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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]

Metal bending tube is widely used in industry while its forming defects extremely affect the bending quality. Among all defects, the bending-inside wrinkling caused by the non-uniform compressive stress is a zero-tolerated defect, particularly when the tube is for transportation. However, the current wrinkling detection approach, suffering from the lack of insight into wrinkling mechanism, is normally posteriori. To obtain the priori wrinkling condition for a certain go-to-bend tube, we put forward a metal tube bending wrinkling hierarchical prediction method based on hybrid-kernel gray wolf optimizer (GWO) support vector machine (SVM). Three typical kernel combinations are utilized for the GWO-SVM prediction model. To verify the proposed wrinkling prediction method, aluminum alloy series tubes are tested. By constructing the 12 typical designations of aluminum alloy tubes' finite element bending simulation case base, the prediction model is trained through three hybrid-kernel GWO-SVMs, respectively. The results are compared with the traditional SVM and GWO-SVM, which show that the proposed hybrid-kernel GWO-SVM model has the best performance for hierarchically predicting bending wrinkling. Analysis of the predicted results shows that when the relative wall thickness is less than 0.015, wrinkling is very likely to occur with any relative bending radius within the range. On the contrary, there is less tendency to wrinkle. At the same time, the smaller the R/D, the higher the hierarchy of wrinkling. This proposed prediction method lays the foundation for metal tube bending wrinkling detection and prevention. [ABSTRACT FROM AUTHOR]

A new technology of local electrically assisted necking and thickening forming of 5A02 aluminum alloy tube is developed, to enhance the quality of tube necking and thickening and increase the thickness of the tube wall in thickening area. Advantages of the electroplasticity of pulse current are utilized to guarantee the forming quality of tube necking and thickening. Process parameters such as thickness of the guide block, contact mode of the upper electrode, and the cooling method were studied. The results indicate that the thicker the guide block, the less prone to premature bending and instability in the forming process. The integral electrode is the most stable and the best heat dissipation effect, which avoids the tube from internal buckling. With the increase of the cooling capacity, the average wall thickness increases first and then decreases. According to these results, a process scheme is designed, with which successful experiments have been performed. And the microstructures of the necking and thickening areas were studied by optical microscope. Local electrically assisted necking and thickening technology shows great benefits in tube extrusion forming. [ABSTRACT FROM AUTHOR]

In this study, an effective artificial neural network (ANN) model was established to predict the bending deformation in a welded square thin-walled aluminum alloy tube structure. The input variables of the ANN model include four controllable positional parameters of welding, whereas the bending deformations in the X-axis and Y-axis directions are considered the target outputs. To estimate the bending distortion rapidly and accurately, a supervised multilayer feed-forward backpropagation (BP) neural network was proposed. A total of 270 finite element (FE) numerical simulations were performed to generate a database for training the designed ANN model. Moreover, a series of experiments were conducted to confirm the accuracy of the FE models. The predicted values from the designed BP neural network and the FE simulation results were compared to evaluate the performance of the proposed ANN model. The comparative study demonstrated that the proposed BP neural network model can accurately predict welding-induced bending deformations within an available range of welding position parameters. [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]