In the CNC cutting process, there are many reasons for errors. The error caused by the tool radial runout is one of the vital factors, which directly affects the shape and surface that the machine tool can achieve under ideal conditions. In the cutting,it influences the accuracy, roughness, unevenness of tool wear and characteristics of multi-tooth tools. The larger the radial runout of the tool, the more unstable the machining state of the tool, and the more it influences the product.
Causes of Radial Runout
Manufacturing and clamping errors of the tool and spindle components cause drift and eccentricity between the tool axis and the ideal rotation axis of the spindle, as well as the specific processing technology and tooling, which may cause the radial runout of the CNC milling machine tool during processing.
1. The influence of the radial runout of the spindle
The main reasons for the radial runout error of the spindle is the coaxiality, its bearing, the coaxiality between the bearings, the deflection of the spindle, etc., The influence on the radial rotation tolerance of spindle varies with different processing methods. 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.
2. The difference of 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 that, the tool will inevitably cause the radial runout. The specific influencing factors are: the fit of the tool and the chuck, the method of loading the tool and the quality of the tool itself.
3. The impact of specific processing technology
What caused the radial runout is a force. The radial cutting force is the radial products of the total cutting force. It will cause the workpiece to bend and deform and produce vibration in the process. It is mainly triggered by factors such as cutting amount, tool and work piece material, lubrication method, tool geometric angle and processing method.
Ways to Reduce Radial Runout
As mentioned in the third point. Reducing the radial cutting force is an important principle to reduce it. The following methods can be used to reduce
1. Use sharp cutting tool
Choose a larger tool 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 clearance angle of the tool cannot be selected too large, otherwise the strength and heat dissipation area of the tool is insufficient. Therefore, it is necessary to choose different rake angles and clearance angles of the tool according to the specific situation. The rough machining can be smaller, but in the finishing machining, considering that reduce the radial runout of the tool, it should be larger to make the tool sharper.
2. Use strong cutting tools
There are mainly two ways to increase the strength of the cutting tool. One is to increase the diameter of the 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 cutting tool. The greater the protruding length of the tool, the greater the deformation of the tool during processing. When processing is in constant change, it will continue to change, resulting to produce a rough workpiece. Similarly, the extension length of the tool is reduced by 20%, it will also be reduced by 50%.
3. The rake face of the tool should be smooth
During processing, the smooth rake face can reduce the friction of the small cut on the tool, and can also reduce the cutting force on the tool, thereby reducing the radial runout of the tool.
4. Spindle taper hole and chuck cleaning
The spindle taper hole and the chuck are clean, and there should be no dust and debris generated in the processing. When selecting a machining tool, try to use a tool with a shorter extension length to load, and the force should be reasonable and even, not too large or too small.
5. Choose a reasonable engagement of the cutting edge
If the engagement of the cutting edge 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, resulting in a rough face. If the engagement of the cutting edge is too large, the tool force increased. It will cause large deformation of the tool and the result as the above same.
6. 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 tool and the surface roughness of the workpiece. When up-milling, the cutting thickness and the load of the tool also changes from small to large, so that the tool is more stable during processing. Note that this is only used for finishing, and down milling is still used when roughing. This is because the productivity of down milling is high and the service life of the tool can be guaranteed.
7. Reasonable use of cutting fluid
Reasonable use of fluid, mainly cooling water solution, has little effect on cutting force. The cutting oil whose main function is lubrication can significantly reduce the cutting force. Because of its lubricating effect, it can reduce the friction between the tool rake face and the chip and between the flank face and the transition surface of the workpiece, thereby reducing the radial runout. Practice has proved that as long as the accuracy of the manufacturing and assembly of each part of the machine is ensured, and the reasonable process and tooling are selected, the influence of the radial runout of the tool on the machining tolerance of the workpiece can be minimized.
Post time: Feb-17-2022