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TRANSCRIPT
Student: Jennifer Monclou
Academic Supervisors: Claudia Marano / Riccardo Gatti
Design SchoolMilan, Italy
A.Y. 2016 – 2017
Graduation thesis:MSc. Design and Engineering
A first approach to study thethermal annealing effect of an object
made of Poly-Lactic Acid (PLA) produced by Fused Deposition
Modeling (FDM) technology
A first approach to study the thermal annealing effect of an object made of Poly-lactic Acid (PLA) produced
By Fused Deposition Modeling (FDM) technology
Jennifer Monclou Chaparro Matricola: 851267
Title to obtain:
MSc. Design and Engineering L.M. Progetto e Ingegnerizzazione del Prodotto Industriale
Relatore:
Claudia Marano Dipartimento di Chimica, Materiali e Ingegneria Chimica “Giulio Natta”
Correlatore:
Riccardo Gatti Dipartimento di Design
Design School Milan, Italy
A.Y. 2016 – 2017
Dame la mano y danzaremos; dame la mano y me amarás. Como una sola flor seremos, como una flor, y nada más...
El mismo verso cantaremos,
al mismo paso bailarás. Como una espiga ondularemos, como una espiga, y nada más…
Gabriela Mistral
A mis padres, mi hermano y los nonos con quienes eternamente andaré.
CONTENTS
Contents
Contents .......................................................................................................................................... 3
1. Introduction ............................................................................................................................... 13
1.2 Main goal ............................................................................................................................. 13
1.3 Methodology ....................................................................................................................... 13
1.4 Project grounds ................................................................................................................... 14
2. Literature Review ...................................................................................................................... 17
2.1 Additive Manufacturing ...................................................................................................... 18
2.1.1 Limitations .................................................................................................................... 20
2.1.2 Advantages ................................................................................................................... 21
2.2 Desktop-level 3D printers ................................................................................................... 22
2.3 Fused Deposition Modeling (FDM) .................................................................................... 24
2.3.1 Types of FDM machines ............................................................................................... 25
2.3.2 Software tools .............................................................................................................. 25
2.3.3 Printing Parameters ..................................................................................................... 28
2.3.4 Poly-Lactic Acid (PLA) filament .................................................................................... 29
2.4 Open design movement ..................................................................................................... 32
2.4.1 e-Nable community ...................................................................................................... 33
2.5 Post-processing for objects produced with FDM .............................................................. 37
2.5.1 Aesthetic purposes ....................................................................................................... 37
2.5.2 Functional purposes ..................................................................................................... 38
2.6 Thermal Annealing .............................................................................................................. 38
2.6.1 Review of PLA annealing methods .............................................................................. 39
2.6.2 Review of annealed PLA research ............................................................................... 44
3. Experiment planning ................................................................................................................. 48
3.1 Uniaxial Tensile Test ............................................................................................................ 49
3.2 Differential Scanning Calorimetry - DSC ............................................................................ 49
3.3 Experiment resources ......................................................................................................... 50
3.4 Experiment workflow .......................................................................................................... 51
4. Experiment execution ............................................................................................................... 53
4.1 First run................................................................................................................................ 54
4.1.2 Producing the samples ................................................................................................. 54
4.1.3 Collecting the data ....................................................................................................... 56
4.1.4 First run findings: dimension variation ....................................................................... 58
4.2 Second run ........................................................................................................................... 60
4.2.1 Geometry variation ...................................................................................................... 61
4.2.2 Water content variation during the annealing ........................................................... 63
4.3 Annealing effect on crystallinity ......................................................................................... 64
4.4 Annealing effect on tensile properties .............................................................................. 69
4.4.1 Apparent Tensile Modulus ........................................................................................... 69
4.4.2 Apparent Tensile Strength ........................................................................................... 73
4.4.3 Material Brittleness ...................................................................................................... 78
4.5 Annealing effect on geometry ............................................................................................ 79
5. Conclusions ................................................................................................................................ 81
References ..................................................................................................................................... 84
List of figures
Figure 1. Shared knowledge phenomenon .................................................................................. 14
Figure 2. Literature review workflow ........................................................................................... 17
Figure 3. 8 Generic steps for the AM process ............................................................................. 18
Figure 4. Process categories for AM ............................................................................................ 19
Figure 5. The AM wheel depicting four major aspects of AM .................................................... 20
Figure 6. AM applications ............................................................................................................. 21
Figure 7. Timeline of 3D printer machines .................................................................................. 22
Figure 8. The RepRap initiative and MakerBot team .................................................................. 23
Figure 9. FDM technology schematic ........................................................................................... 24
Figure 10. Types of FDM machines .............................................................................................. 25
Figure 11. FDM main printing parameters .................................................................................. 28
Figure 12. Stack of FDM filament ................................................................................................. 29
Figure 13. Open Bionics robotic prosthesis ................................................................................. 32
Figure 14. Robohand and e-Nable community ............................................................................ 33
Figure 15. e-Nable community ..................................................................................................... 34
Figure 16. e-Nable wrist power devices ....................................................................................... 35
Figure 17. Prosthesis using a slot on the gauntlet component .................................................. 35
Figure 18. Gauntlet produced flat-shape wise ............................................................................ 36
Figure 19. Gauntlet adjusted with Velcro (detail) ....................................................................... 36
Figure 20. Post-processing for 3D printed objects (aesthetic purposes) ................................... 37
Figure 21. Post-processing for functional purposes .................................................................... 38
Figure 22. Crystallization schematic ............................................................................................. 39
Figure 23. Oven bake method 1 (overview) ................................................................................ 40
Figure 24. Oven bake method 2 findings ..................................................................................... 41
Figure 25. Boiling water method .................................................................................................. 42
Figure 26. Sous vide method ........................................................................................................ 43
Figure 27. Injection moulding annealing findings ....................................................................... 45
Figure 28. PLA fiber composites findings ..................................................................................... 46
Figure 29. Experiment planning ................................................................................................... 48
Figure 30. Example of thermogram output from DSC ................................................................ 49
Figure 31. Experiment resources ................................................................................................. 50
Figure 32. Workflow of experiment ............................................................................................. 51
Figure 33. Experiment planning ................................................................................................... 53
Figure 34. 20% and 35% infill (triangular infill pattern) .............................................................. 54
Figure 35. Measuring with digital image analysis and caliper .................................................... 57
Figure 36. Second run samples .................................................................................................... 60
Figure 37. Setting up the DSC ....................................................................................................... 64
Figure 38. Uniaxial tensile test ..................................................................................................... 69
Figure 39. Infill percentage variations and infill pattern overview ............................................. 70
Figure 40. Tensile test samples .................................................................................................... 73
Figure 41. Specimen structure scheme (layer-wise distribution) ............................................... 76
Figure 44. Crack typology before and after annealing ................................................................ 78
Figure 45. Samples for geometry analysis ................................................................................... 79
List of tables
Table 1. CAD Software examples ................................................................................................. 26
Table 2. Slicing Software examples .............................................................................................. 27
Table 3.Printer control or “client” software examples ............................................................... 27
Table 4. Regular PLA commercial variations ................................................................................ 30
Table 5. High Temperature PLA commercial offer ...................................................................... 31
Table 6. PLA-Layer filament datasheet ........................................................................................ 55
Table 7. First run samples ............................................................................................................. 56
Table 8. Measurement output with caliper (first run) ................................................................ 57
Table 9. Measurement output with digital image analysis (first run) ........................................ 57
Table 10. Comparison of specimen dimension using caliper and digital image analysis (first
run)................................................................................................................................................. 58
Table 11. Second run samples (scheme) ..................................................................................... 60
Table 12. Measurement output for specimens without thermal treatment (second run)....... 61
Table 13. Caliper measurement output for specimens with thermal treatment (second run) 61
Table 14. Digital image analysis measurement output for specimens with thermal treatment
(second run) .................................................................................................................................. 61
Table 15. Apparent tensile modulus variation ............................................................................ 71
Table 16. Example of tensile test output ..................................................................................... 74
Table 17. Apparent tensile test variation..................................................................................... 74
List of graphs
Graph 1. Geometric variation Caliper vs. Scanner (first run) ...................................................... 59
Graph 2. Annealing effect on geometry (second run) ................................................................ 62
Graph 3. Weight variation ............................................................................................................ 63
Graph 4. First DSC thermogram ................................................................................................... 65
Graph 5. Second DSC thermogram .............................................................................................. 68
Graph 6. Load -Elongation plot .................................................................................................... 72
Graph 7. Apparent Stress-Strain plot ........................................................................................... 72
Graph 8. Stress-Strain plot (as-printed, annealed) ...................................................................... 75
Graph 9. Apparent tensile modulus for different infill percentage ............................................ 77
Graph 10. Apparent tensile strength for different infill percentage .......................................... 77
Graph 11. Annealing effect on geometry (average data) ........................................................... 79
List of equations
Equation 1. Water content variation during the annealing ........................................................ 63
Equation 2. Areas of melting and crystallization peaks .............................................................. 66
Equation 3. Value of areas of melting and crystallization peaks ................................................ 66
Equation 4. Melting heat of PLA before and after annealing ..................................................... 66
Equation 5. Degree of crystallinity before and after annealling ................................................. 67
Equation 6. Delta of crystallinity .................................................................................................. 67
Equation 7. Slope of line ............................................................................................................... 71
INTRODUCTION
GLOSSARY
Additive manufacturing: Refers to a process by which digital 3D design data is used to build up
a component in layers by depositing material.
Differential Scanning Calorimetry (DSC): Is a thermoanalytical technique in which the
difference in the amount of heat required to increase the temperature of a sample and
reference is measured as a function of temperature.
Fused Deposition Modeling (FDM): Is a molten material system, characterized by a pre-
heating chamber that raises the material temperature to melting point so that it can flow
through a delivery system. Fused Deposition Modeling extrudes the material through a nozzle
in a controlled manner.
Modulus of elasticity (E): Indicates the relationship between stress and strain in the
deformation of a solid body. It defines the ratio of the stress applied to a body and the
resulting increased strain result without influencing the cross-sectional deformation of the
test body.
Poly-Lactic Acid (PLA): Is a biodegradable and bioactive thermoplastic aliphatic polyester
derived from renewable resources, such as corn starch, cassava roots, starch or sugarcane, is
one of the two most commonly used desktop 3D printing filaments.
Polymers: Is a large molecule, or macromolecule composed of many repeated subunits. The
majority of manufactured polymers are thermoplastic. This property allows for easy
processing and facilitates recycling.
Prosumer: Is part of an emerging dialogue about how technology serves people. While the
consumer is often a passive recipient of technology, a prosumer may help to shape the use of
technologies or otherwise get involved in the products and services provided to them,
because that individual has a certain professional role in the process.
Tensile strength at yield: Is the tensile stress level at which the rise in the stress-strain curve
equals zero for the first time.
