Hydroforming Process Research Articles

Hydroforming of Toroidal Bellows: Process Simulation and Quality Control.

Having higher capacity to undertake pressures and larger compensation ability compared with the U-shape bellows, toroidal or Ω-shape bellows are being more and more widely used in engineering. The wave-shape and wall thickness reduction of bellows are the most important parameters for measuring the hydroforming quality of the bellows. In order to provide references for actual manufacturing, it is valuable to study the factors influencing the hydroforming process and quality of the bellows. In this paper, finite element simulations of the hydroforming process of a monolayer and single-wave toroidal bellows and a two-layer and four-wave toroidal bellows were carried out. Stress and strain distributions before and after unloading were analyzed and the wave height and wall thickness reduction were examined. The numerical results were verified by the actual hydroforming measurements. In addition, ranges of the significant structural or operating factors for producing better bellows were studied and a formula to compute the wall thickness reduction was fitted based on the sufficient numerical results of the hydroforming simulations.

Evolution of Hydroforming Technologies and Its Applications — A Review

Advanced forming technologies have been evolving at a rapid pace with the products applicability in the industrial fields of aerospace and automobile especially for the materials like aluminum and titanium alloys (light weight) and ultra-high strength steels. Innovative forming methods like hydroforming (tube and sheet) have been proposed for industries throughout the world. The ever-increasing needs of the automotive industry have made hydroforming technology an impetus one for the development and innovations. In this paper, the review on various developments towards lightweight materials for different applications is presented. The influencing process parameters considering the different characteristics of the tube and sheet hydroforming process have also been presented. General ideas and mechanical improvements in sheet and tube hydroforming are given late innovative work exercises. This review will help researchers and industrialists about the history, state of the art in hydroforming technologies of the lightweight materials.

Finite element analysis and optimization of tube hydroforming process

Tube Hydroforming is one of the most effective manufacturing processes used in modern times since it satisfies the current robust requirements of the manufacturing industry. It finds enormous applications in the automobile and aerospace sectors owing to the inherent advantages over conventional forming processes, like consumption of less material with no compromise on the part strength. Complex geometries can be developed with high accuracy in less number of manufacturing stages, which would, in turn, reduce the overall manufacturing cost. Such an ability of this process to fabricate products with high strength-to-weight ratios at economical costs make it energy-efficient and it does push a step further towards sustainable and modern innovative manufacturing.This paper presents the development of a detailed nonlinear finite element model for the tube hydroforming process that uses Abaqus/Explicit as a computational tool. Elastic-plastic material constitutive behavior is defined using a flow-stress equation, and the Arbitrary Lagrangian-Eulerian technique (ALE) is used to determine the material flow. Input parameters like applied pressure, initial tube thickness, and die-corner radius are considered against output parameters like formed tube thickness, final part dimensions, and stress concentration. The developed model is validated with a previously published literature by Rakesh A. Shinde et al. (2016), and the results are found to agree for the case of percentage of thickness reduction.Following the work done by Rakesh A. Shinde et al., three different numerical cases are created with different die corner radii and tube thicknesses, for 3 different internal pressure values, viz., 41 MPa, 43 MPa, and 45 MPa. The results obtained in the paper are first replicated, and the research is further extended for different loading/unloading rates and peak load holding times (loading paths). Results indicate the sufficiency of only lower loads to produce the required formability. Accordingly, simulations are also performed for cases of lower pressures. Results show that accurate part dimensions at much lower stress concentrations could be obtained at lower values of pressure. The presented work also looks into the optimisation of the process using a well-established DOE technique – Response Surface Methodology. Accordingly, a multi-objective optimisation is performed, considering 20 simulations for the cases of three parameters and three levels. The significant influencing parameter is also identified.

Development of a Mathematical Model Using Machine Learning for Hydroforming of Non-Circular Protrusion Copper T-Tube

Optimum loading paths for successful tube hydroforming processes have been studied by several researchers. In this paper, an adaptive, heuristic, nonlinear mathematical model (AHNM) was proposed to optimize the loading path of a hydroforming process through adaptive minimization of the internal pressure and axial load of the process. Firstly, Finite Element Analysis (FEA) was used to analyse the hydroforming process where several features of the process were extracted from the FEA for further analyses of the relations among them. To capture these relations and include them in the AHNM, the paper examined several Machine Learning algorithms including Multiple Linear Regression, Multiple Ridge Regression, Decision Tree, and Random Forest. The Multiple Ridge Regression was found to give the highest accuracy to efficiently linear modelling the inputs and outputs of the FEA of the hydroforming process. The AHNM model was implemented, solved, and optimized using several steps of tee protrusion height that create several loading paths. It was found that increasing the number of steps and starting with small increment leads to minimizing the system requirements.

