Variable-diameter Tube Research Articles

A forming method of variable-diameter tubes straightforward from sheet metals

Variable-diameter metallic tubes are extensively used in many industrial applications. They are generally made of pre-formed raw tubes by using the existing processing methods, during which obvious non-uniformity in tube wall thickness inevitably occurs. In this work, a novel method is proposed to form variable-diameter tubes directly from sheet metals by means of the roll-stamp forming technique. A three-pass roll-stamp forming process and corresponding die blocks are designed and implemented to form a demonstrative conical tube. The finite element model of the roll-stamp forming process is established and forming quality is quantitatively evaluated. The initial blank configuration, which is the most important factor for process design, is determined by combining machine learning and multi-objective optimization. The forming experiment is performed, and the conical tube is successfully formed with no significant thinning/thickening of tube wall. The influences of forming direction and conical ratio on the forming process are numerically investigated. The proposed roll-stamp technique provides a novel and effective approach to manufacturing variable-diameter tubes.

Initiation and suppression of Taconis oscillations in tubes with junctions and variable-diameter tube segments

Taconis oscillations represent spontaneous, usually unwanted excitations of acoustic modes in narrow pipes going from warm ambient environment into cold cryogenic space. These oscillations can drastically magnify heat leak and create vibrations undesirable for measurement instruments. In this study, modifications of a classical constant-diameter-tube Taconis setup are investigated. Specifically, variable-diameter tubes were found to strongly affect excitation, with wider tube segments in the warm environment encouraging oscillations, while additions of properly chosen pipe network configurations can supress the oscillations. The low-amplitude thermoacoustic theory, previously developed for thermoacoustic engines and refrigerators, was adapted for modelling Taconis phenomena, accounting for finite-length segments with temperature evolution where thermal-to-acoustic energy conversion takes place. Experiments were conducted using primarily hydrogen as a working fluid to validate theoretical predictions. With the rapid development of various hydrogen storage and transfer systems, it is expected that Taconis oscillations may become an issue, and this study provides an initial modelling framework to assess this phenomenon in hydrogen systems.

Improving forming accuracy of variable-diameter tube by electromagnetic forming using segmented coil

Improving forming accuracy of variable-diameter tube by electromagnetic forming using segmented coil

Deformation characteristics and process optimization in neck-spinning of variable-diameter tube

Deformation characteristics and process optimization in neck-spinning of variable-diameter tube

Enhancing forming accuracy in aluminum alloy variable-diameter tubes through dual-coil controllable electromagnetic forming

High-accuracy forming of aluminum alloy variable-diameter tubes imposes strict requirements on force field design. Although electromagnetic forming has shown unique advantages in enhancing the formability of aluminum alloy materials, its shortcomings lie in the single and difficult-to-adjust force field, which limits its application in variable-diameter tubes. To address this challenge, a novel dual-coil electromagnetic forming approach with good controllability of force field is proposed. Numerical simulations and experiments are both conducted to showcase the superiority of this approach in forming variable-diameter aluminum alloy tubes. The results demonstrate that the forming accuracy of AA6061-O variable-diameter tubes has significantly improved compared to a traditional single-coil system, in which the maximum die-fitting gap is reduced from approximately 2 mm to less than 0.22 mm. Furthermore, it is identified the force field produced by the single-coil system causes a local cavity gap between the tube and the die, which adversely affects the forming accuracy. In contrast, the improved force field produced by the dual-coil system facilitates bottom-to-top deformation of the tube, thereby avoiding undesirable cavity gaps and achieving high forming accuracy. Importantly, the dual-coil forming system offers significant controllability of the Lorentz force field by adjusting the coil discharge, making it suitable for variable-diameter tubes of different sizes without changing the coil structure. This work represents a substantial advancement in controllable tube forming, offering a new approach to force field design and holding promise for extensive applications in the forming of variable-diameter tubes.

