【機(jī)械類(lèi)畢業(yè)論文中英文對(duì)照文獻(xiàn)翻譯】CO2激光熔透焊接時(shí)工件上及焊縫內(nèi)光致等離子體體的特性【PDF英文5頁(yè)word中文翻譯1149字3頁(yè)】【有出處】
【機(jī)械類(lèi)畢業(yè)論文中英文對(duì)照文獻(xiàn)翻譯】CO2激光熔透焊接時(shí)工件上及焊縫內(nèi)光致等離子體體的特性【PDF英文5頁(yè)word中文翻譯1149字3頁(yè)】【有出處】,機(jī)械類(lèi)畢業(yè)論文中英文對(duì)照文獻(xiàn)翻譯,PDF英文5頁(yè),word中文翻譯1149字3頁(yè),有出處,機(jī)械類(lèi),畢業(yè)論文,中英文,對(duì)照,對(duì)比,比照,文獻(xiàn),翻譯,co2,激光,焊接,工件,焊縫,內(nèi)光致,等離子體,特性
Behavior of vaporplasma within the keyhole and above the workpiece during CO2 laser penetration welding 7 Behavior of vaporplasma within the keyhole and above the workpiece during CO2 laser penetration welding Duan Aiqin,Chen Li and Gong Shuili 段愛(ài)琴,陳俐,鞏水利 Abstract In this paper,a highspeed camera and an optical emission monitor were used to study the behavior of vapor plasma during CO2 laser welding of SUS304 stainless stee1Results of optical emission from vaporplasma show that two characteristicfrequency bands exist,100500 Hz and 1 5003 500 HzAt the same time,the changing images ofvapor plasma and bottom pool also confirm that there are two different fluctuation frequency bandsOne of the frequency bands represents the characteristic of vaporplasma within the keyhole,and it is within 167500 HzAnother frequency band is within 1 5003 500 Hz,and it obviously derives from the shielding gasSome factors may cause these frequency differences between the keyhole plasma and the shielding gas plasmaOne of them is that the vaporplasma pressure within the keyhole will ncrease slowly Key words CO2 laser welding,vaporplasma,keyhole,frequency 0 Intr0ductiOn Nowadays,laser welding has been widely used in many fields,such as laser welding of aerospace compo nentsHowever,it needs much higher weld quality be cause of their applied conditionsEspecially,maintaining stability of weld quality for long welds or complex compo nents proves to be difficult,for laser welding of metal is an inherent unstable processThere have been many studies about welding process stability all over the worldRevie wing published study results,it can be found that most of weld quality instabilities can be caused by unstable weld ing processes,especially in CO2 laser weldingThe main reason is that vaporplasma makes stability control diffi culty 一 Vaporplasma is a sort of important physical phenom enon during laser penetration weldingBecause the key hole and molten pool are difficult to be directly observed, most of studies about laser welding processes concentrated on vaporplasma,which can indirectly show the movement of the pool and the keyhole3-41 In addition,many stud ies about vaporplasma have been relative to monitoring weld imperfection by optical emission and acoustic emis sion from vaporplasmaHowever,physical features of va porplasma have not been paid a sufficient attentionFor instance,whether the fluctuation frequency of vaporplas ma within the keyhole is as same as that above the work- piece,how vaporplasma within the keyhole forms and e jects,and so onIn fact,all these fundamental questions are not quite clear This paper presents the study of vaporplasma during CO2 laser welding by highspeed camera and optical emis sion monitor 1 Materials and welding procedure In this study,the experimental material was SUS304 stainless steel with thickness of 2 mmThe laser welding performed using a 4 kW fast axial flow Qmode CO2 laser The images of vaporplasma and molten pool were cap tured by a Phantom V41 high-speed camera with narrow optical filtersThe optical emission was acquired and cal culated by a special plasma monitoring systemAr was used as coaxial gas shielding during laser welding process一 Duan Aiqin,Chen Li and Gong Shuili,National Key Laboratory for High Density Beam Processing Technology,Beijing Aeronautical Manufacturing Research Institute,Beijing,100024 Email:duanaiqintomcorn(Duan Aiqin) CHINA WELDING Vo117 No4 December 2008 2 Results and discussion During CO2 laser welding of SUS304 stainless steel, the typical spectrum from vaporplasma is shown in Fig1This shows that the spectral components in the range of 400700 nm are mostly lines of Ar 11And spec tral lines with higher intensity are within wavelength 400 600 nmThese resuIts show that the fluctl】atinn haracter 50 000 40 000 皇 30 000 嘗20 000 10 000 O istic of optical emission signals of range from 400 nm to 600 nm can describe fluctuation of vaporplasmaExperi mental data had shown that relative intensities of optical e mission in such range of wavelength fluctuate periodically, and