Author Archives: scifablab

From Bottle Caps to 3D-Printing: An open guide

By: J. A. Montoya

 

To the public it is a little known fact that different types of plastic can differ widely on the process that is required in order to recycle them. One common example is plastic bottles, where the bottles and their caps are made of PET and HDPE respectively (frequently Polypropylene is also used as a cap material). At the recycling facility bottles and caps need to be separated because their recycling process is different and this, at a large scale, implies high labor costs and possible waste of some of the material, depending on the separation method that is being used. In general, leaving the caps on the bottles is a better option than throwing them to the dumpster, however, it is important to remember that not every recycling facility around the world is guaranteed to be able to process different types of plastic. A better solution would be to leave the recycling of the transparent part of the bottles (the PET) to a specialized company and make sure that their plastic caps do not end up in a landfill by doing something useful with them at home.

Before going forward, we need to mention that we intend to use the recycled plastic as filament (raw material) for low-cost 3D-printing. The first source of abundant and cheap plastic that always comes to people’s minds is the bottle itself, which is made of PET (recycling code 1) . However, in order to feed this or any other plastic into a 3D-printer, we need first to make plastic filament of a constant diameter. In order to achieve this, PET needs to be heated up to a temperature that renders it soft (not liquid) so that it can be extruded by applying pressure through a hole with a size that will determine the diameter of the filament. The problem that one finds is that in the process of applying heat to PET it crystallizes and becomes brittle. To avoid this crystallization one would have to be very precise in controlling the temperature and the heating/cooling rates of the entire process, in order to keep PET in an amorphous form. The technical challenges inherent to this process make PET less suitable for a DIY project, like the one that we are trying to present here.

While Polypropylene (recycling code 5) is a very popular material to make bottle caps in many countries, in Italy, where we are located, most companies seem to prefer HDPE (recycling code 2) as a material for their plastic bottle-caps. We collected plastic caps in a nearby cafeteria and separated them by their material and color; this is where we noticed the Italian’s preference towards HDPE, since it made approximately 2/3 of the total of collected caps.

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We started the process by shredding the pink-colored HDPE caps. This can be accomplished with some robust kitchen equipment or with specialized hardware.

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The resulting material needed to be dried before it goes into the filament extruder.

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Then the filament extruder temperature was set to 132 C, and the feeding of the plastic could start. Each plastic cap will produce between 80 and 100 cm of filament at diameters around 1.75 mm.

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Keep in mind that the filament comes out of the extruder very hot and it is very irregular at first; you should make sure that the weight of the filament that is hanging, as well as the extruding temperature, feeding rate, pressure, etc., remain constant, so that the diameter of the filament reaches some uniformity. If you are doing this for the first time don’t feed the resulting filament into a Makerbot, or into some high-end 3D-printer, it will get clogged and your warranty won’t cover it, try to get some practice first and measure the diameter at several points, to make sure that it is constant and has the desired thickness.

We repeated the same procedure with some blue HDPE caps and got a much nicer filament out of them, after all this was our second attempt :-)

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Now it comes the printing part. HDPE experienced a big contraction when it cooled after being extruded by the 3D-printer nozzle. We were not able to get it to stick for more than a few seconds to a clean and smooth hot surface, even after heating our printing bed up to 110 C, which exceeded the maximum bed-temperature in our Solidoodle 3D-printer. We then decided to prepare a mixture of ABS plastic with acetone and cover (paint) the plate with it.

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After this procedure the recycled plastic stuck nicely to the blue ABS layer, shown in the picture above.

The main challenge now was that the temperature that is required to guarantee a good flow of HDPE out of the printing nozzle seems to be 220 C or higher. The printer that we were using turned itself off at temperatures above 210 C, as a safety measure. The pink HDPE would stop flowing through the nozzle after just a few minutes because 210 C seemed to be very low for this type of plastic. The blue HDPE filament instead was a bit more amenable to flow at 210 C, but the stress that the extrusion gear was applying on it was too high and eventually surpassed its mechanical limit of stability, causing the filament to bend, which in turn caused it to stop going into the printer’s hot-end and nozzle.

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So far, the final result is not what you would expect from a high-quality filament, but there is still a lot of room for improvement in both extrusion processes, i.e., when producing filament and when printing with it. Have you also experimented with HDPE? Do you have experience with Polypropylene or other plastics not discussed in this post?  Let us know.

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Team:
• Carlo Fonda
• Javier A. Montoya

 

We thank S. Faeta, M. Trivella, N. Bonaventure, and Tamara, for their collaboration during this project. For materials and equipment we received support from the ICTP’s Fabrication Laboratory, which is part of the Science Dissemination Unit (SDU) at ICTP.

Nov-2014

Premiazione di Cromopolis

Il 19 settembre alle 19 presso lo studio Tommaseo in via del Monte 2/1 a Trieste è avvenuta la premiazione del progetto Cromopolis, vincitore del premio Gillo Dorfles al concorso di design 2014 di Trieste Contemporanea. Per maggiori informazioni: link.

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Ricerca del centro iniziale di rotazione del ginocchio.

lo scopo di tale progetto è quello di ricercare il centro di iniziale rotazione del ginocchio, punto anatomico di riferimento nella flesso-estensione di tale articolazione che fisiologicamente presenta un moto associato di roto-traslazione.

