Swarup Bag

Three-dimensional transient heat conduction and thermomechanical analysis for laser spot welding using adaptive heat source

AbstractNumerical modelling of laser spot welding process as an aid to design for welding has gained significant attention in the recent past, because experimental measurements of peak temperature and weld thermal cycle are expensive and often intractable. Accurate knowledge of the temperature history in the weld pool and the surrounding solid substrate are a prerequisite for the estimation of weld joint strength. The present work proposes a three-dimensional (3D) transient conduction heat transfer based coupled thermomechanical analysis of laser spot welding process. To accommodate enhanced heat transfer in weld pool at higher temperature owing to convective flow and greater amount of absorption of the laser energy, an expression for a volumetric heat source that is dimensionally similar to the transient weld pool is considered. The calculated weld pool dimensions have shown fair agreement with similar measured values reported in previous literatures. The calculated weld thermal cycles are subsequently u...

Efficient Estimation Of Volumetric Heat Source In Fusion Welding Process Simulation

Mathematical models of heat transfer phenomena in fusion welding process can provide important physical insight on the mechanism of weld pool development, and compute temperature field and final weld dimensions fairly reliably in several welding systems. In particular, the conduction heat transfer based numerical models are relatively simpler and computationally inexpensive in comparison to the comprehensive heat transfer and fluid flow models although the later can undertake greater physical attributes in weld pool. One significant requirement of the conduction heat transfer based models is the predetermination of a volumetric source term to account for the heat input from the welding heat source. We present here two efficient approaches to define the volumetric heat source term which do not require a-priori information of the final weld joint dimensions, which has always remained a difficult task. The first approach involves an intrinsic mapping of the heat source geometry with the numerically computed melt pool dimensions within the framework of modeling calculations in an iterative manner and is validated for the prediction of final weld dimensions in autogenous gas tungsten arc welds with butt joint geometry. The other approach involves an analytical estimation of the volumetric source term as function of only the welding conditions and the initial weld joint geometry and is examined successfully for the prediction of weld pool dimensions and thermal cycles in tandem submerged arc welds with typical groove joint geometry.

Effect of Preheating in Hybrid Friction Stir Welding of Aluminum Alloy

The controlled energy input into the system by introducing an extra heat source to enhance the material flow along with reduction of the plunging force remains a potential area of considerate for the development of hybrid friction stir welding (FSW) process. Hence, the effect of preheating on the weld joint properties is evaluated using plasma-assisted friction stir welding (P-FSW) process for joining aluminum alloy. A comparative study of mechanical and macro-microstructural characterizations of weld joint by FSW and P-FSW has been performed. Transverse tensile strength of weld joint is approximately 95% of base metal produced by P-FSW and is 8% more than conventional FSW welds. The effect of preheating enhances material flow and dissolution of fine oxide particles by plasma arc results in increase of strength and marginal modification of deformation behavior. The preheating brings uniformly distributed hardness in weld zone and the magnitude is higher in the advancing side with overall increase in average hardness value. Grain sizes are much finer due to the pinning effect of Al2O3 particles that retarded grain growth following recrystallization during P-FSW and thus led to more pronounced reduction in grain size and relatively brittle fracture during tensile loading of welded joint. Overall, the influence of preheating acts quite homogeneously throughout the structure as compared to conventional FSW. However, the results reveal that the development of P-FSW is still in initial stage and needs to improve in various aspects.

Microstructural Influence on Mechanical Properties in Plasma Microwelding of Ti6Al4V Alloy

The complexity of joining Ti6Al4V alloy enhances with reduction in sheet thickness. The present work puts emphasis on microplasma arc welding (MPAW) of 500-μm-thick Ti6Al4V alloy in butt joint configuration. Using controlled and regulated arc current, the MPAW process is specifically designed to use in joining of thin sheet components over a wide range of process parameters. The weld quality is assessed by carefully controlling the process parameters and by reducing the formation of oxides. The combined effect of welding speed and current on the weld joint properties is evaluated for joining of Ti6Al4V alloy. The macro- and microstructural characterizations of the weldment by optical microscopy as well as the analysis of mechanical properties by microtensile and microhardness test have been performed. The weld joint quality is affected by specifically designed fixture that controls the oxidation of the joint and introduces high cooling rate. Hence, the solidified microstructure of welded specimen influences the mechanical properties of the joint. The butt joint of titanium alloy by MPAW at optimal process parameters is of very high quality, without any internal defects and with minimum residual distortion.