Thermal annealing: Commonly used for metals but lately also being used for a postprocessing
treatment of polymers which consists of submitting a sample to a controlled temperature for
a limited time.
Thermal transition: The changes that take place in a polymer when its heated. The melting of
a crystalline polymer and the glass transition are examples of thermal transition.
ABSTRACT
Additive Manufacturing (AM) development is gaining momentum growing both at a high and
low end, the first one involves expensive high-powered energy sources and complex scanning
algorithms where the produced parts features material properties that are equivalent to their
traditionally manufactured counterparts. At the low end there can be found desktop-scale 3D
printers which are eliminating cost barriers and resulting in a sort of democratized
manufacturing where enthusiast users also called prosumers or makers are now able to
interact with a technology that, in the past, was relegated to large manufacturing firms.
Fused Deposition Modeling (FDM) is one of the most popular desktop-scale 3D printers due
to low cost of the machines without sacrificing quality, the large variety of filaments available
on the market that allows to reach different purposes, the relatively small size of the
machines, their efficiency and user-friendly interaction.
The opportunity for this project relays on the popularization of desktop-level AM technology
resulting in a culture of “Do it Yourself” and a growing community driven by shared
knowledge. Where it is revealed the opportunity of contributing with an international
community of volunteers that design and develop prosthesis for children from low income
resources families. In this way the project focuses on the understanding of potential post-
processes based on the FDM technology.
For the experiment it was carried out a Differential Scanning Calorimetry and uniaxial
mechanical test with the purpose of assessing the mechanical properties and thermal
annealing effect on the object made of PLA produced by FDM technology.
Key words: annealing, tensile test, differential scanning calorimetry, fused deposition
modeling, prosthesis, Poly-lactic Acid, semi-crystalline polymer.
RIASSUNTO
Lo sviluppo della produzione baste sull`Additive Manufacturing (AM) è in crescita sia al livello
altamente professionale sia a quello più artigianale, il ambito professionale riguarda al uso di
macchine che hanno bisogno di risorse energetiche elevate e utilizzano algoritmi complessi
ma che alla fine forniscono prestazioni simili a quelle di prodotti ottenuti con i processi di
manifattura tradizionale. Al livello meno professionale si trovano delle stampanti 3D
progettate per piccoli spazi di lavoro che stanno anche eliminando barriere di costo. In
questo caso si tratte di una produzione democratizzata dove gli utenti appassionati qualche
volta chiamati “prosumer”, sono ora in grado di interagire con una tecnologia che, in passato,
è stata relegata a grandi aziende di progettazione e produzione.
Fused Deposition Modeling (FDM) è uno dei più popolari processi di stampa 3D desktop
grazie a basso costo delle macchine senza sacrificare la qualità, grande varietà di filamenti
disponibili sul mercato che consente di raggiungere diversi scopi, dimensioni relativamente
ridotte delle macchine, efficienza e interazione user-friendly.
L'opportunità di questo progetto si basa sulla divulgazione della tecnologia di produzione
additiva a livello desktop, che si traduce in una cultura di "Fai da te" è in una comunità in
crescita guidata da conoscenze condivise. Dove si scopre la opportunità di contribuire con
una comunità internazionale di volontari che progettano e sviluppano protesi per bambini da
famiglie a basso reddito. In questo il progetto si concentra sulla comprensione di potenziali
processi di post-elaborazione basato su un prodotto fatto con la tecnologia FDM.
Sono estate condotti misure di calorimetria differenziale a scansione e prove meccanica di
trazione uniassiale a lo scopo di valutare l’effetto di una ricottura sulla struttura de un
oggetto fatto da acido polilattico (PLA per il suo acronimo in inglese) e le sue proprietà
meccaniche.
Parole chiave: ricottura, test di trazione, scansione differenziale di calorimetria, produzione
additiva, protesi, acido polilattico, polimero semicristallino.
13
1. Introduction
The project starts inside the university classroom as part of the Master Degree in Design &
Engineering, programme that results from the cooperation of three faculties from Politecnico
di Milano: Design, Mechanical Engineering and Material Engineering and Nanotechnology;
along with two professors from Politecnico di Milano, one from the design department with a
background on desktop-level additive manufacturing and the other from the material
engineer department with a vast experience in polymeric materials and experimental
analysis; was made the choice of applying additive manufacturing with an experimental
approach.
The opportunity for this project relays on the popularization of desktop-level additive
manufacturing (AM) technology resulting in a culture of “Do it Yourself” and a growing
community driven by shared knowledge. Where it is revealed the opportunity of contributing
with an international community of volunteers that design and develops prosthesis for
children from low income resources families. In this way the project focuses on the
understanding of potential post-processes based on the FDM technology.
1.2 Main goal
The main goal of the project is to study the thermal annealing effect of an object made of Poly-Lactic Acid (PLA) produced by Fused Deposition Modeling (FDM) technology.
1.3 Methodology
Once the main goal is defined the following workflow will allow to achieve it.
1. Definition of an experiment taking information from two main sources, the prosumer
community and scientific journals.
2. Set a preliminary test to define the sample test geometry and main testing conditions.
3. Study the effect of thermal annealing on the crystallinity degree of a PLA object
produced by FDM technology.
4. Study the effect of thermal annealing on the apparent modulus and tensile strength
of a PLA object produced by FDM technology.
14
1.4 Project grounds
The 3D printing revolution is occurring both a
high end and a low end. One end of the
technology spectrum involves expensive high-
powered energy sources and complex scanning
algorithms. The other end is focused on reducing
the complexity and cost of a well-established AM
process to bring the technology to the masses.
Major advances will continue to be made both at
the high end with direct metal processes that
aim for end-use products as the most noticeable
example; at low end with the desktop-level
machines that will continue to improve while the
cost declines. This 3D printing revolution has
been fed by the idea of sharing as many
technical aspects as possible, this revolution has
been growing thanks to the creation of online
communities that were rapidly feed by
enthusiasts from all around the world and went
beyond the technicalities by exploring more
capabilities and applications on their daily lives.
This community is being called in different ways:
thinkers, makers or prosumers, terms that come
from the “do it yourself” (DIY) culture. Along
with the 3D printing revolution many individuals
are now involved in this culture, phenomenon
that can be seen from the way digital platforms
are used. Several YouTube channels feature
some of the most informative and entertaining
content about 3D printing, addressing subjects
such as 3D printing tutorials, tips and tricks or
product reviews. The major players up until now
are: Thomas Sanladerer (117.600 subscribers),
3D Printing Nerd (151.400), Maker`s Muse
(203.500), I Like to Make Stuff (1’491.000
subscribers) and many more who continue little
by little setting a solid path towards the idea of
shared knowledge.
Figure 1. Shared knowledge phenomenon
15
Other common platforms for the diffusion of 3D printing culture are the ones that act as a 3D
model repository, being “thingiverse.com” the most popular, but with over 20 new websites
currently available ready to offer as much “things” to print as possible.
But none of these 3D models can be created without a software tool which can be found
from completely open-source to licensed products. Users can now use their Computed Aided
Design (CAD) skills with open-source software such as FreeCAD or LibreCAD or even use
systems where the users can interact via a web browser or their mobile phone apps like
Thinkercad or Onshape.
One particular community that has taken the best of shared knowledge, DIY culture and 3D
print all together with a strong social awareness is “e-Nable” a network of volunteers that
design and produce human prosthesis using 3D printing. They support the maker movement
by bringing together designers, engineers, physicians, 3D print enthusiasts, families and
amputees, to create, innovate, re-design and share 3D-printable prosthetics. This global
community of volunteers who are donating their time, talent and resources is able to do so
thanks to the accessibility of 3D models repositories, forums, instructional videos, manuals,
etc. Thus allowing them to produce open-source, low cost prosthetic devices using Fused
Deposition Modeling (FDM) technology which is one the most popular desktop-level 3D
printers giving the low cost and small size of the machines, variety of filaments found the
market, efficiency and user-friendly interaction.
Giving the great diffusion of this initiative there are different prosthesis shapes, post
processing alternatives or methods of assembly. This project is focused on the potential
capabilities of thermal annealing post-process to improve the material mechanical behaviour.
This process usually apply to metals, is also successfully used on semi-crystalline polymers.
Thermal annealing is a post-process commonly used on injection-moulded polymer-based
components in order to enhance the materials tensile and impact strength. There are several
researches reporting the effect of thermal annealing on the polymer structure and its
mechanical behaviour, but few ones about the annealing effects for 3D printed components.
Thus arise an opportunity for studying how to improve certain mechanical behaviour for an
object produced by the same technology this prosthesis are produced. Since the goal of “e-
Nable” community is to reach as many volunteers as possible and let them create these
devices on their own, why not let them enlarge their knowledge by showing the effect of a
particular post-process that might extend the prosthetics service life?
LITERATUREREVIEW
Additive ManufacturingDesktop-level 3D Printers
Fused Deposition Modeling (FDM)Open Design MovementPost-processing for FDM
Thermal Annealing
17
2. Literature Review
A literature review is a text of a scholarly paper,
on the current knowledge about a particular
topic including substantive findings, as well as
theoretical and methodological contributions.
Literature reviews are secondary sources, and
do not report new or original experimental
work and are a basis for research in nearly
every academic field. [1]
For the development of this project there was
used a systematic approach in order to gather
information regarding field, technology and
sources of interest and having as a base the
general and specific objectives already listed in
the previous chapter.
It is important to understand about all the
relevant fields included in the project: FDM
machines and its diverse filaments, thermal
treatment for polymer, Poly-Lactic Acid (PLA)
filament, open source prosthetics movement,
material post-processing, direct scanning
calorimetry (DSC) and material crystallization.
See list on Figure 2.
1. http://www.academicwritingtutor.com/uses-analysis-rhetorical-analysis-article-analysis-literature-review/
Figure 2. Literature review workflow
18
2.1 Additive Manufacturing
Additive manufacturing is the
formalized term for what used to be
called rapid prototyping and what is
popularly called 3D Printing. AM is a
group of emerging technologies that
create objects from the bottom-up by
adding material. The AM process
begins with a 3D model of the object,
usually created by computer-aided
design (CAD) software or a scan of an
existing artifact.
Specialized software slices this model
into cross-sectional layers, creating a
computer file that is sent to the AM
machine. The AM machine then
creates the object by forming each
layer via the selective placement (or
forming) of material. [2]
There are different stages of the AM
process that can be summarise in eight
generic steps (Figure 3) and can be
classified in seven process categories
(Figure 4).
2. Additive Manufacturing Technologies. Ian Gibson, David Rosen, Brent Stucker. Second Edition 2015, Springer
Figure 3. 8 Generic steps for the AM process
Additive Manufacturing Technologies. I. Gibson, D. Rosen, B. Stucker
19
Figure 4. Process categories for AM
20
Fundamentally, the development of AM can be described in four primary areas. The additive
manufacturing wheel in Figure 5 depicts these four key aspects of additive manufacturing. [3]
Figure 5. The AM wheel depicting four major aspects of AM
Input: Electronic information requires to
describe the object in 3D. There are two
possible starting points – a computer or a
physical model.
