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Module 1: Extrusion Based AM and Metal Powder Manufacturing

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Extrusion Additive Manufacturing for Industrial Application

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Extrusion of AM for Industrial Application

Welcome again to the NPTEL course on the future of manufacturing business and the role of
additive manufacturing. I am Chandrashekhar from Wipro 3D Bangalore and along with my
collaborator from IIT Madras professor R K Amit. We are presenting this program with
primary focus on the future of manufacturing business and also the role of additive
manufacturing in this metamorphosis.
(Refer Slide Time: 00:38)

Fundamentally in the initial classes, we understood the categorization additive manufacturing
technologies and we got to describe the characteristics of these 7 verticals encompassing
extrusion, lamination, binder jetting, material jetting, vat polymerization and power bed
fusion and the special technique called directed energy deposition which is connected with
the repair and refurbishment scenario.

Most of our conversations were connected with the metal additive manufacturing technology
of powder bed fusion with a primary focus on laser power bed fusion and we also got to
briefly discuss the technique of stereolithography which works on the principle of
instantaneous curing of photosensitive polymers using lasers.
(Refer Slide Time: 01:48)

In today's discussion, we will focus on two techniques or two processes which have found
favor with numerous industrial contexts as well as individual uses. One is connected with
extrusion technology; other one is connected with vat polymerization.
(Refer Slide Time: 02:11)

It is very important to note that these technologies though they are primarily connected with
non-metallic materials that is that their primary application is connected with thermoplastics,
they have formed an array of applications in sectors connected with aerospace, defense,
transportation and healthcare specifically. These applications range from prototyping, part
substitution, indirect use like a rapid tool and also low-volume production .
(Refer Slide Time: 02:50)

The technology which has gained widespread acceptance among the user groups from
academy, research labs, design groups, small scale units and also large industrial enterprises
is the one which is based on the principle of extrusion. What is shown in this particular
picture is the operational principle of this technology which is widely known in the
commercial context as the fused deposition modeling or FDM in short.

The original patent is credited to Scott Crump who started the premier AM company called
Stratasys. If you look at the operational principle of this extrusion-based AM process, the
feed stock typically is in the form of a filament, a thermoplastic filament and it is drawn into
an extrusion by an extrusion head. The extrusion head consists of a driver gear, an idler, and a
stepper motor. Fundamentally, the movement of the stepper motor influences the feed rate.

The thermoplastic filament which is being drawn by the extrusion head enters the hot end and
it is drawn out in a liquefied state through a nozzle. The deposition of the material which is
being delivered through the nozzle happens on a platform which is also known as print bed
and the print bed has got provision for movement in the z direction and the cartridge
consisting of the extrusion unit and the nozzle has got the provision to move in the x-y
direction.

I am talking about typical configuration which is illustrated here. Indeed, there is going to be
a pressure drop. There is a pressure drop across the extruder and the pressure drop depends
on the viscous properties of the fluid, geometry of the nozzle and the geometry or the
configuration of the liquid liquefied.

(Refer Slide Time: 05:39)

There are two popular methods of extrusion. One is the direct extrusion wherein the extrusion
element is directly connected to the nozzle or hot end. The other one which is known by the
name Bowden extrusion and this extrusion head is mounted on the machine frame. There are
certain pros and cons of each of this configuration. In case of direct extrusion, the retraction
response of the extruding unit is much better, but it has got one inherent disadvantage. The
mass of this entire unit consisting of extruder as well as the hot end is much higher compared
to the Bowden unit.

