TRANSACTIONS OF THE CHINA WELDING INSTITUTION 2003 Vo.24 No.2


CONTENTS

1.Calibrating workpiece position based on simulated annealing
YIN Shuyan, CHEN Zhixiang, LU Zhenyang.
Abstract: Based on the analysis of practical workpiece position calibration, an algorithm for calibrating workpiece position based on simulated annealing was carried out for robot welding. By teaching 3 or more points that were far away from each other and not collinear as possible with the real robot, the position information was obtained implicitly. Then a simulated annealing algorithm was designed for calculating the transform matrix from the model to the real workpiece. It was a universal and precise algorithm. The max calculation error is under 0.02¤@mm max. To a certain extend, teaching error may affect the calibration result. Generally, the calibration error is under 0.5mm, and under 0.9mm in the extreme. If the calibration was performed before path planning, the program generated off line could be downloaded directly to the robot controller. 
Key words: workpiece position calibration; simulated annealing; robot welding

2.Diffusion bonding of TiB2 cermet to TiAl intermetallic
LI Zhuoran, CAO Jian, FENG Jicai.
Abstract: The diffusion bonding of TiB2 cermet to TiAl intermetallic was studied in this paper. The effects of bonding parameters on the microstructure of the joints and mechanical properties was investigated. The results showed that a Ti(Cu, Al)2 intermetallic layer was formed at the interface between TiB2 cermet and TiAl intermetallic when directly diffusion bonding. A TiAlNi2 intermetallic layer and two Ti, Al, Ni solid solution layers were formed at the interface by using Ni interlayer. The shear strength was 103MPa when directly diffusion bonding with bonding temperature T=1223 K, bonding time t=1.8ks and bonding pressure p=80MPa, and the shear strength was 110MPa by using Ni layer with T=1223K, t=1.8ks and p=80MPa.
Key words: TiB2 cermet; TiAl intermetallic; diffusion bonding; interface microstructure

3.Mechanism of cryogenic treatment improving electrode life for spot welding zinc coated steel sheet
WU Zhisheng, SHAN Ping, LIAN Jinrui, HU Shengsun. 
Abstract: In this paper, to improve electrode life of resistance spot welding of hot dip galvanized steel sheet, the way of deep cryogenic treatment of electrodes is put forward. Electrodes for spot welding are treated by deep cryogenic treatment with different deep cryogenic treatment parameters. Deep cryogenic treatment electrodes life experiment is carried out and the experiment results are compared with the non deep cryogenic treatment electrodes life experiment ones. The electrical conductivities of the deep cryogenic treatment electrodes and the non-deep cryogenic treatment electrodes are tested. The SEM area scanning and the SEM back scattering of the electrodes are carried out. The grain degree of deep cryogenic treatment electrodes and the non deep cryogenic treatment electrodes are observed by X Ray Diffraction. The mechanism of cryogenic treatment improving electrode life for resistance spot welding of hot dip galvanized steel plate is summarized. The experimental results show that deep cryogenic treatment makes Cr, Zr in deep cryogenic treatment electrodes emanate dispersedly and makes the grain of deep cryogenic treatment electrodes smaller than non cryogenic treatment ones, so that the electrical conductivity and the thermal conductivity of deep cryogenic treatment electrodes are improved very much ,which make electrode life for spot welding hot dip galvanized steel sheet improve obviously.
Key words: cryogenic treatment; hot dip galvanized steel sheet; spot welding; electrode life

4.Spectral information from different arc spectral window and its droplet transfer
YANG Yunqiang, ZHANG Xiaoqi, LI Junyue, LI Huan.
Abstract: Using spectrum window replace spectrum meter is a precondition to control droplet transfer with spectral information online. Two kinds of spectral window can be selected, that are window dominated by metal spectrum of the electrode and window dominated by shielding gas. Different spectrum windows reflect different information. Two spectral windows were selected and corresponding spectral information were obtained. This paper have given the experiments and analytical results of different spectral window signal, which show the window dominated by metal spectrum of electrode can precisely reflect the droplet transfer in welding arc because of the concentration of the metal vapor affected directly by droplet transfer and the window dominated by shielding gas line spectrum cannot reflect droplet transfer perfectly becasuce of the concentration of the shielding gas particle only affected indirectly by droplet transfer. It is wise to select the spectrum window where metal spectrum concentrates to detect the droplet transfer in welding arc.ª¥
Key words: welding arc; spectral window; different type; droplet transfer; contrast and analysis.

