Analysis and development of aluminum alloy resistance spot welding technology for car bodyZHONG Lihui，HAN Lijun，GUO Yuanbo

Abstract： This article introduces the speciality of aluminum alloy spot welding technology，the structure and characteristics of equipment，and the requirements of aluminum alloy spot welding technology on media，materials，production fixtures and the related auxiliary equipment. The relevant factors influencing the weldability of aluminum spot welding were analyzed. The key influencing factors of aluminum spot welding quality were obtained，through the analysis and testing of equipment welding polarity， power frequency，end face shape and material of electrode cap， welding control mode and welding parameters，etc.. It can provide the innovative directions and methods for improving the spot welding quality of aluminum alloys，prolonging the electrode caps life. It provides the experience for the development of technology in the automotive industry.

Key words： aluminum alloy resistance spot welding;AMF Mode-Force;welding parameters;nugget;crack

Analysis of the influence of stainless steel cladding without preheating on the crack sensitivity of SA-508Gr.3 Cl.1

ZHANG Yabin，LUO Ying，YANG Min，WANG Xiaobin，LI Yuguang，CHEN Haibo，YANG Zhihai（Science and Technology on Reactor System Design Technology Laboratory，Nuclear Power Institute of China，Chengdu 610213，China）. pp 10-15

Abstract： To analysis the influence of cladding without preheating on the crack sensitivity of base metal，the alloy content and heat treatment is investigated by cladding test with parameters for actual product，combined with the mecha-nism of crack occurrence. Research indicates that compared with SA-508Gr.2 Cl.1，content of harden element is reduced and hydrogen is strictly controlled for SA-508Gr.3 Cl.1，which reduces the sensitivity of SA-508Gr.3 Cl.1 to re-heating crack and hydrogen induced crack. Transition cladding of SA-508Gr.3 Cl.1 with preheating and post-heating or stress relieving heat treatment reduces the sensitivity of hydrogen induced crack again. Corrosion-resistant lay of cladding without preheat has little influence on the heat affected zone and base metal. The result of liquid penetrant test and magnetic test indicates that no micro crack exists at the interface of base metal and cladding as well as 3 mm under cladding. The research above concludes that corrosion-resistant cladding without preheating will not increase the risk of under-clad crack of low alloy steel base metal and heat affected zone，reduce the high temperature time for cladding and reduce the probability of hardening phase，which in all make the quality of cladding more reliable.

Key words：stainless steel;cladding without preheating;crack sensitivity;sublayer crack;reactor pressure vessel（RPV）

Sigma phase in tube joints of austenitic heat-resistant steels for ultra supercritical boilers

SUN Xian（Institute of Welding Consumables，Taiyuan Unive-rsity of Technology，Taiyuan 030024，China）. pp 16-25

Abstract： The sigma phases in tube joints of austenitic heat-resistant steels for power boilers were reviewed. The results show that σ phases with different morphologies were precipi-tated in the austenitic heat-resistant steel joints after high temperature aging. There are two conditions for the formation of the σ phase，one is the composition factor，and the other is the temperature factor. Among the factors influencing the formation of σ phase，the influence of chemical composition is very critical and complex;the amount of σ phase precipitation increases with the increase of aging temperature and time;the excessive heat input has a tendency to promote the precipitation of σ phase. After the sample undergoes high temperature creep，the σ phase with network distribution appears in the HAZ coarse grain region，and the creep fracture strength of the joint is significantly reduced. Optimizing the chemical composition of the weld is the necessary condition to control the formation of σ phase in the weld，and reasonable heat input and its technological measures are the sufficient conditions to control the formation of σ phase in the joints.

