| With the development of manufacturing global industry, the welding technology hasbeen used in various industries fields as a basic technology. As a new method of weldingtechnology, friction stir welding (FSW) has been widely used in many important industrialfields in last two decades, such as aerospace, automotive, electronic power, ships and so on. Itcreates considerable social and economic benefits and values. But there are manydisadvantages still existed in the process of FSW. When the work-pieces were welded byFSW, high normal pressure and rotation velocity were needed, which causes severe wear ofpin tool. These disadvantages have not been solved so far. In this research, a new type ofFSW which named electromagnetic FSW is studied. In the new type of FSW, direct current isapplied into pin tool and work-pieces, and electromagnetic coil is set around the tool shoulder.The purpose of the design is to reduce wear of pin tool and save welding material byimproving heat efficiency and reducing normal pressure and rotation velocity. It can also beused in welding of refractory material effectively.Based on the prototype of FSW, a3D model was established by Multi-physics couplingFE software COMSOL Multiphysics in the research. According to transient heat transferunder electromagnetic environment, the distribution and variation rule of temperature andIsothermal layer under different working parameters were analyzed under the different effectof signal heat source and multiple heat sources.Based on the analysis of experimental phenomenon, some conclusions are obtained asfollows:(1) Melting time: As electromagnetic field has been introduced into model in succession,the time when the temperature of work-piece get melting temperature has been reduced underthe same parameter conditions. At the same time, the welding time has been shorted. Thewelding efficiency is improved.(2) Distribution of temperature field and isothermal layer: The area of temperature fieldand isothermal layer distribution are decreased when electromagnetic field is introduced underconstant parameter conditions in succession. When three parameters among the rotationvelocity, normal pressure, moving velocity and induction frequency are constant, the changetrend of distribution area of temperature field and isothermal layer about model is opposite tomutative parameter’s change trend. Regardless of electromagnetic field be introduced，isothermal layer distribution on the front side of the work-piece is thinner than behind side.The temperature gradient on the front side of the work-piece is less than behind side. Afteradding a magnetic field, isothermal layer of tool shoulder distributes as curve surface morphology under the influence of skin effect. The temperature gradient on left of thecenterline is greater than the right side on the tool shoulder.(3) Maximum temperature curve: By contrasting with highest temperature curves ofsingle heat source and multiple heat sources, electromagnetic field’s effect greatly reduces theaxial force and rotation velocity requirement in the same heating efficiency. Simultaneouslyelectromagnetic field’s effect greatly decreases the stiffness of machine axis and input ofmotor power requirement. It also reduces the wear of pin tool and saves welding materials.Adding a magnetic field can save37.5%axial force and33.3%rotation velocity under thesame heating efficiency. The electromagnetic field to some extent solves the problem whichfriction heat can’t weld material for a long time with larger velocity.(4) Length of welding time: Due to the influence of eddy heat， high temperaturedistribution field of the model will move towards the shoulder from the contact area of pintool and work-piece with time addition. When welding time get rated value the maximumtemperature will increase linearly with time addition. So this research involves the way whichmagnetic field loaded can’t be used in friction stir welding for long time.Some useful conclusions are obtained by FE simulation for FSW. To some extent theseconclusions can provide a simulation basis for the new design applied in the future, whichnamed electromagnetic FSW. |
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