CNC machine vibration is a problem that every CNC machine operator will face from time to time. Milling, turning, or drilling are all standard operations that can cause a CNC machine to vibrate. The reasons for this situation are varied. A slipping tool or inadequate workpiece holding can lead to this condition. However, there may be other causes of vibration, and simply reducing the spindle speed and feed rate may not be enough to solve the problem. It is useful to know the cause of the machine vibration, as this can reduce production time. Another advantage is that the value of products made correctly will be higher because due to machine vibration, the production itself takes longer and is less accurate than with properly configured equipment. How to get rid of vibration, and what can be its cause? We write about this below!
What is CNC machine vibration?
Vibration is the unwanted behavior that occurs when machining parts. Vibration is the periodic movement of the tool and workpiece about each other. Vibration can be non-resonant and occur, for example, when using an unevenly worn tool. Non-resonant vibration will usually be constant throughout the machining cycle and can often be easily diagnosed as the cause. Vibration caused by resonant vibration can be determined when you find the right combination of tooling, fixturing, machining strategy, and machine configuration to produce vibration at or near its natural frequency. Such vibrations can be found point-wise on a given tool.
Effects of vibration in CNC
The vibration produced during machining operations results in a poorer surface finish and weakened tool life. In addition, traces of the vibration will be visible on the machined surface, often in the form of wavy patterns or regular marks. If the vibration is of a prolonged nature, it can cause uneven tool wear or even tool breakage. An experienced CNC machine operator knows when a machine is malfunctioning and making an erratic sound. How is the cause of the vibration determined? First, increase the rigidity of the system. Then make feeds at different speeds. You’ll probably make a few mistakes when determining the cause of vibration, but remember that CNC machine vibration can depend on several other factors:
- the specific machine,
- the work holder,
- the tooling,
- the part or machining strategy you are using!
- All of these affect their occurrence.
Machining and CNC machine vibration
A long, thin tool will vibrate (and flex) more easily than a short, thick tool. So choose the tool with the largest appropriate diameter. Try to reduce the amount of tool sticking out of the chuck and make sure it is held firmly. Hydraulic expansion chucks can help you. They generally have good runout accuracy, plus the hydraulic action helps dampen vibration. Proper tool pressure or chip load is also important. Too little, too much, or too much difference in clamping force can cause vibration. CNC milling machines because of too many grooves involved in cutting can receive vibration. You can use fewer grooves and variable-pitch milling cutters to help reduce resonant vibration due to chip load.
The right chuck
Check to see if any of your parts are moving or vibrating. Make sure chuck, vise, vacuum table, or other workpiece holding device is applying sufficient pressure to the workpiece. The pressure should be uniform and take into account the size of the work chuck. Try to avoid clamping only one end of the material. If the workpiece is long, consider using a larger workpiece holding device or additional clamps on a milling machine. On a lathe, consider using a tailstock or support. Vibration dampening can be extremely problematic when working with thin-walled workpieces. In this case, it is a good idea to use a filler material such as plastic or wax.
Choice of strategy
With conventional CNC milling machine paths, the degree of engagement of the cutter itself can vary. This may cause too much force to be applied to the cutter at certain points, which will result in the vibration of the CNC machine. How to get rid of this problem? The best way is to use a constant tool path or reduce the depth of the cut. Another solution is also to change the spindle speed. Do you have a feeling that a resonant vibration is occurring? Try changing the spindle speed. The changes can be minimal – just a 5% difference. Your equipment will have many resonant frequencies and if you just halve the speed, you will probably find a solution. It is interesting to note that some CAM software packages have a feature that continuously changes the spindle speed.
CNC milling machine settings
CNC machines should be set up on a solid concrete floor, free of joints, cracks, or other discontinuities. Also remember that a floor that is soft, flexible, or cracked can increase the vibration of the CNC machine. It is a good idea to install anchoring well or adjust the feet carefully. This will certainly minimize the possibility of vibration. Another factor that affects vibration is the rigidity of the CNC machine and setting the wrong parameters or parts too loosely. No equipment is 100% rigid. If the machine was built in a faulty way, it can dampen vibration poorly. Unfortunately, even when the equipment is good, CNC machine vibration can even be caused by faulty maintenance or equipment repair.
CNC machines can produce some vibration, the effects of which are important from a manufacturing perspective. We have said almost everything about the vibration at work that CNC machines cause. To determine their causes, you must examine several elements that can create the vibration effect. By determining the correct parameters and values of machines – you can avoid this problem. Remember also that the depth of cut will also make a difference when determining the cause of vibration. Nevertheless, during vibration the products will be produced in a defective way, their durability will be less, and in addition, the process itself will be much more prolonged than in the case of correct operation of the machine. Now, some factors can cause a CNC machine to vibrate. From improper chucking to faulty equipment maintenance. If this problem is affecting your equipment, then check the configuration of your CNC machine, change the feed rate, use different machine tool and spindle speed, or use tool holder (such as a tailstock) to stiffen the manufacturing process. Use cutting tools wisely and perform a vibration analysis every time your equipment misbehaves.