Tubular Components Research Articles

Experimental and numerical study on formability in tube bulging: A comparison between hydroforming and rubber pad forming

ABSTRACTFlexible-die forming methods such as hydroforming (HF) and rubber pad forming (RPF) allow producing a variety of complex tubular components that are difficult to fabricate by means of conventional forming. In this paper, firstly, in the bulging of a tube with oil pressure using numerical approach, weld-seam was modeled as a mechanical defect and non-homogeneity factor was calibrated by experimental observations and Vickers micro-hardness testing. Forming limit diagram (FLD), as well as effective plastic displacement factor, was utilized to estimate the initiation and evolution of damage, respectively. Then, with the aim of achieving a defect-free part in RPF process, the effect of lubricating conditions was experimentally and numerically examined. The sound parts were obtained using nylon and drawing oil, respectively, at the tube/rubber and the tube/die interaction surfaces. The results represented that by utilizing the accurate non-homogeneity factor, the numerical method can closely predict the damage in both processes. Also, it was indicated that due to friction in RPF versus HF, the tube was pushed into the bulged zone and the strain path tended to the left side of FLD; therefore, the formability of tube was meaningfully improved.

Design Aspects of a Ring Tension Test Setup and Evaluation of Transverse Material Stress-Strain Curve of Tubular Components Using FE Analysis

Abstract Ring tensile specimens are often used to determine the transverse properties of tubular components due to ease in fabrication and handling. Due to the presence of combined tension, bending, lateral pressure, and friction stresses in the ring tension test setup, it is essential to employ a computational tool in order to evaluate the transverse mechanical properties of these tubes accurately. On the other hand, choice of suitable loading mandrel and loading geometry may facilitate estimation of mechanical properties directly from the tests. In this work, the effect of various types of mandrel design and loading geometries on the load-displacement response of a ring specimen were studied. Finite element analysis with material, geometric, and contact nonlinearities were used in order to simulate the plastic deformation behavior of the specimen in ring tension setup and a novel algorithm was employed to extract the material stress-strain curve from experimental data. In addition, it was observed that a 3-piece mandrel with gage length oriented perpendicular to loading axis produced data which closely fits with the results from finite element analysis.

Numerical Modelling of AlSi7 Tubular Components Flowformed at Elevated Temperature

In small batch manufacturing, flowforming may represent an optimal semi-finishing process for axisymmetric parts, due to its versatility, the reduced material waste, the good geometrical tolerances as well as the improvement of the mechanical characteristics it allows to attain. However, the main limiting factor often lies in the lack of knowledge for the process design, which implies expensive industrial trials often based on trial-and-error approaches. Due to these reasons Finite Element (FE) numerical simulation can provide a significant help in the design and management of the process, but its application is still facing relevant issues, mainly linked to: (i) the complex contact conditions between tooling and part, (ii) the high computation effort due to the 3D geometry rotating at high speed, and (iii) the complex strain paths that the material undergoes.The paper presents an optimized FE model of the flowforming process of AlSi7 alloy tubular components carried out at elevated temperature. An implicit solution scheme and an arbitrary Lagrangian-Eulerian meshing was adopted, while the constitutive parameters of the material model were calibrated on the basis of experimental compression tests carried out in the same thermo-mechanical conditions of the industrial reference process. The influence of the main process parameters, namely thickness reduction, feed rate and mandrel rotation speed were investigated and an algorithm for parametric process charts derivation was finally proposed.

Histologic purity of signet ring cell carcinoma is a favorable risk factor for lymph node metastasis in poorly cohesive, submucosa-invasive early gastric carcinoma.

