List of Symbols

Q Heat generationI Electrical currentR Ohmic resistancet TimeIR InfraredITA Instituto Tecnolgico de AeronuticaLBW Laser Beam WeldingP PressurePEEK Poly-etheretherketonePES Poly-ethersulphonePPS Poly-phenylenesulphidePEI Poly-etherimideT Temperature

Tg Glass transition temperatureTm Melting temperatureUNESP Universidade Estadual Paulista Jlio de Mesquita FilhoUSP Universidade de So Paulo

INTRODUCTION

&RQWLQXRXVEHUUHLQIRUFHGWKHUPRSODVWLFPDWUL[FRPSRVLWHlaminates have shown great promise as materials for current and IXWXUHDLUFUDIWFRPSRQHQWV:KHQFRPSDUHGWRWKHUPRVHWEHUreinforced composite laminates, thermoplastic laminates are HDVLHUWRSURFHVVDVWKH\GRQRWUHTXLUHFRPSOH[FKHPLFDOUHDF-tion nor lengthy curing process, they are easily recycled and do QRWQHHGUHIULJHUDWLRQIRUVWRUDJHGLVSOD\LQJSUDFWLFDOO\LQQLWHVKHOIOLIH7KHUPRSODVWLFFRPSRVLWHVDOVRH[KLELWYHU\ORZOHYHORImoisture uptake, which means their mechanical properties are less degraded under hot/wet conditions, not to mention their higher GDPDJHWROHUDQFHFKDUDFWHULVWLFVDQGJUHDWHUUHSDUDELOLW\SRWHQWLDODVFRPSDUHGWRWKHUPRVHWWLQJPDWUL[ODPLQDWHV1LQJet al., 2007; Sinmazelik, 2006; Jayamol et al., 1998; Mallick, 1993).

doi: 10.5028/jatm.2012.04033912

A Review of Welding Technologies for Thermoplastic Composites in Aerospace ApplicationsAnahi Pereira da Costa1, Edson Cocchieri Botelho1,*, Michelle Leali Costa2, Nilson Eiji Narita3, Jos Ricardo Tarpani4

1 Universidade Estadual Paulista Jlio de Mesquita Filho Guaratinguet/SP Brazil2 Instituto de Aeronutica e Espao So Jos dos Campos/SP, Brazil3 EMBRAER So Jos dos Campos/SP, Brazil4 Universidade de So Paulo So Carlos/SP, Brazil

Abstract: Reinforced thermoplastic structural detail parts and assemblies are being developed to be included in current aeronautic programs. Thermoplastic composite technology intends to achieve improved properties and low cost processes. Welding of detail parts permits to obtain assemblies with weight reduction and cost saving. Currently, joining composite materials is a matter of intense research because traditional joining technologies are not directly transfer-able to composite structures. Fusion bonding and the use of thermoplastic as hot melt adhesives offer an alternative to mechanical fastening and thermosetting adhesive bonding. Fusion bonding technology, which originated from the thermoplastic polymer industry, has gained a new interest with the introduction of thermoplastic matrix composites, which are currently regarded as candidate for primary aircraft structures. This paper reviewed the state of the art of the welding technologies devised to aerospace industry, including the elds that Universidade Estadual Paulista -~lio de Mesquita Filho and Universidade de So Paulo are deeply involved.

Keywords: Aircraft structural joint, Thermoplastic composite, Welding technology.

Received: 05/07/12 Accepted: 03/08/12

DXWKRUIRUFRUUHVSRQGHQFHHERWHOKR#IHJXQHVSEU'HSDUWDPHQWR GH 0DWHULDLV H 7HFQRORJLD)(* $Y $ULEHUWRPereira da Cunha, 333 Bairro Pedregulho / CEP:12.516-410 Guaratinguet/SP Brazil

