fsayed
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@nair @proud_indian @Roybot @jbgt90 @Sergi @Water Car Engineer @dadeechi @kurup @Rain Man @kaykay @Abingdonboy @SR-91 @nang2 @Stephen Cohen @anant_s
@jbgt90 @ranjeet @4GTejasBVR @The_Showstopper @guest11 @PARIKRAMA
@GURU DUTT @HariPrasad @JanjaWeed @litefire @AMCA @SrNair
@Nilgiri @Jamwal's
@Guynextdoor2 @DesiGuy1403
http://www.indiandefensenews.in/2016/07/idn-take-tech-scan-brief-review-of.html?m=1
Now that the Kaveri engine is back in business, it becomes imperative for us to understand what went wrong with the development of the engine.
America's General Electric, Honeywell and Pratt & Whitney; Europe's Rolls-Royce and Snecma; Russia's Klimov and NPO Saturn are the worlds premier jet engine vendors. China has designed nuclear missiles and blasted astronauts into space, but one vital technology remains out of reach. Despite decades of research and development, China, masters of cloning has so far failed to build a reliable, high performance jet engine mainly because reverse-engineering a highly complex turbofan jet engine is very difficult as it involves several complex manufacturing processes. Jet engine technologies relate to materials which includes high-temperature composites and alloys and high precision engineering, which are difficult to copy.
Years of hard work won't go waste:
By any yardstick, the Kaveri turbofan is a technologically complex power plant and deriding Gas Turbine Research Establishment (GTRE) incessantly is rather unjustified. The engine is a two spool, bypass turbofan engine having three stages of transonic low pressure compressor driven by a single stage low pressure turbine. The core turbojet engine of the Kaveri is the Kabini. The core engine consists of a six stage transonic compressor driven by single stage cooled high pressure turbine. The engine is provided with a complete annular combustor with air blast atomiser. The aero-thermo dynamics and mechanical designs of engine components were evolved using many in house and commercially developed software for solid and fluid mechanics. Its three stage transonic fan, designed for good stall margin handles an air mass flow of 78 kg and develops a pressure combustion chamber line ratio of 3:4. Kaveri engine has been designed to achieve a fan pressure ratio of 4:1 and overall pressure ratio of 27:1. These pressure parameters are claimed to be good enough to support the super cruise manoeuvres of an advanced combat aircraft. The development model is fitted with an advanced convergent-divergent variable nozzle.
TROUBLE
The project for design and development of Kaveri engine was sanctioned to achieve the interim flight standard for LCA ‘Tejas’ integration. Though the Kaveri engine was not fully meeting the requirement of LCA ‘Tejas’, it provided a platform for gas turbine technology development in the country. This is as per Press Information Bureau the media arm of the Government of India.
(i) Ab-initio development of state-of-the-art gas turbine technologies
(ii) Technical/technological complexities
(iii) Lack of availability of critical equipment & materials and denial of technologies by the technologically advanced countries
(iv) Lack of availability of test facilities in the country necessitating testing abroad
(v) Non availability of skilled/technically specialized manpower
And one of the major drawbacks the Kaveri engine faced was the reliability of its turbine blades. It also failed the high altitude tests and was too heavy for the Tejas aircraft. Modern aircraft engines must meet extreme demands for performance. Manufacturing jet engines involves state-of-the-art technologies in design, machining, casting, composite materials, exotic alloys, electronic performance monitoring, software engineering and quality control. A high performance turbofan engine will need to incorporate single crystal blade technology, integrated rotor disk and blades and super alloys of nickel and cobalt, a technology which India is yet to master.
While the Tejas needs an engine with 82-90 kN of peak thrust, the Kaveri has only managed 72 kN during flight testing in Russia. This is inadequate for the TEJAS, but the DRDO is still seeking a technological breakthrough with very limited resources. GTRE is now hopeful of upgrading the Kaveri engine to meet the needs of LCA & AMCA in the context of the vastly improved industrial support base in the country that the aero engine development program had helped create. The biggest challenge ahead of GTRE would be how to enhance the power of Kaveri without increasing its size and weight and through incorporating the single crystal turbine blade technology. Efforts are now on to improve the expertise level in the country for developing the high performance nickel and cobalt super alloys used in the manufacture of single crystal blades.
