Manufacture - Inspection

INSPECTION

Fig. 22-15 Advanced integrated manufacturing system (A.I.M.S.).

47. During the process of manufacture, component parts need to be inspected to ensure defect free engines are produced. Using automated machinery and automated inspection, dimensional accuracy is maintained by using multi-directional applied probes that record sizes and position of features.

Manufacture - machining (E.D.M.) Composite materials and sandwich casings

COMPOSITE MATERIALS AND SANDWICH CASINGS 

Fig. 22-14 Some composite material applications.

43. High power to weight ratio and low component costs are very important considerations in the design of any aircraft gas turbine engine, but when the function of such an engine is to support a vertical take-off aircraft during transition, or as an auxiliary power unit, then the power to weight ratio becomes extremely critical.

Manufacture - Capillary drilling

Capillary drilling

Fig. 22-12 Typical automated manufacture of compressor blades.

36. Similar in process to stem drilling but using tubes produced from glass incorporating a core of platinum wire (cathode). A twenty per cent nitric acid solution is passed through the tube onto the workpiece and is capable of producing holes as small as 0.009 in. diameter. Depth of the hole is up to forty times greater than the tube in use and therefore determined by tube diameter.
37. Automation has also been added to the process of electro-chemical machining (E.C.M.) with the intro- duction of 360 degree E.G. machining of small compressor blades, ref. fig. 22-12. For some blades of shorter length airfoil, this technique is more cost effective than the finished shaped airfoil when using precision forging techniques. Blades produced by E.C.M. employ integrated vertical broaching machines which take pre-cut lengths of bar material, produce the blade root feature, such as a fir-tree, and then by using this as the location, fully E.C.M. from both sides to produce the thin airfoil section in one operation.

Manufacture - Stem drilling

Stem drilling
35. This process consists of tubes (cathode) produced from titanium and suitably insulated to ensure a reaction at the tip. A twenty per cent solution of nitric acid is fed under pressure onto the blade producing holes generally in the region of 0.026 in. diameter. The process is more speedy in operation than electro-discharge machining and is capable of drilling holes up to a depth two hundred times the diameter of the tube in use.

Manufacture - machining (E.C.M.)

33. Electrolytic grinding employs a conductive wheel impregnated with abrasive particles. The wheel is rotated close to the surface of the workpiece, in such a way that the actual metal removal is achieved by electro-chemical means. The by-products, which would inhibit the process, are removed by the sharp particles embodied in the wheel.
34. Stem drilling and capillary drilling techniques are used principally in the drilling of small holes, usually cooling holes, such as required when producing turbine blades.

Manufacture - Electro-chemical

ELECTRO-CHEMICAL MACHINING (E.C.M.)

Fig. 22-11 Electro-chemical machining.

30. This type of machining employs both electrical and chemical effects in the removal of metal. Chemical forming, electro-chemical drilling and elec- trolytic grinding are techniques of electro-chemical machining employed in the production of gas turbine engine components.

31. The principle of the process is that when a current flows between the electrodes immersed in a solution of salts, chemical reactions occur in which metallic ions are transported from one electrode to another (fig. 22-11). Faraday's law of electrolysis explains that the amount of chemical reaction produced by a current is proportional to the quantityof electricity passed.
32. In chemical forming, (fig. 22-11), the tool electrode (the cathode) and the workpiece (the anode) are connected into a direct current circuit. Electrolytic solution passes, under pressure, through the tool electrode and metal is removed from the work gap by electrolytic action. A hydraulic ram advances the tool electrodes into the workpiece to form the desired passage.

Manufacture - Electron beam welding (E.B.W.)

Electron beam welding (E.B.W.)

Fig. 22-9 Electron beam welding.

Fig. 22-10 Examples of T.I.G. and E.B. welds.

29. This system, which can use either low or high voltage, uses a high power density beam ofelectrons to join a wide range of different materials and of varying thickness. The welding machine ref. fig. 22-9, comprises an electron gun, optical viewing system, work chamber and handling equipment, vacuum pumping system, high or low voltage power supply and operating controls. Many major rotating assemblies for gas turbine engines are manufac- tured as single items in steel, titanium and nickel alloys and joined together i.e., intermediate and high pressure compressor drums. This technique allows design flexibility in that distortion and shrinkage are reduced and dissimilar materials, to serve quite different functions, can be homogeneously joined together. For example, the H.P. turbine stub shafts requiring a stable bearing steel welded to a material which can expand with the mating turbine disc. Automation has been enhanced by the application of computer numerical control (C.N.C.) to the work handling and manipulation. Seam tracking to ensure that the joint is accurately followed and close loop under bead control to guarantee the full depth of material thickness is welded. Focus of the beam is controlled by digital voltmeters. See fig. 22-10 for weld examples.

Manufacture - Welding

WELDING
27. Welding processes are used extensively in the fabrication of gas turbine engine components i.e., resistance welding by spot and seam, tungsten inert gas and electron beam are amongst the most widely used today. Care has to be taken to limit the distortion and shrinkage associated with these techniques.

Manufacture - Fabrication

FABRICATION

Fig. 22-6 Wide chord fan blade

construction

25. Major components of the gas turbine engine i.e. bearing housings, combustion and turbine casings, exhaust units, jet pipes, by-pass mixer units and low pressure compressor casings can be produced as fabricated assemblies using sheet materials such as stainless steel titanium and varying types of nickel alloys.

26. Other fabrication techniques for the manufacture of the low pressure compressor wide chord fan blade comprise rolled titanium side panels assembled in dies, hot twisted in a furnace and finally hot creep formed to achieve the necessary configu- ration. Chemical milling is used to recess the centre of each panel which sandwiches a honeycomb core, both panels and the honeycomb are finally joined together using automated furnaces where an activated diffusion bonding process takes place, ref. fig. 22-6.

Manufacture - Casting

CASTING

Fig. 22-3 Method of producing an engine component by sand casting.

Fig. 22-4 Automatic investment casting.

20. An increasing percentage of the gas turbine engine is produced from cast components using sand casting, ref. fig. 22-3, die casting and investment casting techniques; the latter becoming the foremost in use because of its capability to produce components with surfaces that require no further machining. It is essential that all castings are defect free by the disciplines of cleanliness during the casting process otherwise they could cause component failure.

21. All casting techniques depend upon care with methods of inspection such as correct chemica composition, test of mechanical properties, radiolog- ical and microscopic examination, tensile strength and creep tests. 22. The complexity of configurations together with accurate tolerances in size and surface finish is totally dependent upon close liaison with design, manufacturing, metallurgist, chemist, die maker, furnace operator and final casting.

Manufacture - Manufacturing strategy

MANUFACTURING STRATEGY 
9. Manufacturing is changing and will continue to change to meet the increasing demands of aeroengine components for fuel efficiency, cost and weight reductions and being able to process the materials required to meet these demands.
10. With the advent of micro-processors and extending the use of the computer, full automation of components considered for in house manufacture are implemented in line with supply groups manufac- turing strategy, all other components being resourced within the world-wide supplier network.
11. This automation is already applied in the manufacture of cast turbine blades with the seven cell and computer numerical controlled (C.N.C.) grinding centres, laser hardfacing and film cooling hole drilling by electro-discharge machining (E.D.M.). Families of turbine and compressor discs are 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.

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.