5.Study activating flux for mild steel
ZHANG Ruihua, FAN Ding, YU Shurong.
Abstract: The effect of activating fluxes on TIG welding of mild steel is studied in this paper. On the bases of analyzing the regulation that affects the penetration and shape of weld, the base component of flux be confirmed. Multi-component compounding is investigated by using orthogonal method, thus the influence pattern of the mass fractions of individual components on the penetration is obtained finally. It has marked effect on the penetration when the mass fraction of SiO2 is 40%.It has distinct effect on the penetration when the mass fraction of TiO2 and Cr2O3 less then 30%.It has distinct effect on the penetration when the mass fraction of halide is on small scale. Considering the appearance of weld, presented activating flux made up of SiO2, TiO2, Cr2O3 and halide for A TIG welding of mild steel. So that the optimal compounding can made the penetration deepened by triple, be able to weld through mild steel plate in thickness of 12¤@mm once and away without groove preparation on the normal welding conditions, appearance of weld is elegant.
Key words: mild steel; A TIG welding; activating flux; study

6.Detection of plasma sheath voltage in plasma arc welding 
SHAN Ping(School of Materials Science and Engineering, Tianjin University, Tianjin 300072,China), YI Xiaolin, HU Shengshun, LU Zhen.
Abstract£ºOn the basis of theory of plasma sheath, the paper expounds the mechanism that plate or probe has negative potential when detecting plasma efflux or plasma cloud. If the probe is located in the plasma, there is a negative electromotive force in the probe. It offers the formula to compute plasma cloud voltage. The value has only something to do with temperature and plasma component. A device of detecting plasma cloud without power supply is designed. The keyhole is formed if the sheath voltage is zero. The experiment proves the theory of the sheath. At the same time, the paper gives the right location of probe to detect the plasma cloud.ª¤
Key words£ºplasma sheath; keyhole; plasma arc welding; sheath voltage

7.Control rules and parameters of CO2 arc welding seam tracking system with ultrasonic sensor
HU Shengsun, LI Shunhua, SUN Dong, Shan Ping
.
Abstract: One kind of the CO2 arc welding seam tracking system with noncontact ultrasonic sensor is presented in this paper. The fuzzy P control theory is applied in this system. Because the control rules and parameters have most bearings on the control characteristics of the system, the control rules and parameters must be optimized to improve the system characteristics. Firstly, the fuzzy P control principle and the self-tuning fuzzy control rules are introduced. Then, the control parameters, such as fuzzy control scale factors ¦Á1, ¦Á2 and output scale factor K, are studied and defined by means of the computer simulation. And the threshold ev of fuzzy-P control is defined. The results of the experiments show that the optimized rules and parameters of fevuzzy-P control by means of the computer simulation are feasible and effective. The CO2 arc welding seam tracking system with ultrasonic sensor which fuzzy-P control is adopted can meet the need of practical welding seam tracking task.
Key word: fuzzy-P control; CO2 arc welding; seam tracking

8.Influence of welding with trailing peening on strain distribution of welded joint of high strength aluminum alloy
XU Wenli, DAI Baochang£¬LIU Xuesong£¬FANG Hongyuan£¬TIAN Xitang.
Abstract: Using experimental mechanical method of moir¨¦ analysis, strain field distributions of LY12CZ aluminum alloy welded joints under different conditions were investigated. The results show that moir¨¦ stripes of conventional welded joint just before fracture are not only few and scattered but also uneven, and the stress mainly concentrates on the poor position welded toes during the tensioning process with the relatively poor mechanical properties of welded joints. When the method of welding with trailing peening is adopted, moir¨¦ stripes of welded joint just before fracture are relatively thick and even due to the strengthening welded toes during the welding process, and fracture position transfers from the welded toes to weld, at the same time the mechanical properties of welded joints are improved greatly than conventional welding which can show that the technology of trailing peening is effective to strengthen welded joints of high strength aluminum alloy. 
Key words: tensile strain£»welding with trailing peening£»moir¨¦ analysis£»joint strengthening

