacturing methods are still higher thanthose achieved using other manufacturing methodssuch as those based on the removal of material.
3.4. By Sector Innovation with Additive Manufacturing. Bothin innovation and in research, advances are going to bedefined by acquiring new materials, more precise, and lesscostly equipment and also by seeking out new sectors for 3Dprinting.
An interesting proposal in this field is that presentedby Wong and his team in 2012 [6]. Six sectors are anal-ysed: lightweight machines, architectural modelling, medicalapplications, improving the manufacturing of fuel cells, andadditive manufacturing for hobbyist and additive manufac-turing in art. We have no doubt that these were the sectors ofinnovation five years ago. However, our analyses show us thatnowadays the additive manufacturing sectors where innova-tion can really be seen are as follows: consumer products,
22 Complexity
20.3 19.5
15.112.1 10.8
86 5.3
3
Additive Manufacturing by sector (%)
Consu
mer
prod
ucts/
Elec
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csM
otor
Veh
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Med
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sAca
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ic In
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Figure 7: The use of additive manufacturing in the different sectors (Wohlers Report 2013).
automotive industry, medicine and medical engineering,aviation industry, architecture, construction, and food.
The degree to which additive manufacturing is used indifferent sectors is shown in Figure 7.
A review of the sectors in which additive manufacturingis currently used is presented as follows.
3.4.1. Consumer-Electronic Products. This sector uses additivemanufacturing to obtain prototypes and models of a multi-tude of articles for the home, sports equipment, toys, etc. It isthe number one customer of those additive manufacturingtechnologies that enable the direct digital manufacture offinished components of high geometrical complexity and thatrequire customisation.
As soon asmaterials that are both flexible and strong evenwhen thin become available, it shall be possible to manufac-ture consumer products such as clothes and footwear usingadditive techniques. The deposition of conductive materialsvia the printing of passive circuit components such asresisters, condensers and coils, diodes, organic light emittingdiodes (OLEDs) and circuit interconnections can only benefitthe production of electronic devices and components.
3.4.2.Motor Vehicles. In this sector additivemanufacturing isbeing used to create prototypes that enable the validation ofengineering processes and, above all, functional and aestheticcomponent design processes. The production of finishedparts is not yet a reality, with the technique only being usedin the customising of certain elements in one-off vehicles.The hope is that the development of new materials and theirapplication of large, high-speed machines will favour the useof additive manufacturing in conjunction with the highlydemanding production criteria inherent to this sector.
3.4.3. Medical/Dental. The application of additive manu-facturing in the medical/dental sector enables physical 3Dmodels to be obtained from processed medical images (3Dscans, TAC) for application in different specialist areas.
The use of additive rapid prototyping technologiesenables preoperative planning processes, the production ofprostheses, and the preparation of surgical templates andguides to be carried out with a higher diagnostic quality andgreater surgical safety in less time and more cheaply than ispossible using conventionalmanufacturing techniques. In thecase of specific and customised implants optimum planningof the surgical process and a reduction of operating times hasalready been achieved.
We must not omit today’s 3D printing of living cells,bioprinting, in which a lot of resources are being invested andwhichwe trustwill soon present some very interesting results.
3.4.4. Aerospace. This market requires additive manufactur-ing to respond to high mechanical and thermal performancedemands, weight reduction, and minimum losses of materialas regards certain components with respect to both polymericand metallic materials, primary titanium, and nickel alloys.The selective sintering of powdered metals has become amanufacturing, repair, and maintenance solution for certaincomponents, e.g., turbine blades, as well as for the manufac-ture of high added value aeronautical tooling.
3.4.5. Architecture. The manufacture of mock-ups and pro-totypes within the architecture and construction sector was,and still is carried out on a significant handicraft basis. Thedevelopment of assisted design systems, with its resultingprogress towards solid modelling systems and the currentBIM systems with respect to building, has enabled theproduction of highly attractive quality digital mock-ups,infographics, and virtual animation of plans and projects.However, the same cannot yet be said about the physicalmock-ups obtained from that digital model of the plan usingadditive mock-up and prototype construction machines. 3Dprinting could well become an essential piece of equipmentin the studios of architects and designers. In Figures 8 and 9,we can see a number of examples of how these techniques are
Complexity 23
Product development Motor vehicles Medical/dental
Architecture Aeronautics Food
Figure 8: AM applications.
Production Jewellery (microfusion) Art and crafts
Textiles-fashion Toys-videogames Sport
Figure 9: Another AM applications.
applied and they clearly show the great potential of additivemanufacturing.
3.4.6. Food. Evenwhen the catering industry is incorporatingnew 3D printing techniques for food, perhaps it is a good ideato discuss the advances being made in this field with regardto the food-health combination, that is, when 3D printingsystems are used to measure out food and structure patients’diets.
