Additive Manufacturing Technologies
Read this article. It covers additive and subtractive manufacturing methods and how technology is changing the future of supply chains. Its presence replacing some conventional manufacturing methods and has increased speed and quality without having to wait for a partner or service provider. Can you describe the limitations of additive manufacturing technologies?
Historical and Current Framework
Many different additive manufacturing (AM) technologies enable the production of prototypes and fully functional artefacts. Although very different in solution, principle, and embodiment, significant functional commonality exists among the technologies.
In order to enter the subject from its origins, before proposing a classification or analyzing the different technologies and their advantages and disadvantages, a chronological analysis of facts will be carried out that will allow us to later base the conclusions. This chronological analysis will be based on dates of publication of works, dates of application for patents, and dates of acceptance of these patents, being aware that in any case the dates in which the developments were reached are always prior to those dates of a public nature.
Without a doubt, the milestone that marked the beginning of additive manufacturing took place on 9th March 1983, when Charles W. Hull successfully printed a teacup on the first additive manufacturing system: the stereolithography apparatus SLA-1, which he himself built.
From then on, there were several advances that paved the way for what is today known as additive manufacturing (Table 1). From a chronological point of view, the most relevant are as follows:
1986. Carl R. Deckard, at the University of Texas, develops a "method and apparatus for producing parts by selective sintering", a first step in the development of additive manufacturing by means of selective sintering (SS).
1988. Michael Feygin and his team at Helisys, Inc. develop a method for "forming integral objects from laminations", an automatic lamination cutting system (laminated manufacturing - LM) that produces layers with the dimensions marked out by the electronic file, layers which will then be bonded to form the final prototype.
1989. Scott S. Crump, at the company Stratasys, Inc., develops an "apparatus and method for creating three-dimensional objects", a first step in the development of additive manufacturing by means of fused deposition modelling (FDM).
1989. Emanuel M. Sachs and his team, at Massachusetts Inst. Technology, develop "three-dimensional printing techniques", a process of injecting binding agent and coloured ink on a bed of powdered material, using the injectors of a conventional ink-jet printer to do so.
Table 1: Key inventions in additive manufacturing (ordered by publication of patent).
Technology | Inventors | Patent | Development centre | Request for patent | Publication of patent | Principle of operation |
Stereolithography SL |
Charles W. Hull | Method and apparatus for production of three-dimensional objects by stereolithography | 3D Systems | 08.08.1984 | 12.02.1986 | Photopolymerization of a photosensitive resin using UV light |
Selective Sintering SS |
Carl R. Deckard | Method and apparatus for producing parts by selective sintering | University of Texas | 17.10.1986 | 21.04.1988 | Selective sintering of powder (fusion – solidification using laser) |
Material Deposition MD |
Scott S. Crump | Apparatus and method for creating three-dimensional objects | Stratasys, Inc. | 30.10.1989 | 01.05.1991 | Deposition of material, using a nozzle, in plastic state (heated by electrical resistance) |
Jet Prototyping (injection) JP |
Emanuel M. Sachs; John S. Haggerty; Michael J. Cima; Paul A. Williams |
Three-dimensional printing techniques | Massachusetts Inst. Technology | 08.12.1989 | 09.06.1991 | Injection of binding agent and coloured ink on a bed of powdered material |
Laminated Manufacturing (cutting) LM |
Feygin, Michael; Pak, Sung Sik |
Forming integral objects from laminations - Apparatus for forming an integral object from laminations | Helisys, Inc. | 05.10.1988 | 18.04.1996 | Cutting and gluing of laminations with the geometry determined for each layer |
As an evolution of Hull's work based on photopolymerization, other processes have been developed:
- Solid Creation System (SCS). Developed by Sony Corporation, JSR Corporation and D-MEC Corporation in 1990.
- Solid Object Ultraviolet Laser Printer (SOUP) Developed by CMET Inc. in 1990.
- Solid Ground Curing (SGC) developed by Cubital Ltd. in 1991
- Inkjet Rapid Prototyping (IRP), the parts are formed by injecting a photopolymer drop by drop which is then cured using ultraviolet light. Developed by Object Geometries Ltd. in 2000, under the name Polyjet.
As an evolution of Deckard's work based on sintering, other processes have been developed:
- Direct
metal laser sintering (DMLS), where the base material is metal powder
and the grains are bonded by sintering, without the grains being fully
fused together.
- Selective
laser melting (SLM), where metal powder is fully fused together and so
the process is not sintering but rather melting.
As an evolution of Crump's work on fused deposition modeling, other processes have been developed:
- Metal
deposition (MD), where a metal filler material (powder jet or wire) is
deposited by a nozzle following the path marked out by the G-code in
the .stl or .amf file.
- Fused
Filament Fabrication (FFF), name from the RepRap community, an open
community at RepRap.org, founded by Adrian Bowyer at the University of
Bath in 2004.
