Investigations of friction stir welding process using finite element method

The aim of this study is to investigate the process of friction stir welding (FSW) by using finite element method (FEM). Currently, the materials that are difficult to be joined with conventional fusion methods can now be easily joined with the method of friction stir welding. In this paper, the welding capability of many different materials with this method has been investigated by using analytical and numeric methods. In this study, a finite element (FE) model was developed for welding process with friction stir welding of AZ31 magnesium alloy. This model was performed by the software of DEFORM 3D finite element in 960, 1,964, and 2,880 rpm rotational speeds and in 10 and 20 mm?min^?1 transverse speeds. The temperature values taken from experiments and the temperature values with FEM are compared, and according to these results, it can be stated that the FE model gives reasonable results with experimental results based on temperatures values. Hence, the FE model can be used to predict other parameters of FSW process in future studies.     

Three-dimensional numerical modeling of the friction stir welding of dissimilar steels

It is now widely recognized that collaboration across the supply chain is a must to be improved to achieve competitive advantage in global markets. Despite the fact that there is a unique well-known concept for supply chain collaboration suggested by the Voluntary Interindustry Commerce and Standards Committee (VICS), it is far from being enough as a solo source for a successful implementation because of being industry-dependent (particular for retail industry), abstract, qualitative, and inflexible. This research fills the gaps in VICS’s method by addressing a holistic and structured Collaborative Planning, Forecasting and Replenishment (CPFR) roadmap, which provides a complete source for practitioners and academicians for effective supply chain collaboration to be implemented widespread across any industry. A real case study was also carried out between an automotive supplier company and its aftermarket customer to demonstrate the benefits of the proposed CPFR roadmap in terms of specified key performance indicators as well as a discussion about how the suggested roadmap behaved in the practice.     

Analyzing dissimilar friction stir welding of AA5754/AA7075

AA5754/AA7075 was butt-welded by friction stir welding, and the joint of each weld case was identified by ultimate tensile strength, percentage of elongation, and hardness. Moreover, the significance of each parameter was investigated, and a mathematical relation was constructed by regression analysis. A defect-free joint was achieved in the case of a weld produced with 1000 rpm of tool rotational speed, 80 mm/min of welding speed, and an 22-mm tool shoulder diameter. Most of the failures are located at the bottom of the pin and side of AA7075. The ultimate tensile strength (UTS) decreases with increasing welding speed (WS) or increasing tool rotational speed (TRS). Hardness distribution in the weld zones varied dependent on the nugget zone formation affected by TRS and WS. The present study also investigated the significance and contribution of each parameter on the UTS by analysis of variance (ANOVA). From the results of ANOVA, the conclusion reached is that the all the parameters have a great influence on UTS. The contributions are 41.41 % for WS, 17.58 % for diameter, and 13.28 % for TRS. Moreover, a full quadratic model was constructed between the parameters and the UTS value. The results show that the variation from the predicted values was between 0.41 % and 10.36 %. The strength of the model was analyzed by R-Sq. The achieved R-Sq is 0.892, which means that there is a strong relation between predicted and actual values.     

Process responses and resultant joint properties of friction stir welding of dissimilar 5083 and 6061aluminum alloys

The effects of combinations of dissimilar aluminum alloys during Friction stir welding (FSW) on the process response and resultant joint properties are experimentally investigated using two dissimilar automotive structural aluminum alloys. Depending on the materials on the advancing and retreating sides of the tool travel direction during FSW, four different material combinations are considered. FSW joints without macroscopic defects are successfully fabricated for the four different material combinations. The optical microscopy results show that the macroscopic material mixing behaviors of the two dissimilar material combinations during FSW are somewhat different from each other, even though the process responses during joining are not much different. The results of the quasi-static tensile tests and EBSD analysis demonstrate that the mechanical behaviors and orientation changes of the joint during tensile deformation are affected by the material locations with respect to the tool travel direction during FSW.

     

Weld temperature effects during friction stir welding of dissimilar aluminum alloys 6061-t6 and 7075-t6

The objective of this work is to establish nominal friction stir [butt] welding process parameters for joining 4.76-mm-thick aluminum alloys 6061-T6 and 7075-T6 and to improve the joint quality via programmed tool offsets. In addition, dynamic tool–workpiece interface temperatures are measured during welding and used to explain the effects of alloy placement and weld tool offset from the joint. Weld tool offsets into the retreating side AA7075 increase the measured tensile strength of the dissimilar joint. The increased joint strength is facilitated by lower average weld temperatures with increasing amount of AA7075 stirred into the nugget.     

