Effects of Gas Metal Arc Welding Techniques on the Mechanical Properties of Duplex Stainless Steel

The study has compared the effect of gas metal arc welding techniques on some mechanical properties of duplex stainless steel. The samples after welded were given post weld heat treatment (quenching in engine and neem oil). After the analyses, it was established that duplex stainless steel can be weld successfully using gas metal arc welding process (GMAW). Both Lubricating oil and neem oil can serve as quenching medium for post welding heat treatment of duplex stainless steel. The results of the studies also show that welding and heat treatment really affect the mechanical properties of the alloy;the control strength was 811.47 MN/m2 while that of the welded samples ranged from 177.07 to 257.32 MN/m2. The control impact energy was 162.70 J, while that of the welded samples ranged from 38.64 J to 56.20 J. The research also shows that the stress relief heat treatment gives better strength (A3 = 331 MN/m2) compared to those that were quenched in lubricating oil (A2 = 329 MN/m2) and neem oil (A1 = 222 MN/m2), but the reverse is the case in terms of toughness.

Development of Evaluation Technique of GMAW Welding Quality Based on Statistical Analysis

Nondestructive techniques for appraising gas metal arc welding（GMAW） faults plays a very important role in on-line quality controllability and prediction of the GMAW process. On-line welding quality controllability and prediction have several disadvantages such as high cost, low efficiency, complication and greatly being affected by the environment. An enhanced, efficient evaluation technique for evaluating welding faults based on Mahalanobis distance（MD） and normal distribution is presented. In addition, a new piece of equipment, designated the weld quality tester（WQT）, is developed based on the proposed evaluation technique. MD is superior to other multidimensional distances such as Euclidean distance because the covariance matrix used for calculating MD takes into account correlations in the data and scaling. The values of MD obtained from welding current and arc voltage are assumed to follow a normal distribution. The normal distribution has two parameters： the meanm and standard deviations of the data. In the proposed evaluation technique used by the WQT, values of MD located in the range from zero tom＋3s are regarded as “good”. Two experiments which involve changing the flow of shielding gas and smearing paint on the surface of the substrate are conducted in order to verify the sensitivity of the proposed evaluation technique and the feasibility of using WQT. The experimental results demonstrate the usefulness of the WQT for evaluating welding quality. The proposed technique can be applied to implement the on-line welding quality controllability and prediction, which is of great importance to design some novel equipment for weld quality detection.

Welding technique studies on the “West-East” pipeline project

This paper described the work of welding process design for the ＂ West-East＂ pipeline project, which is high pressure, large diameter and heavy wall thickness. According to the different geographical situation, climate, culture and the flexibility of the welding methods, this work recommended the semi-automatic process at the east and middle sections and automatic process at the west section of the pipeline project. The manual process is recommended on the tie-in joints and repairs. The double joint pipe and the 3 joint pipe are recommended at the water net place and some in-ditch welding place to reduce the welding volume. Also the special redesigned bevels are recommended for the automatic process and the semiautomatic process. Through all destructive tests, the results shows the welds are meet the requirements of related standards, specifications and design documents.

Process parameters optimization for friction stir welding of RDE-40 aluminium alloy using Taguchi technique

Taguchi approach was applied to determine the most influential control factors which will yield better tensile strength of the joints of friction stir welded RDE-40 aluminium alloy. In order to evaluate the effect of process parameters such as tool rotational speed, traverse speed and axial force on tensile strength of friction stir welded RDE-40 aluminium alloy, Taguchi parametric design and optimization approach was used. Through the Taguchi parametric design approach, the optimum levels of process parameters were determined. The results indicate that the rotational speed, welding speed and axial force are the significant parameters in deciding the tensile strength of the joint. The predicted optimal value of tensile strength of friction stir welded RDE-40 aluminium alloy is 303 MPa. The results were confirmed by further experiments.