Numerical investigation on flow and heat transfer performance of non-Newtonian Bingham fluid in novel spiral wound tube heat exchangers

Based on the field of the coal chemical industry, exploring the applicability of high-performance heat exchangers for coal water slurry and their flow and heat transfer mechanism is of great significance for promoting the development of clean coal technology. In this paper, the flow pattern and forced convection heat transfer of a pair of tandem heated cylinders with different distances were discussed using the bi-viscous Bingham model by numerical simulation. And a novel spiral wound heat exchanger with variable diameter tubes was proposed. The results illustrate that the heat transfer coefficient under unit pressure drop h/△P of the heat exchanger decreases with the increase of the diameter of the variable tubes. When the diameter of variable tubes is 12 mm, h/△P is 19.83% larger than that of the original structure with uniform tube diameter. The empirical correlation between operating and structural parameters and heat exchanger performance is obtained. The research results provide guidance for the design of coal water slurry preheaters and the structural optimization of spiral wound tube heat exchangers.

Analysis on corner wrinkling for axial hydro-forging of variable-diameter tube

Analysis on corner wrinkling for axial hydro-forging of variable-diameter tube

Investigation of thickness variation in axial hydro-forging sequence for variable-diameter tubes

Abstract Axial hydro-forging sequence is an emerging process to form the variable-diameter tubular components. In axial hydro-forging sequence, the excessive thickness thinning of the tube can be reduced and even eliminated by axial compression deformation. In this case, a new type defect is discovered, where the thinning of the transition zone is not decreased and a barrelling defect occurs at the end of the maximum diameter zone. To reveal the reason of the defect and provide a clue to avoid it, the stress distribution, the deformation sequence as well as the thickness distribution are investigated by mechanical analysis, finite element simulation and experiments. Two key process parameters considered in this study include the corner radius and the friction coefficient. The results show that the marked drop of the effective stress in the corner segment of the transition zone caused by the normal concentrated force is the determining factor of the defect in hydro-forging stage. It is shown that the defect can be decreased by increasing the corner radius, but only barrelling defect is decreased by improving friction coefficient. Based on the results, a new improvement approach was proposed in this paper and verified that it can effectively reduce the defect.

Study on barrelling behavior of variable-diameter tubes in axial hydro-forging sequence

Axial hydro-forging sequence is an emerging approach in forming the variable-diameter tubes without thinning. However, after the batch production, a barrelling defect occurs at the end of the maximum diameter zone during the process. To investigate the barrelling behavior of the tube in axial hydro-forging sequence, experiments and finite element simulation were carried out in the present work. It could be concluded that the barrelling formation is attribute to the non-uniform stress distribution and the geometric feature of the tube. Subsequently, the effect of expansion ratio, friction coefficient and transition form on barrelling behavior was investigated. It was found that the degree of the barrelling increased with increasing the expansion ratio, but decreased with reducing the friction coefficient. Moreover, the transition form had a significant effect on the barrelling degree, and the barrelling defect can be eliminated when the transition form with circular arc was employed.

Theoretical and numerical analysis of a new energy-absorbing rock bolt with controllable constant resistance and large displacement

To provide an effective support device for dealing with the instability problems in geotechnical engineering, this paper proposes a new energy-absorbing rock bolt based on the existing energy-absorbing devices, called compression-expansion-friction bolt (abbreviated as the CEF bolt). The CEF bolt mainly consists of two parts, a variable-diameter tube and a hollow cone attached at the distal end of the bar. Controllable constant resistance and large displacement are the characteristics of the CEF bolt. The constant resistance was generated by the expansion of the tube under the compression of the cone, as well as the friction between the tube and cone. And the large displacement was provided by the sliding of the cone relative to the tube. A theoretical model was developed to predict the constant resistance by taking into account the effect of material strain-hardening. Based on the energy conservation law, the effect of shear deformation was also considered. Further, the current model was formulated as three forms to consider different conditions. The predictions of the current theoretical model were in good agreement with existing experimental data. An experimentally validated finite element model was established to study the effects of main parameters on the constant resistance of the CEF bolt, such as cone angle, tube wall thickness, friction coefficient, expansion ratio and the strain-hardening property of the tube. The results of numerical simulation and theoretical analysis show that the constant resistance was directly proportional to the tube wall thickness, friction coefficient, expansion ratio and the strain-hardening modulus of the tube. But the constant resistance increased first and then decreased with respect to the cone angle, with an inflection point existed between 5° and 10°. The shear stress distribution and the deformation of the tube were investigated as well. According to the shear stress distribution, the zone under expasion of the tube can be divided into three characteristic areas: stress concentration area, smooth transition area, and stress re-concentration area. In addition, compared with the large number of experimentally validated numerical results, the wide applicability and sufficient accuracy of the current theoretical model were verified. By taking the derivative of the current theoretical model, the location of the inflection point can be obtained. These results can provide theoretical basis for the design and field application of the CEF bolt, as well as the similar structure.

