CNC machine vibration is a problem that every CNC machine operator will have to face from time to time. Milling, turning or drilling are standard operations that can lead to CNC machine vibration. The reasons for such a situation vary. A slipping tool or improper holding of the object can lead to this state of affairs. However, the causes of vibration can be different, and simply reducing the spindle speed and feed may not be a sufficient method to solve this problem. It is worth knowing the cause of the machine's vibration, as this can shorten production time. Another advantage is that the value of products made correctly will be higher, as due to machine vibrations, the production itself takes longer and is less accurate than when using 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 an undesirable behavior that occurs during part machining. Vibrations are periodic displacements of the tool and the workpiece relative to each other. Vibrations can be non-resonant and occur, for example, when using an unevenly worn tool. Non-resonant vibrations will usually be constant throughout the entire machining cycle and their cause can often be easily diagnosed. Vibrations caused by resonant vibrations can be determined when you find the right combination of tooling, clamping, machining strategy, and machine configuration to produce vibrations at or near the natural frequency. Such vibrations can be pinpointed on a given tool.
Impact of vibrations in CNC
Vibration generated during machining operations results in poorer surface finish and weakens the durability of the tool. Moreover, traces of vibration will be visible on the machined surface, often in the form of wavy patterns or regular markers. If the vibration is prolonged, it can cause uneven wear of the tool, or even its breakage. An experienced CNC machine operator knows when the machine is operating improperly and makes an erroneous sound. How is the cause of vibration determined? First, the rigidity of the system should be increased. Then, feeds should be made at different speeds. While determining the cause of vibrations, you will probably make a few mistakes, but remember that the vibrations of the CNC machine can depend on several other factors:
- specific machine,
- working handle,
- tooling,
- part or machining strategy you use!
All of this affects their occurrence.
Machining and CNC machine vibration
A long, thin tool will vibrate (and bend) easier than a short, thick one. Therefore, choose a tool with the largest appropriate diameter. Try to reduce the amount of tool protruding from the holder and make sure it is firmly held. Hydraulic expansion chucks can help you. They generally have good run-out accuracy, and the hydraulic action helps dampen vibrations. The appropriate tool pressure or chip load is also important. Too little, too much, or too large differences in pressure can cause vibration. A CNC milling machine may receive vibrations due to too many grooves engaged in cutting. You can use a smaller number of grooves and variable pitch end mills to help reduce resonant vibrations caused by chip load.
Proper Grip
Check if any of your parts are moving or vibrating. Make sure that the handle, vice, vacuum table, or other device for securing the workpiece exerts sufficient pressure on the workpiece. The pressure should be uniform and take into account the size of the working grip. Try to avoid clamping only one end of the material. If the workpiece is long, consider using a larger device for holding the workpiece or additional clamps on the milling machine. On the lathe, consider using a tailstock or support. Damping vibrations can be particularly problematic when working with thin-walled items. In such a case, it is worth using a filling material in the form of plastic or wax.
Strategy Selection
In the case of conventional CNC milling paths, the degree of engagement of the mill itself can vary. This can cause too much force to be applied to the mill at certain points, resulting in vibrations of the CNC machine. How to get rid of this problem? It is best to use a constant tool path or reduce the depths of machining. Another solution is also to change the spindle speed. Do you feel that resonance vibration is occurring? Try changing the spindle speed. Changes can be minimal - a difference of 5% is enough. Your equipment will have many resonant frequencies and if you only reduce the speed by half, you will probably find a solution. An interesting fact is that some CAM software packages have a feature that continuously changes the spindle speed.
CNC Machine Vibration and Machine Settings
CNC machines should be set up on a solid concrete floor, free of welds, 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 worth installing the anchoring well or precisely adjusting the legs. This will certainly minimize the possibility of vibrations. Another factor affecting vibration is the rigidity of the CNC machine and setting incorrect parameters, or elements too loosely. No equipment is 100% rigid. If the machine has been built in a faulty manner, it may dampen vibrations poorly. Unfortunately, even when the equipment is good, faulty maintenance or repair of the equipment can cause vibrations in the CNC machine.
Summary
CNC machines can produce certain vibrations, the effects of which are significant from a production standpoint. We have said almost everything about the vibrations at work, which are caused by CNC devices. In order to determine their causes, you need to examine a number of elements that can create an effect in the form of vibration. By establishing the correct parameters and values of machines - you can avoid this problem. However, during vibrations, products will be produced in a faulty manner, their durability will be less, and moreover, the process itself will be much more prolonged than in the case of the correct operation of the machine. Currently, a number of factors can cause vibration of the CNC machine. From improper grip, to faulty equipment maintenance. If this problem concerns your equipment, check the configuration of the CNC machine, change the feed rate and spindle speed, or use additional elements (e.g. a cone) that will stiffen the production process.