Interpolation turning

Interpolation turning has been developed for advanced machining centres and B-axis multi-task machines. A turning operation can be carried out by interpolating with the X and Y-axis in a circular direction and rotating the machine spindle in time with the rotational contour.

The circular movement can either increase or decrease in diameter to produce facing operations or be combined with the Z-axis to produce a bore or outer diameter.

Interpolation turning vs. traditional method

All machine concepts have been developed to provide multifunctional options. Turning, drilling and milling operations can be carried out in sliding head machines all the way to 5-axis machining centres. Turning operations have used a machine axis to rotate the part around the component’s axis of symmetry.

Symmetrical features on non-symmetrical parts have used boring tools for parallel diameters on standard machining centres. However, where contours are required normally circular interpolation by milling or a W-axis head has been required to generate the form.

Interpolation turning does not compete with the metal cutting efficiency of traditional boring or turning operations, however, it does provide a viable option to the traditional way.

Interpolation turning should be considered for new machines where the components have symmetrical features on non-symmetrical components, e.g flanges, seal grooves and non-parallel bores.

Limitations of interpolation turning

The limitations of the method and machines are:

• The revolutions per minute – speed of the X and Y table feed
• Programming support – CAM cycles/post processors
• Spindle torque – as the spindle motor is rotating at a relatively low rpm the depth of cut of the turning operation should not be excessive
• Spindle interface – the coupling should be capable of transmitting a higher level of torque than normally required for milling operations. Steep taper 50 or Coromant Capto® have superior torque transmission than HSK-A

The pictures show the difference in table movement between interpolation turning with traditional tool offset and a tool designed for interpolation turning.

Main benefits with interpolation turning

• A flexible solution, making it possible to use machining centres with modular tool set-ups instead of devoted boring machines with W-axis facing heads
• The component can be machined completely without moving it which is especially beneficial for large non-symmetrical components
• Reduced tool investment costs
• Aluminium bridges are available which helps to keep the tool assembly weight within the machine tool change and magazine capability

Tooling considerations

• The tool radius should be kept relatively close to the component radius being cut to limit the X, Y movement – i.e. large component radius should have cutting tools with large radius or offset from the centre of rotation
• Where longer profiles are needed it is good to have a larger tool radius than the spindle housing. This improves accessibility and process stability by reducing the need for long slender tools
• Ensure that the tool weight, moment and diameter are kept within the capability of the magazine and tool changer

Tooling solutions

Existing modular concepts are combined to provide tailored solutions for the requirements of interpolation turning – each having its position depending on the component feature diameter and geometry.

• Axial Coromant Capto® quick change clamping units with large diameter boring tool slide interface for axially mounted cutting units and clearance of the spindle housing
• Machine interface adaptors combined with Coromant Capto® turning cutting units for internal as well as external features
• Coromant Capto® offset reduction clamping units provide clearance and increased tool radius
• Damped boring bars with modular cutting units for deep boring applications
• Modular turning adaptors and cutting heads held in machine interface adaptors provide a large offset and clearance for profiling
• Cartridges and integrated slides for large diameter boring tools allow large diameter tools to be built for clearance of the spindle housing
• Radial Coromant Capto® clamping units to provide larger offset