Turn milling is defined as the milling of a curved surface while rotating the workpiece around its center point.
Eccentric forms or shapes that differ considerably from those that conventional milling or turning methods produce can often be turn milled. The method allows for high metal removal with superb chip control.
- A cylindrical surface can be produced only when feeding the milling cutter in a radial direction during rotation.
- By simultaneously moving the cutter in two directions, it is possible to produce eccentric surfaces, e.g. cams on shafts.
- Movement in more than 2 axes requires a tool with ramping capabilities.
- To machine a conical shape, 5 axes are required.
- Turn milling of complex profiles, e.g. turbine blades, requires simultaneous movement in 5 (or 4) axes, 2 or 3 for the workpiece and 1 or 2 for the tool.
- It is possible to produce components, such as turbine blades, by feeding the cutter in more than 2 axes while simultaneously rotating the component.
Choice of method
Face turn milling – 4/5 axes
Main method for external machining.
+ Short tool extensions
+ Smaller tool diameters/low torque
+ External/slender components
+ Profiling
− Not a natural cylindrical surface
− Internal.
Periphery turn milling – 3/4 axes
Same principle as for circular milling/ramping, but with component rotating.
Used mainly for internal features.
+ Internal machining
+ Cylindrical surface
+ Narrow slots
+ Thread milling
+ Roundness
− Profiling
− Larger diameters/high torque
− Long overhangs.
Choice of tools
Turn milling cutters for roughing
Turn milling cutters for finishing
* Only when cutting axially and fully loaded with wipers.
How to apply
Cutter position - rectangular inserts/wiper
1 = First cut
2 = Second cut
In face turn milling, one wiper insert is used to generate the straight line contact between the cutter and the machined surface in order to create the cylindrical part of the component. Because the milled surface is convex, the wiper land has to be flat instead of crowned. To cover the full width of the cutter, the tool has to be placed with at least two offsets, first Ew1 during first revolution of the work piece and then moved to Ew2 for a second cut.
Cutter position - round inserts/non-wiper
For producing the flatest possible surface, a small diameter cutter with a width of cut, ae, less than 40% of the effective cutter diameter, Dc, is optimal.
However, the ae needs to be increased in order to obtain the best productivity. This can be done by increasing:
- Cutter diameter
- Ratio of radial engagement – ae/Dc .
To gain acceptable cusp height, the cutter needs to be offset from the center. The amount of offset depends on the ae, and is taken from the diagram for the respective ae/Dc.
Offset and width of cut
Wiper width
Width of cut
For milling a surface that is wider than the cutter diameter, it is necessary to remain in the initial position and then to move the cutter in the axial direction to the required length, which is, however, not more than 80% of the aez1 per revolution. If a 90° shoulder is required, the cutter has to move to a second position, Ew2. This will remove the material in red. The final pass must be taken with an Ew of 0 and one full rotation.
Infeed principle
The milling tool should be fed into the workpiece in the radial direction. The workpiece rotation speed should correspond to the feed/tooth recommended for the insert. The cutter should be fed out axially.
Programming
Detailed information about turn milling programming is provided in the Turn Milling application guide. Contact your local Sandvik Coromant representative for more information.