UNIT III BULK DEFORMATION PROCESSES FUNDAMENTALS OF METAL FORMING There are four basic production processes for producing desired shape of a product. These are casting, machining, joining (welding, mechanical fasteners, epoxy, etc.), and deformation processes.  Metal working reduces any internal voids or cavities present and thus the metal dense.  When materials are subjected to external loads, they get deformed. The deformation may be elastic, plastic or fracture depending upon the load and properties of the material.  Wastage is very small or negligible and production rate is more.

RollingForgingExtrusion Swaging Deep drawing Wire and tube drawing Straight bending

C OLD WORKING When plastic deformation of metal is carried out at temperature below the recrystallisation temperature the process performed on metals are termed as cold working.

Advantages: No heating required. Better surface finish obtained. Superior dimension control. Better reproducibility and interchangeability of parts. Improved strength properties. Directional properties can be minimized. Disadvantages: Higher forces required for deformation. Heavier and more powerful equipment required. Less ductility available. Metal surfaces must be clean and scale-free. Strain hardening occurs (may require intermediate anneals). May produce undesirable residual stresses.

When plastic deformation of metal is carried out at temperature above the recrystallisation temperature the process performed on metals are termed as cold working. Various hot working processes are: Rolling Forging Pipe welding Hot spinning Hot extruding H OT W ORKING

Advantages: High production rate. Fracture is less. Metal is made tougher because pores get closed and impurities are segregated. Deformation energy required is low. The process does not change the hardness and ductility of the metal. Disadvantages: Handling of material is not easy. Heat resistant tools are required which are very expensive. High temperature may promote undesirable causes. Surface finish is poor. Close tolerances can not be held.

W ARM WORKING OR S EMI - HOT WORKING It is defined as the plastic forming of a metal or alloy under conditions of temperature and strain rate, such that the drawbacks of both cola working and hot working are eliminated and their advantages are combined together. Selection of proper temperature is very important. Selection of temperature depends on Dimensional tolerance of the components. The ductility of the material. Yield or Flow strength of metal or alloy. Losses due to oxidation and scaling.

F ORGING Forging is a process in which material is shaped by the application of localized compressive forces exerted manually or with power hammers, presses or special forging machines. The process may be carried out on materials in either hot or cold state. Typical forged parts include rivets, bolts, crane hooks, connecting rods, gears, turbine shafts, hand tools, railroads, and a variety of structural components used to manufacture machinery. The forged parts have good strength and toughness ; they can be used reliably for highly stressed and critical applications.

C LASSIFICATION OF F ORGING

H AND F ORGING

M ETHODS OF FORGING Drop Forging Press Forging Machine Forging Roll Forging Rotary forging

F ORGING M ACHINES Drop Stamp Steam Hammer Pneumatic Hammer Hydraulic Hammer

F ORGING O PERATIONS Upsetting Drawing down Bending Punching Cutting Piercing Swaging or Rotary Forging Flattering Fullering

R OLLING

Shapes

R OLLING M ILL A RRANGEMENT

E XTRUSION Extrusion is the process in which the metal is caused to flow through a restricted orifice so creating an extremely elongated strip of uniform, but comparatively small cross section.

C LASSIFICATION OF EXTRUSION PROCESS Hot Extrusion Forward or Direct extrusion Backward or Indirect extrusion Cold Extrusion Forward extrusion Hydrostatic extrusion Backward extrusion Impact extrusion Cold extrusion forging

H OT EXTRUSION PROCESS Forward or Direct Extrusion process

C OLD EXTRUSION PROCESS HOOKER EXTRUSION OR EXTRUSION DOWN METHOD

B ACKWARD OR INDIRECT EXTRUSION PROCESS

I MPACT EXTRUSION

COLD EXTRUSION FORGING

E XTRUSION F ORCE