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According to Veltkamp (2007), subtractive processes relate to cutting off or

carving out of a large original volume to get end products. These processes are

done through cutting devices that are either point (e.g. a mill), line (e.g. a cutting

wire), or surface (e.g. a saw blade). Therefore, hot wire cutting is a subtractive

process. Hot wire cutting has many advantages in creating formwork for casting.

The key feature of the robotic hot wire cutting (RHWC) system is that it is

subtractive in nature. Unlike most rapid prototyping and manufacturing systems,

which build up parts using additive, layer-by-layer processes, RHWC starts with

a block of polystyrene foam and then cuts this block down to the desired

shape and size using a combination of taut hot wire, straight hot blade and

curved hot blade tools operated by a robot. Taut hot wire and straight hot blade

tools can be used to sculpt planar surfaces and for profile cutting, while curved

hot blades can be used to sculpt 3D and freeform surfaces using multiple toolpasses. The subtractive nature of the RHWC system is most suitable for the

creation of large-size physical models, since subtractive sculpting is much more

efficient than additive manufacturing for large build volumes (as the size of a

physical model doubles, the surface area increases by 4x and the volume

increases by 8x so clearly it is more economic to produce large

models from already solid materials).

Figure 1. Robotic hot wire cutting systems: (a) stationary and (b) hand-held

a b

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The RHWC system will be able to sculpt large scale objects with low material

costs and rapid build times, and it is this advantage that separates RHWC from

other Rapid Prototyping and Manufacturing (RP & M) systems. Whereas most

RP systems have maximum construction dimensions measured in hundreds ofmillimeters and use relatively expensive plastic materials, the construction

volume of the RHWC system can be measured in meters (and can be increased

if necessary by using larger industrial robots) and the working material is

polystyrene foam, which is readily available in large volumes at relatively low cost

throughout the world.

Figure 2. End effectors

a. Taut hot wire

b. Kinetic hot wire

c. Preformed hot wire

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Figure 3. Materials used in hot wire cutting: foam, EPS/XPS polystyrene

a b

Figure 4. Geometry of end product

a. Revolved surface

b. Free-from surface with kinetic hot wire

c. Free-from surface with preformed hot wire

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Figure 5. Solid based cutting process

Figure 6. Architectural potential applications