The world over not many countries have progressed ahead in making jet engines. We have made a good start and despite the delays, proved our capabilities to the best of our abilities. The lessons learnt will not go in vain. India must become self sufficient in making jet engines and our efforts must continue.
INTRODUCTION
Aircraft engines are high-technology products, the manufacture of which involves innovative techniques. Also, aero-engines face up to the need of a continuous improving of its technical capabilities in terms of achieving higher efficiencies with regard to lower fuel consumption, enhanced reliability and safety. Technological viability and manufacturing costs are the key factors in the successful development of new engines. Therefore, the feasibility of enhanced aero-engines depends on the achievements of R&D activities, mainly those concerning the improvement of materials and structures.
Advanced compressor designs are critical to attain the purposes of engine manufacturers. Aircraft engines and industrial gas turbines traditionally use bladed compressor disks with individual airfoils anchored by nuts and bolts in a slotted central retainer. Nevertheless, an improvement of the component disk plus blades is the BLISK, a design where disk and blades are fabricated in a single piece. The term "BLISK" is an acronym composed of the words "blade" and "disk" (from BLaded dISK or blisk = blade integrated disk).
BLISKs are also called integrated bladed rotors (IBR), meaning that blade roots and blade locating slots are no longer required. Both designs are illustrated in Figure 1
Figure 1: Illustrations of the mechanical attachment blade-disk (left) and of a BLISK (right)
BLISKs can be produced by machining from a single forged part or by welding individual blades to a disk structure. Electron-beam and inertia welding have been used for this application (Roder et al., 2003). However, these techniques are generally not recommended in critical applications concerning fatigue (Broomfield, 1986). An interesting alternative technique is linear friction welding.
Hence, this post is devoted to this welding process and its application to manufacture BLISKs of titanium alloys. It is obvious that for such a critical application the integrity of linear friction welds must be totally demonstrated. For that reason, extensive experimental studies were carried out to find the optimum process parameters that assure the reliability of Linear friction welding for the manufacture of BLISK. These results demonstrate that linear friction welds may offer similar tensile and fatigue properties than the corresponding base materials.
1. Friction Welding
Friction welding technologies convert mechanical energy into heat at the joint to be welded. Coalescence of metals takes place under compressive contact of the parts involved in the joint moving relative to one another. Frictional heating occurs at the interface between the workpieces, raising the temperature of the material to a level suitable for forging. Friction welding is a solid state process as it does not cause melting of the parent material.
2. Rotary Friction Welding
Rotary friction welding was the first of the friction processes to be developed and used commercially. There are two process variants: direct drive rotary friction welding and stored energy friction welding. The first one is the most conventional technique and usually is simply known as “friction welding”. It consists in two cylindrical bars held in axial alignment. The moving bar is rotated by a motor which maintains an essentially constant rotational speed. The two parts are brought in contact under a pre-selected axial force and for a specified period of time. Rotation continues until achieving the temperature at which metal in the joint zone reaches the plastic state. Then, the rotating bar is stopped while the pressure is either maintained or increased to consolidate the joint.
The other variant of rotary friction welding is the stored energy process, more often called “inertia welding”. The rotating component is attached to a flywheel which is accelerated by a motor until a preset rotation speed is reached. At this point, drive to the flywheel is cut and the rotating flywheel, with stored energy, is forced against the stationary component. The resultant braking action generates the required heat for welding. Sometimes additional pressure is provided to complete the weld.
3. Linear Friction Welding
Like all the other friction welding techniques, LFW is able to join materials below their melting temperature. However, in LFW a linear reciprocating motion is the responsible of rubbing one component across the face of a second rigidly clamped part using an axial forging pressure. The amplitude of the oscillating motion is small (1 to 3 mm) and the frequency uses to be in the range of 25 to 125 Hz. The maximum axial welding stress is around 100 MPa when titanium alloys are welded and it increases to 450 MPa for nickel pieces.
BLISK PRODUCTION
BLISK machining by high-speed CNC milling machine
BLISK is one of the most original components in modern aero-engines. First used in small engines for helicopters, BLISK was introduced in the 1980’s for military airplanes engines, and it is rapidly gaining position in commercial turbofan and turboprop engines. This is due to its advantages, such as:
weight saving (usually as much as 20-30%): resulting from the elimination of blade roots and disk lugs;
high aerodynamic efficiency: because BLISK diminishes leakage flows;
eradication of the blade/disk attachment, whose deterioration by fretting fatigue is very often the life limiting feature.
