Lecture 8 - Milling

Question 1

3 basic milling types

Answer 1

Slab face end

Question 2

Peripheral/Slab milling

Answer 2

Axis of cutter parallel to machining surface of workpiece

Question 3

Cutting speed equation

Answer 3

cutting speed (Ns) = cutting velocity (Vs) / pi * diameter of cutter (D)

Question 4

Length of cut equation

Answer 4

length of cut = length of workpeice (L) + allowances for approach (La)

Question 5

La

Answer 5

((D/4)^2-((D/2)-d)^2)^0.5

Question 6

Feed of table

Answer 6

measured in inches per minute
amount of metal each tool removes per minute

feed of table (fm) = feed of tooth (ft) *number of teeth(n) * cutting speed (Ns)

Question 7

cutting time equation (slab)

Answer 7

cutting time (t) = length of cut / feed of table (fm)

Question 8

Material removal rate

Answer 8

MMR = Removed Volume / Cutting Time
in case where volume is cuboid

Volume = Length of workpiece * width of workpiece * depth of cut

MMR = W * fm * d

Question 9

Face or end milling

Answer 9

Cutter mounted on spindle having axis of rotation perpendicular to workpiece surface

Question 10

Cutting time equation (face/end)

Answer 10

time = (L +La + overrun (Lo)) / fm

Question 11

Up milling

Answer 11

conventional
cutter rotates against feed direction of workpiece

chips increase in thickness as tooth rotates
depth of cut starts at 0 and increases
tooth initially slides along surface until pressure on material is enough to start cutting
Slide-cut mechanism results in poor surface finish
sliding action causes work hardening on material and dulls cutting edges
smoothness of generated surface depends on sharpness of cutting edges
chips can be carried onto newly machined surface contributing to poorer surface finish
cutter pushes workpiece away and lifts it from table - tends to loosen workpiece from holding device

Question 12

Down milling (climb milling)

Answer 12

cutter rotation in same direction as feed rate

Chips decrease in thickness as tooth rotates
teeth engage at specific point where depth of cut is max.
No slide-mechanism so tool life is longer
Increased load on tooling and machine
chips carried away from cutting surface so cannot damage finish
cutter pulls workpiece towards itself and pushes workpiece down onto table

Question 13

Backlash

Answer 13

Excessive amount of clearance between machine hand wheel screw and nut attached to machine table or slide

Question 14

Planing

Answer 14

can produce accurate flat surfaces, various cross sections with grooves and notches along the length of the workpiece
Cheap compared to milling and grinding

Question 15

Shaping

Answer 15

Used to produce parts much like planning but parts are smaller
Cutting tool moves across fixed workpiece in one direction
Cheap compared to milling and grinding

Question 16

Broaching

Answer 16

Machines internal and external surfaces
Has multiple teeth, each tooth standing slightly higher than previous
Use single pass to machine workpiece
Feed per tooth is change in height of 2 successing teeth called rise per tooth (RPT)

Question 17

Sawing

Answer 17

Cutting operation with blade consisting of many teeth
Each tooth removes small amount of material
Many passes needed to finish machining