published study results also confirmed that it chan ges at an unstable periodicity Ar50 5-204 Ar 5017164, 509 05 Ar | 514178 _ IJ 1 11 I 1 J4 1 l L一一I一卜I J 400 450 500 550 600 650 700 Wavelengthnm Fig1 Spectrum of CO2 laser welding of stainless steel(Laser power 1 650 W and welding speed 1 mmin) Fast Fourier transform(FFr)technique is an useful method that analyzes frequencies of signals,so it was used for identifying characteristic frequency of welding proces ses in this paperF盯spectrum of optical emission during CO2 laser welding of SUS304 stainless steel is given in Fig2It is found that the frequency components of vapor plasma are quite complex and have not a dominant fre quency componentHowever,two characteristic frequency bands exist,one is 100500 Hz(range A)and the other is 1 5003 500 Hz(range B)Infrared(IR:1564 nm)e inission from the welding process can indirectly reveal the radiation of heatThis radiation mostly comes from vapor plasma and molten poo1Fig3 is the raw timedependent 謄g SE+3 茸+3 3K3 2K43 111+3 I卜2 curve of IR optical emission measured during the same process as Fig2This diagram obviously reflects that the IR emission can be separated into fluctuation component and invariable componentIt has been known that the heat radiation from molten pool only changes with the size and temperature of molten poo1And it also has been well demonstrated that,for a stable process,the size and tern- perature of molten pool are almost constant。 So FFT spectrum of IR emission by a 1006 000 Hz band-pass filter is mainly correlated to heat radiation from vapor plasma,as shown in Fig4Both Fig2 and Fig4 have almost the same distributions of frequenciesHowever, their intensities are quite differentFor the IR emission, FrequencyHz Fig2 FFT spectrum of 400600 am optical emission from vaporplasma(Laser power 1 650 W and welding speed 1 mmin) 一 一 審_f0 Behavior of vaporplasma within the keyhole and ab。ve the workpiece during CO 2 laser penetration welding 9 ; 蚤I 。 , | l 一一一一 一一 f Sample position Fig3 Time dependence of IR emission from vaporplasma(Laser power 1 650 W and welding speed 1 mmin) FrequencyHz Fig4 FFT spectrum of IR emission from vaporplasma(Laser power l 650 W and welding speed 1 mmin1 intensity within the range A(100500 rlz)is two times as strong as that within the range B(1 5003 500 Hz)But for 400600 nm optical emission ,intensity within the range A is nearly the same as that within the range BIt can be concluded that there are two different processes and their fluctuation frequencies are within the range A and B respectivelyThe process correlated with the range A has obvious heat effect,but the process correlated with the range B shows obviously irradiance phenomenon Two kinds of vaporplasmas were observed above the workpieee through the highspeed camera with a narrow (a)Two kinds of vaporplasmas filterTheir fluctuation frequencies are obviouslv differ entFig5 shows several typical images of two kinds of va porplasmasFig5a presents simultaneously two vapor plasmas,C area is Ar plasma image and D area is vapor plasma image from the keyhole But in Fig5bthere is only the Ar plasma to be discovered Howeverin Fig5c,the Ar plasma completely disappears and only the vaporplasma from the keyhole is observed Therefore it could be thought that vaporplasmas consist of two differ ent parts deriving from the keyhole and shielding gas re spectivelyCompared with the results of optical emission , (b)Ar plasma (C)Keyhole vapodplasma Fig5 Different states of the vaporplasmas(Laser power 1 650 W and welding speed 1 mmin 1 皇 0葛一0 0 占一 葛一 A1 一0 CHINA WELDING Vo11 7 No4 December 2008 the two different frequency range A and B are obviously caused by these two different vaporplasmasThe follow ing question is which characteristic frequency band repre sents the vaporplasma within the keyhole Changing images of vaporplasma are shown in Fig6One of typical fluctuating period is from 1 Ills to 5 ms,and another process is from 5 IIIS to 8 msIn each fluctuating period,the vaporplasma within the keyhole e jects and then disappears graduallyFrequency of the va D【】rplasma from the keyhole iS within 1 67500 HzThis can also be revealed by images of bottom pool in penetra tion welding processshown in Fig7It can be found that the vaporplasma starts to eject from the bottom pool f t=l ms),and then gradually decrease until disappearance(t 3 ms)The next image(t=4 ins)clearly shows that the Vaporplasma occurs againAnd this process repeats again