Because of this higher mass or higher inertia, they got problems connected with vibration and
this may in turn adversely impact the accuracy, especially if you are talking about high speed

printing. The Bowden extrusion has got inherent advantage of lower mass and hence high-
speed printing is facilitated, but there is a problem since the filament has to move through this

cable many materials including the abrasive materials cannot be handled in the Bowden
extrusion.
(Refer Slide Time: 07:22)

The primary application connected with FDM process in the initial stages was largely
confined to design communication. The example what I have shown in this specific slide is
relevant to an aeroengine accessory drive gearbox housing. As you can see the shape is
extremely complex, the realization of the actual part which is made out of aluminium alloys
or magnesium alloys takes extraordinarily long time in the conventional context. In this
specific case after the concept was made ready, immediately the concept was converted into
full scale FDM replica to facilitate design communication among the groups. It was also
translated into a stereolithography model for enabling experimental tests.
(Refer Slide Time: 08:29)

There are any number of applications of this particular technology connected with assembly
integration studies and the original material which was synonymous with the extrusion
technology was and is ABS material, a thermoplastic material, ABS stand for acrylonitrile

butadiene styrene. It is an engineering plastic which has got adequate yield strength, good
elongation at break, adequate modulus.
(Refer Slide Time: 09:16)

So many applications connected with the design visualization and assembly trials are greatly
facilitated by this workhorse material of extrusion technology. This is one of the case studies
corresponding to assembly integration of the entire aero gas turbine engine. You can see in
this slide the mock unit of, a scaled down unit of aero gas turbine engine consisting of the fan
module, the compressor, the combustor, the turbine, exhaust, the casing, several line
replacement units.

They were all made using ABS parts and assembled together and fundamentally the scaled-
down assembly was extremely useful not only in terms of design communication, but it was

also used as a tool as a facilitator for optimizing the location of LRUs.
Refer Slide Time: 10:25)

The other material which has become synonymous as the workhorse material of the extrusion
technology is PLA. PLA stands for polylactic acid. It can be made from starch and it is highly
affordable. The PLA parts come with adequate stiffness and good detailing and if you look at
the strength and yield properties, they are adequate enough to take care of the prototyping and
also to take care of the testing. Especially in those situations and contexts where the max
stress could be limited to less than 30 megapascal.

In this specific case, what is shown as the direct application of a PLA. FDM usage is
fabrication of a transmission gear assembly of an ornithopter a mechanical bird and
fundamentally this mechanism assembly is responsible for converting the rotary motion into
the flapping motion of ornithopter. So, because of the affordability of this material and
because of the adequate strength which is associated with PLA, the extrusion based additive
manufacturing technology has become a favorite among the design groups,

Startups who are into the development of devices and most importantly the academia which
are interested in conducting optimization studies on new products. So, in this specific case,
about half a dozen variants of the mechanisms were designed, developed and tested in less
than 2 months time without the usage of time-consuming injection molding options by virtue
of integrating the extrusion-based item manufacturing into the development of ornithopters.
(Refer Slide Time: 12:49)

This is one more example connected with the drones, a fixed wing drone and what is notable
in this case is high strength offered by the FDM material called ULTEM developed by
Stratasys. The yield strength is close to 70 megapascal and it has got necessary notched
impact characteristic also. In this case, the structural component connected with a fixed wing
aircraft or drone was realized out of ULTE.

All the electronics including the motors and the sensors were directly integrated into this
FDM structure and the resultant drone was successfully flown in the field drives. So, the
newer materials have enabled the parts which come from extrusion manufacturing not to be
confined only to the prototyping but also for field applications similar to the one which I have
shown in the slide.
(Refer Slide Time: 14:05)

But it is very important to understand that there are several parameters which impact the
strength of the part. The parameters could be connected with the build process like raster
width, the air gaps, the angle, the contour width and the gap, the infill density that you use
and the layer thickness. Several studies have been conducted by contemporary research
groups through various methodologies.

So as to improve the strength of the part corresponding to the usage of ABS, nylon,
polycarbonate and PLA material in extrusion additive manufacturing systems. It is also very
important to plan the support structures and some of the characteristics of parts are also
dependent upon the characteristics of the build system, the type of extrusion that we use, the
nozzle diameter and whether there is a provision for preheating the build plate.