Key words： sigma phase;tube joint;austenitic heat-resistant steel;power boilers;creep properties

Analysis on microstructure and mechanism of high temperature oscillation heat treatment after friction stir welding

DONG Fengbo1，2，F(xiàn)ENG Xiaosong1，LUO Chuanhong3，HUANG Chuanzhen2，LIU Dashuang4（1.Shanghai Aerospace Equipm-ents Manufacturer Co.，Ltd.，Shanghai 200245，China;2.School of Mechanical Engineering，Shandong University，Jinan 250061，China;3.School of Power and Mechanical Engineering，Wuhan University，Wuhan 430072，China;4.School of Materials Science and Engineering，Jiangsu University of Science and Technology，Zhenjiang 212003，China）. pp 26-29

Abstract： Friction stir welding （FSW） was used to weld 2219-O aluminium alloy. The welded joints were treated by high temperature oscillating solid solution heat treatment. The mechanism of abnormal grain growth of FSW joints was studied by analyzing the microstructures before and after heat trea-tment，and the corresponding restraining measures were put forward. The results show that the thermal stability of the weld formed by FSW is poor，the grain is easy to reheat and grow，and the grain size after conventional heat treatment reaches millimeter level. High temperature oscillating solid solution heat treatment around the lower limit of solution temperature can effectively restrain the formation of coarse grains. When the temperature oscillation amplitude is greater than 90 ℃，the grain size of the nugget is about 20 μm in diameter.

Key words：FSW;microstructure;high temperature osci-llation;thermal instabilityStudy on microstructure and mechanical prope-rties of the 6005A-5083 aluminum alloy welded joint

PAN Baiqing，DING Hao，LIU Xiong，WANG Xiangdong（Manufacturing center，CRRC Times Electric Co.，Ltd.，Zhuzhou 412001，China）. pp 30-38

Abstract： In order to improve the quality and reliability，a series of experiments including microstructure observation，room temperature tensile tests，hardness tests and fatigue tests were carried out on 6005A-5083 aluminum alloy arc welded joints. The results show that the 6005A-5083 welded joints are well formed without obvious defects. The slightly Mg segregation is observed near 6005A fusion zone while the microstructure and alloying elements distribute evenly in the 5083 fusion zone. The mean tensile strength，yield strength and elongation of the welded joints are 181 MPa，115 MPa and 7.2%，respectively. The tensile fracture morphology shows ductile characteristic. The fatigue limit obtained through S-N curve is more than 75 MPa. The width of the weld seam is about 10 mm and that between the weld seam and heat affected zone near 5083 base metal is also approximately 10 mm. Whereas the width between the weld seam and heat affected zone near 6005A base metal is about 35 mm. An obvious softening zone is determined in the heat affected zone near 6005A base metal，which might be the weakness point of this joint.

Key words： 6005A-5083 welded joints;microstructure;mechanical properties;argon arc weldingResearch on temper bead welding procedure test of the low alloy steel for reactor pressure vesselJIN Liang1，2，KUANG Yanjun2，HUANG Tengfei2，SUN Guang2，QIU Zhensheng2，CHEN Liang2（1.State Key Laboratory of Nuclear Power Safety Monitoring technology and Equipment，Shenzhen 518172，China;2.China Nuclear Power Design Co.，Ltd.，Shenzhen 518172，China）. pp 39-43

Abstract： The conventional postweld heat treatment （PWHT） can not be applied to the key equipment of nuclear power plant after repair welding during service. In order to solve this problem，a mechanized gas tungsten arc welding （GTAW） is used for temper bead welding procedure test of the low alloy steel for reactor pressure vessel under the preheating conditions at room temperature and 150 ℃ respec-tively，and then the microhardness，microstructure and impact toughness of the heat affected zone （HAZ） are tested. The results show that the microhardness can be effectively reduced by properly controlling the heat input ratios of the first three layers，and the tempered sorbite structure with good compreh-ensive properties can be obtained in the HAZ. Both the impact absorption energies at 0 ℃ and 20 ℃ of the HAZ of the temper bead under the preheating conditions at room temperature are higher than the design requirements.

Key words： reactor pressure vessel;temper bead;heat affected zone;microstructureEffects of welding heat input on the properties of 25Cr35NiNb+microalloyed furnace tube welded joint（1.Hefei General Machinery Research Institute Co.，Ltd.，National Engineering Technical Research Center on Pressure Vessels and Piping Safety，Hefei 230031，China;2.Special Equipment Inspection Station of Hefei General Machinery Research Institute Co.，Ltd.，Hefei 230031，China）. pp 44-47，78