However, naturally, in the field of catering and food ingeneral,major advances are being achieved, which are alreadyin operation in prestigious restaurants or in the production ofdesserts and sweets.
3.5. By Sector Investigation with Additive Manufacturing. Inthe field of research, that is, in the field of the work that isbeing carried out today in research centres and universities,both public and private, there are three approaches
24 Complexity
Figure 10: Example of RepRap machines and parts for replication.
that stand out: materials, equipment, and new fields ofapplicability.
In the field of new materials, a lot of progress is beingmade on biocompatible materials, compound materials, andmetals, each one within a clearly identified field of devel-opment. In these fields, materials with good mechanicalproperties are also being sought; however, at the sametime, progress is being made on the development of elasticmaterials, which open up a whole range of possibilities for3D printing that is yet to be quantified.
In terms of new equipment, greater precision and lowercost are clearly what is being sought after, in order to makethis technology competitive with regard to other conven-tional technologies.
With regard to the new fields of applicability in which,without a doubt, great progress will be made over the comingyears in terms of printing metal materials, we resolve theproblem of the dispersion of metallic liquid when it reachesmolten state, and in terms of bioprinting, we develop newapplications with regard to living tissues, not only in bonesand cartilage, where advances have already been made, butalso in other tissues of the human body, including the visceraand muscles.
3.6. The RepRap Community and Free Software. In 2004Adrian Bowyer founded RepRap [5], an open-code initiativefor building a 3D printer capable of printing out most ofits own components, at Bath University. The vision of thisproject is to make the manufacture of low-cost distributionunits available to people all over the world, thereby enablingthem to create their own products on a daily basis (seewww.RepRap.org).
As the term ‘Fused Deposition Modelling’ had alreadybeen registered by Stratasys, the RepRap Community hascoined the term ‘Fused Filament Fabrication (FFF)’, whichcan be used by anybody without any restriction whatever(under a version 2 GPL licence). Under these terms andconditions anybody can distribute and modify the RepRapmachine, but they must respect the modifications madeunder this licence [21]. In other words, all changes mustremain in the public domain. As the machine is both freeand open-code; anybody can, without having to pay any feeswhatever, build an unlimited number of copies for themselvesor for anyone else using the selfsame RepRap machines to
manufacture the plastic parts of the copies (thereby makingit self-replicating, Figure 10).
Althoughwe know that the RepRapmovement has playedand continues to play a very important role in the develop-ment of additive manufacturing, it is interesting to discusshere that it was not initially accepted by the academic com-munity, as it was considered a subject of minor importance.Only a few years later the subject was accepted, however notas a phenomenon in itself, rather under the consideration ofa machine that could replicate itself, something that everymanufacturing professional knows has been possible sincethe 19th century, with milling machines.
There is an increasing number of meetings of “experts”who analyse what the ‘printing’ of physical objects using 3Dprinters will represent, which is now being seen as one ofthe great industrial revolutions of the next few years, andthere has even been talk of the Third Industrial Revolution.The #Redada sessions are a meeting that allows users andprofessionals to exchange ideas and analyse the possibilitiesopen to them, as in the case of Video 34, “#Redada 18Madrid:TheChallenges of 3DPrinting”, which features a debate aboutthe social trends and the aspects related to culture, civil rights,and technology.
3.7. User and Exchange Communities. The social importanceof this technology has been enormous and, as has alreadybeen said, it is developing in leaps and bounds, therebyenabling engineering students and professionals who spe-cialise in these particular techniques from all over the worldto experiment with their creations and perfect them prior tothe production of full scale versions.
Accessibility to the technology links a series of commu-nities of users and developers who exchange their know-howand experiences in order to continue perfecting the printingsystem and open up new and previously unimaginable fieldsin the process.
Alongside this, these communities of users have devel-oped a series of platforms for exchanging existing 3Dmodelsfor downloading and printing, thus broaching a far fromludicrous idea that involves manufacturers making 3D mod-els of ex-catalogue parts of their products available to users.To a certain extent Google Earth has already done this byallowing the community of Google SketchUp users to uploadmodels of buildings from all over the world in their exact
Complexity 25
location for everybody to enjoy.The fact that the future holdscountless possibilities cannot be too highly stressed. Thereare model upload and download banks such as the Englishlanguage platform Thingiverse and its Spanish counterpartRascomras. Many more exist, and their number increasesby the day, some more creative than others, such as ThePirate Bay (a community for the downloading of all types ofaudiovisual material which has incorporated a new sectionfor 3D models).
The Clone Wars Projects seek to spread the word aboutRepRap technology while at the same time contributing newdesigns and innovative research channels, but not so muchalong self-replication lines.
