Technical Guidance Hardened Steel Machining with CBN - SUMIBORON Edition
■ Recommended Zones for CBN by Workpiece Hardness and Shape
■ Cutting speed recommendations for each part material
1000
Heavy
660
Coated carbide Cermet
CBN - SUMIBORON
Light
330
Ceramic
Carburized or induction hardened material
Bearing Steel
Die Steel
40
45
50
55
60
65
N
Hardness of part material (HRC)
Prone to notch wear
Fairly large amount of wear
Large amount of wear
■ Influence of coolant on tool life
■ Relation between part material hardness and cutting force
● Continuous Cutting
● Interrupted Cutting
Feed Force
Milling of SKD11 to 4 U grooves Cutting speed: v c = 330 SFM
Principal Force Feed Force Back Force
.012
150
Depth of cut: a p = .0079” Feed rate ( f )= .0039 IPR
Dry Oil-based coolant Water soluble emulsion Water soluble
.010
Back Force
Heavy
.008
100
Interrupted Cutting
.006
100
Principal Force
.004
☆ In continuous cutting of bearing steel, there is not much difference between dry and wet cutting.
50
.002
50
Part Material: Cutting Conditions:
Carbon Tool Steel Cutting speed ( v c ) =400 SFM, depth of cut ( a p ) =.0079” Feed rate ( f ) =.0039 IPR
Dry
Wet cut
0
20
40
60
80 100 120 140
0
Cutting Time (min)
0
10
30
50
70
Hardness of Work Material (HRC)
For continuous cutting, the influence of coolant on tool life is minimal. For interrupted cutting, the thermal impact shortens the tool life in wet conditions.
Part material: High Carbon Steel (58 to 62 HRC) Cutting conditions: TPG321 v c =330 SFM, a p =.0059”, f =.0039 IPR Continuous Cutting
Back force increases substantially for harder workpieces.
■ Relation between flank wear and cutting force
■ Influence of part material hardness on cutting force and accuracy
300
Cutting Speed: Depth of Cut : Feed Rate :
v c = 400 SFM a p = .0197” f = .012 IPR, dry
4131 65HRC
Hard zone
Soft zone
Hard zone
Cutting conditions: Cutting speed ( v c ) = 262 SFM Depth of cut ( a p ) = .0059” Feed rate ( f ) = .0039 IPR
200
Part material: Carbon Steel
1055 24HRC
90 70 50 30
100
45 (HS)
0
100
400 300 200
For hardened steel machining, back force increases substantially due to the expansion of flank wear.
External dimensions in the soft zone are smaller due to lower cutting forces.
106N
0 100
0 -10 -20
13μm
0
.002 .004 Flank Wear Width (V B ) (in)
■ Relation between cutting speed and surface roughness
■ Improvement of surface roughness by altering the feed rate Constant Feed Rate Variable Feed Rate
Part material : Alloy Steel 58 to 62HRC Holder : MTXNR2525 Tool : NU-TNMA160408
BN250 V c =120 BN250 V c =150 BN250 V c =180
Previous Edge Position
f
f
0.3
Cutting Conditions: v c =400,500,600 SFM f = .0018 IPR a p = .0059” Wet
0.2
Shifting Notch Location
Stationary Notch Location
0.1
0
0
40
80
120
160
Machining Output (pcs.)
At high cutting speeds, surface roughness is more stable.
☆ Varying the feed rate spreads the notch location over a larger area. → Surface finish improves and notch wear decreases.
N65
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