Of course, BLISK has disadvantages too. The main one is the laborious, and then expensive, manufacturing and repairing processes. Also, an exhaustive quality control is required to ensure reliable performance.
Low pressure compressor of the Eurojet EJ200 Turbofan
As it was commented in the introduction of this post BLISKs can be produced by machining from a single forging or by bonding single blades to a disk-like structure. Depending on the material and also on the design, factors that in turn depend on its location in the engine, each BLISK has its particularities that determine the selection of the manufacturing process.
In the case of BLISKs produced by machining, there are also two possible paths: milling the entire airfoil or using electrochemical material removal processes.
In the case of low pressure compressor stages, where the length of the blades is a significant proportion of the diameter of the total component (disk + blades), machining the BLISK from a single forged raw part is a costly and inefficient way. Therefore, welding the blades to the disk becomes a more effective approach.
A low pressure turbine which houses the low pressure compressor in an EJ200 aero-engine
Full qualification for aero-engine application has been achieved for LFW manufacturing route. Design and manufacturing advantages derived of the fabrication of BLISKs by LFW compared to other processing routes are:
High integrity welding technique;
Low distorsion of the welded parts;
Heat affected zone of very fine grain;
Porosity free;
Possible welding of dissimilar alloys for disk and for blades;
Fabrication of large diameter BLISKs without the need for huge forged pancakes;
Tolerances in position and angles of welded blades are very accurate.
CONCLUSION
The overall conclusion drawn from the industrial experiences and research activities conducted on linear friction welding of Ti alloys for BLISK manufacturing, is that it is feasible to produce, by using linear friction welding, a dual alloy/dual microstructure BLISK with a disk optimised from the viewpoint of low cycle fatigue resistance and optimised blades for high cycle fatigue. It was further proven that it is possible to join different titanium alloys, thereby allowing customizing the blades according to the required temperature capability of a certain stage. India is in the process of mastering this complex and exclusive technology.
@jbgt90 @ranjeet @4GTejasBVR @The_Showstopper @guest11 @PARIKRAMA
@GURU DUTT @HariPrasad @JanjaWeed @litefire @AMCA @SrNair
@Nilgiri @Jamwal's
@Guynextdoor2 @DesiGuy1403
http://www.indiandefensenews.in/2016/07/idn-take-tech-scan-brief-review-of.html?m=1
Now that the Kaveri engine is back in business, it becomes imperative for us to understand what went wrong with the development of the engine.
America's General Electric, Honeywell and Pratt & Whitney; Europe's Rolls-Royce and Snecma; Russia's Klimov and NPO Saturn are the worlds premier jet engine vendors. China has designed nuclear missiles and blasted astronauts into space, but one vital technology remains out of reach. Despite decades of research and development, China, masters of cloning has so far failed to build a reliable, high performance jet engine mainly because reverse-engineering a highly complex turbofan jet engine is very difficult as it involves several complex manufacturing processes. Jet engine technologies relate to materials which includes high-temperature composites and alloys and high precision engineering, which are difficult to copy.
Years of hard work won't go waste:
By any yardstick, the Kaveri turbofan is a technologically complex power plant and deriding Gas Turbine Research Establishment (GTRE) incessantly is rather unjustified. The engine is a two spool, bypass turbofan engine having three stages of transonic low pressure compressor driven by a single stage low pressure turbine. The core turbojet engine of the Kaveri is the Kabini. The core engine consists of a six stage transonic compressor driven by single stage cooled high pressure turbine. The engine is provided with a complete annular combustor with air blast atomiser. The aero-thermo dynamics and mechanical designs of engine components were evolved using many in house and commercially developed software for solid and fluid mechanics. Its three stage transonic fan, designed for good stall margin handles an air mass flow of 78 kg and develops a pressure combustion chamber line ratio of 3:4. Kaveri engine has been designed to achieve a fan pressure ratio of 4:1 and overall pressure ratio of 27:1. These pressure parameters are claimed to be good enough to support the super cruise manoeuvres of an advanced combat aircraft. The development model is fitted with an advanced convergent-divergent variable nozzle.
