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Drawing
Dr. Dmitri Kopeliovich
Drawing is a metal forming process involving pulling a workpiece (cold or hot) through a die providing reduction of the cross section of the workpiece.
The drawing process employs a series of dies with opening of similar shape and of size which is slightly reduced in each consequent die.
As the cross section decreases after passing each die, the length of workpiece increases, requiring corresponding increase of the speed.
The draw force is dependent on the yield strength of the metal, reduction of the cross section area (amount of deformation), contact area of the bar with the die and the coefficient of friction.
Friction and deformation in the die cause heating the workpiece (wire, tube, rod) surface and may result in sticking and breaking.
Contact friction, which is about a half of the total draw force, is controlled by lubricating the bar before it enters the die.
When the total amount of deformation is too large and the wire undergoes hardening as a result of the previous cold work operations, drawing is carried out in steps with annealing after each step.
Dies are made of alloy steel (die steel) hard alloys and diamond (drawing steel wires).
Drawing provides good surface quality and very low dimensions tolerances.
Drawing is used for production of wires (diameter down to 2µm) , seamless tubing, rods and other products from brass and steel.
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