At this point, hardfacing processes using numerical control (NC) should
be mentioned, which are predecessors of fused deposition modeling and
prior to the work of Crump, with the difference being that they were not
based on electronic files generated by means of solid modeling systems.
Although additive manufacturing could date back to automated welding
systems, where a robotic arm controlled by numerical control
(G-code) deposited material in welding or hardfacing operations (which
may be a similar case), it was not until 1983 that this G-code was used
to control a laser that "solidifies" a resin and builds a part using a
virtual model (solid model and .stl file).
As an evolution of the work of Sachs and his team on the injection of
binding agent or base material, other processes have been developed:
- MultiJet Modeling System (MJM) developed by 3D Systems Inc. in 1999, with multiple heads in parallel that move along one axis.
- ModelMaker and Pattern Master, by Solidscape, with one single print head that moves along two axes.
- ProMetal,
division of Extrude Hone Corporation, process that binds together steel
powder and then infiltrates molten bronze to produce a part that is 40%
steel and 60% bronze.
Finally, as an evolution of the work of Feygin and his team based on cutting laminations, other processes have been developed:
- Selective
Deposition Lamination (SDL) Invented in 2003 by MacCormack. The SDL
technique works by depositing an adhesive in the area required, both the
model and the support, and a blade that cuts the outline of the layer.
It is interesting to point out that there are current processes based on
more than one of the contributions stated or on integrated processes.
This is the case of polyjet modeling (PJM), which is said to be a
combination of stereolithography and injection.
Nowadays, the volume of processes, technologies and initialisms is so
high that there is no extensive classification system in operation. In
Table 2
we can see a list of initialisms used in this field, which is by no
means exhaustive, which gives us an idea of how technology is evolving.
Table 2: A sea of initialisms
3DB | three-dimensional bioplotter | LPD | laser powder deposition |
3DP | three-dimensional printing | LPF | laser powder fusion |
AF | additive fabrication | LPS | liquid-phase sintering |
ALPD | automated laser powder deposition | LRF | laser rapid forming |
AM | additive manufacturing | LS | laser sintering |
BM | biomanufacturing | M3D | maskless mesoscale material deposition |
CAM-LEM | computer-aided manufacturing of laminated engineering materials | MD | metal deposition |
DCM | direct composite manufacturing | MD | material deposition |
DIPC | direct inkjet printing of ceramics | MEM | melted extrusion manufacturing |
DLC | direct laser casting | MIM | material increase manufacturing |
DLF | directed light fabrication | MJM | multijet modeling system |
DLP | digital light processing | MJS | multiphase jet solidification |
DMD | direct metal deposition | MS | mask sintering |
DMLS | direct metal laser sintering | M-SL | microstereolithography |
EBM | electron beam melting | PBF | powder bed fusion |
EBW | electron beam welding | PJM | poly jet modeling |
EP | electrophotographic printing | RFP | rapid freeze prototyping |
ERP | electrophotographic rapid printing | RM | rapid manufacturing |
FDC | fused deposition of ceramics | RP | rapid prototyping |
FDM | fused deposition modeling | RPM | rapid prototyping and manufacturing |
FFEF | freeze-form extrusion fabrication | RT | rapid tooling |
FFF | fused filament fabrication | RTM | rapid tool maker |
FLM | fused layer modeling | SALDVI | selective area laser deposition and vapor infiltration |
FLM | fused layer manufacturing | SCS | solid creation system |
HSS | high speed sintering | SDL | selective deposition lamination |
IJP-A | aqueous direct inkjet printing | SDM | shape deposition manufacturing |
IJP-UV | UV direct inkjet printing | SFC | solid film curing |
IJP-W | hot-melt direct inkjet printing | SFF | solid free-form fabrication |
IRP | inkjet rapid prototyping | SGC | solid ground curing |
JP | jet prototyping | SHS | selective heat sintering |
LAM | laser additive manufacturing | SL | stereolithography |
LC | laser cladding | SLA | stereolithography apparatus |
LCVD | laser chemical vapor deposition | SL-C | stereolithography of ceramics |
LDC | laser direct casting | SLM | selective laser melting |
LDM | low-temperature deposition manufacturing | SLP | solid laser diode plotter |
LENS | laser engineered net shaping | SLS | selective laser sintering |
LFFF | laser free form fabrication | SLSM | selective laser sintering of metals |
LLM | layer laminated manufacturing | SOUP | solid object ultra-violet laser printer |
LM | laminated manufacturing | SS | selective sintering |
LMD | laser material deposition | SSM-SFF | semisolid metal solid freeform fabrication |
LMF | laser metal forming | SSS | solid-state sintering |
LOM | layered object manufacturing | UC | ultrasonic consolidation |
LOM | laminated object manufacturing | UOC | ultrasonic object consolidation |
In order to highlight the basic pillars of additive manufacturing in Table 2,
the abbreviations referring to the technologies discussed at the
beginning of this introduction have been highlighted in italic.
