Evaluation of Current, Force and Temperature Signals on Welding Formation of Bobbin Friction Stir Welded AA1100

Understanding process response through measuring process signal provides on-site information in the area of process monitoring, which saves time and costs. The type of signals depends upon the type of process, equipment and machines used through sensors attached on the equipment used in the process. This is an important method for detecting changes in the process that reflect the condition or quality of the weld. The benefits of this method, however, has not been well performed for Bobbin friction welding. This process is different from conventional friction welding due to the different process set-up in term of tooling and parameters, hence the need to evaluate the signal response. Consequently, signal measuring for welding plate AA1100 was carried out. Tool rotation ranged from 750 rpm to 950 rpm with a fixed travel rate of 130 mm/min on a CNC milling machine and a fixed spacing tool. During the joining process, welding temperature, current consumption and welding force were measured. The resulting data were then plotted on the X-Y axis chart and mapped using the welded plate identifying the welding phase. From the welding force and current measurement, it is found that high force and current is detected at the tool entry phase and exit. As the tool moves towards the end of the plate, the temperature increased. The highest current and strength are measured when the spindle speed is at the lowest, while the highest temperature is at the fastest spindle speed. In weld phase, a current of approximately 6.5 A, a force of 1 kN and a temperature of 320º was measured. A maximum weld strength of 102.860 MPa achieved using a speed of 950 rpm. A slow spindle speed at the entrance area and a high spindle speed at the weld phase are needed to optimise the process.

Effect of in situ graphene-doped nano-CeO2 on microstructure and electrical contact properties of Cu30Cr10W contacts

The graphene oxide (GO)-doped nano-CeO2 was introduced into Cu30Cr10W electrical contact composites by ball milling dispersion, freeze-drying, and spark plasma sintering, resulting in excellent mechanical strength and high arc erosion resistance. The effects of GO and CeO2 on the microstructure and properties of the composites were investigated. The arc erosion behavior was investigated by the JF04C electrical contact testing apparatus. Consequently, the uniform distribution of CeO2 nanoparticles hinders the movement of dislocations, GO transformed into reduced graphene oxide (rGO) during high-temperature sintering, and the in situ formation of Cr3C2 between trace carbon atoms and chromium particles at the C–Cu interface, which enhanced the interface combination. Compared with Cu30Cr10W composites, the tensile strength of the two composites was increased by 47 and 36% by importing GO and nano-CeO2, respectively. Finally, electrode material migrated from the cathode to the anode, and the rGO delayed the formation of pits and sharp bumps on the contact surface of the electrode and inhibited diffusion of molten metal; when compared with Cu30Cr10W, the GO/CeO2–Cu30Cr10W composites have better welding force.

Effect of Friction Stir Welding Mode and its Direction Relative to the Rolling Direction of 2024 Alloy on the Structure and Mechanical Properties of its Weld Joints

Introduction. Friction stir welding conditions determines character of thermomechanical impact on welded material, so a critical alteration of even one of condition parameters can result in formation of defects and strength decrease of welded joint. Also an important factor is an orientation of welded material relative to a welding direction since it determines kinetics of material deformation and consequently its final structure and properties. Research efforts of friction stir welding properties generally consist in analysis of final properties of obtained weld joints and its correlation with parameters of welding condition. But to solve a problem of obtaining of weld joints with strength and quality, it’s also important to estimate a welded material resistance to deformation from welding tool impact which could be achieved by monitoring a number of parameters directly in process of welding. The purpose of the work is to research an impact of welding condition parameters and an orientation of welded material’s structure on friction stir welding process behavior and also on structure and strength of weld joints of 2024 aluminum alloy. Results and discussion. By monitoring the torque and welding force, it is shown that as the tool penetration force increases, the material's resistance to deformation increases. When welding is longitudinal to the direction of base metal rolling a torque and a welding force parameters decreases in value of 5-20%. An increase of welding speed provides a growing of material resistance to welding tool movement, at that, a direction of welding doesn’t have a significant impact. With an increase of welding tool rotational speed, a material resistance to deformation decreases, a welding temperature grows and it results in growing of material’s plasticization degree and in improvement of its mass transfer conditions. It is also shown that the welding conditions, which allows welding the 2024 alloy at a temperature of 450 – 500 ºС, provides the degree of plasticization of the material, at which welded joints with a high-quality structure and high mechanical properties are obtained. In this conditions a direction of welding in relation to the direction of base metal rolling has an impact: when welding is longitudinal to the direction of rolling the tensile strength of weld joints reaches a value of 92%, and when welding is transverse - 95% of base material tensile strength.