RECALLABLE TRACKING TECHNIQUE FOR TOP WELD BEADS OF NARROW GAP SUBMERGED ARC WELDING

According to the wire and nozzle movement track in groove, the movement parameters of wire were memorized and recalled for the following top welds by using a single chip computer. In this paper, it was also discussed that the design problems of correcting deviation of wire movement track in narrow gap submerged arc welding process must be noticed in order to obtain the sound welding result.

New Laser-cladding Technique for Welding of Bridge Wires in Detonators

The laser-cladding technique for welding of bridge wires is reported for the first time.The essen- tial feature of this technique different from the cur- rent methods is the realization of mutual melting of workpieces.Thus the stability of products is im- proved in an order of magnitude.The main points of the technique and the microanalyses of the weld- ing spot and other features are given.The technique presented is a novel method of welding between tiny piece and workpiece of different sizes and proper- ties.

Development of welding technique in architectural and construction industry in China

This paper presents the achievements in welding technique for the large industrial buildings and structures in China, including the welding of furnaces,kilns,pots,tanks and pipes, the welding of steel construction of industrial building,high-storied building, gymnasium and steel construction of highway bridge. It mainly cites the new efficient and high-quality processes, equipments and materials used in fabricating typical up-to-date construction projects. The paper discusses the prospects for the technical development in welding materials, process and equipments as per usual requirements of architectural and construction industries.

Study of Corrosion Resistance of Laser Welded Au-Pd-Ag-In Alloy Using Electrochemical Techniques

The aim of this work was to evaluate the corrosion resistance of AuPdAgIn alloy, submitted to laser beam welding, in 0.9% NaCl solution, using electrochemical techniques. Measures of the open circuit potential (OCP) versus time were applied to electrochemical experiments, as well as potentiodynamic direct scanning (PDS) and electrochemical impedance spectroscopy (EIS) on AuPdAgIn alloy, submitted to laser beam welding in 0.9% NaCl solution. Some differences observed in the microstructure can explain the results obtained for corrosion potential, Ecorr, and corrosion resistance, Rp. EIS spectra have been characterized by distorted capacitive components, presenting linear impedance at low frequencies, including a non-uniform diffusion. The area of the laser weld presented corrosion potential slightly superior when compared to the one of the base metal. The impedance results suggest the best resistant corrosion behavior for laser weld than base metal region. This welding process is a promising alternative to dental prostheses casting.

Welding technique and quality of large diameter X70 line pipe for gas transmission of China

X70 grade large diameter line pipe with helical and longitudinal seam SAW was developed and used in West-East Pipeline Project of Petrochina. The operation pressure of the pipeline was designed as 10 MPa, with diameter of 1016 mm OD. This project represents the first high-pressure, large diameter and high strength grade gas pipeline in China. All the factors affecting the safety of the pipeline shall be considered. The welds quality of line pipe is very important for safety of the pipeline. Acicular ferrite type X70 grade pipeline steel was adopted for the base material. The welds performances of X70 line pipes with 1016mm OD and 14.6-21.0 mm WT has reached a very high level, especially of low temperature Charpy V impact toughness of welds metal. Welding technique and quality status of X70 line pipe of China are investigated in this paper.

Three dimensional numerical simulation of welding temperature fields in stainless steel

Three kinds of mathematical models representing welding heat sources are presented. Among them, Gaussian model and double ellipsoidal model are used to analyze the thermal distributions with finite element method. At the same time, this paper analyzed the influences of the heat source models, the latent heat and the welding parameters on the temperature distributions. The comparisons between the simulated results and the experiments show double ellipsoidal model is good for three-dimensional numerical simulations. Furthermore, the adaptive mesh technique is applied in the three-dimensional model which greatly reduces the number of nodes and elements in the simulation.