So, all these parameters connected with the build system also influence the properties and
performance characteristics of the FDM parts. It is important to consider the extent of post
processing to make these parts usable for induced context. A significant amount of time and
effort is required corresponding to improving the surface finish and, in some cases, you may
have to resort to secondary processes like plating and micro peening to improve the surface
quality and to improve the surface integrity.

Incidentally, many parts made out of ABS when they are used for aesthetic purposes in the
context of industrial design. They are subjected to electroless plating procedures by virtue of
which nickel, copper, thin foils of nickel and copper are plated on the surface to improve the
aesthetics.
(Refer Slide Time: 16:45)

In case of the extrusion based additive manufacturing, it is important to consider phenomena
called stringing or unwanted oozing of the material out of the nozzle. So, the speed of the
extrusion head is controlled in such a manner that the oozing of the molten filament through
the hot end does not lead to the creation of unwanted structures called strings. The other
important consideration is about support structures. In all those instances where you have got
thin overhang features, it becomes imperative to make use of support structures.

But thanks to water soluble support structures which have been brought to the forefront by
Stratasys, removal of the supports no longer is a functional issue. So fundamentally in these
cases, the extrusion-based AM systems are provided with two print heads, one corresponding
to the build material, other one corresponding to the support material. In all those spatial

locations where support structures need to be present, the supports are deposited out of water-
soluble materials and these support structures are removed without considerable effort in the

post-processing stage.
(Refer Slide Time: 18:40)

The world of materials connected with extrusion-based additive manufacturing has seen
several innovations. The current list is impressive ranging from thermoplastic polyurethanes
to high impact polystyrenes, nylons, the carbon filled nylons especially in case of high
strength-to-weight applications that are necessary in tooling context, the polycarbonates,
polyetherketoneketone popularly known as PEKK and polyetheretherketone. All these
materials have enabled the scope of applications to get enlarged.
(Refer Slide Time: 19:33)

I would like to pick up some applications in the automotive sector to illustrate the importance
of the wide range of materials in terms of accelerating the use of the additive manufactured
parts in conventional context. What you see in this case is the sand casting of an automotive
housing. The CAD model of the same is indicated here, I think the longest linear dimension is
about 680 mm. In a conventional scenario, this part could have been realized through

carpentry and it could have taken easily about 12 to 16 weeks.

But thanks to the introduction of extrusion-based additive manufacturing the pattern in this
case has been realized with a modular approach. You can see the bottom and top hunch here
and the entire fabrication was done in less than 2 weeks time and the casting of the
automotive housing was done using the engineering material of the need by using the master
patterns that are realized through ABS material.

So, this is an indirect use of additive manufacturing wherein you recognize the fact that the
eventual part needs to be in a certain engineering material and the pattern is made out of
thermoplastic material. Either you can use this pattern in the context of sand casting as is
illustrated in this case or it can also be used in a sacrificial manner in the context of
investment casting. So, the applications of this kind which are plentiful in industrial context
are known as the rapid tooling cases wherein you are making use of the parts indirectly for
meeting the functional needs.
(Refer Slide Time: 22:03)

Here is an example corresponding to the packaging trials of an electronic device with FDM
parts. As you can see here, the small electronic device with an outer diameter of about 65 mm
and a wall thickness of about 3 mm consists of several integral parts including the heat pipes,
including the PCB mounts. So, all these components from the CAD are directly translated
into ABS parts and these parts are assembled and were tested not only to check the assembly
integrity.

In this specific case one more important functional application which was fulfilled was
availability of the cooling air in such a way that the max temperature within this module does
not cross stipulated limits. So, this particular mock assembly was used repeatedly by
introducing certain refinements in the parts and in an experimental rake the trials were
conducted in terms of ensuring the availability of the cooling air for the electronic circuitry.
(Refer Slide Time: 23:30)

This busy slide shows cases the choice of materials that are prevalent in the world of
extrusion-based additive manufacturing. Right on the top you see the thermoplastic polymers
and high-strength plastics and the other one is the polymer matrix composites, could be
GFRP or CFRP. They are used in the aeronautical and automotive sectors for structural
applications.

