Tube Hydroforming Research Articles

Strain Measurements in Free Tube Hydroforming Process

Strain Measurements in Free Tube Hydroforming Process

Developments of methods for improving metal forming operations simulations: material hardening and friction characterization under process conditions

Metal forming operations are optimized by using finite element simulations. The numerical results are strongly dependent on the material data and the friction conditions. The present paper focuses on the tube hydroforming process and methods, developed by the authors, for the evaluation, the closest to the process conditions, of the hardening curve and the friction coefficient. For the hardening curve, an experimental set-up has been developed and instrumented, and an analytical model permits to translate the measures into stress-strain curve. Its capability to evaluate the best plastic criterion and its importance for a good prediction of forces during the tube hydroforming are illustrated. For the friction evaluation, the study of tube expansion in a square section die is proposed. By analyzing the thickness along the perimeter of the shaped tube, it is possible to evaluate the Coulomb’s friction coefficient, which can be different from the evaluation done with the classical pin-on-disk test.

Mathematical Modeling for Prediction of Tube Hydroforming Process using RSM and ANN

Tube hydroforming (THF) is a special manufacturing process used to produce tubular components having applications in aerospace and automotive industries. The present study investigates the effect of process parameters such as coefficient of friction (CF), corner radius (CR) of the die and the axial feeding (AF) of the punch. The bulge ratio and thinning ratio has been evaluated to minimise the defects like bursting, wrinkling and buckling in the tubes. Apart from many parameters, these parameters are chosen to know the effect of each individual parameter on the outcomes namely bulge ratio and thinning ratio. Each factor has varied with three levels and a total of 27 simulations were carried out based on full factorial design. RSM and ANN were applied on the obtained results in order to predict the process parameters effect on the tube hydroforming process. The R-square value of ANN (0.9524 and 0.9517) is much closure to 1 when compared to R-square value of RSM (0.9539 and 0.9509).

Mathematical modelling for prediction of tube hydroforming process using RSM and ANN

Tube hydroforming (THF) is a special manufacturing process used to produce tubular components having applications in aerospace and automotive industries. The present study investigates the effect of process parameters such as coefficient of friction (CF), corner radius (CR) of the die and the axial feeding (AF) of the punch. The bulge ratio and thinning ratio has been evaluated to minimise the defects like bursting, wrinkling and buckling in the tubes. Apart from many parameters, these parameters are chosen to know the effect of each individual parameter on the outcomes namely bulge ratio and thinning ratio. Each factor has varied with three levels and a total of 27 simulations were carried out based on full factorial design. RSM and ANN were applied on the obtained results in order to predict the process parameters effect on the tube hydroforming process. The R-square value of ANN (0.9524 and 0.9517) is much closure to 1 when compared to R-square value of RSM (0.9539 and 0.9509).

Innovative Manufacturing and Application of Fiber Metal Laminate Pipe

Fiber-reinforced metal laminate tube (FMLT) is a multi-layered ultra-hybrid material that cures at fixed pressure and temperature after alternating metal laminates and fiber composites. As with the production process similar to the second-generation GLARE fiber-reinforced metal layer, the management layer of the formed composite layer should have good impact resistance characteristics, and can also be used in the impact-resistant structure of the aircraft, the landing cushion structure of the aircraft, and the body collision Device to protect aviation materials.The composite pipe fittings are made by hydraulic forming technology, which lays a good foundation for the small-scale fine processing of the pipe. In addition, use speckle models and other virtual software simulation models (such as various related software and related formulas) to monitor data before and after hydroforming of fiber-reinforced metal layer tubes, it lays a good data foundation for the hydroforming of pipes and subsequent experiments.The development and performance testing of GLARE composite tube hydraulic forming technology is of great significance to the development of lightweight and safety in the aviation industry and the automobile industry.

An investigation on tube hydroforming process considering the effect of frictional coefficient and corner radius

ABSTRACTTube hydroforming (THF) technology is mostly used in automotive and aerospace industries because of its benefits like high precision, less weight and forming capability of complex shapes. Formability of the tube is the main factor for the consideration of the THF technologies in the industries. Thickness distribution in the bulged area is the key factor for the consideration of hydroformed parts. In the present paper, effects of coefficient of friction and corner radius of the die on bulge height and thickness distribution of the bulged area are studied using finite element method. Mechanical properties required to carry out the numerical simulations are evaluated by tensile, R-bar and pin-on-disc tests. Pin-on-disc experiments are carried out on the chosen material to find the wear and frictional coefficient with varying normal loads. Both numerical and analytical solutions are compared for the internal pressure required to bulge and burst the tube and observed to be in good agreement with each other. This study helps the researchers and industrialists for further understanding of the mechanics involved in the THF process in terms of die design and frictional effects.