A series of workshops have existed all over the worldfor a number of years now. Known as FabLabs (FabricationLaboratories), they are being promoted by the Center ofBits and Atoms (CBA) of the Massachusetts Institute ofTechnology (MIT), at which a lot of hard work is beingdone on this technological revolution in light of the socialchanges it is bringing about. They are equipped with a seriesof computer-controlled machines “for building (almost)anything”: 3D printers, laser cutters, CNC (computerizednumerical control) routers and an electronics laboratory(among many others that vary from workshop to workshop).Worldwide, with respect to the number of Fablabs Spainranks fourth with 7-8 behind the USA, with more than thirty,The Netherlands (9), France (8), and ahead of Germany (6).
4. Discussion
As has been discussed throughout this paper, additive man-ufacturing (AM) processes are considered in many applica-tions as a new industrial revolution. This article conducts anexhaustive study of the current state of additive manufactur-ing. As is shown in Table 2, the technologies and processesthat currently exist are very diverse and, therefore, producinga classification that unites and differentiates all of them beingtruly complex. Thus, this paper proposes several types ofclassifications.
Over recent years, many names have arisen to encompassthese technologies, such as “rapid prototyping”, “rapid tool-ing”, “3D printing”, and “freeform fabrication”. All of theseare commonly accepted; however, “additive manufacturing”is probably that which best brings them all together.
The main advantages associated with these technologiesare the high precision, the possibility of using differentmaterials, and the ability to obtain impossible prototypesusing conventional means. The current limitations includethe high cost of the processes, the time required to obtainthe prototypes, and perhaps the lower resistance they have.Activework is underway to improve these limitations in orderfor additive manufacturing to be competitive with regard toother more conventional means.
It is important to note that within additivemanufacturingthere is no perfect technology for all purposes, rather what weneed to do is to determine the most suitable technologies fora specific use.
For example, in the dental sector, as is discussed byJimenez et al. (2015) [39], in order to manufacture the models
used in the thermoforming of correction splints, technologiesbased on printing by injecting resin (IJP-UV), digital lightprocessing (DLP), and fused depositionmodeling (FDM) arethe most suitable as they offer the best price-quality ratio ofthe model for thermoforming.
Among the agents in the aviation market, metal materialadditive manufacturing technologies, such as ‘Electron BeamMelting’ (EBM), ‘Sintering Laser Melting’ (SLM), or ‘LaserCladding’ (LC), are those that attract most interest, in partic-ular, for part manufacturing, case of the OEM or Tier1; or forpart repair, case of the ‘Maintenance and RepairingOverhaul’(MRO). These manufacturing technologies provide manyadvantages in comparison with other conventional metaltransformation processes (http://www.ctsolutions.es).
Changing sector, 3D printing of architectural models willlead to a reduction in the number of steps, an improveddesign timeframe, and the preservation of the finer detailsof the final architectural design, and therefore its marketniche is on the rise. As discussed by Domınguez et al. (2013)[23], fused deposition modeling machines appear amongthe most suitable for obtaining working models, given theirlow cost (especially in the case of the RepRap models), thespeed of the process, and the possibility of recycling thematerial. Machines projecting binding agent would also besuitable for obtaining models for the client, thanks to theircompetitive prices, good surface finish, wide range of colours,and lack of support fixtures, among other qualities. Although,perhaps, the method most used for architecture is printingvia the sintering of composite powder, thismaterial requires apostprocess to harden it and give it the necessary consistencyand finish for an optimum result (http://sicnova3d.com). Inany case, it is certainly true that, right now, no technologyfully meets all of the requirements of the work specificationsin the field of architecture and construction.Thus, this sectorstill has quite a long way to go.
PolyJet technology produces ultradetailed prototypes,moulds, and even final parts that incorporate smooth rigid,transparent, and flexible materials, which is why it hasbeen the technology most used in the jewellery sectorin recent years. Multimaterial 3D printers produce lifelikemodels with a variety of properties on a single build tray(www.stratasys.com). Regarding jewellery, one of the advan-tages of using 3D printers is speed. The plastic parts take 7 to10 days to be made, whereas metal parts take 10 to 15 days.Other positive points include the cost saving and the fact thatit is possible to retouch the jewellery while it is being printed.
4.1. Immediate Future of Additive Manufacturing. In produc-tion lines, one of the main focal points for improvementin additive manufacturing consists of optimizing its featuresin order to be competitive with regard to conventionalmanufacturing processes in different production lines. Incomparison with the traditional means, the use of additivemanufacturing technologies continues to be too costly.
An important niche for saving in the industrial sec-tor would be the so-called virtual libraries. There is alarge number of fixed assets in all industrial platformswithin what is known as physical replacement parts, spareparts, etc. Many of these items could be saved by means
26 Complexity
of a virtual parts library (https://www.thingiverse.com/,http://www.3dprintfilemarket.com/), which could print suit-able parts or components as and when required.
