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Transcript of IJRAPIDM 4104 de Castro Silveira Et Al. (5) (1)
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Int. J. Rapid Manufacturing, Vol. x, No. x, xxxx 1
Copyright 200x Inderscience Enterprises Ltd.
Design development and functional validation of aninterchangeable head based on mini screw extrusionapplied in an experimental desktop 3-D printer
Zilda de Castro Silveira*and Matheus Stoshy de Freitas
Engineering School of Sao Carlos,
Department of Mechanical Engineering,
University of So Paulo,
Trabalhador sancarlense Avenue,
No. 400, Sao Carlos, S.P., 13566-590, Brazil
E-mail: [email protected]
E-mail: [email protected]
*Corresponding author
Paulo Inforatti Neto, Pedro Yoshito Noritomi,Jorge Vicente Lopes da Silva
Renato Archer Center of Information Technology CTI,
Campinas, Rodovia Dom Pedro I(SP 65),
Km 143.6, 13069-901, Brazil
E-mail: [email protected]
E-mail: [email protected]
E-mail: [email protected]
Abstract: In this work is proposed the conceptual and preliminary design aswell functional validation of a head based on fused deposition modelling(FDM) technology using mini screw applied to experimental 3-D printer(Fab@CTI machine). The polymer Nylon 12 and the biopolymer -PCL(-policaprolactone) in powder form were used to design the barrel-screw anddrive system set-up. The proposed head demonstrated the functionality to carrythe powder material through the variable sections of the screw extrusion andhas generated Nylon filaments with diameter of approximately 0.7 mm withthe tip of 0.4 mm. The morphological characteristics of these filaments wereobserved in scanning electron microscopy (SEM) confirming the mixing of thepowder, generating continuous filaments and structured parts. SEM tests were
made with -PCL using material generated from the feed to compression zonesof the screw extrusion head allowing the visualisation of the adhesion of thegrains in feed section and the complete mixing in the compression zone for the-PCL.
Keywords:desktop 3-D printer; rapid manufacturing; FDM; fused depositionmodelling; design methodology; material reuse; polymer; process control.
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2 Z.C. Silveira et al.
Reference to this paper should be made as follows: Silveira, Z.C.,
Freitas, M.S., Inforatti Neto, P., Noritomi, P.Y. and Silva, J.V.L. (xxxx)Design development and functional validation of an interchangeable headbased on mini screw extrusion applied in an experimental desktop 3-D printer,Int. J. Rapid Manufacturing, Vol. x, No. x, pp.xxxxxx.
Biographical notes:Zilda de Castro Silveira is Professor of the Department ofMechanical Engineering of the Engineering School of Sao Carlos, Universityof Sao Paulo. She obtained DSc title in 2003 from Faculty of MechanicalEngineering, State University of Campinas (UNICAMP), Sao Paulo Brazil, inthe area of Mechanical Design and Solid Mechanics. She obtained the MSc titlein 1999 from Engineering School of Sao Carlos, University of Sao Paulo, in theMechanical Design area. Her researches areas included: design methodologyand numerical optimisation related to development of devices and machinesapplied to additive manufacturing and health area; theoretical and experimentalstudies of the aerostatic ceramic porous bearings applied to ultraprecision
machines and development of the numerical models applied to bonere-modelling.
Matheus Stoshy de Freitas is Masters degree (MSc) of the Department ofMechanical Engineering of the Engineering School of Sao Carlos, Universityof Sao Paulo (USP). He obtained a Bachelors degree in MechanicalEngineering at the same institution. He is a researcher in CTI acting thetheoretical and experimentally studies of mechanical solutions applied toadditive manufacturing.
Paulo Inforatti Neto is graduated in Computer Engineering, has Masterin Mechanical Design at School of Engineering of So Carlos of the StateUniversity of So Paulo (EESC/USP), working with additive manufacturingresearch topics. Currently he is project manager by FACTI at the ThreeDimensional Technologies Division at the Renato Archer Information
Technology Center (DT3D/CTI) coordinating applied researches indevelopment and using of additive manufacture technology to non-conventional applications, mainly in oil and gas research.
