Parametric Optimization of Butt Weld for Minimum Residual Stress

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1 Parametric Optimization of Butt Weld for Minimum Residual Stress Salawadagi Sushant S. & Kumbhar S. B. Dept. of Mechanical Engineering, RIT Sakharale , Sangli, Maharashtra, India sushantsalawadagi@gmail.com Abstract - Metal Inert Gas welding (MIG) process is an important part in many industrial operations. The welding parameters are the most important factors affecting the quality, productivity and cost of welding. This paper presents the effect of welding parameters like welding current, welding voltage, welding speed and weld plate angle of es generated in mild steel plates during welding. In this paper experimental verification of temperature distribution by FEM is carried out, the verified methodology is used for parametric optimization for minimum. The finite element analysis of es in Butt welding of two similar plates is performed with the ANSYS software. The optimum welding parameters are found out by different combination of the welding parameters. The welding parameters of weld specimen for minimum (327MPa) are current 180amp, voltage 23volt, welding speed mm/min, weld plate angle 0 0 and for maximum (663MPa) current 200amp, voltage 25volt, welding speed 428.4mm/min, weld plate angle 90 0 are obtained. The impact the weld specimens minimum and maximum es are checked by using the Charpy test. The impact weld is improved by 31.42%. Keywords - Butt weld, finite element analysis, MIG welding, mild steel,. I. INTRODUCTION Metal Inert Gas welding is one of the most widely used processes in industry. The input parameters play a very significant role in determining the quality of a welded joint. As a result of thermally induced plastic deformations during the welding process, the internal stresses, namely, the welding es remain in the welded components and structures. Residual stress distribution and distortion in weld joints and are strongly affected by structural parameters (geometry and joint type), material parameters (mechanical and physical properties), and welding process parameters (current, voltage, welding speed). The resulting residual stresses have a strong influence on weld deformation, fatigue, creep and buckling. In large steel fabrication industries such as shipbuilding, marine structures, aero-space industry, high speed train guide ways and pressure vessels and piping in chemical and petrochemical industry the problem of es and overall distortion has been and continue to be a major issue. During welding a very complex thermal cycle is applied to the weldment which in turn causes irreversible elastic- plastic deformation and consequently gives rise to the residual stresses in and around fusion zone and heat affected zone (HAZ). For the vast application of welding joints in the industry, analysis of the es in these joints is an important task in mechanical engineering design of the weldments. II. PROCEDURE TEMPERATURE ISTRIBUTION DURING WELDING PROCESS The percentage difference between temperature distribution in experiment and finite element analysis are obtained. The temperature distribution of the welding plate in experimental is nearly equal to the temperature distribution in finite element analysis. From these results it is verified the input conditions used in experimental are also obtained nearly same results in the finite element analysis. Therefore same methodology can use for parametric optimization of weld for minimum. A. Experimentation for Temperature distribution in welding plate In this experiment the butt weld joint made of two similar mild steel plates. The mild steel plates having dimensions 100mm 100mm 6mm are used. The temperature measurement was implemented using K- type thermocouples. This method was used during the metal inert gas (MIG) welding of two similar plate butt joint of mild steel material. First the two welding plate can be arranged. The thermocouples are attached to the welding plate at different distances. The gas flow start and wire feed rate can be adjusted. The values of the voltage and current are set. Then start the welding process. The time required to complete welding process is measured by using the stopwatch. Using the time and distance travelled by the electrode during the welding process calculate the welding speed. The temperature 99

