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The smaller the relative bending radius of the bent tube, the more difficult the tube blank is to be bent. In this paper, the push-bending process for the aluminum tube with a relative bending radius of 0.9D was analyzed through simulation. There was tangential tensile stress concentration occurring at the front endpoint of tube intrados, which increased the risk of cracking. That is because the bending tube's extrados moves less angular distance than its intrados by the uniform lubrication method, causing excessive deformation of the cross-section. Therefore, a differential lubrication method using the lubricant with a larger friction coefficient at intrados and the lubricant with a smaller friction coefficient at extrados was proposed to increase the angular velocity of the tube's extrados. It was found that the differential lubrication method helped avoid excessive thinning at the front endpoint of tube intrados through simulations. Furthermore, push-bending experiments of 5A02 aluminum alloy with a relative bending radius of 0.9D were carried out to investigate this effect. The experimental results showed that the differential lubrication method effectively avoided cracking, which agreed with the simulation results. [ABSTRACT FROM AUTHOR]

The cold push forming method of 1D bending radius (R/D = 1) with small diameter and small bending radius using low-melting-point alloy as filling medium is studied in this paper. The contact states between the outer surface of the filling medium and the inner surface of the tube are proposed to adjust the material flow of the tube blank. Based on ABAQUS/Explicit, simulation methods were used to investigate the effects of the contact modes on the quality of the elbow in four parameters. Experiments were carried out to verify the reliability of the simulations. The results show that the 5A02 thin-walled aluminum alloy tube, of which the diameter D is 12 mm, the thickness t is 1 mm, and the bending radius R is 12 mm, can be successfully fabricated by push bending using low-melting-point alloy as filling medium. The extended length of straight segment increases with the increase of the friction coefficient in the tube, but decreases with that of the outer surface of the tube. And the friction coefficient on the compression side of the medium affects more on the extended length than that on the tensile side. Differential contact modes used to the inner surface of the tube can improve the thickening and thinning of the elbow than uniform contact. The optimal elbow was obtained under the contact Mode 7, when the friction coefficient on the compression side was 0.06 and that on the tensile side was 0.01. [ABSTRACT FROM AUTHOR]

Recent years have witnessed the rapid development of electromagnetic flanging of tubes, which uses coils to generate electromagnetic forces to achieve the deformation with high speed but without contact. However, the electromagnetic force decays dramatically with the increase of distance, resulting in strict requirements of geometrical matching between the coils and the tubes. Usually, new coils should be fabricated for tubes with new sizes, which is inconvenient and uneconomical. Therefore, a more flexible and economical method is proposed in this paper, which introduces a solenoid field shaper into the existing electromagnetic flanging system. By adjusting the structure and the position of the field shaper, the distribution of electromagnetic forces can be reshaped to form tubes with various sizes, without changing the coil, whose cost is much higher than a field shaper. The principle of this method is introduced in detail. Then, an electromagnetic-structure coupled finite element simulation model is established to calculate the forming process. The results show that when forming an A6063-T83 aluminum alloy tube with an inner diameter of 110mm, the discharge voltage can be tuned down from 5.3kV, without field shaper, to 4.6kV, with field shaper. That means the energy consumption of the system can be saved by 25%, and the manufacturing process of the field shaper is simpler than that of the forming coil. What's more, when forming tubes with different sizes, the new method shows higher effectiveness, greater flexibility, and lower cost than the traditional way. [ABSTRACT FROM AUTHOR]

The combination of collision velocity and angle plays a dominant role for the magnetic pulse welding (MPW) of dissimilar metals. During the MPW process of tubes, the combination depends on the key parameters including radial gap, relative lap length (RLL), and discharge voltage. In this work, the numerical simulations are performed to investigate the effects of RLL on the collision velocity and angle. MPW experiments of 5A02 aluminum tube and SS304 steel tube are conducted, and then, peeling tests and compression shear tests for the joints are carried out respectively to study the influence of these key parameters on the MPW joint quality. The simulation results reveal that the impact velocity declines with the enlargement of RLL but increases with the growth of radial gap and discharge voltage. And the collision angle decreases first sharply and then increases gently with the increase of RLL. And the angle also increases with the increasing radial gap but the discharge voltage seems to be less important. Comprehensively, it is found that there exists an optimum value 7/10 for RLL, 1.75 mm for the radial gap, and 16 kV for the discharge voltage to obtain the joints of good quality in this paper, whose shear strength's maximum is up to 48.9 MPa. And the relationship between the radial gap and the voltage is found that the smaller the radial gap, the smaller the corresponding proper voltage for a good joint under the same experimental conditions. [ABSTRACT FROM AUTHOR]

In the majority of electromagnetic tube forming system, the distribution of Lorentz force acting on tube is restricted and has poor controllability, which leads to the tube being unable to meet the requirement of manufacturing flexibly. A new electromagnetic tube-forming method based on the two-stage coils system, which consists of two coils and two independent capacitor banks, has been proposed to improve the distribution mode and controllability of Lorentz force. With higher deformation depth and less occurrence of cracking compared with the conventional one single-coil system; this method has been proved to be effective in improving the deformation behavior of tube in electromagnetic forming through experiments. However, the deformation behavior of tube in this forming method still needs further studies. In this paper, the effect of pulse width of middle-coil current on AA1060 aluminum tube deformation behavior under two-stage coil system is investigated through simulation model, which is based on the combination of current filament method and finite element method. Results show that the short pulse width of the middle-coil current can achieve larger deformation depth of tube under relatively small discharging energy, and the long pulse width of the middle-coil current has good performance in deformed profile. Moreover, the thickness reduction in the case of long pulse width of middle-coil current is less than the case of short pulse width of the middle-coil current under equal deformation depth of tube. [ABSTRACT FROM AUTHOR]

