The causes of tool wear — and how to fix them.
Tool wear has five causes: abrasion, adhesion, diffusion, oxidation and fatigue. Which one wins depends above all on cutting temperature — so on cutting speed. They leave eight recognisable marks on an edge, from even flank wear to fracture, and each mark tells you what to change.
- 5
- Root mechanisms
- 8
- Wear types
- 0.3 mm
- ISO 3685 flank wear limit
- ≈ ½
- Tool life at +20% speed (carbide)
- 1 page
- Printable wear chart
Written by Alok Kanani
Chief Executive Officer, Carbide India
Updated
01 — What causes tool wear
Five mechanisms wear every cutting edge.
Every wear type you'll see on a tool comes from one or more of these. Temperature decides which one dominates: abrasion and adhesion at low cutting speeds, diffusion and oxidation as speed and heat rise.
Low speed · abrasion, adhesion
High speed · diffusion, oxidation
M/01
Abrasion
Hard particles in the workpiece — carbides, oxides, sand in castings — scratch tool material away, like sandpaper. It acts at every cutting speed and is the main cause of flank wear.
M/02
Adhesion
Under heat and pressure, workpiece metal welds to the edge in tiny spots. When those welds shear off, they pull fragments of tool material with them — the mechanism behind built-up edge. Worst at low speeds and with sticky materials such as low-carbon steel, stainless and aluminium.
M/03
Diffusion
At high cutting temperatures — roughly 700–900 °C and above — atoms move between the tool and the hot chip sliding over it, and the carbide surface weakens. The main cause of crater wear on the rake face, and why it grows quickly with cutting speed.
M/04
Oxidation and chemical wear
Cemented carbide starts to oxidise in air at about 600 °C, and rapidly at about 900 °C. Where air reaches the hot edge — at the edges of the contact zone — the surface weakens; it's one contributor to notch wear. Coatings exist largely to block oxidation and diffusion.
M/05
Fatigue — mechanical and thermal
Repeated loading cracks the edge: force swings from interrupted cuts and vibration cause chipping and fracture, and rapid heating and cooling — in milling, the edge swings between about 1,000 °C and cool on every revolution — causes thermal cracks across it.
02 — Types of tool wear
Where each type of wear shows up on the edge.
Eight wear types, each with its own location and look. Find yours on the drawing, then diagnose it below.
- 1Flank wear
- 2Crater wear
- 3Notch wear
- 4Built-up edge (BUE)
- 5Edge chipping
- 6Thermal cracks
- 7Plastic deformation
- 8Fracture
Schematic, not to scale · wear shown in orange
03 — Diagnose
What does your worn edge look like?
Pick what you see. You'll get the likely causes and what to change — speed, feed, geometry, coolant or grade. Check the edge under a loupe or microscope; most wear types look alike to the naked eye.
01 · Flank (clearance) face
Flank wear
An even, shiny wear land on the flank just below the cutting edge, growing steadily as you cut. It's the normal, predictable way a tool wears out — the one you want, because you can plan around it. Size creeps and finish deteriorates as the land widens.
Likely causes
- Abrasion by hard particles in the workpiece
- Cutting speed too high for the grade
- Feed too low — the edge rubs instead of cutting
- Grade not wear-resistant enough for the material
What to change
- Reduce cutting speed
- Increase feed if it's very light
- Move to a more wear-resistant grade or a coated tool
- Change the edge at a set wear limit, before it accelerates
Grade move · Harder — finer grain or less cobalt.
02 · Rake face, behind the edge
Crater wear
A hollow worn into the rake face where the chip slides over it, set slightly back from the edge. As it deepens it weakens the edge until it breaks through — often suddenly.
Likely causes
- High temperature at the chip–tool contact: diffusion and chemical wear
- Cutting speed and/or feed too high
- Long-chipping steels at high speed
- Uncoated grade, or one not meant for steel
What to change
- Reduce cutting speed first, then feed
- Use a coated or more wear-resistant grade
- Use a more positive geometry to cut temperature
- Get coolant to the cutting zone
Grade move · Harder and heat-resistant — a coated grade for steel.
03 · At the depth-of-cut line
Notch wear
A localised notch cut into the edge exactly where it meets the outer surface of the workpiece — much deeper than the wear on the rest of the edge.
Likely causes
- Work-hardened surfaces and materials that harden as they're cut (stainless, heat-resistant alloys)
- Scale, casting or forging skin on the surface
- Oxidation where air reaches the hot edge
- Burrs left by the previous pass
What to change
- Vary the depth of cut between passes so the notch doesn't hit one spot
- Change the entering (lead) angle — tool makers' advice differs by material, so test both ways
- Use a round insert or a larger corner radius to spread the load
- Use a sharper edge in sticky materials such as stainless and heat-resistant alloys
Grade move · Tougher, and coated where oxidation is the cause.
04 · On the edge and rake face
Built-up edge (BUE)
Workpiece metal welded onto the cutting edge, changing its shape. It breaks off from time to time, taking tool material with it — finish turns poor and sizes wander.