Another important section is that of the study of newmaterials. Cellulose, the plant material we have used forcenturies to make paper, has emerged as a new resourcefor better, faster, and cheaper three-dimensional printing,in addition to providing an alternative that is recyclableand biodegradable by nature, according to new research bythe MIT, published in Advanced Materials Technologies. Atpresent, the key raw material for 3D printing is polymers,compounds that are largely synthetic and which use inksto create three-dimensional objects in accordance with themodels via a computer used to execute the three-dimensionalprinting (www.imprimalia3D.com).
A particularly interesting field and one for study is thatof the space sector, where additive manufacturing shouldalso play an important role. The National Aeronautics andSpace Administration of the US (NASA) is seeking a habitatdesign built using a 3D printer that can be used as a base tobuild houses on the surface of Mars. The final objective is toachieve a space design that allows astronauts to stay on the redplanet for long periods at a time. Different projects are beingcarried out to conduct research on materials and explore thepossibilities of 3D technology,whichwouldmeanmany of thenecessary infrastructures could be directly built on theMoonusing, moreover, resources that are already there. This wouldspeed up this large undertaking, as it would notably reducethe amount of parts that would need to be taken to the Moonand then later toMars. 3D technology and the use of resourcesmay help reduce costs both in the long and in the shortterm.
4.2. Connected Industry: Future Prospects of Additive Manu-facturing in the 4.0 Environment—AStudy Is Conducted on thePossibility of Positioning Additive Manufacturing in a ServiceEnvironment. The term Industry 4.0 was coined to describethe smart factory, a vision of computer-aided manufacturewith all of the processes interconnected through the Internetof things (IOT). It is what we know as the industrial Internetof things, I2OT.
It is hoped that the new concept of industry 4.0 willbe able to drive forward fundamental changes on the samelevel as the steam-powered first industrial revolution, themass production of the second, and the electronics andproliferation of information technology that characterisedthe third.
According to Mark Watson, associate director for theindustrial automation of IHS, “The challenge for the fourthindustrial revolution is the development of software andanalytical systems that turn the deluge of data produced byintelligent factories into useful and valuable information.”
Factories with fully computerized production processesare better prepared to respond faster to changes in themarket,as they have integrated greater flexibility and individualiza-tion in their manufacturing processes.
However, in order to obtain real improvements in man-ufacturing efficiency and flexibility, manufacturers must beable to manage and analyse large amounts of data, the biggest
challenge of which will be regarding software. Companiesshould implement Big Data systems capable of managinglarge amounts of data from the manufacturing environmentand conducting an intelligent real-time analysis, providingvaluable information for decision-making, thus optimizingthe processes and increasing business intelligence.
Industrial companies have to take the technological leapto Industry 4.0, in the field of additive manufacturing. Theconcepts and experiences being accumulated in companiesand research institutes need to be passed on to companiesby means of guided visits to leading facilities, induction andpractical training, guided training, diagnosis, specific advice,testing, and prototypes.
Why should additive manufacturing be introduced incompanies in a connected industry setting? The answer issimple: because the following can be achieved:
(i) Creative product design(ii) More customised products with high quality and
performance(iii) DDM (demand driven manufacturing) with less
waste generated and efficient use of energy(iv) Internet (EICTs in general) as a tool with a high
potential to support new supply chain models(v) The consumer as designer and “customiser”(vi) Additive manufacturing as enabling technology
4.3. Additive Manufacturing and B2C/B2B. The majority ofthe work on systematizing and disseminating sales expe-rience and on the techniques, methods, texts, and salesand marketing courses focuses on selling to the consumer,what we call B2C (Business-to-Consumer). However, thevolume of business generated by sales to other companies,B2B (Business-to-Business), is much higher, not to mentioncomplex and different.
Additive manufacturing can take the shape of a serviceactivity and, therefore, it needs to adapt to ensure that thecompanies that are willing to provide this service obtainhigher growth and profitability on sales to other companiesand organizations and also on sales to the consumer, takinginto account the final destination of the additive manufactur-ing service.
The current problem is that there is no vertical platformthat organises the advanced manufacturing technologies andcustomised manufacturing based on additive manufacturing(3DP.)
Current service providers partially facilitate the transac-tion for 3DP solution companies. It must be ensured thatadditive manufacturing is on the cloud as a reliable servicebased on the fact that clients manage the details of theirmanufacturing project in real time: material, size, deliverytime, quality, price, location, and catalogue payment (directe-commerce selection), by means of a quotation or offer.
A global platform must be configured as a network of3DP services: marketplace for B2B vertical offering (Figure 1).The service portfolio should be built around the followingactivities:
Complexity 27
Business model: marketplace, all agents, all orders (largeseries focus), matrix selection, web location, and real-timeall-agents capacity management.
