More than five decades back, new techniques and principles were developed by engineers which utilized pressurized air to create lightweight, rapidly deployable and inexpensive structures such a buildings, furniture etc. They are popular even today due to their functionality and scale.
The team at MIT got inspired by these techniques and pneumatics principles and developed a vision to create large, functional and dynamic pneumatic artifacts called Printflatables.
Printflatables is a unique system of designing and printing static or dynamic pneumatic forms at various scales meant for human use.
The overall process involves using inflexible thermoplastic fabric as raw material, using CNC machine to introduce folds in the fabric and then thermally sealing it. This gives rise to a structure that upon inflation, takes a 3D shape.
The user specifies a desired 3D model which is transformed to 2D fabrication geometry using a design tool. This acts as an input for numerically controlled thermal contact iron that seals layers of thermoplastic fabric.
Since the fabric required for this system requires more stiffness and maximum inflation, therefore, the commonly used materials are thermoplastic polyurethane (TPU) backed Oxford (200 Denier), Tafetta (100 Denier), Ether (70 Denier) and Nylon (70 Denier) fabrics. Sometimes clear PVC (5-8 mil) sheets are also used as a replacement of the above material.
A customized CNC machine was used that functions like an assembly-line with the following sequence: 1) Feed fabric to the machine, 2) Form folds/ mountains, 3) Seal the fabric mountains, and 4) Perform 2D heat sealing and exit the fabric.
1: Feed fabric to the machine
Two layers of fabric are fed to a machine, which has two rollers for friction-less unrolling of fabric. Rollers (a) and (b) are driven in a synchronized manner to pull fabric from the roll and feed two layers of fabric (top and bottom) into the machine. Roller (a) grips the bottom layer of fabric while roller (b) grips both top and bottom layer and push them ahead as they continue to rotate. The bottom layer of fabric has the thermoplastic (TPU) coating facing up and the top layer has it facing down ensuring that the heat sealing results in maximum bond strength.
2: Form folds/ mountains
As depicted in Figure above, there are 4 rollers (a),(b),(c),(d). As the fabric moves forward, these rollers work in such a manner that a mountain or fold is created on the upper layer. Roller (a) and (d) are static but have a braking effect by holding the fabric tightly, while (b) and (c) rotate in synchronized fashion. In this mechanism, while the upper layer keeps sliding, the lower layer remains fixed. So as it passes through roller (c) and fixed roller (d), it forms a mountain like structure.
3: Seal the fabric mountain
As soon as the mountain is formed, a pincher heat seals it using pinching mechanism. The pincher has a static and moving arm, both having a series of plates. The plates on static arm are heated and moving arm plates pushes against the plates of static arm, thus forming a bond in the fabric.
4: 2D heat sealing
A significant portion of the fabrication technique involves 2D heat sealing. This is done using a 3-axis CNC gantry. Once the mountain is sealed as depicted in step 3, all rollers are activated to allow mountain to pass through roller (d) into the CNC gantry for 2D heat sealing; where both the flat fabric and mountain are 2 D sealed.
An inflatable chair was created using this method with 200 Denier TPU-backed Oxford fabric.
As depicted in image above, the chair transforms itself by spiraling on inflation. This structure has 7 angular folds that can be created either by a single large mountain or multiple small mountains. To make the chairs stronger, the team chose 2 mountains for each angle instead of one large fold.
When the structure was deflated it was observed that it took a completely different shape due to weakness in folds; thus it was able to serve as a couch.
This inflation & deflation technique was used in another application, a responsive window blind where this method changed the shape of the blinds for regulating light.
The current method has a limitation that fabric mountain formation is unidirectional. However, the team intends to improve the technique to make more versatile fabric folds and hence more flexible angles. Some of the other areas of improvement identified are:
- Thermal welding is not the best method for sealing, so the team intends to explore Ultrasonic sealing methods.
- Current heat sealing methods allow sealing of only top 2 layers; while scope of improvement is much wider in this case.
- Minimizing manual intervention by automating the processes further is another area that needs to be addressed.
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