As an important engineering material, aluminum alloy profile is widely used in each department of national economy. With polyurethane mandrel in the hollow of the profiles, equal channel angular pressing (ECAP) can be used to refine mechanical properties of these hollow materials with good shape control effects. However, based on existing researches, the hollow profiles are only limited to circular ones. In this paper, a mechanical analysis of a square tube in ECAP with polyurethane mandrel is provided. Through the slab method in different deformation planes, the mechanical mechanism of shape control effects is found. The thicknesses can be maintained as its initial ones after ECAP. Both simulations and experiments are used to verify the calculated results by the analysis. After calculating, most errors between the final and initial thicknesses in both simulations and experiments are less than 10%. [ABSTRACT FROM AUTHOR]

Tubular joint forming by elastomeric bulging (EB) is a feasible way to connect aluminum alloy tubes to high-strength sleeve fittings. It is critical to fully and deeply understand the deformation-induced sealing performance of tubular joints for precise manufacturing of high performance tubular joints. In this paper, thin-walled AA6061-T4 tubular joints fabricated by EB was investigated experimentally and numerically. Firstly, the anisotropic AA6061-T4 tube, the polyurethane elastomer (PUE) tube with hyperelasticity and the 15-5PH stainless steel (SS) sleeve fitting were characterized and modeled. Compared with the explicit algorithm, the implicit axisymmetric finite element (FE) models of the whole joining process, including EB forming and springback, were established. The influence of the groove structure of the sleeve fitting on the shearing-related pull-out strength and sealing-related bonding strength was discussed, and then the reasonable sleeve fitting's structure with two grooves was obtained. Thus, the accurate ranges of extrusion pressure and tube bulging heights were derived for precise control of forming quality. Finally, the experimental set-up and forming dies for EB joining tests were established, and the reliability of these parameters determined by the FE model was verified experimentally. It is concluded that the forming quality of this tubular joint can be controlled precisely based on FE modeling of whole joining process, and thin-walled AA6061-T4 tubular joint fabricated by EB has a reliable seal performance. [ABSTRACT FROM AUTHOR]

It is important for the thin-walled tube with relative bending radius of 1 to be bent with mandrel in order to avoid the defects such as wrinkling and cross-section distortion. In this paper, a novel push-bending method using sectional elastomers as mandrel was proposed to form the 5A02 thin-walled aluminum alloy tube with relative bending radius of 1 and 90° bending angle. Cylindrical polyurethane rubber (CPR) with shore hardness of 80A was chosen as the sectional elastomers. The influence of diameter (d), thickness (t), total length (L), and arrangement of CPR filler on the push-bending deformation of tube was first explored by means of simulations and experiments. According to the simulation results, 5A02 thin-walled aluminum alloy tube with relative bending radius of 1 was successfully fabricated with the sectional CPR as mandrel in the self-developed equipment of push-bending. The experimental results were in good agreement with the simulation results. The optimum parameters of CPR filler in push-bending process were obtained as follows: 37 mm diameter, a piece of CPR with 20 mm thickness contacted with the punch, and other 12 pieces of CPR with 10 mm thickness. [ABSTRACT FROM AUTHOR]

Connection technique of copper and aluminum is a key challenge in refrigeration industry. In this paper, rotary swaging connection process is proposed to connect cooper tube and aluminum tube in physical way. We find the length of overlapped area has a great effect on the joint reliability, and it should exceed the deformation region length. The joint strength is approximately determined by necking. With the reduction of the diameter at the necking area, joint strength first increases and then decreases. Some experiments are carried out to test the joining strength. It is shown that the joints are reliable enough, and joining by rotary swaging method is effective to combine copper and aluminum tubes. [ABSTRACT FROM AUTHOR]

The material flow balance in extrusion die cavity (e.g., porthole, welding chamber, etc.) plays a crucial role in the extrusion process and product quality of hollow aluminum alloy profiles. Therefore, the structures of porthole and welding chamber are always the keys for designing extrusion dies. Based on non-orthogonal structured Euler grids, an automatic optimization program for porthole structure was developed, where the consistency ratio of mass flux in each porthole to corresponding area of filled part of the profile was used as the criterion for evaluating the material flow balance. With the developed codes, the extrusion process of an aluminum square tube with multihole porthole die has been simulated and finally the porthole structures were optimized automatically. Compared with the initial scheme, the material flow balance in the optimized die cavity was greatly improved, and the velocity difference and the standard deviation of the velocity in the cross-section of the profile reduced by 55 and 69 %, respectively. Comparison of the results obtained from the developed codes and those by the commercial software HyperXtrude showed a very good agreement, which verified the optimization algorithm developed in this paper. [ABSTRACT FROM AUTHOR]