(i) Market: B2B focus (could do B2C), KPI-customisedorders.
(ii) Value Chain: global E2E services to B2B verticalclients.
(iii) Technology: E2E open API connecting in real-timeclients and provider’s ERP.
(iv) Product: Manufacturing and high quality / highdefinition.
(v) Expertise: Institute 3DP: industry, research centres,universities ecosystem.
However, the development of additive manufacturing doesnot stop there; the following step was what is now called“bioprinting”, which is the printing of cells and living tissues[38, 50]. The interest in this is mainly due to the shortage oforgans available for transplant and the possibility of avoidingrejection if the organ required can be successfully printedusing the individual’s own cells. Nevertheless, its use is veryimportant in research on new drugs in order to reduce the useof laboratory animals.
3D printing of living cells usually requires the depositionof cells and also the deposit of the support element or matrix.Thismatrix, the place where the cells are going to grow, wherenourishment will be found and onwhich the structure is to beformed, may be liquid, usually called bioink, paste-like, rigidsolid, or elastic solid. Also, solid materials in particular mayor may not be biodegradable [51].
The issue of biodegradation is an added factor in thistechnology, as if this biodegradation occurs too quickly; wewill not obtain the desired results; however, if it occurs tooslowly, there is a possibility that the structure will prevent thedevelopment of the cells and so, in the end, we will not obtainthe desired results this way either. This is why bioprinting iscurrently the focal point of the majority of research projects:it is anticipated that bone regeneration, printing different vitalorgans, printing human skin, etc., will be functionally viablein the near future, as prostheses currently are.
5. Conclusions
(i) Conventional manufacturing is mainly limited byproduction run size and the geometrical complexityof the component, and we are occasionally forcedto use processes and tools that raise the final costof the element. What is more, some manufacturingprocesses do not comply with a commitment to sus-tainable manufacturing (contamination, recycling,etc.).
(ii) Additive manufacturing is one of the key tools fortackling the growth and the creation of added valueand high quality employment.
(iii) Conceptually, the term ‘additive manufacturing’describes the technology in general and it is used
when referring to industrial component manufactur-ing applications and high-performance professionaland industrial equipment. Other terms exist, with thebest known being “rapid prototyping and 3D printing”,in accordance with the scope of the model and thetype of additive machine used.
(iv) Additive manufacturing techniques provide hugecompetitive advantages because they adapt so well tothe geometrical complexity and the customisation of thedesign of the part to be manufactured. The followingcan also be achieved in accordance with the sectorsof application: lighter weight products, multi-materialproducts, ergonomic products, short production runs,fewer assembly errors resulting in lower associatedcosts, lower tooling investment costs, a combinationof different manufacturing processes, optimum use ofmaterial, more sustainable manufacture.
(v) Even though this type of process began as a newindependent technology, nowadays additive manu-facturing is a manufacturing system more, compa-rable to others such as subtractive manufacturing orfoundry.Therefore, the protocols for the classificationof additivemanufacturing processes do not have to bedifferent from those applicable to other manufactur-ing systems.
(vi) The drawbacks are: the finish of complex surfaces canbe extremely rough, long production times, materialswith limited mechanical and thermal properties whichrestrict performance under stress, higher tolerancesthan with other manufacturing methods such as thosebased on material removal.
(vii) The study variables habitually taken into accountwhen choosing the prototyping technology are:resolution-precision, the mechanical and thermal prop-erties of the material, surface finish, production timeand the cost of the prototype.
(viii) Themanufacturing precision is the result of superim-posing different errors in the production of themodelwhich affect the surface quality, the dimensional accu-racy and the final weight of the model.The errors thatoccur in this process are: an error in the conversionof the 3D model into STL format (triangulation ofthe geometry), an error in the decomposition inlayers of the 3D model (exact division of the thick-ness), stepping effect error (orthogonal depositionof the material by layers) and, finally, model infillerror.
(ix) Three-dimensional models with an aesthetic (visual)or assembly objective and functional models capableof withstanding mechanical testing can be achieved.
(x) Additive manufacturing can be applied across manysectors and it can be easily adapted to the demands ofeach of them.
(xi) Design and printing using 3D printers is seen as beingone of the major industrial revolutions of the nestfew years. Proposals exist formaking themanufacture
28 Complexity
of low-cost RepRap distribution units available topeople all over the world via communities of usersand developers who exchange 3D models, know-howand experiences for optimising the manufacturingperformance of a self-replicating 3D printer.
(xii) It still seems puzzling that the first scientific publi-cations relating to the important movement that isadditive manufacturing came to light several yearsafter the development of the first inventions, the firstpatents and even the first commercial communica-tions on the advance.