Solid mechanics-based Eulerian model of friction stir welding

A new Eulerian model is established based on solid mechanics. With comparisons to the experimental data and the ALE model, the current model is validated. The power and the heat generations from pin side surface, pin tip surface, and shoulder contact surface in different rotating speeds are studied. Results indicate that the ratio of the heat input powers from the pin and the shoulder keeps constant in different rotating speeds. The velocity of the material flow around the welding tool and the slipping velocity are both increased with the increase of the rotating speed. The increase of the slipping velocity is the main reason for the increase of the heat input with the increase of the rotating speed. The torque from the shoulder contact surface is the major part of the total torque. The contribution to the total torque from the pin tip surface is the smallest.     

A fully coupled thermo-mechanical model of friction stir welding

This paper presents a new developed fully coupled thermo-mechanical model of the friction stir welding process. Results indicate that the rotation of the shoulder can accelerate the material flow behavior near the top surface. The material deformation and the temperature field can have relations with the microstructural evolution. The texture of the appearance of the friction stir welds can correlate well with the equivalent plastic strain distributions on the top surface. The temperature field in the friction stir welding process is approximately symmetric to the welding line. The material flows in different thicknesses are different. The shoulder can have a significant effect on material behaviors on the top surface, but this effect is greatly weakened when the material gets closer to the bottom surface of the welding plate.     

Computational investigations on reliable finite element-based thermomechanical-coupled simulations of friction stir welding

The finite element method was used in the current work to study the selection of the constitutive models, the selection of the frictional coefficients, the selection of the contact models and the selection of the physical parameters. Numerical results show that the shape of the shoulder can affect the material flows obviously and a total of about 54.3% energy can be transformed into heat in friction stir welding/friction stir processing (FSW/FSP). When the physical parameters are further considered to be functions of temperature, the predicted temperature is lower than the one in which the physical parameters are constant. When strain-hardening effect is considered, the equivalent plastic strain is decreased and the corresponding energy dissipated by plastic deformation is decreased. The effect of the frictional coefficient on the prediction of the temperature field in FSW/FSP is small when the selection of the frictional coefficient is located in a reasonable small extent. The computational costs in the simulation of FSW/FSP are not only affected by the mesh sizes and wave speed but also affected by the mesh distortions. So, mesh distortions should be considered to be minimized in the numerical modeling of FSW/FSP to reduce the computational costs.     

Boundary element analysis of stress singularity in dissimilar metals by friction welding

Friction-welded dissimilar metals are widely applied in automobiles, rolling stocks, machine tools, and various engineering fields. Dissimilar metals have several advantages over homogeneous metals, including high strength, material property, fatigue endurance, impact absorption, high reliability, and vibration reduction. Due to the increased use of these metals, understanding their behavior under stress conditions is necessary, especially the analysis of stress singularity on the interface of friction-welded dissimilar metals. To establish a strength evaluation method and a fracture criterion, it is necessary to analyze stress singularity on the interface of dissimilar metals with welded flashes by friction welding under various loads and temperature conditions. In this paper, a method analyzing stress singularity for the specimens with and without flashes set in friction-welded dissimilar metals is introduced using the boundary element method. The stress singularity index (??) and the stress singularity factor (??) at the interface edge are computed from the stress analysis results. The shape and flash thickness, interface length, residual stress, and load are considered in the computation. Based on these results, the variations of interface length (c) and the ratio of flash thickness (t ₂/t ₁) greatly influence the stress singularity factors at the interface edge of friction-welded dissimilar metals. The stress singularity factors will be a useful fracture parameter that considers stress singularity on the interface of dissimilar metals.     

