Page 241 - The Jet Engine

Manufacture

sequence, estimating and scheduling. Computer
simulation allows potential cell and flow line
manufacture to be proven before physical machine
purchase and operation, thus preventing equipment
not fulfilling their intended purpose.
14. Each casing is manufactured from the lightest
material commensurate with the stress and tempera-
tures to which it is subjected in service. For example,
magnesium alloy, composites and materials of
sandwich construction are used for air intake
casings, fan casings and low pressure compressor
casings, since these are the coolest parts of the
engine. Alloy si eels are used for the turbine and
nozzle casings where the temperatures are high and
because these casings usually incorporate the
engine rear mounting features. For casings
subjected to intermediate temperatures i.e. by-pass
duct and combustion outer casings, aluminium alloys
and titanium alloys are used.

FORGING
15. The engine drive shafts, compressor discs,
turbine discs and gear trains are forged to as near
optimum shape as is practicable commensurate with
non-destructive testing i.e., ultrasonic, magnetic
particle and penetrant inspection. With turbine and
compressor blades, the accurately produced thin
11. This automation is already applied in the airfoil sections with varying degrees of camber and
manufacture of cast turbine blades with the seven twist, in a variety of alloys, entails a high standard of
cell and computer numerical controlled (C.N.C.) precision forging, ret. fig. 22-2. Nevertheless
grinding centres, laser hardfacing and film cooling precision forging of these blades is a recognised
hole drilling by electro-discharge machining (E.D.M.). practice and enables one to be produced from a
Families of turbine and compressor discs are shaped die with the minimum of further work.
produced in flexible manufacturing cells, employing
automated guided vehicles delivering palletized
components from computerized storage to C.N.C.
machining cells that all use batch of one techniques.
The smaller blades, with very thin airfoil sections, are
produced by integrated broaching and 360 degree
electrochemical machining (E.C.M.) while inspection
and processing are being automated using the
computer.
12. Tolerances between design and manufacturing
are much closer when the design specification is
matched by the manufacturing proven capability.

13. Computer Aided Design (C.A.D.) and Computer
Aided Manufacture (CAM.) provides an equivalent
link when engine components designed by C.A.D.
can be used for the preparation of manufacturing
drawings, programmes for numerically controlled
machines, tool layouts, tool designs, operation Fig. 22-2 Precision forging.

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