Technical Guidance The Basics of Milling
■ Relation between engagement angle and tool life
Large diameter
Small diameter v f
Part material feed direction (V f )
v f
Milling Cutters Rotation direction
n
n
n
E
E
Large E
Small E
Insert Engagement Angle (E) The engagement angle denotes
v f
v f
the angle at which the full length of the cutting edge
N
n
n
E
comes in contact with the work material, with reference to the feed direction. · The larger E is, the shorter the tool life · To change the value of E: (1) Increase the cutter size (2) Shift the position of the cutter
Small E
E
Large E
0.4
0.6
0.3 0.2 0.1
Cast Iron
1050
0.4
0.2
-20° 0° 20° 40° 60° 80°
-30° 0° 30° 60° Engagement Angle
Engagement Angle
● Relation between the number of simultaneously engaged cutting edges and cutting force
Normally, a cutting width 70 to 80% of the cutter diameter is considered appropriate, as shown in example d). However, this may not apply due to the actual rigidity of the machine or workpiece, and the machine horsepower.
a)
b)
c)
d)
e)
Time
Time
Time
Time
Time
Milling Cutters
· 0 or 1 edge in contact at same time
· Only 1 edge in contact at any time
· 1 or 2 edges in contact
· 2 edges in contact at any time
· 2 to 3 edges in contact
■ Improving surface roughness (1) Inserts with wiper flat
● Surface roughness without wiper flat
● Surface roughness with wiper edge (difference in face cutting edge)
· Part material: Alloy Steel · Cutter: DPG5160R (per tooth) · v c = 510 SFM f z = .0092 in./t a p = .0787” · Face Cutting Edge Angle (A): 28’ (B): 6’
Feed rate per tooth
Feed rate per tooth
When all of the cutting edges have wiper flats, a few teeth protrude due to inevitable runout and act as wiper inserts. · Insert equipped with straight wiper flat (Face angle: Around 15' to1°) · Insert equipped with curved wiper flat (Curvature: ≈ R500 (example))
(A)
H C
● Surface roughness with straight wiper flat
Feed rate per tooth Feed rate per tooth
(B)
× 2,000
H F
× 100
● Effects of wiper insert (example)
h: Projection value of wiper insert Cast Iron: .002” Al: .001” Wiper Insert ( )
(Only normal teeth)
· Part material: Grey Cast Iron · Cutter: DPG4100R · Insert: SPCH42R · Face runout: .0006” · Runout: .0016”
(2) Wiper insert assembling system A system in which one or two inserts (wiper inserts) protrude with a smooth curved edge just a little beyond the other teeth to wipe the milled surface. (Applicable to WGX Type, DGC Type, etc.)
× 1,000
20 15 10 5
Normal Edge Type h
20
(C)
H W
Feed per revolution
v c = 350 SFM f z = .0571 IPR (C): Normal teeth (D): Per wiper edge
f: Feed rate per revolution (IPR)
(Wiper edge With 1 wiper insert)
× 1,000 20
f
f
20 15 10 5
(D)
H C
H W Hc: Surface roughness with only normal teeth Hw: Surface roughness with wiper insert
N55
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