11 tool wear patterns when machining with end milling cutters

Identify and prevent wear issues on your carbide end mills. Here are some troubleshooting tips for making your tools last longer.

Each wear pattern tells a story about your machining process. Some are expected, like flank wear, while catastrophic fractures are warnings you don’t want to ignore. Here we break down the most common types of wear, what causes them, and how to troubleshoot or prevent them. Because the more you know, the longer your tools last.

Uniformed flank wear

Uniformed flank wear
Being predictable and dependable, flank wear is the ideal wear pattern you want to see on your tools. Saying that, it shouldn’t happen too quickly as this is considered a problem.

Flank wear is a relatively uniform abrasion along the cutting edge. Occasionally, metal from the workpiece makes it look bigger than it is, but you can expect this kind of wear in all materials and if your tool doesn’t fail by another type of wear, this will be the one to end its life.

Actions you could take:

Increase the coolant concentration
Check and balance the feed rate with the type of flank relief
Check if the balance of cutting speed and feed is correct
Verify that the tool is the best choice for the material

Crater wear

Crater wear
Although not that common in milling operations, crater wear is a combination of heat damage, material breakdown and abrasive wear. And if you want a more technical explanation – the heat from the chips decomposes the tungsten carbide grains in the substrate and carbon leeches into the chips (diffusion), wearing a crater on the rake face of the tool.

Actions you could take:

Increase coolant concentration
Balance the feed rate with the type of rake relief
Check if the balance of cutting speed and feed is correct
Verify that the tool is ideal for the material

There is a more specific type of crater wear called point cratering. This wear pattern is caused by the erosion of a localized area on the cutting edge. It is caused by a combination of chemical reactions and a lot of heat and abrasion from the formed chip.

Actions you could take:

Verify your tool selection
Use an adequate amount of coolant
Reduce the cutting speed
Reduce the feed

Chipping

Chipping wear
Chipping is basically a fracturing of the cutting edge. It is typically associated with stability problems and vibrations.

Actions you could take:

Keep the tool length as short as possible
Make sure your set-up is rigid
Check that the tooling is balanced and run-out is within specification
Confirm the cutting parameters are correct
Make sure the tool is suited to the material
Ensure the chips are being evacuated properly

There is a specific type of chipping called point chipping. Mostly associated with stability issues but can also appear when chatter occurs if, for example, the milling strategy isn’t appropriate.

As well as going through all the troubleshooting steps above, you can also:

Check the cutting parameters, as low cutting speeds will lead to chatter
When machining corners, use the trochoidal milling method

Built-up edges

Wear due to built-up edges
A built-up edge is formed when the workpiece material sticks to the rake face of the milling cutter. Often, the material deposited on the tool’s surface can be caused by pressure, friction and/or inadequate cutting conditions.

Actions you could take:

Increase the cutting speed
Increase the coolant concentration and volume
Use a tool suited to the material – flute design, helix, coating and surface condition are important

Notch wear

Notch wear
Notching happens when the carbide erodes in a specific area on the cutting edge. In most cases this is caused when the workpiece rubs against the tool.

Actions you could take:

Verify the geometry of the end mill
Vary the depth of cut if possible
Reduce the cutting speed

Chip evacuation wear

Chip evacuation wear
Not to be confused with notch wear as the two can look very similar, ineffective chip evacuation will also cause the milling cutter to be damaged along the cutting edges.

Actions you could take:

Reduce the depth of cut to allow for proper chip removal on dual core tools
Verify the tool against the material
Verify that the tool is the best choice for the material
Increase the helix angle
Reduce the feed rate or depth of cut

Stair-faced wear

Stair-faced wear
Stair-faced wear happens on the rake face of a cutting tool, right where it meets the flank face along the cutting edge. This kind of wear shows up because of the high friction and heat that build up in the cutting zone, especially when the tool stays in constant contact with the workpiece. Over time, this leads to accelerated erosion or abrasion at that point, forming a noticeable groove or notch on the face of the tool.

Actions you could take:

Increase coolant supply
Reduce feed/speed rates
Use appropriate tool geometry

Flaking

Flaking
Flaking is the loss of small fragments (flakes) from the surface of a cutting tool. It is more noticeable on coated tools, where thermal and mechanical stress causes cracks in the coating, leading to delamination. Common causes include sticky workpiece materials or incorrect cutting parameters.

Actions you could take:

Optimize cutting parameters
Maintain stable machining conditions
Increase coolant/lubrication

Comb cracks

Comb cracking wear
Comb crack wear is damage that appears on the cutting edge or rake face of a tool as a series of crack-like lines resembling the teeth of a comb. These cracks usually form along the cutting edge and are caused by heat during interrupted cutting operations, which are common in milling.

Actions you could take:

Optimize cutting parameters to reduce heat generation
Use coated tools with better thermal resistance
Increase coolant/lubrication
Avoid high cutting speeds or feeds
Use a more suitable substrate

Non-uniformed chipping

Non-uniformed chipping
Non-uniform chipping occurs at random points along the cutting edges, often starting with tiny cracks caused by mechanical or thermal stress. It’s usually triggered by things like interrupted cutting or vibration, an unstable setup, hard spots on the workpiece, or chips getting re-cut. These issues create stress points that gradually wear down the tool, leading to uneven damage.

Actions you could take:

Improve fixturing to reduce vibration
Optimize cutting parameters
Increase coolant/lubrication
Inspect tools regularly for early cracks
Check workpiece material for hardness variations

Catastrophic fracture

$Catastrophic fracture$
A catastrophic fracture is, as the name implies, catastrophic. Complete tool breakage can be caused by a variety of reasons. Mostly mechanical overload on the cutter, excessive vibrations, chip evacuation problems or a previous wear pattern being ignored.
This type of failure not only damages the tool but can also affect the workpiece, machine or even pose safety risks to operators if it occurs during high-speed operations.

Actions you could take:

Improve set-up to reduce chatter and vibrations
Check the run-out of the tool
Keep the length short
Make sure you are using the correct tool holder
Adjust cutting parameters to reduce load on the tool
Make sure chips are evacuated correctly

Give your used end mill a second and third life

So, you think you have come to the end of your tool’s life. But not quite – let’s smoothly transition to reconditioning. Reconditioning means regrinding, reapplying edge preparation or treatment and recoating a milling cutter in such a way that the original performance can be guaranteed, a process that can be done up to three times.

Once your tool has reached this stage, you can reach out to us for more information:

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