【機械類畢業(yè)論文中英文對照文獻翻譯】CO2激光熔透焊接時工件上及焊縫內(nèi)光致等離子體體的特性【PDF英文5頁word中文翻譯1149字3頁】【有出處】

【機械類畢業(yè)論文中英文對照文獻翻譯】CO2激光熔透焊接時工件上及焊縫內(nèi)光致等離子體體的特性【PDF英文5頁word中文翻譯1149字3頁】【有出處】,機械類畢業(yè)論文中英文對照文獻翻譯,PDF英文5頁,word中文翻譯1149字3頁,有出處,機械類,畢業(yè)論文,中英文,對照,對比,比照,文獻,翻譯,co2,激光,焊接,工件,焊縫,內(nèi)光致,等離子體,特性 Behavior of vapor／plasma within the keyhole and above the workpiece during CO2 laser penetration welding 7 Behavior of vapor／plasma within the keyhole and above the workpiece during CO2 laser penetration welding Duan Aiqin，Chen Li and Gong Shuili 段愛琴，陳俐，鞏水利 Abstract In this paper，a high—speed camera and an optical emission monitor were used to study the behavior of vapor／ plasma during CO2 laser welding of SUS304 stainless stee1．Results of optical emission from vapor~plasma show that two characteristicfrequency bands exist，100—500 Hz and 1 500—3 500 Hz．At the same time，the changing images ofvapor／ plasma and bottom pool also confirm that there are two different fluctuation frequency bands．One of the frequency bands represents the characteristic of vapor~plasma within the keyhole，and it is within 167—500 Hz．Another frequency band is within 1 500—3 500 Hz，and it obviously derives from the shielding gas．Some factors may cause these frequency differences between the keyhole plasma and the shielding gas plasma．One of them is that the vapor~plasma pressure within the keyhole will ncrease slowly． Key words CO2 laser welding，vapor／plasma，keyhole，frequency 0 Intr0ductiOn Nowadays，laser welding has been widely used in many fields，such as laser welding of aerospace compo— nents．However，it needs much higher weld quality be— cause of their applied conditions．Especially，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 process．There have been many studies about welding process stability all over the world．Revie— 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 welding．The main reason is that vapor／plasma makes stability control diffi— culty[ 一 ． Vapor／plasma is a sort of important physical phenom— enon during laser penetration welding．Because the key— hole and molten pool are difficult to be directly observed， most of studies about laser welding processes concentrated on vapor／plasma，which can indirectly show the movement of the pool and the keyhole[3-41 ．In addition，many stud— ies about vapor／plasma have been relative to monitoring weld imperfection by optical emission and acoustic emis— sion from vapor／plasma．However，physical features of va— por／plasma have not been paid a sufficient attention．For instance，whether the fluctuation frequency of vapor／plas· ma within the keyhole is as same as that above the work- piece，how vapor／plasma within the keyhole forms and e— jects，and so on．In fact，all these fundamental questions are not quite clear． This paper presents the study of vapor／plasma during CO2 laser welding by high—speed 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 mm．The laser welding performed using a 4 kW fast axial flow Q—mode CO2 laser． The images of vapor／plasma and molten pool were cap— tured by a Phantom V4．1 high-speed camera with narrow optical filters．The optical emission was acquired and cal— culated by a special plasma monitoring system．Ar 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． E—mail：duan—aiqin@tom．corn(Duan Aiqin) CHINA WELDING Vo1．17 No．4 December 2008 2 Results and discussion During CO2 laser welding of SUS304 stainless steel， the typical spectrum from vapor／plasma is shown in Fig．1．This shows that the spectral components in the range of 400—700 nm are mostly lines of Ar 11．And spec— tral lines with higher intensity are within wavelength 400—— 600 nm．These 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 vapor／plasma．Experi— 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． ／— ArⅡ50 5-204 ArⅡ 501．7164，， Ⅱ509 ．05 } Ar |． Ⅱ514．178 _ ● ．IJ ．1 1．1 I ／1 J}4． 1 l L一一I．一^．．卜I ．．J^^ 400 450 500 550 600 650 700 Wavelength／nm Fig．1 Spectrum of CO2 laser welding of stainless steel(Laser power 1 650 W and welding speed 1 m／min) 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 paper．F盯spectrum of optical emission during CO2 laser welding of SUS304 stainless steel is given in Fig．2．It is found that the frequency components of vapor／ plasma are quite complex and have not a dominant fre— quency component．However，two characteristic frequency bands exist，one is 100—500 Hz(range A)and the other is 1 500—3 500 Hz(range B)．Infrared(IR：1564 nm)e— inission from the welding process can indirectly reveal the radiation of heat．This radiation mostly comes from vapor／ plasma and molten poo1．Fig．3 is the raw time—dependent 謄g SE+3 ‘茸+3 3K~3 2K43 111+3 ‘I卜2 curve of IR optical emission measured during the same process as Fig．2．This diagram obviously reflects that the IR emission can be separated into fluctuation component and invariable component．It has been known that the heat radiation from molten pool only changes with the size and temperature of molten poo1．And 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 100——6 000 Hz band—-pass filter is mainly correlated to heat radiation from vapor／ plasma，as shown in Fig．4．Both Fig．2 and Fig．4 have almost the same distributions of frequencies．However， their intensities are quite different．For the IR emission， Frequency／Hz Fig．2 FFT spectrum of 400—600 am optical emission from vapor／plasma(Laser power 1 650 W and welding speed 1 m／min) ∞ 一 一 審_f0 Behavior of vapor／plasma 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 Fig·3 Time dependence of IR emission from vapor／plasma(Laser power 1 650 W and welding speed 1 m／min) Frequency／Hz Fig·4 FFT spectrum of IR emission from vapor／plasma(Laser power l 650 W and welding speed 1 m／min1 intensity within the range A(100—500 rlz)is two times as strong as that within the range B(1 500—3 500 Hz)．