Method: While there are more than 40
vendors for AM systems, the method
employed can be classified as it shown on
the figure 5.
Material: The material can come in solid
or liquid.
Applications: Most of the AM parts are
finished or touched up before they are
used for their intended applications.
2.1.1 Limitations
• Limited for mass production purposes.
On average, AM processes are capable of creating a 1.5 inch cube in about an hour.
Whereas an injection molding machine is capable of making several similar parts in less
than a minute. This AM process limitation is valid only for the production of several
thousand of a product, since tooling must be created for each part one wishes to produce
by injection molding.
• Need for better materials.
Most AM processes use plastic materials that are not well characterized, and the
performance of the relevant products are lower traditionally manufactured counterparts.
Further, in some AM processes, part strength is not uniform—due to the layer-by-layer
fabrication process, parts are often weaker in the direction of the building.
3. 3D Printing and Additive Manufacturing: Principles and Applications. Chua. Leong. World Scientific 4th edition
21
2.1.2 Advantages
The benefits of AM systems are immense
and can be broadly categorised into direct
and indirect ones.
• Direct benefits
Possibility to experiment with physical
models of any complexity in relatively short
time.
Increased part complexity that cannot be
produced by any other means.
The manufacturer can reduce the labour
content of manufacturing, since part-
specific setting up and programming are
eliminated, machining or casting labour is
reduced, and inspection and assembly are
minimised as well reducing material waste.
• Indirect benefits
Reduced time-to-market, resulting in
reduced risk as there is no need to project
customer needs and market dynamics
several years into the future.
Increasing the diversity product offerings
and pursue market niches which are too
small to justify due to tooling cost (including
custom and semi-custom production).
Large availability of products more closely
suited consumer needs. Firstly, the is a
much greater diversity of offerings to
choose from. Secondly, one can buy (and
even contribute to the design of) affordable
built-to-order products. [4]
4.https://3dprintingindustry.com/3d-printing-basics-free-beginners-guide/history/
Figure 6. AM applications
22
2.2 Desktop-level 3D printers
Before talking about desktop-level 3D printers
is important to take a look to the history of this
technology and see for example how the
expiration of older patents has led to an
explosion of development of an array of low-
cost personal 3D printers.
This technology dates back to the 80`s with the
first patent issued to Charles Hull for
stereolithography apparatus who will lately
found one of the largest and most prolific
organizations operating in the 3D printing
sector today: 3D Systems Corporation.
Throughout the 1990’s and early 2000’s a host
of new technologies continued to be
introduced, still focused wholly on industrial
applications and while they were still largely
processes for prototyping applications.
During the mid-90`s, the sector started to
show signs of distinct diversification with two
specific areas of emphasis that are much more
clearly defined today. First, there was the high
end of 3D printing, still very expensive systems,
which were geared towards part production
for high value, highly engineered, complex
parts. This is still ongoing, but the results are
only now really starting to become visible in
production applications across the aerospace,
automotive, medical and fine jewellery sectors,
as years of R&D and qualification are now
paying off. A great deal still remains behind
closed doors and/or under non-disclosure
agreements (NDA). [5]
5. https://www.researchgate.net/publication/289522663_3D_Printing_Pharmaceutical_Manufacturing_Opportunities_and_Challenges
Figure 7. Timeline of 3D printer machines
23
At the other end of the spectrum,
some of the 3D printing system
manufacturers were developing and
advancing ‘concept modellers’, as they
were called at the time. Specifically,
these were 3D printers that kept the
focus on improving concept
development and functional
prototyping, that were being
developed specifically as office- and
user-friendly, cost-effective systems.
The prelude to today’s desktop
machines.
But it wasn’t until January 2009, when
the patent of the FDM technology
expired, that the first commercially
available 3D printer was offered for
sale, it was the RepRap kit. This project
started in England in the University of
Bath and consist on developing a low-
cost 3D printer that can print most of
its own components, but now is made
up of hundreds of collaborators
worldwide. MakerBot company -based
on New York City- builds on the early
progress of the RepRap project which
aimed to help the open-source 3D
printer movement. [6]
The idea of sharing any technical
aspect regarding how to design the
machine, how to build and operate it,
how to fix it or improve several
aspects, growth thanks to the creation
of online communities that were
rapidly feed by enthusiasts from all
around the world.
6. "Reprap the replicating rapid prototyper". Jones, R.; Haufe, P.; Sells, E.; Iravani, P.; Olliver, V.; Palmer, C.; Bowyer, A. (2011)
Figure 8. The RepRap initiative and MakerBot team
24
2.3 Fused Deposition Modeling (FDM)
Objects created with an FDM printer start out as computer-aided design (CAD) files. Before
an object can be printed, its CAD file must be converted to a format that a 3D printer can
understand — usually .STL format. FDM printers use two kinds of materials, a modeling
material, which constitutes the finished object, and a support material, which acts as a
scaffolding to support the object as it's being printed.
During printing, these materials take the form of plastic threads, or filaments, which are
unwound from a coil and fed through an extrusion nozzle. The nozzle melts the filaments and
extrudes them onto a base, sometimes called a build platform or table. Both the nozzle and
the base are controlled by a computer that translates the dimensions of an object into X, Y
and Z coordinates for the nozzle and base to follow during printing.
In a typical FDM system, the extrusion nozzle moves over the build platform horizontally and
vertically, "drawing" a cross section of an object onto the platform. This thin layer of plastic
cools and hardens, immediately binding to the layer beneath it. Once a layer is completed,
the base is lowered to make room for the next layer of plastic. [7]
Figure 9. FDM technology schematic
https://www.additively.com/en/learn-about/fused-deposition-modeling
7. https://www.livescience.com/39810-fused-deposition-modeling.html
25
2.3.1 Types of FDM machines
Since 2009 when there was commercially available a desktop 3D printer, designers, makers,
thinkers and hobbyists have developed different variations for the molten filament
technology, resulting on an offer of some variations. The principle of this machines is the
movement whether the nozzle or the printing bed on the X, Y and Z axis, in this way there can
be founded cartesian, delta, polar or SCARA (Figure 10).
Figure 10. Types of FDM machines
2.3.2 Software tools
There can be said that there are four steps on the path from concept to printed object: the
idea, the digital model, the tool path, and the final print and three layers of software – CAD,
CAM, and “client” – bridge the gaps.
• Computer Aided Design (CAD) Software: Even if the model is scanned from a real object, the user might want to adjust in a CAD program. There are many file formats for 3D models, but almost all 3D printing CAM software expects STL. Unfortunately, not all STL files are printable.
26
• Slicer software: “Slicing” programs translate 3D models into physical instructions for the
printing robot, which can be visualized as a tangle of “tool paths” the print head will
follow to fill in the model`s shape, using the most common output industry-standard G-
code files.
• Printer Control / Client: Is the printer`s control panel. It sends CAM instructions and
provides an interface to control printer functions. As CAM and client programs advance,
they are increasingly being combined into single-interface printing environments. [8]
Table 1. CAD Software examples
Make magazine, special issue: 3D printer buyer´s guide 2014
Program Developer Since Price Notes
Blender
Foundation1999 Free
Renowed, powerful open-source
surfacee-modeling program. Huge
community. Steep learning curve.
Trimble 2000 $0/$590 Pro
Good balance of usability and power.
Built-in "3D Warehuse" model sharing
feature has large community. No native
STL support
Juergen
Riegel,
Werner Mayer
2002 Free
Very powerful, engineering-focused
open-source parametric CAD platform.
Feature set competitive with pro-line
tools.
Clifford Wolf,
Marius Mayer2009 Free
Models are developed by textualscripting
rather thna virtual interaction.
Jon Hirschtick,
John
McEleney
2015 $0
Use model Software as a Service (SAAS).
Use cloud computing, compute-intensive
processing and rendering performed on
Internet-based servers.
MODELING / CAD
27
Table 2. Slicing Software examples
Make magazine, special issue: 3D printer buyer´s guide 2014
Table 3.Printer control or “client” software examples
Make magazine, special issue: 3D printer buyer´s guide 2014
8. Make magazine, special issue: 3D printer buyer´s guide 2014
Program Developer Since Price Notes
Alessandro
Ranellucci2011 Free
Generates G-code from 3D CAD files (STL,
OBJ)
David Braam /
Ultimaker2012 Free
Integrated CAM/client for Ultimaker and
some RepRap-type machines. Fast
CuraEngine slicer run as a background
process. Exports G-code
Bob Sampaio,
Rubens Pereira,
Tiago Soncini
2015 $149
allows you to optimize a model for 3D
printing and to troubleshoot printing.
And it is an ultra-fast slicer
Craftunique 2015 Free
Open multiple .stl, .obj files. Load/save
.gcode generated from other programs.
Gcode toolpath traversal
SLICING / CAM
Program Developer Since Price Notes
ReplicatorG MakerBot 2008 FreeOriginal MakerBot printer client.Largely
superseded by MakerWare
Repetier-Host Kliment Yanev 2011 Free
Best know of three utilities in popular
"Printum" suite. Requires Phyton. Fiddly
installation
Octoprint Gina Hausse 2011 Free
Web-based printer interface offering
"anywhere" control, monitoring, and G-
code visualization.
Afinia 3D Afinia 2012 $0Integrated CAM/client for Afinia/Up
printers. No export
PRINTER CONTROL / CLIENT
28
2.3.3 Printing Parameters
The majority of FDM 3D printed parts are not printed solid. Printing solid parts requires high
amounts of material and long print time resulting in high costs. To optimise the printing
process most parts are printed with solid shells and filled with infill. Shells and infill play an
important role on the quality, appearance and function of FDM printed parts. [9] Other
parameters can be edited depending on the “slicer” software capabilities, Figure 11 depicts
seven of the most common parameters available for editing.
1. Contour width: refers to the width of the molten filament depositing
2. Contour to contour air gap: after the molten filament run is finish and the next run is
about to start there can se set an air gap which can be adjusted smaller or larger
3. Air gap: the space between two deposited filaments
4. Raster width: can be adjusted smaller or larger is the result of a combination of nozzle
and filament diameter, printing speed and molten material extrusion speed
5. Raster angle: is the angle in which the selected pattern will be deposited
6. Number of contours: defined also as the shell or wall thickness
7. Perimeter to raster air gap: is the gap between the deposited filament from the raster
that is forming a pattern as an infill process and the perimeter of the object
Figure 11. FDM main printing parameters
9. https://www.3dhubs.com/knowledge-base/selecting-optimal-shell-and-infill-parameters-fdm-3d-printing
29
2.3.4 Poly-Lactic Acid (PLA) filament
Figure 12. Stack of FDM filament
http://3dinsider.com/abs-vs-pla-shootout/
Another vital element of the FDM technique is the use of a spool of polymeric filament that
will be heated by a resistor on the nozzle and pulled down via a stepper motor. Plenty of
materials are currently used with different temperature ranges, degree of recyclability,
mechanical and chemical properties, colors, prices.
