Lecture Two MSE 257: INDIGENOUS METHODS OF MATERIALS PROCESSING Course Code: MSE 257 Dr. Emmanuel Kwesi Arthur Department of Materials Engineering, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana Email: [email protected] Phone #: +233541710532 Processing Operations Three categories of processing operations: 1. Shaping operations - alter the geometry of the starting work material 2. Property-enhancing operations - improve physical properties of the material without changing its shape 3. Surface processing operations - clean, treat, coat, or deposit material onto the exterior surface of the work 2 Changes? Parts undergo sequence of processes Primary - alter the (“raw”) material’s basic shape or form. Sand casting Rolling Forging Sheet metalworking Secondary - add or remove geometric features from the basic forms Machining of a brake drum casting (flat surfaces) Drilling/punching of refrigerator housings (sheet metal) Trimming of injection molded part flash Tertiary - surface treatments Polishing Painting Heat-treating Joining Types of manufacturing processes Manufacturing How is the input Processes material changed? Sheet Polymer Deformation Casting Metal Processes Machining Finishing Assembly Extrusion Centrifugal Bending Blow molding Boring Anodizing Automated Forging Die casting Blanking Casting Drilling Honing Bonding Rolling Investment Drawing Compression molding Facing Painting Brazing Bar drawing Permanent mold Punching Extrusion Grinding Plating Manual Wire drawing Sand casting Shearing Injection Molding Milling Polishing Riveting Spinning Thermoforming Planing Soldering Transfer molding Turning Welding Sawing ECM, EDM Deformation Processes Starting workpart is shaped by application of forces that exceed the yield strength of the material Examples: (a)Rolling (b) Extrusion (c) Drawing (d) Forging 5 Definition of rolling process Definition of Rolling : The process of plastically deforming metal by passing it between rolls. Rolling is the most widely used forming process, which provides high production and close control of final product. The metal is subjected to high compressive stresses as a result of the friction between the rolls and the Rolling process metal surface. 6 Terminology bloom billet slab Bloom is the product of first breakdown of ingot (cross sectional area > 230 cm2). Semi-finished Billet is the product obtained from a further reduction by products hot rolling (cross sectional area > 40x40 mm2). Slab is the hot rolled ingot (cross sectional area > 100 cm2 and with a width ≥ 2 x thickness). Further rolling steps Plate is the product with a thickness > 6 mm. Mill Sheet is the product with a thickness < 6 mm and width > products 600 mm. Strip is the product with a thickness < 6 mm and width < 7 600 mm. Hot and cold rolling processes Hot rolling The initial breakdown of ingots into blooms and billets is generally done by hot-rolling. This is followed by further hot rolling into plate, sheet, rod, bar, pipe, rail. Hot rolling requires less work but an oxidized surface finish Cold rolling Cold rolling requires more work but increases the yield strength of the material and produces superior surface finish. The cold-rolling of metals has played a major role in industry by providing sheet, strip, foil with good surface finishes and increased mechanical strength with close control of product dimensions. 8 Rolling bloom structural ingot coil slab sheet billet bar rod Extrusion Heated metal plastically Extrusion die yields as it is pushed through a die, producing long pieces with a constant cross-section. Size: 40-foot in length Cross Ram sections Economical production quantities: 1,000 to 100,000 pieces Billet Materials: ductile metals (e.g. aluminum, steel, zinc, copper, magnesium) Drawing Process of producing a wire, bar or tube by pulling on a material until it increases in length Drawing die accompanied with a reduction in its cross-sectional diameter. Cross Size: bar size range 1/8 to 6 sections inches in cross-section, wire size range 0.001 to 3/8 inches. Pulling Material: ductile metals (e.g. Billet force aluminum, steel, copper) Forging It`s a term used for shaping metals and alloys using localized compressive forces. Stresses induced > Yield strength Strain Hardening Type of loading – Compressive, Bending, Shear, Combination of these http://product-image.tradeindia.com/00245643/b/Shaft-Forging-Process.jpg Forging (closed-die) Ram pressure Flash Blocked preform Gutter A process in which material is plastically compressed between 2 halves of a die set by hydraulic pressure or the stroke of a hammer. Size: maximum size limit roughly 36 inches Economic production quantity: 1,000 to 100,000 pieces Categories Hot forging