J. Aerosp. Technol. Manag., So Jos dos Campos, Vol.4, No 3, pp. 255-265, Jul.-Sep., 2012 255

8QOLNH WKHUPRVHWWLQJ UHVLQV WKHUPRSODVWLFV PD\ EHUHPHOWHG DIWHU WKH\ DUH IRUPHG 7KH\PD\ DOVR EH MRLQHGXVLQJVHYHUDOGLIIHUHQWDVVHPEOLQJSURFHVVHV-RLQLQJSOD\Van important role in manufacturing of composite structures in marine, automotive and aerospace industry. Mechanical IDVWHQLQJDQGDGKHVLYHERQGLQJDUHZLGHO\XVHGWRDVVHPEOHmetals or composite components. However, there are disadvantages associated with these methods such as stress FRQFHQWUDWLRQLQGXFHGE\GULOOLQJKROHVLQPHFKDQLFDOIDVWHQ-LQJRUH[WHQVLYHVXUIDFHSUHSDUDWLRQGXULQJDGKHVLYHERQGLQJ1RZDGD\V MRLQLQJFDQEHDFKLHYHGXVLQJYDULRXVZHOGLQJPHWKRGVVXFKDVHOHFWULFUHVLVWDQFHXOWUDVRQLFYLEUDWLRQKRWplate, electromagnetic induction, dielectric/microwave and IR ZHOGLQJ0RX]DNLVet al., 2008; Botelho and Rezende, 2007; Wang and Hahn, 2007; Jones, 1994; Loos et al., 1981). Researches involving welding in composites in Brazil were LQLWLDWHGLQE\)DFXOGDGHGH(QJHQKDULDGH*XDUDWLQJXHWiRI81(63,7$DQG(VFRODGH(QJHQKDULDGH6mR&DUORVRIUSP. The work started in these universities with cooperation RI(PSUHVD%UDVLOHLUDGH$HURQiXWLFD(0%5$(5DFURP\Qin Portuguese) focused on the mechanical and thermal FKDUDFWHUL]DWLRQRIZHOGHGODPLQDWHVRI336VHPLFU\VWDOOLQHPPS thermoplastic polymer) reinforced with continuous KLJKSHUIRUPDQFHEHUV1RZDGD\V81(63LVGHYHORSLQJresistance welding technology whereas USP is advancing in IR lamp welding methodology. 7KLV SDSHU DLPHG WR H[DPLQHGLIIHUHQWZHOGLQJ WHFK-niques for thermoplastic composite laminates devised to structural aerospace applications, focusing on recent developments in this area.

HIGH PERFORMANCE THERMOPLASTICCOMPOSITES FOR AEROSPACE APPLICATIONS

The automotive industry has traditionally produced a wide range of thermoplastic parts with the advantage of shorter SURFHVVLQJWLPHVDQGIXOO\DXWRPDWHGHTXLSPHQWV5D\Botelho et al., 2005; Botelho et al., 2002; Botelho et al., 2001; Todo et al., 2000). ,QWKHODWHVJODVVDQGFDUERQUHLQIRUFHGWKHUPRSODVWLF3(,ODPLQDWHVZHUHUVWXVHGLQ)RNNHUMHWSODQH*XOIVWUHDP* DQG* EXVLQHVV MHWV DQG$LUEXV %HOXJD WUDQVSRUWDLUFUDIWDV WKHUPRIRUPHGRRULQJSDQHOV &RVWDet al., 2010; Vieille et al., 2009; Young and Ye, 2005; Botelho et al., 2003). More recently, thermoplastic composites have found utiliza-WLRQLQODQGLQJJHDUGRRUVZLQJOHWVHOHYDWRUVDLOHURQVDSV

VSRLOHUVVSHHGEUDNHVVODWVWRFLWHDIHZDSSOLFDWLRQV'H)DULDet al., 2011; Rezende et al., 2011; Chevali et al., 2010; Bates et al., 2009; Arici, 2007; Espert et al., 2004; Lee et al., 1993). A wide range of high performance thermoplastic matrices LVDYDLODEOHQRZDGD\VZLWK3((.DQG336WKHPRVWZLGHO\studied and reported. Both of them are semi-crystalline poly-mers, and crystallinity in high-performance polymers is quite LPSRUWDQWDV LWKDVDVWURQJ LQXHQFHRQ WKHLUFKHPLFDODQGmechanical properties. Crystallinity tends to increase stiffness and tensile strength while amorphous areas are more effective LQDEVRUELQJLPSDFWHQHUJ\7KHGHJUHHRIFU\VWDOOLQLW\LVGHWHU-PLQHGE\PDQ\IDFWRUVLQFOXGLQJWKHW\SHRISRO\PHUDQGWKHSURFHVVLQJFRQGLWLRQV1LQRet al., 2009; Mazur et al. 2008). Today, joining thermoplastic composite structures LV EHFRPLQJ LQFUHDVLQJO\ LPSRUWDQW VLQFH WKHUPRSODVWLFcomposite usage is rapidly replacing metallic and thermoset FRPSRVLWHFRXQWHUSDUWVWREHWWHUZLWKVWDQGW\SLFDOVWDWLFDQGfatigue loads applied to aerospace vehicles. Many welding WHFKQLTXHV KDYH EHHQ GHYHORSHG WR MRLQW XQUHLQIRUFHG DQGUHLQIRUFHGWKHUPRSODVWLFSRO\PHUVEXWHDFKWHFKQLTXHKDVLWVown advantages and pitfalls.

