Study of Heat Affected Zone (HAZ) in Friction Welding Process

Transcription

1 JOURNAL OF MECHANICAL ENGINEERING VOL. 1, NO. 1, JANUARY Study of Heat Affected Zone (HAZ) in Fiction Welding Pocess Ali. Moaefadeh Abstact Fiction welding (FW) is a elatively new welding pocess that may have significant advantages compaed to the fusion pocesses as follow: joining of conventionally non-fusion weldable alloys, educed distotion and impoved mechanical popeties of weldable alloys joints due to the pue solid-state joining of metals. Fiction welding is a solid state joining pocess which can be used to join a numbe of diffeent metals. Fiction welding achieves 100 pe cent metal-to-metal joints, giving paent metal popeties. It is the only joining pocess to do this. No addition mateial o filles ae equied and thee ae no emissions fom the pocess. The themal effect of fiction welding that specially depends on the fiction type and tempeatue field of it in wokpiece, is the main key of analysis and optimiation of this pocess, fom which the main goal of this pape has been defined. Numeical simulation of welding pocess in SIMPELC method and by ANSYS softwae fo gaining the tempeatue field of cabon steel, the effect of paamete vaiation on tempeatue field and pocess optimiation fo diffeent cases of electode done. Keywods: HAZ, Fiction, Weld, SIMPLEC, ANSYS, Tempeatue field, wokpiece Howeve, in a pactical situation metal pieces do not spontaneously bond to each othe and fom 1 piece. This is because even polished metal sufaces have a laye of oxide and suface contamination. They ae also not smooth enough fo the atoms to be bought close enough to bond. In fiction welding, the sufaces ae ubbed togethe to bun off the oxide and suface contamination layes and bing the atoms in close enough poximity to bond. I. INTRODUCTION Fiction welding is a solid state joining pocess which can be used to join a numbe of diffeent metals. Fiction welding achieves 100 pe cent metal-to-metal joints, giving paent metal popeties. It is the only joining pocess to do this. No addition mateial o filles ae equied and thee ae no emissions fom the pocess. The pocess involves making welds in which one component is moved elative to, and in pessue contact, with the mating component to poduce heat at the faying sufaces. Softened mateial begins to extude in esponse to the applied pessue, ceating an annula upset. Heat is conducted away fom the intefacial aea fo foging to take place. The weld is completed by the application of a foge foce duing o afte the cessation of elative motion. The joint undegoes hot woking to fom a homogenous, full suface, high-integity weld. Metals ae made up of positive ions floating in a sea of electons(fig.1). Faculty membe of Depatment of Mechanical Engineeing, Mahshah Banch, Islamic Aad Univesity, Mahshah, Ian a_moaefadeh@yahoo.com a.moaefadeh@mahshahiau.ac.i Tel: Fig.1. Fiction Welding Pocess Types of Fiction Welding Rotay Rotay fiction welding is the most common fom of fiction welding and has become the industy standad fo a numbe of pocesses including welding API dill pipes and dill ods, joining of axle cases and spindles and welding of piston ods. Rotay fiction welding involves holding one component still while spinning the othe component and bining the two togethe. Thompson Fiction Welding ae the wold leades in otay fiction welding having supplied ove 500 machines and have ove 45 yeas expeience. In ode fo a join to be successful the following pocesses must take place(fig.2):

2 JOURNAL OF MECHANICAL ENGINEERING VOL. 1, NO. 1, JANUARY A)Pe-Contact: D)Second Fiction: One pat is held stationay in a fixed clamp. The othe pat is held in a otating chuck The second fiction phase continues until sufficient mateial has been extuded B)Fist Fiction: E)Foge: The chuck is acceleated to speed and the pats bought into contact unde a light foce Rotation is stopped the foce inceased and the pats foged togethe C)Second Fiction: F)Weld Complete: The foce is inceased plastic mateial stats to extude fom the weld inteface The weld is complete a full aea, homogenous bond Fig.2. Fiction welding joints

