# Mm Imp Questions

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## Plasticity (Physics)

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1 1. List the various lattice defects.Ans: The List of various Lattice defects is1) Point Defects: Point defects include a) Vacancies b) Self-interstitial atoms c) Substitutional impurity atoms and d) Interstitial impurity atoms!) Linear Defects: linear defects include dislocations these are a) d#e dislocation and  b) Scre\$ dislocation%) Planar Defects: Planar defects include a) &rain boundaries b) T\$in boundaries c) Stac'in# faults 2. Differentiate between Slip and Twinning. Sl.No.SlipTwinning 1The parallel movement of t\$o ad(acent crystal planes relative to one another is slipT\$innin# is a homo#eneous shear \$hich reorients the deformed lattice into a mirror ima#e of the parent lattice across the plane of t\$innin#!The orientation of atoms above and  belo\$ the slip plane is the same after slip deformationT\$innin# produces an orientation difference across the t\$in plane%Slip usually occurs in discrete multiples of atomic spacin#In t\$innin# atoms move only a fraction of inter atomic distanceThe stress re*uired to initiate slip is less than to propa#ate itThe stress re*uired to propa#ate t\$innin# is appreciably less than that re*uired to initiate it+There is a time la# for slipT\$innin# occurs in micro seconds 3. ,hat are the variables \$hich influence the ecrystalisation temperature of a material. Ans: The variables \$hich influence the ecrystalisation temperature of a material are:1)Time at a constant temperature!)/mount of cold \$or'in#%)Purity of metal)0ri#inal #rain sie+)Temperature of deformation2)3eltin# point of metal4) . List out the forging ! uip#ent.Ans: 5or#in# e*uipment may be classified \$ith respect to the principle of operation1)5or#in# hammers: The force is supplied by fallin# \$ei#ht or ram The follo\$in# are for#in# hammersa&ravity drop hammer or 6oard hammers bPo\$er drop hammer !)5or#in# presses: these are t\$o typesa3echanical Presses: the force is supplied by an eccentric cran' \$hich translates rotary motion of a fly \$heel into reciprocatin# linear motion of the press slide b7ydraulic presses: the force is supplied by movin# piston \$hich feeds on hydraulic  pressure of a fluid \$. Draw a planetar% #ill and #ention its i#portance.  2 Ans:Drawing of a planetar% #ill:&#portance of planetar% #ill: 1) It hot reduces a slab directly to strip in one pass throu#h the mill!) ach planetary roll #ives an almost constant reduction to the slab%) The action in the planetary mill is more li'e for#in# than rollin# '. Differentiae between Direct and &ndirect !(trusion.Ans: Sl8oDirect 9trusionIndirect 9trusion 15lo\$ of billet metal is in for\$ard direction and in the same direction as ram 5lo\$ of metal ta'es place in a direction opposite to that of ram movement !There is a relative motion bet\$een billet and container \$alls and hence friction is  prevalent \$hile e9trudin# the billetSince there is no relative movement bet\$een the container \$all and the billet frictional forces are lo\$er%Lubrication is a problem particularly \$hen hot e9trusion ;direct) is done 9tensive lubrication is not needed Pressure re*uired increases \$ith the len#th of the billet Pressure remains constant up to (ust to the end of the e9trusion process+3ore turbulence of billet metal occurs \$ithin the billet hence lot of ener#y #ets \$asted This re*uires more po\$er consumption to e9trude the billet metal Turbulence of billet metal is minimum hence flo\$ of metal is more uniform \$ithin the billet hence ener#y loss is minimum This re*uires less po\$er consumption to e9trude the billet metal2There is no practical limitation to use this  process There are practical limitations because use of hollo\$ ram limits the load \$ithstandin# capacity 47andlin# the e9trudin# metal comin# out throu#h the movin# ram is not a problem7andlin# the e9trudin# metal comin# out throu#h the movin# ram is a problem  ). List the various steps involved in the production of *+ower ,etallurg%* parts. Ans:  3 The various steps involved in the production of *+ower ,etallurg%* parts are: 1)Production of metal po\$ders: 0btainin# the metal po\$ders in a suitable de#ree of fineness and  purity!)3i9in# and 6lendin#: Intermin#lin# of various po\$ders accordin# to the composition%)<ompaction: Sub(ectin# the mi9ed po\$ders to a sufficient pressure in a suitable mould to cause cohesion)Sinterin#: heatin# under controlled atmosphere at a temperature hi#h enou#h to cause diffusion and inter #ranular crystal #ro\$th to occur+)5inishin# operations: these include siin# impre#nation inspection etc -. ive the classification of *Ther#o #echanical treat#ent* #ethods.  Ans:   Dependin# on the temperature at \$hich deformation of austenite ta'es place thermo-mechanical treatments can be classified as7i#h temperature thermo-mechanical treatment ;7T3T) 1)Lo\$ temperature thermo-mechanical treatment ;LT3T)/nother method of classifyin# the treatment is based on the deformation temperature in relation to the critical temperature of steel namely1)Supercritical ;deformin# steel in austenite condition)!)Intercritical ;deformin# ferrite and austenite mi9ture)%)Subcritical ;deformation of austenite belo\$ the lo\$er critical temperature) 9amples of Thermo mechanical treatments : 1)/usformin#!)Isoformin# and%)3arformin# /. !(plain about Shearing process.Ans: Shearing is the separation of metal by two moving blades. In this process a narrow strip of metal is severely plastically deformed to a point of fracture at the surface in contact with the blades. The fracture then propagates inwards to provide complete separation. Clearance between the blades is an important variable in the shearing process. 5orce re*uired to shear a metal is the product of the len#th ;l) cut the sheet thic'ness ;t) and the Shearin# stren#th ;=) of the metal mpirically the ma9imum punch force needed to produce the shearin# is #iven byP ma9  > ?4@ u tl,here @ u is the ultimate tensile stren#th of the metal  4 10. Distinguish between ot woring and cold woring.Sl.No.old woring ot woring 1 ,or'in# of metals and alloys belo\$ their recrystallisation temperature ,or'in# of metals and alloys above their recrystallisation temperature ! Strain ;\$or') hardenin# ta'es placeStrain ;\$or') hardenin# is removed by recrystallisation % Increase in hardness and tensile stren#th \$hile ductility decreases    8o chan#e in mechanical properties  3icrostructure sho\$s distorted #rains alon# the direction of \$or'in#3icrostructure sho\$s e*uia9ed and usually refined #rains + Stress and ener#y re*uired for plastic deformation is more Stress and ener#y re*uired for plastic deformation is less 2  8o o9idation of metal occurs and hence  pic'lin# is not re*uired7eavy o9idation of metal occurs and hence  pic'lin# is re*uired 4 Surface decarburiation in steels does not occur Surface decarburiation in steels is li'ely to occur A 3etals and alloys do not #et embrittled by o9y#eneactive metals #et severely embrittled by o9y#en B Surface finish is #ood Surface finish is not so #ood 1? asy to control the dimensions \$ithin the tolerance limitsDifficult to control the dimensions \$ithin the tolerance limits 11 etains chemical hetero#eneity if presenteduces chemical hetero#eneity of in#ots 11Define a4 Dispersion hardening b4 Strain ageing  Ans: a4 Dispersion hardening
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