1. Chapter #07 Mechanical working of metals.

2. Introduction. The mechanical working of metal is the shaping of metals either in cold or hot state by some mechanical means. Cold working means the subjecting of metal to forces which cause it to go under plastic deformation when it (metal) in the cold state means at room temperature. Hot working is the subjecting of metal to force which cause it to undergo plastic deformation when the metal is in hot state means at some degree of temperature. The processes included are rolling, forging, drawing and extrusion etc. Note. Cast iron can not worked under these processes because it is brittle in nature.

5. Rolling. Rolling is the process of producing basic shapes and flat products like plates, sheets and strips by passing through rolls. Rolling provides the cheapest and most efficient method of reducing the cross sectional area of a piece of metal in such a way that the final thickness is uniform through out the long lengths of the product. Cold rolling. It is usually applied to sheet or plate to make it thinner to give it a better surface finish to maintain a closer tolerance and to increase strength and hardness. Hot rolling. It is usually used to convert ingot into smaller sections known as billets. Hot rolling is used for sheets, plates but mostly used for producing the rods, bars and various structural shapes like rails, angles, girders and channels and so on by making successive passes through rollers which are grooved to produce the desire shapes.

6. Principle of operation. A pair of cylindrical rollers are made of iron or steel rotate in opposite direction (one in clock wise and other is in anti clock wise) with a gape between them which is smaller than the cross section of the piece which is to be rolled. The work piece is entered in to the gape and it passes between the rolls it is squeezed its cross section being progressively reduced. Since the working volume remains constant the result of one pass through the rolls is lengthening of work piece and a precise reduction and shaping of cross section. The reduction accomplished in one pass is commonly with in the range of 10 to 30% so great many passes are normally required. Materials for hot rolling. Ferrous materials. Steel and its alloys. Non ferrous. Al, CU, Mg, Ni, Brass, Bronze, Zn and their alloys. Ferrous and non ferrous powder metals also. Note. Hot rolling is carried out at temperature about 1000 o c for mild steel and 450 o c for aluminum.

7. Types of rolling mill. Generally hot rolling may be done by different rolling mills which are classified on rolling stand design. According to the number of arrangement of the rolls mill stand can be classified in to the following groups. Two high rolling mills. A rolling mill stand (a set of rolls and the housing in which they are mounted) with two rolls mounted parallel one above the other and rotating in one direction. This is also called non reversible stand mill with a constant one direction of rotation around horizontal axes. Such stands are widely used in mills through which the metal passes once a time This type of mill is used for primary break down the metal work piece.

11. Two high reversible stand mill. In this type of rolls are rotate first in one direction and then in other so that the rolled metal may pass back and forth through the rolls for several times. These types of rolls are used for roll the blooms. In this the rolls may be cylindrical with grooves or without grooves of desire width may cut in to them to accommodate the ingots and the various reductions in cross section. These rollers are used for plate, rail, structural like girders, T-iron etc.

12. Three high rolling mill. A three high stand has three rolls with a constant direction of rotation are arranged so that the middle roll is above the bottom and below the top roll. These rolls need not be reversible since the metal can be rolled in one direction between the middle and top and rolled in returning direction between the middle and bottom. Mechanical tilting tables are provided on both sides of stands to raise the work piece and to enter it between middle and bottom rolls. These stands of this type find extensive applications in different shapes.

13. Four high rolling mill. This type of mill have four rolls which are arranged on above to an other in the vertical plane. In this two rolls are small in size which are called working rollers. While other two rollers are larger in size whose to support the working rolls for preventing the deflection of the smaller rolls are called back up rollers. Other advantages of larger rolls is to minimize the pressure when rolling with smaller diameter rolls. These type of mills are used for cold working, and also used to produce flat plates, sheets and strips material of uniform thickness.

14. Tandem rolling mill/continuous mill. This type of rolling mill also called continues mill. It is a set of two or three stand rolls set in parallel alignment so that a continuous pass may be made through each successively without change any direction of material or pause in the rolling process. It can be seen that a continuous mill is fast and requires a minimum of metal handling. How ever a continuous mill is not suitable for small production because of the high cost of equipments there fore it is not flexible for small quantity production. For large quantity production of billets or other products from blooms is most suitable.

15. Ingot. It is the first product from the furnaces which are cast in ingot forms. It is the rectangular beveled shape like foot of cot. Bloom. A bloom is the first break down of ingot. It is square in shape with rounded corners it is 260mm square in size. The blooms are used for convert the shapes of material by rolling in form of girder, channels, rails etc. Billets. It is similar to bloom but smaller in thick ness and obtained by further reducing by hot rolling it is in 50mm to 100mm square in size. The billets are used for making bars, wires, rods etc. Slab. It is also convert from the ingots it is rectangular in cross sectional with 150 to 200mm in size. It is used to make the plates, sheets and strips etc. Plate. Plate is the long, wide and flat it is thick as sheet. Sheet. It is similar form of plate but thin than plate. Rod. Rod is in round in shape smaller than bar. Bar. Bar is very high with a variety of sections in flat round, twisted, square and hexagonal etc.