Progress in Thermomechanical Analysis of Friction Stir Welding

This article reviews the status of thermomechanical analysis of the friction stir welding(FSW)process for establishing guidelines for further investigation,filling the available research gaps,and expanding FSW applications.Firstly,the advantages and applications of FSW process are introduced,and the significance and key issues for thermomechanical analysis in FSW are pointed out.Then,solid mechanic and fluid dynamic methods in modeling FSW process are described,and the key issues in modeling FSW are discussed.Di erent available mesh modeling techniques including the applications,benefits and shortcomings are explained.After that,at different subsections,the thermomechanical analysis in FSW of aluminum alloys and steels are examined and summarized in depth.Finally,the conclusions and summary are presented in order to investigate the lack of knowledge and the possibilities for future study of each method and each material.

3D visualization of the material flow in friction stir welding process

The material flow in friction stir welded 2014 Al alloy has been investigated using a marker insert technique （MIT）. Results of the flow visualization show that the material flow is asymmetrical during the friction stir welding （FSW） process and there are also significant differences in the flow patterns observed on advancing side and retreating side. On advancing side, some material transport forward and some move backward, but on retreating side, material only transport backward. At the top surface of the weld, significant material transport forward due to the action of the rotating tool shoulder. Combining the data from all the markers, a three-dituensional flow visualization, similar to the 3D image reconstruction technique, was obtained. The three-dimensional plot gives the tendency chart of material flow in friction stir welding process and from the plot it can be seen that there is a vertical, circular motion around the longitudinal axis of the weld. On the advancing side of the weld, the material is pushed downward but on the retreating side, the material is pushed toward the crown of the weld. The net result of the two relative motions in both side of the advancing and the retreating is that a circular motion comes into being. Comparatively, the material flow around the longitudinal axis is a secondary motion.

Microstructural analyses of aluminum–magnesium–silicon alloys welded by pulsed Nd: YAG laser welding

Revealing grains and very fine dendrites in a solidified weld metal of aluminum–magnesium–silicon alloys is difficult and thus,there is no evidence to validate the micro-and meso-scale physical models for hot cracks. In this research, the effect of preheating on the microstructure and hot crack creation in the pulsed laser welding of AA 6061 was investigated by an optical microscope and field emission electron microscopy. Etching was carried out in the gas phase using fresh Keller’s reagent for 600 s. The results showed that the grain size of the weld metal was proportional to the grain size of the base metal and was independent of the preheating temperature. Hot cracks passed the grain boundaries of the weld and the base metal. Lower solidification rates in the preheated samples led to coarser arm spacing;therefore, a lower cooling rate. Despite the results predicted by the micro and meso-scale models, lower cooling rates resulted in increased hot cracks. The cracks could grow in the weld metal after solidification;therefore, hot cracks were larger than predicted by the hot crack prediction models.

Application of Nd:YAG Laser Welding to Implantable Neuro-Stimulator

It is difficult to weld the material and structure of implantable neuro-stimulator such as pure medical titanium and irregular outside shield by conventional arc welding methods.Currently there are few reports on the neuro stimulator sealing technology,and none of them have simultaneously considered the quality control methods.In order to develop the sealing procedure and quality control methods,an investigation of applying Nd：YAG laser welding to implantable neuro-stimulator components is carried out.Firstly,the automatic Nd：YAG laser welding system equipped with proper fixture configuration is introduced.A special fixture structure is illustrated and the key point for the device is to reduce the fit-up gap between the two shields.Then,a novel welding process technique is proposed to satisfy the engineering requirements.The optimized process parameters for titanium shell,feedthrough and fastener are provided and concluded by an orthogonal experiment.Finally,different quality control measures such as visual inspection,X-ray detecting and leakage testing,are presented on the final products.The results show that the Nd：YAG laser welding applied on the implanted neuro-stimulator under optimized parameters can prevent welding defects and improve the weld joints quality.Combination of various quality control methods will guarantee the sealing performance and mechanical properties of the products.It is confirmed that the processing procedure and quality methods can not only resolve the process technology on welding ultra-thin structure of medical device,but also provide the reference for other implantable device.