Acrylonitrile Butadiene Styrene (ABS) and Poly(lactic acid) (PLA) are the go-to plastics for
most consumer-grade 3D printers. New types of plastic, blends of plastics with various
additives, and grades of plastic formulated specifically for 3D printing are appearing all the
time. With simple tools it´s even possible to turn pellets or other plastic scrap into usable
filament right in the users office. [10]
PLA (Polylactic Acid) is one of the two most commonly used desktop 3D printing filaments. It
is the "default" recommended material for many desktop 3D printers. PLA is useful in a broad
range of printing applications, has the virtue of being both odorless and low-warp, and does
not require a heated bed. PLA filament is made from annually renewable resources (corn-
starch) and requires less energy to process compared to traditional (petroleum-based)
plastics. Outside of 3D printing, PLA plastic is often used in food containers, such as candy
wrappers, and biodegradable medical implants, such as sutures. [11]
Since there are different types of PLA, in Table 4 and Table are briefly described both for
regular PLA and High Temperature, some specifications for the commercial filaments and
their capabilities.
10. Make magazine, special issue: 3D printer buyer´s guide 2014 guide 2014
11.https://www.matterhackers.com/3d-printer-filament-compare
30
Table 4. Regular PLA commercial variations
https://filaments.ca/pages/temperature-guide#cfpla
Name Print temp. - speed Comments
PLA (Original &
Creative Series)215°C - 235°C
Can be printed both with and without a heated print bed. Heated print: recommended
to set temperature to: 60°C - 80°C
First layer usually 5°C - 10°C higher than subsequent layers.
Glow in the dark use 5°C - 10°C higher.
Sticks well to Blue painter's tape.
Sticks well to extra strong hair spray.
Soft PLA 210°C - 220°C
Print slow. Reccomended print speed:10 - 20mm/s.
Reduce retraction. Build plate, recommended: blue masking tape with a thin layer of
glue stick on top.
Print bed temperature to approximately 60°C - 100°C.
Direct feed printer recommended.
Use a bit of lubricant (like WD40) for bowden tube, although bowden extruders are not
ideal for printing flexible filaments.
Make sure filament is clean (free from hand grease).
Performs best in printers with direct-drive extruders.
Thermochrome
PLAAprox. 210°C
Follow same recommendations as regular PLA.
If printed part is < 29°C it will have an opaque anthracite Grey color.
If printed part is > 29°C it will have a translucent / White color.
EasyFil 2.85mm
PLA210°C - 220°C
Can be printed both with and without a heated print bed. Heated print: recommended
to set temperature to: 35°C - 60°C.
Sticks well to blue masking tape and extra strong hairspray
Print speed: 40 - 80 mm/s
Carbon Fiber
Reinforced PLA190°C - 230°C
Processing is comparable to standard PLA.
No heated bed required.
Due to increased brittleness, process may be less consistent on smaller nozzles and/or
bowden type machines.
Nozzle size: 0.35mm - 0.5mm
High Temperature
PLA190°C - 230°C
Processing is comparable to standard PLA.
No heated bed required, though a heated bed may help crystallize the material after
printing and make oven soaking unnecessary for some parts.
Nozzle size: 0.25mm - 0.5mm
Good results achieved when printing using a .5mm nozzle and direct-drive spring
loaded pinch-roll style extrusion head. Layer adhesion was excellent and warpage was
low.
REGULAR PLA FILAMENT
31
Table 5. High Temperature PLA commercial offer
Name Print temp. - speed Comments Link
Raptor series PLA - high
performance 3D filament210°C - 230°C
No deformation up to 125 ºC
Easy Annealable Process to increase Heat
Deflection Temperature (HDT)
Tensile strength
Bake it in the oven for 5-10min at 100 ºC to
get a better heat resistance
https://www.makergeeks.com/coll
ections/raptor-series-
pla/products/raptor-series-pla-high-
performance-3d-filament-vivid-red-
175mm-1kg
Protopasta: Matte Fiber HTPLA 190°C - 230°C
Can be heat treated to retain more stiffness to
higher temperatures. Dimensional stability is
improved compared to HTPLA without fibers.
The plant-based fibers improve adhesion of
glues and coatings. No Heated Bed Required.
Does not require a wear resistant nozzle.
https://www.proto-
pasta.com/collections/high-
performance-htpla/products/matte-
fiber-htpla-red
rigid.ink: PLA 180°C
Bed temperature: 0-45 °C
Density: 1.24g/cc
Glass Transition Temp: 55-60°C
Tensile strength: 8,383 psi (57.8MPa)
Annealing: 70°C for around 30mins
Adhesives: Super-Glue, Acetone, Epoxy Resins
Polishing: Cannot be acetone smoothed,
needs sanding and polishing.
Painting: Acrylic, cellulose or oil paints
https://rigid.ink/collections/pla-
filaments/products/abs-1-75mm-3d-
filament-0-03mm-tolerance-1kg-
roll
ColorFabb: PLA/PHA195°C - 220°C at 40-
100 mm/s
Blend of PLA/PHA which results in a tougher
and less brittle PLA 3D printing filament. PHA
(polyhydroxyalkanoate) is like PLA a bio-
polyester, making this blend 100%
biodegradeable. Glass Transition Temp: 55°C
www.colorfabb.com
HIGH TEMPERATURE PLA FILAMENT
32
2.4 Open design movement
There are several terms related with a global
knowledge sharing that have being gather throughout
the years: open design, open-source software and
hardware, open collaboration, free software, etc; all of
them aiming for a common goal which is to develop
physical products, machines, software and/or systems
through use of publicly shared design information. [12]
The open-design movement currently unites two
trends. On one hand, people apply their skills and time
on projects for the common good, perhaps where
funding or commercial interest is lacking, for
developing countries or to help spread ecological or
cheaper technologies. On the other hand, open design
may provide a framework for developing advanced
projects and technologies that might be beyond the
resource of any single company or country and involve
people who, without the copyleft mechanism, might
not collaborate otherwise.
Nowadays there are different open source projects
regarding 3D printed prosthesis.
• e-Nable: A global network of volunteers using 3d
printing to give the world a "helping hand."
Website: http://enablingthefuture.org
• Open Biomedical initiative: A global non-profit
initiative created to support the traditional
biomedical field and focused to collaboratively
design, develop and distribute open source 3D
printable health and accessibility supports
Website: http://www.openbiomedical.org/
• Open Bionics: Create affordable bionic hands for
amputees, researchers or hobbysts.
Website: https://www.openbionics.com
12. https://en.wikipedia.org/wiki/Open_design
Figure 13. Open Bionics robotic prosthesis
33
2.4.1 e-Nable community
Is a network of passionate volunteers using 3D
printing to give the World a "Helping Hand.”
They support the Maker Movement in
mechanical hands by bringing together
designers, engineers, physicians, 3D print
enthusiasts, families and amputees, to create,
innovate, re-design and share 3D-printable
prosthetics.
This project started between a professor from
Rochester Institute of Technology and a South
African carpenter who lost some of his fingers
on a shop accident. After professor Schull saw
the story of a carpenter who accidentally cut
off his fingers on a workshop and then was told
that partial hand prosthetics are really
expensive and hard to come by, he decided to
find a solution by himself. He went to google
and found his way to Ivan Owen a puppet and
prophet maker based in Washington state who
had made a big mechanical hand controlled by
fingers as a prophet for a movie. Together they
worked for over a year designing the hand and
eventually come upon a way of 3D printing this
device, they recognized that this device will be
helpful not just to people who chopped of
their fingers but also for people with
congenital syndromes, so they make the
design available online.
At this point professor Schull found this
initiative and decided to give it a push and ask
from makers all over the world -via youtube
comments- to develop these devices and
share them to those in need. Little by little
hundreds of volunteers with 3D pritners
started to appear on a network managed by
Prof. Schull, in this way if a kid needs to access
a hand prosthesis his family should simply
check Prof. Schull map and find someone near
them who can make it. [13]
Figure 14. Robohand and e-Nable community
34
Statistics state that 1 in 1500 children
are born missing fingers or hands and
there are many around the world who
lose them due to war, disaster or
disease. Because children grow so
quickly, there are few prosthetic devices
available to them and those that are
available – can cost thousands of dollars
and many families in the world cannot
afford them.
Now thanks to 3D printing and e-NABLE,
children as young as 3 years old who are
missing fingers or hands, are able to
obtain devices that will allow them to
do things many people take for granted.
This community has another goal that
consists in teaching families how to
create these devices on their own, in
this way the more this knowledge is
spread, the more hands can be created.
To date, e-Nable community have
created nearly 2000 free “body
powered” 3D printed devices in over 40
countries and the numbers grow daily.
Those prosthesis are not only growing
on numbers but also on diversity, as
more designers and engineers join the
community the types of devices are
getting substantial variations in order to
cover more medical pathologies.
13. https://www.youtube.com/watch?v=XQ8tPOqN7WE
Figure 15. e-Nable community
35
2.4.1.1 Weak points of 3D printable prosthesis
One of the main features of the wrist power (Figure 16) prosthesis from e-Nable is the
attachment to the kid arm, the gauntlet count with a couple of slots on which a Velcro strap
is adjusted. Unfortunately this slot (a very common solution for attaching the prosthesis to
the missing limb as seen on Figure 17) represents a weak point because is a feature the user
is constantly adjusting. As a result, the maker community has given solutions such as: printing
the gauntlet completely flat and later on thermoforming it by submerging the desirable area
to fold (Figure 18).
Figure 16. e-Nable wrist power devices
http://enablingthefuture.org/wrist-powered/
Figure 17. Prosthesis using a slot on the gauntlet component
36
Figure 18. Gauntlet produced flat-shape wise
https://www.youtube.com/watch?v=BihhKHjguZY
Figure 19. Gauntlet adjusted with Velcro (detail)
37
2.5 Post-processing for objects produced with FDM
Since 2009 when there was commercially available a desktop 3D printer, designers, makers,
thinkers and hobbyists have explored not different configurations for the FDM machines and
also the filaments which has an application spectrum ranging from aesthetic to functional.
There has been produced filaments infused with carbon nanotubes or glass fibers with the
aim of strengthening the manufactured component, there are also transparent filaments,
elastic, biodegradable or designed to withstand high temperatures.
With the evolution of filament and the development of post-processing techniques for the
objects obtained with FDM technology has come hand-in-hand with same parity of purposes:
aesthetic or functional. Depending on the type of filament there can be done basic post-
processing like: sanding, polishing, coating, painting or some more complex ones like, metal
plating, vapor smoothing, dipping or annealing.
