Process Parameter Optimization of AISI 316L(N) Weld Joints Produced using Flux-Cored Arc Welding Process

Bead on plate welds were carried out on AISI 316L(N) austenitic stainless steel using flux cored arc welding process. The bead on plates weld was conducted as per L₂₅ orthogonal array with statistical design of experiment technique. In this paper, the welding parameters will be optimized based on the weld bead geometry such as depth of penetration, bead width and weld reinforcement. Grey relational analysis and desirability approach are used to optimize the input parameters like wire feed rate, voltage, travel speed and torch angle while considering the multiple output variables simultaneously. Confirmation experiment has also been conducted to validate the optimized parameters.     

Effect of Oxide Fluxes on Depth of Penetration in Flux Bounded Tungsten Inert Gas Welding of AISI 304L Stainless Steel

Flux Bounded Tungsten Inert Gas (FBTIG) welding is a modified TIG welding process in which increased depth of penetration (DoP) can be achieved by laying thin flux coatings on either side of the weld centerline. The effect of three single component fluxes viz., SiO₂, TiO₂ and Cr₂O₃ on bead geometry of autogenous melt runs in AISI 304L stainless steel for the gap between the flux layers varying from 2 to 7 mm, is studied. Results show that DoP can be improved significantly in FBTIG process using single component fluxes. Nature of the flux and the gap between the flux layers influence the weld bead geometry. Among the three fluxes used, SiO₂ is more efficient in improving the DoP. Arc constriction is the predominant mechanism operative in improving the DoP in FBTIG welding. Possibility of change in solidification mode in FBTIG weld metals of stainless steels is highlighted.     

Prediction of laser-spot-weld shape by numerical analysis and neural network

The finite element method (FEM) and neural network were applied for predicting the bead shape in laser spot welding of type 304 thin stainless steel sheets. The parameters of pulsed Nd:YAG laser spot welding such as pulse energy, pulse duration, sheet metal thickness, and gap between sheets were varied for various experiments and numerical simulations. The penetration depth and nugget size of spot welds measured for specimens without gap were compared with the calculated results to verify the proposed finite element model. Sheet metal thickness, gap size, and bead shape of the workpiece without gap were selected as the input variables for the back-propagation learning algorithm of the neural network, while the bead shape of the workpiece with and without gap was considered as its output variable. Various combinations of stainless steel sheet metal thickness were considered to calculate the laser-spot-weld bead shape of the workpiece without gap, which was then used as the input variable of neural network to predict the bead shape for various gap sizes. This combined model of finite element analysis and neural network could be effectively applied for the prediction of bead shapes of laser spot welds, because the numerical analysis of laser spot welding for the workpiece with gap between two sheets is highly limited.     

Effect of Shielding Gas on the Microstructural Evolution in Laser Beam Welded AISI 410 Martensitic Stainless Steel

Laser welding of AISI 410 martensitic stainless steel was attempted in a diffusion cooled RF excited CO₂ slab laser under Gaussian mode with argon and nitrogen as shielding gas. The effect of shielding gas and energy density on the resultant weld bead geometry, microstructure and hardness were assessed and discussed. It has been observed that welds obtained under nitrogen shielding conditions had higher and uniform hardness across the weld metal on account of reduced ferrite content.     

One Modified FE‐model to Simulate the Process Chain of Forming and Welding

This paper presents a possibility of creating a virtual process chain consisting of forming and welding. Independent of any manufacturing process, a variable Finite Element model is introduced. This model can be an input for more than one simulation by means of the Finite Element Method (FEM). The process chain forming and welding is chosen to demonstrate the need and the importance to simulate a process chain in comparison to a single process simulation. Each simulation has its own specifications and intentions. Therefore, an FE‐model for a forming simulation is different from a model for a welding simulation. In this paper a way is shown how to keep the model and the results of a forming simulation for the succeeding simulation of welding. The results of the forming simulation remain as an initial state in the welding simulation. Thereby, a spring‐back behaviour can be modelled. A few adjustments have to be done to satisfy the specifications of the welding simulation. The used material for the integrated simulation is a DC 04 steel. Therefore, metallurgical phases must be considered to achieve sufficient results. For reasons of further industrial applications commercial FE‐solvers are used for calculations. The method of integration is applied to different examples. The verified results are presented and discussed. The simulated transient distortional behaviour of a formed and welded part is presented and compared to a mere welding simulation. A significant improvement of the distortion as a result of the welding simulation is reached by consideration of a previous forming simulation.     