(xiii) It is also strange that the RepRap movement did notgain ground in academic environments at the begin-ning, and only found its niche when the movementwas justified as “machines that can replicate them-selves” when, as is known in technical environments,there were already milling machines available morethan one hundred years earlier that were able to self-replicate.
(xiv) The choice of technology is directly dependent onthe particular application being planned: first theapplication, then the technology. Laser systems arebeing increasingly used, especially in the field offinished part production. In the future, the use of printtechnology systems is going to increase by the day.
Data Availability
The data used to support the findings of this study areincluded within the article.
Conflicts of Interest
The authors declare that there are no conflicts of interestregarding the publication of this paper.
Acknowledgments
The authors would like to express their gratitude for theirsupport to the Escuela Tecnica Superior de Ingenieros Indus-triales of UNED, in the frame of the proyects ICF06-2018 andICF08-2018, and to the Instituto Universitario de Educaciona Distancia of the UNED, via the Proyecto de InnovacionEducativa GID2016-35. In addition, it is necessary tomentionthe additive manufacturing laboratory of ETSI-ICAI, wheresome of the tests have been carried out.
References
[1] 2017, https://es.3dsystems.com/our-story.[2] 2018, http://www.wipo.int/portal/en/index.html.[3] J. Delgado, J. Ciurana, and C. A. Rodrıguez, “Influence of pro-
cess parameters on part quality and mechanical properties forDMLS and SLM with iron-based materials,” The InternationalJournal of Advanced Manufacturing Technology, vol. 60, no. 5-8,pp. 601–610, 2012.
[4] M. M. Espinosa, Introduccion a Los Procesos de Fabricacion,UNED, Madrid, Spain, 2000.
[5] E. Sells, S. Bailard, Z. Smith, A. Bowyer, andV.Olliver, “RepRap:The replicating rapid prototyper: Maximizing customizabilityby breeding themeans of production,” in Proceedings of the 2007World Conference on Mass Customization & Personalization(MCP).
[6] K. V. Wong and A. Hernandez, “A Review of additive manu-facturing,” ISRN Mechanical Engineering, vol. 2012, Article ID208760, 10 pages, 2012.
[7] J. Nylund, Utskrift av Tredimensionell Arkitekturmodell [Bache-lor’s Thesis], Construction Engineering, Vaasa, 2015.
[8] M. Jimenez, J. Porras, I. A. Domınguez, L. Romero, and M.M. Espinosa, “La fabricacion aditiva. La evidencia de unanecesidad,” Interempresas IndustriaMetalmecanica, vol. 235, no.1047, pp. 74–82, 2013.
[9] 2018, https://www.iso.org/committee/629086.html.[10] P. F. Jacobs, “Rapid Prototyping Manufacturing: Fundamentals
of Stereolithography,” Society of Manufacturing Engineers, 1992.[11] 2018, https://www.materialise.com/es/manufacturing/materiales.[12] U.S. Department of Energy, Materials Development and Eval-
uation of Selective Laser Sintering Manufacturing Applications,1997.
[13] 2018, https://www.aenor.com/.[14] E. L. Canedo-Arguelles and M. Domınguez, “Estado actual del
prototipado rapido y futuro de este,” Actas del XI CongresoInternacional de Ingenierıa Grafica, vol. 3, pp. 1242–1255, 1999.
[15] Y. Yan, S. Li, R. Zhang et al., “Rapid prototyping and manu-facturing technology: principle, representative technics, appli-cations, and development trends,” Tsinghua Science and Tech-nology, vol. 14, no. 1, pp. 1–12, 2009.
[16] J. Russell and R. Cohn, Fused Deposition Modeling, Book onDemand, 2012.
[17] R. Noorani, 3D Printing: Technology, Applications, and Selection,CRC Press, 2017.
[18] 2018, http://www.stratasys.com/mx/impresoras-3d/technologies/polyjet-technology.
[19] J. A. Oriozabala Brit, M. D. Espinosa Escudero, and M.Dominguez Somonte, “Additive manufacturing opportunitiesto optimize product design: oportunidades de la fabricacionaditiva para optimizar el diseno de productos,”Dyna Ingenieriae Industria, vol. 91, no. 3, pp. 263–271, 2016.
[20] N. De la Torre, M. M. Espinosa, and M. Domınguez, “Rapidprototyping in humanitarian aid to manufacture last milevehicles spare parts: an implementation plan,” Human Factorsand Ergonomics in Manufacturing & Service Industries, vol. 26,no. 5, pp. 533–540, 2016.
[21] A. Guerrero de Mier and M. D. Espinosa Escudero, “Progressin RepRap: open source 3D printing-avances en RepRap:impresion 3d de codigo abierto,” Dyna Ingenieria e Industria,vol. 89, no. 1, pp. 34–38, 2014.