WELDING PROCESSES

In choosing a structural engineered material for aerospace application, an important consideration is how easy is to manu-facture, join, inspect, repair and replace it in service. One of the many advantages of thermoplastic over thermoset composites LQWKHVHFDVHVLVWKDWWKHUPRSODVWLFPDWULFHVFDQEHPHOWHGDQGreformed. In theory, using adequate temperature and P levels, a FRPSRVLWHODPLQDWHFDQEHUHVKDSHGLQGHQLWHO\ 0DQ\ QRYHO MRLQLQJ WHFKQLTXHV KDYH EHHQ SURSRVHGdeveloped and evaluated for thermoplastic applications in the ODVW\HDUV,QUHJDUGWRIXVLRQERQGLQJPHWKRGRORJLHVWKH\FDQEHVXPPDUL]HGDVIROORZVLQ)LJ

Costa, A.P. et al.

Fusion bonding

Fion ng ogn ng u ng d nius

^in ding sibon dinghsoni ding

/nduon dingDio dingii ding Zsisn ding

,o dsisu sin bonding

,o ding,o gs dingZdin ding

/nd ding >s ding

)LJXUH&ODVVLFDWLRQRISRWHQWLDOIXVLRQZHOGLQJWHFKQLTXHVIRUWKHUPRSODVWLFFRPSRVLWHV$JHRUJHVet al., 2001).

J. Aerosp. Technol. Manag., So Jos dos Campos, Vol.4, No 3, pp. 255-265, Jul.-Sep., 2012256

6HYHQPDLQZHOGLQJWHFKQLTXHVDUHGHVFULEHGEHORZDFFRUG-ing the order they appear in the schematic provided in Fig. 1.

Ultrasonic welding

Ultrasonic welding is a process in which high frequen-FLHVDUHXVHGW\SLFDOIUHTXHQFLHVUDQJHIURPWRN+]in order to induce molecular motion, thus creating friction, ZKLFKLVFRQYHUWHGWRKHDW7KHDELOLW\WRZHOGWZRRUPRUHcomponents using ultrasonic welding depends on material physical properties, frequency and amplitude of ultrasonic ZDYHDQGMRLQWGHVLJQ7KLVMRLQLQJSURFHVVFDQEHDSSOLHGLQGLVWLQFWO\WRDPRUSKRXVZHOGLQJWHPSHUDWXUHEHWZHHQWKHTg and TmDQGVHPLFU\VWDOOLQHSRO\PHUVZHOGLQJRFFXUVDWWKHPHOWLQJSRLQW/HY\et al., 2008; Siddiq and Ghassemieh, .UJHUet al. 2004; Ageorges and Ye, 2002). Figure 2 presents a schematic of an ultrasonic welding PDFKLQHXVLQJDSLH]RHOHFWULFWUDQVGXFHUE\ZKLFKWKHRVFLO-ODWLRQVDUHJHQHUDWHGE\DSSO\LQJHOHFWULFDOSRZHUDWKLJKfrequency. All ultrasonic welding systems are composed of WKHVDPHEDVLFHOHPHQWVLDSUHVVWRSXWWKHWZRRUPRUHSDUWVWREHDVVHPEOHGXQGHUPLLDQHVWRUDQYLOLQZKLFKWKHSDUWVDUHSODFHGDQGDOORZLQJWKHKLJKIUHTXHQF\YLEUD-WLRQ WREHDSSOLHG LLLDQXOWUDVRQLFVWDFNFRPSRVHGRIDWUDQVGXFHULYDFRQYHUWHU WRFRQYHUW WKHHOHFWULFDOVLJQDOLQWRDPHFKDQLFDOYLEUDWLRQYERRVWHUWRPRGLI\WKHDPSOL-WXGHRI WKHXOWUDVRQLFYLEUDWLRQYLDVRQRWURGH WRDSSO\WKHPHFKDQLFDOYLEUDWLRQWRWKHSDUWVWREHZHOGHGYLLDQultrasonic generator to provide and control the ultrasonic HQHUJ\$JHRUJHVet al..UJHUet al., 2004; Yousef-pour et al., 2004; Siddiq and Ghassemieh, 2008; Levy et al., 2008; Ageorges and Ye, 2002). 7KHDSSOLFDWLRQRIXOWUDVRQLFZHOGLQJLVTXLWHH[WHQVLYHLQPDQ\ LQGXVWULDOEUDQFKHV LQFOXGLQJHOHFWULFDOFRPSXWHU