Energy Losses Estimation During Pulsed-Laser Seam Welding

The finite-element tool SYSWELD (ESI Group, Paris, France) was adapted to simulate pulsed-laser seam welding. Besides temperature field distribution, one of the possible outputs of the welding simulation is the amount of absorbed power necessary to melt the required material volume including energy losses. Comparing absorbed or melting energy with applied laser energy, welding efficiencies can be calculated. This article presents achieved results of welding efficiency estimation based on the assimilation both experimental and simulation output data of the pulsed Nd:YAG laser bead on plate welding of 0.6-mm-thick AISI 304 stainless steel sheets using different beam powers.     

Multi-objective Optimization of Welding Parameters in Submerged Arc Welding of API X65 Steel Plates

Submerged arc welding(SAW)is one of the main welding processes with high deposition rate and high welding quality.This welding method is extensively used in welding large-diameter gas transmission pipelines and high-pressure vessels.In welding of such structures,the selection process parameters has great influence on the weld bead geometry and consequently affects the weld quality.Based on Fuzzy logic and NSGA-II(Non-dominated Sorting Genetic Algorithm-II)algorithm,a new approach was proposed for weld bead geometry prediction and for process parameters optimization.First,different welding parameters including welding voltage,current and speed were set to perform SAW under different conditions on API X65 steel plates.Next,the designed Fuzzy model was used for predicting the weld bead geometry and modeling of the process.The obtained mean percentage error of penetration depth,weld bead width and height from the proposed Fuzzy model was 6.06%,6.40% and 5.82%,respectively.The process parameters were then optimized to achieve the desired values of convexity and penetration indexes simultaneously using NSGA-II algorithm.As a result,a set of optimum vectors(each vector contains current,voltage and speed within their selected experimental domains)was presented for desirable values of convexity and penetration indexes in the ranges of(0.106,0.168)and(0.354,0.561)respectively,which was more applicable in real conditions.     

Pulsed Nd:YAG laser welding of copper using oxygenated assist gases

The effects of using oxygenated assist gases on the weldability and weld properties of Nd:YAG, pulsed laser welds in copper (Cu) have been evaluated. It was found that the effective absorptivity of the Cu increased as the oxygen content of the Ar assist gas was increased. This facilitated laser welding of Cu at much lower laser powers and increased weld penetration. The use of oxygenated assist gas promoted nucleation and growth of submicroscopic oxide particles within the weld metal. These particles dispersion-strengthened the weld metal, thereby increasing both weld metal hardness and strength. However, when O₂ concentrations in the assist gas were greater than 90 pct, weld metal embrittlement due to excessive volume fractions of oxides was observed. The use of oxygenated assist gas also led to excessive cold lapping and poor bead quality. The bead quality was improved, however, by ramping-down the laser power before terminating each pulse.     

Modelling of Stress State,Centre Consolidation and Roll Force in Billet Rolling

Roll pressure models have been derived from theoretical studies, FEM simulations and experimental investigations. A model developed from slip line field theory has been shown to fit well to the experimental results. The Finite Element simulations overestimated the pressure function. This is a common problem in hot rolling experiments, since the problem of measuring the correct rolling temperature makes the estimation of the yield strength very difficult. The difference between the FE calculations and the experimental measurements is a measure for the error in the experimental temperature measurements rather than for the accuracy of the Finite Element Method. Traditional modelling has not been an appropriate tool to evaluate the material flow in the centre of the billet. In spite of the fact that the entire stress state can be modelled by slip line field theory, the slip lines which determine the stress state in the centre coincide for actual geometries only in one single point. Thus the strain increments are known only in that single point. Since a material element passes that point instantaneously, it is not possible to find any finite strains in the centre by integrating any incremental function. By FEM, strain modelling is simple and the possibility to consolidate a porous bloom or ingot core can be determined. FE modelling requires an entirely new approach to the modelling problem. It is not reasonable to use FEM to evaluate only the temperature distribution for the use in roll force models from the previous century. Instead, a fully thermomechanically coupled FE model is suggested. However, the calculation time is still far too long to be used for on‐line control purposes. For this application hybrid modelling can be a solution, where off‐line FE models are combined with empirical modelling, and simplified models can be used for the process control.     

Increasing Rigidity and Strength using Local Effects of Bead‐on‐Plate Laser Welding Seams

In order to achieve graded strength properties and to improve the rigidity of metallic materials, side effects of the laser joining process are used. Local physical and geometrical effects which have only been observed as side effects are to be used purposefully. The investigations take place in context of the SFB 675 “high‐strength metallic structures and joints by setting up scaled local material properties”. The energy needed to produce bead‐on‐plate welding seams can be limited to a small area of the workpiece by using a focused laser beam with a diameter of tenths of a millimetre. The heat affected zone of a laser beam is very small. In comparison to other welding procedures, lower heat input is the main reason that basic material characteristics remain unaffected after welding. The progressive development of laser beam sources to higher available laser output power has extended their spectrum of use in the field of joining technologies [1, 2]. It should be pointed out that local physical and geometrical effects can be used to achieve specific material characteristics. Bead‐on‐plate laser welding seams were produced to demonstrate that strength and rigidity can be increased in metal sheets. First investigations are carried out on the micro‐alloyed high‐strength steel H340LAD. The sheets were tested using tensile tests and also with 3‐point and 4‐point bending tests. Six different specimens were investigated, one without welding seams and five with different laser based welding seam types. The tensile and bending tests showed that higher forces were needed to rupture or to bend the laser welded specimens. Furthermore, the investigations showed that the strength of the specimens was increased in comparison to the specimens without welding seam.     

