Hot-wire foam cutter
Encyclopedia
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.
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.
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
.
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.
Polystyrene
Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...
foam and similar materials. The device consists of a thin, taut metal wire, often made of nichrome
Nichrome
Nichrome is a non-magnetic alloy of nickel, chromium, and often iron, usually used as a resistance wire. Patented in 1905, it is the oldest documented form of resistance heating alloy. A common alloy is 80% nickel and 20% chromium, by mass, but there are many others to accommodate various...
or stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
, or a thicker wire preformed into a desired shape, which is heated via electrical resistance
Electrical resistance
The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element; the inverse quantity is electrical conductance, the ease at which an electric current passes. Electrical resistance shares some conceptual parallels with the mechanical...
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.
Types of wire used
- Preformed, manually or with pliers.
- Tensioned, held tight by a frame with springs or (equivalently) by a bow. Many indicate a preference for single-strand stainless steel wire over nichrome wire, in diameters ranging from .008 inches(0.2032mm) to .020 inches(0.508mm) for frame-tensioned cutters. Musical instrument strings and leader wire used for fishing lures are readily available and inexpensive. Commercial cutting equipment often uses the nickel-based alloy wire Rene 41René 41René 41 is a nickel-based high temperature alloy developed by General Electric which retains high strength in the 1200/1800°F temperature range...
, a high-strength alloy which maintains most of its tensile strength at cutting temperatures.
Foams suitable for hot-wire cutting
All thermofusible expanded foams. This means those materials that melt at a relatively low temperature:- Expanded polystyrene (blocks of expanded white balls).
- Extruded polystyrene (in blue, green, gray, pink or purple smooth plates, depending on the manufacturer).
- Polymethacrylimide low density rigid foam (Rohacell), excellent mechanical properties but very expensive.
- Flexible expanded polypropylenePolypropylenePolypropylene , also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes...
foams, ideal for shock protecting. - PolyethylenePolyethylenePolyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
foams, flexible and tear resistant. - Custom materials, such as the foams used in flexible fuel tanks to reduce explosion risks.
Preformed wire
A preformed wire is attached to a handle. The operator manually guides the wire through the foam to cut freeform shapes.Handheld
A short tensioned wire is attached to a handle. The operator manually guides the wire through the foam to cut freeform shapes.Simple manual table
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.
Template-guided manual table
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
Kerf
Kerf and similar can mean:* kerf, the width of a cut* Kerf, a poetry collection by Peter Sanger* Kerala E.N.T. Research Foundation , a hospital at Kollam in Kerala in India...
.
Computer Numerically Controlled
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
Lathe
A lathe is a machine tool which rotates the workpiece on its axis to perform various operations such as cutting, sanding, knurling, drilling, or deformation with tools that are applied to the workpiece to create an object which has symmetry about an axis of rotation.Lathes are used in woodturning,...
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.
Wire length limits
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.Speed and temperature tuning
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.Uses
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