ppt

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ADVANCED AGILE MANUFACTURING
POWDER BED FUSION TECHNOLOGY OF
METAL ADDITIVE
PRESENTED BY:
J.THANGA THIRUPATHI
M.SIVA SUBRAMANIAN
THIRD YEAR.,
DEPARTMENT OF MECHANICAL ENGINEERING,
GOVERNMENT POLYTECHNIC COLLEGE,
TUTICORIN,
Mail Id: gpcplacements@yahoo.com Ph.: 0461-2311647

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ABSTRACT:
Additive manufacturing is a novel method of manufacturing parts
directly from digital model by using layer by layer material build-up approach.
This tool-less manufacturing method can produce fully dense metallic parts in
short time, with high precision. Features of additive manufacturing like freedom
of part design, part complexity, light weighting, part consolidation and design for
function are garnering particular interests in metal additive manufacturing for
aerospace, oil & gas, marine and automobile applications. Powder bed fusion, in
which each powder bed layer is selectively fused by using energy source like laser
or electron beam, is the most promising additive manufacturing technology that
can be used for manufacturing small, low volume, complex metallic parts. This
review presents evolution, current status and challenges of powder bed fusion
technology. It also compares laser and electron beam based technologies in terms
of performance characteristics of each process, advantages/disadvantages,
materials and applications.

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INTRODUCTION
Additive manufacturing (AM), also known as 3D printing, is a
process of joining materials to make objects from 3D model data, usually layer
upon layer, as opposed to subtractive manufacturing methodologies. This tool less
manufacturing approach can give industry new design flexibility, reduce energy
use and shorten time to market .Main applications of additive manufacturing
include rapid prototyping, rapid tooling, direct part production and part repairing
of plastic, metal, ceramic and composite materials. Recent advancements in
computation power of electronics, material& modelling science and advantages
offered by AM technology have shifted focus of AM from rapid prototyping to
direct part production of metallic parts. The two main parameters of any metal
AM process are type of input raw material and energy source used to form the part
. Input raw material can be used in the form of metal powder or wire whereas
laser/electron beam or arc can be used as energy source as shown in Fig.1. AM
machine requires CAD model of the part in the .stl (stereo lithography) file format.
Specialized slicing software then slices this model into number of cross sectional
layers. AM machine builds these layers one by one to manufacture complete part
. Thickness of these layers depends on the type of raw material and the AM
process used to manufacture the given part. Every AM manufactured part has
inherent stair case like surface finish due to layer by layer build up approach.
Metal AM processes can be broadly classified into two major groups, - Powder
Bed Fusion based technologies (PBF) and Directed Energy Deposition (DED)
based technologies. Both of these technologies can be further classified based on
the type of energy source used. In PBF based technologies, thermal energy
selectively fuses regions of powder bed . Selective laser sintering/melting
(SLS/SLM), laser cusing and electron beam melting (EBM) are main
representative processes of PBF based technologies. In DED based technologies
focused thermal energy is used to fuse materials (powder or wire form) by melting
as they are being deposited. Laser Engineered Net Shaping (LENS), Direct Metal

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Deposition (DMD), Electron Beam Free Form Fabrication
(EBFFF) and arc based AM are some of the popular DED based technologies.
This paper describes laser and electron beam based powder bed fusion
technologies of metal additive manufacturing and their applications.
POWDER BED FUSION (PBF) ADDITIVE MANUFACTURING
The powder bed is in inert atmosphere or partial vacuum to provide shielding of
the molten metal. An energy source (Laser or electron beam) is used to scan each
layer of the already spread powder to selectively melt the material according to
the part cross section obtained from the digital part model. When one layer has
been scanned, the piston of building chamber goes downward and the piston of
the powder chamber goes upward by defined layer thickness.Coating mechanism
or roller deposits powder across build chamber which is again scanned by the
energy source. This cycle is repeated layer by layer, until the complete part is
formed. The end result of this process is powder cake and the part is not visible
until excess powder is removed. Build time required to complete a part in PBF
based processes is more as compared to DED technologies but, higher complexity
and better surface finish can be achieved which requires minimum postprocessing.
Several parts can be built together so that build chamber can be fully utilized .
Schematic of the PBF technology is shown in Fig.2. These processes inherently
require support (of same material as part) to avoid collapse of molten materials in
case of overhanging surfaces, dissipate heat and prevent distortions. Supports can
be generated and modified as per part requirement during preprocessing phase and
the same has to be removed by mechanical treatment during post-processing phase
. After support removal, part may undergo post processing treatments like shot
peening, polishing, machining and heat treatment depending on the requirement.
Some critical components may even require hot isostatic pressing (HIP) to ensure
part density. Selective Laser Sintering (SLS) or Direct metal laser sintering

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(DMLS) from EOS, Selective Laser Melting (SLM) from Renishaw and SLM
solution and laser cusing from Concept Laser are some of the popular PBF based
technologies which use laser as energy source whereas electron beam melting
(EBM) from ARCAM is PBF based technology which uses electron beam as
energy source.