Abstract： In this paper， six groups of welding heat input were used to weld the 25Cr35NiNb+microalloyed ethylene cracking furnace tubes. The weld structure and high temperature durability of each group of welding heat input were studied. The results show that under the condition of 1 050 ℃ and 25 MPa，when the welding heat inputs are 9 kJ/cm and 11 kJ/cm，the high temperature lasting fracture time are 132 h and 119 h respectively. When the welding heat inputs are 6 kJ/cm，8 kJ/cm，12 kJ/cm and 16 kJ/cm， the high temperature lasting fracture time are 78 h，84 h，105 h and 109 h respectively. When the range of welding heat inputs is 9～11 kJ/cm，the 25Cr35NiNb+microalloyed furnace tube welding joint can obtain longer high temperature rupture time. The microstructure observation shows that the microstructure of weld metal is obviously different under different welding heat input，which is the main reason for the change of high temperature durability of welded joint.

Key words： ethylene cracking furnace tube;welding heat input;weld structure;high temperature durabilityFillet welds recognition based on inter-frame matching denoisingXIE Sheng，WEI Xin，LIANG Ziming（School of Electrome-chanical Engineering，Guangdong University of Technology，Guangzhou 510006，China）. pp 48-53

Abstract： There is a lot of noise interference in the welding image，and processing it is the premise of weld recognition. To deal with the image denoising problem of passive visual weld tracking system，a denoising method based on inter-frame matching is proposed. Through combining the ORB（Oriented FAST and Rotated BRIEF）algorithm with the RANSAC（Random Sample Consensus） algorithm，the single response matrix between the two frames of images is obtained，and the welding parts in the two frames are aligned by this method. By using the gray level replacement of the image between frames，the spatter area is replaced by the welding piece image to obtain the weld image without spatter. Aiming at the interference of the straight line of the edge of the welding piece in the fillet welding，three straight line fitting algorithms， least square method，hough transform and RANSAC，are compared. The results show that the RANSAC algorithm can better resist the interference of a large number of outliers and the precision can be up to 2 pixels，which can meet the requirement of weld tracking.

Key words： seam tracking;passive vision;fillet weld;feature matching;linear fittingStudy on plasma surfacing technology of nickel base alloy for a 20CrNiMo componentCHEN Xingdong1，2，GUO Yang1，2，HUANG Lan1，2，HUANG Tao1，2，HUANG Li1，2，WANG Dayong1，2（1.Dongfang Turbine Co.，Ltd. of Dongfang Electric Corporation，Deyang 618000，China;2.State Key Laboratory of Long-Life High-temperature Materials，Deyang 618000，China）. pp 54-59

Abstract：In this paper，the hardfacing technology of nickel based cemented carbide layer prepared by plasma powder spray welding on a 20CrNiMo product is studied，and the PT，microstructure，hardness and SEM scan are analyzed. The experimental results show that the preparation procedure of cemented carbide layer has good repeatability，smooth bond line and no defects. There is a precipitate reducing band about 100 μm away from the bond line，a 2.5 μm wide white bright band at the bond line， and a about 100～200 μm wide diffusion band at the side of the base metal of the bond line. The microstructure of the diffusion band is a mixture of pearlitic ferrite and WC. Through SEM-EDS analysis，the microstructure of the welding layer is composed of γ - Ni solid solution matrix and interdendritic carbide eutectic structure. The hardness testing of the hardfacing layer is evenly distributed，and the hardness meets the requirements. At the same time，the welding layer has the characteristics of work hardening.

Key words： plasma spray welding;WC;nickel base cem-ented carbide;microstructure

Analysis on the formulation of international standard （ISO 9606-1） welder examination itemsSHAO Hui（Harbin Welding Training Institute，WTI Harbin，Harbin 150046，China）. pp 60-64，83

Abstract： According to the ISO 9606-1（2017） of the fusion welder examination standards for steel，it analyzes how to for-mulate welder examination items，which aims to help companies correctly interpret the ISO 9606-1 standards and formulate reasonable welder examination items to meet the requirements of personnel qualification in the welding system certification of companies. This paper makes a comprehensive and detailed analysis on the selection of welder examination standard， welding method，specimen type，weld type，base metal and welding filler material coverage，butt weld cladding metal thickness coverage，fillet weld material thickness coverage，pipe outer diameter coverage，welding position and weld details，in combination with specific examples. The responsible personnel in charge of welding can choose reasonable and correct welder examination items according to the specific analysis results，so as to achieve the best economy.