The development of a novel forming limit diagram under nonlinear loading paths in tube hydroforming

The loading paths of tubular parts containing the characteristic of variable diameter during hydroforming are nonlinear and similar to the loading paths during tube hydro-bulging tests. Therefore, the forming limit determined by hydro-bulging tests is very suitable for guiding the forming of this kind of parts. However, traditional forming limit diagram (FLD) cannot present the nonlinear loading paths. In this paper, a theoretical analysis model for tube hydro-bulging tests is developed first. And then the stress paths and strain paths during bulging with fixed-ends and free-ends are analyzed through the theoretical model and finite element simulations. The results show that as the length-diameter ratio of the bulging zone ranges from 1.0 to 3.0, stress paths and strain paths are obviously nonlinear. For hydro-bulging with fixed-ends, the axial-hoop stress ratio changes gradually from 0.5 towards 1.0, and the strain state changes from plane strain state towards equal-biaxial tension state. For hydro-bulging with free-ends, the stress ratio changes gradually from 0 towards 0.5, and the strain state changes from simple tension state towards plane strain state. In order to give a better characterization of the forming limit of tubes under nonlinear loading paths, a novel FLD combining the geometric parameter of the tubular part is proposed. Two FLDs of an AA6061 aluminum alloy seamless tube under different end conditions are determined by experiments. The results show that both in hydro-bulging with fixed-ends and with free-ends, a higher forming limit is expected when using a smaller length-diameter ratio. As the new FLD can give direct presentation of limit strains together with the end condition and the length-diameter ratio in tube hydroforming, it can be used directly for the analysis and optimization of actual tube hydroforming processes, instead of the simple evaluation of the formability of raw materials.

A new method for hydroforming of thin-walled spherical parts using overlapping tubular blanks

Tube hydroforming is an advanced metal forming processes, which is widely used to form various tubular parts. Axial feeding is usually used to avoid excessive thinning in hydroforming of a variable-diameter part. However, wrinkling defects are susceptible to occur easily under the axial loading if the wall thickness of the tube is small. A new method was proposed to enhance the expansion ratio and improve the thickness distribution for hydroforming of thin-walled spherical parts using overlapping tubular blanks. A special loading tool was created and AISI 304 stainless steel blanks were used for the experimental research. The effects of blank shapes and normal constraints were studied on wrinkling defects of the overlapping blanks. The results show that wrinkling defects at the inner layer of the overlap are prevented by using curved-edge blanks. Wrinkling defects at the outer layer of the overlap is eliminated by using normal constraints. Finally, a sound thin-walled spherical part was obtained by using an overlapping tubular blank. The maximum expansion ratio is 60% and increased by 30.2% compared with that of conventional hydroforming using a closed cross-sections tube. The maximum thinning ratio was 32.4%, which was decreased by 29.3%. In general, it is feasible to use an overlapping blank to form a variable diameter part. The maximum expansion enhances significantly and the thickness distribution improves apparently.

Influence of Lubricants on Coefficient of Friction in Tube Hydroforming

In this paper, the effect of different lubricants on coefficient of friction in tube hydroforming using mathematical model is presented. To determine the minimum coefficient of friction in tube hydroforming, a mathematical model is used based on tube upsetting method. The presented models uses the given geometrical parameters of the tube to estimate optimized inner pressure (pi) and optimized initial thickness of the tube (S0) obtained from the mathematical model. Using optimized inner pressure (pi) and optimized initial thickness of the tube (S0), minimum COF (µ) between tube and die interface is determined. Experiments are carried out on manufactured component metal expansion bellows using different geometrical parameters, materials SS304, SS316 and SS316L with lubricants Enklo68, Enklo47, Enklo32, Enklo100 and ethylene glycol. The influence of these lubricants on COF for each material is investigated.

