Bending Hot Wire to Cut Foam Into Unique Shapes

Two of the most common fabrication methods are additive manufacturing and subtractive manufacturing. “Additive manufacturing” is usually used to describe technology like 3D printing, where material is built up to form the object. “Subtractive manufacturing” is far more diverse and covers everything from CNC machining to plasma cutting to waterjet cutting. Hot-wire cutting is another type of subtractive manufacturing in which a thin wire is heated up to a high temperature in order to cut smoothly through material like Styrofoam (closed-cell extruded polystyrene foam). This robot is able to bend that hot wire in order to cut far more complex objects than is typically possible.

A typical hot-wire foam cutter has a length of thin nichrome wire strung taught between two posts. When electric current passes through that nichrome wire the resistance causes it to heat up to somewhere around 200 degrees Celsius. That’s hot enough to quickly and easily melt extruded polystyrene foam in order to achieve smooth cuts. Hot-wire foam cutters can be handheld for performing manual cuts, or attached to a machine or robot to repeatedly achieve precise cuts. The latter, for example, is often used to cut packing foam to size. But, because the wire is taught, those cuts have to be straight.

This “RoboCut” robot has two arms, and holds the hot nichrome wire between the arms. By moving and twisting its arms, the robot can control the bend in the wire to achieve an arc shape or even an “S” shape. The nichrome wire is relatively thick so that the bend is more predictable and stable. Those bends allow for far more complex cuts. For example, a concave bowl would be impossible to cut with a straight wire — there is just no way to get the wire into the cavity with cutting the walls of the bowl. This robot could cut that bowl easily by simply giving the wire an arc bend that fits into the cavity. RoboCut’s capabilities were demonstrated by cutting a three-dimensional rabbit out of foam, along with a number of other shapes. Because the cutting process is quick, this technology could be used for rapid prototyping that is faster than other methods.