thumb|Drawing silver wire by hand pulling
thumb|200px|Drawing thicker silver wire by cranked pulling
Wire drawing is a metalworking process used to reduce the cross-section of a wire by pulling the wire through one or more dies. There are many applications for wire drawing, including electrical wiring, cables, tension-loaded structural components, springs, paper clips, spokes for wheels, and stringed musical instruments. Although similar in process, drawing is different from extrusion, because in drawing the wire is pulled, rather than pushed, through the die. Drawing is usually performed at room temperature, thus classified as a cold working process, but it may be performed at elevated temperatures for large wires to reduce forces.
Often intermediate anneals are required to counter the effects of cold working, and to allow further drawing. A final anneal may also be used on the finished product to maximize ductility and electrical conductivity.
An example of product produced in a continuous wire drawing machine is telephone wire. It is drawn 20 to 30 times from hot rolled rod stock.
Lubrication
Lubrication in the drawing process is essential for maintaining good surface finish and long die life. The following are different methods of lubrication:
- Wet drawing: the dies and wire or rod are completely immersed in lubricants
- Dry drawing: the wire or rod passes through a container of lubricant which coats the surface of the wire or rod
- Metal coating: the wire or rod is coated with a soft metal which acts as a solid lubricant
- Ultrasonic vibration: the dies and mandrels are vibrated, which helps to reduce forces and allow larger reductions per pass
- Roller die Drawing (also referred as Roll drawing): roller dies are used instead of fixed dies to convert shear friction to rolling friction with dramatic reduction in the drawing forces as reported by Lambiase. When roller dies are adopted, the drawing stages are composed by 2-4 idle rolls and the wire is pulled within the rolls clearance. This type of solution can be easily adopted also to produce flat or profiled drawn wires.
Various lubricants, such as oil, are employed. Another lubrication method is to immerse the wire in a copper(II) sulfate solution, such that a film of copper is deposited which forms a kind of lubricant. In some classes of wire the copper is left after the final drawing to serve as a preventive of rust or to allow easy soldering.
Mechanical properties
The strength-enhancing effect of wire drawing can be substantial. The highest strengths available on any steel have been recorded on small-diameter cold-drawn austenitic stainless wire.
Drawing dies
thumb|Diagram of a carbide wire drawing die
Drawing dies are typically made of tool steel, tungsten carbide, or diamond, with tungsten carbide and manufactured diamond being the most common. For drawing very fine wire a single crystal diamond die is used.