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A.Laser based systems (DMLS/SLM/Laser cusing)
Selective laser sintering (SLS) is the first among many
similar processes like Direct Metal Laser Sintering (DMLS), Selective Laser
Melting (SLM) and laser cusing. SLS can be defined as powder bed fusion process
used to produce objects from powdered materials using one or more lasers to
selectively fuse or melt the particles at the surface, layer by layer, in an enclosed
chamber . It was developed by Carl Deckard in 1986 and commercialized by DTM
Corporation in 1992 . The first commercial metal sintering machine EOSINT
M250, was introduced in 1995 by the EOS from Germany . SLM is an advanced
form of the SLS process where, full melting of the powder bed particles takes
place by using one or more lasers. It was developed by Fockele and Schwarze
(F&S) in cooperation with the Fraunhofer institute of laser technology in 1999 and
then commercialized with MCP Realizer250 machine by MCP HEK Gmbh (now
SLM Laser cusing is similar to SLM process where laser is used to fuse each
powder bed layer as per required cross section to build the complete part in the
enclosed chamber. It was commercialized by Concept laser Gmbh (Germany) in
2004. The term laser cusing comes from letter ‘C’ (concept) and theword fusing.
The special feature of laser cusing machine is the stochastic exposure strategy
based on the island principle. Each layer of the required cross section is divided
into number of segments called “islands”, which are selected stochastically during
scanning. This strategy ensures thermal equilibrium on the surface and reduces
the component stresses . Most of these systems use one fiber laser of 200W to 1
KW capacity to selectively fuse the powder bed layer. The build chamber is
provided with inert atmosphere of argon gas forreactive materials and nitrogen
gas for non-reactive materials. Power of laser source, scan speed, hatch distance
between laser tracks and the thickness of powdered layer are the main processing
parameters of these processes . Layer thickness of 20-100 μm can be used

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depending on the material. All of these processes can manufacture fully dense
metallic parts from wide range of metal alloys like titanium alloys, inconel alloys,
cobalt chrome, aluminium alloys, stainless steels and tool steels.
Most of the laser based PBF systems have low build rates of 5-20 cm3/hr and
maximum part size that can be produced (build volume) is limited to 250 x 250 x
325 mm3 which increases part cost and limits its use only for the small sized
parts. So in recent years, the machine manufactures and the research institutes are
focusing on expanding the capabilities of their machines by increasing the build
rates and the build volumes. SLM solution from Germany has launched SLM500
HL machine in 2012 which uses double beam technology to increase the build rate
up to 35 cm3/hr and has a build volume of 500 x 350 x 300 mm3.Two sets of
lasers are used in this machine, each set having two lasers (400W and 1000W).
This means four lasers scan the powder layer simultaneously. EOS from Germany
has just launched (2013) EOSINT M400 machine which is having a build volume
of 400 x 400 x 400 mm3 and uses one 1KW fiber laser to increase build rate
.Concept laser and Fraunhofer institute for laser technology (ILT) have developed
largest AM machine for metals (Xline1000R) with build volume of 630 x 400 x
500 mm3 and build rate upto 100 cm3/hr . Details of the process capabilities in
terms of build volumes build rates and scan speeds of some PBF machine models
are given in the Table2.

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Electron beam melting (EBM)
EBM is another PBF based AM process in which electron beam is used to
selectively fuse powder bed layer in vacuum chamber. It was commercialized by
ARCAM from Sweden in 1997. Electron beam melting (EBM) process is similar
to the SLM with the only difference being its energy source used to fuse powder

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bed layers: here an electron beam is used instead of the laser . In EBM, a heated
tungsten filament emits electrons at high speed which are then controlled by two
magnetic fields, focus coil and deflection coil as shown in Fig.4a. Focus coil acts
as a magnetic lens and focuses the beam into desired diameter up to 0.1 mm
whereas deflection coil deflects the focused beam at required point to scan the
layer of powder bed . When high speed electrons hit the powder bed, their kinetic
energy gets converted into thermal energy which melts the powder . Each powder
bed layer is scanned in two stages, the preheating stage and the melting stage. In
preheating stage, a high current beam with a high scanning speed is used to preheat
the powder layer (up to 0.4 - 0.6 Tm) in multiple passes. In melting stage, a low
current beam with a low scanning speed is used to melt the powder . When
scanning of one layer is completed, table is lowered, another powder layer is
spread and the process repeats till required component is formed. The entire EBM
process takes place under high vacuum of 10-4 to 10-5 mbar. The helium gas
supply during the melting further reduces the vacuum pressure which allows part
cooling and provides beam stability . It also has multi-beam feature which
converts electron beam into several individual beams which can heat, sinter or
melt powder bed layer ARCAM EBM system uses high power electron beam of
3000W capacity to melt powder bed layers. Electron beam power, current,
diameter of focus, powder pre-heat temperature and layer thickness are main
processing parameters of the EBM. Layer thickness of 50-200 μm is typically used
in this process. EBM systems can work with wide range of materials like titanium
alloys (Ti6Al4V, Ti6Al4V EI), cobalt chrome,Titanium aluminide, inconel (625
and 718), stainless steels, tool steels, copper, aluminium alloys, beryllium etc