La curiosità di approfondire tale argomento, è nata da quanto scritto da Insall (il padre delle protesi del ginocchio) che aveva messo in luce la “scarsa significatività degli studi sulla cinematica del ginocchio basati su una localizzazione anatomica del centro di istantanea rotazione”.

La prima fase del progetto ha l’obiettivo di creare tramite stampa 3D di basso costo a tecnologia FDM un modello didattico che riproduca il movimento fisiologico rototraslatorio tra un capo articolare femorale ed un capo articolare tibiale. Gli attuali modelli, infatti, quelli ad esempio riproposti sugli scheletri che troviamo nelle aule di anatomia, semplificano tutta la meccanica flesso-estensioria con un semplice perno che determina un puro moto rotatorio. Ciò fa sì che mentre sui libri vengono riportate descrizioni particolarmente accurate sulla fisiologia di questo moto articolare, nella pratica lo studente non ne può assolutamente apprezzare gli effetti.

ModelloGinocchioAnteriore   ModelloGinocchioParticolarePosteriore

Dalle foto sopra riportate è possibile notare il tipo di movimentazione a “cerniera” che normalmente viene utilizzata per l’articolazione del ginocchio.

 Nello specifico, il moto roto-traslatorio prevede che i condili femorali per i primi 25-30° di flessione (della coscia sulla gamba), rotolano sui piatti tibiali; successivamente, dai 30° in poi, al moto di rotazione si associa una traslazione che diventa sempre più importante con l’aumentare della flessione (fai clik sull’immagine per attivare l’animazione).

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Math Exhibition using Low-cost 3D Printers: 3D model conversion tools

To print the mathematical shapes of the project “Math Exhibition”, I’ve selected the Ultimaker printers that are available, amongst others, in the SciFabLab.

There are two of the “original” model, one with a dual extruder.

After months of use, my overall assessment is positive: they are good machines, fast and accurate, despite some minor defect.

For these printers I’ve used the Cura program to “compile” the 3D model and transform it into a set of G-code instructions to send to the printer.

Actually, the Cura command “Load Model File” enables the loading of 3D models in these formats: STL, or OBJ, DAE, AMF, etc.

The first problem that has occurred in Project “Math Exhibition” was the fact that some of the 3D models were provided in X3D format, that “Cura” is not currently able to import.

Before performing other steps, it was necessary to convert the X3D files in STL format.
For this operation I have tested the use of two tools:

  1. Meshlab (open-source, developed by the ISTI – CNR research center, http://meshlab.sourceforge.net/)

  2. Netfabb (http://www.netfabb.com/)

Format conversion with Meshlab

Select: File – Import mesh

Select the x3d file. (for example: distel_200mm_full.x3d).

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To export in new file format: File – Esport as:

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Format conversion with Netfabb

Select: Project – New Project

Project – Add part

Select the x3d file. (for example: distel_200mm_full.x3d).

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To export in new file format: Part – Esport part – as STL (Ascii)

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Marco Rainone

Servizio TGR FVG sull’inaugurazione dello SciFabLab ICTP

Con un po’ di ritardo (il servizio è andato in onda lunedì 18 agosto, l’inaugurazione è avvenuta martedì 12 agosto) pubblichiamo la registrazione di questo servizio, trasmesso durante l’edizione delle 14:00 del Telegiornale Regionale (purtroppo l’edizione delle 19:40, nella quale si è potuto vedere un montaggio differente di immagini ed interviste, non è stata resa disponibile integralmente negli archivi web della RAI).

Presentazione della ricerca: “Studio e Fattibilità di Stampa 4D”

Buongiorno,

con questa comunicazione  viene dato avvio ad un sintetico e cadenzato aggiornamento in merito alla ricerca che chi scrive sta svolgendo presso ICTP – SciFabLab.

Tale ricerca riguarda la realizzazione, mediante stampanti tridimensionali a basso costo, di elementi plastici che risultino essere deformabili post stampa, e che, con opportune manipolazioni, possano suscitare, nell’osservatore, una percezione spaziale dell’oggetto molto diversa da quella dell’elemento in condizione di riposo.

La parte iniziale dello studio si pone come fine quello di realizzare semplici elementi deformabili in maniera reversibile, ovvero, entro predeterminate sollecitazioni, in maniera elastica.

La ricerca di elementi che presentino caratteristiche elastiche conduce “naturalmente” ad effettuare stampe di oggetti che riproducano le tradizionali molle meccaniche; l’intento è quello di ottenere informazioni, prima di carattere qualitativo, sul comportamento della struttura stampata in presenza di sollecitazione fisiche.

Nei successivi aggiornamenti verranno documentati questi primi oggetti realizzati.

 

Math Exhibition using Low-cost 3D Printers: introduction

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The inspiration for this project was born when a colleague of Enrique Canessa has referred to this site:
http://imaginary.org/hands-on/four-math-sculptures
where are displayed beautiful representations of curves or surfaces described by mathematical formulas, reproduced with kind of professional 3D printers.


Naturally, professional printers have accuracy and print quality that absolutely can’t be compared with low cost 3D printers.
We asked whether, applying various techniques and precautions, objects of a certain complexity that are normally made with professional printers, could be reproduced also with low-cost models and which was the quality that could be reached in prints.