The vibration of the lathe during the processing is accompanied by the phenomenon of tool vibration and tool hitting, which causes chatter marks on the workpiece surface, high rework rate and scrap rate. Where do we need to start the investigation?
1. Workpiece and tool aspects
(1) Workpiece aspects
1) External turning of slender shafts. Generally, if the distance between the cutting point and the clamping point exceeds 3 in aspect ratio, the tool is prone to vibration. You can consider changing the process; 2) External turning of thin-walled parts; 3) Turning of box-shaped parts (such as sheet metal welding structural parts); 4) Cutting of super-hard materials.
(2) Tool reasons
1) Using forming blades for forming turning; 2) The angle of the tool, especially the main deflection angle, back angle and front angle; 3) The sharpness of the blade; 4) Is the radius of the tool tip too large; 5) Are the cutting parameters appropriate.
First, eliminate the problem of the tool. First, check the rigidity of the turning tool itself. Is it not clamped? Is it extended too long? Is the gasket uneven? Then check whether the turning tool (boring tool) is worn? Is the tool tip radius or the wiper blade too wide? Is the back angle of the turning tool too small? Check whether you are using a 90-degree tool or a 45-degree tool, and try to change it.
In addition, too small a tool feed (feed rate) may also be a cause of chattering, which can be slightly adjusted to increase it. Adjust the speed, single-tool cutting depth, and feed rate to try to eliminate the resonance point.
2. Check the causes of the machine tool and the clamping part
1) Check whether the live center is extended too long and whether the bearing is good. There is a plane rolling bearing combination inside. If you really doubt it, you can replace it with a dead center, and pay attention to the lubrication of the center hole; 2) Check the clamping condition of the tailstock top, and whether the left and right inside, upper and lower inside are not concentric with the machine tool spindle under the clamping condition; 3) Tighten the large, medium and small slides, especially the middle slide; 4) If the tailstock part of the machine tool cannot be checked temporarily (points 1 and 2, some benchwork foundation is required), you can try to run the tool from the clamping end to the tail. Reverse turning can eliminate the lack of force at the tail end to the greatest extent; 5) If there is still a problem in step 4, check the spindle. Of course, if it is a three-grip, check whether the spiral groove is damaged. The four-grip is manually self-adjusted, so there is no need to check.
3. Use other countermeasures to suppress tool vibration
If your spindle is really tight, and the workpiece is not a thin-walled hollow part or overhanging too long, there is no problem with chuck clamping. Use other countermeasures to suppress tool vibration.
There are some more specific and practical methods currently used in the processing site.
1) Reduce the working weight of the part that causes vibration, the smaller the inertia, the better; 2) Fix or clamp the place with the largest vibration, such as the center frame, work holder, etc.; 3) Improve the rigidity of the processing system, such as using a tool holder with a higher elastic coefficient or using a special anti-vibration force with a dynamic damper to absorb impact energy; 4) Work hard on the blade and the working rotation direction; 5) Change the shape and angle of the tool, the smaller the radius of the tool nose, the better, to reduce cutting resistance. The side rake angle must be positive to make the cutting direction closer to vertical. The back rake angle is best to be positive, but the chip removal and chip cutting ability will be relatively poor. Therefore, a grooved cutter can generally be used to make the rake angle negative, but still maintain the positive cutting effect.
