Basic Manufacturing Processes Abdul Khader AA Manufacturing Processes • Manufacturing processes refer to the processes of producing articles of definite shape, size and properties • In this unit, manufacturing processes involving forging are discussed Abdul Khader AA Manufacturing Processes Forming Deforming Machining Joining Surface Property Processes processes processes finishing modificati Processes on Casting Forging Turing Welding Metallic Annealing coating Power Extrusion Milling Brazing Normalizing metallurgy Anodizing Rolling Grinding Soldering Tempering Plastic Plastic coating technology Sheet metal Shaping Riveting working Buffing EDM Swaging Lapping Electroplating Thread rolling Abdul Khader AA Mechanical working of metals • Mechanical working of metal refers to plastic deformation of a metal under the action of mechanical pressure to change dimensions, properties and or surface conditions. • Mechanical working processes include a number of processes like Rolling, forging, extrusion, drawing and press working • The stress induced in the part are greater than the yield strength and less than the fracture strength of the material except in sheet metal works like shearing, piercing and blanking Abdul Khader AA Objectives of Mechanical working of metals 1. To reduce the original block to the finished dimensions. 2. To improve the mechanical properties. 3. Refinement at grain structure. 4. Directional control of "flow lines". 5. Break up and distribution of unavoidable inclusions. Abdul Khader AA Classification of Mechanical working 1. Hot working 2. Cold working Abdul Khader AA Hot working • The working of a metal above their recrystallization temperature at which new grains are formed is called hot working. • The hot working should be carried above the recrystallization temperature but below the melting point. Abdul Khader AA Advantages of Hot working • Refinement of grain structure is achieved. • Elimination of porosity and blow holes in steel. • Greater flexibility in chaning shape and size due to reduction in elastic limit. • A uniformity is established due to proper distribution of impurities throughout the mass. • Improved mechanical properties like, ductility, toughness, elongation etc. • The power required to finish the part from ingot is less. • Directional property resulting from a fibre structure is obtained Abdul Khader AA Disadvantages of Hot working • Poor surface finish by rapid oxidation or scaling due to high temperature. • Close tolerance cannot be maintained due to poor surface finish. • Reduced tool life due to high temperature. • Tooling and handling costs are high. Abdul Khader AA Hot working Processes • Hot rolling • Hot forging • Hot extrusion • Hot piercing • Hot drawing • Hot spinning • Piping and Tube production. Abdul Khader AA Cold working Processes • The working of a metal below their recrystallization temperature is known as cold working. • Most of the cold working processes are performed at room temperature. • When material is cold worked the resulting change in material shape causes changes in grain structure. • The effect of cold working on the structure of steel is to distort or elongate the grain in the direction of flow of metal. Abdul Khader AA Cold working Processes - Advantages 1. Improved surface finish. 2. Scale free and bright surface. 3. Closer dimensional tolerances. 4. Increased strength and hardness of metal. 5. Recrystallization temperature for steel is raised Abdul Khader AA Cold working Processes - Disadvantages 1. Only small sized components can be cold worked as it requires greater forces. 2. Residual stresses are setup in the metal. 3. Grain structure is distorted. 4. Higher costs 5. Metals having less ductility cannot be cold worked at room temperature. Abdul Khader AA Cold working Processes - List 1. Cold rolling. 8. Cold extrusion. 2. Cold forging. 9. Cold squeezing. 3. Cold drawing, embossing. 10. Cold seaming. 4. Cold bending. 11. Cold rivetting stamping. 5. Cold shearing, trimming, 12. Cold peening. notching, punching, blanking. 13. Cold sizing, coining and 6. Cold spinning. hobbing. 7. Cold bulging. Abdul Khader AA Cold Working v/s Hot Working Factor Cold working Hot working Temperature Working below recrystallization Working above temperature. recrystallization temperature. Grain structure Distorted Refined Force required Higher force is required to cause Lower force is required deformation Slag inclusion The presence of nonmetallic Avoid contamination of the weld substances in the metal or metal by atmosphere. contamination of weld metal by Proper removal of slag between atmosphere. layers of metal. Residual stresses Induced Not Induced Surface finish Better Poor Speed Slow process Faster process Complicated shape Can not be produced Can be produced easily Machines Large and Heavy Comparatively small & light Abdul Khader AA Rolling Process Abdul Khader AA Rolling Process • Rolling is a metal forming process in which the metal is passed between the rolls to get a desired shape by plastic deformation. • Rolling may be classified into hot rolling and cold rolling depending upon the temperature at which the metal is rolled Abdul Khader AA Hot Rolling Process 1. Hot rolling process is done above the recrystallization temperature. 