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An accurate constitutive model lays an analytical foundation for the thin-walled tube plastic joining process. This study obtained the best-fitted constitutive model to accurately simulate the steel/aluminum thin-walled tubes cracking during plastic joining. The process of establishing the constitutive model comprises three parts: 1) The flow stress model of AA6061 was determined by comparing the fit of seven flow stress models and experiments, and the model parameters were calibrated using a genetic algorithm. 2) A method combined with experiment and simulation was adopted to obtain the failure parameters in the ductile fracture criterion. 3) Combinations of different ductile fracture criteria and yield criteria were implemented into the VUMAT subroutine to simulate uniaxial tension. The constitutive model of AA6061 was determined based on the comparison of simulation and experiment. Subsequently, the constitutive model was applied to the cracking prediction of the steel/aluminum thin-walled tube plastic joining process. The predicted cracking was compared with the experimental cracking. Finally, the cracking risk areas were evaluated by the forming limit diagram. The results indicated that the Voce-Swift model could better reflect the trend of AA6061 flow stress and the genetic algorithm could effectively improve the Voce-Swift model fitting accuracy. The uniaxial tensile simulation suggested that the Cockcroft-Latham criterion combined with the Hill48 anisotropic criterion could accurately predict the fracture of AA6061. Moreover, the steel/aluminum joint simulation cracking matched very well with the experiment, which verified the validity of the constitutive model in predicting cracking during the plastic joining process. Finally, the aluminum/aluminum joint simulation result proved that the risk of cracking in the upper tube was more significant than in the lower tube. The AA6061 tube with poor plasticity should be the lower tube to improve the formability of the steel/aluminum joint. [ABSTRACT FROM AUTHOR]

A structure for joining 6061T6 aluminum alloy tube and AZ31B magnesium alloy shaft via the magnetic pulse crimping process was proposed. The forming process, mechanical properties, failure modes, and corrosion behaviors of the joint were studied. The results showed that the enormous Lorentz force drove the wall of aluminum alloy tube to move towards the groove of magnesium alloy shaft at high velocity, thus realized mechanical locking and formed joint. Through torsion tests, it was found that the mechanical properties of the joint with different process parameters varied. There were two failure modes for joint: torsional separation and torsional crack. Specifically, discharge time, groove angle, and discharge energy for torsional crack were, respectively, 1, 90°, and 28 kJ and 3, 90°, and 25 kJ. The maximum torque was up to 961.99 N·m under discharged twice, 90° groove angle, and 25-kJ discharge energy. Through neutral salt spray corrosion tests, it was found that the maximum torque only decreased by 28.03% after corrosion for 192 h. It indicated that the corrosion resistance of joint was good relatively. [ABSTRACT FROM AUTHOR]

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]

Grain size gradient materials are a type of new structural material with the advantages of both coarse and fine grains. To study the effect of normal gradient grain on the mechanical properties and microstructure of aluminum alloy tubes during hydroforming, the normal gradient grain distribution of the outer fine and inner coarse grains was obtained using spinning and annealing methods, and the biaxial stress was determined using hydraulic bulging experiments. Gradient grain tubes with thicknesses of 300, 475, and 575 μm were obtained through spinning and annealing at different temperatures; the tensile strengths of the tubes were 79, 89, and 109 MPa; the maximum expansion rates were 18%, 17%, and 10%; and the work-hardening indices were 0.19, 0.20, and 0.17, respectively, under biaxial stress. With an increase in the refined grain area, the density of the low-angular grain boundaries (LAGBs) increased and the chance of stitching dislocation increased in the process of intragranular deformation, causing an increase in strength. However, the increase in the refined thickness weakened the compatible deformation due to a reduction in the number of large grains, leading to a decrease in plasticity. The obtained quantitative relationship between gradient grain and strength/ductility can be applied to guide production of aluminum alloy tubular parts in the aerospace and automotive industries. [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]