Likely causes
- Cutting speed too low (cutting temperature too low)
- Sticky, ductile materials: low-carbon steel, stainless, aluminium
- Negative or blunt geometry
- Too little or the wrong coolant
What to change
- Increase cutting speed
- Use a sharper, more positive geometry
- Use a PVD-coated or cermet grade that metal sticks to less
- Improve coolant concentration and supply
Grade move · Not usually a grade problem — change speed and geometry first.
05 · Along the cutting edge
Edge chipping
Small pieces broken out along the edge, rather than worn away. The edge looks ragged; finish suffers and chipping usually runs into fracture if ignored.
Likely causes
- Interrupted cuts and shock loads
- Vibration and an unstable setup
- Grade too hard (brittle) for the job
- Edge too sharp or weak for the load; hard inclusions
- Built-up edge breaking away
What to change
- Use a tougher grade
- Use a stronger edge: a hone or chamfer, a negative land
- Reduce feed, especially at entry and exit
- Improve rigidity: shorter overhang, better clamping
Grade move · Tougher — more cobalt or coarser grain.
06 · Across the cutting edge
Thermal cracks
Fine cracks running at right angles across the edge, like the teeth of a comb. Pieces between the cracks eventually break out.
Likely causes
- Rapid temperature cycling: the edge heats in the cut and cools out of it — typical in milling
- Coolant applied unevenly or intermittently to a hot edge
- Varying chip thickness or depth of cut
What to change
- In rough milling, run dry; where coolant is needed, keep it generous and constant
- Use a tougher grade, or one with a thinner (PVD) coating
- Reduce cutting speed
Grade move · Tougher, thermal-shock resistant.
07 · Edge and nose
Plastic deformation
The edge has sagged or bulged under heat and pressure — the carbide softened and was pushed out of shape. Often shows as an edge depression at the nose, followed by rapid flank wear or breakage.
Likely causes
- Cutting temperature too high: speed and feed too high together
- Hard workpiece material
- Grade too soft (too much binder) for the heat
- Too little coolant
What to change
- Reduce feed first if the edge is pushed down; cutting speed first if the flank bulges
- Move to a harder grade with less binder and good hot hardness
- Use a stronger geometry and a larger nose radius
- Improve coolant
Grade move · Harder — less cobalt.
08 · The whole edge or corner
Fracture
A large part of the edge or the whole corner has broken away. It's the end point of other problems — chipping, cracks, notch or crater wear left to grow — or an overload.
Likely causes
- Excessive load: feed or depth of cut too high
- Grade too hard for the shocks in the cut
- Unstable setup or vibration
- Other wear left too long
What to change
- Change edges earlier, at a set wear limit
- Reduce feed and depth of cut
- Use a tougher grade and a stronger geometry
- Check insert seating and clamping; improve rigidity
Grade move · Tougher, and a stronger edge geometry.
04 — Speed, feed & tool life
Cutting speed is the biggest lever on tool life.
Speed sets cutting temperature, and temperature drives the fastest wear mechanisms. Feed matters less, and depth of cut least — so when edges wear too fast, look at speed first.
Taylor's tool-life equation, V·Tn = C, puts numbers on it. V is cutting speed, T is tool life, and n and C depend on the tool material and the job. Because n is small — around 0.25 for carbide — a modest rise in speed takes a large bite out of tool life.
It also shows a trade-off that's easy to miss: pushing speed gets each part done faster, but each edge removes lessmetal before it's worn out. The right speed is the one with the lowest cost per part, counting tool changes and downtime — not the fastest one.
Tool life
48%
of today's — about 7.2 min instead of 15.0 min per edge
Metal removed per edge
58%
Faster cutting, but each edge does less work before it's worn out.
Taylor: V·Tⁿ = C · Carbide: published n ≈ 0.2–0.5 · An estimate for comparing options — real tool life depends on the job
05 — Tool life
When is a cutting tool worn out?
On the shop floor: when parts drift out of size, the finish deteriorates, or noise and cutting forces climb. In a tool-life test, when the wear reaches a set limit — and the standard limits are useful targets for your own edge changes.
- Average flank wear, VB
- 0.3 mm
- When the flank wear land is even along the edge.
- Maximum flank wear, VB max
- 0.6 mm
- When the land is uneven — scratched, chipped or grooved.
ISO 3685 flank-wear criteria for carbide tools in turning tests
Wear doesn't grow at a steady rate. A new edge wears quickly as it beds in, then slowly and steadily for most of its life, then faster and faster once the wear land is large enough to raise heat and force.
Change the edge before that last zone.Run past it and the cost isn't just the insert: it's scrapped parts, a damaged holder and an unplanned stop. Most shops set a part count per edge from experience; measuring the wear land on a few edges with a loupe or toolmaker's microscope tells you whether that count is right.
06 — Grade choice
Let the wear pick the grade.
Carbide grades trade wear resistance against toughness. Less cobalt binder and finer grain make carbide harder and more wear-resistant; more cobalt and coarser grain make it tougher against chipping and impact.
