ijrapidm 4104 de castro silveira et al. (5) (1)

8/10/2019 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]


*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




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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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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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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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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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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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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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.

References

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