lecture)13:)machining)i · department)of)materials)science)and)engineering 1 nc#state#university...
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NC#State#UniversityDepartment)of)Materials)Science)and)Engineering 1
MSE#440/540:#Processing#of#Metallic#Materials
Instructors:)Yuntian)ZhuOffice:)308)RBIIPh:)[email protected]
Lecture)13:)Machining)I
NC#State#University
• Cutting(action(involves(shear(deformation(of(work(material(to(form(a(chip,(and(as(chip(is(removed,(new(surface(is(exposed:((a)(positive(and((b)(negative(rake(tools
Machining
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Machining(Operations
• Most(important(machining(operations:– Turning– Drilling– Milling
• Other(machining(operations:– Shaping(and(planing– Broaching– Sawing
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• Single(point(cutting(tool(removes(material(from(a(rotating(workpiece(to(form(a(cylindrical(shape(
Turning(and(Drillng
! Used(to(create(a(round(hole,(usually(by(means(of(a(rotating(tool((drill(bit)(with(two(cutting(edges
https://www.youtube.com/watch?v=Mn9jpqI8rao&feature=related
NC#State#University
• Rotating)multiple/cutting/edge)tool)is)moved)across)work)to)cut)a)plane)or)straight)surface
• Two)forms:)(c))peripheral)milling)and)(d))face)milling
Milling
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Cutting'Tool'Classification1. Single3Point'Tools
– One'dominant'cutting'edge– Point'is'usually'rounded'to'form'a'nose'radius– Turning'uses'single'point'tools
2. Multiple'Cutting'Edge'Tools– More'than'one'cutting'edge– Motion'relative'to'work'achieved'by'rotating'– Drilling'and'milling'use'rotating'multiple'cutting'edge'tools
NC#State#University
Cutting'Conditions'in'Machining• Three'dimensions'of'a'machining'process
– Cutting'speed'v – primary'motion– Feed'f – secondary'motion– Depth'of'cut'd – penetration'of'tool'below'original'work'surface
• For'certain'operations'(e.g.,'turning),'material'removal'rate'RMR can'be'computed'as'
RMR ='v&f&d
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• Simplified*2,D*model*of*machining*that*describes*the*mechanics*of*machining*fairly*accurately*
Orthogonal*Cutting*Model
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Chip%Thickness%Ratio
where%r =%chip&thickness&ratio3%to =%thickness%of%the%chip%prior%to%chip%formation3%and%tc =%chip%thickness%after%separation
• Chip%thickness%after%cut%is%always%greater%than%before,%so%chip%ratio%is%always%less%than%1.0%
c
ottr =
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Determining)Shear)Plane)Angle
• Based)on)the)geometric)parameters)of)the)orthogonal)model,)the)shear)plane)angle)Φ)can)be)determined)as:)
where)r =)chip)ratio,)and)α =)rake)angle
!!"
sincostanr
r#
=1
NC#State#University
• (a)%Chip%formation%depicted%as%a%series%of%parallel%plates%sliding%relative%to%each%other,%(b)%one%of%the%plates%isolated%to%show%shear%strain,%and%(c)%shear%strain%triangle%used%to%derive%strain%equation
Shear%Strain%in%Chip%Formation
NC#State#University
Chip%Formation
• More%realistic%view%of%chip%formation,%showing%shear%zone%rather%than%shear%plane
• Also%shown%is%the%secondary%shear%zone%resulting%from%tool=chip%friction
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Four%Basic%Types%of%Chip%in%Machining
NC#State#University
Four%Basic%Types%of%Chip%in%Machining
! Ductile%materials! Low;to;medium%cutting%speeds! Tool;chip%friction%causes%portions%of%chip%to%adhere%to%rake%face
! BUE%forms,%then%breaks%off,%cyclically
Serrated%Chip
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• Generating*shape:*(a)*straight*turning,*(b)*taper*turning,*(c)*contour*turning,*(d)*plain*milling,*(e)*profile*milling
Generating*Shape
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• Forming)to)create)shape:)(a))form)turning,)(b))drilling,)and)(c))broaching
Forming)to)Create)Shape
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• Combination*of*forming*and*generating*to*create*shape:*(a)*thread*cutting*on*a*lathe,*and*(b)*slot*milling
Forming*and*Generating
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Turning'Operation
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More%Operations%Related%to%Turning
• (d)%Form%turning,%(e)%chamfering,%(f)%cutoff
NC#State#University
Methods(of(Holding(Workpiece(in(a(Lathe
• (a)(Holding(the(work(between(centers,((b)(chuck,((c)(collet,(and((d)(face(plate
http://www.youtube.com/watch?v=Q7QUiCJJmew
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More%Operations%Related%to%Turning
• (g)%Threading,%(h)%boring,%(i)%drilling
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Operations+Related+to+Drilling
• (a)+Reaming,+(b)+tapping,+(c)+counterboring
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More%Operations%Related%to%Drilling
• (d)%Countersinking,%(e)%center%drilling,%(f)%spot%facing
NC#State#University
Two$Forms$of$Milling
• (a)$Peripheral$milling$and$(b)$face$milling$
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Types&of&Peripheral&Milling• (a)&Slab&milling,&(b)&slotting,&(c)&side&milling,&(e)&straddle&milling,&and&(e)&form&milling
NC#State#University
Types&of&Face&Milling• (a)&Conventional&face&milling,&(b)&partial&face&milling,&(c)&end&milling,&and&(d)&profile&milling&using&an&end&mill
NC#State#University
Types&of&Face&Milling
• (e)&Pocket&milling&and&(f)&contour&milling
https://www.youtube.com/watch?v=U99asuDT97I
https://www.youtube.com/watch?v=9OsNUi_o6C4
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• Similar(operations,(both(use(a(single(point(cutting(tool(moved(linearly(relative(to(the(workpart
Shaping(and(Planing
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Shaper
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• A#multiple#tooth#cutting#tool#is#moved#linearly#relative#to#work#in#direction#of#tool#axis
Broaching
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Broaching
Advantages:1• Good1surface1finish• Close1tolerances• Variety1of1work1shapes1possible1Cutting1tool1called1a1broach• Owing1to1complicated1and1often1custom@shaped1geometry,1tooling1is1expensive1
NC#State#University
Power&Hacksaw
• Linear&reciprocating&motion&of&hacksaw&blade&against&&work
! Rotating&saw&blade&provides&continuous&motion&of&tool&past&workpart
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Geometric)Factors)Affecting)Surface)Finish
• Effect)of)(a))nose)radius,)(b))feed,)and)(c))ECEA
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Ideal&Surface&Roughness
where&Ri =&theoretical&arithmetic&average&surface&roughness8&f =&feed8&and&NR =&nose&radius
NRfRi 322
=
NC#State#University
Work%Material%Factors
• Built2up%edge%effects%• Damage%to%surface%caused%by%chip• Tearing%of%surface%when%machining%ductile%materials
• Cracks%in%surface%when%machining%brittle%materials%
• Friction%between%tool%flank%and%new%work%surface
NC#State#University
Effect&of&Work&Material&Factors
• Multiply&theoretical&surface&roughness&by&the&ratio&of&actual&to&theoretical&roughness&for&the&given&cutting&speed&to&obtain&estimate&of&actual&surface&roughness
NC#State#University
HW#assignment
• Reading#assignment:#Chapters#17
• Review#Questions:#15.4,#15.5,#15.11,#16.2,#16.5,#16.6,#16.13,#16.14
• Problems:#15.1,#15.3,#15.4,#15.6,#15.10,#16.1,#16.2,#16.6,#16.8,
Department#of#Materials#Science#and#Engineering 37