Key words： international standard ISO 9606-1;welder qualification examination;formulation of items

Analysis of overproof for leakage rate of welding line in high temperature alloy measuring pressure conduitSHI Chunshan1，2，GUO Dazhi2（1.Sichuan Aerospace Sunkun Technology Co.，Ltd.，Chengdu 610100，China;2.Sichuan Boiler Senior Technical School，Chengdu 610400，China）. pp 65-68

Abstract： A high temperature alloy pressure conduit in helium mass spectrometer leak detection，the side seam leakage rate，by using chemical composition analysis，metallographic examination and fracture analysis method analyzes the causes of leakage rate exceeds bid. The results showed that the inner surface of the weld was seriously oxidized due to the failure of argon gas protection in the tube during welding，and thermal cracks formed on the outer surface of the weld center during the second welding of the weld. The leakage of the catheter was mainly due to the fact that a large number of oxides on the inner surface of the weld reduce the strength of the weld，and the outer surface of the weld had been polished，forming a stress concentration at the grinding place. Under the effect of the hydraulic air-tightness test and repeated assembly of the catheter，the thermal crack developed plastically and formed a passage through the wall thickness.

Key words： high temperature alloy;conduit;hot crack;overproof of leakage ratetudy on underwater laser wire filling welding procedure of 921A steelDU Shixuan1，ZHU Jialei2，TANG Ruohui2，JIAO Xiangdong2，JIANG Xin2，WANG Kai2，LI Congwei2（1.College of Mechanical and Electrical Engineering，Beijing University of Chemical Technology，Beijing 100029，China;2.College of Mechanical Engineering，Beijing Institute of Petroleum and Chemical Tec-hnology，Beijing 102617，China）. pp 69-72

Abstract：Laser wire filling welding method is used with different welding parameters and welding environments by using 16 mm thick 921A marine steel as the base metal. The metall-ographic analysis and mechanical property test are carried out for the weld. The influence of the main welding parameters such as laser defocusing distance，wet water depth，environm-ental pressure and welding speed on the welding quality are studied. The results show that the depth and width of penetr-ation reduce gradually as the environmental pressure increases，and the weld height decreases slightly as the pressure increase. When the water depth is within 4 mm，the weld is relatively smooth without obvious appearance defects;when the water depth increases to 5 mm，the uniformity of the weld becomes poor;when the water depth increases to 7 mm，the weld is difficult to form，and there are only burn marks on the surface of the base metal. The width of penetration decreases first and then stabilizes gradually as the defocusing distance increases. The depth of penetration reduces gradually as the defocusing distance increases. The appearance of weld is best when defocusing distance is about 20 mm.

Key words： 921A steel;laser wire filling welding;under-water welding;welding quality

Study on MAG welding procedure of BS960E high strength bainite steel for heavy duty vehicle

JIANG Yong1，F(xiàn)ENG Renjin1，ZHANG Chengzhu2，LIU Yan2，LIU Yang1，CAI Xin1，QIN Xiangchun1? ? ?（1.Meishan CRRC Logistics Equipment Co.，Ltd.，Meishan 620010，China;2.South-west Jiaotong University，Chengdu 610031，China）. pp 73-78

Abstract： BS960E bainite high strength steel is selected for new heavy duty vehicle. The excellent MAG welding proc-edure of BS960E bainite high strength steel is obtained by means of optimizing welding groove and controlling current and voltage. On this basis，the dynamic and static characteristics of MAG welding power supply and the droplet transfer behavior are further explored by using high speed photography and online welding monitoring technology，and the metallographic structure of the welded joint is analyzed. The results show that the welding current is stable and welding voltage is low under the optimal procedure conditions，and the metal transfer mode presents one droplet per pulse. The microstructure of the joint is mainly tempered martensite，acicular ferrite and granular bainite，which makes the hardness of the weld higher than that of the base metal.