Effects of Process Parameters upon the Shape Memory and Pseudo-Elastic Behaviors of Laser-Welded NiTi Thin Foil

This article discusses the effects of laser welding parameters such as power, welding speed, and focus position on the weld bead profile, microstructure, pseudo-elasticity (PE), and shape memory effect (SME) of NiTi foil with thickness of 250 μm using 100W CW fiber laser. The parameter settings to produce the NiTi welds for analysis in this article were chosen from a fractional factorial design to ensure the welds produced were free of any apparent defect. The welds obtained were mainly of cellular dendrites with grain sizes ranging from 2.5 to 4.8 μm at the weld centerline. A small amount of Ni₃Ti was found in the welds. The onset of transformation temperatures (A _s and M _s ) of the NiTi welds shifted to the negative side as compared to the as-received NiTi alloy. Ultimate tensile stress of the NiTi welds was comparable to the as-received NiTi alloy, but a little reduction in the pseudo-elastic property was noted. Full penetration welds with desirable weld bead profiles and mechanical properties were successfully obtained in this study.     

Intelligent Modeling Using Adaptive Neuro Fuzzy Inference System (ANFIS) for Predicting Weld Bead Shape Parameters During A-TIG Welding of Reduced Activation Ferritic-Martensitic (RAFM) Steel

Reduced-activated ferritic-martensitic steels are considered to be the prime candidate for structural material of the fusion power plant reactor design. Tungsten inert gas (TIG) welding is preferred for welding of those structural materials. However, the depth of penetration achievable during autogenous TIG welding is very limited and hence productivity is poor. Therefore, activated-flux tungsten inert gas (A-TIG) welding, a new variant of TIG welding process has been developed in-house to increase the depth of penetration in single pass welding. In structural materials produced by A-TIG welding process, weld bead width, depth of penetration and HAZ width decide the mechanical properties and in turn the performance of the weld joints during service. To obtain the desired weld bead geometry, HAZ width and make a reliable quality weld, it becomes important to develop predictive tools using soft computing techniques. In this work, adaptive neuro fuzzy inference system is used to develop independent models correlating the welding parameters like current, voltage and torch speed with bead shape parameters like weld bead width, depth of penetration, and HAZ width. During ANFIS modeling, various membership functions were used. Triangular membership function provided the minimum RMS error for prediction and hence, ANFIS model with triangular membership functions were chosen for predicting for weld bead shape parameters as a function of welding process parameters.     

基于ANSYS的钛合金管口激光焊接有限元模拟

基于热弹塑性有限元方法,建立激光焊接过程的热力学计算模型,利用三维有限元分析软件ANSYS,开发其APDL二次语言,使用“生死单元”技术,实现了对BT20钛合金管口激光焊接过程温度场和应力场的有限元模拟。结合数值计算,对有限元模拟问题进行分析,并讨论了激光焊接过程采用瞬间空冷10s后,试件内部的应力分布情况。     

2 250 mm带钢热连轧机板形调控性能改善与提高

以2 250 mm热连轧精轧机为对象,通过有限元仿真,针对末机架在轧制薄带钢时因出现工作辊端部压靠而引起的整机板形控制性能劣化问题,进行了多种工况的定量研究,得出轧件规格和轧制力对工作辊端部压靠的产生及压靠程度的影响,揭示了工作辊端部压靠对轧机板形控制性能的严重负面影响.通过比较研究轧机抵抗工作辊端部压靠的能力,提出了采用基于变接触轧制策略的变接触支承辊初始辊形设计的技术对策,并在投入实际生产使用后取得了明显效果.     