Movable Die and Loading Path Design in Tube Hydroforming of Irregular Bellows

Manufacturing of irregular bellows with small corner radii and sharp angles is a challenge in tube hydroforming processes. Design of movable dies with an appropriate loading path is an alternative solution to obtain products with required geometrical and dimensional specifications. In this paper, a tube hydroforming process using a novel movable die design is developed to decrease the internal pressure and the maximal thinning ratio in the formed product. Two kinds of feeding types are proposed to make the maximal thinning ratio in the formed bellows as small as possible. A finite element simulation software “DEFORM 3D” is used to analyze the plastic deformation of the tube within the die cavity using the proposed movable die design. Forming windows for sound products using different feeding types are also investigated. Finally, tube hydroforming experiments of irregular bellows are conducted and experimental thickness distributions of the products are compared with the simulation results to validate the analytical modeling with the proposed movable die concept.

Numerical analysis of hydroforming process control using variable blankholder force

Hydroforming was developed to provide a cost effective means to produce relatively small quantities of drawn parts or parts with asymmetrical or irregular contours that are difficult to obtain by conventional stamping. This paper presents a study of hydroforming process with variable blankholder force in order to assure the parts quality. The main idea is to decompose the blankholder function of the elementary zone of the part contour corresponding to the linear and curvilinear zone. For each zone different blankholder force is applied in correlation with the hydrostatic pressure. A numerical analysis using finite element modelisation is performed considering different sets of blankholder forces and hydrostatic pressures, as process parameters. An optimum is determined in order to avoid parts defects (thickness reduction, wrinkles, fracture) for such types of parts.

Multi-objective optimisation of tube hydroforming process on IF steel using Taguchi-based principal component analysis

Tube hydroforming is one of the eccentric metal shaping procedures, especially utilised as a part of the automotive industry. This process has accentuated much consideration inferable from its diversified applications. To emphasise, aerospace and automotive industries depend much upon this procedure. Earlier most of the researchers worked on the material characterisation and the process parametric impacts of tube hydroforming process. However, very few have attempted on the Multi-objective optimisation of the critical process parameters. In this work, commercial finite element code PAM-STAMP 2G is utilised to do the simulations in view of L27 orthogonal array. Hence a multi-objective optimisation was studied that simultaneously maximises the bulge ratio and minimises the thinning ratio by Taguchi-based principal component analysis (PCA), which is novelty of this work. The present work aims at exploring the impact of geometrical, process and material parameters on aforementioned responses using analysis of variance (ANOVA).

A comprehensive damage criterion in tube hydroforming

In the present study, the Johnson-Cook damage model is proposed as a comprehensive damage criterion to predict all types of probable failures in tube hydroforming process. Also, the Johnson-Cook material model is used to predict the profile of hydroformed tubes and their dimensions. The validity of numerical results was verified using experimental results obtained in this study. Moreover, because of the importance of friction force in this process, existing between the tube and die, the friction coefficient is determined using the ring compression test, separately. The comparison of experimental and numerical results shows that Johnson-Cook damage model can predict all of the possible failures in tube hydroforming process correctly, both in terms of location and loading conditions. And this model does not predict any failure if, the tube is hydroformed perfectly. Additionally, it was cleared that the Johnson-Cook material model is a proper model to predict the profile of hydroformed tubes with remarkable accuracy. Also, it was found that the loading path and creation of a proper wrinkling have a determinative and vital role in the prosperity of the process.