2 can be generated during the welding procedure is measured by using the thermocouples. The generated temperature can be measured by using temperature indicator. Typical welding parameters taken in this study are current 180amp, voltage 23volts, welding speed 428.4mm/min. The amount of heat input during welding Q was calculated as follows. Heat input rate (Q) =V I 60/U (J/mm) (1) V = voltage, I = current, U= welding speed. mild steel plates shown in Fig.1 was simulated. The sample analysis of the temperature distribution in butt welding plate is carried out in the ANSYS software. The eight-node brick elements with linear shape functions are used in meshing the model. The element type SOLID70, which has a single degree of freedom, was used for the thermal analysis. In this analysis first prepare the model and then by using the same input data as per the experiment calculate heat input. This heat input is apply at the butt weld joint then the temperature distribution is generated in welding plates. The temperature is measured at the same distance as per the experiment. Fig.2 3D model of closed Butt-weld joint Fig.1: Temperature distribution in welding plate by experiment B. Temperature distribution in welding plate by FEM The temperature dependant thermal material properties for the plates, heat affected zone (HAZ) and the filler weld material were assumed to be the same, see Table I. For the mechanical material properties, same material models were used for the weld beads and the base materials according to the yield strength. Thermal Specific Yield Young s Temp Conductivity Density expansion Poisson s 0 heat C (J/kg 0 (W/m 0 C) (kg/m 3 stress Modulus ) coefficient Ratio c) (MPa) (10-5/ 0 (GPa) c) Table. I Temperature dependent material properties The 3D model of a closed butt-weld joint of two Fig.3Temperature distribution in welding plate by FEM C. Comparison of Temperature distribution by experiment and FEM The comparison of the temperature distribution between the experiment and the finite element analysis is shown in Table II. The temperature distribution of the welding plate in experimental is nearly equal to the temperature distribution in finite element analysis. From these results it is verified the input conditions used in experimental are also obtained nearly same results in the finite element analysis. 100

3 Distance Temp. by Temp. by Percentage (mm) Expt. ( 0 C ) FEM ( 0 C ) difference Table.II Comparison of Temperature Distribution by experiment and FEM III. RESIDUAL STRESS CALCULATION BY FEM SOFTWARE If In this study, the weld plate angle (A), current (I), voltage (V) and welding speed (v) are considered as the welding parameters. As these parameters can significantly affect the es generated during welding. For calculation of the es these welding parameters are selected. The parameters are assumed as shown in the Table III. Weld angle Current (Amp ) Voltage (Volt) Welding speed (mm/min) A. Coupled field analysis Table.III Welding Parameters The process of welding is simulated by the FE method. The welding process computation can be split into two solution steps thermal and mechanical analyses. To simplify the welding simulation, it is computationally efficient to perform thermal and mechanical analyses separately. It is assumed that changes in the mechanical state do not cause a change in the thermal state. But a change in the thermal state causes a change in the mechanical state. Firstly, the computation of the temperature history during welding is completed and this temperature field is applied to the mechanical model as a body force to perform the analysis. This work includes FE models for the thermal and mechanical welding simulation. To develop suitable welding numerical models it necessary to consider the process parameter (welding speed, filling material supplying, etc.), the geometrical constraints, the material nonlinearities and all physical phenomena involved in welding. The element type SOLID70, which has a single degree of freedom, was used for the thermal analysis. For the structural analysis the element type SOLID185, with three translational degrees of freedom at each node, was used. Fig.4 Residual stresses in welding plate Since the thermal field has a strong influence on the stress field with little inverse influence, a sequentially coupled analysis works very well. Moreover, a 3-D FE analysis is the optimum method of as certaining the thermal cycle of welding. Therefore, in this paper, the welding process is simulated using a sequentially coupled 3-D thermo-mechanical FE formulation based on the ANSYS code. For both the thermal and mechanical analyses, temperature dependent thermophysical and mechanical properties of the materials are incorporated. Table. IV Optimization of welding parameters by FEM 101

4 B. Testing of Minimum and maximum weld specimen The minimum and the maximum weld specimens are measured by using the impact test. The charpy test is used to measure the impact minimum 327MPa and maximum 663MPa weld specimen. The size of specimen 10mm 6mm 55 mm long is used for charpy test. The welding parameters of weld specimen for minimum (327MPa) are current 180amp, voltage 23volt, welding speed mm/min, weld plate angle 0 0 and the welding parameters of weld specimen for maximum (663MPa) are current 200amp, voltage 25volt, welding speed 428.4mm/min, weld plate angle 90 0 are obtained. weld specimens after Charpy test completed are shown in the fig 5. (a) Table. V Impact minimum weld specimen Impact minimum residual stress weld (Kg.m) minimum residual stress weld (Kg.m) Average Impact minimum Table.VI Impact maximum weld specimen Impact maxmum residual stress weld (Kg.m) maxmum residual stress weld (Kg.m) maxmum C. Minimum and maximum weld Specimens The impact minimum and maximum weld specimens is measured by using the Charpy test. For minimum weld specimens J impact energy is required and for maximum weld specimens J impact energy is required. The minimum and maximum (b) Fig.5 (a) Minimum and (b) maximum weld Specimens IV. RESULTS AND DISCUSSION By using FEM methodology at different combinations of the welding parameters the residual stresses generated in the butt weld plate is calculated. (a) 102