Electromagnetic forming (EMF) is a technology that uses Lorentz force to drive the deformation of light alloy. In the processing of small metal pipe fittings, attraction forming is beneficial to reduce the design requirements of forming coils and the application cost of actual tooling. However, the attractive dual-frequency current method requires strict matching between currents. This will lead to difficulty in controlling and changing the attractive force, thus reducing the uniformity of the deformation of the workpiece. To solve this problem, a field shaper is introduced to optimize the distribution of electromagnetic force and improve the uniformity of pipe forming. The finite element model including circuit field, electromagnetic field, and structure field was established, and the bulging of an aluminum alloy pipe fitting with a radius of 10 mm and a length of 40 mm under the action of 9-kV power supply was simulated. The results show that the deformation uniformity is increased by 15% and the degree of shape change is increased by 8.9% with the addition of field shaper. It is proved that field shaper can improve the uniformity of pipe fitting. [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 Lorentz force distribution on a tube is the dominant factor that determines the tube deformation behavior in the electromagnetic forming process. However, the existing forming technologies in this field are mainly based on a single-coil system, which results in a relatively fixed Lorentz force distribution and makes it difficult to control the forming process or the final tube shape. To solve this problem, a three-coil forming system composed of three sub-coils and two pulsed power supplies is developed for tube forming in this work. Both numerical simulation and experimental results show that the three-coil system can be easily applied to alter the Lorentz force distribution through adjusting the discharge voltage of sub-coils, providing an effective way to improve the deformation uniformity and control the deformation shape. It is found that an AA6061-O aluminum alloy tube with an inner diameter of 76 mm and a thickness of 2 mm can be deformed with a homogeneous deformation range of about 23.56 mm via the three-coil system in the experiments, while the range is only about 11.48 mm under the same conditions when using the conventional single-coil system. Meanwhile, it is demonstrated that the three-coil system can achieve a variety of tube shapes including concave and convex profiles with different uniformity. The developed method and obtained results are of good value for expanding the application of electromagnetic tube forming. [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]

Wrinkling is a significant challenge associated with the forming of tubes via diameter reduction. The work reported herein employed elastoplastic principles to assess the external pressure diameter reduction forming process by generating a strain diagram showing the occurrence of critical instability. This diagram can be used to effectively predict the appearance of wrinkling defects during forming. The Donnell linear buckling theory together with a bilinear material model was used to derive an expression for the critical external pressure leading to wrinkling instability, employing constant tube end conditions and a uniform external pressure, and the effects of forming conditions and material parameters on wrinkling were explored. During experimental trials, AA6061 tubes were formed via diameter reduction in conjunction with varying heat treatment conditions using the solid granule medium forming process. A Vialux portable mesh strain tester was employed to collect relevant data to verify the critical instability points, and the effects of various factors on resistance to wrinkling were investigated. An analysis of the experimental results demonstrates that the conclusions of the theoretical analysis are correct. [ABSTRACT FROM AUTHOR]

To solve the drawbacks of thinning and poor thickness uniformity in tube hydroforming, a novel method known as axial hydro-forging sequence was developed. In this method, the deformation zones will be subjected to compression deformation throughout the hydro-forging stage to decrease the thinning and improve the thickness distribution compared with the traditional tube hydroforming. To verify the feasibility of this method, experiments and finite element simulations were designed and conducted. Subsequently, the effects of the internal pressure, friction, and reduction on thickness distribution were investigated. The results indicated that the thinning ratio can be decreased significantly by compression deformation. And the thickness of the deformation zone increases with increasing reduction. Furthermore, the thickness uniformity can be improved by a thickness "self-uniformity" in the hydro-forging stage, which was attributed to the von Mises stress distribution. It is demonstrated that the thickness distribution is related to the friction coefficient, but has little dependence on the internal pressure. Experimental and simulation results show that axial hydro-forging sequence is practicable to produce the variable-diameter tube. [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]

At this present work, the feasibility of producing seamless tubes through recycling of aluminum machining chips via the double-step friction stir consolidation (FSC) process was investigated. This process was done in two distinct steps. At the first step, the chips are loaded into the container and slightly compacted, and then a rotating tool with a designated diameter is plunged into the chips at a chosen rotational speed and feed rate. Due to the frictional heating, the softened materials are compressed and merged to form a consolidated cylindrical bulk material eventually. In the second step, a rotating tool that is smaller in diameter than the first tool is again plunged into the recycled round bars at a selected rotational speed and feed rate, forcing the material radially outwards and afterwards forming tubes. The results show that the process is a feasible solution for producing structurally sound, void-free tubes directly from machining chips at two simple steps. A numerical model was implemented to predict the evolution of the main field variables including temperature, density, and strain in the process. [ABSTRACT FROM AUTHOR]

Friction between the tube and spinning tools is one of the main factors that affected the uneven deformation in hot power backward spinning process of a high-strength casting aluminum alloy tube, which has a significant and complicated influence on the onset of the ellipticity in the process. To study the effect of the friction on the ellipticity, a 3D coupled thermo-mechanical FE model of the process was built based on ABAQUS/Explicit code and validated by experiment. Then, the influence law and the mechanism of friction between the spinning tools and tube on ellipticity of the tube during the process were studied. The results show that the ellipticity increases gradually with the increase of the friction between the roller, mandrel, and tube, while the effects of them on the ellipticity are relatively small in the first three passes. In pass 1, the ellipticity deceases progressively with the increase of the friction between the unloading ring and tube, and it increases slightly in passes 2, 3, and 4. In addition, the optimal combinations of the friction coefficient for each pass in the process were obtained based on the intuitive analysis of orthogonal experiment. Then, the selection principle of the friction coefficients was proposed to control the ellipticity of the process. The achievements of this study can provide a guideline for determining the friction coefficient between the spinning tools and tube during hot power backward spinning process of the high-strength casting aluminum alloy tube. [ABSTRACT FROM AUTHOR]

