Fundamentals Of Machining Flashcards
State common machining operation
- Turning - work piece rotate, curring tool layers of material as it move to the left.
- slab Milling - rotating cutting tool remove material from surface
- end milling - rotating cutter travel along a depht in work piece producing cavity.
- cutting - tool move radially inward removing piece from bulk of blank
Define turning
Tool set to a cutting dept, move from right to left at a certain feed rate (mm/rev)
Common term in cutting process diagram
Rake angle (a) , relief angle (@), depth of cut, depth of chip, flank, shear angle
Factor influencing machining op
Chips, temp, cut spd/depth/feed/fluid, angle, wear, machinibility
Major independent variable
Tool material/coat/shape/surface finish/sharpness/characteristic, workpiece material and condition, cutting spd/feed/depth/fuild, workholding/fixturing.
Cutting ratio
r= To/Tc =sin @/ cos (@-a)
Shear angle preditions
@ = 45 + a/2 -b/2
b = friction angle
Velocity of chip
Vc = vsin@/ cos(@-a)
Shear velocity
Vs = Vcosa/cos(@-a)
Continous chip
- From high rake angle and/or high cutting spf.
- good surface finish
- bad for auto (tangled)
Built up edges chip
- from layers of material deposited onto tool
- breaks up eventually and carried awy to side of tool
- deposited randomly on surface
- poor surface finish
- prevent by increasing rake angle which decrease depth of cut
Discontinued chip
-from hard brittle material
- segments may be firmly or losely attached
- brittle failure takes place along shear plane before plastic flow occurs
- occurs from low rake angle (large depth of cut)
Serrated chips
-semi continuous chips with low and high shear strain
- from low thermal conductivity and strength metals
Chip breaker
-cuts chip
- can be build in or is a piece of metal
Relationship between angle of oblique tool and chips
As angle increase, chips becomes more tightly curled
Cutting force
Fs = Fc cos @ - Ft sin @
Fn = Fc sin @ - Ft cos @
coeff Friction = (Ft+ Fc tan a)/(Fc - Ft tan a)
Wear patterns in tool
Flank wear - wearing pattern on relief
Crater wear - crater on face
Chipped cutting edge - break awy of cutting edge
Thermal craking - discolouration
Built up edge - rises on edge
Catastrophic failure - whole edge missing
Taylor tool life equation
VT^n = C
VT^n d^x f^y = C
Hardness and tool life
Tool life decrease as hardness increase
Spd and life
High spd = low life
Temp and crater wear
Crater wear increase with temp
Dull tool
Become negative rake angle in lower depth, cuz tool ride over material and burnished(rubbing) surface, raise temp cuz surface residual stress