Hydroforming analysis of exhaust pipe connectors

Abstract In this work, a hydroforming analysis of an exhaust pipe clamp adaptor made of galvalume steel was performed. Deformation and failure of galvalume exhaust pipe connectors and its coatings via the hydroforming process were studied. An explicit type (LsDyna) numerical analysis approach was adapted for the development of the hydroforming process. Pressure rate, unconstraint length, residual stress, strain hardening, and spring-back effects were considered in the analysis. The failure of tubular parts was evaluated via a forming limit diagram (FLD) according to Hill- Swift criteria. The hydroforming process was developed according to three models, which are found in the safety forming region of FLD studies. Minimum thickness values obtained from the experiments were compared with finite element analysis (FEM). The maximum percentage thinning ratio in the tubular section was more than 18 - % at 65 MPa internal pressure. The relationship between thickness reduction at plastically work hardening regions and residual stress was discussed. The deformation characteristics of the produced connector headers were also analyzed by scanning electron microscopy (SEM) and micro Vickers hardening measurements. The FEM analysis and FLD examination indicated that the failure did not occur in hydroformed specimens, whereas damage was observed at coated’ plastic work regions through microscopical investigation.

Effect of Tube Material and Heat Treatment Temperatures on Tube Formability During Tube Hydroforming Process

Tube hydroforming (THF) is a process that makes use of fluid means to form the tubular samples into desired form. In the present work, two materials SS 304 and AA-1100 tube samples were heat-treated at various temperatures, viz., as-received, 150 °C, 200 °C and 250 °C to know their effect on the formability. Heat-treated samples were tested for the mechanical properties using universal testing machine, and the obtained results were utilized for carrying out the numerical simulations of THF process. Simulations were performed at various L/D ratios to attain various strain paths with different heat treatment temperature results. The effects of the aforementioned parameters on bulge height, internal pressure and FLD were investigated. The obtained results from both the materials through numerical simulations were validated by the analytical model. The simulation results were observed to be in good agreement with the analytical model.

Hydroforming analysis of exhaust pipe connectors

Abstract In this work, a hydroforming analysis of an exhaust pipe clamp adaptor made of galvalume steel was performed. Deformation and failure of galvalume exhaust pipe connectors and its coatings via the hydroforming process were studied. An explicit type (LsDyna) numerical analysis approach was adapted for the development of the hydroforming process. Pressure rate, unconstraint length, residual stress, strain hardening, and spring-back effects were considered in the analysis. The failure of tubular parts was evaluated via a forming limit diagram (FLD) according to Hill- Swift criteria. The hydroforming process was developed according to three models, which are found in the safety forming region of FLD studies. Minimum thickness values obtained from the experiments were compared with finite element analysis (FEM). The maximum percentage thinning ratio in the tubular section was more than 18 - % at 65 MPa internal pressure. The relationship between thickness reduction at plastically work hardening regions and residual stress was discussed. The deformation characteristics of the produced connector headers were also analyzed by scanning electron microscopy (SEM) and micro Vickers hardening measurements. The FEM analysis and FLD examination indicated that the failure did not occur in hydroformed specimens, whereas damage was observed at coated’ plastic work regions through microscopical investigation.

Construction of 6061-T6 aluminum alloy constitutive model based on hot bulging test and study on the non-isothermal hydroforming process

Due to the high requirements of drawing equipment and process, it is relatively rare in the field of aluminum alloy sheet forming to introduce soft or sticky fluid medias as soft mold into the course of hydroforming with a non-isothermal condition that maintaining the temperature of high pressure liquid differs to the ones of molds. Consequently, in this paper, the material stress-strain curve in the temperature range is obtained by the bidirectional tensile hot bulging test which contains compress to sheet’s thickness, and can best meet the characteristics of non-isothermal hydroforming in mechanics compared with unidirectional hot stretching. Based on analysis of stress-strain of 6061-T6 aluminum alloy, its constitutive equation on the basis of an original model of processing hardening rate is established for finite elements numerical simulation, and a highly accurate setting range of forming temperature can be confirmed to provide guidance for practical manufacturing accordingly. Result of the study suggests, by applying the constitutive model mentioned above, simulation on non-isothermal hydroforming can reach a desirable effect; The non-isothermal condition set reasonably causes an enhance to the junction of straight wall and round corner, and a deduce of thickness reduction rate simultaneously, limit height increases as a result. Besides, the fluency of blank located in the flange improves to a great extent when its temperature is well set. The position of the 1 mm wall thickness constant line of the workpiece is further reduced, so that the forming quality of the workpiece is remarkably improved.