TRANSIENT TEMPERATURE FIELDS AND RESIDUAL STRESS FIELDS OF METALLIC MATERIALS UNDER WELDING

Based on the situation of welding thermal conduction and thermo-elasto-platicity research, this paper explores some problems in this field. First, the boundary element method for nonlinear problems is improved by linearization of nonlinear problems and used in welding thermal conduction analysis. Second, the thermo-elasto-plastic finite element method is used for the welding stress calculation, in which the phase transformation is considered by the 'equivalent linear expansion coefficient method'. The comparison of the calculated results with experimental data shows that the methods provided in this paper are available.

FEATURES OF THYRISTOR COMMUTATORS OPERATION OF WELDING CURRENT UNDER PULSED-ARC WELDING

This article presents the special requirements and features of the thyristor commutators of the welding current.Advantages of pulsed - arc welding are described.Specificity of the thyristor commutators op- eration is presented. Semiconductor converter simulation allowing to create the engineering calculating techniques are considered.

Development of an engineering－practical expert system for arc welding and its shell

The major functions of an engineering-practical expert system(ESW) and the main features of an expert system development tool(QHWEST) for arc welding procedure are introduced. A brief description is given for the development background, process and principal techniques of the two software systems.

The Studies of the Welding Processes and Procedures on the West-East Pipeline Project

The West East pipeline project attracted the attention from all over the world for its long distance, huge diameter, complex geographic conditions, and diversified welding techniques being applied.In this paper the detail welding process and procedures used in the project are discussed and the distinguished achievements on welding techniques of China pipeline construction are described.

Q345B/304异种钢激光填丝焊接工艺与性能研究

为了提高异种钢焊接质量,采用激光焊技术填充ER308L焊丝对Q345B低合金钢与304不锈钢两种异质材料进行焊接。在不同的激光功率下,采用金相显微镜、扫描电镜、能谱仪等对焊接接头进行了深入的表征和分析。结果表明,当激光功率高于3 kW时,接头处得以焊透,4 kW、4.5 kW和5 kW这3种焊缝截面均呈现束腰现象,且焊缝组织均为典型的板条状马氏体,其中5 kW焊接件焊缝所含的板条马氏体更加细小,表现出最高的硬度值;4 kW焊接件的抗拉强度达到590 MPa,随着激光功率的增大,焊接件的抗拉强度逐步下降;焊缝中主要出现了Cr_(2)Ni_(3)、Fe_(2)Ni_(3)、α-Fe等相,没有大量出现对质量有较大影响的M_(23)C_(6)和σ相等有害相。采用激光填丝焊接技术能够实现Q345B/304异种钢的高质量焊接。

马鞍山长江公铁大桥Z3号桥塔施工关键技术

巢马城际铁路马鞍山长江公铁大桥主航道桥为(112+392+2×1120+392+112)m三塔钢桁梁斜拉桥,Z3号桥塔为超高多肢钢-混组合塔,高308 m。上塔柱钢结构高87.5 m,分13个吊装节段,最重505 t;中、下塔柱混凝土结构高217.5 m,分38个节段液压爬模施工;钢-混结合段高3 m,内部采用PBL键+剪力钉+高强度钢锚杆+高强度混凝土结构形式。在中塔柱设置钢管临时横撑控制塔柱线形及应力;下横梁采用落地支架法分层施工,与对应塔柱同步浇筑;钢-混结合段混凝土采用C60细石补偿收缩混凝土+高强度灌浆料,保证了混凝土施工质量;采用工厂“2+1”立体匹配制造、“提升站+运输栈桥”钢塔节段转运等技术,并研制15000 t•m超大型塔吊,实现了钢塔柱大节段的制造、整体滩地运输和吊装;钢塔节段间采用栓焊组合连接形式,通过设置工艺隔板、双面坡口等措施控制了钢塔焊接变形;利用定位桁架临时锁定钢塔合龙段实现了钢塔的精确合龙,定位桁架受力及变形均满足要求。