CHAPTER 5 Manufacture of Steel Products (Deformation Processing Metals) OBJECTIVES At the end of this lesson, student will be able to: Explain the plastic deformation and elastic deformation Differentiate hot working and cold working Name and describe two group of plastic Describe rolling, forging, extrusion and drawing process Issues to address…. -Plastic Deformation -Recrystallization -Hot Working -Deformation of the material by different processing operation: - Forging - Rolling - Extrusion - Drawing Deformation of Material Elastic and Plastic Deformation: Elastic deformation – an object returns to its original dimension when the stress acting upon it is removed. Plastic deformation - distortion of metal under applied stress that stretches the material beyond its elastic limit. Recrystallization and Recrystallization Temperature. Recrystallization - the process in which, at the certain temperature range, a new grains are formed, replacing the older grains. Recrystallization temperature - The temperature at which complete recrystallization occurs within a specified time. 1 Recovery, Recrystallization and Grain Growth Recrystallization Recrystallization decreases the density of dislocation, lowers the strength, and rises the ductility of the metal. Lead, tin, cadmium, and zinc recrystallize at about room temperature. So, it do not work harden when cold worked. Recrystallization depends on the degree of prior cold work. The more cold work, the lower the temperature for recrystallization occur. The amount of cold work increases, the number of dislocations and the amount What is hot working and cold working? Cold working-When plastic deformation is carried out at room temperature Hot working - when deformation occurs above the recrystallization temperature. Hot Working Metal Temperature in °F (°C) Aluminum Copper Gold Iron Lead Magnesium Nickel Silver Tin Zinc 300 (150) 390 (200) 390 (200) 840 (450) below room temperature 300 (150) 1100 (590) 390 (200) below room temperature at room temperature Recrystallization temperature for common metals. New grain structure of metal during hot rolling process. Hot Working Advantages of hot working: 1. Increase in strength. 2. Increase in ductility and toughness of wrought products compared to cast products. Disadvantages of hot working: 1. Deformation energy at high temperature – occur some surface oxidation, which result in materials loss and poor final surface finish. 2. The structure and properties are generally not so uniform as in metals that have been cold worded because the deformation is always greater in the surface layers than in the interior. 3. Interior grains will cool more slowly, leading to increased grain growth for the interior. Rolling Process Rolling is the process of reducing the thickness or changing the cross section of a long workpiece by compressive forces applied through a set of rolls. Most popular metalworking process because of the capability for large production to accuracy tolerances. Rolling can be either a primary process, as in continuous casting to bloom for further cold rolling, or a secondary process, as in producing such items as household aluminum foil. Typical applications are in the rolling of plastics, powder metals, ceramic slurry and hot glass Various flat-and shaperolling processes. Rolling Process Two groups of rolling: 1. Hot Rolling: The product of the first hot rolling operation is called a bloom, slab and billet. Carried out above recrystallization temperature. Used for further process in cold rolling mills. 2. Cold Rolling: Carried out at room temperature. Better final surface finish, good tolerances and mechanical properties compared to hot working. Produce various types of rolled product, with thickness as low as 0.05 mm. Rolling consists of the rolls, bearings, housing and power drive to control the speed and pressure of the rolls. The equipment for hot and cold rolling is essentially the same but differences in the roll materials, lubricants, cooling system and process parameters. Rolls – made up of cast iron and cast steel. Lubricants: Hot rolling – for ferrous metals is usually carried out without lubricant. For non ferrous metals used a variety of compounded oils, emulsions and fatty acids Cold rolling - mineral oils, emulsions, paraffin and fatty oils. As the metal passes through the rolls its original equiaxed grains are elongated relative to the degree of deformation Elongated grains provide directional bend-strength properties. Rolling Process Four major types of rolling mills: 1. Two-high rolling mills 2. Three-high rolling mills 3. Four-high rolling mills 4. Cluster rolling mills Rolling Process Products of rolling processes: 1. Foils - less than 0.2 mm thick, used for cans, electrical applications, building insulation and in the printing industry. 2. Sheets - between 0.2 mm and 6mm in thickness used extensively in transport applications such as automobile body panels, airframes and the hulls of boats. 3. Plate - any rolled product over 6 mm in thickness, used for airframes, military vehicles and structural components in bridges and buildings. Forging Process Forging is a basic process in which the workpiece is shaped by compressive forces applied through various dies and tooling The basic methods (or processes) to make a forged part. 1. Open Die Forging 2. Impression die forging (Close Die Forging) 3. Blocker 4. Conventional 5. Precision Fig 14.1 (a) shows schematic illustration of the steps involved in forging a knife. (b) Landing-gear components for the C5A and C5B transport aircraft, made by forging. (c) General view of a 445 MN (50,000 ton) hydraulic press. Open Die Forging Open die forging is performed between flat dies with no precut profiles is the dies and reduced in height by compressing it. Impression Die Forging In impression-die forging, the workpiece takes the shape of the die cavity while being forged between two shaped dies. This process usually is carried out at elevated temperatures for enhanced ductility of the metals and to lower the forces. Fig (a) shows through (c) Stages in impression-die forging of a solid round billet. Note the formation of flash, which is excess metal that is subsequently trimmed off. (d) Standard terminology for various features of a forging die Impression Die Forging (Close Die Forging): Open Die Forging: Extrusion In extrusion, a cylindrical billet is forced through a die in a manner similar to squeezing toothpaste from a tube or extruding Play-Doh® in various crosssections in a toy press. Typical products made by extrusion are railings for sliding doors, window frames, tubing having various cross-sections, aluminum ladders, and numerous structural and architectural shapes. The Extrusion Process There are three basic types of extrusion. In the most common process (called direct or forward extrusion), a billet is placed in a chamber (container) and forced through a die opening by a hydraulically driven ram (pressing stem or punch). In indirect extrusion (also called reverse, inverted, or backward extrusion), the die moves toward the unextruded billet. Fig below shows different types of extrusion: (a) indirect; (b) hydrostatic; (c) lateral. Cold working process Sheet Forming Drawing Spinning Sheet forming Roll Forming: This process is used for forming continuous lengths of sheet metal and for large production runs. The metal strip is bent in stages by passing it through a series of rolls. The parts are then usually sheared and stacked continuously. Stretch Forming: the sheet is clamped along its edges and then stretched over a die or form block, which moves upward, downward, or sideways, depending on the particular machine. Stretch forming is used primarily to make aircraft wing skin panels, automobile door panels, and window frames Drawing •Drawing: A round sheet-metal blank is placed over a circular die opening and is held in place with a blank holder. The punch travels downward and forces the blank into the die cavity, forming a cup . Deep Drawing Numerous parts made of sheet metal are cylindrical or box shaped, such as pots and pans, all types of containers for food and beverages, stainless-steel kitchen sinks, canisters, and automotive fuel tanks. The process generally is called deep drawing because of its capability for producing deep parts THANK YOU…..