2.5.1 Aesthetic purposes
FDM parts often depend on aesthetics or appearance making post processing an important
stage in the production of FDM parts.
Figure 20. Post-processing for 3D printed objects (aesthetic purposes)
https://www.3dhubs.com/knowledge-base/post-processing-fdm-printed-parts
38
2.5.2 Functional purposes
A persistent issue with 3D printed parts is strength and durability, they are not as strong as
injection molded parts, nevertheless giving the evolution of this technology towards
domestic use and a sort of democratization many people are now using 3D printed parts in
production scenarios, mainly due to various techniques for strengthening parts.
Figure 21. Post-processing for functional purposes
2.6 Thermal Annealing
Originally used in metallurgy to increase the strength of metal objects. Annealing is one of several “heat treatments” that are used to change the physical properties of metal without changing the metal’s existing shape. [14] The fundamentals of the annealing process have been adapted to the plastics field. In the
plastics industry, annealing is the process of heating a plastic part up to half the polymer
melting temperature for a moderate period before cooling it down to room temperature.
Fused Deposition Modeling (FDM) involves heating the printing material so that it can be extruded. Once extruded, the material then cools to form the printed object. Plastic is a fairly poor conductor of heat. This means that heated plastic tends to cool unevenly. This uneven cooling introduces stress into a printed object.
14. https://en.wikipedia.org/wiki/Annealing_(metallurgy)
39
Typically, with any material internal defects are evident and create internal stresses which weaken its overall strength. To minimize the effect of these grains, annealing can be done to soften the material, relax the grain structures causing the internal stresses, and allow new, strain-free grains to form as replacements. At microscopic level, the structure of the plastic is unorganised and rather amorphous. Heating the plastic, extruding and cooling it reorganizes this structure into a more organised crystalline form. These crystals tend to be large, broadly similar to those that exist in metal after initial heating and cooling. [15]
Also, when the polymer approaches or reaches its
glass transition temperature, the molecular chains
have enough energy to enter into a rubber
amorphous state. In this state, they are able to
rotate, move, stretch, etc. This releases some of the
tensile and compression forces that resulted from
uneven cooling. Both of these things, in turn, makes
the plastic stronger, stiffer and more resistant to the
stresses that cause failure.
2.6.1 Review of PLA annealing methods
Current methods for annealing 3D printed
components can be found mostly on makers digital
platforms (patreon.com, makerweeks.com), video-
sharing websites (youtube.com), development digital
platforms (GitHub), and other platforms with
contents of interest for the desktop 3D print
community (rigid.ink, all3dp.com).
15. https://rigid.ink/blogs/news/how-to-anneal-your-3d-prints-for-strength
Figure 22. Crystallization schematic
40
2.6.1.1 Oven bake method 1
Youtuber Tomas Sanladerer designed a series of
experiments to evaluate the effect of annealing on
different FDM 3D printed components made of
PLA and other polymers. [16]
Heat treatment (oven settings): 110 ºC for 60
minutes. PLA Glass transition temperature (Tg): 60
- 65 ºC; PLA melting temperature (Tm): 173 - 178
ºC. Printing two test pieces (unheated and heated)
and load them until they break and to have a
glimpse of the plastic yield strength.
Temperature stability: Giving the few technological
resources this variable was evaluated from a non-
scientific approach and therefore the results were
qualitative values. He poured boiled water over the
printed components and saw if they kept their
shape.
Stiffness: During the load test for the mechanical
strength he visually evaluated how much the part
deformed under the load before breaking.
Results for the High Temperature PLA (HTPLA)
(Protopasta): Annealed specimen scored the same
load strength of the unannealed one and but a
20% increase in stiffness was observed. The
temperature stability of the annealed part was
significantly higher than the untreated one.
Results for the PLA: Both strength and stiffness
increased after the thermal annealing respectively
of about 40% and 25%. Temperature stability was
as good as for the HTPLA part. So as long as one
can compensate for the shrinkage and some
warping, a heat treatment significantly seems to
improve the stiffness, tensile strength and gives
excellent heat resistance.
16. Tomas Sanladerer channel - https://www.youtube.com/watch?v=YcQHbaVeD7I
Figure 23. Oven bake method 1 (overview)
41
2.6.1.2 Oven bake method 2
Youtuber Stefan from “CNC Kitchen” channel designed a series of experiments to find out the
temperature resistance of annealed PLA, PETG and ABS. [17]
The oven method was chosen over boiling water bath because the parts don`t get in touch
with water that can potentially degenerate the material (consider also PLA absorbs water). If
the parts are small (100x10x3 mm) 30 minutes should be enough. Temperature was 110 ºC
(above Tg, below Tm for PLA), and the temperature in the oven was increased in 10ºC steps
and held it for 5 minutes.
Results: The HTPLA started softening at 55ºC, at 60ºC standard PLA fall out, the annealed
specimens on the other hand were fine; at 80ºC both PETG specimens started to soften
significantly, as well as the unannealed HTPLA (from 3dk Berlin); at 110ºC both ABS
specimens failed as expected; at 160ºC the standard annealed PLA started to soften; the
annealed HTPLA, performed well at 180ºC (Figure 24).
A second experiment with other commercial PLA specimens was carried out with similar
results as the previous experiment. In summary unannealed PLA was not suitable for high
temperatures and failed around 60ºC, the use of special high temperature filaments (3dk
Berlin and Multec PLA-HT) also didn`t work hen unannealed, but after the thermal treatment
(shrinkage happened) they perform better. All of the specimens shrank in length from a
negligible 0.2% for HTPLA to almost 8% for black PLA, they also shrank in width and grew a
little on their thickness.
Figure 24. Oven bake method 2 findings
https://www.youtube.com/watch?v=vLrISrkg46g
17. CNCKitchen channel - https://www.youtube.com/watch?v=vLrISrkg46g
42
2.6.1.3 Boiling water method
Youtuber Joe Mike Terranella applied a thermal treatment to a spool holder (assembly of 3
components: 1 arm and 2 threaded shafts) by submerging the parts on boiling water at
200ºC for 10 minutes. After letting the parts cool down for 20 minutes. [18]
The results were qualitative: he quickly tried to bend the parts and manually screw back the threated ones. In summary, the parts seemed to improve their stiffness and the threads worked well together. The filament used was the high-performance raptor PLA. This filament was designed to be annealed, manufacturer recommends baking it in the oven for 5-10 minutes at 100 ºC.
Figure 25. Boiling water method
https://www.youtube.com/watch?v=WmTGU3r53VU&t=4s
18. Joe Mike Taranella channel https://www.youtube.com/watch?v=WmTGU3r53VU&t=4s
43
2.6.1.4 Sous vide method
Is a method of cooking in which food is vacuum-sealed in a plastic pouch and then placed in a
water bath or steam environment for longer than normal cooking times (usually 1 to 7 hours,
up to 48) at an accurately regulated temperature much lower than normally used for
cooking, around 55 to 60 °C for meat.
The intent is to cook the item evenly, ensuring that the inside is properly cooked without
overcooking the outside, and to retain moisture. Justin Lam performed a heat treatment with
this kitchen technique and gadget designed by himself. [19]
He assessed the effect of annealing on the maximum load reached. The experiment consisted
on using a camera to capture the scale measurement at peak force of a sample being pressed
by a column drill manually moved.
Figure 26. Sous vide method
19. Justin Lam - http://justinmklam.com/posts/2017/06/sous-vide-pla/
44
2.6.2 Review of annealed PLA research
Several papers can be founded in literature regarding:
• Annealing effect on mechanical properties
• Material crystallinity degree
• Material microstructure
Whether the test sample was obtained by injection moulded or extrusion.
Other papers studied the annealing effect depending on the material, such as:
• Plain PLA
• PLA fibers or composites
Other publications regarding mechanical behaviour of objects obtained by 3D printing
technologies were consulted, where among other topics it was studied the mechanical
behaviour influenced by process parameters.
The most relevant papers are briefed in the following chapters.
2.6.2.1 Annealing conditions for injection-molded poly(lactic acid)
On this paper it was studied the effect of annealing time and temperature on the material
crystallinity degree and mechanical performance of injection-molded PLA parts. For this
experiment a series of injection-molded PLA samples underwent a heat treatment and then
were placed in an oven to test their heat resistance. Annealed specimens showed very little
or no deformation at all, suggesting annealing results in higher heat resistance and
potentially mechanical performance.
The PLA samples had a maximum crystallinity of about 49%. Maintaining the oven/annealing
temperature at 80°C (for 30 minutes) led to the fastest rate of crystallization, whereas 65°C
(for 31 hours) had the slowest rate. The log-log plot of the degree of crystallinity versus the
annealing time at various temperatures shows the same slope.
This shows that maximum crystallinity can be achieved even at lower temperatures, as long
as the material is given enough time to sufficiently undergo recrystallization. Increasing the
overall crystallinity improved the mechanical performance and heat resistance of PLA. [20]
20. Annealing conditions for injection-molded poly(lactic acid), L.Sheng. Y. Srithep, Society of Plastics Engineers, Plastic Research Online, 2014
45
Figure 27. Injection moulding annealing findings
2.6.2.2 Effect of thermal annealing on the mechanical and thermal properties of
polylactic acid-cellulosic fiber biocomposites.
In this work PLA biocomposites were produced with different fiber types via extrusion and
injection molding. Annealing at 105 ºC for 60 minutes was applied to determine the effect of
a thermal treatment on the mechanical behaviour of these biocomposites. [21]
The tensile and flexural strengths decreased when fiber content was increased. The Dynamic
Mechanical Thermal Analysis (DMTA) results showed that the addition of agave, coir or pine
fibers improved the dynamic modulus of neat PLA, and annealing can substantially increase
the maximum use temperature of these materials.
46
Figure 28. PLA fiber composites findings
21. Effect of thermal annealing on the mechanical and thermal properties of polylactic acid-cellulosic fiber composites. A. A.Pérez-Fonseca, J. R. Robledo-Ortíz, R. González-Núñez, D.
Rodriguez
EXPERIMENTPLANNING
Tensile TestDifferential Scanning Calorimetry
Experiment ResourcesExperiment Work-flowSpecimen Geometry
48
3. Experiment planning
The final goal of this project is to support
the “e-Nable” community showing results
of an experiment focused on the
performance improvement of Poly-Lactic
Acid (PLA) used in prosthesis by submitting
this printed object to a thermal treatment.
Nevertheless, this is just the first step of
this project and a simplification on the
gauntlet component was done, thus a
simple specimen was used in place of the
prosthesis part.
A general description of the techniques
used in the work is briefly reported in the
following paragraph:
The experiment work consisted first in the
delimitation of the shape and the structure
of the 3D printed object and later a
preliminary mechanical test was carry out.
Uniaxial tensile tests were then performed,
to evaluate the mechanical performance of
a 3D printed object before and after the
thermal annealing.
Differential scanning calorimetry was
adopted to evaluate the annealing induced
PLA structure modification in the 3D
printed product.
