Material_PLASTIC -- Wahlfach Modell und Gestaltung FS20

Plastic

Tanguy Caversaccio, Claire Debons, Yuning Song

Material Characteristics

The word plastic comes from the Greek “plastikos” meaning to grow or form and was first used to describe what could be deformed without rupturing. Materials are called plastic when they are formed of long chain molecules, aka. polymers.
Plastics have many advantages: they are often cheap, easy to transform, resistant to water, to shock and to corrosion. They can come in many shapes and colors according to the tints and fillers they are mixed with or the way they are handled. Many types of classification exist for plastics. They can be classified by the chemical structure of their polymers, the processes used in their synthesis or by their various physical properties. There is a differentiation that can be made between the thermo­plastic and thermo­­setting (duroplastic) polymers. The thermo­plastics can be indefinitely melted and molded again because they do not undergo a chemical change in their composition once they are melted. These generally soften at 60-130°C and melt at 95-260°C. On the other hand however, the thermosetting plastics are those that experience a chemical transformation when they are heated and can therefore only be melted and shaped once. This curing generally happens at a temparature above 200 °C.
Types of plastics include: polypropylene (PP), polystyrene (PS), high impact polystyrene (HIPS), acrylonitrile butadiene styrene (ABS), polyethylene terephthalate (PET), polyester (PES), polyamides (PA) (Nylons), polyvinylchlorid (PVC), polyurethane (PU), polycarbonate (PC), and polyethylene (PE).

Name                                     
Plastic

Chemical Formulas         
depends on the type of plastic:
PVC : CH2=CHCl
polyethylene : (C2H4)n (most common plastic used today for packaging)
epoxy resin : C21H25ClO5

Molecular Weight             
PVC : 93.9 g/mol
Polyethylene : 28,05 g/mol
Epoxy resin : 392.9 g/mol

Technique A: 3D Printing

Every 3D printer builds parts based on the same
main principle: a digital model is turned into a physical three-dimensional object by adding material one layer at a time. This is where the alternative term Additive Manufacturing comes from. 3D printing is a fundamentally different way of producing parts compared to traditional subtractive (CNC machining) or formative (injection molding) manufacturing technologies.
In 3D printing, no special tools are required (for
example, a cutting tool with certain geometry or
a mold). Instead the part is manufactured directly onto the built platform layer-by-layer, which leads to a unique set of benefits and limitations.

There are many different types of filament that can be used for 3D printing, and their number is steadily increasing. They depend on the shapes you want to create. PLA is the most common, it is a thermoplastic based on corn starch, an excellent base for manufacturing so-called composite materials. The majority of filaments such as metals, wood, stone use a PLA base which is filled with these additive dusts.
There are many other types of filament: ABS (Acrylonitrile Butadiene Styrene), PC (Polycarbonate), Nylon, PET (Polyethylene Terephthalate), Flexible, PP (Polypropylene), etc.

Requirements                    
3D printer
3D software

Tools (Filaments)             

Technique B: Sand 3D Printing

The sand printer is a type of 3D printing that appeared in the 1990s with a collaboration between the company Generis and MIT. This technique uses sand to make 3D printing. The sand can be silica sand, ceramic or even metal dust. The technique consists of injecting a binder into the sand in order to create 3D shapes or molds for other materials such as aluminium for example.
What is interesting about this technique is that it is similar to filament 3D printing which allows to create complex shapes (layer by layer) but it is done cold. This is a great advantage because it allows to set up much larger printing surfaces with less energy. The machine creates a first sand base and then injects the binder into the sand at the point of the shape. When the 3D shape is finished all the unused sand can be use for a new print. The latest inventions, notably in ETH, have made it possible to develop sand mold printing for concrete. There is also the possibility to print metal parts with powder glued together in the sand. 3D sand printing is therefore a very promising technique. Also the molds creations possibilities for concrete or metal will completely revolutionize the ancestral molding techniques.

Requirements                    
well ventilated area
3D sand printer
3D softwares

Tools_____________
silica sand [SiO2]
ceramic powders (ex. Silicon carbide [SiC])
metalic powders (ex. Cobalt Chrome [CrCo]
precision cleaning tool

Technique C: Resin: silicone molding and casting

To caste an object in resin, one must create a negative mold. Most often, the mold is made out of silicone. The main reason for this is that silicone is highly flexible and thus allows you to unmold the desired object easily.
A silicone mold is made of two elements: silicone rubber and a hardener. The most important factor when creating the silicone mold is the degree of hardness. This is determined by the balance between the silicone rubber and the hardener. In order not to waste silicone, it is important to calculate the volume of silicone you need and to follow the instructions for the amount of hardener needed by weighing both the silicone and the hardener. When pouring the silicone, to avoid air bubbles, it is important to pour it slowly with a very thin jet. After the silicone has been poured, tapping the edges of the mold helps release the air bubbles inside the mold. The resin is obtained by mixing a synthetic resin with a curing agent: the two combined liquids create
an exothermic reaction that hardens quickly. The different types of resin that can be used are polyester resin, polyurethane resin, epoxy resin, acrylic resin, and silicone resin. Resin is generally transparent but can be colored using tints and fillers. Once the resin has been molded in the silicone, it can easily be shaped and sanded.

