Drilling processes
Cutting speed V (m/min) The undeformed chip area Ac
h = chip thickness to be
removed by each drill
lip.
X = cutting edge angle
d (mm) = outer
which is constant and
diameter of the drill. depends on the
particular application.
N (rev/min) = drill b = undeformed chip
rotational speed. length
S = feed rate
Cutting forces, torque, and power
Drilling Time
The time necessary for drilling or enlarging a through hole of length l
(mm) is determined by
Example
Problem: A drilling operation is to be performed with a 12.7 mm diameter twist drill in
a steel workpiece. The hole is a blind hole at a depth of 60 mm and the point angle is
118°. The cutting speed is 25 m/min and the feed is 0.30 mm/rev. Determine
(a) The cutting time to complete the drilling operation,
(b) The main cutting force (if ks = 2200 N/mm2),
(c) The drilling power and drilling torque
(d) Material removal rate during the operation, after the drill bit reaches full diameter.
Comment: Assume that the hole depth of 60 mm includes the tip of the tool.
turning processes
Cutting speed, feed, and machining time
Surface Roughness
Elements of undeformed chip
▪ Depth of cut (t):
▪ The chip cross section area (shaded
d: initial diameter of
area) Ac: workpiece in mm,
df: diameter of the
machined (final) surface.
h: chip thickness
b: workpiece contact
length with the cutting
tool.
x: the main cutting edge
angle (45 to 90)
Cutting forces, power, and removal rate
Example
A steel rod 200 mm long and 75 mm diameter is being reduced to 60 mm in
diameter allover its length in one travel. The machine spindle rotates at 1000 rpm
whereas the tool is moving at an axial feed of 0.5 mm/rev. Calculate
Material removal rate (mm3/min.).
Machining time (min). (assume la= lo =5 mm)
The specific cutting energy in N/mm2 if the consumed power is 1.5 kW.
Main cutting force. The maximum surface roughness for tool nose radius 1.25
mm.
