GLO BAL EN GIN EERS
&
TECH N O LO GISTS REVIEW
The super sonic par ticle deposition or cold spr ay method is a r elatively new pr ocess by w hich coating of ductile mater ials or composite mater ials with significant ductile phase content can be pr oduced w ithout significant heating of the spr ayed pow der . The kinetic ener gy of the par ticles is sufficient to pr oduce lar ge defor mations and high inter facial pr essur e and t emper atur e, w hich appear to pr oduce a solid state bond (Gilmor e et al., 2010). Super sonic par ticle Deposition (SPD) was initially developed in the mid-1980s at the Institute for Theor etical and Applied Mechanics of the Siber ian Division of the Russian Academy of Science in Novosibir sk (Gr ujicic et al., 2004). Exper iments w er e per for med in a super sonic w ind tunnel w ith ver y small par ticles entr ained in the high velocity gas str eam. The er osive behavior of this par ticle-laden flow on an object in the w ind tunnel w as studied. It was discover ed that above a par ticular minimum par ticle velocity, the abrasion caused by the par ticles changes to adhesion of the par ticles, i.e., a coating is for med on the object. This effect is enhanced by an incr ease in gas temper atur e (Stoltenhoff et al., 2002). The global maintenance, r epair and ser vices industr y in aviation industr y involve dimensional r estor ation or tooling r epair for metal mold. Standar d pr actice, manual that pr ovided by OEM of the par t will be r efer r ed and if the defect, example chipped r otor blade is exceed it r epair able limit, the par t is consider ed scr ap. In this case, Cold spr ay pr ocess can pr ovide total solution thr ough deposition the thick coating of the same mater ial with the substr ate to the chipped ar ea w ithout build inter nal str ess. This will pr ovide cost saving thr ough r e-use of the par t. Ther mal spray technique also involved in dimensional r estor ation or t ooling r epair but it lead to build up int er nal str ess in the par t, influence fatigue failur e of the par t. Application of heat in ther mal spr ay also lead to higher por osity compar e to cold spr ay technique and it influence the str ength and shor ten the life of the par t. Objective of this paper is to study cold spr ay technique as potential solution in dimensional r estor ation for aviation industr y in Malaysia.
2.0 THEORETICAL OVERVIEW
Cold spr ay pr ocess is a technology in w hich metal, composite or polymer par ticles gener ally 1-50 µm in diameter ar e acceler ated to velocities in a range betw een 300-1500 m/ s by entr ainment in a super sonic jet of
A BSTRA CT
The global Maintainence , Repairing and Overhaul (MRO) services industry is forecast to be worth US$65 billion by 2020. Malaysia plans to become a regional hub for aircraft maintenance and repairs. The country was currently ranked fifth in Asia and tenth in the world in terms of aircraft maintenance, repair and overhaul. Maintenance or repair technique play a major role in increasing useful life of the aerospace part and it increase the confident level of the user. Supersonic particle deposition has attracted serious attention because it unique thick dimensional restoration properties can be obtained by the process that is not achievable by thermal spraying. This uniqueness is due to the fact that dimensional restoration deposition takes place without exposing the spray or substrate material to high temperature and its ability to perform a bonding with the underlying material without the creation of heat affected zones which are typical of other deposition processes, thermal spray and are undesirable in many structural applications. This paper is an outcome to discuss supersonic particle deposition process as potential repair technique for aircraft metal mould, which is widely acclaimed for and on top of that, re-use of material will contribute to cost saving and in-haze the environment.
Key w ords: Cold Spray, Supersonic Particle Deposition, Repair, Metal Mould, Aircraft.
Global Engineers & Technologist s Review , Vol.3 No.2 (2013)
© 2013 GETview Limit ed. All right s reserved
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compr essed gas pow der par ticles to impact a solid sur face. The cold spr ay pr ocess utilizes Nitr ogen or Helium as a car r ier gas w ith pr essur es r anging betw een 100-500 psi. The car r ier gas is heated w ithin the gun to temper atur es up to about 600°C (Gr ujicic et al., 2004). Compr essed gas of an inlet pr essur e ent er s of an inlet pr essur e and flow s thr ough a conver ging / diver ging DeLaval-type nozzle to attain a super sonic velocity. The solid pow der par ticles ar e meter ed into the gas flow upstr eam of the conver ging section of the nozzle and acceler ated by the r apidly expanding gas to achieve higher gas flow velocities in the nozzle, the compr essed gas is often pr e-heated. These dr oplets then impact in a substr ate to give a high yield of a par tially solid deposit of contr olled shape. This deposit is cooled by the gas str eam and solidification is completed at much slow er r ates than the initial cooling r ates in spray. Par ticle bonding in cold spr ay pr ocess is due to high r ate defor mation of the par ticle, adiabatic shear instability and r equir es high par ticle velocity > Vcritical (Gr ujicic et al., 2004).