Pedro Yoshito Noritomi is graduated in Mechanical Engineering, has Masterand PhD in Computational Mechanics at Campinas State University(UNICAMP) working with bioengineering research topics. Currently he isresearcher at the Three Dimensional Technologies Division at the RenatoArcher Information Technology Center (DT3D/CTI) coordinating thebioengineering initiative of the division and using his expertise incomputational modelling and simulation applied to other demand, mainly in oiland gas research.
Jorge Vicente Lopes da Silva is a PhD in Chemical Engineering, MSc inElectrical Engineering and BSc in Electrical engineering. He created andcoordinates, since 1996, the Three-dimensional Division at CTI Renato Archer.Under his supervision this division develops application and research projectswith industry and universities in Brazil and abroad. He is member of manyscientific committees and invited speaker of the most relevant conferences inthe area of 3D printing.
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Design development and functional validation 3
1 Introduction
Recently, there was an increasing development in rapid prototype technologies as well as
a real perspective to use additive manufacturing in the area of health, with highly
complex geometries, specifically the ones of tissue and bone engineering. The term rapid
prototyping (RP) a.k.a additive manufacturing, is widely used in industry to describe the
process to rapidly create a system or a component in a stage just before the final product
or before commercialisation. The American Society for Testing and Materials (ASTM)
define Additive Manufacturing (AM) as the process of joining materials to make objects
from 3-D model data, usually layer-upon-layer, as opposed to subtractive manufacturing
(ASTM, 2010) without the need of conventional process planning as used on machining
or conformation processes. Commercial AM machines generally need a high quantity of
material to start working and build parts; additionally there are operational constraints
settings and they are configured to use proprietary materials from the suppliers andmanufacturers. These constraints hinder advances in research areas that include materials
development and process. By these conditions, it becomes interesting the development of
technologies in open source 3-D printers with reduced dimensions, due the small
quantities of feedstock and more freedom towards the software and hardware
development. Another motivation for this work is the increasing market related to
desktop 3-D printers, with a crescent number of brands using different materials and
techniques of deposition. The most common technologies used in desktop 3-D printer
included: the fused deposition modelling (FDM) commercial processes consider the raw
material as thermoplastic material fed in the form of a flexible filament rolled in a coil.
The filament is guided into the head by a device controlled by integrated numerical
command, where pulleys are responsible for feeding wired material and pushes it into a
heated channel, causing it to melt and to be extruded through a nozzle in the opposite end
of the channel. Other technique uses the extrusion by a syringe which occurs by the
compression of the material within a deposition chamber and the subsequent extrusion of
this material through a needle. Any of these processes, coupled to a (x,y,z) controlled
displacement system enables prototyping 3-D models (Gibson et al., 2010). In the case in
study, the development of a screw extrusion head, the material enters in a powder form in
the superior part of the device, being carried to the lower parts getting melted in the way
by the use of a tubular resistance acquiring a continuous and viscous consistence enabling
its extrusion through a nozzle tip in the end of the process. The success or fail in this
process rely in the capacity of producing continuous filaments that can be deposited in a
3-D printing platform permitting the construction of parts. In the case of using
biomaterials it permits the fabrication of scaffolds that can be defined as a temporary
porous structure used to promote cells growth where its function is to allow a structural
support to the formation of new biological tissues (Ikegami, 2007). The goal of thiswork is to present the design development and functional validation of an interchangeable
screw extrusion head with variable section to be used in a desktop 3-D printer based on
FDM approach. It was made a calculation methodology for the extrusion screw and
transmission system. A validation of the conceptual design for industrial and biomaterials
applications, respectively, were carried out using polyamide (Nylon 12) and -PCL
producing continuous filaments and entire parts. The SEM analyses were made with
these materials and the results presented morphological characteristics appropriated to
polymer structure extrusion used in additive manufacture purposes.
