Technical Guidance Cutting Edge Failure & Countermeasures for Machining Hardened Steel - CBN
Insert Failure
Cause
Countermeasures
· Select a more wear-resistant grade (eg BNC2010, BN1000 or BN2000) · Reduce the cutting speed to v c =660 SFM or less (higher feed rate also reduces tool-to-work contact time)
Flank Wear
· Grade lacks wear resistance
· Cutting speed is too fast
· Use an insert with a larger relief angle
Crater Wear
N
· Grade lacks crater wear resistance
· Select a higher efficiency grade (eg BNC2010, BNX25 or BNX20)
Breakage at Bottom of Crater
· Reduce the cutting speed to v c =660 SFM or less and increase the feed rate (low speed, high feed) (higher feed rate alone also reduces tool-to-work contact time)
· Cutting speed is too fast
Flaking
· Grade lacks toughness
· Select a tougher grade (eg BNC2020 or BN2000)
· Select an insert with a stronger cutting edge (Increase negative land angle and perform honing)
· Back force is too high
· If the grade is tough enough, improve the cutting edge sharpness · Change to a grade with a higher notch wear resistance (e.g. BNC2010 or BN2000) · Increase cutting speed (500 SFM or more)
Notch Wear
· High stress at boundary
· Change to the Variable Feed Rate method, which alters the feed rate in fixed output intervals
· Increase negative land angle and perform honing
· Change to a micro-grained grade with a higher fracture resistance (e.g. BNC300 and BN350)
Chipping at Forward Notch Position
· Impact to front cutting edge is too large or occurs constantly
· Increase the feed rate (higher feed rates are recommended to reduce chipping)
· Select an insert with a stronger cutting edge (Increase negative land angle and perform honing) · Change to a grade with a higher fracture resistance (e.g. BN350 or BNC300) · Reduce feed rate · Use an insert with a larger side cutting angle · Use an insert with a larger nose radius · Select an insert with a stronger cutting edge (Increase negative land angle and perform honing)
Chipping at Side Notch Position
· Impact to side cutting edge is too large or occurs constantly
Thermal Crack
· Completely dry conditions are recommended
· Thermal shock is too severe
· Select a grade with better thermal conductivity
· Reduce cutting speed, feed rate, and depth of cut to decrease the machining load.
N68
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