The ceramic slurries and clays based on alumina and zirconia kind of solutions they are
widely used in dentistry as well as for the purposes of insulation objects. The metal-polymer
composites providing solutions based on pure metals like Copper, Cobalt and also alloys,
high performance super alloys like in Inconol 718, Inconol 625, Aluminum 6061, Ti6242
have actually enabled the parts from extrusion based additive manufacturing to be directly
used for tooling applications, for fixture development and also for series production.

Some of the esoteric applications of this particular technology are connected with food
industry, even chocolate solutions or chocolate slurries have been tried out to make bespoke
chocolates using the technology of extrusion. In the recent times we have also seen flurry of
activities connected with bioprinting and fabrication of minute scaffold structures using

bioinks. So, the entire facilitation of the applications in context ranging from bio sector to
consumer goods to aeronautical to automotive and medical have been propelled to some
extent by the technology related improvements and to a large extent by the material
innovations.
(Refer Slide Time: 26:21)

Here is an interesting case study connected with sheet metal forming using FDM tooling.
This is one of the favorite applications in the world of auto sector for making parts such as
engine cradle, radiator and instrument panel, support beams, suspension components and in
few contexts, it has also been used for making the airframe components. The sheet metals
with the thickness ranging from almost half mm to 2.5 mm out of aluminium alloys, steels,
titanium, and nickel alloys are formed using the AM tooling.

It has been reported that the AM tooling was able to sustain pressures up to 70 megapascal
and up to 600 cycles of forming with no designable surface degradation. Incidentally, the
materials like polycarbonate and ULTEM provide one more functional advantage. They do
not adhere to metal, so they have got inherent lubricity. So, especially in case of low volume
manufacturing, it has been proven that there are several advantages connected with the cost
reduction and time compression by using the forming tools through materials like
polycarbonate and ULTEM based on the extrusion additive manufacturing technology.
(Refer Slide Time: 28:16)

The other materials which are connected with the extrusion process are the thermoplastic
polyurethanes similar to what you see in the insert diagram here. They are typically used in
case of flexible hoses and ducts and the elongation at break is close to about 500 percentage
and the handling of this thermoplastic polyurethanes is slightly different compared to more
viscous materials.

It has been proven in multiple contexts that the making of customized solutions connected
with flexible hoses can be done by integrating TPU into extrusion based additive
manufacturing. PETG has also been configured for the extrusion based additive
manufacturing and there are special materials which are connected with the flame-retardant
performance as well as electrical housings using the polyetherimide and ASA options.
(Refer Slide Time: 29:35)

One important application which has found favor with orthopedic surgeons as well as
maxillofacial surgeons is about developing patient specific tools using the technology of
extrusion based additive manufacturing. In this case, the input data could come from an x-ray
or a CT scan and using special purpose pre-processing software. This data is converted into a
CAD model, a 3D CAD model and this data in turn is used as the input for 3D printing on an
extrusion based additive manufacturing system.

It has been proved in different contexts that development of patient specific surgical tools and
planning of implants are greatly facilitated because of these parts which come out of
extrusion based additive manufacturing system and they can also be sterilized. They can be
used for the purpose of patient communication, also communication with the peer medical
practitioners.
(Refer Slide Time: 31:12)

It is important to understand that the configuration of the extrusion-based additive
manufacturing system has also undergone certain changes, certain refinements in the recent
times. The original configuration was based on the cartesian model. So, we had the extrusion
head moving across or along the orthogonal axis, but in course of time we had new
configuration called the delta configuration wherein typically the build plate is stationary.

It does not move in the z direction and if you see it is circular in its shape and the extrusion
head is mounted on three articulating arms. So fundamentally the extrusion head can move in
any direction in xyz space and the z height in this specific configuration is substantially
higher compared to the configuration connected with cartesian coordinate system. We have

also seen the emergence of polar 3D printer wherein just need to use two engines.

