In present research work, friction stir welding of armour grade aluminium alloy, which is having excellent strength to weight ratio, has been done at low heat input rate (rotational speed of 600 rpm, travelling speed of 75 mm/min) and tool tilt angle of 2.5°. Tungsten carbide tool with a shoulder diameter of 15 mm was used to produce the joint. Tensile strength and microhardness of welded sample were measured at three different locations i.e. at the start, middle and end of the weld. The lowest value of tensile strength was obtained at the start of the weld while the maximum tensile strength was observed at middle of the weld and having the value of 378.672 MPa which is 82.32% of base metal along with 15.26% elongation. There is a large gap between the lower and the maximum value of tensile strength. The middle of the weld has less fluctuation in microhardness value as compared to the start and end of the weld. While the maximum value of microhardness was obtained on the advancing side at the start of the weld with the value of 187.4 Hv. Microstructural image shows the presence of craters and segregation in the weld surface. XRD result signify the presence of intermetallic compound Al 12 Mg 17 in the welded zone.

A novel friction sintering process is used to obtain large copper foam plates using sintering and dissolution process. The process ensures easy and quick removal of the sintered product. Heat and pressure generated by downfeed of rotating tungsten tool pressed against a “top plate” results in solid-state sintering of copper powder particles. The large sized sintered part was obtained by providing a scan path for tool covering the “die” containing Cu-NaCl mixture. Note that no pre-compression of Cu-NaCl is done before the start of the process. Compaction and sintering both happen during the course of friction sintering. Scanning electron microscopy (SEM) images of fracture surface indicate that pore morphology is dictated by the morphology of NaCl particles. Temperature increases with the increase in plunge depth. The stress-strain curves for obtained foam in compression are similar to the reported in.

Friction stir welding (FSW) has been successfully applied to join dissimilar materials in engineering applications. Fundamental understanding on the underlying physical principles of the dissimilar FSW process is generally required to achieve strong and reliable joints. In this study, we aim to develop a theoretical and numerical model based on computational fluid dynamics (CFD) in order to analyze the in-process heat transfer and material flow during the dissimilar FSW of aluminum and steel. The model describes the coupling behavior between the material distribution, thermal-mechanical properties, interfacial friction, heat generation and transfer. To account for the different material behaviors in stirring zone, a VOF-based approach is adopted. In this paper, preliminary numerical simulation is conducted. Simulation results show that the current modeling approach has the capability to capture the material mixing during the dissimilar FSW of aluminum and steel. The predicted temperature field is shown to be asymmetrical, which is attributed to the different properties of aluminum and steel. The predicted thermal history agrees with the experimental measurements in the literature.

The process of friction stir welding involves high tool forces and requires robust machinery; the forces involved make tool wear a predominant problem. As a result, many alternatives have been proposed in decreasing tool forces such as laser assisted friction stir welding and ultra-sound assisted friction stir welding. However, these alternatives are not commercially successful on a large scale due to scalability and capital/maintenance costs. In an attempt to reduce forces in a cost-feasible manner, electrically-assisted friction stir welding (EAFSW) is studied in this work. EAFSW is a result of applying the concept of electrically-assisted manufacturing ( i.e ., passing high direct electrical current through a workpiece during processing) to the conventional friction stir welding process. The concept of EAFSW is a relatively new adaptation of conventional frictional stir welding, which is well established. The expected benefits are reduction in the feed force and torque, which allow for improved processing productivity as well as the possibility for deeper penetration of the weld.

The objectives of this work are to develop an improved temperature measurement system for Friction Stir Welding (FSW). FSW is a novel joining technology enabling welds with excellent metallurgical and mechanical properties, as well as significant energy consumption and cost savings compared to traditional fusion welding processes. The measurement of temperatures during FSW is employed for process monitoring, heat transfer model verification and process control, but current methods have limitations due to their restricted spatial and temporal resolution and have found only few industrial applications so far. Thermocouples, which are most commonly used, are either placed too far away from the weld zone or are destructively embedded into the weld path, and therefore fail to provide suitable data about the dynamic thermal phenomena at the tool-workpiece interface. Previous work showed that temperatures at the tool shoulder-workpiece interface can be measured and utilized for closed-loop control of temperature. The method is improved by adding an additional thermocouple at the tool pin-workpiece interface to gain better insight into the temperature distribution in the weld zone. Both thermocouples were placed in through holes right at the interface of tool and workpiece so that the sheaths are in contact with the workpiece material. This measurement strategy reveals dynamic temperature variations at the shoulder and the pin within a single rotation of the tool in real-time. Due to the thermocouple’s limited response time and inherent delays due to physical heat conduction, the temperature response is experiencing attenuation in magnitude and a phase lag. Heat transfer models were constructed to correct for this issue. It was found that the highest temperatures are between the advancing side and the trailing edge of the tool. Further work is needed to increase the accuracy of the correction. Experimental results show that the weld quality is sensitive to the measured interface temperatures, but that temperature is not the only factor influencing the weld quality. The dynamic temperature measurements obtained with the current system are of unmatched resolution, fast and reliable and are likely to be of interest for both fundamental studies and process control of FSW.

Friction Stir Welding is a solid state ‘green’ welding method developed by The Welding Institute (UK). An internal thermal mapping instrument has been developed which allows for symmetrical mapping of the thermal fields developed by a Friction Stir Welding tool as it passes through the material being welded. This symmetrical mapping conclusively documents statistically the asymmetrical nature of the heat sources within the friction stir welding process. The various models in the literature are compared against these results. A model developed by the authors using classic metal cutting theory predicts the observed thermal fields. A successful predictive model will facilitate tool optimization and welding schedules, while optimizing the mechanical properties of the weld.

Current Friction Stir Welding (FSW) process modeling research is concerned with the detailed analysis of local effects such as material flow, heat generation, etc. These detailed thermo-mechanical models are typically solved using finite element or finite difference schemes and require substantial computational effort to determine temperature, forces, etc. at a single point in time. Dynamic models describing the total forces acting on the tool throughout the entire welding process are required for the design of feedback control strategies and improved process planning and analysis. In this paper, empirical models relating the process parameters (i.e., plunge depth, traverse rate, and rotation speed) to the process variables (i.e., axial, traverse, and lateral forces) are developed to understand their dynamic relationship. First, the steady-state relationship between the process parameters and variables is constructed, and the relative importance of each process parameter on each process variable is determined. Next, the dynamic process response characteristics are determined using Recursive Least-Squares. The results indicate that the steady-state relationship between the process parameters and variables is well characterized by a nonlinear power relationship, and the dynamic responses are well characterized by low-order linear equations. Experiments are conducted that validate the developed FSW dynamic models.