How to reduce tool runout in CNC milling?
The error caused by the radial runout of the tool directly affects the minimum shape error and geometric shape accuracy of the machined surface that can be achieved by the machine tool under ideal processing conditions. The larger the radial runout of the tool, the more unstable the processing state of the tool, and the more it affects the processing effect.
▌ Causes of radial runout
1. The impact of the radial runout of the spindle itself
The main reasons for the radial runout error of the spindle are the coaxiality error of each spindle journal, various errors of the bearing itself, the coaxiality error between the bearings, the spindle deflection, etc., and their influence on the radial rotation accuracy of the spindle varies with the processing method.
2. 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 and the rotation center of the spindle are inconsistent, the radial runout of the tool will inevitably occur.
The specific influencing factors are: the matching of the tool and the chuck, whether the tool loading method is correct, and the quality of the tool itself.
3. The impact of specific processing technology
The radial runout of the tool during processing 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, and is the main component force that affects the quality of workpiece processing. It is mainly affected by factors such as cutting amount, tool and workpiece material, tool geometry, lubrication method and processing method.
▌ Methods to reduce radial runout
The radial runout of the tool during processing is mainly because the radial cutting force aggravates the radial runout. Therefore, reducing the radial cutting force is an important principle to reduce radial runout. The following methods can be used to reduce radial runout:
1. Use sharp tools
Select a larger tool rake angle to make the tool sharper to reduce cutting force and vibration.
Select a larger tool back angle to reduce the friction between the main back face of the tool and the elastic recovery layer of the transition surface of the workpiece, thereby reducing vibration. However, the rake angle and back angle of the tool cannot be selected too large, otherwise it will lead to insufficient strength and heat dissipation area of the tool.
It can be smaller during rough processing, but in fine processing, in order to reduce the radial runout of the tool, it should be larger to make the tool sharper.
2. Use strong tools
First, the diameter of the tool bar can be increased. Under the same radial cutting force, the tool bar diameter increases by 20%, and the radial runout of the tool can be reduced by 50%.
Second, the extension length of the tool can be reduced. The larger the extension length of the tool, the greater the deformation of the tool during processing. The tool is in constant change during processing, and the radial runout of the tool will change continuously, resulting in an uneven surface of the workpiece. Similarly, if the extension length of the tool is reduced by 20%, the radial runout of the tool will also be reduced by 50%.
3. The front cutting edge of the tool should be smooth
During processing, the smooth front cutting edge 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.
4. Clean the spindle taper and chuck
The spindle taper and chuck should be clean, and there should be no dust and debris generated during workpiece processing.
When selecting a processing tool, try to use a tool with a shorter extension length. When cutting, the force should be reasonable and uniform, not too large or too small.
5. Reasonable selection of cutting depth
If the cutting depth is too small, the machining will slip, which will cause the tool to continuously change the radial runout during machining, making the machined surface rough. When the cutting depth is too large, the cutting force will increase accordingly, resulting in large tool deformation. Increasing the radial runout of the tool during machining will also make the machined surface rough.
6. Use reverse milling during finishing
During forward milling, the gap position between the lead screw and the nut changes, which will cause uneven feeding of the worktable, resulting in impact and vibration, affecting the life of the machine tool and tool and the machining surface roughness of the workpiece.
When using reverse milling, the cutting thickness changes from small to large, the tool load also changes from small to large, and the tool is more stable during machining. Note that this is only used during finishing. For rough machining, forward milling should still be used because forward milling has high productivity and the tool life can be guaranteed.
7. Reasonable use of cutting fluid
Reasonable use of cutting fluid Aqueous solution with cooling as the main function has little effect on cutting force. Cutting oil, which mainly acts as a lubricant, can significantly reduce cutting force.
Practice has proved that as long as the manufacturing and assembly accuracy of each part of the machine tool is guaranteed and reasonable processes and tooling are selected, the impact of the radial runout of the tool on the machining accuracy of the workpiece can be minimized.
Post time: Jul-05-2024