Quick, low-cost, and high-quality manufacturing is considered a key factor in today’s industry. Therefore, researchers have turned to inventing new methods and technologies for meeting such industrial requirements. Liquid impact forming is one such method which is being increasingly developed in different industries, such as automotive and aerospace. Considered to be a tube hydroforming process, this forming method utilizes liquid pressure to produce the desired shape. In this study, the liquid impact forming process, which was applied to a thin-walled tube made of 6063 aluminum alloy, was experimentally and numerically investigated. In the experimental section, a new die was designed and manufactured for deforming the cross section of the aluminum tube into a hexagonal profile. To investigate the characteristics of the hexagonal profile obtained from the forming process, tensile and three-point bend tests were performed. According to the results obtained from the tensile test, the tensile yield strength in the workpiece increased by 21 MPa due to work hardening. The results obtained from the three-point bend test indicated that the flexural strength of the circular tube was greater than that of the hexagonal profile due to its greater moment of inertia. The numerical results included plastic equivalent strain distribution, variations in the profile thickness, and the force required for the forming process. Upon comparing the workpiece thicknesses obtained from numerical simulation and measurements, a good agreement was observed. [ABSTRACT FROM AUTHOR]

In this study, steel/aluminum clad tubes with metallic bond were fabricated by spin bonding process, and the effects of spinning process parameters and post-annealing treatment on bond strength of 1020St/AA3A21 interface were investigated. The results show that firm metallic bond was formed at elevated temperatures. Bond strength increased with the increasing of thickness reduction, while feed rate exhibited insignificant influence on the bond strength. The maximum bond strength was achieved under the spinning temperature of 200 °C and thickness reduction of 50%. Annealing treatment at 400 to 500 °C for 1 h reduced the bond strength due to the softening of Al base metal. The Fe/Al intermetallic compounds were formed when the annealing temperature increased up to 550 °C, leading to the failure of interface bond. Large residual stresses caused the bending deformation of clad tubes, which could be released by annealing at 300 °C for 1 h and cooling down at the speed of 30 °C/h without penalty of bond strength. Spin bonding exhibited particular advantage in producing clad tube of dissimilar metals with high bonding strength. [ABSTRACT FROM AUTHOR]

Electromagnetic forming (EMF) and electrohydraulic forming (EHF) are typical high speed forming technologies characterized with improved formability of sheet metal, single-sided die, and high precision deformation of parts. In this work, the bulging experiments of aluminum alloy tubes by EMF and EHF were performed to investigate the attaching-die capability, wall thickness, working hardness, and residual plasticity of deformed tubes. The results showed that the bulged tube by EMF is of low attaching-die capability, remarkable rebound, serious thinning of wall thickness, and prone to rupture in the outer corner. However, the parts by EHF process are of high attaching-die capability, almost no rebound, relatively uniform thickness, and remarkable fillet filling in the inner corner. The load mechanism contributes to the different deformation results of both processes. With the almost equivalent deformation, the tensile deformation ability of EHF part is better than that of EMF one, and the discharge energy efficiency of the former is higher than that of the latter. [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]

Magnetic pulse cladding (MPC), a new technology, is proposed in this study to fabricate often utilized bi-metal tubing in engineering applications with an outer tubular component consisting of structurally strong material and an inner tubular layer of corrosion-resistant material. The MPC process includes an innovative feature that allows the outer and inner tubes to electromagnetically bond together by a sequential expansion process to form a mechanical bond between the tubes at the interface. The MPC process was experimentally arranged to produce an Al/Fe bi-metal tube with an outer carbon steel tube and an internal aluminum tube. A mechanical test was then applied to characterize bonding strength of the Al/Fe bi-metal tube. Significant process parameters including discharging voltage, radial gap, and feeding length were identified based on bonding strength influence. Overall feasibility was demonstrated for the MPC process in electromagnetic expansion pattern in the production of bi-metal tubing. [ABSTRACT FROM AUTHOR]