The prediction of biologic behavior of poorly cohesive early gastric carcinoma (EGC) is an important issue in the selection of the treatment modality. To elucidate the risk factors for lymph node metastasis (LNM) of poorly cohesive EGC, we focused on the histologic purity of the poorly cohesive component and evaluated the impact of this factor on LNM. We divided poorly cohesive EGC into (1) pure signet ring cell (SRC) carcinoma, which was defined as composed only of signet ring cells or poorly cohesive cells and (2) mixed SRC carcinoma, defined as poorly cohesive carcinoma with minor tubular components. We reviewed the clinicopathologic features, including age, sex, location, size, depth, lymphovascular invasion (LVI), LNM, ulceration, and intestinal metaplasia between the two groups in a large series of poorly cohesive, submucosa-invasive EGC (n=317). LNM was found in 58 cases (18.3%). Mixed SRC carcinoma histologic type (p<0.001), larger tumor size (more than 2cm) (p=0.012), and the presence of LVI (p<0.001) were associated with LNM. Pure SRC carcinomas accounted for 56.2% (178/317) of the cases. Fourteen pure SRC carcinomas (7.8%) showed LNM, whereas 44 mixed SRC carcinomas (31.9%) exhibited LNM (p<0.001). On multivariate logistic regression, the presence of LVI (odds ratio 6.737; 95% confidence interval 2.714-16.720; p<0.001) and mixed SRC carcinoma histologic type (odds ratio 4.674; 95% confidence interval 2.370-9.216; p<0.001) were independent predictors of LNM in poorly cohesive, submucosa-invasive EGC. The presence of a tubular component in SRC carcinoma was a risk factor for LNM in poorly cohesive, submucosa-invasive EGC. On the basis of this finding, we propose that the presence of a minor tubular component or the purity of the poorly cohesive/SRC carcinoma component should be reported in daily pathologic practice.

Joining of tubes by gas detonation forming

For many applications, such as in structural components, it is required to join two tubes - sometimes with dissimilar material properties. Only few research studies have investigated the joining of tubular metallic components by means of high-velocity forming processes. In this paper, we present the novel process of joining of two tubes by a gas detonation pressure wave. In particular, the joining of a copper and a steel tube is discussed by means of a finite element study and a conducted experiment.

Development of discharge-pulsed equipment for applied studies of magnetic-pulsed welding processes

The construction of universal pulsed welding equipment for producing stamped-welded thin-wall structures is described. A dual action press was designed for preliminary static and pulsed loading in solid-phase welding of materials. In the process of pulsed-discharge welding, the weld zone is subjected to the thermal effect by passing current and applying pressure using an induction-dynamic drive. The main element of the drive is the induction coil. The energy source is a high-voltage generator of pulsed currents. A special measuring stand has been developed for applied studies and determination of the conditions of magnetic-pulsed welding forming of tubular components. The system can be used to fix the amplitude values and the frequency of discharge current and magnetic pressure and also the RLC parameters of the discharge circuit of the pulsed-current generator. The dual action press and the measuring stand are used in a section for producing lightweight stamped-welded screened casings of board cables for space systems.

Mitigation of Stress Corrosion Cracking Susceptibility of Machined 304L Stainless Steel Through Laser Peening

The paper describes an experimental study aimed at suppressing stress corrosion cracking susceptibility of machined 304L stainless steel specimens through laser shock peening. The study also evaluates a new approach of oblique laser shock peening to suppress stress corrosion cracking susceptibility of internal surface of type 304L stainless steel tube. The results of the study, performed with an indigenously developed 2.5 J/7 ns Nd:YAG laser, demonstrated that laser shock peening effectively suppresses chloride stress corrosion cracking susceptibility of machined surface of type 304L stainless steel. In the investigated range of incident laser power density (3.2-6.4 GW/cm2), machined specimens peened with power density of 4.5 and 6.4 GW/cm2 displayed lower stress corrosion cracking susceptibility considerably than those treated with 3.2 and 3.6 GW/cm2 in boiling magnesium chloride test. Oblique laser shock peening, performed on machined internal surface of a type 304L stainless steel tube (OD = 111 mm; ID = 101 mm), was successful in introducing residual compressive surface stresses which brought about significant suppression of its stress corrosion cracking susceptibility. The technique of oblique laser shock peening, in spite of its inherent limitations on the length of peened region being limited by tube internal diameter and the need for access from both the sides, presents a simplified approach for peening internal surface of small tubular components.