[22] W. E. Frazier, “Metal additive manufacturing: a review,” Journalof Materials Engineering and Performance, vol. 23, no. 6, pp.1917–1928, 2014.
[23] I. Domınguez, L. Romero, M. Espinosa, and M. Domınguez,“Impresion 3D de maquetas y prototipos en arquitectura yconstruccion,” Revista de la construccion, vol. 12, no. 2, pp. 39–53, 2013.
[24] G. N. Levy, R. Schindel, and J. P. Kruth, “Rapid manufacturingand rapid tooling with layer manufacturing (LM) technologies,
Complexity 29
state of the art and future perspectives,” CIRP Annals - Manu-facturing Technology, vol. 52, no. 2, pp. 589–609, 2003.
[25] D. T. Pham and R. S. Gault, “A comparison of rapid prototypingtechnologies,” The International Journal of Machine Tools andManufacture, vol. 38, no. 10-11, pp. 1257–1287, 1998.
[26] J. P. Kruth, “Material increase manufacturing by rapid proto-typing techniques,” CIRP Journal of Manufacturing Science andTechnology, vol. 40, no. 2, pp. 577–639, 1991.
[27] M. Greul, F. Petzoldt, M. Greulich, and J. Wunder, “Rapidprototyping moves on metal powders,” Metal Powder Report,vol. 52, no. 10, pp. 24–27, 1997.
[28] B. Derby and N. Reis, “Inkjet printing of highly loaded particu-late suspensions,”MRSBulletin, vol. 28, no. 11, pp. 815–818, 2003.
[29] I. Gibson, D. W. Rosen, and B. Stucker, Additive ManufacturingTechnologies: Rapid Prototyping to Direct DigitalManufacturing,Springer, New York, NY, USA, 2009.
[30] C. B. Williams, F. Mistree, and D. W. Rosen, “A functionalclassification framework for the conceptual design of additivemanufacturing technologies,” Journal of Mechanical Design, vol.133, no. 12, p. 121002, 2011.
[31] 2018, https://www.astm.org/.[32] 2018, https://www.iso.org/home.html.[33] A. S. Wu, D. W. Brown, M. Kumar, G. F. Gallegos, and
W. E. King, “An Experimental Investigation into AdditiveManufacturing-Induced Residual Stresses in 316L StainlessSteel,” Metallurgical and Materials Transactions A: PhysicalMetallurgy andMaterials Science, vol. 45, no. 13, pp. 6260–6270,2014.
[34] M. Xia, D. Gu, G. Yu, D. Dai, H. Chen, and Q. Shi, “Selectivelaser melting 3D printing of Ni-based superalloy: understand-ing thermodynamic mechanisms,” Chinese Science Bulletin, vol.61, no. 13, pp. 1013–1022, 2016.
[35] S. E. Zeltmann, N. Gupta, N. G. Tsoutsos, M. Maniatakos, J.Rajendran, and R. Karri, “Manufacturing and security chal-lenges in 3D printing,” JOM:The Journal ofTheMinerals, Metals& Materials Society (TMS), vol. 68, no. 7, pp. 1872–1881, 2016.
[36] B. C. Gross, J. L. Erkal, S. Y. Lockwood, C. Chen, and D. M.Spence, “Evaluation of 3D printing and its potential impact onbiotechnology and the chemical sciences,”Analytical Chemistry,vol. 86, no. 7, pp. 3240–3253, 2014.
[37] S. H. Huang, P. Liu, A. Mokasdar, and L. Hou, “Additivemanufacturing and its societal impact: a literature review,” TheInternational Journal of Advanced Manufacturing Technology,vol. 67, no. 5-8, pp. 1191–1203, 2013.
[38] W. Zhu, X. Ma, M. Gou, D. Mei, K. Zhang, and S. Chen,“3D printing of functional biomaterials for tissue engineering,”Current Opinion in Biotechnology, vol. 40, pp. 103–112, 2016.
[39] M. Jimenez, L. Romero, M. Domınguez, and M. M. Espinosa,“Rapid prototyping model for the manufacturing by thermo-forming of occlusal splints,” Rapid Prototyping Journal, vol. 21,no. 1, pp. 56–69, 2015.
[40] L. Romero,M. Jimenez,M.D.M. Espinosa, andM.Domınguez,“New design for rapid prototyping of digital master casts formultiple dental implant restorations,” PLoS ONE, vol. 10, no. 12,pp. 145253–145313, 2015.
[41] M. M. Espinosa and M. Domınguez, “La ingenierıa concur-rente, una filosofıa actual con plenas perspectivas de futuro,”MetalUnivers, vol. 16, pp. 16–20, 2003.
