Today we will learn about drawing process Working and its types like wire drawing, rod drawing and tube drawing. Drawing is a metal forming process used to reduce cross section and increase length of work piece. This process associated with tensile force which distinguishes it from other metal forming processes like extrusion, forging etc. In this process a large cross section work piece is forced to pass through a die which has smaller opening comparing cross section area of work piece. This will plastically deform the work piece by decreasing its cross section area and increases its length. This process is used for making wires, rods, tubes etc.
Requirement of Drawing Process:
- The material should have sufficient ductility so it can sustain tensile force.
- The material should possess high tensile stress.
- The rod or wire should be properly cleaned and dust or scale free before drawing.
- It should be properly lubricated to reduce friction associated with operation.
Drawing process can be divided into following three types.
A wire is a circular, small diameter flexible rod. Wire drawing is an cold working process. It is an operation to produce wire of various sizes within certain specific tolerances. This process involves reducing diameter of thick wire by passing it through a series of wire drawing dies with successive die having smaller diameter than the preceding one. Mostly die are made by chilled cast iron, tungsten carbide, diamond or other tool material. The maximum reduction in area of wire is less than 45% in one pass.
Rod drawing is similar process like wire drawing except it is rigid and has larger diameter compare to wire. This process need heavier equipment compare to wire drawing because the wire can be coiled but a rod should be kept straight. The work piece is first fed into die and pulled by a carriage which increase its length and decrease its cross section. Now the rod is to be cut into sections.
Tube drawing is also similar to other two processes except it uses a mandrel to reduce wall thickness and cross section diameter of a tube. This mandrel placed with die and the work piece is pulled by a carriage system as describe in rod drawing. The tube is either circular or rectangular. It also required more than one pass to complete drawing operation.
All drawing process works on same principle. Its working can be summarized as follow.
- First a hot rolled rod is created by other metal forming processes like forging, extruding, centrifugal casting etc.
- Now the rod is made pointed to facilitate the entry into the die.
- The dust or other scale particle should clean from the rod. This process is done by acid pickling.
- Now the prepared skin is coated with lubricant. This process uses either sulling, coppering, phosphating or liming process. Sulling is a process of coating with ferrous hydroxide. In phosphating magnesium or iron phosphate is coated. Cu and Sn are used for lubricant high strength material. Oil and grease use for wire drawing and soap is used for dry drawing.
- Now the rod is pulled through various dies to convert it into desire shape. The die is affected by several stresses so it is made by high strength alloy steel like tungsten carbide etc.
- This process is used for making wire of copper, aluminum etc. which are used in electrical industries.
- Paper clip, helical spring etc. are wire drawing product.
- Small diameter rods and tubes are drawing product.
- It is used to produce large length of small cross section.
This is all about basic principle of drawing process types like wire drawing, rod and tube drawing. If you have any query regarding this article ask by commenting. If you like this article, don’t forget to share it on your social networks. Subscribe our website for more interesting articles. Thanks for reading it.