Insert wear and machining problems: causes and remedies
Look at the cutting edge after machining: the type of wear tells you what to change. Find your case, read the causes and apply the remedies in order, one at a time.
| What you see | Problem | First thing to try |
|---|---|---|
| Even wear land on the flank | Flank wear | Reduce Vc, harder grade |
| Hollow on top of the edge | Crater wear | Reduce Vc, CVD grade with Al₂O₃ |
| Edge pushed down or bulging | Plastic deformation | Reduce Vc and feed, harder grade |
| Notch at the depth of cut | Notch wear | Vary ap, 45° entering angle or round insert |
| Material welded onto the edge | Built-up edge | Increase Vc, positive geometry |
| Small chips along the edge | Chipping | Tougher grade, reinforced edge |
| Broken edge or corner | Breakage | Reduce feed and ap, stronger insert |
| Cracks perpendicular to the edge | Thermal cracks | Constant coolant or dry cutting |
| Noise and wavy marks | Vibrations | Less overhang, smaller nose radius |
| Long chips that wrap around | Uncontrolled chips | Increase feed, suitable chipbreaker |
| Rough or uneven surface | Poor finish | Lower feed or larger nose radius |
Flank wear
This is normal, predictable wear: an even, shiny land on the flank below the cutting edge. It is measured as VB; when it exceeds about 0.3 mm (0.2 mm in finishing) the insert should be changed.
Causes
- Cutting speed too high
- Grade not wear-resistant enough
- Feed too low: the edge rubs instead of cutting
- Abrasive material (cast irons, steels with carbides)
Remedies
- Reduce Vc by 10–20%
- Switch to a harder, more wear-resistant grade (CVD)
- Increase the feed slightly
- Use coolant continuously
Crater wear
A hollow on the rake face behind the cutting edge, caused by heat and chemical diffusion with the steel. If it grows too far it weakens the edge until it breaks.
Causes
- Temperature too high: high Vc or feed
- Grade without an aluminium oxide layer
- Insufficient coolant
Remedies
- Reduce cutting speed and feed
- Choose a CVD grade with an Al₂O₃ layer
- A more positive chipbreaker that generates less heat
- Improve the coolant supply
Plastic deformation
The edge sinks or bulges near the corner: heat and pressure exceed the strength of the carbide. It leads to out-of-tolerance dimensions and sudden breakage.
Causes
- Cutting temperature too high
- Feed or depth too high for the nose radius
- Grade too tough and not hard enough
- Hard materials or superalloys
Remedies
- Reduce speed and feed
- Harder grade with better hot hardness
- Larger nose radius
- Plenty of well-directed coolant
Notch wear
A deep notch on the edge exactly at the depth-of-cut line. Typical of stainless steels, superalloys and parts with a casting or forging skin.
Causes
- Work hardening of the material (stainless steels, superalloys)
- Hard skin, scale or oxides on the part
- Always the same depth of cut
- 90° entering angle
Remedies
- Vary the depth of cut from one pass to the next
- Smaller entering angle (45°) or a round insert
- Tougher grade (PVD) with a sharp edge
- Reduce the cutting speed
Built-up edge
Workpiece material welds onto the edge and breaks off in pieces, taking fragments of the insert with it. The surface becomes dull and torn.
Causes
- Cutting speed too low
- Gummy material: aluminium, stainless steel, low-carbon steels
- Negative geometry or honed edge
- No coolant or insufficient coolant
Remedies
- Increase the cutting speed
- Positive geometry with a sharp, polished edge
- Smooth PVD coating, or uncoated carbide for aluminium
- Plenty of coolant
Edge chipping
Small pieces missing along the edge: the edge cannot withstand the shocks. It quickly worsens the finish and comes before breakage.
Causes
- Interrupted cut (holes, slots, uneven surfaces)
- Vibrations or weak clamping
- Grade too hard and brittle
- Edge too sharp for the application
- Built-up edge breaking away
Remedies
- Tougher grade
- Stronger chipbreaker (roughing) or reinforced edge
- Reduce the feed when entering and leaving the part
- Improve rigidity and clamping
Insert breakage
The edge or corner breaks off cleanly. It can also damage the toolholder and the part: it is the first problem to avoid.
Causes
- Feed or depth too high for the geometry
- Grade too brittle
- Insert too small or too thin
- Wear allowed to grow too far
- Insert or toolholder seat not properly clamped
Remedies
- Reduce feed and depth of cut
- Larger, thicker or negative insert
- Tougher grade
- Change the insert before wear becomes excessive
- Check seat, screw and clamp
Thermal cracks
Fine cracks perpendicular to the edge, typical in milling: each edge heats up and cools down on every revolution. Over time they turn into chipping.
Causes
- Constant temperature changes (interrupted cut)
- Intermittent coolant
- Cutting speed too high
Remedies
- In milling, cut dry or with plenty of constant coolant
- Tougher grade, more resistant to thermal shock
- Reduce the cutting speed
Vibrations
High-pitched noise, regular wavy marks on the part, poor finish and irregular wear. The cause is almost always a lack of rigidity.
Causes
- Excessive overhang of the tool or boring bar
- Large nose radius with a small depth of cut
- Weak part or clamping
- Geometry too negative, high cutting forces
Remedies
- Reduce the overhang; carbide boring bars for long overhangs
- Smaller nose radius
- Positive, sharp geometry
- Increase the feed or change the cutting speed
- In milling: differential pitch and fewer teeth engaged
Long, uncontrolled chips
Chips wrap around the part or the tool in long curls: a risk for the operator, scratches on the surface, machine stops.
Causes
- Feed too low for the chipbreaker
- Depth of cut outside the chipbreaker range
- Chipbreaker not suited to the material
Remedies
- Increase the feed
- Choose the chipbreaker by depth of cut and feed: finishing (GF, BF, SF), medium (GM, BM, SM), roughing (GR, BR)
- Increase the depth of cut if possible
- High-pressure coolant
Poor surface finish
Roughness too high, or a surface that is shiny in some areas and dull in others. Theoretical roughness depends on feed and nose radius: Ra ≈ f² / (32·r).
Causes
- Feed too high for the nose radius
- Worn edge or built-up edge
- Vibrations
- Cutting speed too low
Remedies
- Reduce the feed or use a larger radius
- Change the edge at the first sign of wear
- Increase the cutting speed
- Cermet for bright finishes on steels