Edges wearing away smoothly — flank wear, crater, plastic deformation — mean the grade is tough enough but not hard enough. Move up and to the right on the map.
Edges chipping, cracking or breaking mean the opposite: move to a tougher grade, even at some cost in wear life.
The map plots our own grades by their published impact and wear ranks — from extra-fine CIF06 (6% cobalt, 91 HRA) for metal cutting to coarse CID25 (25% cobalt) for heading dies that take millions of blows.
Full grade chart →How to choose a grade: grain size & cobalt →Coated vs uncoated carbide →
07 — Beyond machining
Tool wear doesn't stop at cutting tools.
Mining buttons, dies and wear parts wear by the same mechanisms — abrasion, heat, fatigue — and their marks are just as readable. These are the parts we make.
08 · Wear chart
One page for the machine.
Every wear type, its most likely cause and the first thing to change — print it and pin it up by the machine.
Tool wear — quick reference
carbideindia.com/resources/tool-wear
1Flank wear
Where · Flank (clearance) face
Cause · Abrasion by hard particles in the workpiece
Change · Reduce cutting speed
2Crater wear
Where · Rake face, behind the edge
Cause · High temperature at the chip–tool contact: diffusion and chemical wear
Change · Reduce cutting speed first, then feed
3Notch wear
Where · At the depth-of-cut line
Cause · Work-hardened surfaces and materials that harden as they're cut (stainless, heat-resistant alloys)
Change · Vary the depth of cut between passes so the notch doesn't hit one spot
4Built-up edge (BUE)
Where · On the edge and rake face
Cause · Cutting speed too low (cutting temperature too low)
Change · Increase cutting speed
5Edge chipping
Where · Along the cutting edge
Cause · Interrupted cuts and shock loads
Change · Use a tougher grade
6Thermal cracks
Where · Across the cutting edge
Cause · Rapid temperature cycling: the edge heats in the cut and cools out of it — typical in milling
Change · In rough milling, run dry; where coolant is needed, keep it generous and constant
7Plastic deformation
Where · Edge and nose
Cause · Cutting temperature too high: speed and feed too high together
Change · Reduce feed first if the edge is pushed down; cutting speed first if the flank bulges
8Fracture
Where · The whole edge or corner
Cause · Excessive load: feed or depth of cut too high
Change · Change edges earlier, at a set wear limit
General machining guidance · Grade: wears smoothly → harder · chips or cracks → tougher · Carbide India, Nashik
09 — Questions
Tool wear questions.
Q/01What are the main causes of tool wear?
Five mechanisms cause tool wear: abrasion by hard particles in the workpiece, adhesion (workpiece metal welding to the edge and tearing tool material away), diffusion of tool material into the hot chip, oxidation and chemical attack, and fatigue — mechanical shocks and thermal cycling that crack the edge. Which one dominates depends mostly on cutting temperature, so cutting speed is the biggest single factor.
Q/02What are the types of tool wear?
The common types are flank wear, crater wear, notch wear, built-up edge, edge chipping, thermal cracks, plastic deformation and fracture. Flank wear is the normal, predictable kind; the others usually point to a specific cause you can fix — speed, feed, grade, geometry or coolant.
Q/03Which cutting parameter affects tool wear the most?
Cutting speed. It drives cutting temperature, and temperature drives the fastest wear mechanisms. Feed has a smaller effect and depth of cut the smallest. Taylor's tool-life equation captures this: with a typical carbide exponent (n ≈ 0.25), a 20% rise in cutting speed roughly halves tool life.
Q/04How do you know when a cutting tool is worn out?
In practice, when parts go out of size, finish deteriorates, cutting forces or noise rise, or the wear land reaches a set limit. The ISO 3685 tool-life test uses an average flank wear land of 0.3 mm (or 0.6 mm maximum where wear is uneven) as the end-of-life criterion for carbide tools. Many shops simply change edges after a fixed number of parts set from experience.
Q/05What is the difference between flank wear and crater wear?
Flank wear is an even land on the clearance face below the edge, caused mainly by abrasion; it grows steadily and predictably. Crater wear is a hollow on the rake face behind the edge, caused by heat — diffusion and chemical wear — where the chip slides over the tool. Flank wear is reduced with a more wear-resistant grade; crater wear with lower speed and a coated, heat-resistant grade.
Q/06How can tool wear be reduced?
Match the grade to how the tool fails — harder if it wears smoothly, tougher if it chips or cracks; run the right cutting speed for the grade; avoid feeds so light the edge rubs; use a coated tool for heat-related wear; keep the setup rigid; apply coolant consistently (or not at all in milling where it causes thermal cracks); and change edges at a set wear limit before wear accelerates.
Q/07Does the carbide grade affect tool wear?
Yes — it's one of the biggest levers. Less cobalt binder and finer grain make carbide harder and more wear-resistant; more cobalt and coarser grain make it tougher against chipping and fracture. If edges wear away smoothly, move harder; if they chip, crack or break, move tougher.
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