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2 Considerations about extrusion process
The choice of the conformation method used in a specific polymer depends on
some factors, as the choice of the polymer, geometry and size of the final part. In the case
on a thermoplastic polymer, the rheological properties (flow curves, melting point),
operational temperature, cooling time after the process should be considered, in the case
of a thermofix, its considered the temperature and curing time. The temperature or
melting point describes the phase transformation of a crystal solid for a liquid. According
to Chung (2000) the melting point term is used only for crystalline polymers, because
amorphous polymers without crystallisation do not present the same melting point
(it can occur up to Glass Transition Temperature (Tg), for amorphous thermoplastics
polymers). Chung (2000) describes the melting process as a change in solid/
liquid behaviour in amorphous or semi-solid polymers. According Rauwendaal (2001),
the polymer processing in extruders involves the use of any kind of solid material fed tothe extrusion screw, which is melted and carried by the screws rotation until the end of
course. The designs of a single or double extrusion screw are the most common
configurations in industrial polymer processing.
There are many mechanisms used to pump liquids with low and high viscosity.
According to White and Potente (2003) for highly viscous liquids usually two different
principles are used:
positive displacement pumps, where the fluid fills enclosed chambers and is moved
forward by the mechanical movement of the parts of the machine (ram extruder in
processing of thermoplastic)
drag flow pumps, in this case the fluid fills a region between two surfaces, where one
is in motion.
The relative movement of the two surfaces drags the fluid along a channel, gradually
pressurising and forcing it through a die. The second mechanism has some technical
solutions developed along the years, but the simplest machine is the drum flow pump or
drum extruder invented by Gabrielli (1952) apnd White and Potente (2003). In this
machine, the material to be pumped is put on an annular space between the rotating drum
and surrounding barrel. The rotation of the drum carries the liquid to a position where
there is a wiper bar that diverts the liquid into the die. The die pressurises the liquid and a
pressure gradient develops along the length of the channel between the drum and the
barrel. A complete study about behaviour of extrusion processes involve an estimative on
thermo-physical parameters, mainly related to screw, where its geometry, polymer
rheology, and processing conditions must be considered. Breaux et al. (2009), Chung
(2000) and White and Potente (2003) describe the extrusion process to a standard singlescrew extruder into three zones related with screw design. The performance of an
extrusion process can be improved substantially by optimisation of the screw design.
Summarising, the screw performs three basic functions:
solid conveying function
melting function
metering or pumping function.
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Design development and functional validation 5
In most applications, these three functions occur simultaneously along screw length and
they are strongly interdependent. The size of a screw is described by its diameter andlength or length-to-diameter (L/D) ratio. Chung (2000) used geometrical names to the
three different sections:
Feeding section at the hopper end with a constant, deep channel depth called
feeding depth. In this region conveying of a solid bed from compacted pellets
occurs. Pressure increases steeply along the screw but cannot reach high values in
smooth barrel extruder without the phenomenon of melting of the superficial layer in
contact with the barrel hence releasing any extra pressure.
Metering section or pumping section at the die end with a constant, shallow channel
depth called metering depth. Breaux et al. (2009) define this zone as delay
where the molten film of polymer increases in thickness and possibly permeates the
solid bed itself. This condition occurs at the end of the feed zone of the screw. A compression section (or transition section or melting section) between the feeding
section and the metering section with a decreasing channel depth.
In this region occurs the melting process, when the melt film has increased up to a point
where it runs through the solid bed of ever decreasing width as presented in Figure 1.
Breaux et al. (2009) identify a forth section in the direction of the end of the
compression zone and in the metering zone the solid bed is completely melted and there
is melt conveying only. Throughput in the conveying zone is the combination of screw
rotation that provides the drag flow and the pressure gradient in the screw channel. When
the pressure gradient is positive it blocks the drag flow, while it promotes the flow when
it is negative. Throughput is constant along the channel, while pressure development start
from atmospheric pressure and ends at back pressure imposed on the screw in the case of
injection moulding, or at atmospheric pressure at the die exit in the case of extrusion. For
the extrusion process, the level of back pressure is the result of the combination of die
and screw.