TROUBLE
The project for design and development of Kaveri engine was sanctioned to achieve the interim flight standard for LCA ‘Tejas’ integration. Though the Kaveri engine was not fully meeting the requirement of LCA ‘Tejas’, it provided a platform for gas turbine technology development in the country. This is as per Press Information Bureau the media arm of the Government of India.
(i) Ab-initio development of state-of-the-art gas turbine technologies
(ii) Technical/technological complexities
(iii) Lack of availability of critical equipment & materials and denial of technologies by the technologically advanced countries
(iv) Lack of availability of test facilities in the country necessitating testing abroad
(v) Non availability of skilled/technically specialized manpower
And one of the major drawbacks the Kaveri engine faced was the reliability of its turbine blades. It also failed the high altitude tests and was too heavy for the Tejas aircraft. Modern aircraft engines must meet extreme demands for performance. Manufacturing jet engines involves state-of-the-art technologies in design, machining, casting, composite materials, exotic alloys, electronic performance monitoring, software engineering and quality control. A high performance turbofan engine will need to incorporate single crystal blade technology, integrated rotor disk and blades and super alloys of nickel and cobalt, a technology which India is yet to master.
While the Tejas needs an engine with 82-90 kN of peak thrust, the Kaveri has only managed 72 kN during flight testing in Russia. This is inadequate for the TEJAS, but the DRDO is still seeking a technological breakthrough with very limited resources. GTRE is now hopeful of upgrading the Kaveri engine to meet the needs of LCA & AMCA in the context of the vastly improved industrial support base in the country that the aero engine development program had helped create. The biggest challenge ahead of GTRE would be how to enhance the power of Kaveri without increasing its size and weight and through incorporating the single crystal turbine blade technology. Efforts are now on to improve the expertise level in the country for developing the high performance nickel and cobalt super alloys used in the manufacture of single crystal blades.
The world over not many countries have progressed ahead in making jet engines. We have made a good start and despite the delays, proved our capabilities to the best of our abilities. The lessons learnt will not go in vain. India must become self sufficient in making jet engines and our efforts must continue.
INTRODUCTION
Aircraft engines are high-technology products, the manufacture of which involves innovative techniques. Also, aero-engines face up to the need of a continuous improving of its technical capabilities in terms of achieving higher efficiencies with regard to lower fuel consumption, enhanced reliability and safety. Technological viability and manufacturing costs are the key factors in the successful development of new engines. Therefore, the feasibility of enhanced aero-engines depends on the achievements of R&D activities, mainly those concerning the improvement of materials and structures.
Advanced compressor designs are critical to attain the purposes of engine manufacturers. Aircraft engines and industrial gas turbines traditionally use bladed compressor disks with individual airfoils anchored by nuts and bolts in a slotted central retainer. Nevertheless, an improvement of the component disk plus blades is the BLISK, a design where disk and blades are fabricated in a single piece. The term "BLISK" is an acronym composed of the words "blade" and "disk" (from BLaded dISK or blisk = blade integrated disk).
BLISKs are also called integrated bladed rotors (IBR), meaning that blade roots and blade locating slots are no longer required. Both designs are illustrated in Figure 1
Figure 1: Illustrations of the mechanical attachment blade-disk (left) and of a BLISK (right)
BLISKs can be produced by machining from a single forged part or by welding individual blades to a disk structure. Electron-beam and inertia welding have been used for this application (Roder et al., 2003). However, these techniques are generally not recommended in critical applications concerning fatigue (Broomfield, 1986). An interesting alternative technique is linear friction welding.
Hence, this post is devoted to this welding process and its application to manufacture BLISKs of titanium alloys. It is obvious that for such a critical application the integrity of linear friction welds must be totally demonstrated. For that reason, extensive experimental studies were carried out to find the optimum process parameters that assure the reliability of Linear friction welding for the manufacture of BLISK. These results demonstrate that linear friction welds may offer similar tensile and fatigue properties than the corresponding base materials.
1. Friction Welding
Friction welding technologies convert mechanical energy into heat at the joint to be welded. Coalescence of metals takes place under compressive contact of the parts involved in the joint moving relative to one another. Frictional heating occurs at the interface between the workpieces, raising the temperature of the material to a level suitable for forging. Friction welding is a solid state process as it does not cause melting of the parent material.
