Post on 02-Jun-2018
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Machining Operations
Generally performed after other manufacturingprocesses (casting, forging, ) Other processes create the general shape of the workpart Machining provides the final shape, dimensions, finish, and
special geometric details that other processes cannot create
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Most important machining operations: Turning Drilling Milling
Other machining operations: Shaping and planing Broaching Sawing
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Primary Machining Parameters
Cutting Speed (v) Primary motion Peripheral speed m/s ft/min
Feed (f)
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econ ary mo on Turning: mm/rev in/rev Milling: mm/tooth in/tooth
Depth of Cut (d) Penetration of tool below original work surface Single parameter mm in
Resulting in Material Removal Rate (MRR)MRR= v f d mm3/s in3/min
where v= cutting speed; f= feed; d= depth of cut
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Turning Parameters Illustrated
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Figure 22.5 - Turning operation [Groover (2004), p.503]
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Drilling
Creates a round hole ina workpart
Contrasts with boringwhich can only enlarge
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an existing hole Cutting tool called a drill
or drill bit
Customarily performedon a drill press
Figure 21.3 (b) drilling[Groover (2004), p.501]
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Milling Parameters Illustrated
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Figure 21.3 - Two forms of milling:
(a) peripheral milling, and (b) face milling[Groover (2004), p.516]
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Machining Operations &Parameters
Operation Type Speed Feed Depth of Cut
Turning:workpiece rotates
single point cutting
Surface speed(periphery) of
workpiece
Parallel to theworkpiece axis*
(*except parting/grooving)
Tool penetrationbelow originalwork surface
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Drilling:tool rotates
single pass cutting
Surface speed(periphery) of
tool
Parallel to thetool axis
Tool penetrationbelow originalwork surface
(depth of hole)
Milling:tool rotates
multi-point cutting
Surface speed(periphery) of
tool
Perpendicular tothe tool axis
Tool penetrationbelow originalwork surface
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Cut Types: Roughing &Finishing
Cut Type
Number
of
PassesSpeed Feed Depth of Cut
Roughing:
1 + Low High
High
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removes largeamounts to getclose to shape
0.4 - 1.25 mm/.015 - .050 in/
2.5 - 20 mm.100 - .750 in
Finishing:achieves final
dimensions,tolerances, andfinish
1 - 2 High Low
0.125 - 0.4 mm/
.005 - .015 in/
Low
0.75 - 2.0 mm
.030 - .075 in
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Turning
A single point cutting tool removes materialfrom a rotating workpiece to generate arotationally symmetric shape
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Types of cuts: Facing Contour turning Chamfering Parting (Cut-off) / Grooving Threading
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Turning Parameters Illustrated
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Figure 22.5 - Turning operation [Groover (2004), p.503]
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Facing
Tool is fedradially inward
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Figure 22.6 (a) facing
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Contour Turning
Instead of feeding thetool parallel to the axisof rotation, tool follows a
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necessarily straight(thus creating acontoured form).
Figure 22.6 (c) contour turning
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Right & Left Hand Tools
Right Hand Tool: Cuts from right to left
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Left Hand Tool:
Cuts from left to right
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Chamfering
Cutting edgecuts an angle onthe corner of the
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cylinder, forminga "chamfer"
Figure 22.6 (e) chamfering
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Parting (Cutoff) / Grooving
Tool is fedradially intorotatin work at
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some location tocut off end ofpart, or provide
a groove
Figure 22.6 (f) cutoff
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Threading
Pointed form toolis fed linearlyacross surface of
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parallel to axis ofrotation at a largefeed rate, thus
creating threads
Figure 22.6 (g) threading
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Figure 22.7
Engine Lathe
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an enginelathe,showing itsprincipal
components
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Chuck
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Figure 22.8 (b) three-jaw chuck
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Turret Lathe
Manual operation is replaced by aturret that holds multiple tools
Tools are rapidly brought into action by
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indexing the turret Tool post is replaced by multi-sided turretto index multiple tools
Applications: high production work thatrequires a sequence of cuts on the part
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CNC Turret Lathe
Tool Turret
Spindle Speed
+ X-axis
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SpindleCross Slide
+ Z-axis
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CNC Lathe: Air-Operated Chuck
Ri ht Hand
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Profile Tool
Chuck
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CNC Lathe: Tool Turret
Tool Turret
Left HandProfile Tool
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Right Hand
Profile Tool
Grooving /Parting Tool
Tool Holder
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Machining Calculations:Turning
Spindle Speed - N (rpm)
v = cutting speed Do = outer diameter
Feed Rate - fr (mm/min -or- in/min) f = feed er rev
oD
vN =
ff =
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Depth of Cut - d (mm/rev -or- in/rev) Do = outer diameter Df = final diameter
Machining Time - Tm (min)
L = length of cut
Matl Removal Rate - MRR (mm3/min -or- in3/min)
2
fo DD
d
=
r
mf
L
T =
dfvMRR=