and again during whole welding processThe statistical data show that fluctuation frequency of the vaporplasma from the keyhole is within 167500 Hz,just as same as the results of optical emission =1 ms t=2InS t=3ms t=4ms t=5InS t=6mS t=7ms f=8ms =9IllS 拄10ms Fig6 Changing images of vaporplasma above the weld(Laser power 1 650 W and welding speed 1 mmin) 扛l ms t=2IllS f=3 Ills t=4ms =6ms t=7ms t=8ms t=9Ills t=3ms Fig7 Changing images of bottom pool(Laser power 1 650 W and welding speed 1 mrain) l0 HIS Behavior of vaporplasma within the keyhole and above the workpiece during CO2 laser penetration welding ll The physical process associated with frequency of the range B has been discussed in the other article 。which showed the features of vaporplasma arising from the shiel ding gas above the workpiece The fluctuation frequency of the vaporplasma within the keyhole is different from the shielding gas plasma a bove the workpieeeThe reason is mainly that formation of these two kinds of vaporplasmas are quite differentThe shielding gas plasma is caused by the process,which gas is heated to high temperature and then ionizes rapidly When its pressure reaches to a certain value,the plasma will explode and then disappear rapidlyHowever,the formation of the vaporplasma within the keyhole is quite differentWhile laser beam acts on workpiece,vaporiza tion will generate within the keyhole;then the vapor is heated to temperature higher than the boiling point;finally heated vapor explodes and ejects from both top and bottom 0f the weld under the condition of fullpenetration weld ingAccording to forming principle of two kinds of vapor plasmas during fullpenetration welding,three factors may cause theseFirstly,because of existence of bottom key hole,the pressure of the vaporplasma within the keyhole will increase slowlyMost vaporplasma within the key hole comes from vaporization of base metal,but most shielding gas plasma derives from shielding gas heated and ionized directlyFinally,higher vaporization pressure can be remained in the keyhole,but shielding gas plasma is in free and explodes at lower pressure 3 Conclusions For CO,laser welding of SUS304 stainless steel, some conclusions about vaporplasma are as follows: (1)The spectrum shows that the spectral components in the range of400700 nm are mostly lines ofArand most intense spectral lines are within 400600 nm (2)The study of optical emission from vaporplas ma,both for 400600 nm and IR emission,shows that the frequency components of the vaporplasma are quite complex and have not a dominant frequency component However,two characteristic frequency bands exist,one is 100500 Hz and the other is 1 5003 500 HzThe process correlated with 100500 Hz frequency component has obvious heat effect (3)Changing images of vaporplasma and bottom pool captured by high speed camera confirm that there are two kinds of vaporplasmasAnd their fluctuation frequen- ties are obviously differentThese vaporplasmas derive from the keyhole and shielding gas respectivelyThe sta tistical data show that fluctuation frequency of the vapor plasma in the keyhole is within 1 67500 Hz,just as same as the resuhs of optical emission References 1 Zhang X DMechanism and prevention of process instability in CO2 laser weldingBeijing:Tsinghua University,1997(in Chinese) 2Duley W WLaser weldingNew York:John Wiley&Sons Inc,1998 3Aalderink B J,Aarts R G K M,Jonker J B,et a1Study of the optical emission during Nd:YAG laser welding of AA5182Congress Proceedings ICALEO,San Francisco, California,USA,October 47,2004:1122 4 Naito YPenetration characteristics in YAG laser and TIG arc hybrid welding,and arc and plasmaplume behavior during weldingProceeding of Welding Association,2006,24(1): 3238 5Duan A Q,Chen LDynamic behavior of plasma in CO2 laser welding of stainless stee1Transactions of the China Welding Institution,2005,26(11):1720(in Chinese) 6Duan A Q,Chen LMolten pool and temperature field in CO2 laser weldingChina Welding,2006,15(1):3033
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機(jī)械類(lèi)畢業(yè)論文中英文對(duì)照文獻(xiàn)翻譯
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【機(jī)械類(lèi)畢業(yè)論文中英文對(duì)照文獻(xiàn)翻譯】CO2激光熔透焊接時(shí)工件上及焊縫內(nèi)光致等離子體體的特性【PDF英文5頁(yè)word中文翻譯1149字3頁(yè)】【有出處】,機(jī)械類(lèi)畢業(yè)論文中英文對(duì)照文獻(xiàn)翻譯,PDF英文5頁(yè),word中文翻譯1149字3頁(yè),有出處,機(jī)械類(lèi),畢業(yè)論文,中英文,對(duì)照,對(duì)比,比照,文獻(xiàn),翻譯,co2,激光,焊接,工件,焊縫,內(nèi)光致,等離子體,特性
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