Figure 1 Processing zones to a single screw
Source: Adapted from Manrich (2005)
It is important to realise that conventional extruders have large dimensions compared
with the device developed in this study. With the intention of built a functional device
with the same capabilities of a conventional extruders, but with reduced dimensions,
developed concepts and methods for these industrial extruders where used and based on
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these, a calculation methodology was made. With this calculation methodology it was
proposed the verification, dimensioning and choosing of the main components as screwextrusion, stepper motor, worm gear and barrel. The vertical configuration designed to
the screw extrusion head allows better use of space design as well as the arrangement of
the drive system.
3 Case study
For a desktop 3-D printer an alternative and interchangeable head design the users
requirements and technical characteristics were defined:
Raw materialrelated to the use of different forms (pellets, powder, solids) and
in reduced amount. In bioengineering applications the use of powder material to
generate prototypes is highly indicated due to commercial availability. The use ofpowder raw material is common in the polymer industry, especially in injection
and extrusion moulding. In non-commercial AM machines, specifically desktop
3-D printers, the solutions found are: syringe injection (Malone and Lipson, 2007),
thermoplastic filament extruder (Inforatti Neto et al., 2012) and transport extrusion
system for previously melted biopolymer (Almeida et al., 2008); all of them on open-
source design.
Operational performance, related to flexible platforms, reduced dimensions, again
use of different raw materials and low cost. In commercial machines, technical
solutions are protected by patents included control systems and combined
mechanisms, making the purchase price of the machinery and raw material, as well
as the cost of maintenance is too high and even unfeasible to non-industrial users.
In this way, a new branch from Fab@Home, named Fab@CTI 3-D printer, showed
in Figure 2(a) and (b), offer low cost, open platform to the assembly of a mini screw
extrusion head based on FDM deposition technology.
Figure 2 (a) Fab@CTI desktop 3-D printer and (b) syringe head extruder and fused depositionmodelling head (see online version for colours)
(a) (b)
Source: Inforatti Neto et al. (2012)
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Design development and functional validation 7
The Fab@CTI 3-D printer platform was designed from of the following demand:
definition of the application demand: tissue engineering (production ofscaffolds)
and small mechanical components
utilisation environments:research laboratories including research centres and
universities
machine volume:460 410 470 mm
mass: 2550 kg.
Inforatti Neto (2013) presented a technical design feasibility of the mini screw with
variable section head. The users requirements composed by users researcher were raised
at design phase and obtained from quality function deployment (QFD) analysis described
in Cheng and Melo Filho (2007). The list of users requirements was translated into
technical characteristics which supports the constructive solutions choice to mechanical
design of extrusion mini-head. The most important users requirements identified by
QFD were:
powder as raw material
continuous feeding and process control
low quantity of materials (adequated to the behaviour of the research demands)
reuse of polymer power from commercial additive manufacturing machines
filament modelling raw material to the use in FDM head (Fab@CTI)
interchangeabale tip nozzles.
The -PCL was the biomaterial chosen for the device trials and this material is related to
other previous studies (Rezende et al., 2012; Inforatti Neto et al., 2012) in the health
area. The choice of the polyamide is related to the reuse of material discarded
from commercial machines. In this case, the availability of the material in the laboratory
(CTI), in its non-degraded and degraded form, result of previous prototyping processes
by selective laser sintering (SLS) and second, its wide use in industrial parts.
4 Development of conceptual design
The conceptual design uses the technical requirements which are identified as having
greater importance in the phase before (informational design). There are some which
have the objective to proportion a technical system to be understood as functions of thedesign subsequently related to technical items or components, and, on a higher abstract
level, find innovative solutions or just improvements of technical solutions. The outcome
of this step for the preliminary design is one or more sketches of technically viable
solutions. For the development of the mini-head design of extrusion functions of
technical developments of the head and of the structure material functions technical
elements inside the 3-D printer system were extracted, which is presented in Figures 3
and 4, using one of the engineering techniques of systems that relate Energy (E); Material
(M) and Signal (S).