Experimental and Numerical Investigation of a Miniature Additively Manufactured Vortex Tube

Abstract Ranque–Hilsch vortex tubes are simple devices that can produce a cooling effect using compressed air. A key advantage of vortex tubes is the lack of moving solid parts; however, their efficiencies are relatively low. The present study focuses on the development of a miniature variable-diameter tube using additive manufacturing. A metal-based 3D printing technique was utilized to fabricate this vortex tube monolithically. Computational fluid dynamics simulations employing software star-ccm+ with a compressible Reynolds-Averaged Navier–Stokes (RANS) approach and the elliptic-blending lag k-epsilon turbulence model have been applied to model thermofluid processes inside the vortex tube, to good agreement with the experiment. A temperature decrease of 13.3 °C and a cooling power of approximately 4 W were experimentally achieved with a pressure ratio of 4 in the air at normal conditions. This result shows promise for the goal of utilizing additive manufacturing to design and build complex-geometry vortex tubes intended for use with cryogenic fluids.

Experimental and numerical investigation on axial hydro-forging sequence of 6063 aluminum alloy tube

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.

Experimental study of the plugging–matching relationship between elastic particles and formation pore throats

Low-cost modified rubber powder DBR elastic particles with good temperature and salt resistance were selected to investigate the plugging–matching relationship between the elastic particles and formation pore throats. The elastic deformation coefficient of the particles was measured using a custom-built uniaxial compression experimental device. Based on the ideal model and arrangement of spherical particles, a calculation method for the pore throat size was determined according to the statistical results of pore size measurements in the simulated formations (sand packs). The injection properties of DBR particles with different diameters in different permeability simulated formations were studied using a sand-filled tube displacement device. Through comprehensive analysis, the injection pressure fluctuation frequency, injection surface filter cake situation, particle entry depth, and plugging pressure, it was found that the elastic particle plugging matching coefficient (defined as the particle to pore through diameter ratio) range was 0.21–1.10 at different particle injection concentration(≤5wt%), and it is further proposed that the matching coefficient for elastic particles can be converted to that for rigid particles by dividing through by the elastic deformation coefficient, which may prove useful in guiding profile control and water plugging operations in the field. Finally, the different stages in the plugging and migration mechanisms of elastic particles in formation pore throats were illustrated using a visual variable diameter tube model. The model clearly showed that particle backflow disturbance is an adverse factor affecting particle plugging.

Axial hydro-forging sequence for variable-diameter tube of 6063 aluminum alloy

To overcome the problems in forming the variable-diameter tubes by tube hydroforming, such as excessive thinning and high internal pressure, a new approach named axial hydro-forging sequence was proposed. In this approach, the tube was expanded to fill the die cavity firstly and then the thinning ratio was reduced by axial compression deformation produced in axial hydro-forging sequence. To demonstrate the feasibility of this approach, two mechanical conditions were theoretically analyzed in this study include axial hydro-forging condition and deformation sequence. Based on the plastic energy method, a critical wrinkling model for axial hydro-forging sequence was established to calculate the critical wrinkling internal pressure. It was observed that there was a critical wrinkling internal pressure in the axial hydro-forging sequence, and the critical wrinkling internal pressure increased with increasing the tube axial shortening and material strength coefficient, but decreased with the increase of strain hardening coefficient. At the same time, an analytical model based on mechanical analysis was developed to discuss the deformation sequence for different deformation zones. The results showed that the deformation sequence of the three characteristic zones in the process was as follow: maximum diameter zone > transition zone > guide zone, which satisfied the requirement of reducing the thinning ratio. Finally, experiments along with the finite element simulation were performed to validate the analytical model, and effects of key process parameters on tube forming were revealed. As a result, variable-diameter tubes were successfully produced by this approach, which indicated that the axial hydro-forging sequence is a feasible forming approach for the fabrication of tubes with variable diameters.