Investigation of the generation mechanism of the internal pressure of metal thin-walled tubes based on liquid impact forming

Liquid impact forming (LIF) is a new type of composite forming method based on tube hydroforming (THF) and stamping forming. It has high efficiency and low energy consumption, with no need for external pressure source, so LIF has good development prospect and application value in the field of lightweight and integrated manufacturing. In order to investigate LIF technology, the generation mechanism of the internal pressure was analyzed in this paper. Firstly, based on the theory of the liquid volume compression, the change law of the cavity volume of metal thin-walled tubes was analyzed according to size parameters of the tube and dies during the forming process. The mathematical relationship between the internal pressure in the tube cavity and clamping parameters (clamping speed and clamping height) was obtained under the impact load. Then, the theoretical maximum internal pressure Pmax1 was discussed under different die cavities. Furthermore, the relationship between the internal pressure in the tube and the clamping time under different die cavities with a same clamping speed was obtained according to the transient dynamic analysis by ANSYS Workbench. At the same time, the simulated maximum internal pressure Pmax2 and the calculational maximum internal pressure Pmax were acquired under different die cavities. In addition, the LIF experiments were performed using a simple and suitable device to verify the calculational maximum internal pressures under die cavities with different side lengths. Through the comparison of the calculational and experimental maximum internal pressures, it is not difficult to find that the values of both showed a good agreement and the maximum deviation is 10.27%. The research results indicate that the theoretical equation of internal pressure of metal thin-walled tubes based on LIF is reliable, and it will lay a good foundation for further study.

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.

Sensitivity analysis of process and tube parameters in free-bending processes

Free-bending processes are used to manufacture highly-complex profile shapes for different kinds of industry sectors. This paper focuses on the enhanced version of the MOS bending technique (6DOF), which is used by BMW to produce semi-finished products for the tube hydroforming process. In order to achieve a better process understanding, the bending process was analyzed with regard to process and tube parameters. In the first experimental bending series, the process precision was measured and evaluated by standard deviation and process capability. In the second bending series, the analysis focuses on the weld seam position and the wrinkling behavior of the tube. The correlations shown between process parameters and the resulting bending geometry are the basis for the validation of a process simulation model developed in LS-Dyna. Therefore, the comparison of experimental data and data measured numerically represents a good agreement. The FEM model was used to perform a numerical based sensitivity analysis of the bending process in relation to process and tube parameters. The result identifies the main factors contributing to the free-bending process.

Multistage Axial Hydro-Forging Sequence: A New Forming Approach for Manufacturing of Double-Stepped Tubes

To manufacture the large-expansion-ratio double-stepped tube without thinning, a new approach known as multistage axial hydro-forging sequence has been proposed in this study. The whole forming process is divided into five stages. Compared with traditional tube hydroforming, the thickness can be increased by axial compression deformation to reduce the thinning ratio and enhance the forming capacity of the tube in hydro-forging stage and double-stepped hydro-forging stage, respectively. The proposed multistage axial hydro-forging sequence process was implemented by experiments along with the finite element simulation to validate its feasibility. The suitable loading path to prevent defects such as wrinkle and thinning was discussed. The results showed that double-stepped tube with large expansion ratio can be produced successfully with movable dies’ design. There is no thinning in the final tube, particularly in all stepped area, and a better thickness distribution could be achieved. As a result, the proposed multistage axial hydro-forging sequence can be a feasible forming approach for the fabrication of large-expansion-ratio double-stepped tubes with high reliability.

Tube Material Properties Determination and Final Forming Pressure Calculation of Hydraulic Formed Corrugated Tubes

Abstract In this article, a test method to determine the tube material properties and two methods to calculate the final hydraulic forming pressure of corrugated tubes are presented based on the plastic incremental theory. Numerical simulation and hydroforming experiment are carried out to demonstrate the reasonability of these methods. Simulation results show that tube force state during corrugated tube hydroforming is similar to that during tube local free hydraulic bulge. By comparison of final forming pressure, respectively, obtained from calculation, and hydroforming experiment, all of these methods are proved reasonable. Numerical simulation results also indicate that the two calculation methods still retain accuracy under different transition filet radius, although transition filets are ignored in calculation of final hydraulic forming pressure calculation.