9.Relation of dynamic and output characteristic in CO2 short circuit arc welding
YANG Lijun, LI Junyue, LI Huan, XUE Haitao.
Abstract: CO2 short circuit arc weld process, widely applied to manufacture industry, should be matched with such a power source system with good dynamic characteristic. Based on the careful analysis to the process dynamic characteristic and output characteristic according to the electric circuit theory and welding property of short circuiting transfer process, this paper breaks through the traditional idea, a confused and independent idea in relation to output characteristic control and dynamic characteristic control. Then a new viewpoint is put forward in which the CO2 short circuiting arc welding process, a close relation occurs between output characteristic and dynamic characteristic. For one thing, the dynamic process can not be explained on the basis of the dynamic characteristic control. For another thing, the dynamic characteristic is related to the output characteristic and restricted by that. Furthermore, an idea about the fastest responding and controllable dynamic characteristic of a welding power source has been developed. Great theoretical meaning is attached to the analysis with clear math language to the relationship between the above two kinds of characteristics.ª¥
Key words: dynamic characteristic; output characteristic; math analysis short circuit; transfer; CO2 arc welding

10.Nucleation process of resistance spot welding of aluminum alloys
CHENG Fangjie, SHAN Ping, LIAN Jinrui, HU Shengsun.
Abstract: Because the contact resistance in spot welding of aluminum alloys is random and non-continuous in distribution, and also the aluminum alloys have excellent electric and heat conduct ability, the nucleation process has the unique properties. In this paper, the nucleation process is studied by the numerical simulation and experiments, separately. The results indicates that the nucleation of aluminum alloy is significant different from the traditional spot welding process. This nucleation process could be divided into three stages: the random nucleation stage, the radial extension and merger stage and the thickness extension stage. The features of each stage are discussed. Especially, when welding with 50Hz AC power source, the former two stages will be finished within the first half cycle and a initial nugget is formed. So the first half cycle is a key factor for the quality of the welding spot. Referring to these features of each stage, some suggestions are given for the control of the spot welding of aluminum alloys.
Key words: aluminum alloys; resistance spot welding; nucleation process; numerical simulation

11.TEM analysis of microstructure in welding zone of P91 heat-resis-tant steel
LI Yajiang, ZHOU Bing, WANG Juan.
Abstract: Uner the condition of tungsten inert gas (TIG) welding+shielded metal arc welding(SMAW)technology, the microstructure in the welding zone of P91 heat resisant steel is researched by means of SEM,X-ray diffractometry (XRD) and TEM. The size of the test piece is 234mm¡Á26mm.The test results indicate that when the heat input (E) of TIG welding is 8.5~11.7kJ/cm and the heat input of SMAW is 13.3~21.0kJ/cm, the microstructure in the weld metal is composed of austenite and a little amount of ferrite. The sub-structure of austenite is crypto-crystal lath martensite, which has included regular angle. There were some spot precipitates in the martensite base which was confirmed by TEM analysis. There are some carbide (lattice constant is 1.064nm) at the boundary of grain and inside the grain, most of which is Cr23C6.ª¥
Key words: heat-resistant steel; welding; microstructure

12. Influence of laser cladding parameters on microstructure and wearª²resistance of Niª²based alloy coatings WU Ping, JIANG En'yong, ZHAO Ci, ZHOU Changzhi, TANG Xi'nan.
Abstract: Ni-based alloy coatings and Ni/WC composite coatings were prepared on Q235 steel by thermal spray and larser cladding. The influences of the laser power on the properties of coatings were widely studied. The results showed that the high quality coatings with uniform WC particles distribution, low dilution and good combination with the substrate can be obtained under the optimized laser power. In the Ni/WC composite coatings, WC particles partly dissociated at the edge, and many needle like dendrites grew epitaxially from the surface of the partially melted WC particles under the proper laser power. This can improve the microhardness of the coating and significantly combined the WC particles with the matrix alloy. When the laser power is too large, WC particles at the top of the coating were burned and remained WC particlels sank to the bottom of coating. Acoordingly, there is a sharp transition in hardness at the interface between the coating and the substrate. It easily brings about cracks and fatigue failure, and does not help to improve the wear resistance of the coating.ª¥
Key words: Ni-based alloy; laser cladding; Ni/WC composite coating; wear resistance

12.Stress field analysis of brazed joint between diamond and hard alloy
XU Chao, SUN Fenglian, QIN Youqiong, MENG Gongge.

