What is Tube Drawing?
Tube drawing (also known as tube sinking) is a metalworking technique in which the size of larger diameter tube is reduced to a smaller diameter by drawing a tube through a die.
High quality tubes with precise dimensions and good surface finish can be manufactured by using tube drawing.
The tube drawn over mandrel process is used to manufacture more accurate tubes, but it requires more energy during the tube drawing operation.
In the beginning of the tube sinking process, one end is collapsed and fed through the die.
This end is clamped with the travelling carriage and the carriage is moved away from the die by hydraulic or mechanical means.
The simple tube drawing operation is less accurate, hence the tube is drawn over the mandrel to get better accuracy.
In tube sinking process, the lubricant is used to reduce the friction between the metal and the die.
The die material should be strong enough to resist the temperature and pressure of the metal.
So the dies used in tube drawing are made up of alloy steel or more often it is made of tungsten carbide.
Types of tube drawing
There are mainly 5 types of tube drawing operations.
Let’s discuss each of these tube drawings one by one.
#1) Tube sinking
Tube sinking is a simple tube drawing operation without the use of mandrel.
Tube sinking method is the cheapest and simplest type of tube drawing, but the surface finish obtained by the tube sinking method is not so good.
In tube sinking, the thickness of the tube can not be reduced but its inner diameter and outer diameter can be reduced easily.
The quality of the tube surface decreases if the thickness of the tube increases.
#2) Rod drawing
In rod drawing (sometimes called as mandrel drawing), the tube is drawn over a mandrel.
In simple words, the mandrel is used to define the inner diameter of the tube during the tube drawing.
By using rod drawing, the tubes of shorter length and good surface finish can be drawn.
Also this process is applicable for manufacturing of tubes that have small inner diameter, because of the available sizes of mandrel.
#3) Fixed plug drawing
In fixed plug type drawing (stationary mandrel type), the mandrel is used at the end of the die to define the inner diameter of the tube.
This is the oldest tube drawing method and it gives better surface finish than any other tube drawing methods.
#4) Floating plug drawing
As the name suggests, the mandrel in this process is not fixed. But it is held by friction forces between the mandrel and tube.
The floating plug drawing is capable of drawing longer tubes, hence it is used in oil well tubing.
#5) Tethered plug drawing
Tethered plug drawing is a combination of fixed plug drawing and floating plug drawing.
In this type of drawing, the mandrel is semi floating, that means it is allowed to float but it is still anchored via tether.
This type of drawing is suitable for straight tubes only and it gives better surface finish than rod drawing.