HYBRID SYSTEM In order to achieve a skeleton-membrane integrated system, we used PLA (Polylactic Acid) filaments and LDPE (Low Density Polyetylene) stretch film rolls, as proxy materials. They are both thermoplast polymers with specific distinct physical properties which are important for our material system. Relatively low melting temperature of PLA makes it easy to cut and deform. Joining PLA without additional adhesive or second material is not as efficient. PLA is quickly overheated and looses some of its flexible properties. Therefor a PLA to PLA joint is brittle and weaker than the original material. Fast cooling time though makes the joint still efficient. Parallel we introduced PCL as a second material to join the PLA rods. PCL is fairly strong and has a very low melting point of about 65°C, but its cooling time is extremely high. For us it still works as a proxy material considering the introduction of robots into the manufacturing process, providing precision and durability. High tensile strength and elongation property of LDPE stretch film lead us to use the material as wrapping material, the membrane component, taking over tension forces of the PLA structure. One of the main properties of LDPE we are interested in, is the very thin foldable foil we could easily create surfaces from by wrapping, but also diversify strength by repeated wrapping of the material. Friction is increased and is used to enhance the surfaces performance and alter transparency. After the LDPE membrane is wrapped around the PLA structure, it is shrunk by blowing hot air onto the surface. The LDPE attempts to minimize surface forcing the material to produce higher inner tension and is clinging around the PLA rod skeleton. At the end of this process, the plastic skin provides an imprint of the given geometry.  Finally the PLA-PCL proxy material system will be replaced with 3 mm mild steel rods and metal inert gas (mig) welding as joint strategy. MIG-welding is a welding process where the object to be welded is grounded to the machine, a high load of amperes is used to artificially bypass the electric circuit, producing a very hot spark and melting the steel to be weld-able. In less than a second the welded spot is cooling down to a temperature maintaining rigidity. Not only cooling and joining processes are extremely fast, but the most beneficial attribute is that the joint becomes stronger than the initial material through welding. This phenomenon is a required material property, complimenting our material system. Strong connecting details are bending resistend and the slightly more bendable rod itself is a necessity to react onto compression forces through wrapping of the LDPE membrane, to become more stable and solid as a whole. In order to scale up it is important to maintain a constant equilibrium between the two elements, skeleton and skin, which is achieved through a sensibility for profile thickness, geometric assembly and frequency.
Polymers Duroplast Elastomers Thermoplast Thermoplastic Thermosetting Formed under heat / pressure hardened by cooling Formed under cool temperature hardened by heat / pressure Multi process-Reusable Recyclable Single Process-Not Reusable Toxicity
1 Membrane Material: LDPE Price per kg: 1,97 GBP Melting: 95°C Cooling Time: aprx. 24 sec E Modulus: 400 MPA 2 Segment Material: PLA Price per kg: 33,30 GBP Melting: 210°C Cooling Time: aprx. 40 sec E Modulus: 500 MPA Energy required: 0.24 kW 3 Connection Material: PCL Method: Manual Heatgun Welding Price per kg: 89,70 GBP Melting: 60°C Cooling Time: aprx. 240 sec E Modulus: 470 MPA Energy equired: 0.24 kW
PRINCIPAL DESCRIPTION The name polymer comes from it’s molecular configuration. Many repeated subunits form one molecule or macromolecule. Because of many potential combinations, polymer molecule chains flourish a great variety of properties. Biologic and synthetic differentiations can be made, which three main branches are defined under the family of polymers: Duroplasts, Thermoplastics and Elastomers. Even though they are all considered polymers the property contrast between them is very high. This becomes a critical differentiation factor when it comes to material behaviour and mechanical properties. Optical properties become easily distinguishable but are not as important for us. A common way for differentiation between polymers is by comparing their macromolecular structural combination. Duroplasts macromolecules are connected in a net-like manner, molecules are connected in a rigid ways which does not allow them to freely move. Thermoplastics molecule chains mostly lie next to each other so they can freely move alongside, which allows them to be formed by heating and hardened by cooling. Elastomeres form sort of nests of molecular connection, by mechanically pulling elastomeres apart they deform, releasing regenerates the old form which the polymer slowly reforms back to. The most common polymers: Duroplasts: Melamine-Formaldehyde-Resin (MF), Aminoplast (UF) Thermoplastics: Polyethene (PE), Polypropene (PP), Polystyrene (PS), Polyvinyl chloride (PVC), Polyamide (PA), Polymethylmethacrylate (PMMA), Polycaprolactone (PCL), Polylactic Acid (PLA), Low Density Polyethylene (LLDPE) Elastomere: Polyurethane (PUR)