Key words： bainite high strength steel;MAG welding;high speed photography;metal transfer

Effect of interpass temperature on impact toug-hness of 18MND5 steel welded joint for nuclear power

LIU Tiegang1，WU Yidang1，WANG Defu1，GAO Dianbao2，HUANG Zhengfeng2（1.China Nuclear Power Engineering Co.，Ltd.，Shenzhen 518124，China;2.CFHI Dalian Nuclear Power and Petrochemical Equipment Co.，Ltd.，Dalian 116113，China）. pp 79-83

Abstract： In this paper，a series of submerged arc welding experiments were carried out to study the effect of interpass temperature on the impact toughness of 18MND5 steel welded joint for nuclear power. The results show that when the int-erpass temperature is below 250 ℃，the interpass temperature has little effect on the impact toughness of the weld. When the interpass temperature is above 250 ℃，the impact toughness of 18MND5 steel welded joint decreases as the interpass tempe-rature increases. When the interpass temperature is over 350 ℃，the impact toughness of the welded joint reduces greatly. This further proves the rationality of strictly controlling the interpass temperature in the welding process required by relevant man-ufacturing standards and specifications.

Key words：interlayer temperature;impact toughness;steel for nuclear power;submerged arc welding

Effect of riveting force on the geometric characteristics of self-piercing riveting joint of aluminum/steel

LI Jianjun1，HOU Pingjun2，HE Yugang3，QIU Ranfeng3

（1.Auto-body factory，F(xiàn)irst Tractor Company Limited，Luoyang 471004，China;2.School of Electro-Mechanical，Luoyang Vo-cational & Technical College，Luoyang 471003，China;3.School of Materials Science and Engineering，Henan University of Science and Technology，Luoyang 471023，China）. pp 84-87

Abstract： Aluminum alloy and low carbon steel plates are joined by self-piercing riveting，in which aluminum alloy plate is used as upper plate and low carbon steel plate is used as lower plate，respectively. The variation of the geometric charac-teristics of joint cross section with riveting force is observed and analyzed. When the riveting force increases，the bell-mouth diameter，rivet leg expansion and amount of undercut of the joint increase，while the lower plate raised height and bottom angle margin of the joint reduce. In the range of 16～24 kN riveting force，the bottom thickness of the joint varies slightly; when the riveting force is over 24 kN，the bottom thickness suddenly reduces as the riveting force increases. The results show that the shear load of the joint increases first and then decreases as the riveting force increases，and the maximum shear load reaches about 5.88 kN when the riveting force is 24 kN.

Key words： aluminum alloy;steel;self-piercing riveting

Study on influence factors of dilution rate in overlaying of nickel base alloy on S271 low alloy steel

HUANG Weidong，BAI Zhonglian，YE Yihai，WANG Jian，LUO Xuzhen，WANG Fei，PAN Xiaodong，LI Hongjun

（Nuclear Power Institute of China，Chengdu 610041，China）. pp 88-92

Abstract： Aiming at the overlaying of 690 nickel base alloy on S271 low alloy steel for nuclear power plant，the influence factors of single layer single pass welding dilution are studied. The results show that the dilution rate of weld is related to welding speed，wire feed rate and welding current. When the welding current and welding speed are constant，the dilution rate reduces as the wire feed rate increases;when the welding current and wire feed rate are constant，the dilution rate incre-ases as the welding speed increases;when the welding speed and wire feed rate are constant，the dilution rate increases as the welding current increases. However，when the heat input，welding current and voltage are constant，changing the wire feed rate and welding speed will hardly affect the dilution rate of weld.

Key words： overlaying;dilution rate;low alloy steel;nickel base alloy;welding technology

Pilot production plan of petroleum drilling rig based on lean method

LIU Guorong，YAN Yongqing，HUANG Qiang，ZHOU Jun，GUO Changwei（Sichuan Honghua Petroleum Equipment Co.，Ltd.，Deyang 618000，China）. pp 93-95，104

Abstract： In the process of manufacturing industry deve-lopment，lean production has evolved from a common production management concept to a new generation of management phil-osophy through continuous practice until it is maturely applied to automobile，aviation，electronic products，medical and health industries. The new production mode has created numerous business miracles in the development of world-famous enterp-rises，but in the petroleum drilling rig industry based on heavy steel structure riveting and welding processing，this production method is still in the initial stage of exploration. Based on the current situation of drilling rig production in X company，the sustainable improvement points of drilling rig production is analyzed by combining with modern advanced manufacturing mode，and a specific implementation plan is made by applying lean principle and improvement method. The expected goal of the plan is to get rid of the old production at the present stage，to make the drilling rig riveting and welding production trans-ition from extensive mode to intensive mode，and finally to achieve the win-win goal of the enterprise and employees.