Study on microstructure and mechanical properties of dissimilar steel joint developed using friction stir welding

In the present study, microstructure and mechanical properties of dissimilar weld of structural steel and ferritic stainless steel (FSS) plates of thickness 3 mm were investigated. The plates were butt welded by friction stir welding and defect-free welds were produced at a traverse speed of 20 mm/min and rotational speed of 508 rpm using a tungsten carbide tool. The weld joint consisted of alternate bands of both steels resembling an onion ring pattern. In the weld joint, six distinct regions were found including both the base metals. The stir zone of structural steel revealed refined grain structure of ferrite, pearlite, and martensite whereas in ferritic stainless side, highly refined ferritic grains with grain boundary martensite was observed and also confirmed by x-ray diffraction (XRD). The hardness of the weld joint varies from 186 to 572 HV. This scatter of hardness in stir zone is due to the presence of metal from both sides. The ultimate tensile and yield strengths of the transverse weld specimens was higher than the structural steel base metal whereas lower than the ferritic stainless steel, having fracture from structural steel side.     

搅拌摩擦焊工具的研究现状

搅拌焊工具技术是搅拌摩擦焊工艺最重要的因素。搅拌焊工具主要由肩部和焊针组成，焊接薄板时，旋转的肩部和工件之间摩擦产生的热量是主要热源，而随着板厚的增加，更多的热量必须靠旋转的焊针和工件摩擦产生。焊接工具的主要作用是保证连接区材料产生足够的塑性变形，并控制焊针周围塑性体的流动，形成优质的焊接接头。     

Finite element modeling for maximum temperature in friction stir welding and its validation

This paper presents a new scheduling method for a flexible manufacturing system (FMS) in a Petri net framework. Petri nets can concisely model multiple lot sizes for each job, the strict precedence constraint, multiple kinds of resources, and concurrent activities. To decrease the likelihood of rejecting the critical markings, our algorithm adopts an improved checking method for previous generated marking. To reduce the computation complexity, an elaborate scheme is applied, which performs A* search locally and backtracking search globally in the reachability graph of the Petri net. Some numerical experiments are carried out to demonstrate usefulness of the algorithm.     

Ultrasonic thermometry for friction stir spot welding

This investigation presents the feasibility of ultrasonic temperature measurement of friction stir spot welding (FSSW). FSSW is an automated solid state joining process. Thermal profiles of the weld zone are crucial for implementing informed process changes to improve weld quality. Ultrasonics present a novel and non-invasive method of monitoring changes in temperature.Ultrasonic time of flight (TOF) measurement method is used to calculate the temperature of Al 6061 as it is heated. Comparisons of the ultrasonic temperature calculations with thermocouple readings confirm the accuracy of the ultrasonic system. The ultrasonic signal is then recorded during spot welding and processed. The results show that ultrasonic technology is a feasible method of monitoring the heating and cooling profiles of the weld zone during welding. The paper also discusses challenges presented by the system as well as recommendations for its future implementation in the friction stir welding manufacturing industry.     

Using TRIZ methods in friction stir welding design

Welding is an extremely important joining method in the manufacturing process. For the last few years, the friction stir welding (FSW) method has significantly increased the quality of a weld. However, FSW has a slightly short research and application progress. The related applied experiences are not prevalent. Therefore, FSW has a lack of reference information on related welding applied design, such as fixture, joining, and integrated design. This article intends to combine innovative design methods in the application of FSW design. Additionally, this article establishes the applied design mode of FSW through case analysis to assist engineers or design personnel who are not familiar with the FSW process. This will help to decrease trial and error or failure risks in the welding process of fixture design. Encountered welding difficulties are thus solved after being guided by the theory of inventive problem solving (TRIZ) design method. By combining traditional TRIZ design methods, this article also refers to other TRIZ methods proposed by some scholars because work will often encounter various engineering challenges. This article hopes to provide welding design personnel with innovative design ideas under research and for practical application.     

Microstructures and mechanical properties of friction stir welded dissimilar steel-copper joints

Welding dissimilar metals by fusion welding is challenging. It results in welding defects. Friction stir welding (FSW) as a solid-state joining method can overcome these problems. In this study, 304L stainless steel was joined to copper by FSW. The optimal values of the welding parameters traverse speed, rotational speed, and tilt angle were obtained through Response surface methodology (RSM). Under optimal welding conditions, the effects of welding pass number on the microstructures and mechanical properties of the welded joints were investigated. Results indicated that appropriate values of FSW parameters could be obtained by RSM and grain size refinement during FSW mainly affected the hardness in the weld regions. Furthermore, the heat from the FSW tool increased the grain size in the Heat-affected zones (HAZs), especially on the copper side. Therefore, the strength and ductility decreased as the welding pass number increased because of grain size enhancement in the HAZs as the welding pass number increased.