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A model is developed to obtain the friction stir welding (FSW) induced stress in structures, which includes the welding process and the cooling process. The characteristics of the welding stress are presented in the analytical results. A detailed numerical simulation is also performed to verify the effectiveness of the proposed model. Numerical results of the welding stress agree well with the welding stress obtained from the analytical model. Then, the effects of process parameters of FSW on the welding stress are studied by using the analytical model. The process parameters involve the depression depth of the welding tool, the rotational speed, and the advancing speed. The calculated results show that the radial stress in the welded structure decreases with the increase of the depression depth. Larger tensile stress appears beneath the tool shoulder with the increase of the rotational speed. Higher advancing speed introduces lower tensile stress in the welded structure. [ABSTRACT FROM AUTHOR]

Friction Stir Spot Welding (FSSW) of AA5052-H32/HDPE/AA5052-H32 sandwich sheets is performed at six different tool rotational speeds to evaluate the optimum range. The mechanical performance, hook formation, grain size, hardness and temperature distribution are evaluated. Lap shear test, cross tension test, peel test and uni-axial tensile test are conducted. A comparative assessment has been made between the bimetallic and the sandwich sheets after FSSW. The optimum rotational speed for joining the sandwich sheet is 1800 rpm and beyond, where the joint strength and extension to failure are found to be acceptable. In hook formation, two hooks are prominently seen in the sandwich sheets, while it is only one hook in the bimetallic sheets. The hook width increases and the hook height decreases with increase in rotational speed. A mechanism has been proposed to explain such phenomenon. The peak temperature increases with increase in rotational speed and it gets reduced in sandwich sheet as compared to bimetallic. The polymer layer takes a part of the heat flux during stirring to reduce the peak temperature in sandwich system. The bimetallic joints are stronger than sandwich sheet joints showing better joint strength and extension at failure in almost all the tests. Joint hardness distribution supports such performance. Nugget pull-out and partial nugget failure are observed during joint failure of sandwich sheets. [ABSTRACT FROM AUTHOR]

In electrochemical machining (ECM), a passive film is generally present on the anode surface at low current density but is broken down at high current density in a passivating electrolyte. This film can impede unwanted metal dissolution in a low-current-density region and thereby improve the accuracy of ECM. However, it may sometimes affect metal dissolution at high current density. In this paper, the breakdown time of the passive film is determined for different current densities by varying the applied anodic potential pulses. It is found that the breakdown time has a significant magnitude of a few seconds, which can be long enough to affect metal dissolution in ECM. To illustrate the effect of the breakdown time of a passive film, ECM tests with cylindrical electrodes at different rotational speeds are conducted. The results indicate a correlation between the breakdown time and the rotational speed. At a high rotational speed, the surface of the anode workpiece is always in a passive state due to the existence of the breakdown time of a passive film, and hardly any material is removed. When a slower rotational speed is used, the steel passivity can be overcame, and a high material removal rate is obtained. A numerical simulation of the current density distribution on the cylindrical anode surface is performed, and the relationship between total metal dissolution time and breakdown time is found. It is seen that the breakdown time of the passive film can have a strong effect on the metal removal rate in ECM. [ABSTRACT FROM AUTHOR]

Double-sided lapping process is a key technology for obtaining high efficiency and flatness in fabricating plane-parallel workpiece surfaces, such as wafers, optical windows, seal rings, etc. However, the formation of the concave and convex surface shapes of workpieces was rarely investigated in the previous research, and the mechanism was unknown. This paper establishes a new kinematic model to clarify the formation mechanism of concave and convex surface shapes, in which the workpiece eccentricity and rotation in the planetary wheel are considered for the first time. The measurement and control method of workpiece rotational speed in the planetary wheel is proposed. The formation of the concave and convex surface shapes is validated experimentally by adjusting the rotational speed of the workpiece, and the results show a good consistency with the calculation results. A flatness error convergency method is proposed based on the surface shape formation mechanism, and flatness superior to 5 µm is achieved on Φ200 × 2 mm thin copper substrates. [Display omitted] • The formation mechanism of convex and concave surface shapes is clarified. • Workpiece's eccentricity and rotation are supplemented to general kinematic model for the first time. • The measurement and control methods for workpiece rotational speed are developed. • A flatness error convergency method is proposed. • Flatness superior to 5 µm is achieved on Φ200 × 2 mm thin copper substrates. [ABSTRACT FROM AUTHOR]

The effect of the rotational speed and dwell time on the joint interface microstructure and tensile-shear strength of friction stir spot welded Al-5083 aluminum/St-12 steel alloy sheets was investigated. Joining of the sheets was performed using an alternative friction stir spot welding (FSSW) process in which the welding tool tip did not penetrate into the lower steel sheet. Rotational speeds of 900 and 1100 rpm were applied in association with the dwell times of 5 to 15 s to weld the samples. Thermal history was recorded during the joining process. Interfacial microstructure, formation of intermetallic compounds (IMCs) at the joint interface and the fracture locations were studied using stereo, optical and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). The used alternative process was successful to join the sheets. For both of the applied rotational speeds, there were optimum dwell times (10 and 12 s for the rotational speeds of 1100 and 900 rpm, respectively) to reach the maximum failure loads. The increasing trend of the strength as a function of the dwell time was related to the formation of a thin intermetallic (IM) layer at the joint interface. The decreasing trend was attributed to the formation of a relatively thick IM layer at the joint interface as well as the grain growth of aluminum at the exit-hole periphery where the final fracture occurred. The IM reaction layer thickness of 2.3 μm was found to be a critical thickness. Compared to the rotational speed of 1100 rpm, stronger joints were achieved by application of 900 rpm rotational speed. [ABSTRACT FROM AUTHOR]

Abstract: The joining of ceramic–metal can be done using different techniques such as brazing, diffusion bonding, and friction welding. However, the mechanism of ceramic–metal joining has still not been fully understood. In this study, an alumina rod was bonded to a mild steel rod via the friction welding technique by using an Al 1100 sheet as an interlayer. The diameters of the rods were both 10mm, respectively. A friction pressure of 20MPa and a forging pressure of 40MPa were used. Rotational speed was maintained at 900rpm and friction times from 2 to 20s were applied. The joining strength was determined through a four point bending test. The maximum bending strength, 240MPa was obtained when the friction time of 20s was used. Under optical microscope and scanning electron microscope observation, the bonding aluminum interface was clearly obtained. Mechanical interlocking and close contact between the alumina–aluminum and aluminum–mild steel were observed at magnifications of 3000×. The strength of alumina–steel bonding is much dependent on the wettability of the alumina surface by the partially molten aluminum interlayer and the existence of mechanical interlocking between the interlayer and mild steel. [Copyright &y& Elsevier]