3 JOURNAL OF MECHANICAL ENGINEERING VOL. 1, NO. 1, JANUARY The otay fiction welding pocess is inheently flexible, obust and toleant to diffeent qualities of mateials. The paametes involved ae the otational speed, time and foce applied. Thee ae optimum paametes fo each paticula weld that Thompson Fiction Welding have calculated though yeas of expeience. Howeve, as the pocess is inheently obust and flexible, deviations on these paametes can still give a good weld. In linea fiction welding the same pinciples apply as otay. One component is held still while the othe is moved at speed and the two ae bought togethe. The diffeence is that the moving component does not otate, it is made to oscillate lateally. The weld times fo pats ae simila no matte how big the pat. Due to the geomety, otay fiction welding does not have any fiction in the cente of the otating pat. This potion of the weld must heat up conventionally athe than due to fiction. This is not the same fo a linea fiction weld. Fiction occus thoughout the weld suface. This means that weld times ae vey quick and do not vay hugely fom pat sie to pat sie. The lagest linea fiction weld eve poduced at Thompson Fiction Welding had a weld time of aound 4 seconds. Axial momentum consevation equation: 1 ( ) ( 2 j B (2 1 ( ). (3) Enegy consevation equation: 1 ( h) ( h) 1 k h k h ( ( c c j E p j E R, p (4) II. NUMEIRCAL SIMULATION Conside the two cylindical bas with adius R ae to be welded as shown in figue 1. The bas ae assumed to be semiinfinite in diection. Ba 1 is otating with an angula velocity w, while ba 2 is stationay. At the suface of the intesection of the two bas, the coefficient of fiction It and the pessue p ae assumed to be constant and unifom thoughout the suface. The themal diffusivities ae given by al and a fo ba 1 and ba 2 espectively. Likewise, the themal conductivities and the heat tansfe coefficients ae given by k1,hl and k,h espectively. The jet velocity of inet gas aount the inteface is Vj and ambient tempeatue is Too. The diffeential Equations (1) (4) ae solved iteatively by the SIMPLEC numeical pocedue: Mass continuity equation: 1 ( ( 0 (1) Radial momentum consevation equation: 1 2 ( ( 1 j B (2 ( 2 2 (2) In the solution of Equation (1) (4), special attention needs to be put on the enegy effects on the electode suface. At the cathode suface, additional enegy flux tems should be included in Eq. (4) because of themionic cooling due to the mission of electons, ion heating, and adiation cooling [2]. Finite-Element techniques: 1-Finite elements modeling, types and popeties fo model diffeent pats. 2- The definition of mateial popeties 3- paamete definition 4- Loading 5- Bounday and initial value definition III. ADVANTAGES OF FRICTION WELDING Fiction welding has become industy standad in a numbe of applications. Some of the advantages of the pocess ae detailed below: Weld monitoing can insue 100% weld quality Fiction welding poduces a 100% coss sectional weld aea

