搅拌摩擦焊接过程中搅拌头转速对材料流动的影响

使用有限元方法模拟了不同搅拌头转速下,搅拌摩擦焊接过程中Al6061～T6材料的三维流动,以及材料流动与搅拌头转速的关系,结果表明,在搅拌摩擦焊接过程中,后退侧的材料流动较前进侧更为剧烈,并且随着搅拌头转速的增加,材料流动也会得到不同程度增强,搅拌头前方的材料在搅拌头的推动作用下向上涌起,被旋推到搅拌头后方并向下运动,该过程的周而复始是促使搅拌摩擦焊接顺利完成的主要原因,等效塑性应变等值线的形状与材料热影响区,热力影响区以及搅拌区的边界形状具有较好的对应关系,随着搅拌头转速的增加,等效塑性应变随之增加。     

搅拌针形状影响搅拌摩擦焊过程金属塑性流动规律的数值模拟

考虑材料参数随温度的变化关系以及搅拌工具的实际结构,利用Fluent流体力学软件建立了搅拌摩擦焊的有限体积模型,对搅拌针的形状影响材料塑性流动行为的规律进行了研究.结果表明,材料的流动速度随着到焊件表面以及到搅拌针旋转轴的距离增加而减小;当减小搅拌针的锥角以及减小搅拌针的螺纹槽宽度时,焊件内部材料的流动速度得到提高.当搅拌工具在焊接过程中顺时针旋转时,对于左螺旋搅拌针,搅拌针附近的材料向下流动,而热力影响区材料的流动方向向上,此规律与右螺旋搅拌针时相反.     

Numerical simulation of effect of rotational tool with screw on material flow behavior of friction stir welding of Ti6A14V alloy

The rotational tool is put forward, which is composed of the one-spiral-flute shoul-der and the rotational pin with screw. Using the turbulent model of the FLUENT software, material plastic flow behavior during the process of friction stir welding of Ti6Al4V alloy is researched by the numerical simulation method and then the effect of rotational tool geometry on material flow during the welding process is attained. The results show that the flow direction of the material near the rotational tool is mainly the same as the rotational direction of the tool while the material near tool flows more violently than the other regions. For the tapered rotational pin, the flow velocity of material inside the workpiece decreases with the increase of the distance away from the workpiece surface because of the change of pin diameter. For the rotational tool, the flute added to the shoulder and the screw added to the pin can greatly increase the flow velocity of material during the welding process while the peak value of the flow velocity of material appears on the flute or the screw. Moreover, the rotational tool with the one-spiral-flute shoulder is better than the tool with the concentric-circles-flute shoulder. Decreasing the width of pin screw and increasing the diameter of pin tip are both good for the increase of flow velocity.     

2024铝合金板搅拌摩擦焊接塑性材料流动的可视化检测与数值模拟(英文)

将薄铜片作为标示材料镶嵌于2024铝合金板中,经搅拌摩擦焊接焊后,用金相法观察其最终位置。参考材料流动的可视化实验结果,建立搅拌摩擦焊传热与材料流动的三维数值分析模型。搅拌针附近塑性材料流动速度分布模式的计算结果与可视化实验结果基本一致。当焊接速度一定时,随搅拌针旋转速度的提高,搅拌针附近塑性材料流动加剧。焊核区形状与尺寸的计算结果与实测数据吻合。     

Analysis of effect of tool geometry on plastic flow during friction stir spot welding using particle method

The effect of tool geometry on the plastic flow and material mixing during friction stir spot welding (FSSW) is investigated using the particle method approach. For spot welds made with a cylindrical pin tool with flat shoulder, the model predicts the material flow at the pin periphery to be in the upward direction and the material is pushed downward beneath the shoulder giving rise to the resultant hook geometry. Other pin geometries evaluated include tapered pin, inverse tapered pin, triangular pin, convex shoulder, and concave shoulder. With good correlation with experimental trials, this model is then used to predict the material flow for spot welds. The material flow, and thereby the resultant hook formation, is quantified using numerical methods and is expressed as standard deviation of the particle movement. A triangular pin with a concave shoulder is the preferred tool geometry from the current study that results in high strength spot welds.     