Figure 29. Experiment planning
49
3.1 Uniaxial Tensile Test
Generally speaking, uniaxial tensile test consists on a sample loaded in tension by
experiencing opposing forces acting upon opposite faces located on the same axis that
attempt to pull the specimen apart. Values that may be measured from this type of test:
tensile strength, ultimate strength, elongation, modulus of elasticity, yield strength, Poisson’s
ratio, and strain hardening.
The test sample often take the shapes of bars, strings, strands, coupons, dog bones, and
dumbbells depending upon the material, the tensile grip, and test performed on the sample.
3.2 Differential Scanning Calorimetry - DSC
Is a thermoanalytical technique in which measures the heat flow into or from a sample as it is
either heated, cooled or under isothermal conditions.
One of the most important features of semi-crystalline plastics is the polymer’s crystallinity
degree. This refers to the overall level of crystalline component in relation to its amorphous
component. The percent of crystallinity are related to many of the properties of semi-
crystalline polymer like: brittleness, toughness, modulus, optical clarity or creep. [22]
Figure 30. Example of thermogram output from DSC
22. DSC as Problem Solving Tool: Measurement of Percent Crystallinity of Thermoplastics. W.J. Sichina, International Marketing Manager
50
3.3 Experiment resources
Figure 31. Experiment resources
51
3.4 Workflow of experiment
Figure 32. Workflow of experiment
EXPERIMENTEXECUTION
First RunSecond Run
Annealing Effect on CrystallizationAnnealing Effect on Tensile Properties
Annealing Effect on Geometry
53
4. Experiment execution
Figure 33. Experiment planning
54
4.1 First run
4.1.2 Producing the samples
Considering the ASTM D638-14 and the grip of the universal testing machine [23] a preliminary
experiment was determined. Type IV and V (table 6) specimens are commonly used for
thickness lower than 4 mm which fits the capability of the testing machine pressured air
clamps. Although the standard suggests using dog bone shape, specimens with a constant
width were used: thus, the slope is suitable to the measure of the apparent tensile modulus
and for a better visual observe of any possible specimen warping a frequent problem after a
thermal treatment on PLA.
Two different infill percentages were used, the lowest value 20% is the suggested infill for a
gauntlet component from the “e-Nable” prosthesis database forums [24]. The highest value
35% was used to have a significant reference. The infill pattern was also suggested by the e-
Nable community. (Figure 34)
Figure 34. 20% and 35% infill (triangular infill pattern)
Eight samples were produced (table 7) with the Atlas 4030 printer (provided from CR Design
Studio), the G-code was generated with Simplify3D slicer software with the following printer
settings:
• Filament diameter: 1.75 mm
• Default printing speed: 60 mm/s
• Nozzle diameter: 0.4 mm
• Primary layer height: 0.2 mm
• Top solid layers: 4
• Bottom solid layers: 4
• Outline/Perimeter shells: 2
• Print bed temperature: 50 ºC
• Nozzle fusion temperature: 218 ºC
• Infill angle: 60, -60
55
During all the test it was used the same type of filament. It was chosen a regular PLA spool from the company KeyTech, the datasheet can be seen on Table 6. [25]
Table 6. PLA-Layer filament datasheet
23.A study of the effects of process parameters on the performance of a 3d printed product in polylactic acid. G. Savarese, C. Marano, R. Gatti. Politecnico di Milano 2016
24.https://www.thingiverse.com/thing:1453190
25. https://help3d.it/prodotto/pla-layer/
Property test condition Standard Unit Values 50% RH
Tensile Strength ISO 527 MPa 52
Elongation Strength ISO 527 % > 20
Flexural Stress ISO 178 MPa 85
IZOD Impact, notched ISO 180/1A kJ/m2 22
H.D.T. Method A (1,80 Mpa) ISO 75 ºC 65
Density ISO 1183 g/cc 1,25
Fire Resistance (3,2 mm) UL94 HB
Melt Temperature Range ºC 200 - 230
Mechanical Properties
Thermal Properties
Other Properties
Processing
Description
Appl ications
PLA-Layer KT001 NAT. Fi laments
PLA-Layer KT001 is a 3D Printing filament in Polylactic Acid with good printable quality
3D Printing prototyping technologies (Fused Filament Fabrication -FFF)
56
4.1.3 Collecting the data
The samples were kept for 30 and 60 minutes at 100ºC in a convection oven (Mazzali
thermair from CMIC Department “Giulio Natta” of Politecnico di Milano) and then quickly
cooled down to room temperature. Sample dimensions (length, thickness and width) were
measure before and after 24 hours after the thermal treatment.
Dimension measurement was performed in to ways (Figure 35):
• Using a dial caliper (0.02 mm)
• By the analysis of digital image obtained with a scanner (Epson V33)
The caliper measurement has an accuracy of 0.02 mm while the digital image analysis could
be thought to have a higher measure accuracy.
The dimension measurement obtained from the caliper is an analogic measurement directly
read on it, while the ones obtained from the image analysis must undergo a calibration for
the image pixel to mm conversion.
The dimensions were measured on 3 points along each axis; a mean value and the standard
deviation were then evaluated. Table 8 and Table 9 are an example of how the data was
collected.
Table 7. First run samples
Temp. ºC Time (min)
20-IV-30
Lenght (X) 115 20-V-30
Height (Y) 19 35-IV-30
Widht (Z) 3 35-V-30
20-IV-60
Lenght (X) 63.5 20-V-60
Height (Y) 19 35-IV-60
Widht (Z) 3 35-V-60
20
35
Type Code Infill %
20
35
IV
Sample
V
Annealing
30
100
60
57
Figure 35. Measuring with digital image analysis and caliper
Table 8. Measurement output with caliper (first run)
Table 9. Measurement output with digital image analysis (first run)
DifferenceRelative
DifferenceDifference
Relative
DifferenceDifference
Relative
Difference
X1 63.25 X1 62.92 -0.33 -0.005 Y1 19.08 Y1 18.94 -0.14 -0.007 Z1 3.08 Z1 3.20 0.12 0.039
Y2 19.10 Y2 18.98 -0.12 -0.006 Z2 3.07 Z2 3.16 0.09 0.029
Y3 19.05 Y3 18.94 -0.11 -0.006 Z3 3.08 Z3 3.16 0.08 0.026
MEAN DIFF MEAN DIFF -0.123 MEAN DIFF 0.097
MEAN REL
DIFF
MEAN REL
DIFF-0.006
MEAN REL
DIFF0.031
STANDV STANDV 0.001 STANDV 0.007
SEMIDISP SEMIDISP -0.001 SEMIDISP 0.006
annealed
20-V-30
Dimensions CALIPER (mm)
X
as-printed annealed as-printed annealed as-printed
ZY
DifferenceRelative
DifferenceDifference
Relative
DifferenceDifference
Relative
Difference
X1 64.23 X1 62.98 -1.25 -0.0195 Y1 19.4 Y1 19.07 -0.33 -0.017 Z1 3.26 Z1 3.37 0.11 0.034
Y2 19.40 Y2 19.05 -0.35 -0.018 Z2 3.24 Z2 3.34 0.1 0.031
Y3 19.42 Y3 18.94 -0.48 -0.025 Z3 3.22 Z3 3.22 0 0.000
MEAN DIFF MEAN DIFF -0.387 MEAN DIFF 0.070
MEAN REL
DIFF
MEAN REL
DIFF-0.020
MEAN REL
DIFF0.022
STANDV STANDV 0.004 STANDV 0.019
SEMIDISP SEMIDISP -0.016 SEMIDISP 0.017
annealed
20-V-30
Dimensions Digital Image Analysis (mm)
X Y Z
as-printed annealed as-printed annealed as-printed
58
4.1.4 First run findings: dimension variation
The data are reported in a bar graph (Graph 1): in this way is possible to compare the level of
accuracy from the two used methods. The results showed there is no dependence of
dimension variation of the specimen with respect of infill percentage. Some specimens
shrank in the X and Y axis and expanded on the Z axis (20-V-30), others shrank on all axis (20-
IV-30), other shrank on X and Y axis and stayed the same on Z axis (35-IV-30).
The least consistent data comes from the specimens that were annealed for 30 minutes and
the ones with shortest length, the sample 20-IV-30 when measured with caliper showed a
shrinkage on the Z axis and when measure with ImageJ showed an expansion (Table 10). This
could be due to:
• An error while setting the scale on the software for digital image analysis (ImageJ) or
when doing the measure with the computer mouse
• The difficult task of measuring a wall thickness variation for a width of 3 mm (axis X
and Y measured with caliper and digital image analysis showed the same trend)
• An error while placing the specimen on the scanner surface due to a warpage of the
specimens along its shortest dimension
There was no significant warping irrespective of the specimen shape used. For the further
tensile tests the length pays an important role because it`s related with the gauge length.
Table 10. Comparison of specimen dimension using caliper and digital image analysis (first run)
CaliperDigital image
analysisDiff. (img analysis/cal)
X-30 -0.5% -1.9% 3.8Y-30 -0.6% -2.0% 3.3Z-30 3.1% 2.2% 1.4X-60 -0.4% -1.6% 4.0Y-60 -0.6% -1.9% 3.2Z-60 -0.2% 2.7% *X-30 -0.3% -1.9% 6.3Y-30 -0.5% -2.4% 4.8Z-30 2.3% 2.2% 1.0X-60 -0.4% -1.6% 4.0Y-60 -2.1% -2.0% 1.1Z-60 3.3% 0.2% 16.5 **X-30 -0.4% -0.6% 1.5Y-30 -3.9% -0.7% 5.6Z-30 -0.4% 4.2% 10.5 **X-60 -0.4% -1.7% 4.3Y-60 -0.8% -2.7% 3.4Z-60 -0.2% 0.2% *X-30 -0.3% -1.8% 6Y-30 -0.5% -2.2% 4.4Z-30 0.0% 0.4% 0.4X-60 -0.4% -1.7% 4.3Y-60 -0.8% -2.7% 3.4Z-60 -0.2% 0.2% *
Repetition
*contradictory data **large difference
Repetition
Code
59
Graph 1. Geometric variation Caliper vs. Scanner (first run)
60
4.2 Second run
Eight samples were produced (specimen shape IV) with same printing settings as said in
chapter 4.1.2 (infill percentage: 20% and 35%). Six samples heated for 60 minutes at 100ºC.
Samples 35-60-As and 20-60-As (As = without thermal treatment) didn`t undergo to the
thermal treatment in this way they were the reference for the tensile test.
Table 11. Second run samples (scheme)
Figure 36. Second run samples
Temp. ºC Time (min)
35-60-As * No No
35-60-1
Lenght (X) 115 35-60-2
Height (Y) 19 35-60-3
Widht (Z) 3 20-60-As *
20-60-1
20-60-2
20-60-3
* As-printed: this samples will be the reference for the thermal treatment
Type Sample Code Infill %Annealing
60IV
35
20
100
61
4.2.1 Geometry variation
To analyse the geometric variation the data collection was carried out in the same way as
said in the previous chapter. The experiment was replicated in order to verify the results.
