Causes and Prevention of Breakage of small-diameter end mills

Causes and preventive measures for the breakage of small-diameter end mills

First, analysis of the cause of the breakage

Insufficient rigidity of the cutting tool

Small-diameter end mills (especially long and thin ones) have relatively low rigidity and are prone to breakage during cutting due to vibration or uneven force distribution.

The runout of the tool itself and the runout of the clamping tool will intensify the vibration and further reduce the stability of the tool.

The cutting parameters are unreasonable

Insufficient cutting speed: If the cutting speed is not sufficient, the cutting characteristics of the tool cannot be fully utilized, resulting in excessive cutting force.

Excessive cutting depth: Especially at the corner, sudden changes in cutting depth can cause the tool to bear sudden loads, leading to breakage.

Excessive feed rate: An excessive feed rate will increase the cutting resistance, causing the tool to break.

Clamping and fixture issues

Insufficient clamping force: There is an oil film between the inner hole of the tool holder and the outer diameter of the tool handle, resulting in insufficient clamping force and making the tool prone to loosening or falling off.

Wear of the tool holder: If the tool holder is used for too long, the port will wear into a conical shape, which may cause the tool to break at the port of the tool holder.

Workpiece clamping and processing conditions

Unstable workpiece clamping: If the workpiece becomes loose or rotates during the processing, it will cause uneven force on the tool and increase the risk of breakage.

Poor chip removal: Chip blockage can cause feed difficulties, impose additional loads on the tool, and easily lead to breakage.

Tool wear and passivation

Wear of the cutting edge of the tool or failure to passivate it will lead to an increase in cutting force and make the tool prone to breakage.

Second, preventive measures

Improve the clamping accuracy of cutting tools

Use thermal expansion tool holders with high clamping accuracy, strictly control the tool runout accuracy, and reduce vibration.

Before clamping, clean the handle and the inner hole of the tool holder, remove the oil film, and ensure sufficient clamping force.

Optimize cutting parameters

Increase cutting speed: Select an appropriate cutting speed based on the material of the tool and the workpiece to fully leverage the cutting characteristics of the tool.

Control the cutting depth: Avoid excessive cutting depth, especially at corner areas. Cycloidal tool paths can be used to balance the cutting depth.

Reduce feed rate: Appropriately lower the feed rate to reduce cutting resistance and lower the risk of tool breakage.

Improve the clamping and processing conditions of the workpiece

Ensure stable workpiece clamping: Use appropriate fixtures and clamping methods to prevent the workpiece from loosening or rotating during the processing.

Improve chip removal conditions: Use wet milling to ensure sufficient flow of cutting fluid and a reasonable supply direction (such as from the rear at an Angle or from the upper side horizontally) to prevent chip blockage.

Tool selection and maintenance

Select the appropriate cutting tool: Choose the suitable type of cutting tool (such as 2-edge or 3-edge end mills) based on the processing requirements to avoid chip blockage.

Regularly inspect tool wear: Replace severely worn tools in a timely manner to prevent an increase in cutting force due to tool passivation.

Tool passivation treatment: Passivate and chamfer the tool or increase the chamfer to enhance the tool’s durability.

Processing technology optimization

Adding a pre-processing procedure: In the processing of complex shapes, adding a pre-processing procedure makes the cutting depth uniform and consistent, reducing the sudden load on the tool.

Adopt circular interpolation: When the feed direction changes, use circular interpolation or temporarily stop to reduce the feed rate before and after the direction change and decrease the risk of tool breakage.

Equipment maintenance and inspection

Regularly check the wear of the tool holder: Replace the severely worn tool holder in time to prevent the tool from breaking due to the wear of the tool holder port.

Check the rigidity of the machine tool: Ensure that the spindle, guide rails and other components of the machine tool are in good condition to avoid tool breakage due to machine tool vibration.