Simulation of 3D material flow in friction stir welding of AA6061-T6

This paper reports the numerical simulation of the 3D material flow in friction stir welding process by using finite element methods based on solid mechanics. It is found that the material flow behind the pin is much faster than that in front of the pin. The material in front of the pin moves upwards and then rotates with the pin due to the effect of the rotating tool. Behind of the pin, the material moves downwards. This process of material movement is the real cause to make the friction stir welding process continuing successfully. With the increase of the translational velocity or the rotational velocity of the pin, the material flow becomes faster.     

Modeling the Material Flow and Heat Transfer in Reverse Dual-Rotation Friction Stir Welding

Reverse dual-rotation friction stir welding (RDR-FSW) is a novel modification of conventional friction stir welding (FSW) process. During the RDR-FSW process, the tool pin and the assisted shoulder are separated and rotate with opposite direction independently, so that there are two material flows with reverse direction. The material flow and heat transfer in RDR-FSW have significant effects on the microstructure and properties of the weld joint. A 3D model is developed to quantitatively analyze the effects of the separated tool pin and the assisted shoulder which rotate in reverse direction on the material flow and heat transfer during RDR-FSW process. Numerical simulation is conducted to predict the temperature profile, material flow field, streamlines, strain rate, and viscosity distributions near the tool. The calculated results show that as the rotation speed of the tool pin increases, the temperature near the tool gets higher, the zone with higher temperature expands, and approximately symmetric temperature distribution is obtained near the tool. Along the workpiece thickness direction, the calculated material flow velocity and its layer thickness near the tool get lowered because the effect of the shoulder is weakened as the distance away from the top surface increases. The model is validated by comparing the predicted values of peak temperature at some typical locations with the experimentally measured ones.     

铝合金搅拌摩擦点焊接头塑化金属流动形态分析

在搅拌摩擦点焊过程中,塑化金属的流动形态是影响焊点成形及接头力学性能的主要因素。通过采用镶嵌标识材料的方法,研究了搅拌摩擦点焊过程中接头塑化金属的流动形态。结果表明,在焊点横截面上,匙孔两侧塑化金属发生塑性变形的宽度基本相同,从焊点表面到底面,塑性变形区宽度逐渐减小。在焊点的上部,塑化金属主要受轴肩的作用,在轴肩摩擦力和材料之间的剪切力作用下沿搅拌针旋转的方向运动,随着距焊点表面距离的增大,塑化金属沿搅拌针旋转方向的运动趋势逐渐减小。搅拌针周围的塑化金属在搅拌针螺纹向下的压力作用下,以螺旋状向焊点底部运动,运动到焊点底部后受底板的阻碍和未塑化金属的挤压作用从搅拌针四周向焊点上部运动。     

Analysis of tool geometry in dissimilar Al alloy friction stir welds using optical microscopy and serial sectioning

Abstract

The influence of tool geometry on material flow during friction stir welding of dissimilar aluminium alloys is investigated. Sheets of Al 2024 and Al 6061 alloys are friction stir welded in lap and butt configurations using different welding conditions. Optical microscopy with serial sectioning is utilised to systematically study material flow when small variations are made to the tool pin. It is shown that three flat features on the pin impose vertical material flow which can promote intermixing. When a threaded tool is used, the material flow and formation of the intermixed region depends on the orientation of the base materials, since the differences in viscosity of material on the advancing versus retreating side of the tool will inhibit intermixing. Decreasing the travel speed will promote intermixing by increasing the residence time to compensate for the differences in material viscosity that otherwise limit intermixing.     

焊缝金属厚度方向的流动与洋葱瓣花纹的形成

研究了在铝合金薄板与铜箔交替叠加的多层板搅拌摩擦焊过程中焊缝金属的塑性流动行为.结果表明,用带螺纹的搅拌针焊接时,搅拌针周围金属沿螺纹在焊缝厚度方向产生剧烈的流动,在螺纹端部脱离搅拌针并向周围挤压母材,形成实心环形挤压区,与周围母材有明显的界面.洋葱瓣花纹是实心环形挤压区在焊缝横截面上的表现形式.搅拌针表面的螺纹提供金属在焊缝厚度方向流动的驱动力.搅拌头顺时针旋转时,用左螺纹搅拌针焊接的焊缝横截面上,洋葱瓣花纹的中心偏向焊缝底部;用右螺纹搅拌针焊接的横截面上,花纹的中心偏向焊缝表面.     

