by ANTONIO VENTRAMINI

Coolingboiling light

February 2011

Avio in Pomigliano d’Arco is an historical site inthe world of both civil and military aircraft

component production. Having made its waythrough complex corporate events, it has

never lost sight of the right path for maintainingits exact level of excellence.

by ANTONIO VENDRAMINI

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February 2011

It may seem unusual that an article that sets out to show the excellence of the Avio Group in designing and producing airplane and helicopter engines (both civil and military) begins by speaking about an aircraft that is due to land on water because its two engines have lost power. And yet this precise idea was indirectly provided by Gaetano De Chiara, engineer and director of Production Technologies for the combustors and post-combustors of these engines in the Avio premises at

Pomigliano d’Arco. This took place when, during a visit to the production area of the premises in Campania, we were shown various combustion chambers for engines called APU (Auxiliary Power Unit) and De Chiara said: “A little known fact is that all airplanes feature this type of auxiliary engine, usually placed on the tail with the functions that are typical of the starter engine in our cars:supplying energy to the services of theairplane when it is stationary on theground (obviously with the main engines

switched off) and to give energy for starting these same engines. It is an extremely small and compact engine (the diameter of the part shown in the diagram is around 400 mm), but has extremely important functions, as can be seen when last year passengers were saved after an airplane made an emergency landing on the River Hudson following the loss of power to the two main engines. While this was possible thanks to the skill of the pilot, it was also due to the performances

Combustion chamber of the APU starter for aircraft. This

departing from La Guardiaairport in New York to land

on water.

The company

HEAT SHIELD Cross-section view of the EJ200 engine

barrier in the right part

February 2011

Airbus A320, which featured various parts produced at AVIO in Pomigliano. We received numerous letters of thanks in relation to this incident from the various United States authorities and directly from Airbus”. To give readers a quick reminder of the events of January 25th 2009: Flight 1549 left La Guardia airport in New York at 3.26pm. After two minutes the two engines of the aircraft were obstructed by a number of birds that were shut inside; Captain Chesley B. Sullenberger decided to reactivate the APU engine that has

thus providing the energy necessary for controlling the aircraft like a glider and directing it, with a U-turn, to make a water landing after 3 minutes (at 3.31pm) on the River Hudson.” The swift response of the APU enabled 150 passengers and 5 crew

This explains the sign that is still hanging in testament to the past. Thesituation remained unchanged until1986 when Alfa Romeo was concededto ALENIA. In 1997, the company wasacquired by the Fiat Group and mergedwith Fiat Avio; in 2001 it was, in turn,transferred to the American investmentfund Carlyle and then, in 2006, to theEnglish fund Cenven that today holds85% of the shares. A minority share ofaround 15% is in the hands of Finmec-

indispensable in the aeronauticsection and divides its aeronauticactivities over three productive sites:

production focuses mainly on theproduction of combustion chambersfor engines, static parts of the turbinemodules and servicing of civil engines,while the second site is in Rivalta (TO).This is where the rotating parts andtransmission boxes are produced. Athird site in Brindisi works on largescalestructural parts and servicingmilitary engines.All of the AVIO production sites, follow

members to be saved”. At the end ofthe meeting, De Chiara told us that thecompany had received variouscommendations as the functionality ofthe parts installed on that APU alsocontributed to the saving of lives.

The history of the company is very longand still echoes the sign displayed atthe entrance: “Alfa Romeo Avio”, whichno one has wished to remove, almostas a wish to maintain a piece of history,not of the company per se, but of thewhole national aeronautic industry.Mr De Chiara tells us more: “Thecompany was founded in 1934 toproduce the aforementioned “radialengines” that Alfa Romeo had put onto

the Italian aeronautic tradition and are among the most internationally

the sector. So much so that today Aviois a recognized partner of the highest order of the major manufacturers of engines for civil aviation, such as General Electric, Honeywell, Pratt & Whitney, Rolls Royce and Snecma. Moreover, Avio works in all segments of civil transport: from business jets thatoperate on international routes, toairplanes for regional transport.Over the years Avio in Pomigliano has developed a considerable know-howthat has led it to be involved in produc-ing combustion chambers for new generation engines: For example, those that are featured on the latest genera-

before a more suitable expression!) in these years. We refer to the GEnx engine for the Boeing 787 and 747-8, the Trent 900 for the Airbus A380 and the SaM146 for the new airplanesproduced by the Russian Sukhoi.Today anyone who would like todevelop a new engine for the aeronau-tic sector can turn to Avio, safe in the

answer.

"In this regard . Mr De Chiara explainsto us – we have developed a new combustor that is currently in the

demonstration of the technology thatAVIO has on combustors in both a

part relative to military supply, Avio has a considerable background, so much so that it takes part in the main programmes with both design and production roles.“Among the various programmes in which we are involved – explains DeChiara – are activities both in Europe,where we work on the EJ200 engines

on the Turboprop TP400 for the cargo‘A400M’, both of worldwide promi-nence, as in the case of the latestgeneration F136 engine for the multi-purpose F35 ‘Joint Striker Fighter’ of the USAF.

The components

As mentioned, combustion chambers of engines are produced in the PomiglianoAvio premises. This fundamentalcomponent is placed between the compressor, in the front part, and the turbine, which is in the rear part. A mixture of high-pressure nebulized fuel is burned in the combustion chamber.In military airplanes, after the turbine,we have the so-called “post-burner” thatinvolves the combustion of the exhaustgases from the turbine. The post-burneris only used occasionally: for examplefor going faster than the speed of

obviously entails exceptional fuel consumption).Laser technology plays an importantrole in both the production of turbofansand turboprops: the laser

Avio also performsother integration,

inspection tasks for the propellers of the airplanes intended fornational armed forces,for which it is the company of reference.