The deformation and microstructure of Ti-3Al-2.5V tubular component for non-uniform temperature hot gas forming

In this paper, three 70 % expansion ratio Ti-3Al-2.5V tubular parts were formed by non-uniform temperature hot gas forming with different temperature distributions. The deformation behavior, thickness distribution, microstructure, and mechanical property of tubular parts were studied. The result shows that a suitable temperature difference between forming zone and transition zone is beneficial for axial feeding, which promote the thickness distribution uniform. The number of wrinkles in forming zone is affected by the temperature distribution. There are two wrinkles, one wrinkle, and three wrinkles when the temperature differences are 0, 50, and 15 °C, and the max thinning ratio is 24.9, 24.1, and 18 %, respectively. When the temperature difference is 15 °C, the microstructure and mechanical property is uniform.

Finite element method formulation in polar coordinates for transient heat conduction problems

The aim of this paper is the formulation of the finite element method in polar coordinates to solve transient heat conduction problems. It is hard to find in the literature a formulation of the finite element method (FEM) in polar or cylindrical coordinates for the solution of heat transfer problems. This document shows how to apply the most often used boundary conditions. The global equation system is solved by the Crank-Nicolson method. The proposed algorithm is verified in three numerical tests. In the first example, the obtained transient temperature distribution is compared with the temperature obtained from the presented analytical solution. In the second numerical example, the variable boundary condition is assumed. In the last numerical example the component with the shape different than cylindrical is used. All examples show that the introduction of the polar coordinate system gives better results than in the Cartesian coordinate system. The finite element method formulation in polar coordinates is valuable since it provides a higher accuracy of the calculations without compacting the mesh in cylindrical or similar to tubular components. The proposed method can be applied for circular elements such as boiler drums, outlet headers, flux tubes. This algorithm can be useful during the solution of inverse problems, which do not allow for high density grid. This method can calculate the temperature distribution in the bodies of different properties in the circumferential and the radial direction. The presented algorithm can be developed for other coordinate systems. The examples demonstrate a good accuracy and stability of the proposed method.

Loading path and microstructure study of Ti-3Al-2.5V tubular components within hot gas forming at 800 °C

Hot tube gas forming is a forming technology, whose ultimate goal is forming a uniform cross-section blank tube into a complex shape die cavity with varying cross-sections without necking, wrinkling, or buckling by applying of axial feeding and internal pressure at elevated temperature. In this paper, the effects of feeding speed and internal pressure on the quality of formed tubular components were studied by theoretical analysis, FEM simulation, and experiment. The microstructure evolutions at four typical positions were analyzed by electron back-scattered diffraction (EBSD). The mechanical properties of tubular component were tested by the uniaxial tensions and hardness tests. A good tubular component can be formed under a two-stage loading path at 800 °C, the feeding speed is 0.1 mm/s and the internal pressure is 5 MPa during the first feeding stage while the feeding speed is 0.2 mm/s and the internal pressure is 7 MPa during the second feeding stage. At the forming zone, the grains are significantly elongated along the hoop direction. Compared with the as-received tube, the tensile strength of parts reduces about 6 % along axial direction.

Process modeling and optimization of the staggered backward flow forming process of maraging steel via finite element simulations

Flow forming is used to produce thin-walled high-precision tubular components. A 3D thermo-mechanical finite element model for staggered backward flow forming of a cylindrical workpiece of maraging steel has been developed using Abaqus/Explicit. The effect of tip radius of the rollers and friction between the rollers and the workpiece has been considered. Simulations have been carried out at different process conditions to study the state variables, such as stresses and strains obtained during the deformation. The model has been benchmarked for thickness reduction and roll forces against the experimental results and analytical solutions, respectively. The effect of flow forming process variables, such as feed rate and reduction ratio, on the stress/strain distribution and roll forces have been studied. An increase in feed rate from 1 to 2.33 mm/s leads to an increase of 7 % in effective plastic stress. An increase of 72 % in equivalent plastic strain has been observed when the reduction ratio is increased from 23 to 33 %. In addition, a parametric study has been conducted to study ovality, diametral growth, roll forces, stresses, and strains as a function of process parameters. The circularity of the tube is a very important geometrical feature in the flow forming process. It is imperative to study the key parameters affecting the circularity of the preform. Eight process variables have been considered in a response-surface-based computer design of experiments to minimize the ovality. The feed rate, reduction ratio, and the attack angle of the roller Z are found to be most significant parameters in order to control the circularity of the tube. Among all process variables, the reduction ratio is found to be the most significant parameter. The order of their relative significance is reduction ratio, feed rate, and the attack angle of the roller Z.