Modeling and Experimental Verification of Material Welding Characteristics for Low Current Switching Devices

Material welding failure considerably influences the electrical lifetime and reliability of low current switching devices. However, relevant studies on methods for calculating the threshold welding current and welding area under milli-Newton scale load forces are very limited. In this paper, the welding characteristics of metal material, including the threshold welding current, welding area and welding force are studied by using theoretical calculations and experiments. The comparison between the theoretical calculation and experimental results shows the accuracy of the built model. Further, the effects of mechanical load force and load current on welding force and welding area of representative metal materials are investigated. It is found that the anti-welding ability of metal materials depends not only on the exerted load force and current, but also the electrical resistivity, the thermal conductivity, the tensile strength, and the melting temperature of the materials.

Cr effects on the electrical contact properties of the Al2O3-Cu/15W composites

In order to investigate the effects of chromium on the electrical contact properties of the Al2O3-Cu/15W composites, vacuum hot-pressing sintering and internal oxidation methods were employed to fabricate the Al2O3-Cu/15W and Al2O3-Cu/15W5Cr composites. The microstructure was analyzed by scanning and transmission electron microscopy. The electrical contacts testing was performed using the JF04C testing machine at 30 V DC with 10-30 A current. The effects of Cr on the comprehensive properties, arc erosion morphology and welding force of the electrical contacts were investigated. The mass transfer mechanism was discussed. It was demonstrated that the Al2O3 nanoparticles pinned dislocations. The diffraction spots of the Cu matrix and the γ-Al2O3 disclose an orientation relationship of <103>Cu//<103>γ−Al2O3,{020}Cu//{040}γ−Al2O3. A typical arc erosion morphology, such as needle-like and coral structures was formed, which provides significantly enhanced arc erosion resistance of the contact material. Compared with the Al2O3-Cu/15W composite, the Al2O3-Cu/15W5Cr composite has a lower welding force. The two composites present two distinct mass transfer trends before and after 25 A. The final mass transfer direction of the composites is from the cathode to the anode. The Al2O3-Cu/15W5Cr contacts have less mass change under all testing conditions.

Experimental Study on Dynamic Welding of AgW60, CuW60 and Cu Contact Materials in Symmetrical and Asymmetric Pairing at 270VDC/200A

<p>With the use of contact material simulating test device, experiments are conducted for the contact materials AgW60, CuW60 and Cu and their different pairing under the conditions of DC voltage and current 270VDC/200A and surrounding atmosphere of carbon dioxide and nitrogen. The welding resistance, average welding force and the relationship between welding force and the number of operations during welding were measured and analyzed. Experiments show that the anti-welding ability of the three materials in the symmetric pairing of carbon dioxide and nitrogen is ranked as AgW60&gt;Cu&gt;CuW60. The "intermediate effect" occurs in the anti-welding properties of the asymmetric pairing. The relationship between the number of operations required for each welding and the average average welding force is approximately an inverse proportional function.</p>

Friction Stir Resistance Spot Welding of Aluminum Alloy to Advanced High Strength Steel

A hybrid friction stir resistance spot welding (RSW) process is applied for joining aluminum alloy 6061 to TRIP 780 steel. Compared with conventional RSW, the applied current density is lower and the welding process remains in the solid state. Compared with conventional friction stir spot welding (FSSW) process, the welding force is reduced and the dissimilar material joint strength is increased. The electrical current is applied in both a pulsed and direct form. With the equal amount of energy input, the approximately same force reduction indicates that the electro-plastic material softening effect is insignificant during FSSW process. The welding force is reduced mainly due to the resistance heating induced thermal softening of materials. With the application of electrical current, a wider aluminum flow pattern is observed in the thermo-mechanically affected zone (TMAZ) of weld cross sections and a more uniform hook is formed at the Fe/Al interface. This implies that the aluminum material flow is enhanced. Moreover, the Al composition in the Al–Fe interfacial layer is higher, which means the atomic diffusion is accelerated.