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Figure 3 Material-energy-signal flows to a 3-D printer
Figure 4 Material-energy-signal flow to the deposition mini-extrude head
Inside the technical system 3-D printer, the production of the prototype piece is the
principal function of the machines engineering design. In Figure 7(b) the production
process of the piece is detailed, and for each described function, decisions of the design
should be made based on conventional and alternative solutions which contemplate
restrictions of this design, as there is the heads weight in relation to the machine,
reduced spaces, and portability and low costs. Thus, starting from the information
obtained with the QFD, a set of the designs parameters was chosen to find technical
solutions. To organise the choice of solutions a morphologic picture was mounted,
presented in Figure 5.The first option of technical solutions is presented by the arrows, to attend the
designs restrictions described beforehand as shown by Table 1.
The choice of the deposition material in the form of powder was made in function of
its availability on the market and the possible mixtures with additives and other materials.
The step motor to start the head was chosen for its control facilities and adjustment
beforehand tested with the systems of injecting by syringe and filament.
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Design development and functional validation 9
Figure 5 Morphologic analysis
Table 1 Partial value analysis to the extrusion head
Components Design functions Partial cost (U$) Percentage
Structure Support head set-up 363.10 16.6
Barrel Extrusion screw housing 335.19 15.4
Extrusion screw Transport, melting and homogenise thematerial
837.98 38.5
Stepper motor Supply energy/power to transmissionsystem
90.50 4.14
Gearbox Reduce the velocity and increase the
screws torque
335.19 15.3
Microtubular resistance Heat the extrusions material 111.73 5.12
Temperature sensor Measure the temperature 18.44 0.84
Nozzle Deposit the material 16.75 0.77
Mechanical coupling Join the shafts 33.52 1.54
Thermal blanked Isolate thermally the head set-up 22.35 1.02
Ball bearings Support shafts and friction minimisebetween elements
22.351.02
Total cost 2187.1 100
The heads structure will be interchangeable to couple with other processes of deposition
(Inforatti Neto, 2007; Inforatti Neto et al., 2012). A big part of the fixation done
together with screws, mainly due to the easiness with which they can be bought,
mounted, and subsystems can be maintained. In this first study, the extrusion will be
made with a simple screw to test the concept of extrusion in the deposition process, so the
polymers thermal effects in the cylinder part of the screwof the materials chosen, the
easiness of assembly and manufacture can be studied. The die of extrusion is
interchangeable to enable diverse diameters of the thread of material when exiting the
machine. So, different resolutions and superficial finishings of the piece are possible.
The feeding of the material is done by gravity using a mixer consisting of a rotating shaft
coupled to the screw during the feeding phase to avoid the compression of the material.
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The raw-material for the extrusion is made of polymers and was chosen because of it is
so easily manipulated in the extrusion process. The mechanism of heating up will becarried out by electric resistances because they can be wrapped around the external
cylinder in the extrusion process to guarantee controlled heating throughout the whole
process of extrusion. On the basis of the data provided by the suppliers and our own data
on estimates for the Fab@CTI printer an initial estimate for the costs of the extrusion
head was made, presented in Table 1. The analysis of the value has the purpose to
estimate the costs of each one of the components as well as their functions making it
possible to analyse the economic impact of each part of the head more precisely. This is
because of the choice of the material of the screw: titanium alloy (changed by stainless
steel) for the extruder and the difficulty to find a commercially produced screw with the
required dimensions (~150 mm long and 7 mm in diameter). With the procedures
adopted, the conception design and the initial costs (based on Value Analysis Technique)
of the head were estimated and are represented in Table 1, and an outline of the technicalsolution for the extrusion head is presented in Figure 6.
Figure 6 Schematic view of extrusion head
5 Calculation procedures
With the aim to ensure strength and performance required, calculations to define the
geometries of the extrusion screw and barrel were done. Calculation procedure was based
on technical literature of standard industrial extrusion screw. A functional prototype was
fabricated and assembled. From the theory described in item 4, were obtained the main
design parameters of the barrel-screw and actuation system. Usually, the screws are not
subjected to a high bending force because they run inside a strong rigid barrel and the
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Design development and functional validation 11
clearance between screw and barrel is small, around 0.00050.002 (White and Potente,
2003). The small gap between screw and barrel prevents solidification by cooling of themelt. Leakage flow caused by the clearance between the inner barrel and screw flight
reduces the melting efficiency also. Then, the manufacturing process of extrusion screw,
in this case, must have high precision. The critical strength requirement is mechanical
resistance to torque that is very dependent of polymerics material type. In this step, a
pre-calculation was made considering some geometric and fluid characteristics to the
mini screw as well as the head extruder. In this step, calculations were made considering
some geometric and fluid characteristics to the extrusion screw as well as the head
extruder in general. The flowchart presented in Figure 7(a) shows a simplified sequence
of calculations applied in a single screw extrusion head to a portable 3-D printer
(Fab@CTI). The procedure of the calculation was based on Rauwendaal (2001) and
Chung (2000).
