共查询到20条相似文献,搜索用时 0 毫秒
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《Science & Technology of Welding & Joining》2013,18(3):361-368
AbstractBased on the tridimensional Gauss distribution of power density, a general double ellipsoid welding heat source model has been developed. This model not only consists of all the characteristics of a double ellipsoid model, but also can deal with the situation where, under an external disturbance, the arc's backbone is not perpendicular to the work surface. This general double ellipsoid model is validated by measured results of the temperature field during twin wire welding. Using the non-linear finite element software Marc, the temperature field during twin wire welding was calculated using both the double ellipsoid heat source and the general double ellipsoid heat source. The thermal cycling curves and the weld pool cross-section obtained by the general double ellipsoid heat source tally well with the experimental results. 相似文献
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《Science & Technology of Welding & Joining》2013,18(5):597-603
AbstractBased on the Green's function method, a mathematical model allowing for the latent heat of fusion and solidification is developed to describe the steady state, two-dimensional heat flow during welding of thin plates. It is demonstrated that the latent heat has a pronounced effect on shape and size of the weld pool and mushy zone. The thermal efficiency of base metal fusion by a line heat source η t can exceed 0·4839 considerably if the latent heat is taken into account. It is shown that the known simplified approaches for considering the latent heat can introduce large errors into the estimation of η t. The calculated and experimental weld pool shapes are compared. 相似文献
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The heat input from arcs to weld pool in twin-arc gas metal arc welding (GMAW) with a common weld pool is investigated by high-speed photography. The characteristics of arc shapes and droplet transfer are studied and then the models for heat flux distribution on top surface of weld pool and enthalpy distribution of metal droplets transferred into weld pool are established. By using the model, 3-D geometries of weld pools in twin-arc GMAW with a common weld pool are predicted. Corresponding welding experiments on mild steel plates are carried out and the results indicate that the predicted shape of weld bead on cross section shows good agreement with measured one. 相似文献
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《Science & Technology of Welding & Joining》2013,18(6):701-705
AbstractThis paper deals with the sufficient conditions under which instantaneous heat source can be considered as welding heat source instead of moving source. Temperature rises calculated by instantaneous source and moving one were compared. The applicable conditions of the instantaneous heat source with errors of 1% and 5% were found. This enables us to select either moving or instantaneous source with information of welding speed, thermal diffusivity and the distance from the weld centre line to the interested location. Approximate equations to determine the maximum temperature rise using a moving source were proposed and the accuracy of their calculation was proved to be ~99%. 相似文献
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《Science & Technology of Welding & Joining》2013,18(1):113-119
AbstractA model of gas metal arc welding was developed that solves the magnetohydrodynamic equations for the flow and temperature fields of the molten electrode and plasma simultaneously, to form a fully coupled model. A commercial finite-element code was extended to include the effects of radiation, Lorentz forces, Joule heating and thermo-electric effects. The model predicts the shape of the free surfaces of the molten metal as the droplets form, detach, and merge with the weld pool. It also predicts the flow, temperature, and electric field. Material properties and the welding parameters are the input variables in the model. The geometry of the numerical model was constructed to fit an experimental apparatus using an aluminium electrode and an argon shielding gas. Droplet frequency measurements were used to verify the model's predictions. For a typical arc, the temperature of the plasma can range up to 20 000 K, where there is more uncertainty in the thermophysical properties of the plasma, and the properties in this range are highly non-linear. For this range, the material properties of the model were adjusted to obtain a better fit between the numerical and the experimental results. The model and experimental results were comparable. 相似文献
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《International Journal of Cast Metals Research》2013,26(1-4):131-134