方坯软接触结晶器电磁场分布及弯月面形状的数值模拟

应用有限元与边界元相结合的方法，通过求解电磁场的H－φ方程和边界积分方程，进行了方坯软接触结晶器内电磁场和弯月面处钢液形状的数值模拟，结果表明，作用在钢液自由表面边缘向里向下的电磁力是使弯月面向内弯曲的直接原因，采用有切缝的铜结晶器时弯月面向弯曲的程度比采用石英结晶器时小。     

Modeling of laser keyhole welding: Part II. simulation of keyhole evolution,velocity, temperature profile,and experimental verification

This article presents the simulation results of a three-dimensional mathematical model using the level set method for laser-keyhole welding. The details of the model are presented in Part I.^[4] The effects of keyhole formation on the liquid melt pool and, in turn, on the weld bead are investigated in detail. The influence of process parameters, such as laser power and scanning speed is analyzed. This simulation shows very interesting features in the weld pool, such as intrinsic instability of keyholes, role of recoil pressure, and effect of beam scanning. For verification purposes, visualization experiments have been performed to measure melt-pool geometry and surface velocity. The theoretical predictions show a reasonable agreement with the experimental observations.     

Intelligent Modeling Combining Adaptive Neuro Fuzzy Inference System and Genetic Algorithm for Optimizing Welding Process Parameters

Modified 9Cr-1Mo ferritic steel is used as a structural material for steam generator components of power plants. Generally, tungsten inert gas (TIG) welding is preferred for welding of these steels in which the depth of penetration achievable during autogenous welding is limited. Therefore, activated flux TIG (A-TIG) welding, a novel welding technique, has been developed in-house to increase the depth of penetration. In modified 9Cr-1Mo steel joints produced by the A-TIG welding process, weld bead width, depth of penetration, and heat-affected zone (HAZ) width play an important role in determining the mechanical properties as well as the performance of the weld joints during service. To obtain the desired weld bead geometry and HAZ width, it becomes important to set the welding process parameters. In this work, adaptative neuro fuzzy inference system is used to develop independent models correlating the welding process parameters like current, voltage, and torch speed with weld bead shape parameters like depth of penetration, bead width, and HAZ width. Then a genetic algorithm is employed to determine the optimum A-TIG welding process parameters to obtain the desired weld bead shape parameters and HAZ width.     

Investigation on Tensile Behaviour of Laser Welded Al–Mg–Sc–Zr In Situ TiB<Subscript>2</Subscript> Reinforced Metal Matrix Composite

The objective of the present work is to investigate the tensile behavior on laser welded Al–Mg–Sc–Zr in situ nano TiB₂ composite. Al–3.5Mg–0.15Sc–0.075Zr–1TiB₂ composite was melted in a resistance heating furnace. TiB₂ was formed during in situ reaction of K₂TiF₆ and KBF₄ salt mixture at 750 °C for 60 min. Welding was done using Nd:YAG pulsed laser source JK 600 (GSI make) using a robotic (IRB1410 of ABB) laser set up. The autogenous welding experiments were carried out using some of the significant parameters such as frequency—75 Hz, laser beam energy—8.10 J, pulse width—2.5 ms and welding speed—5 mm/s. It was observed that laser beam power played a major role and lower value of energy with higher repetition rate resulted better and uniform weld bead with full penetration. Five different processing methods were utilized to investigate the mechanical and metallurgical properties namely: (a) as cast (AC), (b) as cast followed by welding (AC + W), (c) as cast followed by aging (AC + A), (d) as cast followed by aging and then welding (AC + A + W) and finally (e) as cast followed by welding and then aging (AC + W + A). The ageing treatment followed was heating the samples at 300 °C for 5 h followed by air cooling. The obtained results infered that apart from the obvious superior properties shown by as cast followed by aging treatment (AC + A: 248 MPa); the AC + W + A specimens showed better properties (235 MPa) along with AC + A + W specimens (226 MPa). The fracture surface analyses revealed the following: (a) the weld region in the laser welded as cast material did not show any TiB₂ in the structure probably due to the fact that temperature experienced during laser welding process might have melted the particles and was dissolved in the solid solution, (b) the interface of the weld-base region showed the presence of few TiB₂ particles which lost their hexagonal shape due to preferential melting along the edges. (c) The fracture morphology of both AC + A + W and AC + W + A specimen’s showed typical mixed mode fracture with fine precipitates along the interface. The strength increased in AC + W + A at the expense of ductility due to formation of Al₃Sc precipitates.     

轧机有限元—优化—CAD集成系统的研究

本文集工程优化设计、有限元分析方法、计算机辅助设计（ＣＡＤ）技术三者于一体，开发了适合中小型轧机的高效、实用的工程设计软件系统。该系统能时机座进行结构参数优化、有限元分析、形状优化以及有限元前后置处理功能。     

模具的合金堆焊研究

用合金堆焊模具，是在普通碳结构钢的基体上堆焊合金钢或硬质合金作为模具工作部分，以提高模具寿命及耐用度，降低模具成本.介绍了模具合金堆焊的工艺、焊接设备、堆焊材料的选用以及堆焊产生的同题及其防止措施．