An example of combustion chamberfor a turbojet engine

for civil airplane. Notethe thermal protection

barrier in the upperinner part

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Structural parts of the EJ200 engine produced in the Avio premises in Pomigliano

The drilling

February 2011

Drilling of a combustionchamber using the Prima NorthAmerica Laserdyne 790XL systemwith the Nd:YAG Aurora P50 source(with peak power of 50 kW)produced by the same company

basically provides the cooling micro-

the correct functioning of the warmparts of the engine (landing covers andcombustion chambers). The laser is alsoassigned to 2D and 3D trimming ofmetal plates that make up the statoryparts of the engines. Let’s look at themin detail.

Gaetano De Chiara, engineer, tells us:“Avio has been among the leadingEuropean manufacturers of statoryengine parts for airplanes, to invest inlaser technology for the production of micro-holes for cooling. In two of three-dimensional drilling systems produced by the English company AmChem, using the Nd laser sources: YAG mod. 704 produced by JK Lasers, company that was at that point part of the Canadian group Lumonics. It involved driven sources, with an average power of 400 W, able to supply a peak power of 20 kW useful for performing these perforations “on the

of these (from 4-6) occurs so that it always strikes the material in the same position.While productivity is high as a result ofthis adopted solution, this speed of execution is countered by certain limitations on the precision ofthe diameter of the holes and,consequently, in the capacity of aircreated.“Each component – explains De Chiara– undergoes the creation of a number of micro-holes by oscillating at between 30,000 and 40,000 thatrequire between 30 and 40 oscillatingwork hours. The quality of the holesis related to the various geometric and

these is undoubtedly the taper thatis intrinsic in a multiple-percussionoperation, and is increased by the factthat this takes place on moving parts.Among the second are the thickness ofmaterial recast along the walls of thehole or at its entrance and the presenceof burr at the exit. Two solutions areadopted – De Chiara continues – tocontrol the functioning of the laserholes: direct

0.5 mm, on plates with thicknesses ranging from 0.8 to 1 mm,inclusive”. “Subsequently – De Chiara

with 5 Laserdyne 790 5-axis systems byPrima North America of the PrimaIndustrie Group. These machines areequipped with Aurora P50 Nd: YAGsources (with an average power of

developed by the same Americancompany for micro-drilling applica-tions”. When dealing with perforationsproduced by following oscillatinginclinations of between 18° and 30°, itis important to bear in mind that thecombustion chambers may also bewithout covers and, therefore, these

requirement of providing a well-de-

Therefore the DOF technology is used, which involves the creation of holes using successive laser impulseswhile the structure of the chamber is placed in rotation around its own axis, with a synchronized speed with the pulse train, in such a way that the succession of these (from 4-6)

Laser trimming of a combustion chamber crownusing the Rapido system. Inthe left part is noted part ofthe shuttle table for cutting

The cut

(1) Technological Process Innovation via Engineering and Satistical KnowledgeIntegration – B. Palumbo, G. De Chiara, R. Marrone – Springer 2009

February 2011

using a pneumatic pistol, it practically

holes created: this ratio grants the

necessary, the parameters of the laser are varied in order to create holes with larger or smaller dimensions in order tocompensate the results or indirectlycontrolling the diameter withcalibrated pins. In both cases checksare performed on a sample to metallur-gically examine the sections of theholes produced”.The problem becomes complicatedwhen it involves structures of thechambers that have been housed (withplasma deposit techniques) withthermal barriers ( with thicknesses thatvary from 0.5 to 1.2 mm) in both nickeland cobalt-based superalloys. Thesebarriers are used to protect thestructures of the chambers from the

-tures and the mechanical vibrations ofthe entirety of the engine.In this case the simple DOF techniquewas not able to guarantee the desiredquality and it was, therefore, necessaryto resort to the drilling technique, withwhich each hole was produced by a microscopic circumferential cut.

holes, avoiding most ofthe defects mentioned, but has thedisadvantage of limited productivity.“The solution described – continues DeChiara – has progressed for over 6years, until, with the help of theresearchers of the Department ofAerospace Engineering at “Federico II”University in Naples, we have devel-oped a DOF drilling process using amethod based on technical statistics(1). A statistically structured approachalso granted unexpected results fromtechnical experts and the discovery ofnew settings for the application of theDOF: Fundamentally, instead ofkeeping the cause unaltered (a succession of laser pulses based on a same constant peak power), attention

-fore, operating (on the basis of statistical considerations of a large series of experimental analysis) with sequences of pulses with variable peak powers”.“This – elaborates Mr De Chiara - has allowed us to merge quality andproductivity also in the perforatingsections of combustion chambers withthe deposits of thermal barriers”.

“For us – De Chiara continues – thecutting operation is less relevant andcrucial than the drilling process.Until 2006, a very normal drillingmachine was used to cut the plate. Thissolution has lost its appeal, however,as, in addition to low rhythms and arelatively low cutting precision for ourstandards, it did not allow us to thentrim the three-dimensional structurescreated”.It was then also to resort to laser forthis phase: the choice fell to a Rapido

CP 4000 model CO2 source.This system is equipped with a simple

plate sheets and rotary table, at twostations, which hold the structuresproduced for supporting the deep-drawn pieces trim. This single systemprovides the solution for both the 2Dand 3D cutting requirements.

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