Abstract: Using ANSYS finite element software, the stress field of brazed joint which brazing filler metal is Ag-Cu-Ti was simulated between diamond and hard alloy by the means of the transient nonlinear analysis, it is predicted that the filler metal thickness has effect on residual stress and its distribution. Accordingly, the stress field of the region of diamond, filler metal and hard alloy is obtained and then the danger region in stress field is found by the analysis to various data groups. The brazing experiment is finished in vacuum furnace, the brazed joints with different filler metal thickness are obtained by different pressure on them. The shearing strength tests indicate it isn't that the more the thickness of filler metal is, the less stress in the filler metal is. The optimum thickness of filler layer exists. The experiment results agree with the calculated results.ª¥
Key words: ANSYS; finite element; welding stress

13.Discussion and investigation on mechanism of welding residual stresses in mild steel
YOU Min, ZHENG Xiaoling, YU Haizhou.
Abstract: It is analyzed the limitation of traditional viewpoint which related the welding residual stresses only to the exitence of plastic compressive deformation in weld and base metal. The authors believe that the method used in material mechanics called "section separating method" is not suitable for analysis of transverse residual stress in butt joint and the restrained contraction of weld during cooling plays a very important pole to residual stress forming procedure. Although the actions of the residual compressive strains and the residual contractive thermal strains are equivalent for causing the welding residual stress, it is useful distinguishing them to develop new measures relieving and adjusting the welding residual stress in practical joints. It is analyzed and modified to the application of inherent strain theory that should include mainly plastic tensile strains to welding residual stress. The very high residual stresses are measured by Mathar method from the experiment of depositing a soldering pass onto the mild steel plate under the condition of the temperature rising of the base metal lower than that needed for plastic compressive strains appearing, which verified the important role of restrained contracting of weld to the mechanism of welding residual stress. It is found that the strains measured have a close relation to the environment temperature for the great difference in linear expanding coefficient between the steel and the solder.ª¥
Key words: welding residual stress; forming mechanism; restrained contraction; inherent strain; soldering

14.Granular bainite in microstructures after welding and its effects on impact toughness in STE355 steels
YIN Guiquan, ZA Xianzhu, LU Baizhong.
Abstract: The effects of technology parameters of stimulated welding thermal cycle (peak temperature Tmax and cooling time t8/5) on microstructures and impact toughness of HAZ in low carbon microalloying Ti-Nb steel STE355 were studied. The microstructures were etched by special interference technology and granular bainite and M-A constitucents were shown clearly in optical microscope. The observations were proved by electron microscope. The results show that coarsening of microstructures and decrease of toughness must take place with raising Tmax and increasing t8/5 (lowering cooling rate).Growing and thickening of ferrite in boundary and in grains and growing of M-A constituents are detrimental to toughness improvement.
Key words: welding; microalloying Ti-Nb steel; microstructure; M-A constituent; toughness

15.Solid phase welding between 40Cr and T10A after surface laser quenching
YANG Yunlin, ZHAO Ning£¬MA Kui£¬WANG Changsheng£¬WANG Wenyan£¬XU Xiangmin.
Abstract: The feasibility and the influencing factors of solid phase welding between the structural steel 40Cr and tool steel T10A were explored under the condition of the surfaces to be laser quenched. The results show that super fine grain on sarface can be gotten after the pretreatment of surface laser quenching. With the condition of pre pressed under 37¡«56.6MPa at the welding temperature of 750¡«780¡æ,the strength of joint is up to or close to that of base metal in a short time pressure welding.
Key words: 40Cr steel£»T10A steel£»solid phase welding£»laser quenching

