Gear technology improves precision

Edited by the Engineeringtalk editorial team Dec 13, 2005

Winbro Group integrates Harmonic Drive gear technology into machine tools to improve precision and reliability.

The Winbro Group is integrating gear technology into its machine tools to improve precision and reliability.

Supplied by Harmonic Drive, the gear systems have replaced traditional gearbox and motor assemblies and let Winbro reduce the size and weight of tool heads, reduce the effects of backlash and improve positional accuracy and repeatability.

Based in Coalville, Winbro produces custom built machining centres for manufacturers of gas turbines for the aerospace and power generating industries.

In each case, turbines require high operating temperatures to function efficiently, and can be in excess of the melting point of the materials used for the turbine blades.

To overcome this, turbine blades, nozzle guide vanes, combustors and other components use complex air cooling techniques, with each part having many tens or hundreds of cooling holes drilled through its outer surfaces, through which cool air from the turbine compressor is drawn.

The shape, size and angle of these holes are critical to ensure that a boundary film of cooling air is formed along the surface of the component, to separate it from the hot turbine gasses without affecting the operating temperature and thus the efficiency of the turbine.

The Winbro machining centres have been developed for drilling precise patterns of cooling holes in turbine parts.

Project Manager, Chris Clements, said: "Parts such as blades and vanes often have complex shapes and the holes have to be drilled at precise locations on the surface of the component".

"The geometry of each hole has to be accurately machined to produce the correct flow pattern".

Depending on the application, Winbro manufactures machining centres that use either Nd:YAG lasers or EDM technology for precision drilling applications.

Lasers generally have the advantage of faster drilling speeds, while EDM has the advantage of improved metallurgical results and also can drill holes where direct line of sight is not possible.

The gear units comprise three basic component parts - an elliptical wave generator, flexspline and circular spline - which fit one within the other to form an integrated unit.

The overall construction lets each component be used as the input, output or fixed part, so the gear unit can be used for reduction gearing, gearing for increasing speed, or differential gearing.

Clements said: "Used on our latest laser systems, Harmonic Drive's units used with directly coupled encoders allow us to achieve rotary accuracies of 20 arc seconds, with repeatability being 10 arc seconds".

Winbro has also incorporated Harmonic Drive's FHA hollow shaft servo actuator into the work piece manipulator and laser head on its machines.

This actuator has a large central hollow shaft which allows the laser beam to be directed through the gear unit or other services such as pneumatics, hydraulics and electrics.

It is available with an absolute position output shaft encoder providing direct measurement of output shaft position and eliminating the need for referencing.

Its feedback systems are compatible with most major controller manufacturers.

"This has saved us valuable development time and reduced both the space and number of components that are needed in the tooling head," said Clements.