5 The welding parameters combination of weld specimen for maximum (663MPa) are current 200amp, voltage 25volt, welding speed 428.4mm/min, weld plate angle 90 0 obtained. (b) (c) Fig.6 (a), (b), (c) Residual stresses at different combinations of the welding parameters When the current, voltage and angle of the weld plate is increase the es are also increases. When the welding speed is increase the es are decreases. minimum maxmum Percentage Difference Table.VII Impact minimum and maximum weld The welding parameters combination of weld specimen for minimum (327MPa) are current 180amp, voltage 23volt, welding speed mm/min, weld plate angle 0 0. V. CONCLUSION The temperature distribution results of the welding plate in experimental procedure are nearly equal to the temperature distribution results in FEM. From these temperatures distribution results it is verified the input conditions used in experimental procedure are also obtained the same results in the finite element analysis. For optimization of the welding parameters different combinations of the current, voltage, welding angle, welding speed are used. If the values of the current, voltage, welding speed are increase the residual stresses are increases. The higher es 561MPa, 663MPa distribution was at edge angle30, 90 respectively and lower 327MPa distribution was at 0 0. Optimum parameters for the weldability of Mild steel specimen of dimension The optimum welding parameters for the weldability of mild steel weld specimen of dimension100mm 100mm 6 mm for minimum (327MPa) are current 180amp, voltage 23volt, welding speed mm/min, weld plate angle 0 0 and for maximum (663MPa) current 200amp, voltage 25volt, welding speed 428.4mm/min, weld plate angle 90 0 are obtained. The impact strength of weld is improved by 31.42%. VI. REFERENCES [1] Dragi Stamenković, MSc (Eng),Ivana Vasović, BSc (Eng), Finite Element Analysis of Residual Stress in Butt Welding Two Similar Plates Scientific TechnicalReview,Vol.LIX,1,2009 [2] S. P. Tewari, Ankur Gupta,Jyoti Prakash, Effect Of Welding Parameters On The Weldability Of Material, Mechanical Engineering Department, Institute Of Technology, Banaras Hindu University Varanasi , U.P., India [3] Li Yajiang, Wang Juan, Chen Maoai And Shen Xiaoqin, Finite element analysis of residual stress in the welded zone of a high strength steel, Bull. Mater. Sci., Vol. 27, 2, April 2004, pp Indian Academy of Sciences. Key Laboratory of Liquid Structure and Heredity of Materials, Ministry of Education, Shandong University, Jinan , China [4] Viorel Deaconu, Finite Element Modelling of Residual Stress A Powerful Tool in the Aid of 103

6 Structural Integrity Assessment of Welded Structures 5th Int. Conference Structural Integrity of Welded Structures (ISCS2007), Timisora, Romania, Nov 2007 [5] A.M. Paradowskaa, J.W.H. Price, R. Ibrahim, T.R. Finlayson The effect of heat input on distribution of steel welds measured by neutron diffraction, Journal of Achievements in Materials and Manufacturing EngineeringVOLUME 17 ISSUE 1-2 July- August 2006 [6] M.Jeyakumar, T Christopher, R Narayanan & B Nageswara Rao, Residual Stress Evaluation in Butt Welded Steel Plates Indian Journal of Engineering & Material Sciences Vol.18, Dec 2011, pp [7] Dr. Hani Aziz Ameen, Khairia Salman Hassan & Muwafaq Mehdi Salah, Influence of the Butt Joint Design of TIG Welding on the Thermal Stresses, Eng. & Tech. Journal, Vol.29, 14,