16.Microstructure feature analysis of fusion welded joint of wrought Mg-alloy
MIAO Yugang, LIU liming, ZHAO Jie, Yu Dekai.
Abstract: In this paper, the microstructures, phase constituent and microzone analysis of AZ31B wrought Mg-alloy welded joint were investigated by optical microscope, XRD and EPMA. The results showed that the fibrous structure of AZ31B Mg-alloy disappeared; the fine crystal grain appeared in weld metal and the microstructure of heat affected zone (HAZ) obviously became coarse. The fine equiaxed grains were observed in the weld metal, the microstructure at room temperature consists of ¦ÄMg phase and compound of ¦Ã-MgnAl12. It found the Mg content in the weld metal is lower than parent metal, however, Al content is higher than parent metal, at the same time there are the segregation of Mg, Al and Zn elements in weld metal.
Key words: magnesium alloy; fusion welding; microstructure

17.Shape parameter determination of double ellipsoid heat source model in numerical simulation of high energy beam welding
WANG Yu, ZHAO Haiyan, WU Su, ZHANG Jianqiang, LIU Dianbing.
Abstract: Double ellipsoid heat source model is often used in numerical simulation of high energy beam welding. The precision and efficiency of computation are greatly influenced by the shape parameters of model. Due to lack of quantitative formula, the shape parameters have to be obtained by repeating tentative calculations by experience before. And the tentative calculation is affected by random factors to a great extent. Therefore an algorithm is presented so that the shape parameters can be calculated by empiric formula, also the algorithm is verified as valid by FEM computation. It indicates that parameters needed in simulation can be easily obtained by simple analytical calculation. By using this algorithm, the tentative calculations can be omitted, and the efficiency and precision of computation can be improved greatly.ª¥
Key words: high energy beam welding£»double ellipsoid heat source model£»analytical method£»FEM

18.Powder surfacing of carbonelectrode arc constrained by argon
ZHOU Yusheng, YU Fengfu, HE Wenxiong.
Abstract: Powder surfacing has been performed by carbon electrode arc constrained by argon in this paper. Its dilution rate is much lower than that of other arc surfacing and its transfer coefficient of alloy elements is high. It is regarded that the lower dilution rate is related to homogeneous distribution of temperature and pressure of the arc and deoxygenization of the arc gas. The depth of melt pool can be made to be homogeneous by homogeneous distribution of radial temperature and pressure£¬which leads to the lower dilution rate. The middle temperature has improved deposition efficiency and is benefit for reducing burning of alloys. The deoxygenization of the arc gas and the protection of argon are benefit for reducing burning of alloys so as to increase the transfer efficiency of alloy elements£¬and increase wettability of the bead layer to workpiece. The synthesis results are that the dilution rate of surfacing of carbon electrode arc constrained by argon is low and the transfer coefficient of alloy elements is high.
Key words: constrained arc; powders surfacing; dilution rate; transfer efficiency

19.Study on increasing density of SHS centrifugal method metal/ceramic composite pipes
YANG You, ZHAO Hongyun, WU Hua£¬YAN Li, XU Xiaodan.
Abstract: Combining the self-propagating high temperature synthesis technology (SHS method) and the centrifugal technique, a uniform ceramic layers and metal/ceramic composite pipes can be formed. The structure, phase component and distribution of ceramic layers were studied by X-ray diffraction and scanning electronic microscopy. The density, hardness and wear resistance of composite pipes were also tested. The results show that during solidification and densifying of ceramic with the addition of SiO2,finishing temperature of solidification of the SHS reaction was decreased. Thus it allowed more time for the release of the gases and improved the fluidizing of the ceramic liquid. Therefore, the density of ceramic layers was improved.ª¥
Key words: self-propagating high temperature synthesis; centrifugal technique; ceramic layers; densifying

20.Numerical simulation on temperature field in laser welding
XUE Zhongming, GU Lan, ZHANG Yanhua.
Abstract: The character of keyhole model in laser welding is deeply analyzed. Based on that, the appropriate models of heat source are applied. The quasi-steady and transient temperature fields with a moving line heat source and a gauss heat source are studied. By using MATLAB and ANSYS, laser welding temperature fields are calculated and simulated separately. Comparison between the two results has showed the precision of the models. Finally, the comparison between the experiment results and the simulated results has also validated the applicability of the keyhole model and gauss heat source model.ª¥
Key words: laser welding; temperature field; finite element; ANSYS