Determination of Constitutive Relationships of Tubular Materials at Various Strain Rates Using Hydro-Bulging Experiments

Liquid impact forming (LIF) is a rapid tube hydroforming technique. The deformation behaviour of a metal tube may be different in LIF from that in tube hydroforming. A constitutive equation or equivalently an equivalent stress-strain relationship is generally used to describe the deformation behaviour of metals. The purpose of this work is to model the deformation behaviour of tubular materials in LIF using the Johnson-Cook (JC) structural model. LIF hydro-bulging experiments combined with the analytical approach based on the membrane theory and the force equilibrium equation were used to determine the model coefficients A, B, C, and n in the equations for SS304 stainless steel tubular materials. Finite element (FE) simulations of hydro-bulging under various impact velocities were carried out to validate the resultant JC model. The relationship between the strain rates and impact velocities was determined, the bulging heights between the equivalent stress-strain curves at different impact velocities were analysed, and the bulging heights obtained by FE simulations and experimental results were compared. The results show that the proposed approach using the JC model is suitable to define the stress-strain behaviour of tubular materials in LIF.

Analytical model for tube hydro-forging: Prediction of die closing force, wall thickness and contact stress

The new forming technology – tube hydro-forging (THFG) was completely different from traditional tube hydroforming, the die closing force instead of internal pressure is the deformation force to compress the cross-section and increase the thickness, also result in a special contact stress state. In this paper, a mathematical model is developed to determine the strain and stress along the tube wall, also predict the die closing force, thickness distribution and contact stress; furthermore, the effects of various factors on the die closing force, thickness distribution and contact stress were discussed. At last, finite element analyses and experiments of THFG are conducted. The experimental and simulation results of die closing force, thickness distribution and contact stress are compared with the theoretical results to verify the correctness of this mathematical model. This model can provide a guideline for determining the technique parameters and designing rational die, also helps in understanding the mechanism of THFG.

A Study on the Shape deviation rate of Hydroforming of Seamed tubes Based on Two Different Velocity

Due to the low price, the seamed tubes are used more and more widely in various industrial fields in recent years. The difference in material properties between the weld zone of the parent metal zone of the thin-walled seamed tubes, the deformation of the hydraulic bulging under the same conditions will also be different, thus resulting in an inconsistency in the overall bulging of the seamed tubes. In this paper, the hydraulic bulging experiment of the seamed tubes at low and medium velocity, and the shape deviation law of the seamed tubes at different velocity are obtained. In the first half of the bulging, the seamed tubes at the medium velocity drops faster than the low velocity shape deviation rate, and the medium velocity is closer to circle; in the second half of the bulging, the medium velocity is go up faster than the low velocity. The shape deviation rate is higher before the tubes are burst, but the medium velocity’s radial average bulge height is smaller than the low velocity.

Dynamic Frictional Characteristics of TP2 Copper Tubes during Hydroforming under Different Loading and Fluid Velocities

Tube hydroforming (THF) experiments were performed on TP2 copper tubes under different loading velocities and fluid velocities using a self-developed measurement system to investigate dynamic frictional characteristics in the guiding zone. The results show that the coefficient of friction (COF) dynamically changes during forming experiments and decreases with tube deformation. The average descending rate and amplitude of the COF increase with increasing loading velocity. Microscopically, the micro-protrusions on the tubular surface are flattened, and the surface scratches are finer and more uniform, as the loading velocity increases, resulting in a decrease in COF. At the same external loading velocity, the COF increases with increasing fluid velocity and is also extremely sensitive to it. Moreover, improving and predicting the formability of such tubes by accurately adjusting and controlling fluid velocity in THF is valuable and critical for the future.

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.

A new method to produce T-shaped tubular fittings with experimental and simulation results.

A tube is an important structural element for fluid manipulation in piped networks in many industries. Tube branching is achieved using tube fittings of various shapes, including T, Y, X, and L shapes. This study proposes a new innovative technique to produce T-shaped tubular fittings. The technique uses a specially designed die setup where a tube is placed inside a T-shaped die cavity and a metallic insert is used to deform the tube into the cavity, creating the T-fitting shape. Experimental and numerical methods are used to evaluate the process. The main outcome of this research is the successful creation of T-shaped copper tube fittings using a technique similar to tube hydroforming without the need for internal pressure. This technique could be modified to assist the production of T-fittings with thicknesses outside the hydroforming limits.