POLYLACTIC ACID (PLA) Polylactic Acid or short PLA is used for many applications. It is also extrudable since it is also an thermoplastic, but the melting temperature is higher than the melting temperature of PCL, which makes it more heat resistant. Mostly though PLA is known for it’s 3D-Printing filament application. Temperatures around 200 °C make the thermoplastic almost liquid and also easily operate-able. Even though the operating temperature of PLA is way higher than the operating temperature of PCL the face change, soft to hard, hot to cold is quicker. One of the major disadvantages of PLA compared to PCL is that once the filament has been heated and extruded it becomes very stiff but brittle, while PCL’s reformable cycle is almost infinite. This property was at the end the crucial factor to dismiss PLA as our material to be used for the substructure frame. Also standing in conflict with one of our main objectives to create design process, adaptive and reshape-able throughout time.1  Density: 1.210-1.430 g/cm3 Heat Deflection Temperature: 49 - 52 °C Melting temperature: 150-160 °C Tensile strength: 61 - 66 N/mm2 Solubility in water: Insoluble Toxic Level: Non Toxic
POLYCAPROLACTONE Polycaprolactone is mostly used in the medical field. Artificial tissue is engineered, but also orthopaedic moulds are created with PCL. The most interesting upside of PCL is it’s low melting point and easy deform-ability, which make the material unique. Granulate palets can be heated up with warm water and bring the material in seconds to it’s optimal operating temperature. Deformation can be easily achieved by hand. PCL is very interesting for our project because of it’s well combination with other plastics and low delta of phase change between hard and soft. For especially because the fabrication strategy is not like classical 3D-Printing processes where layer by layer is printed. But an adaptive 3D-printing process, printing in space, with hot material connecting on to cold existing structures. One of the biggest challenges to work with the material to achieve the highest possible fidelity is to control the temperature extremely precise, so we can distinguish between soft bendable parts and hard supporting nodes as references for new structure.  Density: 1.145 g/cm3 Elastic, elongation: 56% to 93% Melting temperature: 60 °C Tensile strength: 264.8 N/mm2 (melt extruded PCL) Glass transition: -60 °C temperature Toxic Level: Non toxic Combines well with other plastics Easily fabricated
LOW DENSITY POLYETHYLENE (LDPE) LLDPE is a thermoplastic mostly known for it’s use in foil, and more specific cling film production. It’s high tensile strength and elongation property lead us to use the material as the wrapping component, taking over tension forces of the structure. One of the main properties of LLDPE we are interested in is the very thin fold-able foil we could easily create surfaces from by wrapping, but also through strong wrapping of the material friction is increased and can be used to enhance the surfaces performance. Common manufacturing methods are: Transition metal catalyst initialized polymerization process done in solution phase or gas phase reactors.  Density: 0.915 g/cm3 Elastic, elongation: 500% Melting temperature: 50 °C Tensile strength: 30 N/mm2 Stretch film, elongates under stress High load capacity Low manufacturing energy use
Metal Alloys Nonterrous Cast irons Steels Ferrous Low alloy High alloy Plain Stainless Tools High-carbon Medium-carbon Low-carbon Plain High strength low alloy Plain Heat treatable
1 Membrane Material: LDPE Price per kg: 1,97 GBP Melting: 95°C Cooling Time: aprx. 24 sec E Modulus: 400 MPA 2 Segment Material: Mild Steel Price per kg: 6,75 GBP Melting: 1400°C Cooling Time: aprx. 0.75 sec E Modulus: 200.000 MPA Energy required: 1.64 kW 3 Connection Material: Copper Electrode Method: MIG-Welding Price per kg: 9,75 GBP Melting: 1083°C Cooling Time: aprx. 1.6 sec E Modulus: 117.000 MPA Energy required: 1.26 kW
MILD STEEL Mild steel is an alloy of iron and a low carbon proportion. It is manufactured with the Bessemer’s process1, which makes it possible, to produce large quantities, the production of the material efficient and thus cheap2. Modern steel making uses iron ore, which is smelted into pig iron inside a blast furnace3. Iron ore is smelted so the iron is detached, naturally iron has too much carbon to be steel so the carbon value has to be reduced. The reproduction process also allows for other materials to be added and purify the alloy, giving the steel a variation of properties like better conductivity, strength, corrosion protection or aesthetics. Most steels can be hardened by heat treatment, the most common treatment is called annealing. Recrystallization through heating and cooling extruded mild steel rods, results in reduction of internal stresses and defects. Typically temperatures for the annealing process ranges between 260°C and 760°C. The materials consistency also compliments welding without any further treatment. After the mild steel production process rust prevention may be applied and has to be removed prior to welding. Welding is not only used to connect two pieces of steel, it also has an other useful side effect. MIGwelding produces a high enough temperature to anneal the connection and the steel which is connected, resulting in a stronger connection detail compared to the initial material. Density: 7700 kg/m3 4 Elongation Value: 6 - 7% 5 Melting temperature: 1427 °C 6 Tensile strength: 841 MPA 7
 Image 36. Steel profiles
 Image 37. Steel casting