In the CNC MACHINING process, there are many reasons for machining errors. The error caused by the tool radial runout is one of the important factors, which directly affects the minimum shape error and the machined surface geometry accuracy.
In actual cutting, the radial runout of the tool affects the machining accuracy, surface roughness, uneven wear of the tool, and the cutting process characteristics of the multi-tooth tool. The greater the radial runout of the tool, the more unstable the machining state of the tool, and the more obvious the impact.
Causes of radial runout
Tool manufacturing errors and clamping errors cause drift and eccentricity between the tool axis and the ideal rotation axis of the spindle, as well as specific processing techniques and tooling, which may cause radial runout of CNC milling machine tools during processing.
The influence of the radial runout of the spindle itself
The main reasons for the radial runout error of the main shaft are the coaxiality error of each journal of the main shaft, various errors of the bearing itself, the coaxiality error between the bearings, and the deflection of the main shaft. Their influence on the radial rotation accuracy of the spindle varies with the processing method. These factors are formed in the process of manufacturing and assembling the machine tool, and it is difficult for the operator of the machine tool to avoid their influence.
- The impact of the inconsistency between the tool center and the spindle rotation center
When the tool is installed on the spindle, if the center of the tool is inconsistent with the center of rotation of the spindle, the tool will inevitably cause radial runout. The specific influencing factors are the fit of the tool and the chuck, whether the method of loading the tool is correct, and the quality of the tool itself.
- The impact of specific processing technology
The radial runout of the tool during machining is mainly because the radial cutting force aggravates the radial runout. The radial cutting force is the radial component of the total cutting force. It will cause the workpiece to bend and deform and produce vibration during processing, which is the main component that affects the quality of the workpiece. It is mainly affected by factors such as cutting amount, tool and workpiece material, tool geometric angle, lubrication method, and processing method.
Methods to reduce radial runout
The radial runout of the tool during machining is mainly because the radial cutting force aggravates the radial runout. Therefore, reducing the radial cutting force is an important principle to reduce the radial runout. The following methods can be used to reduce radial runout:
- Use sharp knives
Choose a larger rake angle to make the tool sharper to reduce cutting force and vibration. Choose a larger clearance angle of the tool to reduce the friction between the main clearance surface of the tool and the elastic recovery layer of the transition surface of the workpiece, thereby reducing vibration. However, the rake angle and the back angle of the tool cannot be selected too large, otherwise, the strength and heat dissipation area of the tool will be insufficient. Therefore, it is necessary to select different tool rake angles and back angles according to the specific conditions. The rough machining can be smaller, but in the finishing machining, for the consideration of reducing the radial runout of the tool, it should be larger to make the tool Sharper.
- Use strong tools
There are two main ways to increase the strength of the tool. One is to increase the diameter of the tool holder. Under the same radial cutting force, the diameter of the tool holder increases by 20%, and the radial runout of the tool can be reduced by 50%. The second is to reduce the protruding length of the tool. The greater the protruding length of the tool, the greater the deformation of the tool during processing. When processing is in constant change, the radial runout of the tool will continue to change, resulting in a workpiece Similarly, if the machining surface is not smooth, the extension length of the tool is reduced by 20%, and the radial runout of the tool will also be reduced by 50%.
- The rake face of the tool should be smooth
During processing, the smooth rake face can reduce the friction of the chips on the tool, and can also reduce the cutting force on the tool, thereby reducing the radial runout of the tool.
- Spindle taper and chuck cleaning
The spindle taper hole and the chuck are clean, and there should be no dust and debris generated during the processing of the workpiece. When selecting processing tools, try to use tools with a shorter extension length, and the force should be reasonable and even when loading the knife, and not too large or too small.
- Choose a reasonable amount of knife
If the amount of the tool is too small, the phenomenon of machining slippage will occur, which will cause the continuous change of the radial runout of the tool during machining, and the processed surface will not be smooth. When the amount of the tool is too large, the cutting force will increase, which will cause the tool to deform and increase the radial runout of the tool during processing, which will also make the processed surface not smooth.
- Use up milling in finishing
As the position of the gap between the lead screw and the nut changes during down milling, it will cause uneven feed of the worktable, resulting in shock and vibration, affecting the life of the machine and the tool and the surface roughness of the workpiece.
- Reasonable useof cutting fluid
The cooling effect of the aqueous solution has little effect on the cutting force. The cutting oil whose main function is lubrication can significantly reduce the cutting force. Due to its lubricating effect, it can reduce the friction between the tool rake face and the chip and the friction between the flank face and the transition surface of the workpiece, thereby reducing the radial runout of the tool.