A hot-wire foam cutter is a tool used to cut polystyrene foam and similar materials. The device consists of a thin, taut metal wire, often made of nichrome or stainless steel, or a thicker wire preformed into a desired shape, which is heated via electrical resistance to approximately 200°C. As the wire is passed through the material to be cut, the heat from the wire vaporises the material just in advance of contact.
The depth of the cut is limited only by the wire length. Width of cut is limited by throat, if any.
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All thermofusible expanded foams. This means those materials that melt at a relatively low temperature:
A preformed wire is attached to a handle. The operator manually guides the wire through the foam to cut freeform shapes.
A short tensioned wire is attached to a handle. The operator manually guides the wire through the foam to cut freeform shapes.
Hot wire foam cutting tables can use a vertical or a horizontal wire, usually with a horizontal table used as a guide or for securing the foam work piece.
A table with a vertical wire is mainly used by hobbyists to cut small and complex shapes such as letters. Only prismatic members can be cut on this type of table.
Tables with horizontal wires are heavily used in construction and packaging. The cutting wire is attached to tracks on either side of the table enabling it to be moved up and down making cuts very exact. This table type can also perform angular cuts.
A horizontal-wire manual table that uses templates placed on each side of a foam block to guide a taut hot wire to form a prismatic or tapered shape. The hot wire, tensioned with a bow or by springs attached to a rigid frame, can be propelled through the foam by hand or with a cord and pulley mechanism connecting each end of the hot wire to a weight. This method is widely employed by hobbyists to produce foam cores for model airplane wings.
Template-guided cutter accuracy is highly dependent on operator skill at fixturing the foam and guiding the hot wire along the templates. Accuracy is also affected by the precision to which the templates are formed and proper assessment and handling of kerf.
Computer Numerically Controlled (CNC) stages on each side of a block of foam guide a tensioned hot wire to form a prismatic or tapered shape. This is a four degree of freedom CNC system (one each X and Y on each side of the foam block).
Accuracy is affected by the precision of the stepper motors, backlash of drive systems, and stiffness of the races supporting the end effectors which hold the tensioned wire.
Some CNC hot-wire cutters offer lathe attachments, which can be used with either stretched or preformed wire. Lathe attachments allow cutting of spiral shapes, and are often used to create concrete forms for ornamental and structural items, such as planters and stairway balusters and newels.
The practical limit to the length of a tensioned cutting wire is the tendency of the wire to sag under the force of gravity, which requires higher tension for longer wires. Some CNC cutting machines place the ends of the wire above and below the workpiece, with the wire being mostly vertical, to counter this problem.
Cutting speed and wire temperature combine to determine the thickness and consistency of kerf. For a given wire temperature, an attempted motion in excess of the wire's ability to melt the foam can lead to wire drag and poor surface finish of the cut foam. Conversely, dwelling in the foam any longer than strictly required to melt the cut path can lead to excessively thick kerf. A nonuniform feed rate can lead to a kerf of varying thickness.