The transmission system chosen was a gearbox (worm gear). This first choice hasconsidered the high transmission ratio as well as the space restrictions. The polymers
viscosities were considered to selection of the stepper motor and those are directly related
with power and torque characteristics represented in Figure 7(b).
Figure 7 (a) Flowchart related to calculation procedure and (b) design parameters to choice of thegearbox (see online version for colours)
(a)
(b)
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Nylon 12 was the first polymeric material used to obtain some important materials
properties such as the relationship: shear rate and linear velocity. Polyamide (Nylon 12)is a semi-crystalline polymer which is highly hygroscopic and because of this
characteristic it should be taken to a greenhouse with air ventilation, before being
processed. Its processing temperature is higher than 240C, having a melting temperature
in a narrow range and oxidises easily when exposed to hot air and it presents low
viscosity after being fused. With these properties this material needs a dosage zone with a
constant shallow canal, to avoid fluctuations due to its low viscosity. The control of
polyamide viscosity in different extrusion velocities, rheometry analysis of virgin and
degraded materials were considered and the objective was the determination of
rheological curves of these samples at 225C. From the rheometry analysis it was
possible to observe the shear strength of the non-degraded polyamide is significantly less
than the degraded one, probably due to the thermal and mechanical solicitation, which are
suffered in previous processing, this information are available in Inforatti Neto (2013).This means when leaking, through the extrusion process the non-degraded polymer offers
less resistance to shearing, and therefore needs less energy in the activation of the
extrusion screw to flow along the extruders body. However, the rheometry analysis
indicated a higher resistance in the case of -PCL shearing and thus, calculation of the
gearbox was based on the torque moment of -PCL. Figure 8 presents the input design
data and calculated design parameters.
Figure 8 (a) Main input and output design parameters and (b) AISI stainless steel 304for mini-screw (see online version for colours)
(a)
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Design development and functional validation 13
Figure 8 (a) Main input and output design parameters and (b) AISI stainless steel 304
for mini-screw (see online version for colours) (continued)
(b)
6 Detail design: mock-up and functional prototype
The screw extrusion design presents three sections and it was developed considering
mechanical strength to the torque caused by the turning into the viscous melted polymer
material. The mixer in the feed section was proposed to avoid the caking of the powder
material which would cause the locking of the screw and bubbles formation in the
polymer material. Figure 9(a) presents a mock-up of the constructive solution for
extrusion head and Figure 9(b) presents the functional head assembly stand alone for
preliminary experimental tests.
Figure 9 (a) Mock-up and (b) functional mini screw head (see online version for colours)
(a) (b)
7 Preliminary experimental tests: interchangeable mini screw headvalidation
From the detailed design, it was generated a mock-up to verify the assembly system
and kinematics aspects. The following step was the manufacturing of a functional
prototype. Machining processes and additive manufacturing were used in the fabrication
of this prototype. Finally, experimental tests were conducted to investigate the capacity
of extrusion head to generate continuous filaments from powder raw material.
The preliminary tests showed the generation of continuous filaments with no large
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variations in diameter, where Nylon 12 was successfully extruded with diameter
filaments of 0.75 mm (mean width value) according to Figure 10.
