Mechanical working of metals By Anil Kumar S Asst professor Mechanical Definition :- • The Mechanical working of metal is defined as the plastic deformation of metals under action of externally applied forces. Plastic deformation :- Introduction :- • It reduces internal voids & cavities, this makes metal dense. • Impurities present in the metal also get elongated with the grains. • Improves the mechanical strength. .The metal is subjected to mechanical working for the following purpose:- • To reduce the original block or ingot into desired shape. • To refine grain size Hot working & cold working :- • Mechanical working of metals is described into. • As hot working and cold working • Depending upon whether the metal is worked above or below the recrystallisation temp. Recrystallisation :- • Under the action of heat & force the atoms reach a certainly high energy level, the new structure starts forming which is termed a recrystallisation. Hot working :- • Process carried above recrystallisation temperature. • For lead & tin recrystallisation temp is below room temp. • Heated to plastic state& then pressure is applied. • Pressure applied is different in different process. HOT WORKING PROCESSES ARE:- • Hot rolling • Hot extrusion • Hot forging Hot forging Hot rolling Hot Extrusion :- Advantages :- • The porosity of metal is eliminated. • Grain structure is refined. • Hot work require much less force. • Giving rise to better mechanical properties Limitations :- • some metals cannot be hot worked because of their brittleness. • It produces poor surface finish, due to rapid oxidation on the metal surface. • Due to the poor surface finish, close tolerances cannot be maintained. • The correct temp. range for working is difficult to maintain Cold working :- • The working of metals below their recrystallisation temperature is known as cold working. • Most of cold working process are performed at room temperature . Advantages :- • Cold working produces a good surface finish, close dimensional tolerance. • Does not result in weight loss during working. • It produces considerable increase in strength and hardness, and reduces ductility. • By repeatedly cycling a material through stages of annealing and cold working, a very strong material can be produced. Limitations :- • The stresses are set up in the metal which remain in the metal, unless they are removed by subsequent heat treatment . • Some materials which are brittle cannot be cold worked. • Since the material has higher yield strength at lower temperature. Cold forging Cold rolling Cold extrusion Press working :- • Press working may be defined as chip less manufacturing process • By which various components are made from sheet metal. • These process are generally carried out at room temperature Classification of press operations :- • Cutting operation • Forming operation Stamping :- Various press working operations :- • BLANKING • PIERCING • NIBBLING • BENDING • COINING • DRAWING Blanking :- Piercing :- Nibbling :- Sheet metal Bending :- Complex parts such as U-sections channel sections of different profiles can be produced by doing multiple bends. Following types of bending :- Coining :- used to produce coins, medallions Drawing :- automotive bodies and fuel tanks, cans, cups, kitchen sinks, and pots and pans. ?????