1.BULK DEFORMATION PROCESSESROLLING

2. For more help contact meMuhammad Umair BukhariEngr.umair.bukhari@gmail.com www.bzuiam.webs.com03136050151 3. INTRODUCTION 4. CLASSIFICATION PRIMARY WORKING operations are those that take a solidpiece of metal (generally in form of ingot) & break it downsuccessively into shapes such as slabs, billets & plates. Traditionally this includes processes like forging, rolling &extrusion. SECONDARY WORKING operations involve furtherprocessing of the products from primary working in to finalproducts like bolts, sheet metal parts & wires. 5. CLASSIFICATION BULK DEFORMATION is the processing of work pieceswhose surface area-to-volume ratio (or surface area-to-thickness ratio) is relatively small. In bulk forming processesthere is always a change in thickness or cross-section ofwork piece. Includes: rolling, forging, extrusion & drawing of rod &wire. SHEET-FORMING operations the surface area-to-thicknessratio is relatively high. In general the material is subjected toshape changes. No thickness changes. 6. ROLLING This is the process of reducing the thickness or changing thecross-section of a work-piece by compressive forces exertedby a pair of rotating rolls. The products are flat products, like: plates & sheets. Plates are used for structural applications like bridges, ships& nuclear vessels. Sheets (generally 6mm or less in thickness) are used forautomotive, beverage cans, office & kitchen equipment. 7. ROLLING Hot rolling is a hot working process where large pieces ofmetal, such as slabs or billets, are heated above theirrecrystallization temperature and then deformed betweenrollers to form thinner cross sections. While cold rolling increases the hardness and strength of ametal, it also results in a large decrease in ductility. Thusmetals strengthened by cold rolling are more sensitive to thepresence of cracks and are prone to brittle fracture. Recrystallization temperature The minimumtemperature at which complete recrystallization occurs in. 8. HOT ROLLING Hot rolling produces thinner cross sections than cold rollingprocesses with the same number of stages. Hot rolling, dueto recrystallization, will reduce the average grain size of ametal while maintaining a certain soft microstructure, whereas cold rolling will produce a hardened microstructure. Hot rolling is primarily concerned with manipulatingmaterial shape and geometry rather than mechanicalproperties. Primary working is always hot rolling. Recrystallization & Annealing temperatures. 9. ROLLING IngotsBillets/blooms/slabs bars/rodswires, nails, pipes, sheets, plates Bloom: square cross-section Slab: rectangular Billets: A billet is a bar of steel with a square cross-sectionwhose dimensions are usually less than about 6 inches (15cm) by 6 inches (15 cm). 10. Making barbed wire A steel ingot is heated until it is about 2192F (1200C), thenrolled between grooved rolls until it has reached the proper size.Giant shears cut the billet to the desired length; then it is allowedto cool. The steel billet is again heated and rolled until it has been shapedinto a round bar 0.2 inch (5.6 mm) in diameter, known as a wirerod. The wire rod is rolled into a coil weighing as much as 3,969pounds (1,800 kg), which is shipped to the wire manufacturer. 11. Hot rolling Advantages :1. Larger deformation can be accomplished and more rapidlyby hot working since the metal is in plastic state.2. Porosity of the metal is considerably minimised.3. Concentrated impurities, if any in the metal are disintegratedand distributed throughout the metal.4. Grain structure of the metal is refined and physicalproperties improved. 12. Hot rolling Disadvantages :1. Due to high temperature a rapid oxidation or scale formation takes place on the metal surface, leading to poor surface finish and loss of metal.2. On account of the lost of carbon from the surface of the steel piece being worked the surface layer loses its strength, which is a disadvantage when the part is put to service.3. This weakening of the surface layer may give rise to crack which may ultimately result in fatigue failure of the part.4. Close tolerances cannot be maintained.5. It involves excessive expenditure on account of high cost of tooling. This, however, is compensated by the high production rate and better quality of products 13. Cold Rolling Quarter Hard, Half Hard, Full Hard stock have higheramounts of reduction. This increases thei) yield point;ii) grain orientation andiii) material properties assumeiv) ductility decreases. Quarter Hard material can be bent (perpendicular to thedirection of rolling) on itself without fracturing. Half hard material can be bent 90; full hard can be bent 45. 14. Cold rolling advantages and limitations1.Better dimensional control than hot working is possible because the reduction in size is not much.2.Surface finish of the component is better because no oxidation takes place during the process.3.Strength and hardness of the metal are increased.4.It is an ideal method for increasing hardness of those metals which do not respond to the heat treatment.5.Only ductile metals can be shaped through cold working.6.Over-working of metal results in brittleness and it has to be annealed to remove the same.7. Subsequent heat treatment is mostly needed to remove the residual stresses set up during cold working.