AbstractA large proportion of research on soldered joints focuses on the effects of stress on the service life of a solder joint. However, the shape of a joint also has a great effect on its service life. During the reflow process, the solder joint experiences heating, melting, cooling and then solidification. Conventionally, the shape of a solder joint is often predicted using the energy method after the reflow process. This, however, does not consider the evolution of the solder alloy during reflow. In this study, a computer aided analytical system is developed based on computational heat transfer and fluid dynamics techniques to simulate the shape evolution of solder joints during reflow. Experimental observations of the shape evolution of the joint during reflow were also conducted. The simulation results obtained for a solder ball 760 μm in diameter on a rectangular pad were found to be consistent with the experimental observations. 相似文献
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《Science & Technology of Welding & Joining》2013,18(6):717-724
AbstractA three-dimensional finite element model for the prediction of the distortion and residual stresses induced during electron beam welding is described. The model is validated by butt welding experiments on two Inconel 718 plates. A particular effort is made to determine a good model for the heat input. A combined conical and double ellipsoid heat source is used to model the deep penetration characteristic of the electron beam and this source is calibrated using the results from a separate thermodynamic simulation, using the ELSIM finite difference code. Parallel computation is used to reduce the overall simulation time in the coupled thermomechanical simulation of welding. The agreement between calculations and experiments is good with respect to the residual stresses. Measured and computed deformations agree qualitatively although they differ in magnitude. 相似文献
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《Science & Technology of Welding & Joining》2013,18(5):544-549
AbstractA three-dimensional (3D) precipitate and matrix model was used to investigate the role of precipitates as nucleation sites of creep void in the heat affected zone (HAZ) of a welded joint of high Cr ferritic heat resistant steels at high temperature and low stress. Several factors affecting creep void initiation, such as Young's modulus of precipitate and precipitate size, were studied. The material properties of the matrix were investigated for the regions of coarse grained HAZ, fine grained HAZ and base metal in the welded joint. The results show that creep void occurs easily in the fine grained HAZ region because of the deterioration in material properties and coarsened precipitates in this zone 相似文献
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《International Heat Treatment & Surface Engineering》2013,7(1-2):40-44
AbstractThis work presents a modelling approach for the simulation of the microstructure evolution during solution heat treatment in technical, multi component superalloys. This model is based on a theoretical approach and calclations. All calculations start with the simulation of solidification, as the as-cast microstructure is the starting condition to simulate the subsequent heat treatment. The model takes into account typical length scales, diffusion, morphological and constitutional aspects of the alloys. Simulations are performed for an alloy with several alloying elements. It is proposed that with the aid of the simulations optimised solution heat treatments can be derived. 相似文献
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《Science & Technology of Welding & Joining》2013,18(6):539-549
AbstractAn analytical thermal model of conduction mode double sided arc welding (DSAW) has been derived and used to predict the weld pool dimensions and shapes and temperatures within 2˙5 and 1˙15 mm thick AA5182 Al alloy sheets as functions of the primary DSAW parameters. Separate Gaussian distributed arc heat sources from a plasma arc welding and gas tungsten arc welding torch were assumed to act on the top and bottom surfaces of the sheets. There was excellent correlation between observed and predicted DSAW weld pool dimensions and shapes provided that suitable values for arc efficiencies and distribution coefficients for the two separate arcs were used in the model. The model is capable of predicting weld pool dimensions and shapes of both full and partial penetration conduction mode DSAW welds made in Al alloy sheet, the welding speed at which there is a transition from full to partial penetration welding and the speed above which no melting occurs. 相似文献
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《Science & Technology of Welding & Joining》2013,18(5):521-527
