Each type of wear tells a story about your machining process. Some are to be expected, such as rake face wear, while catastrophic fractures are warnings you don’t want to ignore. Here, we’ll break down the most common types of wear, their causes, and how to troubleshoot or prevent them. Because the more you know, the longer your tools will last.
Consistent Rake Face Wear
Example of uniform rake face wear on a solid carbide end mill:
Rake face wear is predictable and reliable—it’s the ideal wear pattern you want to see on your tool. That said, it shouldn’t occur too quickly, as this is considered a problem. Rake face wear resembles relatively uniform wear along the tool’s cutting edge. Sometimes, metal from the workpiece can make the wear appear more severe than it actually is, but you can expect this type of wear to occur with all materials. If your tool does not fail due to other types of wear, this will eventually bring its service life to an end. Steps you can take: Increase the coolant concentration.
Check and balance the feed rate with the type of rake angle; verify that the balance between cutting speed and feed rate is correct; confirm that the tool is the best choice for the material.
Front Face Wear
Example of crescent-shaped wear on a solid carbide end mill:
Although not common in milling operations, crescent-shaped wear is a combination of thermal damage, material decomposition, and abrasive wear. For a technical explanation: the heat generated by the chips causes the tungsten carbide particles in the matrix to decompose, allowing carbon to diffuse into the chips and form “crescent-shaped” wear on the tool’s rake face.
Increase coolant concentration.
Balance feed rate with the rake angle type.
Check whether the cutting speed and feed rate are properly balanced.
Verify that the tool is suitable for the material.
There is a more specific type of crescent-shaped wear known as pitting. This wear pattern is caused by erosion in localized areas along the cutting edge.
It results from a combination of chemical reactions, the significant heat generated by the forming chips, and mechanical wear. Actions you can take: Verify your tool selection; use a sufficient amount of coolant; reduce the cutting speed; reduce the feed rate.
Micro-chipping
Example of micro-chipping on a solid carbide end mill:
Micro-chipping is essentially a form of fracture along the cutting edge. It is typically associated with stability issues and vibration. You can take these actions:
Keep the tool length as short as possible.
Ensure your setup is rigid.
Check that the tool is balanced and that runout is within specifications.
Confirm that the cutting parameters are correct.
Ensure the tool is suitable for the material.
Ensure chips are properly evacuated.
There is a specific type of micro-chipping called point chipping. It is primarily related to stability issues but can also occur during chatter, such as when the milling strategy is inappropriate. In addition to completing all the troubleshooting steps mentioned above, you can also: Check the cutting parameters, as low cutting speeds can cause chatter. When machining corners, use a helical milling method.
Weld
Example of wear caused by a weld on a solid carbide end mill:
A weld forms when workpiece material adheres to the front face of the end mill. Typically, material deposits on the tool surface are caused by pressure, friction, and/or inappropriate cutting conditions. Steps you can take: Increase the cutting speed; increase the coolant concentration and flow rate; use a tool suitable for the material—flute design, helix angle, coating, and surface finish are all critical.
Flute Wear
Example of flute wear on a solid carbide end mill:
Flute wear occurs when the carbide erodes in specific areas along the cutting edge. In most cases, this is caused by friction between the workpiece and the tool. Steps you can take: Verify the geometry of the end mill; if possible, adjust the cutting depth; reduce the cutting speed.
Chip-Ejection Wear
Example of chip-ejection wear on a solid carbide end mill:
Do not confuse this with flute wear, as the two look very similar; ineffective chip evacuation can also cause damage to the end mill along the cutting edge. Steps you can take: Reduce the cutting depth to ensure proper chip evacuation on two-flute tools; verify that the tool is suitable for the material; confirm that the tool is the best choice for the material; increase the helix angle; reduce the feed rate or cutting depth
Step-Face Wear
Example of step-face wear on a solid carbide end mill:
Step-face wear occurs on the rake face of the cutting tool, specifically where the cutting edge meets the flank face. This type of wear is caused by high friction and heat buildup in the cutting zone, particularly when the tool remains in continuous contact with the workpiece. Over time, this leads to accelerated erosion or wear, resulting in visible grooves or ruts on the tool’s surface. Steps you can take: Increase coolant flow, reduce feed rate/speed, and use an appropriate tool flute geometry.
Spalling
Example of spalling on a solid carbide end mill:
Spalling refers to the loss of small fragments (flakes) from the surface of a cutting tool. It is more pronounced on coated tools, where thermal and mechanical stresses can cause cracks within the coating, leading to delamination. Common causes include sticky workpiece materials or incorrect cutting parameters. Steps you can take: Optimize cutting parameters; maintain stable machining conditions; increase coolant/lubrication
Comb-like Cracks
Example of comb-like crack wear on a solid carbide end mill:
Comb-like crack wear refers to a series of crack-like lines resembling comb teeth that appear on the cutting edge or rake face of the tool. These cracks typically form along the cutting edge and are caused by heat generated during intermittent cutting operations, which is common in milling. Actions you can take: Optimize cutting parameters to reduce heat generation; use coated tools with better thermal resistance; improve coolant/lubrication; avoid high cutting speeds or feed rates; use a more suitable substrate. Non-uniform micro-chipping: Example of non-uniform micro-chipping on a solid carbide end mill
Non-uniform micro-chipping can occur at any point along the cutting edge, typically starting with microscopic cracks caused by mechanical or thermal stress. It is typically triggered by factors such as intermittent cutting or vibration, unstable clamping, hard spots on the workpiece, or chip re-cutting. These issues create stress points that gradually wear down the tool, leading to uneven damage. Steps you can take: Improve clamping to reduce vibration; optimize cutting parameters; increase coolant/lubrication; regularly inspect the tool for early cracks; check for variations in workpiece material hardness
Catastrophic Fracture
Example of catastrophic fracture on a solid carbide end mill:
Catastrophic fracture, as the name implies, is disastrous. Complete tool fracture can result from a variety of causes, including mechanical overload, excessive vibration, chip evacuation issues, or previously overlooked wear patterns. If this type of failure occurs during high-speed operations, it not only damages the tool but can also affect the workpiece, the machine tool, or even pose a safety risk to the operator.
Improve your setup to reduce chatter and vibration.
Check the tool runout regularly.
Maintain a short tool length for better rigidity.
Ensure you use the correct tool holder.
Adjust cutting parameters to reduce the load on the tool.
Ensure proper chip evacuation during machining.
E-mail: cykc@cykcgroup.com.cn