Mechanical working of metals

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  • Manufacturing Technology Mechanical Working of Metals In this method no machining process is carried out, but it is used to achieve optimum mechanical properties in the metal. The wastage of material in metal working process is negligible or very small. But the production is very high compared to other process.
  • Manufacturing Technology Types of Metal Working or Processing Methods Mechanical processing Hot working Cold working Thermal processing Annealing Recovery, recrystallization and growth Heat treatments Both of these are used to control properties of the final product
  • Manufacturing Technology Hot Working: T>0.5Tm Mechanical working of a metal above the recrystallization temperature but below the melting point is known as hot working. The temperature at which the complete recrystallization of a metal take place with in a specified time The recrystallization temperature of metal will be about 30 to 40% of its melting temperature. Types Forging Rolling Extrusion Drawing
  • Manufacturing Technology Hot Working Advantages Force requirement is less Refined grain structure No stress formation Quick and Economical Suitable for all metals Disadvantages Poor surface finish Less accuracy Very high tooling and handling cost Sheets and wires cannot be produced
  • Manufacturing Technology Cold Working :T 6.35 mm ] SHEET [ t < 6.35] STRIP[ t = 6.35 & b = 600 mm ] FOIL [ t < 1.5 mm & b= 300mm ] TERMINOLOGY
  • Angle of contact or Angle of bite The Angle subtended at the centre of the roll by arc AB ( Metal in contact with the roll) Rolling Pass The feeding of material between the rolls once Rolling mill Consists of rolls , bearings& Housings and Drive for applying power to rolls TERMINOLOGY Contd.,
  • Flat Flat Rolling Process Rolling Process Flat Rolling Process
  • Flat Rolling Process Metal strip enters the roll gap The strip is reduced in size by the metal rolls The velocity of the strip is increased the metal strip is reduced in size Factors affecting Rolling Process Frictional Forces Roll Force and Power Requirement
  • h0/2 h1/2 CL B L A R R R-h/2 GEOMETRY OF ROLLING
  • The angle of bite can be expressed as; tan = = L/R The length of contact, L= sqrt{R(ho-hf)} h0 is the strip thickness at start and R is the roll radius h0-hf = 2R (2)
  • Schematic Illustration of Various Roll arrangements
  • Schematic Illustration of various roll arrangements : (a) two-high; (b) three- high; (c) four-high; (d) cluster mill
  • Shape-Rolling Operations Various shapes can be produced by shape rolling Bars Channels I-beams Railroad rails Roll-pass design requires considerable experience in order to avoid external and internal defects
  • Stages in Shape Rolling of an H-section part. Various other structural sections such as channels and I-beams, are rolled by this kind of process.
  • Ring Rolling A thick ring is expanded into a large diameter ring The ring is placed between the two rolls One of which is driven The thickness is reduced by bringing the rolls together The ring shaped blank my be produced by: Cutting from plate Piercing Cutting from a thick walled pipe Various shapes can be produced by shaped rolls Typical applications of ring rolling: Large rings for rockets Gearwheel rims Ball-bearing and roller-bearing races Can be carried out at room temperature Has short production time Close dimensional tolerances
  • RING ROLLING (a) Schematic illustration of Ring-rolling operation. Thickness reduction results in an increase in the part diameter. (b) Examples of cross- sections that can be formed by ring-rolling
  • Thread Rolling Cold-forming process Straight or tapered threads are formed on round rods by passing the pipe though dies Typical products include Screws Bolts
  • Production of Seamless Pipe & Tubing Rotary tube piercing (Mannesmann process) Hot-working process Produces long thick-walled seamless pipe Carried out by using an arrangement of rotating rolls Tensile stresses develop at the center of the bar when it is subjected to compressive forces
  • Defects in Rolled Plates & Sheets Undesirable Degrade surface appearance Adversely affect the strength Sheet metal defects include: Scale, Rust, Scratches, Gouges, Pits, & Cracks May be caused by impurities and inclusions Wavy edges result of roll bending Alligatoring complex phenomenon