14
ME 324 Manufacturing Engineering
Prof. Sonal Padalkar
Milling Operation
Up
Down
Rotation axis is parallel to the work piece surface
depth-of-cut = d; feed per tooth = f;
chip depth-of-cut = tc
workpiece speed = v
cutter travel distance = lc, to reach full depth-of-cut.
Milling Operation
Down milling
Matt surface
Groves / path on the surface
Less material needs to be removed
Can be done by down milling
Up vs. Down Milling
Conventional milling is called up milling
o The cutter rotates CCW
o Chip is thin at the beginning
o Chip is thick as cutting continues
o Cutter pushes workpiece upwards
o Screws holding work piece get
loose
In down milling or climb milling
o Cutter rotates CW
o Maximum chip thickness at point of contact with work
piece.
o Dulls teeth quickly.
o Work piece pulled into the cutter
Milling Operation
In milling the cutting speed, V, is given by
𝑉𝑉 = 𝜋𝜋 𝐷𝐷𝐷𝐷
D = Cutter diameter
N = Rotational speed of the cutter
The chip thickness is given as
𝑡𝑡𝑐𝑐 = 2𝑓𝑓
𝑑𝑑
𝐷𝐷
f = Feed per tooth
d = Depth of cut
To find the feed per tooth (chip load), use the equation
𝑣𝑣
𝑓𝑓 =
𝑁𝑁𝑁𝑁
v = Linear speed (feed rate)
n = Number of teeth on the cutter periphery
Milling MRR and Cutting Time
Cutting time for milling is given by
𝑙𝑙 + 𝑙𝑙𝑐𝑐
𝑡𝑡 =
𝑣𝑣
l = Length of the workpiece
lc = Extent of cutter’s first contact with the workpiece
Determining material removal rate for milling is accomplished
using the expression
𝑙𝑙𝑙𝑙𝑙𝑙
= 𝑤𝑤𝑤𝑤𝑤𝑤
𝑀𝑀𝑀𝑀𝑀𝑀 =
𝑡𝑡
w = Width of cut (l>>lc)
Face (End) Milling Operation
(c) Conventional
milling
(a) Action
of insert in
face milling
(b) Climb milling
Rotation axis is perpendicular to the work piece
surface
(d) Dimensions of face milling
The width of cut not necessary
to be equal to radius of cut
Face Milling Cutter
Terminology for face milling cutter
Relative Position of Cutter and Insert: Face milling
(b) Insert positions
towards the end of cut.
(a) Relative position of cutter &
insert as it first engages with
workpiece in face milling.
In all figures, the cutter spindle is perpendicular
to the page and rotates clockwise.
(c) Examples of exit angles of insert, showing
desirable (positive or negative angle) and
undesirable (zero angle) positions.
Forces acting on inserts decrease gradually to zero
Forces acting on inserts decrease suddenly
Cutting Speeds in Milling
Approximate range of recommended cutting speeds for milling operations
Micro-milling Examples
Meso-scale milling machine Coolant applied micro-milling
Micro-milling Tool
Fresh new tool
After machining 26 channels
Machining Parameters:
0.1 mm x 0.2 mm x 25 mm channel is machine by ø0.101um carbide milling tool
at 10 um depth of cut; 75mm/min feed rate, 10,000 rpm; oil mist coolant
applied.
Effect of Tool on Surface Finish
(Micro – milling of pure copper)
1st
24th
4th
14th
35th
o Tool wears out with increased milling
o Surface finish becomes rough
40th
100 um
Indication of Tool Wear
1st channel
14th channel
24th channel
40th channel
Increase in force with tool wear
Types of Milling Machines
(a) Horizontal – spindle column
and knee type milling machine
(b) Vertical – spindle column and
knee type milling machine
Broaching
• Broaching is where a tool, with successively increasing tooth size,
creating the desired shape with a single pass.
• Broaching is similar to sawing, with the exception that a saw requires
multiple passes, and the teeth are not increased in size along the
length of the tool.
• Broaching can be used for grooves, flat surface features, and holes of
various geometry.
Internal and Surface Broaching
Typical parts made by internal broaching
Parts made by surface broaching
Broach Action and Terminology
Cutting action of a broach
Terminology of a broach