automotive, aerospace, energy, medical and packaging. In particular, aerospace industry employs this methodology to MRLQWOLJKWZHLJKWWKHUPRSODVWLFPDWUL[FRPSRVLWHPDWHULDOVDQGDQXPEHURIVWXGLHVKDYHEHHQFRQGXFWHGWRQGRSWLPXPparameters and process windows to produce high quality ZHOGV6LGGLTDQG*KDVVHPLHK.UJHUet al., 2004). /DS MRLQW VKHDU VWUHQJWKVRIRUGHURI03DKDYHEHHQLQIRUPHG IRU 336FDUERQ EHU ODPLQDWHV ERQGHG XOWUDVRQL-FDOO\.DJDQDQG1LFKROV7KLVPHWKRGZDVDOVRXVHGE\Lockheed-Georgia to weld together thermoplastic/graphite tape PDWHULDOIRUWKH&+HUFXOHVDLUFUDIW/HY\et al., 2008).

Induction welding

Induction welding utilizes inductive heating for melting GRZQSRO\PHUPDWUL[LQWKHMRLQLQJ]RQH7KHFRPSRQHQWVWR EH ZHOGHG DUH VXEPLWWHG WR DQ DOWHUQDWLQJ HOHFWURPDJ-QHWLFHOG:KHQWKHUHDUHHOHFWULFDOO\FRQGXFWLYH ORRSV LQWKHFRPSRQHQWHJGXHWRFDUERQEHUUHLQIRUFHPHQWHGG\FXUUHQWVDUHLQGXFHGUHVXOWLQJLQHIFLHQWORFDOL]HGKHDWLQJRI WKH ODPLQDWH*ODVVEHU UHLQIRUFHPHQWV DUH HOHFWULFDOO\QRQFRQGXFWLYHVRWKDWH[WULQVLFHOHFWURPRJQHWLFVXVFHSWRUVHJPHWDOJULGVKDYHWREHLQFRUSRUDWHGWRWKHFRPSRVLWHDUUD\to convert the magnetic energy into thermal energy. In the FDVHRIIHUURPDJQHWLFPDWHULDOVK\VWHUHVLVHIIHFWVFRQWULEXWHIXUWKHUWRKHDWLQJ7KHKHDWLQJLVEDVHGRQWZRPHFKDQLVPVnamely, the energy dissipation due to Joule heating and energy dissipation due to magnetic hysteresis. The heat generation is GHVFULEHGE\(T.DJDQDQG1LFKROV, 2005):

Q = I 2 R t

7KHDERYHHTXDWLRQHVWDEOLVKHVWKDWKHDWLQJGHSHQGVRQWLPHtRKPLFUHVLVWDQFHR), and the square of the induced HOHFWULFDOFXUUHQWI7KHFXUUHQWLVLQGXFHGE\DQDOWHUQDW-LQJPDJQHWLFHOG VR LW WKHUHIRUHGHSHQGVRQ WKH LQGXFWRUJHRPHWU\WKHFRLOFXUUHQWDQGWKHGLVWDQFHWRWKHPDWHULDOLQWKHFDVHRIWKHPDWHULDOWREHZHOGHGLVQRWLQVLGHWKHFRLODVGHSLFWHGLQ)LJ0RVHUet al..DJDQDQG1LFKROV 2005; Yousefpour et al., 2004; Stokes, 2003; Velthuis and Mitschang, 2003; Hou et al., 1999). .DJDQ DQG1LFKROV UHIHU WR WKUHH FDWHJRULHV RIKHDWLQJVRXUFHVGXULQJLQGXFWLRQZHOGLQJRIEHUUHLQIRUFHGthermoplastic composites:

EHUKHDWLQJKHDWLQJLVWKHUHVXOWRI-RXOHORVVHVGXHWRWKHLQKHUHQWUHVLVWDQFHKHDWLQJRIEHUV0RVHUet al., 2008);

A Review of Welding Technologies for Thermoplastic Composites in Aerospace Applications

)LJXUH6FKHPDWLFRIDQXOWUDVRQLFZHOGLQJPDFKLQH

GLHOHFWULFK\VWHUHVLVKHDWLQJWKLQOD\HURIPDWUL[PDWHULDODWWKHERQGLQJOLQHVHSDUDWHVEHUVIURPWKHFRQVROLGDWHGlaminates. A capacitor is then created and dielectric heat-ing occurs due to the movement of charge and rotation of WKHPROHFXOHVEHWZHHQWKHEHUV6WRNHV

FRQWDFW UHVLVWDQFH KHDWLQJ KHDWLQJ RFFXUV RQ ORFDWLRQVZKHUH WKH EHUEHU FRQWDFW LV KLJK FURVVRYHU SRLQWVLQWKHFDVHRIZRYHQIDEULFV7KLVWKHRU\H[SODLQVZK\VHYHUDO IDEULF W\SHVKDYHDGLIIHUHQWKHDWLQJJHQHUDWLRQ9HOWKXLVDQG0LWVFKDQJ

)LJXUH6FKHPDWLF LOOXVWUDWLRQ RI D PDJQHWLF HOG DQG HGG\FXUUHQWJHQHUDWHGE\DHOHFWURPDJQHWLFFRLO.DJDQDQG1LFKROV

A special type of induction welding is the so-called (PDZHOGERQGLQJ +HUH WKHUPRSODVWLF SDVWHV ZLWK PHWDOSDUWLFOHV DUH H[WUXGHG LQ YDULRXV VKDSHV GHSHQGLQJ RQ WKHZHOGLQJ]RQHJHRPHWU\DV WKH\IRUPWKHERQGLQJEHWZHHQthe joining parts. The Emaweld-process is fast compared to conventional induction welding. However, due to the metal SDUWLFOHVLQWKHZHOGLQJOOHUHYHQVPDOOFUDFNVOHDGWRQRWFKHVin the welding zone thus reducing the mechanical properties RIWKHMRLQW+RXet al. 1999). $VIRUYLEUDWLRQZHOGLQJVLQJOHODSMRLQWVKHDUVWUHQJWKVRIRUGHURI03DKDYHDOVREHHQUHSRUWHGIRULQGXFWLRQZHOGHG336FDUERQEHUODPLQDWHV$GGUHVVHGLQYHVWLJDWLRQVFRPSDU-ing resistance and induction welding showed that, under equivalent heating conditions, induction welded specimens GLVSOD\HGKLJKHUVKHDUVWUHQJWKV.DJDQDQG1LFKROV *UXPPDQ$LUFUDIW/DERUDWRULHV.DJDQDQG1LFKROVUHSRUWLQGXFWLRQKHDWLQJDVKLJKO\VXLWDEOHIRUERWKWKHFRQVWUXF-WLRQDQGUHSDLURIFDUERQEHUUHLQIRUFHGWKHUPRSODVWLFSDUWVRIWKH)$DLUFUDIWKRUL]RQWDOVWDELOL]HUOHDGLQJHGJHGHPRQVWUDWLRQ

FRPSRQHQWXVLQJWKHJUDSKLWHEHUVDVWKHFRQGXFWLQJHOHPHQW6WUXFWXUDOHOHPHQWVSURGXFHGE\WKLVPHWKRGFRPSDUHGIDYRU-DEO\WRWKRVHPDQXIDFWXUHVE\DXWRFODYHFRFRQVROLGDWLRQ 7KHH[DPSOHVDERYHVKRZWKDWLQGXFWLRQKHDWLQJFDQEHXVHGIRUZHOGLQJRIWKHUPRSODVWLFEHUUHLQIRUFHGFRPSRVLWHVDQGDFFHSWDEOHERQGLQJSURSHUWLHVDUHREWDLQHG

