End milling is one of the commonly used processes in mechanical processing, with the advantages of high processing efficiency and high precision. However, various problems will be encountered during the end milling process, affecting the processing quality and efficiency. In order to better perform end milling, it is crucial to understand the common end milling processing problems and their corresponding solutions.
Tool Breakage When End Mill Into or Pulling Out the Workpiece
At the moment of cutting into or pulling out the workpiece, the load on the end mill increases sharply, exceeding the end mill’s bearing capacity, resulting in breakage. The longer the cutting edge, the worse its rigidity, and it is more likely to vibrate and deform during the cutting process, eventually leading to breakage. Improper settings of parameters such as cutting speed, feed rate and cutting depth can also cause tool overload and cause breakage.
End mills with better rigidity can withstand greater impact loads and are not easy to break. When performing heavy-duty cutting or cutting workpieces with large vibrations, end mills with better rigidity should be given priority. Select the appropriate end mill specifications and try to shorten the cutting edge length. For deep hole processing, multiple tools of different lengths can be used for roughing and finishing. According to the processing material, tool material and processing conditions, reasonably select parameters such as cutting speed, feed rate and cutting depth to avoid tool overload.
End Mill Breakage During Normal Processing
Excessive feed rate and cutting depth will cause excessive cutting load on the end mill, exceeding the strength limit of the tool and causing breakage. Factors such as the end mill’s extended length is too long, the number of blades is too small, and the material is inappropriate will cause the tool to have insufficient rigidity, vibrate during the cutting process, weaken the tool strength, and eventually break. The debris generated during the cutting process is not discharged in time, and accumulates at the tool edge, increasing the cutting resistance, aggravating tool wear, and even causing breakage. The heat generated during the cutting process is not dissipated in time, causing the end mill to overheat, softening the tool material, reducing strength, and causing breakage.
Appropriately reducing the feed rate and cutting depth can effectively reduce the cutting load and reduce the risk of end mill breakage. Ensure that the end mill is correctly installed with the fixture or chuck, and the clamping force is appropriate to prevent the tool from loosening or falling off during the cutting process. Increasing the spindle speed, increasing the coolant flow, and choosing the right cutting fluid can effectively improve chip removal conditions and reduce the risk of tool breakage. Change dry milling to wet milling (using cutting fluid) and use it with a vortex tube gun to reduce tool temperature and avoid tool overheating. If the wet milling fluid supply direction is supplied from the front, change it to supply from the oblique rear or horizontally from above, and the coolant flow should be sufficient.
End Mill Breaks When Feed Direction Changes
When the feed direction of the end mill changes, the cutting force on the end mill will also change suddenly, which will cause the tool to generate a momentary impact load. If the impact load exceeds the strength limit of the tool, it will cause the tool to break. The change in the feed direction of the end mill will change the relative motion state of the tool and the workpiece, which will cause changes in the friction and cutting force between the tool and the workpiece, and may also cause the end mill to break. The change in the feed direction of the end mill will cause the vibration of the tool to intensify. If the vibration amplitude is too large, it will cause the tool to break.
When the feed direction of the end mill changes, circular interpolation can make the movement trajectory of the end mill smoother, reduce the amplitude and speed of the force change on the tool, and thus reduce the risk of end mill breakage. If conditions permit, the feed of the tool can also be temporarily stopped, and then the feed can be started in the new direction. Before and after the feed direction of the end mill changes, appropriately reducing the feed rate can reduce the amplitude of the force change on the tool, thereby reducing the risk of tool breakage. Selecting an end mill with sufficient rigidity and suitable material, and using a suitable fixture or spring chuck can increase the clamping force of the tool, prevent the tool from loosening or falling off during the cutting process, and thus reduce the risk of tool breakage.
Partial Chipping of the End Mill Tip
Partial chipping of the end mill tip is a common phenomenon of tool wear. Excessive feed rate, cutting depth, or high hardness of the processed material leads to excessive cutting resistance, which exceeds the strength limit of the end mill tip. The end mill tip diameter is too small, the material is inappropriate, etc., resulting in insufficient rigidity of the tip, which is prone to vibration and deflection during the cutting process, and eventually leads to chipping. The heat generated during the cutting process cannot be dissipated in time, resulting in excessive temperature at the tool tip, softening the tool tip material, reducing tool tip strength, and ultimately causing chipping.
Appropriately reduce feed rate and cutting depth, select end mill tool materials with appropriate hardness, and regularly sharpen the tool to keep the cutting edge sharp. Using wet milling and auxiliary cooling devices such as eddy current tube guns can effectively reduce tool temperature and avoid overheating of the tool tip.
The Surface of the Workpiece is Glossy, But the Bumps are Large
If the feed rate is too large, the milling cutter will cut more material from the workpiece each time, resulting in larger grooves and obvious bumps on the workpiece surface. The fewer the number of milling cutter blades, the more material each blade needs to cut per unit time, which increases the friction between the tool and the workpiece, causing deeper scratches on the workpiece surface. After the end mill is worn, the sharpness of the blade decreases, the cutting effect deteriorates, and the surface of the workpiece becomes rough and uneven.
Appropriately reducing the feed rate can reduce the amount of material cut each time, thereby reducing the impact of the end mill on the workpiece and making the workpiece surface smoother. High-edge end mills can reduce the amount of material cut by each blade per unit time, thereby reducing the friction between the tool and the workpiece, making the workpiece surface more delicate. Regularly checking the wear of the end mill and replacing severely worn tools in time can ensure the sharpness of the tool, improve the cutting effect, and make the workpiece surface smoother.
Smaller Finishing Dimensions
Any end mill has certain geometric errors, which will directly affect the accuracy of the processing dimensions. The end mill will gradually wear during use, causing the tool size to change, resulting in smaller processing dimensions. The geometric error of the machine tool will also cause the processing size to be smaller. For example, if the guide rail of the machine tool is not straight, it will cause the tool’s motion trajectory to deviate, resulting in smaller processing dimensions. During the milling process, due to the heat generated by cutting, both the tool and the workpiece will undergo thermal deformation, resulting in smaller processing dimensions.
Choosing an end mill with good rigidity and correctly installing and clamping the tool can reduce the vibration of the tool during the cutting process and improve the processing accuracy. Choosing a suitable fixture and correctly installing and clamping the workpiece can prevent the workpiece from loosening or offsetting during processing. Regularly inspect and calibrate machine tools to improve their geometric accuracy and reduce the impact of their geometric errors on machining accuracy.