Gradient electromagnetic forming (GEMF): A new forming approach for variable-diameter tubes by use of sectional coil

A new gradient electromagnetic forming (GEMF) approach that utilizes the gradient electromagnetic force generated by use of a sectional coil is proposed to meet force-field requirements concerning deformation of specially shaped variable-diameter tubes. To demonstrate the development of this approach, a variable-diameter tube made of copper-nickel alloy was formed via GEMF, as an example. An efficient geometric design for the sectional coil was established, and effects of the gradient electromagnetic force field on metal flow have been discussed along with investigation of the effects of key process parameters on tube forming. The deformation mechanism of GEMF has also been explained. Feasibility of the GEMF approach has been validated based on the accurate deformations of variable-diameter tubes made of copper-nickel alloy and characterized by a maximum die-fitting gap of less than 0.4 mm. Moreover, optimal combination of the coil proportion coefficient (85%) and discharge voltage (18 kV) have been obtained to ensure high forming accuracy. It was observed that the gradient electromagnetic force field prevented occurrence of stress concentrations by effectively improving stress distributions. Consequently, the forming accuracy and quality of variable-diameter tubes was significantly improved using the GEMF approach.

Numerical simulation analysis of multi-physical coupling field with abrasive flow precision polishing variable-aperture tube

In the fields of aerospace, precision machinery and energy, there are variable-diameter tubes for many key components. Abrasive flow polishing technology is an effective precision polishing technology for finishing the workpiece with an internal cavity structure. This technology can improve the quality of part finishing, reduce stress concentration, and reduce the surface roughness of the workpiece, and ultimately can improve the performance of the workpiece. In this paper, variable-aperture tube is taken as the research object, and the characteristics of abrasive flow in the multi-physics coupling field are studied by numerical simulation, and the collision removal effect between the abrasive particle and the wall surface is analyzed. We also discussed the control law of the abrasive grain flow processing quality and provided theoretical guidance for abrasive grain flow polishing of this type of part.

Study of Bulging-Pressing Compound-Deforming Automobile Axle Housing with a Common Press

The conventional hydroforming process for automobile axle housing needs a large-tonnage press and has the drawback of the dome part being apt to burst due to the large thinning. A new forming technology, bulging-pressing compound-deforming for automobile axle housing, is proposed, which is suitable for the large variable-diameter tube parts with special-shaped cross-sections. The initial tube is made into the axisymmetric peforming tube after the ends necked and the middle hydroformed, and which then is pressed into the axle housing sample by the dies. For a small automobile axle housing, the process tryout and the pressing dies were designed, and the axle housing samples were successfully produced with a common press. Compare with the conventional hydroforming process, the forming corner radiuses of present samples are smaller and the internal pressure decreased 60%. The results show that the process has the advantages of good corner-filling ability and low internal hydraulic pressure.

Pressure losses of two-phase flow in a variable-diameter tube

An effective tube with a diameter of 25.6 mm possessed terminal sections of smaller diameters (16.8 and 21.4 mm). When a steady film flow is realized in the terminal sections, only nonsteady regimes are possible primarily in the basic median section (pulsed regime or nonsteady film). Pressure losses related to the pulsed regime are determined by computational means using the principle of additivity on the basis of measured values of total pressure losses in the variable-diameter tube.

Conditions of ascending cocurrent flow in variable-diameter tubes

The working tube of diameter 25.6 mm had terminal portions of smaller diameters (16.8 and 21.4 mm). When a steady film flow is realized in the terminal portions, only unsteady conditions (flooding or unsteady film) are possible in the main middle portion. A diagram of flow modes (falldown, pickup, fluctuating flow, unsteady film flow, steady film flow, etc.) is constructed in phase (water–air) flow rate coordinates. Entrainment boundary, incomplete wetting, and types of wave modes are noted.

Diagrams for determination of film thickness in an ascending cocurrent flow

A theoretically obtained relationship between specific reflux density and film thickness in an ascending cocurrent flow (laminar wave-free flow of liquid over a vertical plane) is examined. A diagram for determination of the film thickness in constant-diameter tubes for a water-air system, and correction curves for this diagram are presented. A diagram is constructed for determination of the film thickness in variable-diameter tubes, which is more general — not constrained by specific properties of the liquid and gaseous phases. Examples of the use of the diagram are presented.