Microwave welding

7KH SRVVLELOLW\ RI XVLQJ PLFURZDYH WR ZHOG SDUWV KDVH[LVWHGVLQFHWKHGHYHORSPHQWRIWKHPDJQHWURQLQWKHV,WVXVDJHLQWKHIUHTXHQF\UDQJHIURPWR*+]KDVEHHQreported in the literature to weld thermoplastic composites .Xet al., 2003; Wise and Froment, 2001; Chung-Yuan et al., 1999; Vodicka, 1996). 0RVWWKHUPRSODVWLFGRQRWH[SHULHQFHDWHPSHUDWXUHULVHZKHQLUUDGLDWHGE\PLFURZDYHV+RZHYHUWKHLQVHUWLRQRIDPLFURZDYHVXVFHSWLEOHLPSODQWDWWKHMRLQWOLQHDOORZVORFDOKHDWLQJWRWDNHSODFH,IWKHMRLQWLVVXEMHFWHGVLPXOWDQHRXVO\to microwaves and an applied P melting of the surrounding SODVWLFUHVXOWVDQGDZHOGLVIRUPHG6XLWDEOHLPSODQWVLQFOXGHPHWDOVFDUERQRURQHRIDUDQJHRIFRQGXFWLQJSRO\PHUVEXWZKLFKHYHULVVHOHFWHGEHFRPHVDFRQVXPDEOHLQWKHZHOGLQJSURFHVV

dielectric loss factors using focused microwave energy :LVHDQG)URPHQW$W\SLFDOVFKHPDWLFRI WKHVHWup is shown in Fig. 4. Joint elements with low-to-medium GLHOHFWULFORVVIDFWRUVUHTXLUHQRHOHFWURPDJQHWLFDEVRUEHQWPDWHULDO LQ WKHERQGOLQH7KH WHPSHUDWXUHRI WKHERQGOLQHincreases and reaches the polymer TmDVWKHERQGOLQHSDVVHVunderneath the focused microwave energy. Meanwhile, localized fusion occurs in the presence of P, resulting in a weld. Joint elements with high dielectric loss factor UHTXLUHHOHFWURPDJQHWLFDEVRUEHQWPDWHULDOVDWWKHLQWHUIDFH8QGHUPLFURZDYHUDGLDWLRQ WKHHOHFWURPDJQHWLFDEVRUEHQWPDWHULDOVDEVRUEPLFURZDYHHQHUJ\PRUHUDSLGO\WKDQMRLQWelements, and then evaporate, leaving a localized melting ]RQH DW WKH ERQGOLQH 7KH IXVLRQ ERQGLQJ RFFXUV LQ WKHERQGOLQHLQWKHSUHVHQFHRIP, producing a weld. Materials DQGVROYHQWVZLWK2+&212DQG1+ERQGVDUH W\SLFDOHOHFWURPDJQHWLF DEVRUEHQWPDWHULDOV 'XULQJ WKHZHOGLQJprocess, some of these materials evaporate and some remain LQWKHZHOGDUHD.Xet al., 2003; Wise and Froment, 2001; Chung-Yuan et al., 1999; Vodicka, 1996).

)LJXUH6FKHPDWLF VHWXS IRU PLFURZDYH KHDWLQJ

Hot plate welding

7KHUPDOZHOGLQJLVDIXVLRQERQGLQJPHWKRGRORJ\WKDWEDVL-FDOO\FRQVLVWVLQKHDWLQJSRO\PHUPDWUL[FRPSRVLWHVSLHFHVDWWKHLUinterface causing a decrease of viscosity thus allowing polymer chains to interdifuse as the surfaces are held tightly together, with IXUWKHUVORZFRROLQJIRUMRLQWFRQVROLGDWLRQ

/%: KDV EHHQ HQYLVLRQHG DV D VXLWDEOH WHFKQLTXH IRUjoining thin, as well as medium to thick thermoplastic components used in the aeronautic sector. Moreover, size, JHRPHWULFDO UHTXLUHPHQWV DQG VSHFLFDWLRQV RI DHURQDXWL-FDOSDUWVDUHFODLPHGWREHPRUHHDVLO\IXOOOHGE\DSSO\LQJ