Given the large number of initiatives and processes that are developed
and patented every day, there is no doubt that additive manufacturing is
a technology that will set the standards for many productive processes
in the short and medium term. One more proof of this is that the
European Union has decided that manufacturing in general and additive
manufacturing in particular shall be one of the key tools to tackle some
of the European challenges and their subsequent objectives, above all
economic growth and the creation of added value and high-quality jobs.
This decision is generating the setting up of research and innovation
support and promotion programmes aimed at achieving a situation in which
additive manufacturing enables the provision of both high-value
products and competitive services.
All over the world the additive manufacturing industry is beginning to
respond to global, national, and regional standardisation needs via a
series of working groups in which the European Union is a key
participant: the ISO/TC 261, Additive manufacturing; the ASTM Committee
F42 on Additive Manufacturing Technologies; the CEN/TC 438, additive
manufacturing; or the AEN/CTN 116, Sistemas industriales automatizados.
The ISO standard (ISO 52900) defines additive fabrication as follows:
"Manufacturing processes which employ an additive technique whereby successive layers or units are built up to form a model".
The terms habitually used in conjunction with additive manufacturing
have been evolving at the same pace as the technological developments,
and it is convenient to establish a framework of reference that enables
an analysis to be carried out of the developments made and of the
standardisation required for the future:
- "Desktop manufacturing", perhaps the first name, in line with the names at the time (1980s) such as desktop computer, desktop design.
- "Rapid Prototyping". This
was the first term used to describe the creation of 3D objects by way
of the layer-upon-layer method. The technologies that currently exist
enable the manufacture of objects that can be considered as being
somewhat more than "prototypes".
- "Rapid
tooling". When it became clear that the additive manufacturing system
not only enabled us to build prototypes, but also moulds, matrices and
tools, this name began to be used to differentiate it from rapid
prototyping.
- "3D Printing".
This is the most commonly used term. The term "low-cost 3D printing" is
frequently coined when we use printers that domestic or
semi-professional users can afford.
- "Freeform Fabrication".
Is a collection of manufacturing technologies with which parts can be
created without the need for part-specific tooling. A computerized model
of the part is designed. It is sliced computationally, and layer
information is sent to a fabricator that reproduces the layer in a real
material.
- "Additive Manufacturing".
This is the most recent term applied and it is used to describe the
technology in general. It is commonly used when referring to industrial
component manufacturing applications and high-performance professional
and industrial equipment.
An evolution can be seen in this sequence from obtaining prototypes
(with purely aesthetic and geometric goals at the beginning) to simple
functional parts, tools, and moulds, to obtain complex functional parts
such as those currently obtained via additive manufacturing in the metal
industry.
The difference between these techniques is reduced to the application
for which the additive manufacturing technology is used. This means that
a rapid prototyping technique can be used as a possible technology for
the rapid manufacturing of elements, tools, or moulds. It answers the
following questions: how would it be possible to manufacture a ball
joint fully mounted in its housing without having to manufacture the
elements separately prior to their assembly? And is the mass or
individual production of this unit possible at an affordable price
(Figure 1)?
Figure 1 Ball joint mounted in its housing [8].
A characteristic common to the different additive manufacturing techniques is that of the need for a minimum number of phases in the manufacturing process starting with the development of the "idea" by the designer through to obtaining the finished product (Figure 2).
Figure 2 Phases of the additive manufacturing process.
Obviously, the scheme proposed by Yan and his team is a generalization since not in all AM processes G-Codes are created, and preprocessing is not contemplated (necessary in some processes).In the process described above the designer can perform the entire
product manufacturing operation from start to finish. The involvement of
another technician is not necessary for carrying out any complementary
operations. However, it must be taken into account that, during the
process and prior to manufacture, the designer must know the determining
factors of the end product in order to be able to select the most
suitable manufacturing technique, make the necessary modifications to
the geometrical data file (stl or amf file), and review the NC code. The
designer must, therefore, have a full overview of and the necessary
training in all of the phases of the process.
This article contains a full and up-to-date description of the benefits
and drawbacks of the most important manufacturing methodologies and
processes that exist within the scope of the additive manufacturing
concept, of the characteristics of the models manufactured and their
associated costs, of the functional models, the applications, and the
sectors of influence. At the end, there is a reference to the RepRap
community and free software due the importance they acquired last years.
It is important to establish the variables that currently support the
implementation of additive manufacturing and its relation to the basic
principles of each technology, which allow detecting the advantages and
limitations of each of them. In Figure 3,
the relationship between the main variables that intervene in the
development of additive manufacturing is shown: technologies, materials,
type of models, associated costs, and visual appearance. The current
scope of these variables and their evolution can be seen in the
subdivision that is presented in a circular diagram.
Figure 3 Table of contents.