2. Rotary Friction Welding
Rotary friction welding was the first of the friction processes to be developed and used commercially. There are two process variants: direct drive rotary friction welding and stored energy friction welding. The first one is the most conventional technique and usually is simply known as “friction welding”. It consists in two cylindrical bars held in axial alignment. The moving bar is rotated by a motor which maintains an essentially constant rotational speed. The two parts are brought in contact under a pre-selected axial force and for a specified period of time. Rotation continues until achieving the temperature at which metal in the joint zone reaches the plastic state. Then, the rotating bar is stopped while the pressure is either maintained or increased to consolidate the joint.
The other variant of rotary friction welding is the stored energy process, more often called “inertia welding”. The rotating component is attached to a flywheel which is accelerated by a motor until a preset rotation speed is reached. At this point, drive to the flywheel is cut and the rotating flywheel, with stored energy, is forced against the stationary component. The resultant braking action generates the required heat for welding. Sometimes additional pressure is provided to complete the weld.
3. Linear Friction Welding
Like all the other friction welding techniques, LFW is able to join materials below their melting temperature. However, in LFW a linear reciprocating motion is the responsible of rubbing one component across the face of a second rigidly clamped part using an axial forging pressure. The amplitude of the oscillating motion is small (1 to 3 mm) and the frequency uses to be in the range of 25 to 125 Hz. The maximum axial welding stress is around 100 MPa when titanium alloys are welded and it increases to 450 MPa for nickel pieces.
BLISK PRODUCTION
BLISK machining by high-speed CNC milling machine
BLISK is one of the most original components in modern aero-engines. First used in small engines for helicopters, BLISK was introduced in the 1980’s for military airplanes engines, and it is rapidly gaining position in commercial turbofan and turboprop engines. This is due to its advantages, such as:
weight saving (usually as much as 20-30%): resulting from the elimination of blade roots and disk lugs;
high aerodynamic efficiency: because BLISK diminishes leakage flows;
eradication of the blade/disk attachment, whose deterioration by fretting fatigue is very often the life limiting feature.
Of course, BLISK has disadvantages too. The main one is the laborious, and then expensive, manufacturing and repairing processes. Also, an exhaustive quality control is required to ensure reliable performance.
Low pressure compressor of the Eurojet EJ200 Turbofan
As it was commented in the introduction of this post BLISKs can be produced by machining from a single forging or by bonding single blades to a disk-like structure. Depending on the material and also on the design, factors that in turn depend on its location in the engine, each BLISK has its particularities that determine the selection of the manufacturing process.
In the case of BLISKs produced by machining, there are also two possible paths: milling the entire airfoil or using electrochemical material removal processes.
In the case of low pressure compressor stages, where the length of the blades is a significant proportion of the diameter of the total component (disk + blades), machining the BLISK from a single forged raw part is a costly and inefficient way. Therefore, welding the blades to the disk becomes a more effective approach.
A low pressure turbine which houses the low pressure compressor in an EJ200 aero-engine
Full qualification for aero-engine application has been achieved for LFW manufacturing route. Design and manufacturing advantages derived of the fabrication of BLISKs by LFW compared to other processing routes are:
High integrity welding technique;
Low distorsion of the welded parts;
Heat affected zone of very fine grain;
Porosity free;
Possible welding of dissimilar alloys for disk and for blades;
Fabrication of large diameter BLISKs without the need for huge forged pancakes;
Tolerances in position and angles of welded blades are very accurate.
CONCLUSION
The overall conclusion drawn from the industrial experiences and research activities conducted on linear friction welding of Ti alloys for BLISK manufacturing, is that it is feasible to produce, by using linear friction welding, a dual alloy/dual microstructure BLISK with a disk optimised from the viewpoint of low cycle fatigue resistance and optimised blades for high cycle fatigue. It was further proven that it is possible to join different titanium alloys, thereby allowing customizing the blades according to the required temperature capability of a certain stage. India is in the process of mastering this complex and exclusive technology.
I suggest a name like 'Tejaswi' or even 'Agnipath'.......would the 'Gabbar Singh' of 'Sholay' be so impactful with a name like 'Bobby Darling'??........think about it man!! 