Key words： lean production;rive welding;petroleum dri-lling rig;drilling rig production;continuous improvement

Comparison and analysis of nugget detection standards in resistance spot welding

WANG Dachen1，LIU Xiaoqin1，LU Lianwen1，WANG Ting2

（1.CRRC Changchun Railway Vehicles Co.，Ltd.，Changchun 130022，China;2.College of Materials Science and Engineer-ing，Jilin University，Changchun 130021，China）. pp 96-99

Abstract： Taking resistance spot welding nugget detection of stainless steel rail vehicle as an example，the paper analyzes JIS E 4048 and EN15085，which are commonly used in resistance spot welding in rail vehicle manufacturing industry，as well as the relevant requirements for resistance spot welding nugget size specified in American Aerospace code AWS d17.2/D17.2M：2013，and compares and analyzes the welding defects and nugget thickness with examples. The results show that American AWS standard is more strict than other standards.

Key words： rail vehicle;resistance spot welding;nugget detection;spot welding standard

Effects of DC double-pulse MIG welding on the microstructure and properties of 5A06 aluminum alloy weld

HUANG Hao1，ZHOU Honggang1，GENG Yangmo1，ZHOU Wei2，PENG Guanghua1（1.Jianglu Machinery and Electronics Group Co.，Ltd.，Xiangtan 411100，China;2.Xiangtan Military Representation Office of the Chinese Land Force，Xiangtan 411100，China）. pp 100-104

Abstract： 5A06 aluminum alloy sheet welding with tradi-tional TIG and MIG welding technology is usually inefficient and results in poor mechanical performance as well as cannot meet requirements. For this critical problem，the DC double pulse MIG welding experiments of 5A06 aluminum alloy sheets were carried out. The effects of DC double pulse MIG welding technology on the microstructure and mechanical properties of the welded joints were investigated by optical microscopy，scanning electron microscopy and tensile testing machine. The results show that when the wire feed speed is 5 m/min，welding speed is 50 cm/min，pulse frequency is 3 Hz，wire extension is 12 mm，and protective gas is high purity Ar gas with a flow rate of 25 L/min，the beautiful weld surface with fish scale figure are obtained，there is a large amount of the fine equiaxed grain in weld zone and the gas pores in the weld cross section reduce. The welded joint has good tensile property，and tensile strength of the welded joint is above 90% of the base metal.

Key words： DC double pulse MIG welding;5A06 alum-inum alloy;weld microstructure;mechanical property

Study on microstructure and performance of nu-clear island steel lining submerged arc welding joint

HUANG Qinghui，XIANG Jiebo（China Nuclear Power Engin-eering Co.，Ltd （CNPEC），Shenzhen 518000，China）. pp 105-109

Abstract： The performance of nuclear island P265GH steel lining submerged arc welding （SAW） welding joint was studied on chemical composition，microstructure and mechanical prop-erties. The results show that the double-sided SAW with low heat input for steel lining plate is stable，and the welded joint performance meets the specification requirements，demonstr-ating the feasibility of the double-sided SAW with low heat input. In view of the construction experience of steel lining prefabrication assembly， the matters needing attention in the SAW construction of steel lining plate are put forward， which provides a reference for the quality control of subsequent nuclear island steel lining assembly construction.

Key words： nuclear power plant;P265GH steel lining plate;submerged arc welding;low heat input;microstructure;mechanical properties

The cracking repair of traction seat support plate for transportable pressure vessel tank

HUANG Daotao，LU Peng，ZHONG Linzhi，LUO Jun

（The Special Equipment Inspection and Research Institute of Guangxi Zhuang Autonomous Region，Nanning 530219，China）. pp 110-112

Abstract： The repair process of traction seat support plate cracking for transportable pressure vessel tank was expounded. According to the documents of transportable pressure vessel tank，the structure and characteristics of the traction seat support plate，the reason of cracking is analyzed and the repair plan is determined. The cracking of traction seat support plate is successfully solved by replacing the same material and thick support plate，adding the pin traction seat support plate，processing proper welding groove，and choosing reasonable welding procedure. And the tank traction support is repaired on time and in good quality，and a good evaluation and effect are gained.