Figure 10 Filaments generated from polyamide (Nylon 12) (see online version for colours)
This initial test is important to demonstrate the capacity to transform the polymer powder
in a melted polymer. The expected performance for the feed section is carrying the
material to the downstream sections. The continuous filaments obtained reflect an
adequate performance in the compression and metering section. In these sections, the
rising pressure forces the melted polymer through the nozzle tip with the aim to produce
continuous filaments demonstrating the conceptual design of create filaments from
powder using polymers in a screw extruder of small proportions. This concept is based
in an idea of using the known extrusions process in a small scale. In Figure 12, it is
shown the nozzle tip of the extrusion head performing the manufacturing a PolyamideNylon 12 15 layers block, without air gap, and 0.8 nozzle tip, showing the capacity of
generating parts extruding layer by layer as it is required in rapid prototype purposes. The
morphological characteristics were analysed with scanning electron microscopy (SEM).
The photomicrographs were obtained in the Instrumental Chemical Analysis Center of
the So Carlos Chemical Institute (CAQI/IQSC/USP) in ZEISS LEO 440 (Cambridge,
England) with detector OXFORD (model 7060) equipment, operating with electron beam
of 15 kV. The samples were covered with 10 nm of gold in a sputter Coating System
BAL-TEC MED 020 (BAL-TEC, Liechtenstein) and it was maintained in desiccators
until the moment of the analysis.
Figure 11 (a) Nylon 12 filaments and (b) photomicrographs
(a) (b)
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Design development and functional validation 15
It is possible to observe in Figure 11(a) that the filament generated from Nylon 12
powder is homogeneous. In Figure 11(b), it can be seen that the material has a solidsurface without any pore or surfaces discontinuities.
For the -PCL material, SEM micrographs shows the total transformation of the
grains in feed section to solid homogenous material in compression section, the scheme
in Figure 13(a) and (b) shows the sections where the -PCL was collected and the
micrographs also. Figures 12(a) and (b) present an experimental test generating a scaffold
manufacturing with polyamide.
Figure 12 (a) The extrusion head constructing a Scaffold; (b) detailed view on the nozzle tip and(c) Scaffold generate (see online version for colours)
Figure 13 (a) SEM for -PCL showing the material state and (b) morphological aspects in feedand compression sections
(a) (b)
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8 Conclusions
The innovative characteristics presented in this work are based on the fact that
the feeding of material is in powder form, its extrusion into filament and transformation
in the form of deposition layers occurs simultaneously. Control of process parameters
such as temperature and extrusion output stream of material contributing to the quality
of the material constituting the 3-D model obtained. The miniaturisation of the sub-
assembly barrel-screw applied to AM machines is other important aspect of this design
development. The preliminary tests of the head showed the capacity of extruding melted
material producing continuous filaments demonstrating the performance of each section
of the screw extrusion. The transmission system, including the stepper motor, presented a
satisfactory performance, mainly related to driving control systems, once it was shown
the screw extrusion head capability to fabricate a block composed by various layers
characterising the application in additive manufacturing. The results present the potentialof this interchangeable screw extrusion head to provide new opportunities for desktop
3-D printers in several applications using powder as feedstock with the aim to generate
3-D models.
The use of QFD support the identification of the more important design
characteristics that lead the choices during design development. The use of mock-up and
additive manufacturing are important to previously identify assembly failures reducing
the design time. The preliminary tests of the head showed the capacity of extruding
melted material (SEM photomicrographs), which showed homogeneous and continuous
filaments, a necessary condition for layer deposition purposes demonstrating the
performance of each section of the screw extrusion. The results present the potential of
this interchangeable screw extrusion head to provide new opportunities for desktop 3-D
printers in several applications using powder as feedstock with the aim to generate 3-D
models. In direction of new additive manufacturing correlated areas as health, tissue
engineering and biomaterial applications, this new device presents results using -PCL as
powder material and has demonstrated its capacity to produce scaffolds. As future works,
it is proposed the optimisation of the extrusion process using design of experiment (DOE)
and RSM looking for the best mechanical settings coupling with material properties. The
use of new materials, in specific thermoplastics, is a promising area towards the material
sciences applications in additive manufacturing, more specifically, in desktop 3-D printer
machines. The blend or mixture of two or more kinds of polymers in feed section and its
respective study is another possibility of research.
Acknowledgements
The authors thank to the CNPq (Brazilian Counsel of Technological and Scientific
Development) for the financial support.
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