One connected with r, other one connected with theta. So, in case of 3D printers which are
based on polar configuration, you have a rotary table and you got a gantry system which
moves in a radial direction. So, the advantage of the polar coordinate-based 3D printer is that
you just need to use only two engines instead of three engines that are synonymous with the
cartesian 3D printer.

The simplest form of extrusion based additive manufacturing is the usage of a robotic arm. A
single robotic arm with mobility in xyz direction and connected with an extrusion source is
found to be adequate enough for realization of the parts. Needless to mention in this case the
surface finish as well as the part fidelity will be significantly inferior to what you see in case
of systems that operate on cartesian coordinates.
(Refer Slide Time: 33:54)

There are also other variants of the process. In some of the cases the feedstock comes in the
form of rod, so it is not a filament but it is a rod. So, to push the rod we need to use greater
amount of force, maybe this is facilitated by piston or rollers. In other cases, we have also
seen usage of pellets. The pellets are small granules of thermoplastic. They are driven to the
nozzle by a rotating screw or a piston and the entire unit is contained within an extrusion
barrel.

So, the whole extrusion barrel is heated along with the nozzle, but the advantage of this
particular variant is the cost of pellets is significantly less compared to the cost of the

filaments and hence realization of large structures becomes economical. It has been reported
that pedestrian bridges with a length of almost 24 meters with a width of almost 4 meters
have been successfully printed by hot extrusion of pellets.

The other opposite of hot extrusion of the pellets is the cold extrusion of flurries. The
feedstock in this case is a viscous suspension of solid powder particles and it could be
ceramic slurry, it could be liquid chocolate or clay and you do not make use of hot nozzle in
this case and after the material is deposited, we need to wait for certain time for the drying to
happen.
(Refer Slide Time: 35:56)

The technology of extrusion based additive manufacturing has seen several new phenomena
emerging and one of the most important things is the development of free and open source
hardware. Dr. Adrian Bowyer from University of Bath started this movement called RepRap
in 2014. Fundamentally, RepRap stands for self-replicating rapid prototyping systems. The
entire configuration corresponding to the hardware and software of this extrusion based
additive manufacturing system saw active contribution of volunteers from several parts of the
world.

This particular model also got repeated again in the projects connected with the Fab at Home
and LulzBot3D printer and they were all associated with open source hardware projects for
DIY 3D printers and these moments connected with open source hardware has led to
emergence of several startups and also to reduction in the prices of the extrusion-based AM
systems in a significant manner so much so that there are tens of thousands of extrusion-

based additive manufacturing systems that are operating currently in high schools. In
elementary schools and also in the tinkering labs spread across the length and width of the
country.
(Refer Slide Time: 37:44)

Coming to the industrial context, one important innovation which has marked the emergence
of the usage of metal polymer composite parts needs our attention. In this case, the metal
could be any of the choices like Bronze, Copper, Nickel, Aluminum, Inconel, titanium as I
described a few minutes ago and the metal polymer composite is extruded akin to the process
that I have described already.

It requires industry grade printers which have got provision for operations at high
temperature and in many of the cases even the print bed on which the part is printed is
preheated. So, what happens in handling metal polymer composite parts is the realization of a
green part at the end of the extrusion site. So, the green part is not dimensionally stable and
the green part consists of nearly 20% binder and approximately about 80% metallic material.

