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Factors that influence vibration


To minimize vibration tendencies:

  • Use a large entering angle and positive rake angle
  • Use small nose radii and point angle
  • Use a positive macro geometry
  • Control the wear pattern and ER-treatment on the micro geometry
  • Depth of cut should be larger than the nose radius.

Lower radial force gives less radial deflection and fewer problems with vibration. For best results; use a radial depth of cut that is larger than the nose radius when using a 90° entering angle (0° lead angle). If the radial depth of cut is smaller, a 45° entering angle will give you equal results.

  

Vibration tendency​
Entering angle​
Lead angle ​
Nose radius and point angle. mm (inch)
Macro geometry​
Micro geometry​
Depth of cut related to nose radius
 

 

Be aware that re-directing forces can reduce deflection:

  • Entering angle as close to 90° as possible (lead angle 0°) will maximize the portion of feed force coming back from the workpiece in the axial direction. A force in the axial direction will give less tool deflection than equal forces in the radial direction.
  • For internal turning the entering angle should never be less than 75° (lead angle 15°).
  • The more positive the rake angle, the less cutting forces are needed to machine the component. Less cutting forces means less deflection.
  • Less force in the radial direction giving less radial deflection
Force direction: mainly axial​ Force direction: both axial and radial​
Negative rake angle increases cutting forces​ Positive rake angle gives less cutting forces​

 


Ft = tangential forces and Fr = radial forces

Insert point angle

Select an insert shape relative to the entering angle and accessibility requirements of the tool. One rule of thumb is to always choose the smallest possible nose radius to reduce vibration tendencies. When it comes to point angle, there are two paths to choose:

  • A small insert point angle will improve tool stability, give good clearance of a trailing surface, and small chip area variations if the tool starts vibrating in a radial direction
  • A large insert point angle gives insert strength and reliability but requires more machining power, since a larger cutting edge is engaged in the cut




 

Positive geometries

Positive geometries and positive rake angles generate less cutting forces and less deflection of the tool. Therefore, choose the most positive geometry you can, with a chip-breaker suitable for your cutting data. This may decrease the wear resistance and edge strength somewhat, as well as the chip-control, so vibration control is always a balance.

 
 

Wiper inserts

Wipers are usually not first choice when it comes to avoiding vibration, as the increased cutting forces and radial deflection are difficult to overcome. In very stable conditions, however, wiper inserts can provide true benefits in surface finish and increased cutting data.

 

 

Edge rounding

A small edge rounding (ER) gives lower cutting forces in all directions. This means easier cutting action and less deflection of the tool. Ground inserts have smaller edge rounding than direct pressed inserts, which is true also for uncoated or thin-coated inserts.​

 

M = Direct pressed inserts​

G = Ground insert, normally with smaller ER​

E = Ground insert for closer tolerances and sharp edge​

 

Cutting data

Excessive insert wear, such as flank wear must be avoided, as it changes the clearance between the tool and the component wall, which can cause vibration problems. 

 
Cutting speed, vc

Correct cutting speed will avoid built-up edge, which influences surface finish, cutting forces and tool life.

  • Excessive cutting speed can generate flank wear, which reduces security and reliability, due to chip jamming, poor chip evacuation and insert breakage, especially when machining deep holes
  • Cutting speeds which are too low will generate built-up edge
  • Uneven wear pattern will decrease tool life and surface finish, so pay careful attention to wear pattern
  • Workpiece material has a great impact on what cutting speed you can apply
Depth of cut, ap, and feed, fn

The combination of ap and fn is important to achieve the best possible chip areas. Two rules of thumb:

  • Program ap larger than the nose radius
  • Program for an fn that is a minimum of 25% of the nose radius, depending on what surface finish is required

One of the first things to consider if you experience vibration when machining with long overhangs is to increase the feed and as second remedy change the cutting speed. Usually, the best results are achieved with higher cutting speed.

Chip area
  • If the chip area is too large, the cutting forces are too large
  • If the chip area is too small, the friction between tool and workpiece is too great and a rubbing effect can occur

 

 
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