The nominal dimension on each axis (x, y, z) was an average of the measurement done on 3
points.
This time the results were more consistent but the ones along thickness or Z-axis: the larger
variation was obtained with the digital image analysis, almost 3 times larger measure than
with the caliper (Graph 2). Therefore for the third run the measurement will be done only
with the caliper.
Table 12. Measurement output for specimens without thermal treatment (second run)
Table 13. Caliper measurement output for specimens with thermal treatment (second run)
Table 14. Digital image analysis measurement output for specimens with thermal treatment (second run)
X1 114.52 Y1 19.04 Z1 3.10
X2 114.50 Y2 18.94 Z2 3.10
X3 114.54 Y3 18.88 Z3 3.08
Xa 114.52 Ya 18.95 Za 3.09
20-60-As
Dimensions CALIPER (mm)
X1 115.52 Y1 19.03 Z1 2.93
X2 115.58 Y2 18.91 Z2 2.97
X3 115.65 Y3 18.83 Z3 2.95
Xa 115.58 Ya 18.92 Za 2.95
20-60-As
Dimensions SCAN (mm)
DifferenceRelative
DifferenceDifference
Relative
DifferenceDifference
Relative
DifferenceX1 114.48 X1 114.32 -0.16 -0.001 Y1 19.02 Y1 18.96 -0.06 -0.003 Z1 3.08 Z1 3.02 -0.06 -0.019
X2 114.50 X2 114.50 0.00 0.000 Y2 18.94 Y2 18.86 -0.08 -0.004 Z2 3.10 Z2 3.10 0.00 0.000
X3 114.58 X3 114.76 0.18 0.002 Y3 18.82 Y3 18.74 -0.08 -0.004 Z3 3.06 Z3 3.08 0.02 0.007
MEAN DIFF 0.007 MEAN DIFF -0.073 MEAN DIFF -0.013
MEAN REL DIFF 0.000 MEAN REL DIFF -0.004 MEAN REL DIFF -0.004
STANDV 0.001 STANDV 0.001 STANDV 0.014
SEMIDISP SEMIDISP SEMIDISP
20-60-1
Dimensions CALIPER (mm)
X Y Z
as-printed annealed as-printed annealed as-printed annealed
DifferenceRelative
DifferenceDifference
Relative
DifferenceDifference
Relative
Difference
X1 115.49 X1 114.09 -1.40 -0.012 Y1 19.01 Y1 18.69 -0.32 -0.017 Z1 3.00 Z1 2.93 -0.07 -0.023
X2 115.48 X2 114.59 -0.89 -0.008 Y2 18.89 Y2 18.71 -0.18 -0.010 Z2 2.96 Z2 2.91 -0.05 -0.017
X3 115.64 X3 115.27 -0.37 -0.003 Y3 18.80 Y3 18.54 -0.26 -0.014 Z3 2.95 Z3 2.92 -0.03 -0.010
Xa 114.65 Xa 18.65 Xa 2.92
MEAN DIFF -0.887 MEAN DIFF -0.253 MEAN DIFF -0.050
MEAN REL DIFF -0.008 MEAN REL DIFF -0.013 MEAN REL DIFF -0.017
STANDV 0.004 STANDV 0.004 STANDV 0.007
SEMIDISP SEMIDISP SEMIDISP
Dimensions DIGITAL IMAGE ANALYSIS (mm)
X Y Z
as-printed annealed as-printed annealed as-printed annealed
20-60-1
62
Graph 2. Annealing effect on geometry (second run)
63
4.2.2 Water content variation during the annealing
PLA can absorb water from the air it is reported that PLA can absorb up to 6% in weight if
water. [26] Water act as a polymer plastifier (a chemical compound added to a polymer in
order to produce a softer plastic material) and can affect both PLA modulus and tensile
strength. Thus, it is important to check that the evaporated water content in the PLA in the
As-printed sample and in the thermally treated one are fairly the same.
The water loss during the thermal annealing was determined by weighting the sample before
(Wo) and after (Wf) annealing. The delta of water content variation can be calculated with the
following equation.
∆𝑊 = 𝑊𝑓 − 𝑊𝑜
𝑊𝑜
Equation 1. Water content variation during the annealing
As seen in Graph 3 the thermal treatment cause water loss less than 0,3% in weight. The
samples were kept at 23ºC and 43% relative humidity for 24 hours. Graph 3 shows also the
sample weight Ioss due to water absorption.
It takes about one day for the samples to absorb the same content as into the As-printed
sample. Never the less the water content variation is very small and can be neglected.
Graph 3. Weight variation
26. Water absorption and enzymatic degradation of poly(lactic acid)/rice starch composites. G.H.Yewa, A.M.Mohd Yusofa, Z.A.Mohd, IshakaU.S.Ishiakub
64
4.3 Annealing effect on crystallinity
In order to understand the level of
crystallinity of the printed PLA, a thermal
analysis was carried out to observe the
thermal transitions of the polymer.
With the Differential Scanning Calorimetry
(DSC) it is possible to measure the
temperature and the heat flow associated
with transitions that occur in the sample:
glass transition temperature (Tg), melting
temperature (Tm) and the enthalpies of
fusion.
During the test an inert atmosphere is
maintained in the furnace with a continuous
flow of nitrogen, that distributes the heat
evenly between the sample and the
reference. A thermocouple system collects
the temperature data and sends them to a
computer which processes them to generate
the output, a thermogram: thermal flow-
time/ thermal-flow temperature.
Two scans were performed:
• First scan: 7,9 mg of the material was
heated from 23ºC up to 250 ºC at a
heating rate of 10ºC/min (Graph 4)
• Second scan: 7,9 mg of the material
was initially heated up to 100ºC
(exothermic heating that simulates
the annealing conditions used for the
previous specimens) and kept at this
temperature for 120 minutes, then let
cool down to 23ºC at 10ºC/min
(Graph 5)
Figure 37. Setting up the DSC
65
Graph 4. First DSC thermogram
66
From the thermogram of the first scan heat flow/time certain information is revealed: During the heating phase an endothermic step can be observed at around 61°C, corresponding to the glass transition temperature (Tg). The first exothermic peak at 94,28°C corresponds to material crystallization. The melting of the material begins at 160°C and ends at 174,76 °C (Tm). The recrystallization peak, which was observed just before the melting peak, may be due to the restructuring of certain existing crystalline structures at high temperature. The specimen produced by 3D print has a low degree of crystallinity because from the thermogram can be seen that it crystallizes when heated. The degree of crystallinity can be calculated by measuring the difference between the areas of the melting peaks (Aas 2 + Aas 3) and the crystallization peak (Aas 1).
𝐴𝐴𝑠2 + 𝐴𝐴𝑠3 > 𝐴𝐴𝑠1
Equation 2. Areas of melting and crystallization peaks
30,35 𝐽/𝑔 + 5,76 𝐽𝑔 > 18,79 𝐽/𝑔
Equation 3. Value of areas of melting and crystallization peaks
Since the melting enthalpy is larger than then crystallization enthalpy it can be said that the polymer is partially crystalline. From the second test it can be observed that there is no exothermic peak neither during the
isothermal step nor in the following heating ramp: the crystallization of the material has
occurred and completed during the heating up to 100ºC. At this point it is not accurate to say
what is the most optimum exposure time and temperature, giving that glass transition
temperature (Tg) can occurs from 58 to 71 °C at a rate of 10°C/minute and finding the
optimum conditions is out of the project scope.
The melting heat of PLA material before annealing (CAs) and after annealing (Cp) calculations
can be seen in the following equations:
𝐶𝑝 = 26,56 + 7,61 = 34,17 𝐽/𝑔
𝐶𝐴𝑠 = (30,35 + 5,76) − 18,79 = 17,32 𝐽/𝑔
Equation 4. Melting heat of PLA before and after annealing
67
The degree of crystallinity before annealing (XAs) and after annealing (XP) can be calculated with the following equation:
𝑋𝐴𝑠 = 𝐶𝐴𝑠
𝐶𝑃𝐿𝐴 × 100% =
17,32
93= 18,6 %
𝑋𝑃 = 𝐶𝑃
𝐶𝑃𝐿𝐴 × 100% =
34,17
93= 36,7 %
Equation 5. Degree of crystallinity before and after annealling
𝐶𝑃𝐿𝐴 = 𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 100% 𝑚𝑒𝑙𝑡𝑖𝑛𝑔 ℎ𝑒𝑎𝑡 𝑜𝑓 𝑃𝐿𝐴 [27]
The delta of crystallinity can be calculated with the following equation:
∆ 𝐶𝑟𝑦𝑠𝑡𝑎𝑙𝑙𝑖𝑛𝑖𝑡𝑦 % = 𝑋𝑃 − 𝑋𝐴𝑠
𝑋𝐴𝑠 × 100
∆ 𝐶𝑟𝑦𝑠𝑡𝑎𝑙𝑙𝑖𝑛𝑖𝑡𝑦 % = 36,7 − 18,6
18,6 × 100 = 97 %
Equation 6. Delta of crystallinity
It can be observed that:
• annealing increases the crystallinity degree
• the final crystallinity degree reached is lower than the maximum value reported in the
literature (L. Sheng et al.), which was around 49%
27. Fischer EW, Sterzel HJ, Wegner G. Investigation of the structure of solution grown crystals of lactide copolymers by means of chemical reaction. Kolloid-Zu Z-Polymer
68
Graph 5. Second DSC thermogram
69
4.4 Annealing effect on tensile properties
The tensile test was done on the Hounsfield Universal
Testing Machine from the CMIC Department “Giulio
Nata” of Politecnico di Milano.
For the tensile test an electromechanical
dynamometer Hounsfield, with load cell of 5 kN was
used. It was connected and managed remotely from a
PC.
A pneumatic clamping system was used. In order to
make the test properly is necessary to place
accurately the specimen within the clamps: the
clamp’s zone must be the same on both the edge of
the specimen.
During this phase it is necessary to remove the
preload, which comes out as a result of the
specimen’s compression in the clamps. This preload
could distort the final results if not properly removed,
but it is a simple procedure that can take place
through the machine. It is also important to correctly
align the specimen along the loading direction.
The test was performed at constant displacement
rate: 2 mm/min. Using specimen Type IV with a 100%
infill with a triangular infill pattern, the gauge length
was 103 mm.
The tensile test gives as output the difference
between lengths of the specimen compared to the
applied load, every moment during the test.
4.4.1 Apparent Tensile Modulus
It is important to underline that the specimen used for the tensile test was printed reproducing the structure of the e-Nable prosthesis as reported previously, thus, the tensile test allows to characterize the structure and not the material itself. So what is measured from the tensile test will be referred to an apparent modulus and tensile strength.