http://www.paul-chen-swords.com/content/images/katana- forging- http://www.verdigrismetals.co.uk/work%20being%20 process-1-rough-forging.jpg made/hot%20forged%20steel%201.jpg Cold forging http://www.coldforge.com/img/Cfp1.gif http://www.coldforge.com/img/Cfp1.gif Forging Materials Almost all metals and alloys can be forged. Ferrous alloys Aluminum alloys Brass and Bronze Copper alloys Titanium alloys What happens in forging? http://www.sssforge.com/images/pic-01.jpg Types of Forging Hammer Forging (Flat Die) Instantaneous Load Intermittent blows Steam or Air pressure Poor surface finish http://rrforging.com/yahoo_site_admin/assets/ima ges/forge3.354112844_std.jpg Types of Forging Press Forging Slow continuous pressure Pressure extends deep into material Greater proportion of energy transferred to material Better surface finish http://img2.tradeget.com/forginghammer%5CWJ0Y6F6 G1forging_manipulator_with_open_die_forging_press.jpg Types of Forging Die Forging http://www.firthrixson.com/images/forgings.jpg http://www.msm.cam.ac.uk/doitpoms/tlplib/metal-forming-2/figures/closeddieforge_sml.jpg Material is forced to fill the recessions Complex shapes can be obtained Close dimensional tolerances can be achieved Advantages of Forging Some common advantages of forging are given as under. 1) Forged parts possess high ductility and offers great resistance to impact and fatigue loads. 2) Forging refines the structure of the metal. 3) It results in considerable saving in time, labor and material as compared to the production of similar item by cutting from a solid stock and then shaping it. 4) Forging distorts the previously created unidirectional fiber as created by rolling and increases the strength by setting the direction of grains. 5) Because of intense working, flaws are rarely found, so have good reliability. 6) The reasonable degree of accuracy may be obtained in forging operation. 7) The forged parts can be easily welded. Disadvantages of Forging Few dis-advantages of forging are given as under. 1) Rapid oxidation in forging of metal surface at high temperature results in scaling which wears the dies. 2) The close tolerances in forging operations are difficult to maintain. 3) Forging is limited to simple shapes and has limitation for parts having undercuts etc. 4) Some materials are not readily worked by forging. 5) The initial cost of forging dies and the cost of their maintenance is high. 6) The metals gets cracked or distorted if worked below a specified temperature limit. 7) The maintenance cost of forging dies is also very high. Applications of Forging Almost all metals and alloys can be forged. The low and medium carbon steels are readily hot forged without difficulty, but the high-carbon and alloy steels are more difficult to forge and require greater care. Forging is generally carried out on carbon alloy steels, wrought iron, copper-base alloys, aluminum alloys, and magnesium alloys. Stainless steels, nickel based super-alloys, and titanium are forged especially for aerospace uses. Producing of crank shaft of alloy steel is a good example which is produced by forging. Forging processes are among the most important manufacturing techniques utilized widely in manufacturing of small tools, rail-road equipment, automobiles and trucks and components of aero plane industries. These processes are also extensively used in the manufacturing of the parts of tractors, shipbuilding, cycle industries, railroad components, agricultural machinery etc. Defects In Forged Parts Defects commonly found in forged parts that have been subjected to plastic deformation are as follows. a) Defects resulting from the melting practice such as dirt, slag and blow holes. b) Ingot defects such as pikes, cracks scabs, poor surface and segregation. c) Defect due to faulty forging design. d) Defects of mismatched forging because of improper placement of the metal in the die. e) Defects due to faulty design drop forging die. f) Defects resulting from improper forging such as seams cracks laps. etc. g) Defects resulting from improper heating and cooling of the forging part such as burnt metal and decarburized steel. Some well identified common forging defects along with their reason are given as under. Removal of Defects In Forging Defects in forging can be removed as follows: 1) Surface cracks and decarburized areas are removed from forging parts by grinding on special machines. Care should also be taken to see that the job is not under heated, decarburized, overheated and burnt. 2) Shallow cracks and cavities can be removed by chipping out of the cold forging with pneumatic chisel or with hot sets. 3) The parting line of a forging should lie in one plane to avoid mismatching. 4) Destroyed forgings are straightened in presses, if