AbstractIt is useful to develop a numerical model for various welding positions in order to understand welding phenomena. Welding simulation models for a particular application could help in offline robot programming and online robot control. The objective of this study was to develop a tungsten inert gas (TIG) welding simulation model for various workpieces of different shapes. The present model may be easily applied to several workpiece configurations. This article deals with a model for circumferential welding of a pipe to a plate of mild steel, and aluminium alloys. The calculated results clarify that a homogeneous weld is hardly obtained at a fixed pipe welding position due to gravity, and that weld bead shape varies sensitively with wall thickness in pipe to plate welding. It is concluded that the model proposed in this article is useful to simply simulate TIG welding and provides a powerful means to estimate the optimum process parameters in welding practice. 相似文献
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视觉图像检测是实现GMAW焊接质量控制的重要步骤。针对焊接图像稳定性差、噪声大的特点,提出了一种基于复合视觉和形态学模糊检测的算法。该算法采用双CCD采集焊接视觉图像并使用数学形态学理论处理图像,通过将该图像检测算法应用于焊接动态过程中的熔池图像处理,结合闭环模糊PID控制理论,一套完整的GMAW焊过程质量控制系统得以实现。MAG焊工艺试验表明,该控制系统可以有效地克服焊接过程中的外界干扰,从而保证焊接质量的稳定。 相似文献
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《International Journal of Cast Metals Research》2013,26(4):254-258
AbstractThermal analysis technique relies on the cooling curve obtained when the sample is cooled in a sampling cup. This may not represent the cooling behaviour of the real casting. The microstructure developed during solidification depends not only on the nucleation and modification potential of the melt but also on the thermal gradient imposed during solidification by the mould. The factors affecting the thermal gradient are the mould material and casting section thickness. In the present investigation the effect of modification melt treatment, cooling rate and casting section thickness on the thermal analysis parameters of A357 alloy was studied. It is found that the dimensionless heat flux parameter is high for small section thickness castings. The metal/mould interfacial heat flux is high in a copper mould. Thermal analysis parameters of A357 alloy are found to be affected significantly by the combined action of modification, chilling and section thickness. 相似文献
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《Science & Technology of Welding & Joining》2013,18(5):455-459
Abstract45MnMoB steel was joined by transient liquid phase (TLP) bonding using three two step heating processes. The joining area was first heated up to 1250°C and kept for 5 s, and then cooled down to 1210, 1220 and 1230°C named second holding temperature respectively and kept for 120 s. The interface morphology of the bond made using two step heating process was also compared with that of conventional TLP bond at a constant temperature. The results show that two step heating process can produce a cellular interface at the initial stage, which is different from the planar interfaces associated with conventional TLP bonding. No bond interface can be found in the final joint by two step heating process and the microstructure of joint is similar to that of base metal. With the increase in second holding temperature, oxide scale particles and porosities in the bond region are decreased noticeably both in size and amount, and the bond strength is increased. The bond fails at the base metal and no failure occurs when the joint is tensioned and bent to 180° at 1250 and 1230°C respectively. Therefore, two step heating process can produce a homogenous joint, free of bond interface and identical in composition and properties to that of the base metal. 相似文献
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针对脉冲MIG焊接试验过程建立了复合热源模型,并采用有限元软件ABAQUS对板厚15 mm的Al-Mg-Zn铝合金进行了多层多道脉冲MIG焊接的传热过程数值模拟. 根据复合热源和单一双椭球热源进行计算对比. 结果表明,该组合热源可以较好的模拟脉冲MIG焊接不同道次的熔池形貌,并且降低热源校准难度. 同时,基于建立的复合热源模型,文中引入非线性弹性边界条件表征实际夹具工装,对脉冲MIG焊接过程的应力和变形分布进行仿真模拟,其中焊后变形分布规律和试验测量具有较好的一致性. 相似文献
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Ji CHEN ) Chuansong WU ) ) MOE Key Laboratory for Liquid-Solid Structure Evolution Materials Processing 《金属学报(英文版)》2011,(6):457-465
The momentum of strong backward flowing melt jet and the thermal action from transferred droplets are two dominating factors affecting the formation of humping bead in high speed gas metal arc welding (GMAW). Appropriate describing the influence of the distribution mode of droplet heat content in the weld pool is essential to understand the physical mechanism of humping bead formation. Based on the experimental results, four kinds of droplet heat content distribution modes are proposed and employed to calcu... 相似文献