/%:WHFKQLTXHUDWKHUWKDQDOWHUQDWLYHWHFKQRORJLHV/DEHDVet al., 2010). LBW allows joining thermoplastics, provided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joining separate parts ensuring full continuity of the resin system without the addition of an adhesive system and avoid-LQJDOVRULYHWLQVWDOODWLRQOHDGLQJWRDQXPEHURIVXEVWDQWLDOadvantages, such as cost savings, weight reduction, and PDQXIDFWXULQJF\FOH WLPHUHGXFWLRQDVZHOODVDFFHSWDEOHERQGVWUHQJWK/DEHDVet al., 2010). Only few studies of the application of LBW process for the joining of structural thermoplastic composites such as FDUERQ3((.RUFDUERQ336DUHDYDLODEOH LQ WKH OLWHUDWXUHVR WKDWUHOLDEOHDSSOLFDWLRQRI/%:WHFKQRORJ\IRU MRLQLQJprimary aeronautic parts made of thermoplastic composites VWLOO UHTXLUHV VLJQLFDQW GHYHORSPHQW DQG LQYHVWLJDWLRQ/DEHDVet al., 2010).

REMARKABLE CONCLUSIONS

)URPWKLVPDQXVFULSWLWFDQEHFRQFOXGHGWKDWQRWRQO\RQHMRLQLQJWHFKQRORJ\FDQEHDSSOLFDEOHWRDOOVLWXDWLRQV$OOMRLQ-ing methodologies showed in this work present advantages and GUDZEDFNVDQGWKH\PD\EHPRUHRUOHVVVXLWDEOHWRDSDUWLFXODU

A Review of Welding Technologies for Thermoplastic Composites in Aerospace Applications

Figure 7. Schematic of infrared lamp welding system conceived to join thermoplastic laminates highlighting the infrared radiation source, polymer parts deployment and pressing SODWHV

DSSOLFDWLRQ GHSHQGLQJ RQ LWV VSHFLF UHTXLUHPHQWV )XVLRQERQGLQJPHWKRGVSUHVHQWDKXJHSRWHQWLDOIRUYROXPHLQWHQVLYHapplications in which short processing cycles are necessary. 7KHVHERQGLQJSURFHVVHVRIIHUDGGLWLRQDODGYDQWDJHVLQFOXGLQJreduced surface preparation requirements, reprocessing, recy-FODELOLW\DQGLPSURYHGLQWHJULW\GXUDELOLW\$PRQJWKHYDULRXVWHFKQLTXHVRIWKLVFDWHJRU\WKHPRVWPDWXUHRQHVDUHXQGRXEW-edly the ultrasonic, induction and the resistance welding. Process integration is a critical aspect of joining technol-ogy. Particular requirements of each joining techniques should EHFROODWHGLQGHVLJQVFRGHVLQRUGHUWRLQWHJUDWHWKHVHUHTXLUH-ments at the very early stage of the design process. ,QVLGHRIWKLVFRQWH[WVLQFH81(63DQG863KDYHJHWinvolved in development and/or application of welding technolo-JLHVLQDHURVSDFHHOG(PSKDVLVRIWKHZRUNLQ81(63LVLQthe development of the resistance welding technology associated ZLWKWKHHQYLURQPHQWDOLQXHQFHRQWKHWKHUPDODQGPHFKDQL-cal properties of thermoplastic laminates, whereas USP is in the forefront of IR lamp welding methodology and advanced destructive and nondestructive characterization of the joints. 0RVW RI WKH GDWD LQ WKLV SDSHUZHUH REWDLQHG IURP WKHliterature, since this manuscript is a state-of-the-art review. Therefore, such data do not provide information for deals of UHSHDWDELOLW\RUUHSURGXFLELOLW\DQGWKH\DUHXVHIXORQO\IRUan initial mapping of potential techniques over a wide range RIZHOGSURFHVVLQJFRQGLWLRQVDQGSDUDPHWHUVWREHXVHGLQDHURVSDFHHOG

Acknowledgements

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$JHRUJHV &

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