Numerical modelling of 3D plastic flow and heat transfer during friction stir welding of stainless steel

Abstract

Three-dimensional (3D) viscoplastic flow and temperature field during friction stir welding (FSW) of 304 austenitic stainless steel were mathematically modelled. The equations of conservation of mass, momentum and energy were solved in three dimensions using spatially variable thermophysical properties using a methodology adapted from well established previous work in fusion welding. Non-Newtonian viscosity for the metal flow was calculated considering strain rate and temperature dependent flow stress. The computed profiles of strain rate and viscosity were examined in light of the existing literature on thermomechanical processing of alloys. The computed results showed significant viscoplastic flow near the tool surface, and convective transport of heat was found to be an important mechanism of heat transfer. The computed temperature and velocity fields demonstrated strongly 3D nature of the transport of heat and mass indicating the need for 3D calculations. The computed temperature profiles agreed well with the corresponding experimentally measured values. The non-Newtonian viscosity for FSW of stainless steel was found to be of the same order of magnitude as that for the FSW of aluminium. Like FSW of aluminium, the viscosity was found to be a strong function of both strain rate and temperature, while strain rate was found to be the most dominant factor. A small region of recirculating plasticised material was found to be present near the tool pin. The size of this region was larger near the shoulder and smaller further away from it. Streamlines around the pin were influenced by the presence of the rotating shoulder, especially at higher elevations. Stream lines indicated that material was transported mainly around the pin in the retreating side.     

Modeling of material flow in friction stir welding process

This paper presents a 3D numerical model to study the material flow in the friction stir welding process. Results indicate that the material in front of the pin moves upwards due to the extrusion of the pin, and then the upward material rotates with the pin. Behind the rotating tool, the material starts to move downwards and to deposit in the wake. This process is the real cause to make friction stir welding process continuing successfully. The tangent movement of the material takes the main contribution to the flow of the material in friction stir welding process. There exists a swirl on the advancing side and with the increase of the translational velocity the inverse flow of the material on the advancing side becomes faster. The shoulder can increase the velocity of material flow in both radial direction and tangent direction near the top surface. The variations of process parameters do have an effect on the velocity field near the pin, especially in the region in which the material flow is faster.     

A study of texture patterns in friction stir welds

Texture patterns on transverse, longitudinal and horizontal cross-sections in friction stir welds (FSW) have been studied experimentally, and their variations with welding parameters have been analyzed. Numerical simulations of the FSW process have been carried out to understand the texture patterns. Results of this study suggest that the texture patterns are complex but a dominant theme is the appearance of bands, which occur in the advancing-side material. The banded pattern on the transverse cross-section is often in the form of onion rings. The spacing between the bands on the longitudinal and horizontal cross-sections equals the distance traveled by the welding tool in one revolution. The texture patterns are found to correlate well with equivalent plastic strain contours from simulations of the corresponding FSW process, suggesting that the texture patterns may be formed because periodically spaced material regions experience very different levels of plastic deformation during the FSW process.     

Effects of pin geometry on the material flow behavior of friction stir spot welded 2A12 aluminum alloy

A three dimensional finite volume model was established by the ANSYS FLUENT software to simulate the material flow behavior during the friction stir spot welding (FSSW) process. Effects of the full-threaded pin and the reverse-threaded pin on the material flow behavior were mainly discussed. Results showed that the biggest material flow velocity appeared at the outer edge of the tool shoulder. The velocity value became smaller with the increase of the distance away from the tool surface. In general, material flows downwards along the pin thread when the full-threaded pin is used. Meanwhile, both the materials of the upper and the lower plates flow towards the lap interface along the pin thread when the reverse-threaded pin is used. The numerical simulation results were investigated by experiment, in which 2A12 aluminum alloy was used as the research object. The effective sheet thickness (EST) and stir zone (SZ) width of the joint by the reverse-threaded pin were much bigger than those by the full-threaded pin. Accordingly, cross tension failure load of the joint by the reverse-threaded pin is 23% bigger than the joint by the full-threaded pin.     

