As the Cross section area of the wire decreases, mechanical & electrical properties are increased. This is why wire has to be drawn to smaller sizes after casting. Wire Drawing usually starts with 9 mm rod. For aluminium and steel wire it can be larger in diameter where in Copper wire the most common size is 8mm copper rod. Drawing is a simple process; the wire is pulled through series of dies. The size of the wire reduced 10-25 % over each die. Starting from 9 mm , wire needs to be pulled through more than one die. Wire gets harder and more rigid after passing through drawing die. Wire has to be annealed if the reduction in diameter is over %50. Annealing can be applied as intermediate process or afterwards. For example, widely used wire "0,50mm" in diameter will be drawn and redrawn many times starting from 8.0 mm untill diameter is reduced to 0,50 mm. Annealing after drawing and reducing the size of the diameter would maximize ductility and minimize conductor resistance.
Most common drawing dies are made of Tungsten carbide, and Diamond. There are several different types of drawing process. We can divide wire drawing processes by either drawing die is rolling or fixed , wet or dry drawing.
Dies ,pulleys and wire are completely dipped in lubricant. Less friction
results in better surface of finished wire and longer die life.
Dry drawing: Wire passes through lubricant first before going through drawing die. Wire's surface is coated with lubricant which helps to minimize fricton power between the wire and die.
Fixed Drawing Set of drawing dies fixed on drawing plates. Wire size is reduced as each die is passed. It can be applied as either wet or dry drawing. Fixed drawing dies have minimum 3 different angles. Approaching angle , entering angle , leaving angle. These 3 angles should be calculated regarding the cross section reduction ratio and wire material. Different metals and non-metals would use different angles.
Roll drawing: Rolling dies replacing fixed dies. Rolling dies have advantage of less friction which results in less pulling power and bigger size reduction per die. Roll drawing also decreases the number of dies in one sequence.
Lubricants are used to reduce friction between wire , die and pulleys. Whether it is either shear friction or rolling friction drawing process requires use of a lubricant. It is the lubricant makes it possible to produce drawn wire with fine surface, not to mention longer life of dies. There wide variety of lubricants used commercially. Oil is used widely as lubricant. Durability and viscosity of the lubricant plays a big roll in the quality of the finished product and drawing speed.