It has to be subjected to catalytic debinding so that we can get rid of the binder in the quickest
turnaround time. The strength of the part may not see significant improvement, but after the
catalytic debinding what you get is a brown part which is dimensionally stable and the brown
part is subjected to sintering and post sintering it is subjected to series of post processing of
operations making the part amenable for functional applications.
(Refer Slide Time: 39:58)

So important to note that in this case the nozzle temperature could be as high as 250 degree
centigrade and the print speed could be limited and the print bed temperature need to be
somewhere between 50 degrees centigrade to 80 degrees centigrade and we have to deploy
100% infill density, but after going through the necessary post-processing operations of
debinding and sintering what you get are the metallic parts, in this specific case the properties
corresponding to SS316 are shown. As you can easily infer the tensile strength, the yield
strength, the elongation and the impact characteristics of what you get through a metal
polymer-based composite are adequate enough for meeting the needs of wide area of
industrial usages.
(Refer Slide Time: 41:05)

It is because of the phenomena of this kind that there are many instances which are emerging
in the aeronautical, automotive, manufacturing and tooling sectors wherein the low volume

batch production is being attempted through industry grade 3D printers. What do you mean
by industry grade 3D printers? Typically, if you are talking about the desktop 3D printers, the
build envelope is limited to about 250 mm in xyz directions.
The accuracy could be about 1 to 1.5% and layer thickness is just limited about 0.2 mm. So
all these parameters contribute to two important characteristics. The accuracy could be
limited and the throughput could also be limited, but if you look at the industrial 3D printers
similar to the ones which are shown in this slide as the options, then the parts could be built
with higher layer thickness and the build envelope in sometimes could be as high as about a
meter in xyz directions.

The accuracy could significantly increase to about 0.15% to 0.2% which are commensurate
with the expectations of a designable engineering user so it has been observed that low
volume batch production in manufacturing and tooling industry has been facilitated with the
parts made out of nylon and polycarbonate using these industry grade 3D printers. One more
technology which has been used with the similar kind of felicity for low volume batch
production in the context of dentistry and hearing aid industry is the digital light processor.
(Refer Slide Time: 43:04)

So, we did spend some time in understanding the operational principle of stereolithography.
In case of stereolithography, what happens is the CAD data governs the movement of a UV
laser beam on the surface of photosensitive polymer which is put in a VAT and because of
the interaction between the laser beam and the UV curable resin, the resin undergoes
instantaneous transformation from liquid phase to solid phase, but the fundamental element in

this case happens to be a laser.
(Refer Slide Time: 44:06)

In recent times, the process of stereolithography has been substituted by a technology called
digital light processor. What do you mean by digital light processing is there is no usage of
any laser beam. You have got a light source and you have got micromirror assemblies.
(Refer Slide Time: 44:30)

Fundamentally the light source, it was developed way back in 1987 by Texas Instruments,
consists of tens of thousands of micromirrors of the dimensions of 8 by 8 microns which are
arranged in a rectangular array. Each of this micromirrors is pivoted and depending upon the
electrostatic attraction it can be made to swivel by about 12 degrees in either direction and the
movement of this micromirror fundamentally leads to the curing of that small area which is in
the line of focus. So, the introduction of this technology of the micromirrors has led to an

emergence of new process of VAT polymerization and this process is known as digital light
processing.
(Refer Slide Time: 45:33)

The other option is connected with LCDs.
(Refer Slide Time: 45:39)

In this case you have got a backlight, there is a polarizer, you have got analyzer and between
the polarizer and analyzer you have got a quarter wave plate. Fundamentally through optical
elements, you are able to translate the movement of the light wave in such a manner that the
light is enable to pass only in those zones where you want the polymerization to happen. In
all other instances, the analyzer cuts off the signal and there are no moving parts.

The entire motion of the light waves is only enabled through optical elements. This particular
technology which is devoid of the usage of laser beams and moving elements has led to mass
customization of the products in medical industry, both for dentistry as well as the hearing
aids.
(Refer Slide Time: 46:56)

Typically, in a dental context, the data is generated by usage of an intraoral scanner device
and you have got special purpose dental CAD software which converts the scanned data into
a CAD model.
(Refer Slide Time: 47:21)

So when you do the necessary pre-processing, we set up parameters such as exposure time
and the layer thickness and if fundamentally let us say the part is about 100 mm tall and if
you use a layer thickness of about 50 microns, you are talking about 2000 layers, but unlike