Figure 38. Uniaxial tensile test
70
By the way is expected that any annealing effect on a material structure affect also the mechanical behaviour of the specimen itself. Test were performed on specimens with 15%, 25%, 35% and 100% infill.
Figure 39. Infill percentage variations and infill pattern overview
71
The apparent elastic modulus (E) was experimentally determined from the slope of the apparent stress-strain curve. Since the test was repeated in order to verify the results, the founded value for Modulus was the average between the two tests. The slope of a line was founded for both As-printed and Annealed specimen, this were the equations in which both had high R-squared values (percentage of the response variable variation that is explained by a linear model):
𝑌 = 723.8𝑥 𝑅2 = 0.999
𝑌 = 758.6𝑥 𝑅2 = 0.991
Equation 7. Slope of line
The cross-section area was taken from the nominal values measured for each specimen. For
each output it’s possible to calculate the resistance to lengthwise stress and the percentage
elongation with these equations:
𝜎 = 𝐿𝑜𝑎𝑑 (𝑁)
𝐴𝑟𝑒𝑎 (𝑚𝑚2) 𝜀 =
𝐸𝑙𝑜𝑛𝑔𝑎𝑡𝑖𝑜𝑛 (𝑚𝑚)
𝐺𝑎𝑢𝑔𝑒 𝐿𝑒𝑛𝑔ℎ𝑡 (𝑚𝑚) × 100
The apparent stress-strain curve for one As-printed (As) and annealed (P) specimen (100%
infill) was plotted.
Table 15. Apparent tensile modulus variation
As-printed (As) Annealed (P)
728.4 760.9 ± 2.8
Apparent Tensile Modulus (MPa)
Δ Tensile Modulus %
5%
72
Graph 6. Load -Elongation plot
Graph 7. Apparent Stress-Strain plot
73
4.4.2 Apparent Tensile Strength
Generally speaking the tensile strength of a material is the maximum amount of tensile stress
that can take before failure, such as breaking or permanent deformation. Tensile strength
specifies the point when a material goes from elastic to plastic deformation, if any.
Dog bone shape specimen used (standard ASTM D638-14). Twelve samples were produced
on the Delta Atlas4030 3D printer with same printing settings as listed on chapter 4.1.2. and
the settings for the universal machine were kept.
Figure 40. Tensile test samples
74
Table 16. Example of tensile test output
Table 17. Apparent tensile test variation
Gauge Lenght
Elongation
[mm]Load F, [N] σ [MPa] ε ΔL=Elong/L L [mm]
ε %
(ΔL/L)*100
0 1 0.025900026 0 -
0.002 1.166667 0.030216706 1.94175E-05 0.0018852%
0.005 2.333333 0.060433385 4.85437E-05 0.0047130%
0.009 4.166667 0.107916783 8.73786E-05 0.0084834%
0.012 5.833333 0.151083476 0.000116505 0.0113112%
0.016 7.666667 0.198566874 0.00015534 0.0150815%
0.019 9.333333 0.241733566 0.000184466 0.0179093%
… … … … …
103
Tensile test data Stress-Strain data
As-printed
As-printed (As) Annealed (P)
20.1 21.3 ± 1.9
Apparent Tensile Strength (MPa)
Δ Tensile Stength %
5.6%
75
Graph 8. Stress-Strain plot (as-printed, annealed)
The apparent tensile strength curve for one as-printed and one annealed specimen (100% infill) can be seen plotted on Graph 8. In Table 17 the apparent maximum stress (σmax) and the corresponding apparent strain
(εσmax) measured for as-printed (As) specimen and for annealed specimen (P) are obtained.
The improve in the apparent mechanical behaviour is relatively small in compared to the reported by Turning et al. who studied the annealing conditions for injection-molded Poly-Lactic Acid and revealed in tensile strength of 14% with respect to the untreated specimen, in this case the annealing allowed to reach a maximum PLA crystallinity degree of 48%.
76
4.4.2.1 Effect of infill percentage on mechanical performance
Tensile test in mechanical performance was performed also on samples with different infill
percentage with the aim of finding a correlation between apparent tensile strength, infill
percentage and annealing effect.
In Graph 9 can be observed that the apparent modulus is fairly the same irrespective of the
infill percentage. This result is expected considering that the specimen layer “sandwich”
structure (Figure 41) with a shell thickness equal to 1/3 of the specimen thickness. In each
shell the infill percentage is 100% and thus its rigidity is significantly higher than a core or
hollow rigidity.
One would be expected that the annealing treatment increase the apparent rigidity for each
infill percentage but it wasn`t observed.
As for the apparent strength (Graph 10), as expected 100% infill specimen shows the higher
strength. For the lowest infill percentage, no trend was observed.
Figure 41. Specimen structure scheme (layer-wise distribution)
77
Graph 9. Apparent tensile modulus for different infill percentage
Graph 10. Apparent tensile strength for different infill percentage
78
4.4.3 Material Brittleness
A material is brittle if, when subjected to stress, it breaks without significant plastic deformation. Brittle materials absorb relatively little energy prior to fracture, even those of high strength. From the Figure 44 can be seen a more brittle behaviour for the annealed specimen breaking at smaller strain than the as-printed one. Also looking at the thermal treated sample it can be observed that a more brittle fracture occurs. This can be visually verified by zooming the cracked area from both tested samples before and after annealing.
Figure 42. Crack typology before and after annealing
.
79
4.5 Annealing effect on geometry
Figure 43. Samples for geometry analysis
Referring to the preliminary a 20x20x20 mm cube (printed in the same Delta Atlas4030
machine) was produced to better observe any variation after the annealing treatment (Figure
45).
The samples were marked on the faces that were then measured. To simplify the
measurement by doing by hand using the dial caliper. The measurement was repeated 3
times in order to verify the data.
The specimens shrank on all directions with a relatively low variation, X-axis (0.41%), Y-axis
(0.13%), Z-axis: (0.42%).
Some shrinkage was expected but this result showed that the annealing effect on the geometry when using regular PLA produce a small variation. It is a positive outcome because after performing a thermal treatment one does not need to compensate for a shrinkage effect.
Graph 11. Annealing effect on geometry (average data)
CONCLUSIONS
81
5. Conclusions
This study is a first approach to evaluate the annealing effect on the physical structure of PLA
in a FDM printed object and its mechanical behaviour. Differential Scanning Calorimetry test
and tensile test were thus performed to measure the PLA crystallinity degree, the apparent
tensile modulus and strength before and after the thermal annealing.
This project is focused on the study of annealing effect of the performance from FDM
technology made of Poly-Lactic Acid through an experimental approach: there are very few
works in the scientific literature dealing with this topic, which up to now have been approached
only empirically.
The project was inspired by the current maker movement that is exploring more and more
post-processing as a method for adding value to their 3D printed components and the market
which is providing solutions in the same direction. Therefore, expanding the study of a thermal
treatment effect on different commercial PLA filaments is an open door that students with a
background on product design, material selection awareness and basic engineering
fundamentals should keep seeking.
There was no clear correlation for the maximum tensile strength according to different infill
percentages, this can be the result of the type of infill pattern, number of shells or layer height,
a further study on the annealing effect taking into account the previous variables can revealed
more cogently data.
Further mechanical testing in different loading conditions could be performed to better
reproduce the actual bending condition of the 3d printed part in the prosthesis.
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Moreover, the study of annealing treatment for the interaction effect between the number of
shells or layers is worth wise to be explored through a Design of Experiments (DoE) approach.
The slot feature on gauntlet component from a prosthesis designed by e-Nable community
testing in bending condition can be suggested. Also opening the opportunity for performing
further studies such as: dynamic modulus, thermal properties, impact strength, flexural
properties or tensile properties.
REFERENCES
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References
Books
• Additive Manufacturing Technologies. Ian Gibson, David Rosen, Brent Stucker. Second
Edition 2015, Springe
• Design and analysis of experiments. D. Montgomery. 8th Edition. 2013
• 3D Printing and Additive Manufacturing: Principles and Applications. Chua. Leong. World
Scientific 4th edition
Scientific Papers
• "Reprap the replicating rapid prototyper". Jones, R.; Haufe, P.; Sells, E.; Iravani, P.; Olliver,
V.; Palmer, C.; Bowyer, A. (2011).
• Annealing conditions for injection-molded poly(lactic acid), L.Sheng. Y. Srithep, Society of
Plastics Engineers, Plastic Research Online, 2014.
• Effect of thermal annealing on the mechanical and thermal properties of polylactic acid-
cellulosic fiber composites. A. A. Pérez-Fonseca, J. R. Robledo-Ortíz, R. González-Núñez, D.
Rodriguez
• DSC as Problem Solving Tool: Measurement of Percent Crystallinity of Thermoplastics.
W.J. Sichina, International Marketing Manager
• A study of the effects of process parameters on the performance of a 3d printed product
in polylactic acid. G. Savarese, C. Marano, R. Gatti. Politecnico di Milano 2016
• Water absorption and enzymatic degradation of poly(lactic acid)/rice starch composites.
G.H.Yewa, A.M.Mohd Yusofa, Z.A.Mohd, IshakaU.S.Ishiakub
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Websites
• https://3dprintingindustry.com/3d-printing-basics-free-beginners-guide/history/
• https://www.livescience.com/39810-fused-deposition-modeling.html
• https://www.3dhubs.com/knowledge-base/selecting-optimal-shell-and-infill-parameters-
fdm-3d-printing
• https://www.matterhackers.com/3d-printer-filament-compare
• https://en.wikipedia.org/wiki/Open_design
• http://enablingthefuture.org/
• http://www.openbiomedical.org/
• https://www.openbionics.com/
• https://rigid.ink/blogs/news/how-to-anneal-your-3d-prints-for-strength
• http://justinmklam.com/posts/2017/06/sous-vide-pla/
• https://www.thingiverse.com/thing:1453190
• https://help3d.it/prodotto/pla-layer/
• https://www.researchgate.net/publication/289522663_3D_Printing_Pharmaceutical_Ma
nufacturing_Opportunities_and_Challenges
Magazines / Reports
• Make magazine, special issue: 3D printer buyer´s guide 2014
• Could 3D Printing Change the World? T. Campbell, C. Williams, O. Ivanova, B. Garrett
Video-sharing websites
• How 3-D printed arms are changing kids' lives around the world.
https://www.youtube.com/watch?v=XQ8tPOqN7WE
• Tomas Sanladerer Youtube channel. https://www.youtube.com/watch?v=YcQHbaVeD7I
• CNCKitchen YouTube channel. https://www.youtube.com/watch?v=vLrISrkg46g
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• Joe Mike Taranella YouTube channel
https://www.youtube.com/watch?v=WmTGU3r53VU&t=4s
• Thermoforming a gauntlet for an e-NABLE hand.
https://www.youtube.com/watch?v=BihhKHjguZY