During the extrusion process of aluminum alloy, the ram velocity should be well controlled, since it is an important parameter affecting the profile quality and extrusion productivity. The effects of ram velocity on conventional porthole die extrusion have been investigated by some researchers, while its influence on pyramid die extrusion has not been fully clarified. Thus, in this study, the pyramid die extrusion process for producing a hollow rectangular aluminum tube was comprehensively investigated by performing analysis of steady state, transient state, and billet skin tracking. Importantly, the effects of ram velocity on some evaluation parameters of pyramid die extrusion, such as the material flow behavior, extrudate temperature, extrusion force, transverse weld, quality of longitudinal weld, and back end defect, were overall investigated. The results show that the flowing velocity, extrudate temperature, extrusion force, and welding pressure tend to increase as the increase of ram velocity, while the length of transverse weld is reduced at higher ram velocity. However, the effect of ram velocity on the back end defect is quite slight. Moreover, the advantages and shortcomings of pyramid die were also discussed by comparing with the conventional porthole die. [ABSTRACT FROM AUTHOR]

The effect of extrusion method and lubrication on formability of aluminum tubes in hydroforming is experimentally investigated. First, the formability differences between seamless and porthole aluminum 6063 and 6260 alloy tubes, at T1 and T6 heat treatment conditions, are studied using free bulging. Second, the performances of a wide range of lubricants are ranked using zone-dependent friction tests, e.g., guiding zone and expansion zone, which emulate the two different interface mechanics existing in a THF operation. Results showed that seamless tubes, under any condition, give 5 % more expansion compared to porthole. Also, if a tube has T6 condition, seamless shows clear formability advantage over porthole. However, porthole is found to be quite satisfactory for tubes at T1 condition since they achieved more than %10 expansion. 'Zone-dependent' (expansion zone and guiding zone) lubrication tests are conducted using wet and dry lubricants. Results showed that while a dry lubricant performed best in the expansion zone, a wet lubricant performed best in the guiding zone. [ABSTRACT FROM AUTHOR]

To predict and control wall thickness distribution of thin-walled rectangular 3A21 aluminum alloy tube, the experiments of rotary draw bending process under multi-dies constraints are conducted. It is found that the thickness changing rates in middle bent zone are large, and the maximum values are obtained nearby the tube ridges. The effects of core die, pressure die, mandrel die, and bend die on thickness changing rate are significant. And the thinning rate increases with increase of core number, bend velocity, clearance between tube–pressure die interface and mandrel extension, but it decreases with increase of bend radius and boost velocity of pressure die. The thickening rate increases with increase of core number, boost velocity of pressure die and clearance between tube–wiper die interface, but it decreases with increase of bend radius and bend velocity. [ABSTRACT FROM AUTHOR]

Aluminum rectangular tube is the key component in the field of microwave transmission whose service condition requests strict dimensional accuracy and internal surface quality. To meet these requirements, a newly developed plug featuring a tiny boss club structure in the sizing zone has been proposed in the plug drawing process. The optimal combination of the dimensions in the boss club has been obtained using the method of 3D finite element simulation and orthogonal experimental design. The plastic strain distribution, the contact status between the tube inner surface and the plug, the dimensional accuracy of the formed part, and the forming load have been compared between conditions where the traditional linear-type plug and this new type of plug have been used, respectively. It can be seen clearly that when the plug with a tiny boss club structure is adopted, the contact quality is better and the larger plastic strain exists on the inner surface of the tube, which is very crucial in improving the surface finish of the formed part. Meanwhile, the deviation of wall thickness and the axial length in the formed part is smaller based on the new type of plug. The experiment of the drawing process with two types of plugs has been carried out in which the surface finish of the inner tube surface and the wall thickness have been measured and compared. Experiment result shows that the dimensional accuracy and inner surface quality meet the requirements of the service condition when the plug with a tiny boss club structure is employed. [ABSTRACT FROM AUTHOR]

Flow forming technology is widely used in the production of the axisymmetric industrial parts. The advantage of flow forming process over other manufacturing methods such as press forming is use of simple tooling, reduced forming loads due to localized deformation, and enhanced mechanical and surface quality of finished parts. In this study, the effects of thickness reduction on the mechanical properties and spinning accuracy are experimentally investigated on 7075-O aluminum tube. A prototype spinning machine has been designed and manufactured. The effects of spinning accuracy, surface roughness, percentage of elongation, yield strength, and the ultimate strength as a function of thickness reduction are experimentally examined. The experimental results show that with increment of thickness reduction, the yield strength, ultimate strength, surface hardness, and crystal refining increase, and on the other hand, it has adverse effect on diameter growth, geometrical accuracy, surface roughness, and percentage elongation of spun tube. [ABSTRACT FROM AUTHOR]