FAILURE CATALOGUE
Sharp notch on the edge at depth-of-cut line; witness mark on the surface.
Super duplex, IN718, Waspaloy, super austenitic
Work-hardened layer from the previous pass plus oxide skin; the edge always working at the same point.
Vary the depth of cut pass to pass. Spread wear with a round insert. Strengthen the edge preparation.
Material welded to the edge, shiny; surface rough and inconsistent.
904L, 254 SMO, CP Ti, Inconel 625, aluminium
Cutting speed too low; edge too passive; insufficient coolant.
Increase cutting speed (not decrease). Sharper positive geometry. Raise coolant pressure.
Pit on the rake face; the edge weakens from inside and fails suddenly.
Steel, P91, 4340, cast iron
Diffusion wear — cutting temperature too high.
Reduce Vc. Thicker CVD coating. Direct coolant onto the rake face.
Edge crushed and collapsed; dimensional drift and surface degradation.
Superalloys, hardened steel, armour
Cutting force plus temperature exceeded the substrate's strength.
Harder substrate grade. Reduce Vc and f. High-pressure coolant. Larger corner radius.
Irregular small break-outs along the edge.
Castings, bimetal, interrupted cuts, composites
Impact, vibration, weak clamping, interrupted cutting.
Strong hone / T-land. Tough grade. Increase rigidity, shorten overhang.
Parallel cracks perpendicular to the edge, comb-like.
Milling, superalloys, stainless
Intermittent coolant → thermal-shock cycling.
Either fully dry or fully flooded. Half measures are the worst option.
Even, predictable wear land on the flank.
All materials; fast in Al-Li, cast Al, GFRP
Normal wear mechanism.
Acceptable. Set a VB criterion and plan tool life around it.
Separation of composite plies, especially at hole exit.
CFRP, GFRP, aramid
Axial force too high; no backing; dull tool.
Compression geometry, exit support, sharp diamond tooling, reduce feed at exit.
Thin hard brittle layer on the surface; white in metallography.
Hardened steel, PH stainless, IN718, Ti
Excess temperature plus a dull tool → phase transformation at the surface.
Change the tool earlier. High-pressure coolant. An acceptance criterion in aerospace — confirm by metallography.
Oxygen-rich hard brittle surface layer on titanium.
Ti alloys (usually from heat treatment)
Oxygen diffusion at high temperature.
Must be fully removed by machining; any remaining layer reduces fatigue life.
Material embrittles; unexpected fracture during machining.
Duplex, super duplex, super austenitic
Holding in the high-temperature range (welding, incorrect heat treatment).
Not a machining cause — question the raw-material history, measure hardness and phase balance.
Part goes out of tolerance once released from the fixture.
Thick aluminium plate, thin walls, Invar
Residual stress release; heating; clamping force.
Symmetric roughing, intermediate stress relief, stepped passes, low clamping force.
Regular wave pattern on the surface; characteristic sound.
Thin walls, long overhang, titanium, superalloys
Regenerative chatter; insufficient system rigidity.
Shorten overhang, change the ap/ae ratio, shift spindle speed (stability lobe), variable-pitch tooling.