How to reduce vibration during CNC machining?

In CNC milling, vibrations can occur due to the limitations of cutting tools, tool holders, machine tools, workpieces or fixtures. To reduce vibration, there are a few strategies to consider.

Cutting tool

For face milling, the direction of the cutting force must be considered

When using a 90° milling cutter, the cutting force is mainly concentrated in the radial direction. In the long overhang condition, this will cause the milling cutter to deflect; However, low axial forces are advantageous when milling thin-walled/vibration-sensitive parts

The 45° milling cutter produces evenly distributed axial and radial forces

Round insert milling cutters direct most of the force upwards along the spindle, especially at small depth of cut. In addition, the 10° milling cutter transmits the main cutting force into the spindle, reducing vibrations due to long tool overhangs

Choose the smallest possible diameter for the operation

DC should be 20-50% larger than AE

Choose thinning and/or unequal pitch milling cutters

Light weight milling cutters are advantageous, such as those with an aluminum cutter body

For unstable thin-walled workpieces, use large principal declination = small axial cutting force; In the long tool overhang case, small declination = high axial cutting force is used.

hilt

With the Coromant Capto? modular tool holder system, it is possible to assemble tools of the required length while maintaining high stability and minimal runout.

Keep the tool assembly as rigid as possible and as short as possible

Choose the largest possible adapter diameter/size

Use Coromant Capto? adapters suitable for oversized milling cutters and avoid using reduced diameter adapters

For small size milling cutters, tapered adapters are used if possible

In an operation where the last pass is deep in the part, the extended tool is used at the predetermined position. Adjust the cutting data according to each tool length

If the spindle speed exceeds 20,000 rpm, a dynamically balanced cutting tool and shank are used

Anti-vibration milling cutters

Milling vibrations can become more pronounced if overhangs are greater than 4 times the tool diameter, and Silent Tools? anti-vibration cutters can significantly increase productivity.

Cutting edges

To reduce cutting forces:

Choose light-duty geometry-L with sharp cutting edges and thinly coated grades

Use a blade with a small tip arc radius and a small parallel edge band

Sometimes, vibration tendencies can be reduced by adding more damping to the system. Use a cutting edge geometry with a larger negative rake angle and a slightly worn cutting edge.

Programming of cutting data and toolpaths

Be sure to position the milling cutter off-center relative to the milling surface

For KAPR 90° long-edge milling cutters or end mills, use a small radial depth of cut (max. ae = 25%×DC) and a large axial depth of cut (max. ap = 100%×De)

For face milling, small depth of cut AP and high feed FZ are used as well as round inserts or high feed milling cutters with small declination angles

Vibration in corners is avoided by programming large circular passes, see Inner corner milling

If the chip thickness becomes too thin, the cutting edge will scrape instead of cutting, creating vibration. In this case, the feed per tooth should be increased

machine tool

Machine condition can have a large impact on milling vibration trends. Excessive wear of the spindle bearings or feed mechanism will result in poor machinability. Carefully select machining strategy and cutting force direction to take full advantage of machine stability.

Every machine tool spindle has unstable areas that are prone to vibration. The stable cutting area is described by the stability diagram and increases with increasing speed. Even speed increases as low as 50 rpm can change the cutting process from a state of vibration instability to a stable state.

Workpieces and their fixtures

When milling thin-walled/pedestal parts and/or when the fixture is less rigid, consider the following:

The fixture should be close to the machine tool table

Optimize toolpath and feed direction towards the highest machine/fixture strength for the most stable cutting conditions

Avoid machining in a direction where the workpiece is not adequately supported

When the fixture and/or workpiece is less rigid in a particular direction, conventional milling reduces vibration tendencies

When the fixture is less rigid, use the feed direction towards the machine table 

Note that the first cut should be performed at 1/2 of the second cutting depth, the second cut at 1/2 of the third cutting depth, and so on.