Advantages of cold spr ay technology ar e low temper atur e pr ocess, w hich it oper ate below melting point of metals and this will contr ibute to por osity contr ol below 1%. High density deposits for dimensional r estor ation can be done for thick coating at high deposition rate and fr ee for m also can be fabr icate because of compr essive r esidual str esses contr ibute fr om low temper atur e pr ocess w ithout cr eation of inter nal str ess in the par t.
3.0 CASE STUDY
Air cr aft fair ing is a str uctur e in air craft design used to reduce dr ag and impr ove appearance. Joggle is a par t in the nickel shell mold fair ing for Air bus A380 as depicted in Figur e 1(b). Pr oblem w ith this joggle ar e un-even thickness of the joggle and this w ill lead to un-even fair ing str uctur e for A380 as show n in Figur e 1(a).This joggle alr eady under go ther mal spr ay tr eatment to over come un-even thickness pr oblem but it not successful.
(a) (b)
Figure 1 : joggl e (a) under goes t her mal spr ay pr ocess, uneven t hickness and scr atches, (b) insufficient t hicknes.
This joggle is fabr icated fr om Nickel, if using cold spr ay technique to r estor e thickness to this joggle ar ea, the same mater ial must be used as show n in Figur e 2. Pow der feed stock for nickel gener ally is nickel, Ni, 99.7% basic mixtur e w ith aluminum,Al,99.5%, zinc,Zn,99.7% and alumina,Al203,92%. Par ticle size w ill be r ange -45 to
5µm. Car r ier gas temper atur e for nickel pow der coating mater ial is 350-500°C, Gun pr essur e w ill be 100-200psi w ith Gun tr aver se speed 40mm/ second and pow der feed r ate w ill be 18 gr am per minute. Standoff distance w ill be 10-25mm. Typical coating or r estor e dimensional pr oper ties using all the par ameter s above will be deposition efficiency up to 32 %, por osity volume less than 0.5 % w ith Har dness 76-79HRB and bond str ength 6500psi.
(a) (b)
Figure 2 : Joggle (a) un-even t hickness (b) additional thickness r equir ed.
4.0 CONCLUSION
Dimensional r estor ation or tooling r epair for aircr aft par t can be done using cold spr ay technology. This technology can pr ovide cost saving thr ough r e-use of par t by dimensional r estor ation pr ocess and in-haze envir onment by saving ener gy consumption. It r ecommended this technology for aviation industr y in Malaysia, in-line w ith Malaysia plans to become a r egional hub for aircr aft maintenance and r epair s and MRO ser vices industr y is for ecast to be w or th US$65 billion by2020.
Global Engineers & Technologist s Review , Vol.3 No.2 (2013)
© 2013 GETview Limit ed. All right s reserved
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5.0 ACKNOWLEDGEMENT
This w or k collabor ation Faculty of Engineer ing Technology, Univer sity Technical Malaysia Malacca, (UTeM) and CTRM Aviation Sdn.Bhd, Malaysia.
REFERENCES
[ 1] Gilmor e, D.L., Dykhuizen, R.C., Neiser , R.A., Roemer , T.J. and Smith, M.F. (1999): Par ticle Velocity and Deposition Efficiency in The Cold Spr ay Pr ocess, Jour nal of Ther mal Spr ay Technology, Vol.8, Iss.4, pp.576-582.
[ 2] Gr ujicic, M., Zhao, Z.L., de Rosset, W.S. and Helfr itch, D. (2004): Adiabatic Shear Instability based Mechanism for Par ticle/ Substr ate Bonding in the Cold-Gas Dynamic-Spr ay Pr ocess, Jour nal Mater ials & Design, Vol.25, pp.681-688.
