Friday, July 6, 2012

Manufacture - Introduction



INTRODUCTION 

1. During the design stages of the aircraft gas turbine engine, close liaison is maintained between design, manufacturing, development and product support to ensure that the final design is a match between the engineering specification and the man- ufacturing process capability. 
Fig. 22-1 Arrangements of a triple-spool turbo-jet engine.
2. The functioning of this type of engine, with its high power-to-weight ratio, demands the highest possible performance from each component. Consistent with this requirement, each component must be manufactured at the lowest possible weight and cost and also provide mechanical integrity through a long service life. Consequently, the methods used during manufacture are diverse and are usually determined by the duties each component has to fulfil.
3. No manufacturing technique or process that In any way offers an advantage is ignored and most available engineering methods and processes are employed in the manufacture of these engines, In some instances, the technique or process may appear by some standards to be elaborate, time consuming and expensive, but is only adopted after confirmation that it does produce maximized  component lives comparable with rig test achieve- ments.

4. Engine components are produced from a variety of high tensile steel and high temperature nickel and cobalt alloy forgings. A proportion of components are cast using the investment casting process. Whilst fabrications, which form an increasing content, are produced from materials such as stainless steel, titanium and nickel alloys using modern joining  techniques i.e., tungsten inert gas welding, resistance welding, electron beam welding and high temperature brazing in vacuum furnaces.

5. The methods of machining engine components include grinding, turning, drilling, boring and broaching whenever possible, with the more difficult materials and configurations being machined by electro-discharge, electro-chemical, laser hole drilling and chemical size reduction. 
6. Structural components i.e., cold spoiler, location rings and by-pass ducts, benefit by considerable weight saving when using composite materials.


7. In addition to the many manufacturing methods, chemical and thermal processes are used on part finished and finished components. These include heat treatment, electro-plating, chromate sealing, chemical treatments, anodizing to prevent corrosion, chemical and mechanical cleaning, wet and dry abrasive blasting, polishing, plasma spraying, elec- trolytic etching and polishing to reveal metallurgical defects. Also a variety of barrelling techniques for removal o! burrs and surface improvement. Most processes are concerned with surface changes, some give resistance to corrosion whilst others can be used to release unwanted stress.
8. The main structure of an aero gas turbine engine is formed by a number of circular casings, ref. fig. 22- 1, which are assembled and secured together by flanged joints and couplings located with dowels and tenons. These engines use curvic and hurth couplings to enable accurate concentricity of mating assemblies which in turn assist an airline operator when maintenance is required.

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