Finite element simulations of deformation behavior in equal channel angular pressing using a rotated die

A new die design for equal channel angular pressing (ECAP) of square cross-section billet was proposed by a 45 rotation of the inlet and outlet channels around the channel axes. ECAP utilizing the rotated and conventional dies was simulated in three dimensions using the finite element method. Conditions with different material properties and friction coefficients were studied. The billet deformation behavior was evaluated in terms of the spatial distribution of equivalent plastic strain, plastic deformation zone and load history. The results show that the rotated die appears to produce billets with a smaller deformation inhomogeneity over the entire crosssection and a greater average of equivalent plastic strain at the cost of a slightly larger working load. The billet deformation enters into a steady state earlier in the case of the rotated die than the conventional die under the condition of a relatively large friction coefficient.     

焊接参数对搅拌摩擦焊搅拌区材料融合的影响

用率相关本构模型模拟了搅拌摩擦焊接过程,研究了焊接参数的变化对搅拌摩擦焊接构件横截面上材料变形的影响.通过对不同过程参数下等效塑性应变的研究,分析了搅拌区及热力影响区内焊缝中心线两侧材料的融合情况,根据变形分布,从理论上判断焊接参数的变化对焊接质量产生的影响.结果表明,在靠近焊接构件下部材料的融合随着搅拌头转速的增加和焊速的减小趋于良好,但是搅拌头转速过高有可能导致焊接缺陷的产生.     

搅拌摩擦焊接过程中材料流动形式

采用完全热力耦合模型对搅拌摩擦焊接过程进行模拟,并详细分析了搅拌摩擦焊接过程中的材料流动形式.结果表明,模型可以成功预测搅拌摩擦焊接过程材料流动和温度分布情况.通过对搅拌头周围材料流动的研究,分析了搅拌摩擦焊接过程中飞边现象形成的主要原因.研究了搅拌摩擦焊接构件不同厚度上材料的三维流动形式,通过与二维情况的比较证实,二维情况下的材料流动数值模拟结果对应于搅拌摩擦焊接构件靠近下表面部分的材料流动情况.从等效塑性应变的分布也能证实搅拌头轴肩对靠近上表面的材料行为具有明显影响,而对下表面附近材料行为影响较弱,从而说明二维情况对应三维情况靠近下表面的部分.     

Determination of the traverse force in friction stir welding with different tool pin profiles

ABSTRACT

A methodology is developed for the estimation of the traverse force in friction stir welding (FSW) for various pin profiles by combining the results of numerical modelling and experimental monitoring. The effect of pin profiles on the traverse force is evaluated by introducing a modified ratio of the plastic deformation zone, which is obtained by numerical modelling. The formula is validated with the experimental data in the literature and indicates that the traverse force decreases exponentially with increasing ratio of the plastic deformation zone. The proposed methodology provides a concise approach for the estimation of the traverse force for various pin profiles in FSW and can be adopted for the design and assessment of the FSW tool.     

三维搅拌摩擦焊接传热与塑性流动分析模型

为研究搅拌摩擦焊接过程热流相互作用下的温度场、速度场和粘度场,将材料看成是层流、粘性、非牛顿流体,基于流体力学理论,建立了搅拌摩擦焊接过程的三维热流分析模型.给出了焊接过程热输入与搅拌头的旋转频率、工件运动速度、搅拌头尺寸及材料发生屈服时的剪应力的数学关系式,并将其作为热边界条件加入到了模型中.结果表明,搅拌头前部温度低于后部,温度梯度前部大于后部;受搅拌头周围材料流动的影响,接近搅拌针的区域,后退侧温度高于前进侧;材料上部速度、粘度受轴肩影响较大,下部主要受搅拌针影响;计算得到的热力影响区与试验结果有较好的对应关系.     

搅拌针表面形状对焊缝金属轴向迁移的影响

采用不同表面形状的搅拌针对20 mm厚7075铝板进行焊接,分析其对焊缝金属沿轴向迁移的影响.结果表明,使用圆锥形搅拌针焊接时,随着旋转速度增加,焊核区面积、塑化金属沿两边向上迁移高度先增大后减小,疏松区面积则先减小后增大.同一焊缝中焊核区内塑化金属沿前进边向上迁移高度大于返回边.采用375 r/min旋转速度焊接时获得的焊核区面积、塑化金属向上迁移高度最大,疏松区面积最小.而使用三角平面搅拌针焊接时,瞬时空腔的出现增强了沿焊缝水平方向上"抽吸-挤压"效应,同时改善塑化金属沿轴向上的流动性,导致疏松缺陷消失.