Requirements                    
ideal air temperature for silicone: 18° to 22°
normal pressure

Tools                                      
wood or cardboard for silicone mold
silicone + hardener
resin + curing agent
scale
hot glue gun
mixing cup and wooden mixing stick
coloring

Technique D: Injection Molding

Injection molding process refers to the process of making molten semi-finished parts of certain
shape through operations such as press-urization, injection, cooling, and separation. It is a method of stirring a completely melted material by a screw at a certain temperature, injecting it into the mold cavity with high pressure, and cooling and solidifying to obtain a molded product. It is most commonly used to process both thermoplastic and thermosetting polymers, with the volume used of the former being considerably higher.
This method is suitable for mass production of parts with complex shapes and is one of the most important processing methods. The advantages of the injection molding method are fast production speed, high efficiency, automatic operation, and the possiblity to recycle used materials.

Requirements                    
electricity
ventilation

Tools                                      
injection molding machine
plastic pellets
mold with a desired cavity
gloves

Example: The shingles of a pavillion or the scales of a creature

To built the pavilion model with the aspect of a dancing monster reminded of Hayao Miyazaki’s fables, Tim Cousin used two techniques to create his pavilion.
Using Grashhoper he was able to define the white structure printed in ABS plastic with a basic 3D printer.
This structure is then dressed with sand tiles
made with a Z-Corp 3D sand printer with Powder
made of starch and plaster, connected by binder and flexible epoxy infiltran. These tiles have the
same shape and are printed in different colors.
He wanted to make a model that is the most assisted by machines. As soon as he had finished printing the white structure and the multi-colored tiles, he just had to place them in their notch.

Author / Modelmaker     
Tim Cousin

Project / Year                     
2019

Material                                
ABS
Silica sand and Binder

Techniques                          
3D sand printer
3D printer

Example: KU.BE Silicone & Resin

This model was created by Atelier La Juntana to represent an architectural project called KU.BE
by MVRDV, ADEPT and SLA.
Each piece of the model was individually created and molded in silicone in order to be reproduced in resin. According to the different places and functions of the building, the pieces each have a specific shape and color.
The pieces were made in tinted polyester resin. The surface of the pieces show that they were treated after having been unmolded. Cut and sanded, the individual pieces were manipulated
to create this symbiotic construction where every piece is individual but finds its place when the whole project is put together.
The base of the model was casted from white polyester resin. In order to create this base, the
mold and counter-mold were created by covering the original wooden base with a layer of clay and then a layer of plaster that filled the casting boards. By removing the the clay the mold is made visible and ready for the silicone rubber to be poured creating the mold. This method is especially useful when creating larger objects with a high degree of precision.

Author / Modelmaker     
Atelier La Juntana

Project / Year                     
KU.BE, House for Culture and Movement/2014

Material
Colored polyester resin

Techniques
Silicone molding
Resin molding

Example: Precious Plastic

The recycling project Precious Plastic’s open­source machines, which shred and remold old plastic, are being used to recycle plastic and turn it into face shields, respirator masks and handsfree door handles to fight the coronavirus.
Designers and makers that use the Precious Plastic machines are repurposing them to make items needed by local health care workers.
Their injection molding machines can manu­facture personal protective equipment (PPE) 75 times faster than a 3D printer. Shredder machines take sorted plastic waste and turn it back into useable flakes of plastic. Separate machines, including an injection molder, an extruder or a rotation molder, turn the flakes back into useful objects.
To make the items, the plastic is heated to over
200 degrees Celsius which sterilises the plastic and it has previously been cleaned. The injected items also benefit from not being porous like 3D printed counterparts, ensuring bacteria and viruses can’t hide inside the plastic.

Author / Modelmaker     
Dave Hakkens

Project / Year                     
Precious Plastic / 2020

Material                                
Recycled plastic

Techniques                          
Injection molding

Resources / Literature

KU.BE model + resin molding http://www.atelierlajuntana.com/KU.BE-1.html, 03.06.2020

Resin molding, https://acrylgiessen.com/en/how-to-make-silicone-moldsfor-resin/, 03.06.2020

Plastic properties, https://www.emachineshop.com/properties-of-plastic/, 03.06.2020

Plastic properties, https://en.wikipedia.org/wiki/Plastic, 03.06.2020

Tim Cousin: “SHINGLES CREATURE / SCALES PAVILLION”, https://palarc.cargo.site/Shingles-Creature, 2019.

All3DP, “Sand 3D Printer – What Exactly Is It?”,
https://all3dp.com/2/sand-3d-printer-what-isit, 27.04.2019.

Malloy, Robert A. Plastic Part Design for In­jec­tion Molding. Munich, Vienna, New York, 1994.

India Block, “Recycled plastic turned into face shields for coronavirus pandemic”,
Retrieved from https://www.dezeen.com/2020/04/08/precious-plastic-coronavirus-recycled-face-shields-respirator-masks-handles/, 08.04.2020

Instructables. Home Injection Molding, 09.11.2017. Retrieved from https://www.instructables.com/id/Home-Injection-Molding/

Tucker, E., Dave Hakkens updates Precious Plastics recycling machines. Retrieved
from https://www.dezeen.com/2016/04/14/davehakkens-updates-open-source-precious-plasticrecycling-machines/, 07.04.2020