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COMPARISON BETWEEN SLM AND EBM
As compared to the SLM system, the EBM has higher build
rates (upto 80cm3/hr because of the high energy density and high scanning speeds)
but inferior dimensional and surface finish qualities . In both the SLM/EBM
process, because of rapid heating and cooling of the powder layer, residual stresses
are developed. In EBM, high build chamber temperature (typically 700- 9000C)
is maintained by preheating the powder bed layer. This preheating reduces the
thermal gradient in the powder bed and the scanned layer which reduces residual
stresses in the part and eliminates post heat treatment required. Preheating also

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holds powder particles together which can acts as supports for overhanging
structural members. So, supports required in the EBM are only for heat conduction
and not for structural support. This reduces the number of supports required and
allows manufacturing of more complex geometries. Powder preheating feature is
available in very few laser based systems where it is achieved by platform heating.
In addition, entire EBM process takes place under vacuum since, it is necessary
for the quality of the electron beam .Vacuum environment reduces thermal
convection, thermal gradients and contamination and oxidation of parts like
titanium alloys . In SLM, part manufacturing takes place under argon gas
environment for reactive materials to avoid contamination and oxidation whereas
non-reactive materials can be processed under nitrogen environment. So it can be
expected that EBM manufactured parts have lower oxygen content than SLM
manufactured parts .
In spite of having these advantages, EBM is not as popular as SLM because of its
higher machine cost, low accuracy and non-availability of large build up volumes.
Characteristic features of SLM and EBM are summarized
APPLICATIONS OF METAL ADDITIVE MANUFACTURING
Metal AM started to gain attention in aerospace, oil and gas,marine,
automobile, manufacturing tools and medical applications because of the
advantages offered by this process. First, it can reduce buy to fly ratio considerably
which is the ratio of input material weight to final part weight. Forconventional
manufacturing processes, buy to fly ratio for aerospace engine and structural
components can be as high as 10 : 1 and 20 : 1 respectively. AM can produce near
net shape using layer by layer addition of materials as per requirement which can
reduce buy to fly ratio up to 1 : 1 . AM can produce highly complex parts and
provide freedom in part design. It can be used for structural optimization by using
finite element analysis (FEA) to get benefit in terms of light weighting. It can also

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produce lattice structures with low density, high strength, good energy absorption
and good thermal properties which can be used for light weighting and better heat
dissipation in applications like heat exchangers in aerospace, automobile and
computer industries . Fig. 5 shows conventional and optimized door bracket
manufactured by AM where internal ‘bamboo’ structure is used for lightweighting
Conventionally manufactured part may require a number of different
manufacturing processes like casting, rolling, forging, machining, drilling, and
welding etc. whereas, same part can be produced by using AM which eliminates
required tooling and produces part in single processing step. Every part
manufactured by AM can be unique and produced in very short time which
enables mass customization AM also reduces assembly requirements by
integrating number of parts required in assembly into a single part. It reduces
overall weight, decreases manufacturing time, reduces
number of manufacturing processes required, reduces cost and material
requirements and optimizes required mechanical properties . GE has integrated
fuel nozzle assembly of 20 small parts into single fuel nozzle part of cobalt chrome
material which is under testing phase. It is 25 % lighter and five times more
durable than conventional assembly. Oak Ridge National Laboratories has
manufactured lightweight, compact underwater robotic system (Hydraulic
manifold) in which the robot base, hydraulic reservoir, and accumulator are
integrated into a single lightweight structure AM can enhance part performance
and add value to the product as parts can be designed for function. Injection
moulding tools can be provided with conformal cooling channels (Fig. 7) which
increases cooling efficiency and reduces the cycle time. Different types of lattice
structures can be used to achieve unique properties like improved heat dissipation,
structures with negative poisons ratio and improved energy absorption
characteristics. A negative poisons ratio increases impact resistance, fracture
toughness and shear resistance

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SUMMARY AND CHALLENGES OF PBF TECHNOLOGIES
Though significant progress and technological advancement have
been made by the PBF AM technology, performances in terms of speed, accuracy,
process control and cost effectiveness still needs to improve. Knowledge of
processing-structure-property relationship for existing materials is required to
predict part performance. In-process quality monitoring and closed loop control
systems are required to improve the consistency, repeatability and uniformity
across machines. Closed loop melt pool temperature control system has proven its
significance in deposition based LENS (Laser engineered net shaping) process by
maintaining desired quality of part. Such close loop melt pool temperature control
system has still remained as a challenge for SLM systems. Early stage defect
detection through in-process quality monitoring could save required raw material
and manufacturing time. Better understandings of physical and metallurgical

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mechanisms responsible for variation in properties are required for predictive
process modelling. AM part cost is still on the higher side for some applications.
Increasing build speeds of AM machines, designing more complex geometries and
reducing assembly requirements could reduce required part cost and widen
application areas of AM in future.
REFERENCES
1. Metal Additive manufacture engineering by J.Wooten
2. Metal Additive manufacture engineering by J.Verliden
3. www.wikipedia.com
4. www.google.com