The cutting edge
To reduce the cutting forces:
- Choose a light cutting geometry, -L, with a sharp edge, and a grade with a thin coating
- Use inserts with small corner radii and small parallel lands
Sometimes adding more damping to a system can decrease the vibration tendencies. Use a more negative cutting edge geometry and a slightly worn cutting edge.
Cutting data and tool path programming
- Always position the cutter off-centre in relation to the milled surface
- With KAPR 90° long edge cutters or end mills, use low radial immersion: max
ae= 25% DC and high axial cut: max
ap = 100%
- In face milling, use a small depth of cut,
ap, and high feed,
fz, with round inserts or high feed cutters with small entering angles
- Avoid vibrations in corners by programming a large path radius, see milling inside corners
- If the chip thickness becomes too low, the cutting edge will rub rather than cut, causing vibration. In such instances, the feed per tooth should be increased
The machine tool
The machine condition can have a large influence on milling vibration tendencies. Excessive wear on the spindle bearing or feed mechanism will result in poor machining properties. Choose machining strategies and cutting force directions carefully to take full advantage of the machine stability.
Each machine spindle has natural areas which are prone to vibration. The areas of stable cutting are described as stability lobes, and increases as the rpm increases. Even a small increase, as low as 50 rpm, can move a cutting process from unstable, with vibration, to stable.
Workpiece and its fixture
Consider the following when milling components with thin wall/base and/or when the fixture is weak:
- The fixture should be close to the machine table
- Optimize the tool path and feed direction towards the machine's/fixture’s strongest node to obtain the most stable cutting conditions
- Avoid machining in directions where the workpiece is poorly supported
- Up milling can reduce vibration tendencies when fixture and/or workpiece are weak in a specific direction
For weak fixtures, use a feed direction into
Note that the first step should be made at
half the depth of the second, third, etc.
Read more about vibration causes and solutions