Heat transfer analyses in friction stir welding of aluminium alloy

This work is aimed to develop a heat transfer model of friction stir welding process and subsequently to utilize the same for transient thermal analysis under differential influence of process parameters. The heat generation is assumed due to friction and plastic deformation at the tool–workpiece interface. A contact state variable is defined to estimate the amount of heat generation due to plastic deformation. The symmetric heat flux at the interfaces of flat tool shoulder surface, tool pin side, and bottom surfaces acts as heat input to the system by neglecting the effect of transverse tool speed. The heat generation from both the side and bottom surfaces of pin plays a significant role for the development of the temperature. Thermal history of friction stir welded AA1100 and AA6061 is estimated by developed numerical model and is compared with experimental results under similar welding conditions, thus validating the developed model. The experiments reveal that the temperature distributions are not symmetric with respect to welding line and maximum temperature occurs behind the tool pin. With the addition of heat generation due to plastic deformation, the heat transfer model precisely predicts the maximum temperature and time–temperature profiles at different welding conditions.

An improved harmony search algorithm with dynamically varying bandwidth

The present work demonstrates a new variant of the harmony search (HS) algorithm where bandwidth (BW) is one of the deciding factors for the time complexity and the performance of the algorithm. The BW needs to have both explorative and exploitative characteristics. The ideology is to use a large BW to search in the full domain and to adjust the BW dynamically closer to the optimal solution. After trying a series of approaches, a methodology inspired by the functioning of a low-pass filter showed satisfactory results. This approach was implemented in the self-adaptive improved harmony search (SIHS) algorithm and tested on several benchmark functions. Compared to the existing HS algorithm and its variants, SIHS showed better performance on most of the test functions. Thereafter, the algorithm was applied to geometric parameter optimization of a friction stir welding tool.

On the effect of tool offset in hybrid-FSW of copper-aluminium alloy

ABSTRACT Tool offset is one the most significant parameters in joining of dissimilar materials by friction stir welding (FSW) process. An investigation is carried out on the effect of tool offset toward thermal history, material flow pattern, mechanical properties, welding force, and weld joint morphology. It was found that offsetting toward aluminum side along with a plasma-assisted heat source is an efficient approach to address one of the most important apprehensions in aluminum-copper solid-state welding process. The offset influences the amount of intermetallic at the joint interface and in-effect impacts on final strength and material flow behavior. The optimum and continuous layer of intermetallic produces the maximum weld joint strength. The specimen welded with optimum tool offset shows the highest strength using 55 A plasma current in hybrid friction stir welding process.

Prediction of welding sequence induced thermal history and residual stresses and their effect on welding distortion

Stiffened plate panel is the major structural part of a fabrication industry where fillet welding joint is one of the most important fabrication techniques. Large stiffened structures are generally joined by several welding passes which generates thermal stresses and angular deformation. Tensile residual stresses which are generated due to welding in the weld region may lead to early failure of the structure when subjected to cyclic loading. The weld-induced residual distortion causes dimensional inaccuracy and needs rework to achieve the desired shape. Use of multiple welding passes without any optimized welding sequences typically leads to an increased degree of nonuniform heating and cooling, i.e., creating complex welding residual stress and angular deformation in the structure. In this present study, the effect of four different welding sequences on submerged arc welded fillet joint has been studied. A finite element-based numerical model has been developed to predict the thermal profile, welding residual stress, and angular deformation. The developed model considers temperature-dependent material property and material deposition by using element death and birth technique. The results have been compared with experimental one. In the effect of welding sequence on residual stress, angular deformation has been studied. Thus, the developed model presents the effect of welding sequence on the weld induced residual stresses and distortions which provide one of the most optimal welding sequence for enhanced fabrication process.

Numerical simulation of welding-induced residual stress in fusion welding process using adaptive volumetric heat source:

The mechanical properties of a weldment structure are influenced by the level of residual stress generated during fusion welding process. The experimental determination of residual stress is cumbersome and not free from measurement errors. A sophisticated numerical model is relatively easy approach to predict residual stress due to the advancement of high performance computational technology. However, the integration of all process physics to make a sophisticated numerical model is ever demanding. The present work is motivated in that direction and involves a finite element based numerical model for simulation of welding-induced residual stresses. A thermal model using adaptive volumetric heat source has been used to estimate temperature distribution. Subsequently, the thermal history is used to perform stress analysis for butt welded plates using three different fusion welding processes. The material behaviour is assumed as elasto-plastic in nature. The calculated results and their trend have been validated with experimental results available in open literature.

Modelling of heat transfer in submerged arc welding process

In this work, an analytical model for transient temperature distribution during submerged arc welding for joining two steel plates is presented. The conservation of energy equation is used to represent the thermal behaviour of the submerged arc welding process. A three-dimensional double-paraboloid shape for volumetric heat source with Gaussian distribution is considered for electric arc during welding, and a parabolic-shaped cross section for the weld pool is considered. A set of experiments is conducted to determine the geometric parameters. The final analytical solution considers effect of the electric arc, convective heat transfer from the exposed surface and heat of molten electrode material. Subsequently, the prediction is compared with experimentally predicted temperatures where a good agreement is found.