Key words： transportable pressure vessel;tank;plate cracking;repair welding procedure

Automatic welding technology of 9% Ni steel vertical weld in LNG tank

WEI Baocheng，YANG Shangyu，GUO Ying（Offshore Oil Eng-ineering Co.，Ltd.，Tianjin 300461，China）. pp 113-116

Abstract： This paper compares and analyzes several methods of butt welding of 9% Ni steel vertical weld in large LNG tank，and introduces the advantages of TIP-TIG and pendulum welding technology in DPS-3G automatic welding system. It is considered that DPS-3G automatic AC gas tungsten arc welding technology can completely solve the industry pro-blem of side wall incomplete fusion of 9% Ni steel narrow groove welding. At the same time，the low temperature impact toughness of -196 ℃ is excellent，the performance and quality of welding joint are reliable，the first pass rate of non-dest-ructive testing is high，high efficiency welding is realized，the construction period is greatly shortened，and the construction cost is saved.

Key words： LNG tanks;9% Ni steel;fully-automatic wel-ding technology;vertical welds;pendulum welding

Design of a special welding machine for longit-udinal seam welding of long and thin-wall cylinder

MENG Lingtao（CRRC Qiqihar Rolling Stock Co.，Ltd.，Qiqihar 161002，China）. pp 117-121

Abstract： Long and thin-wall cylinder are widely used in the machinery industry for the cylinder walls of various types of storage tanks. Its quality is extremely important to the safety requirements. In view of the cross-section structural stress and seam length during splicing welding，it is difficult to control the welding quality or finish the inner surface. This paper presents a special welding machine design for longitudinal seam welding of long and thin-wall cylinder. By integrating the new beam-pressing and the new arm-locking structure，the elastic deformation of the steel plate during the bending and clamping can be counteract to ensure the welding accuracy. Based on single-sided welding and double-sided forming technology，the existing cylinder welding process flow and inner-side forming control are optimized to improve the welding efficiency and quality. Experiments show the design of this special machine meets the welding requirements of long and thin-wall cylinder.

Key words： welding machine;single-sided welding and double-sided forming;long and thin-wall cylinder;longitudinal weld

Practice and application of arc tracking techno-logy of robot welding in the loader fuel tank

ZHANG Hongbo1，LUO Chuanxiao2（1.School of Architectural Construction，Jiangsu Vocational Institude of Architectural Technology，Xuzhou 221004，China;2.XCMG Earth Moving Machinery Business Unit，Xuzhou 221000，China）. pp 122-126

Abstract： The tank is one of the important structural components of loader. This article introduces a kind of welding robot system used for fillet weld of loader tank， which has arc tracking function. Analyze the key factors that affect the arc tracking effect of melting gas arc welding. Under the condition of reasonable selection of welding parameters，fillet weld parameters and workpiece dimension parameters，the welding robot can realize stable arc tracking welding，high quality tank fillet welds were obtained. This provides technical guidance for the application of welding robots in fuel tank production.

Key words： welding robot;the fuel tank;arc tracking;melting gas arc welding

The analysis and verification of the best efficiency point of long distance wireless energy transmission System

HUANG Xiaofan，LI Kangwen，DAI Ruipeng，HE Xinhong

（Southwest Jiaotong University，Chengdu 610000，China）. pp 127-131

Abstract： For the common inefficient transmission problem in the existing long distance magnetic coupling resonant wireless power transmission system，the resonant topology circuit struct-ure，coil coupling coefficient，coil internal resistance and other factors of the transmission system are comprehensively analyzed. Impedance matching and shielding methods are adopted. Through modeling analysis of series resonance and calculation of transmission efficiency， the matching impedance value of the maximum efficiency point is obtained. The aluminum plate is used to surround the coil to reduce leakage flux，thus reducing transmission loss. Through theoretical analysis，simulation and experimental verification，the maximum wireless power transm-ission efficiency is 78.9% when the transmission distance is 1 meter and the impedance matching load is 53Ω.

Key words： wireless power transmission;long distance; impedance matching;maximum efficiency point