Pressure-assisted forming of non-concentric tubular cross sections with solid medium

Pressure-assisted forming of tubes allows producing a wide variety of tubular components that are difficult or impossible to fabricate by means of conventional tube forming. In contrast to previous investigations in the field that were almost exclusively focused on the utilization of fluids (tube hydroforming) or elastomers (tube rubber forming) as pressuring medium, the subject matter of this article is centred in the utilization of low melting point, recyclable, metallic alloys as solid pressurizing medium. The aims and scope of the article are centred on the feasibility of forming straight carbon steel tubes into complex gooseneck geometries with non-concentric cross sections using lead as a solid pressuring medium and employing a double-action cam-driven tool system. The presentation is focused on the tool system, on its adequacy to produce customized tubular components, on the required forming forces and on the typical modes of deformation that result from the different movements provided by the vertical and horizontal actuators of the double-action tool system. Results and observations confirm that the utilization of a double-action tool system with a solid pressurizing medium to assist plastic deformation and prevent collapse can be successfully and effectively employed to fabricate non-concentric tubular cross sections for prototypes and small batches of lightweight components.

Urinary gamma-glutamyl transferase (GGT) as a marker of tubular proteinuria in dogs with canine leishmaniasis, using sodium dodecylsulphate (SDS) electrophoresis as a reference method

In order to assess if urinary γ- glutamyl transferase (GGT) identify tubular proteinuria in leishmaniotic dogs, the GGT/urinary creatinine (UC) ratio was calculated in 39 leishmaniotic dogs. According to sodium dodecylsulphate–agarose gel electrophoresis, the dogs had albuminuria (A, n = 10), glomerular (G, n = 3), tubular (T, n = 4) or mixed proteinuria (M, n = 22). The median GGT/UC ratio was 0.3, 0.3, 2.2, and 7.5, in groups G, A, M, and T, respectively. Statistically significant differences were found between groups G and M (P = 0.002), G and T (P < 0.001), A and M (P < 0.001), and A and T (P < 0.001). Median values were higher in dogs with tubular components of proteinuria (M/T, 2.5) than in dogs without tubular components of proteinuria (A/G, 0.3), and in dogs with tubular proteinuria (T, 7.5) than in dogs with non-tubular proteinuria (NT, 1.0). GGT/UC values >0.81 or >2.64 could identify dogs in the M/T or T groups, respectively. Therefore, GGT/UC might be useful for the management of leishmaniotic dogs.

Numerical and analytical approaches for improving the die design in the radial forging process of tubes without mandrel

Radial forging without a mandrel offers a cost effective method for production of tubular components. However, nonuniform deformation, thickness variation, poor surface quality and undesirable residual stress distribution are the problems which should be overcome in order to achieve an optimal process. In this paper, radial forging dies with curved-shape profiles are proposed to alleviate some of the mentioned difficulties. Finite element simulations are used to prove the advantage of the proposed dies over the conventional linear dies. A novel analytical approach based on the slab method of analysis is developed to verify the finite element modeling. The obtained results provide useful guidelines for design and optimization of the radial forging process without mandrel.

Identification of structural and morphogenesis genes of Pseudoalteromonas phage φRIO-1 and placement within the evolutionary history of Podoviridae

The virion proteins of Pseudoalteromonas phage φRIO-1 were identified and quantitated by mass spectrometry and gel densitometry. Bioinformatic methods customized to deal with extreme divergence defined a φRIO-1 tail structure homology group of phages, which was further related to T7 tail and internal virion proteins (IVPs). Similarly, homologs of tubular tail components and internal virion proteins were identified in essentially all completely sequenced podoviruses other than those in the subfamily Picovirinae. The podoviruses were subdivided into several tail structure homology groups, in addition to the RIO-1 and T7 groups. Molecular phylogeny indicated that these groups all arose about the same ancient time as the φRIO-1/T7 split. Hence, the T7-like infection mechanism involving the IVPs was an ancestral property of most podoviruses. The IVPs were found to variably host both tail lysozyme domains and domains destined for the cytoplasm, including the N4 virion RNA polymerase embedded within an IVP-D homolog.