4 JOURNAL OF MECHANICAL ENGINEERING VOL. 1, NO. 1, JANUARY Fa supeio weld integity compaed to MIG welding a) Limited opeato taining equie full automation also possible The weld cycle is fully contolled by the machine Repeatable esults Fiction welding is a solid state pocess and does not suffe fom inclusions and gas poosity. Fiction welding equied no consumables theefoe becomes moe cost effective ove time Fiction welding typically will complete a full coss sectional weld in 15% of the time it take MIG welding to poduce an 85% coss sectional weld. b) Fiction welding equies no special weld inteface pepaation welding) No post machining is needed fo fiction welded components in many cases Dissimila mateials can be joined with no alloying of the mateial IV. RESULTS AND DISCUSSION Fig.3. Conclusions fo tempeatue field: a) tempeatue field b)cabon steel tempeatue field The local heat tansfe coefficient N u(» hd / kf fo a nonotating cicula cylinde in ai steam is given by Keith and Bohn [9]and shown in figue 2. This is used in obtaining the Biot numbe vaiation aound the stationay ba. Accoding to Chiou and Lee,a moe unifom heat tansfe ate can be achieved in the case of otating cylinde in the coss-flow, theefoe the heat tansfe coefficient (Biot numbe) aound the otating ba is taken to be cicumfeentially unifom. An explicit cental diffeence scheme in space is used by selecting appopiate mesh sies and numbe of nodes in each diection to ensue accuacy of the solution. The time step sie fo the stability of the numeical backwad diffeence scheme is also detemined and used in the solution. The main objective of this study is to investigate the effect of the jet velocity on the tempeatue ise aound the vicinity of the weld inteface. Theefoe, the themal conductivity is assumed to be constant and the heat adiation is neglected in the pesent solution, although these effects can easily be implemented in the numeical scheme. Conclusions fo fluid tempeatue field cabon steel tempeatue field, completely shown in Fig.3. A peson acting as Fie Watche must be standing by with suitable fie extinguishing equipment duing and fo some time afte welding o cutting if Combustibles (including building constuction) ae within 10 metes. Combustibles ae futhe than 10 metes but can be ignited by spaks. Openings (concealed o visible) in floos o walls within 10 metes may expose combustibles to spaks. Combustibles adjacent to walls, ceilings, oofs, o metal patitions can be ignited b adiant o conducted heat. Afte wok is done, check that aea is fee of spaks, glowing embes, and flames. Any tank o dum which has contained combustibles can poduce flammable vapous when heated. Such a containe must neve be welded on o cut, unless it has fist been cleaned as descibed in AS , the S.A.A. Cutting and Welding Safety Code. This includes a thoough steam o caustic cleaning (o a solvent o wate washing, depending on the combustible's solubility), followed by puging and ineting with nitogen o cabon dioxide, and using potective equipment as ecommended in AS Wate-filling just below woking level may substitute fo ineting. Hollow castings o containes must be vented befoe welding o cutting. They can explode. Neve weld o cut whee the ai may contain flammable dust, gas, o liquid vapous. Exposed conductos o othe bae metal in the welding cicuit, o ungounded electically alive equipment can fatally shock a

5 JOURNAL OF MECHANICAL ENGINEERING VOL. 1, NO. 1, JANUARY peson whose body becomes a conducto. Ensue that the machine is coectly connected and eathed. If unsue have machine installed by a qualified electician. On mobile o potable equipment, egulaly inspect condition of tailing powe leads and connecting plugs. Repai o eplace damaged leads. Fully insulated electode holdes should be used. Do not use holdes with potuding scews. Fully insulated lock-type connectos should be used to join welding cable lengths. Teminals and othe exposed pats of electical units should have insulated knobs o coves secued befoe opeation. The output fluid tempeatue field fom nole showing heat tansfe way between electical ac and electode and envionment, with elated tempeatues is completely dawn in Fig.4. Fo study the tempeatue vaiations in plasma axis and its heat tansfe to electode accoding to diagam (Fig.5), the tempeatue field of electical ac in its symmety axis with standoff is dawn. In this diagam, in each distance fom nole to wokpiece suface, the desied tempeatue can be deived. Themal conductivity vaiation and themal specific of cabon steel ae shown in Fig.6,7. Fig.6. Themal conductivity of cabon steel Fig.4. Electical ac tempeatue field Fig.7. Themal specific of cabon steel Fig.5. The tempeatue field of electical ac in its symmety axis by standoff. Fig.8. shows a BSE image of the inclusions. White shows the aeas whee the espective element is found, and black shows a lack of that element. By compaing Fig.8, it can be seen most of the sulfuis in the inclusions, as expected.