21.AC PMIG arc welding power source and arc length control
HANG Zengxiang, YIN Shuyan, HUANG Pengfei.
Abstract: The control mode of AC PMIG welding is a pulse with a droplet in a cycle. Pulse current is designed in arc EP time, while the other time is basic current in a cycle. Dynamic process of current is controlled quickly by the first inverter, and arc polarity is controlled by the second inverter of arc welding power source. Double closedª²loop is used in control system. Arc current is controlled by inner loop, and arc voltage and arc polarity is controlled by outer loop through 80C196KC single chip microcomputer. According to the signals of arc voltage errors and arc state, four control regulations and counting measure of control parameters are designed. Varying frequency is used to control AC pulse frequency in normal welding state. It has been proved that the welding process has high stability and even droplet transfer with the proposed control scheme.ª¥
Key words: alternating current; MIG welding; power source; control

22.Transfer behaviors of carbon and manganese of fluxª²cored wire in gas shielded arc welding
GUI Chibin, ZENG Haibin, WU ping'an, YU Chaofei.
Abstract: In this paper, the transfer behaviors of carbon and manganese of flux cored wire in gas shielded arc welding were studied. The experimental results show that the element Mn was the lose regardless of CO2 or Ar+20% CO2 shielding gas and as the oxidizability of the arc or the wire increases the lose aggravates. Therefore, by decreasing the oxidizability of the arc or the wire Mn lose can effectively decrease. For the element C,as the oxidizability of the wire increases the transfer changed from increase to lose and as the oxidizability of the arc increases the transfer increase occurs more easily. Therefore, by decreasing the oxidizability of the arc and by increasing oxidizability of the wire, the transfer increase can be restrained.ª¥
Key words: transfer behavior of element; gas shielded arc welding; flux cored wire

23.Effect of secondary thermal cycle on intragranular ferrite
YU Shengfu, YU Yangchun, XIE Mingli, LI Zhiyuan.
Abstract: The influence of secondary thermal cycle on intragranular ferrite was investigated by physical simulation method. The rule of non-metallic inclusions distribution and the their sizes and density were measured with automatic image analyzer, and the chemical compositions and the figures of non-metallic inclusions that inducted the formation nucleation of intragranular ferrite had been analyzed with transmission electron microscopy and X-ray microanalysis. The results show that secondary thermal cycle has little effect on the chemical compositions, sizes and figures and density of non-metallic inclusions that inducted the formation nucleation of intragranular ferrite. The non-metallic inclusions beneficial to nucleation and growth of intragranular ferrite during secondary thermal cycle are oxidation products of Ti, Mn, Si, Al ,such as TiO, MnO, SiO2, Al2O3 and the sulphides of Mn and Cu, such as MnS, CuS and£¨Mn£¬Cu£©S. As the cooling time from 800¤@¡æ to 500¤@¡æ is 10 seconds, the sympathetic nucleation of intragranular ferrite are found. First intragranular ferrite has large boundary energy and high density dislocation during the cooling process. These two factors are the main driving forces to the sympathetic nucleation and growth of intragranular ferrite.ª¥
Key words: intragranular ferrite; secondary thermal cycle; inclusion; sympathetic nucleation

24.Microstructure and wear resrstance of copper base alloy surfacing weld of plasma arc surfacing
CAI Youqing
Abstract: By using plasma arc method a copper base alloy surfacing weld was formed on steel Q235,with Sn-P bronze powder with nickel base alloy powder. The microstructures of surfacing weld and bond area have been studied by means of optical metallography, SEM and XRD. Hardness and wear resistance of the surfacing weld bave been measured. The result shows that the bond between surfacing weld and base metal is metallurgical bond, and bond line is clear. Surfacing wled has a low rate of dilution. The surfacing weld with copper base alloy DGCu150 consists of ¦Á-Cu phase£¬¦Ä phase£¬¦Å phase£¬Cu3P. The surfacing weld with copper base alloy DGCu150+nickel base alloy DGNi50A consists of ¦Á-Cu phase£¬¦Ä phase£¬¦Å phase£¬Cu3P,¦Ã-Ni£¬Ni2B£¬CrB£¬(Fe£¬Ni)23C6£¬ (Cu, Ni)23C6 and Fe5Si2B2. As the increasing of nickel base alloy powder, the thickness of bond area increases and hardness and wear vesistanee of the surfacing weld improved greatly.
Key words: plasma arc surfacing; copper based alloy; microstructure; wear resistance