16. Forging. Introduction. It is defined as the plastic deformation of metals at elevated temperatures in to the predetermined size and shape using compressive forces exerted through some type of die by hammer or by machines. Forging processes. There are so many processes but some most important are give below. Hammer/smith forging. This is also called open die forging because the metal to be forged is heated to the required temperature in the furnace and placed on the anvil. It is then hammered to desire shape either with the help of help of hand hammer or mechanical hammers. Moreover it is a slow and old process and there fore un suitable for mass productions.

20. Drop/die forging. Drop forging process makes use of closed impression dies to over come the difficulties encountered in hammer forging. In this the impact pressure of hammer blows is repeated. Due to this impact load the metal plastically deform and confirm to the shape of the dies. The final shape of the product from the raw material is achieved successively. Forging is adopted to both ferrous metals and their alloys as well as to non ferrous alloys. Crank shafts and connected rods are the best examples of forging products. Advantages. Uniformity of qualities for parts subject to high stress and loads. Weight saving, less machining/no machining is required, smooth surface, high speed of production rate, can be easily welded. Disadvantages. High cost of tools. High tool maintenance.

21. Extrusion. Introduction. Extrusion is a metal working process that produces long lengths of uniform X-sectional area from a metal billet. Extrusion is mainly a hot working process generally with cast billets and producing different types of sections. An extrusion press has three major components, the container, die and ram. Extrusion is more widely used in fabrication of ferrous/non ferrous metals and their alloys can also be successively processed. In this generally a heated billet is placed in the container and forced out through die by ram or plunger is called squeezed. The metal takes X- section the shape of the die. Extrusion is an un complicated hot metal working manufacturing process that can produce some of the most complex shapes of all the hot working manufacturing processes. Extrusion process is used to manufacture, rods, tubes, a variety of circular, square, rectangular, hexagonal and other shapes in solid and hallow form. Channels like, I, Z, T and other sections are also produce. Extruded sections find almost infinite uses, some of which in.

23. Applications of extrusion. Transportation, (ships, automobile, railroad and air craft industry.) Construction industry. (making building). Oil industry. (as drill pipe and pipe lines). Military uses. (armor plate, guns, and other weapons). Chemical and nuclear power industry. (extruded tubing's).

24. Extrusion methods. Direct extrusion. It is defined as when the metal is squeezed through the die in the direction of applied force the process is called direct extrusion. Or in other words in this the material is in motion and the die is stationary. In direct extrusion. It is defined as when the die is squeezed through the metal in the direction of applied force the process is called in direct extrusion. Or in this the metal is stationary while the die is in motion. Impact extrusion. The impact extrusion is a cold working process. Since it extrudes metal without the application of heat. It is usually limited to use with soft non ferrous metals like lead, tin and aluminum. Metal tubes of lead and aluminum made by impact extrusion are being used as container for a variety of domestic material such as shaving cream, tooth paste and medicine tubes etc. In this process a small un heated blank metal is placed on the die cavity. A pointed punch descend swiftly on the blank metal which flow upward and around the punch there by forming a tube shape parts.

27. Deep drawing. Drawing. Drawing refer to the shaping by a punch press of a flat blanks of sheets in a to various geometric shapes of which cup, cylinder and box shapes are most common example of this process. The process of drawing is basically that of forcing the flat sheet of metal in to a die cavity with a punch. The force exerted by punch must be sufficient to draw the metal over edge of the die opening and in to the die. The metal flow is similar to a viscous fluid. Deep drawing. Deep drawing is a special case of drawing of sheets. It is defined when the length of the object to be drawn is deeper i-e more than its width or diameter is called deep drawing. For example. Milk churns and washing machine tubs are deep drawn objects. Deep drawing demands very high ductility in sheet stock it means only those metals or alloys are to be used for deep drawing which have excellent ductility. Process. In this method the blank is placed over stationary die calculate the pressure exerted from the punch against the blank. The blank forced in to the shape of required die.

28. Wire drawing. It is defined as it is the process by which we decrease the diameter and increase the length of the rods by applying the pulling force and pass from the dies in the wires is called wire drawing. Process. In this process first stats as an extruded rod which to be coiled. The initial drawing is done on a large machine which is called deep wire drawing machine draws the rod through a die as it coil by using suitable tongs enough of the rod is pulled through the die so that it can be attached to the power reel. This power reel is rotate continuously the drawing operation until the entire rod passed through the die. The resulting products from rod a wire with increasing length and smaller cross section. N.B in this process the rod metal should be ductile other wise the rod may be break. the dies which are used for this they should extra hard, mostly tungsten carbide dies are used. THE END.