What is Wire Drawing?
Wire drawing (or bar drawing) is a bulk deformation operation of metals in which the cross section of the wire (or rod or bar) is reduced by pulling it through a die opening.
Wire drawing is similar to metal extrusion, except that the wire is pulled rather than pushed through a die.
Wire drawing is generally done at a room temperature and hence it is a cold working operation.
Sometimes, the wire drawing is performed at higher temperatures if metals to be drawn have a larger diameter.
When the pulling of wire is done, the pressure is set up on the wire and its plastic deformation takes place which reduces its diameter.
The inner surface of the die is lubricated by using proper lubricant which reduces the friction during wire drawing.
In the beginning of the wire drawing operation, the end of the wire is first reduced and it is made into a point shape to insert it through the die opening.
This reduction of thickness at the end of wire is done by either hammering, rolling, filing or swaging operation.
This end is gripped with the help of a gripper and then its pulling is carried out.
During the wire drawing of metals, the volume of metals remains the same, so the length of the drawn wire increases as its diameter reduces.
If more reduction is required then the wire is drowned in successive steps by passing it through multiple dies (see above image).
The final drawn wire is then wound on the drum.
Types of Wire Drawing
There are basically 2 types of wire drawing techniques.
- Hot wire drawing
- Cold wire drawing
Let’s see each of these types of wire drawing one by one.
#1) Hot wire drawing
Hot wire drawing is generally used for drawing the wires which have higher thickness.
By heating the metal at higher temperature, they can be drawn with less force.
By hot wire drawing, the crystals are refined in the metal and the work-hardening of the metal does not take place.
The disadvantage of hot wire drawing is that it requires a large amount of thermal energy to heat the metal before drawing.
Also the cooling of dies is necessary to prevent it’s damage.
#2) Cold wire drawing
The cold wire drawing is a wire drawing operation which is carried out at room temperature.
For most of the wire drawing operations, the cold wire drawing operation is preferred.
This is suitable for thin wires, as it requires less pulling forces.
By cold wire drawing, the material gets work-hardened and wires with good surface finish are obtained.
Example/Applications of wire drawing
The examples/applications of wire drawing are mentioned below.
- Steel wires, copper wires, as well as wires of other ductile metals can be drawn easily by wire drawing.
- By using wire drawing, various sections can be made such as round section, square section, etc.
- Various other applications of wire drawing includes;
- Electrical wiring
- Paper clips
- Spokes of wheels
- String for musical instruments, etc.