Mill-Turn Composite Process

 

Mill-turn is defined as the milling of surfaces on a rotating workpiece around its center.

 

Mill-turn methods are often used to machine eccentric shapes, which differ significantly from shapes machined by traditional milling or turning processes. This method offers a high metal removal rate and excellent chip control.

 

During rotation, feeding the milling cutter radially can machine cylindrical surfaces.

 

By moving the milling cutter simultaneously in two directions, eccentric surfaces, such as cams on shafts, can be machined.

Moving along more than two axes requires tools with helical interpolation capabilities.

 

To machine tapers, five-axis movement is necessary.

 

Mill-turning complex profiles (e.g., turbine blades) requires simultaneous movement along five (or four) axes, with the workpiece moving along two or three axes and the tool moving along one or two axes.

 

Parts such as turbine blades can be machined by rotating the workpiece while feeding the milling cutter along more than two axes.

 

 

I Mill-Turn Process Selection

 

1. Face Mill-Turn - 4/5 Axes

The primary method for outer diameter machining.

 

+ Short tool overhang

+ Smaller tool diameter/low torque

+ Outer diameter/elongated parts

+ Contour cutting

- Non-natural cylindrical surfaces

- Inner diameter turning

 

▲ Outer Diameter Machining

 

2. Peripheral Mill-Turn – 3/4 Axes

The principle is similar to circular interpolation milling (inner/outer), but in mill-turn, both the workpiece and the milling cutter rotate. It is mainly used for inner diameter machining.

 

+ Inner diameter machining

+ Cylindrical surfaces

+ Narrow grooves

+ Thread milling

+ Circularity

- Contour cutting

- Larger diameter/high torque

- Long overhang

 

    

▲ Inner Diameter Machining

 

 

II How to Apply Mill-Turn

 

1. Tool position – Rectangular insert/Wiper

Milling cutter position

 

▲Milling Cutter Position

 

Cutting Width

 

▲Cutting Width

 

1 = First cutting

2 = Second cutting

 

In face mill-turn operations, a wiper insert is used to generate linear contact between the milling cutter and the work surface, allowing the cylindrical portion of the part to be machined.

 

Since the machined surface is convex, the wiper must be flat, not crowned. To cover the full width of the milling cutter, it must be offset at least twice: the first offset (Ew1) occurs during the first rotation of the workpiece, and then it moves to Ew2 for the second cutting.

 

2. Milling Cutter Position – Round Insert/Non-Wiper

 

  ▲ Milling Cutter Position

 

▲ Corresponding ae/DC chart

 

To machine the flattest surface possible in a mill-turn operation, it is best to use a small-diameter milling cutter with a cutting width (ae) less than 40% of the effective milling cutter diameter (DC).

 

However, to achieve optimal productivity, ae needs to be increased. This can be done by increasing the following parameters:

 

- Tool diameter

- Radial depth of cut – ae/DC

 

To obtain an acceptable peak height, the milling cutter needs to be offset from the center. The offset depends on ae and can be found from the corresponding ae/DC chart.

 

3. Offset and Cutting Width

 

Wiper Insert Width

 

▲ Wiper Insert Width

 

Cutting Width

 

▲ Cutting Width

 

 

When machining surfaces wider than the milling cutter diameter, the cutter must be kept in the initial position and then moved axially to the desired length, but each revolution should not exceed 80% of aez1. If a 90° shoulder is required, the tool must be moved to the second position Ew2.

 

4. Feed Principles

In the mill-turn process, the milling cutter should be fed radially into the workpiece. The workpiece speed should correspond to the recommended feed per tooth for the insert. The tool should exit axially.

 

▲ Feed Principles