6 JOURNAL OF MECHANICAL ENGINEERING VOL. 1, NO. 1, JANUARY distibutions fo the moving ac wee non-axisymmetic and the peaks shifted to the ac moving diection. The bittle natue of the welded pat was investigated using tensile tests, impact tests, and SEM photogaphs. Seveal heat teatments wee investigated in an attempt to estoe the ductility of the samples. No heat teatment could be found that estoed the ductility and impact stength. The 416 can be fiction welded with adequate tensile stength, but thee was a sevee loss of ductility and impact stength due to the eoientation of the sulfide inclusions. The conclusions deived fom the pesent study can be summaied as follows: 1- The tempeatue unifomity can not be achived duing a welding pocess especially when the themal conductivity of the pats to be welded is low. 2- Low Reynolds numbe yields shap ise of inteface tempeatues and deceases the time equied fo welding pocess, howeve it causes lage adial tempeatue vaiation. Fig.8. SEM (BSE) image of inclusions(500x), Location of S (500X), Location of Mn (500X) V. CONCLUSIONS Exposed conductos o othe bae metal in the welding cicuit, o ungounded electically alive equipment can fatally shock a peson whose body becomes a conducto. Ensue that the machine is coectly connected and eathed. If unsue have machine installed by a qualified electician. On mobile o potable equipment, egulaly inspect condition of tailing powe leads and connecting plugs. Repai o eplace damaged leads. Fully insulated electode holdes should be used. Do not use holdes with potuding scews. Fully insulated lock-type connectos should be used to join welding cable lengths. Teminals and othe exposed pats of electical units should have insulated knobs o coves secued befoe opeation. A 3D mathematical model fo the metal tansfe pocess in FRICTION WELDING was fomulated in this aticle. A complete model descibing the FRICTION WELDING welding pocess is developed, howeve, the computation of the tansient solution of the complete model was pohibitively time-consuming and beyond the capability of the cuent PCs. In ode to study the plasma ac inteaction with metal duing the metal tansfe pocess, some simplifications have been made. A case of an axisymmetic ac was studied fist using this 3D model fo the veification pupose. The numeical esults ageed well with the pevious two-dimensional studies. A case of a moving ac was then computed to demonstate the 3D capability of the model. The esults evealed that the timeinvaiant Gaussian assumption fo the distibutions of the ac pessue, heat flux, and cuent density on the wokpiece suface did not epesent of the eal situation. The calculated 3- High Reynolds numbe deceases the adial tempeatue vaiation fo the otating ba, but inceases the cicumfeential tempeatue vaiation especially in the stationay ba. 4- The plastic ange tempeatue needed fo welding pocess may neve be eached fo high Reynolds numbes at locations whee heat tansfe coefficient is high. 5- The ba with lowe themal conductivity should be the otating one in ode to achieve moe unifom tempeatue distibution in welding of diffeent mateials. REFERENCES [1] S. Tashio, M. Tanak, L. Muph, and J. Lowke, "Pediction of enegy souce popeties of fee-buning ac" Welding Jounal, Mach 2008, pp [2] A. Moaefadeh, "Numeical simulation of tempeatue field by Plasma ac welding Pocess in stainless steel" IREMOS Jounal, Febuay 2010, pp [3] A.Moaefadeh, " Choosing Suitable shielding gas fo themal optimiation of GTAW pocess, IREME Jounal, Sep 2010 [4] E. Goman, " New developments an application in Fiction welding " Welding Jounal, July 2004, pp [5] Y. Wang, and Q. Chen, "On-line quality monitoing in Fiction welding " Jounal of Mateials Pocessing Technology, Januay 2005, pp

7 JOURNAL OF MECHANICAL ENGINEERING VOL. 1, NO. 1, JANUARY [6] H. Kyselica, "High Fequency evesing ac switch fo plasma welding of Aluminum" Welding Jounal, May 2005, pp [7] G. Langfod, "Plasma keyhole ac welding of stuctual stainless steel joints" Welding Jounal,Feb2005, pp [8] ANSYS Help system, Analysis Guide & Theoy Refeence Ve. 9,10 Biogaphy Ali Moaefadeh Faculty membe of Depatment of Mechanical Engineeing, Mahshah Banch, Islamic Aad Univesity, Mahshah, Ian Tel: