Exhibitions

What are the benefits to the MRO?

Knowing if a set of components will or will not meet specification prior to assembly cannot be understated. The build process becomes more predictable allowing better scheduling and planning and even increasing throughput; use of the Aerospect system in nearly all cases reduces the build time by greater than 40%.
The Aerospect software provides better control of inventory by matching in-tolerance parts that may have failed when joined as assemblies; this represents a substantial cost saving by avoiding the need to re-work components.

 

Benefits to the end user

Like all transport industries fuel prices and more importantly environmental issues are forcing change to engine technology and in particular the aerospace industry.
One of the benefits of a well aligned Compressor and Turbine is the ability to reduce the clearance between the rotor and stators of the assembly, this makes for a more fuel efficient engine passing on huge savings to the airline operator. Improving engine alignment also decreases vibration and increases bearing life and as a direct consequence increases “Time on Wing” again making a large cost saving.

 

Benefits to the environment

As previously stated the more aligned the High Pressure compressor the more fuel efficient the engine becomes and in turn the lower the emissions, fractions of a percentage in efficiency relates to thousands of tonnes reduction in CO2 emissions. An accurate and smooth running engine will produce less vibration and as a consequence noise pollution is kept to a minimum.

Aerospect system for stacking the GE90 High Pressure Compressor and turbine assemblies.

The Aerospace industry has been using Aerospect systems to stack turbine components for over 10 years now, so when we were asked to develop a system for stacking GE90 components our engineers rose to the challenge.

 

The GE90 is the worlds most powerful turbofan engine with a thrust rating up to an incredible 115,000 lb, in fact the GE90 – 115B set the world record for thrust levels (commercial aircraft)  by attaining 127,900 pounds of thrust during final certification back in 2002; the previous record was set by the same engine back in 2001.

Not only does the GE90 engine hold the record for being the most powerful commercial jet engine it also holds the record for the longest flight by a commercial airliner. Powering a 777-200LR the flight from Hong Kong to London took 22Hours 42 minutes and covered 13,422 miles (21,601Km). Those that have flown from Hong Kong to London will realise that this was not the shortest route between these locations, in actual fact the flight went over the pacific, across the US and over the Atlantic.
It is for this purpose that Boeings 777 wide-body aircraft utilise the popular GE90 to ensure fast and efficient flights over long distances.

To achieve these levels of performance the engine build process has to be controlled to a high degree of accuracy and in particular the High Pressure compressor and High pressure turbine. The high pressure compressor is made up of a number of components all of which have to be stacked together in such a way that the rotation of the compressor is true to axis. This is critical particularly as the High Pressure Compressor can turn at speeds greater than 10,000 rpm, any out of balance situation along with axial run-out errors will manifest themselves in a number of ways.

This is where the Aerospect stack prediction system comes in to use, the Aerospect system (see fig 1) allows engine MRO and manufacturers to build component parts of the engine in such a way that axial and radial rotational errors are kept to a minimum.

The Aerospect employs a simple philosophy “if the part rotates then the best method of measurement is in rotation”.

The system consists of a high load capacity air bearing spindle that allows component weights of up to 2500Lb. Made from hardened tool steel mounted on a granite plate the spindle provides a high degree of accuracy while maintaining the shop floor robustness required during the engine build and alignment process. Measurements are taken using multiple gauge heads conveniently located on adjustable columns and arms, these posts and arms provide easy access to relevant features and assemblies of the compressor.

The large column allows measurement of the complete high pressure compressor from the Low pressure compressor inlet right through to the High pressure compressor outlet. Piece parts or the entire compressor stack are held on a large diameter heavy duty table top with full centre and level capability. An intuitive set up screen and real time profile display greatly enhances the set up process ensuring fast and accurate components alignment. The methodology employed to stack the GE90’s compressor is powerful yet simple in concept. The powerful software package developed in conjunction with GE allows the user to measure the mating surfaces and datum’s of individual assemblies to establish run-out values along with their angular directions; these values are stored in the Aerospect software.

When it comes to stacking, the user can carry out a virtual build of the complete compressor or individual assemblies using pre-measured parts, each of which has been marked with an SP value (Stack Projection value) and angular position. The Aerospect stack prediction software will tell the user not only if these stacked parts will meet the defined axial tolerance but will also propose the best orientation of the components (see inset).

The user can then start the build process but at the same time continue to measure the stacked components as their built. The first part of the high pressure compressor (stage 1 disk) is placed on a specially made hydraulic chuck; this fixture allows the user to grip the component on the inner shaft using a preset and specified load (see inset). Two gauges located at the base of the Aerospect system are then used to establish an axis of rotation on the shaft while all adjustable gauges are used to measure radial and axial run-out of the connecting portions of the compressor.

These gauges allow measurement of lower and upper surfaces (flatness mode) as well as inner and outer diameters (roundness mode).The next stages of the compressor can be placed on the stage 1 disk and located in an angular position as specified by pre-defined calculations and measurements. Once these stages are put together its possible to re-establish a new stack prediction value and position ready for the next part of the build. This sort of process continues until the complete compressor is built up.
Those who are involved in building compressors and other engine assemblies will be aware of the painful experience of stacking two components only to find that their combined run-out values put the assembly out of tolerance. This is particularly painful when the two parts have been joined by heating or cooling, the separation of which is not easy and can be costly in terms of time not to mention the possibility of damage during separation.

 

The Aerospect system greatly reduces the likelihood of having to breakdown the compressor saving time and money. Not only does the GE90 HPC require good alignment but the point at which the compressor connects to the high pressure turbine is also critical. Misalignment of these joints can cause a banana or crank type action that greatly affects the performance of the combined parts. The Aerospect Stack prediction system ensures alignment of the compressor and turbine assembly is kept to an optimum.

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