Test 1 Machining Flashcards
Types of Machining
Straight turning, cutting off, slab milling,
CNC Machine
Computer Numerical Control, one machine does all the work. Run off of computer programs
Forging
shaping of metal using pressure
Tolerances
dimensions must lie within a certain range
Cutting Ratio
r=To/Tc, depth of cut divided by chip thickness
Rake Angle
tool face angle to vertical plane (alpha)
Rake face
face touching chip
shear angle
angle of shear plane to cutting direction
Primary shear zone
where chips break off, place of the highest shear strain
Secondary shear zones
second largest area of shear strain
Chip Velocity
Vc= V(To/Tv)=Vr
Power
V*Fc, need to know to determine power requirements to produce efficiently
Power dissipated by
friction and heat, plastic deformation, 1.) shear along shear angle 2.) friction along chip/tool interface
Areas of high heat
rake face- tool/chip interface
Flank face
tool workpiece interface
Rake face
too/chip interface
Taylor Tool Life Equation
(VT)^N=C or (C/V)^(1/n)=T where T is time and V is cutting speed
Heat
causes degregation, most heat goes into work piece but tool is smaller, faster speed, high temp
Wear
Velocity*pressure/hardness; it is the result of relative motion times pressure
Hardness
changes with temperatire
Ways to save money on tool
mount expensive tool on cheap mount; coat inexpensive material with expensive material
Coolant
removes heat, lubricates tool/work piece interface, and washes away chips
Alternative Coolants
liquid nitrogen, mist cooling, dry lubrication
Problems with coolants
expensive, have to dispose of safely
Wear Limit
when tool is no longer useful;
Effect of velocity on wear
increasing speed increases heating rate, which increases tool temperature, which increases wear
Tool Wear Curves
Initially fast in break in zone, levels out, then rapidly increases in failure zone (no longer useable)
Milling
workpiece is fed past a rotating cylindrial tool, with cutting edges perpendicular to the direction of the field
machining advantages
it is very accurate and can cut within toleraces
Tooling failure
gradual wear, fracture failure, temperature failuew
Failure
occurs at rake face and flank
Failure region
point at which wear begins to accelerate
Important tool properties
toughness, hot hardness, wear resistance
Maximize Production Rates
part handling time, machining time, tool change time
Minimize cost
part handling, machining time, tool change cost, tooling cost
Tool life Plots
use log-log plot to find C
Machining Time
Tm=piDiameterlength/*feed rate/Velocity
Velocity and time/cost
higher velocity, lower time, higher cost