2. For hot rolling of metals they are first cast into ingots moulds of suitable form. 3. The hot rolling consists of compressing and lengthening the metal as it is fed between two rolls. 4. The flow of metal during rolling is continuous and almost entirely in longitudinal in direction. Abdul Khader AA Cold Rolling Process 1. Cold rolling process occurs below the recrystallization temperature. 2. For cold rolling the sheets, hot rolled metal is used 3. Before cold rolling the metal is properly cleaned by immersing in an acid solution, washed in water and dried. 4. the metal at room temperature is fed in between two rolls in which the squeezing action of the rolls gives the desired thickness and shape 5. Cold rolling gives smooth and bright surface finish and desired tensile strength, stiffness and hardness is achieved. 6. Cold rolling is generally used for bars, rods, sheets and strips Abdul Khader AA Rolling Mills Rolling can be done by using rolling mills. Rolling mills are of the following types : 1. Two high rolling mill. 2. Three high rolling mill. 3. Four high rolling mill. Abdul Khader AA Two High Rolling Mills Non Reversing Reversing Abdul Khader AA Two High Rolling Mills • It consists of two rolls placed top and bottom with constant direction of rotation about the horizontal axis • These rolls are supported by bearings in housing and placed over a rigid stand. The direction of the roller is fixed and cannot be reversed. • For second pass, the stock is returned to the entrance of the rolls by carrying it back • This method of reduction is in only one direction which slows down the process, • An alternative procedure is to use the two high reversing mill in which the direction of rotation of the rolls is reversed after each pass Abdul Khader AA Three High Rolling Mills Abdul Khader AA Three High Rolling Mills 1. A three high rolling mill consists of three rolls mounted one over the other as shown in figure 2. This arrangement eliminates the disadvantages of two high rolling mill and-also need of reversing the rolls. 3. ln this case the top and bottom rollers are drive rolls which revolve in the same direction and middle one rotates by friction in opposite direction. 4. The workpiece is passed between upper and middle rolls in one direction and then passed in reversed direction between middle and lower rolls. 5. Lifting stands are provided on one or both the sides of the stand to raise and lower the bar after each pass. 6. All the three rolls rotate continuously in a same fixed direction and are never be reversed. Abdul Khader AA Four High Rolling Mills Abdul Khader AA Four High Rolling Mills • A four high rolling mill consists of four horizontal rolls, two bigger in size and two smaller in size two smaller in size. • Smaller size rolls initiate the rolling operation and the bigger rolls back up the rolling operation by the two smaller rolls. • This arrangement reduces the tendency of smaller rolls to deflect during rolling • This is used for both hot rolling and cold rolling Abdul Khader AA Drawing Principle • Drawing is pulling the metal through a die or a set of dies to achieve reduction in diameter. • The material to be drawn is reduced in diameter for a short distance at one end by swaging to permit it into the die orifice and gripped in jaws • This process requires a very large forces in order to pull the metal through the die. • To reduce the frictional force between the die and the metal, the die is kept well lubricated. Abdul Khader AA Wire Drawing Abdul Khader AA Wire Drawing • The principle of wire drawing operation consists of extruding a rod through a die thereby causing reduction in cross-sectional area of rod • The wire is drawn by pulling the rod through several dies of decreasing diameter in order to obtain very thin wire. • For wire drawing, the rod obtained from hot rolling process is cleaned and lubricated and then fed into the wire drawing dies held in casing. • The end of the rod is pulled by tongs on the other end to reduce the thickness, depending upon the thickness to be reduced Abdul Khader AA Deep Drawing Abdul Khader AA Deep Drawing • Deep drawing is defined as a Process of making cup shaped parts from sheet metal blanks. • The blank is first heated to working temperatures to provide sufficient plasticity. • The heated blank is then placed in position over the die • The punch is hammered over the heated blank which pushes the metal through die to form a cup. • The process may be repeated through a series of successively smaller dies and punches. Abdul Khader AA Extrusion • Extrusion is a process of pushing the heated billet through the metal orifice with high pressure to produce the desired shape • A large force is required in extrusion, so most of the metals are hot extruded.