[42] L. Rodriguez Parada, M. Dominguez Somonte, and L. RomeroCuadrado, “Analysis and validation model of design proposalsthrough flexible prototypes: Modelo de analisis y validacion
de propuestas de diseno mediante prototipos flexibles,” DynaIngenieria e Industria, vol. 91, no. 5, pp. 502–506, 2016.
[43] I. Farina, F. Fabbrocino, G. Carpentieri et al., “On the reinforce-ment of cement mortars through 3D printed polymeric andmetallic fibers,” Composites Part B: Engineering, vol. 90, pp. 76–85, 2016.
[44] C. Gosselin, R. Duballet, P. Roux, N. Gaudilliere, J. Dirren-berger, and P. Morel, “Large-scale 3D printing of ultra-highperformance concrete - a new processing route for architectsand builders,”Materials & Design, vol. 100, pp. 102–109, 2016.
[45] P. Wu, J. Wang, and X. Wang, “A critical review of the useof 3-D printing in the construction industry,” Automation inConstruction, vol. 68, pp. 21–31, 2016.
[46] S. Fernandez,M. Jimenez, J. Porras, L. Romero,M.M. Espinosa,andM. Domınguez, “Additive manufacturing and performanceof functional hydraulic pump impellers in fused depositionmodeling technology,” Journal of Mechanical Design, vol. 138,no. 2, pp. 24501–24504, 2016.
[47] J. Sun, W. Zhou, D. Huang, J. Y. H. Fuh, and G. S. Hong, “Anoverview of 3Dprinting technologies for food fabrication,” Foodand Bioprocess Technology, vol. 8, no. 8, pp. 1605–1615, 2015.
[48] A. Guerrero-De-Mier, M. M. Espinosa, and M. Domınguez,“Bricking: A new slicing method to reduce warping,” ProcediaEngineering, vol. 132, pp. 126–131, 2015.
[49] J. Zhang and Y. G. Jung, Additive Manufacturing: Materi-als, Processes, Quantifications and Applications, Butterworth-Heinemann, 2018.
[50] S. V. Murphy and A. Atala, “ 3D bioprinting of tissues andorgans,” Nature Biotechnology, vol. 32, no. 8, pp. 773–785, 2014.
[51] R.Domınguez,M.M. Espinosa, L. Romero, andM.Domınguez,Impresion 3D en Ingenierıa Medica, VI Encuentro de Investi-gacion - IMIENS, Madrid, Spain, 2016.
[52] E. Sells, S. Bailard, Z. Smith, A. Bowyer, andV.Olliver, “RepRap:The replicating rapid prototyper: maximizing customizabilityby breeding the means of production,” SSRN eLibrary, 2010.
[53] M. Paulic, T. Irgolic, J. Balic et al., “Reverse engineering of partswith optical scanning and additive manufacturing,” ProcediaEngineering, vol. 69, pp. 795–803, 2014.
[54] 2018, https://www.sculpteo.com/es/servicios/fabricacion-aditiva/.[55] FundacionCOTECpara la InnovacionTecnologica, “Fabricacion
aditiva,” Documentos COTEC sobre OportunidadesTecnologicas, 2011, http://informecotec.es/media/N30 FabricAditiva.pdf.
[56] M. Fernandez-Vicente, W. Calle, S. Ferrandiz, and A. Conejero,“Effect of infill parameters on tensile mechanical behavior indesktop 3D printing,” 3D Printing and Additive Manufacturing,vol. 3, no. 3, pp. 183–192, 2016.
[57] B. P. Conner, G. P. Manogharan, A. N. Martof et al., “Makingsense of 3-Dprinting: Creating amap of additivemanufacturingproducts and services,”AdditiveManufacturing, vol. 1-4, pp. 64–76, 2014.
[58] R. V. Rao, Decision Making in the Manufacturing Environment:Using Graph Theory and Fuzzy Multiple Attribute DecisionMaking Methods, Springer Science & Business Media, 2007.
[59] S. P. Sethi and Q. Zhang, Hierarchical Decision Making inStochastic Manufacturing Systems, Springer Science & BusinessMedia, 2012.
[60] S. H. Khajavi, J. Partanen, and J. Holmstrom, “Additive man-ufacturing in the spare parts supply chain,” Computers inIndustry, vol. 65, no. 1, pp. 50–63, 2014.
30 Complexity
[61] S. Meyers, L. De Leersnijder, J. Vleugels, and J.-P. Kruth,“Direct laser sintering of reaction bonded silicon carbide withlow residual silicon content,” Journal of the European CeramicSociety, vol. 38, no. 11, pp. 3709–3717, 2018.
[62] X. Wang, M. Speirs, S. Kustov et al., “Selective laser meltingproduced layer-structured NiTi shape memory alloys with highdamping properties and Elinvar effect,” Scripta Materialia, vol.146, pp. 246–250, 2018.
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