Fixture loading of aerospace casings and compressor stators

Citation

(1999), "Fixture loading of aerospace casings and compressor stators", Aircraft Engineering and Aerospace Technology, Vol. 71 No. 5. https://doi.org/10.1108/aeat.1999.12771eab.010

Fixture loading of aerospace casings and compressor stators

Fixture loading of aerospace casings and compressor stators

Keywords: Aerospace, Engines, System 3R

System 3R workholding pallets with Zerofix reference chucks (Plate 2) are reported to be simplifying and speeding up the loading of aerospace casings and stator assemblies for the leading aero engine manufacturer based in the East Midlands. Stators are the static components in an engine between which the compressor blades pass.

Plate 2 A 1.4m diameter System 3R circular workholding pallet showing the four Zerofix reference chucks. The casing and stator assembly can be seen through the large central hole.

System 3R Zerofix pallets and chucks are believed to be significantly improving the holding capabilities and speed set-up time by introducing their X, Y, Z referencing that consistently ensures repeatable accuracy to within a few microns. According to System 3R, it means that each engine's sections can be pre-set outside of the vertical lathe machine and then the entire unit dropped onto the holding chucks.

The casing and stator machining process takes place on two new Mazak Mega Turn CNC machines operating within a specially built "cocoon" adapted from an area of an existing high-tech production workshop. It is an enclosed, dust free zone that has highly efficient air-conditioning installed to maintain a constant 20úC temperature throughout.

The aero engines that this highly specialised unit handles are mainly for Airbus and Boeing aircraft.

The project engineer, says: "There are three things which Zerofix has provided for us. It has given us a reliable and consistent load, it has taken out operator variability by giving us accurate repeatability, and it is quick. It has enabled us to reduce set up times considerably. There is no clocking or clamping; it is all self contained. The only thing we have got to worry about is cleanliness because it is very important to keep dust to a minimum, or eliminate it completely.

"Because metal parts expand and can affect accuracy, it is crucial that the area where the machining takes place is maintained at a special temperature of 20úC þ 2úC."

The thinning/grinding process uses a total of 20 circular Zerofix pallets, each 1.4m diameter, supporting a fixture. There are different pallet fixtures for different casings and the maximum overall weight is up to 3 tons when fully loaded.

While there are always two pallets on the machines, the other pallets can be set up so that running time is maximised, and down time is minimised. Both machines are fitted with 100mm thick custom-made base plate and fixture assemblies. These are jig bored on the machines so they always remain true to the machines' axes.

System 3R Refix primary location dowels, specially developed for the application, allow two piece fixtures to be accurately assembled. These are expanding pins that ensure the fixture is accurate to within 0.010mm.

According to System 3R, its Zerofix pallet system has now been used with 100 per cent success on various aircraft projects in the UK, where set up speed and accuracy are crucial to the production process, because it provides the ultimate in accurate repeatability. It is said to be a robust system, which is thought to be particularly suited to holding large and heavy workpieces using hydraulic clutches and reference rings.

An additional plus point which Zerofix claims for the East Midlands application is the systems inherent flushing function that cleans all reference surfaces before the engine components are locked into place.

Further details are available from System 3R Limited. Tel: +44 (0)1844 274455; Fax: +44 (0) 1844 348800; E-mail: javelin@dial.pipex.com