Producing Thin-Walled Tube of Pure Copper by Severe Plastic Deformation of Shear Extrusion

Abstract A severe plastic deformation method entitled shear extrusion (SE) was proposed to form thin-walled tubular components. This process was validated by experiments in which a pure copper tube was used as investigation object. The effect of SE on grain refinement and strength improvement was assessed. The results of optical microscope observation show a significant grain refinement as well as the increased grain misorientations for the samples processed by four passes of SE. The TEM analysis shows that the dislocation refinement of shear strain is the main reason during the SE process, followed by strain localization leading to dynamic recrystallization. The hardness of undeformed copper cube sample is ∼400 MPa, while that of as extruded sample is up to ∼1070 MPa. The increase of the hardness is mainly caused by the dislocation generation.

가변 단면을 가지는 비대칭 얇은 관 부품의 액압성형 연구

Abstract Hydroforming of a non-axisymmetric thin-walled tubular component with variable cross sections was analyzed. In order to solve the sealing problem which occurred due to the thin and non-axisymmetric shape, the use of a lead patch on the punch, which had been successful in hydroforming of thin tubes, was evaluated. A lead patch was attached to the punch to solve the sealing problem, which was caused by the stress gradient in the non-axisymmetric shape. FEM and experiments were also performed to analyze these sealing problems associated with the punch shape and non-axisymmetric shape. Finally, the lead patch was attached at tube surface where intensive local strain concentration would occur to enhance the hydroformability. These methods were successfully used to fabricate non-axisymmetric thin-walled tubular component with variable cross sections that had previously failed during traditional hydroforming. Key Words : Hydroforming, Thin-wall Tube, Non-axisymmetric Shape, Variable Cross Sections, Sealing Problem, Lead Patch

Experimental investigation on fabrication of Al/Fe bi-metal tubes by the magnetic pulse cladding process

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.

Enhancing hydroformability of nonaxisymmetric part with variable cross section

Methodology to enhance hydroformability of nonaxisymmetric thin-wall tubular component with variable cross sections was investigated in this study. In order to solve punch leakage problem occurred at nonaxisymmetric thin tube, the leak-resistive punch was suggested. Attaching lead at contact region of tube and punch was implemented to prevent leakage occurred due to uneven pressure distribution between punch and tube. And lead patch has also been attached at locally strain-concentrated tube surface to retard strain-concentrated necking. To validate the proposed enhancing methodology, nonaxisymmetric thin-wall tubular model part with variable cross sections has been hydroformed. The successful fabrication of model part that had previously failed during conventional hydroforming processing confirms the feasibility of proposed methodology.

Practicality and formability of integrally stiffened tube hydro-assisted forming

To achieve integrally stiffened tubular component, a new technology named as hydro-assisted forming was put forward, which successfully realized integral component forming. Experiment and finite element simulation were conducted to explore the practicality and formability of stiffened tube hydro-assisted forming. Based on plastic mechanics, the critical mechanics condition was analyzed and given. At last, the shape error and thickness distribution were given in detail. The results indicate that internal pressure induces not only tensile hoop stress but also “backward” bending moment, which are useful to eliminate wrinkle defect. But it is worthwhile to note that buckling defect would happen if the internal pressure was too high due to the effection of rib initial deflection. Shape accuracy is sensitive to internal pressure. Geometric error decreases as internal pressure, but increases after the internal pressure reaches a certain degree. Both welding residual stress and thermal deformation are successfully eliminated due to plastic deformation happens during hydro-assisted forming process. In view of hydro-assisted forming process, sound thickness distribution is an effortless advantage for bending deformation has less effection on thickness distribution. The maximum thinning ratio is only 5 % for hydro-assisted forming, which is far less than that of tube hydroforming. At last, an integrally stiffened tubal component with ellipticity of 2 was formed successfully by hydro-assisted forming technology, which rib height reaches 10 mm.