But for 400—600 nm optical emission ，intensity within the range A is nearly the same as that within the range B．It can be concluded that there are two different processes and their fluctuation frequencies are within the range A and B respectively．The 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 vapor／plasmas were observed above the workpieee through the high—speed camera with a narrow (a)Two kinds of vapor／plasmas filter．Their fluctuation frequencies are obviouslv differ— ent．Fig．5 shows several typical images of two kinds of va． por／plasmas．Fig．5a presents simultaneously two vapor／ plasmas，C area is Ar plasma image and D area is vapor／ plasma image from the keyhole ．But in Fig．5b．there is only the Ar plasma to be discovered ．However．in Fig．5c，the Ar plasma completely disappears and only the vapor／plasma from the keyhole is observed ．Therefore it could be thought that vapor／plasmas consist of two differ— ent parts deriving from the keyhole and shielding gas re— spectively．Compared with the results of optical emission ， (b)Ar plasma (C)Keyhole vapodplasma Fig·5 Different states of the vapor／plasmas(Laser power 1 650 W and welding speed 1 m／min 1 皇 0葛一0 0 占一∞ ∞葛一 A1 一0 CHINA WELDING Vo1．1 7 No．4 December 2008 the two different frequency range A and B are obviously caused by these two different vapor／plasmas．The follow— ing question is which characteristic frequency band repre— sents the vapor／plasma within the keyhole． Changing images of vapor／plasma are shown in Fig．6．One of typical fluctuating period is from 1 Ills to 5 ms，and another process is from 5 IIIS to 8 ms．In each fluctuating period，the vapor／plasma within the keyhole e jects and then disappears gradually．Frequency of the va— D【】r／plasma from the keyhole iS within 1 67—500 Hz．This can also be revealed by images of bottom pool in penetra’ tion welding process．shown in Fig．7．It can be found that the vapor／plasma 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 Vapor／plasma occurs again．And this process repeats again and again during whole welding process．The statistical data show that fluctuation frequency of the vapor／plasma from the keyhole is within 167—500 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 Fig．6 Changing images of vapor／plasma above the weld(Laser power 1 650 W and welding speed 1 m／min) 扛l ms t=2IllS f=3 Ills t=4ms ￡=6ms t=7ms t=8ms t=9Ills t=3ms — Fig．7 Changing images of bottom pool(Laser power 1 650 W and welding speed 1 m／rain) l0 HIS Behavior of vapor／plasma 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 vapor／plasma arising from the shiel— ding gas above the workpiece． The fluctuation frequency of the vapor／plasma within the keyhole is different from the shielding gas plasma a— bove the workpieee．The reason is mainly that formation of these two kinds of vapor／plasmas are quite different．The 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 rapidly．However，the formation of the vapor／plasma within the keyhole is quite different．While 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 full—penetration weld— ing．According to forming principle of two kinds of vapor／ plasmas during full—penetration welding，three factors may cause these．Firstly，because of existence of bottom key— hole，the pressure of the vapor／plasma within the keyhole will increase slowly．Most vapor／plasma within the key— hole comes from vaporization of base metal，but most shielding gas plasma derives from shielding gas heated and ionized directly．Finally，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 vapor／plasma are as follows： (1)The spectrum shows that the spectral components in the range of400—700 nm are mostly lines ofArⅡ．a(chǎn)nd most intense spectral lines are within 400—600 nm． (2)The study of optical emission from vapor／plas— ma，both for 400—600 nm and IR emission，shows that the frequency components of the vapor／plasma are quite complex and have not a dominant frequency component． However，two characteristic frequency bands exist，one is 100—500 Hz and the other is 1 500—3 500 Hz．The process correlated with 100——500 Hz frequency component has obvious heat effect． (3)Changing images of vapor／plasma and bottom pool captured by high speed camera confirm that there are two kinds of vapor／plasmas．And their fluctuation frequen- ties are obviously different．These vapor／plasmas derive from the keyhole and shielding gas respectively．The sta— tistical data show that fluctuation frequency of the vapor／ plasma in the keyhole is within 1 67—500 Hz，just as same as the resuhs of optical emission． References [1] Zhang X D．Mechanism and prevention of process instability in CO2 laser welding．Beijing：Tsinghua University，1997．(in Chinese) [2]Duley W W．Laser welding．New York：John Wiley&Sons Inc．，1998． [3]Aalderink B J，Aarts R G K M，Jonker J B，et a1．Study of the optical emission during Nd：YAG laser welding of AA5182．Congress Proceedings ICALEO，San Francisco， California，USA，October 4—7，2004：11—22． [4] Naito Y．Penetration characteristics in YAG laser and TIG arc hybrid welding，and arc and plasma／plume behavior during welding．Proceeding of Welding Association，2006，24(1)： 32—38． [5]Duan A Q，Chen L．Dynamic behavior of plasma in CO2 laser welding of stainless stee1．Transactions of the China Welding Institution，2005，26(11)：17—20．(in Chinese) [6]Duan A Q，Chen L．Molten pool and temperature field in CO2 laser welding．China Welding，2006，15(1)：30—33．