Process parameters selection in manufacturing of sharp conical parts based on Taguchi design of experiments

Among the sheet metal forming processes, hydrodynamics deep drawing and hydromechanical deep drawing process are two main types of the deep drawing process that can fabricate complicated parts. In the hydroforming process, the blank is formed to the desired shape by applying a considerably high hydraulic pressure. In this article, the selection of the process parameters will be investigated during the manufacturing of a pure copper sharp conical part by finite element analysis and experimental tests. Two finite element models are developed for hydrodynamics deep drawing and hydromechanical deep drawing processes. After verification of the FE model by experimental results, the effect of process parameters includes the applied pressure, friction coefficient, die radius and blank holder force on thinning of the blank are investigated. The thinning ratio of blank is calculated in different zones of the conical part under different working conditions determined according to the Taguchi design of experiment methods. Signal to noise ratio analysis has been carried out and the influence of process parameters on the thinning ratio is determined at different zones of the conical part. The results show that the friction coefficient has an important role in the thinning of the conical nose while at the lateral surface of the cone, the die radius is the most effective parameter on the thinning ratio. The results show that by implementing statistical tools (Taguchi method and signal to noise ratio analysis), it is possible to select the proper process parameters conditions and fabricate defect-free parts. In addition, a non-linear regression equation is developed for prediction of thinning ratio in the hydrodynamics deep drawing and hydromechanical deep drawing processes.

Simultaneous hydroforming of bulge- and T-zone in 304 stainless steel and 70/30 brass tubes

Hydroforming process is largely used for the production of tubular parts in various industries, and has advantages such as less weight, higher quality, more strength and fewer production cost compared to the conventional methods of production. The aim of this study is forming a tube-shaped part with a special geometry that has both bulge- and T-zones with tube hydroforming process. The forming operations were performed on 304 stainless steel and 70/30 brass tubes, and a finite element (FE) model was used to achieve the best forming conditions. To validate FE model, firstly, several experimental tests were performed with different process parameters, and then the results were compared with the FE model in terms of the formed profile and the distribution of thickness. After validation of FE model, various pressure paths were studied and the best one between them was chosen. Finally, the part was formed correctly by the selected pressure path without defects like wrinkling or tearing, and the desired geometry was fully filled.

A novel gripper for multiaxial mechanical testing of microtubes at elevated temperatures.

The success of a microtube hydroforming (μTHF) process heavily depends on the material properties of microtubes, which can reveal the material response under multiaxial stress and influence the formability of hydroformed products. However, these material properties are not well understood because of the limited availability of material testing apparatus that would permit control of axial force and internal pressure simultaneously to mimic realistic μTHF loading. The main purpose of this study is to develop a set of grippers that can transfer required testing loads under fully coupled combinations of axial force and internal pressure. The grippers are designed so that they may be kept at the safe working temperature even when tests are carried out at higher temperatures. The grippers are also designed to fit in a load frame that is integrated in a scanning electron microscope for in situ material testing. The capabilities of the grippers are demonstrated by performing uniaxial and multiaxial material tests on SS304 microtubes with 1 mm outside diameter and 0.15 mm nominal tube wall thickness. The finite element simulations and experimental results show that the designed grippers can firmly hold the specimen and thus enable tensile, compression, torsion, and microtube bulge material tests to be accurately performed.

Hybrid Forming - A Novel Manufacturing Technique for Metal-LFT Structural Parts

<div class="section abstract"><div class="htmlview paragraph">Hybrid structural parts combining aluminum or steel sheets with long glass fiber reinforced thermoplastics (LFT) offer a great opportunity to reduce component weight for automotive applications. But due to high manufacturing cost, metal-LFT hybrid components are still scarcely used in automotive large-scale production. Thus in this work a novel cost- and time efficient manufacturing process for simultaneous metal sheet forming and compression molding of long fiber reinforced thermoplastics to manufacture automotive lightweight components is presented. In this manufacturing process, which is referred to as “Hybrid forming”, a fiber reinforced thermoplastic melt is used as a forming medium in the manner of well-known hydroforming processes. After forming the metal sheet by polymer melt in combination with the rigid die, the melt solidifies and forms a local reinforcement structure in the hybrid component. Since the metal sheet is pre-coated with a bonding agent prior to the forming process, a firmly bonded connection between metal and LFT can be achieved.</div><div class="htmlview paragraph">For proof of concept a longitudinal control arm in a multi-link rear axle is chosen. By utilizing Hybrid forming a hybrid steel-LFT control arm is manufactured with weight savings of 20 % with regard to the metal reference component. Weight savings are derived by reducing the metal thickness and compensate stiffness and strength with local load-conforming LFT ribs. The metal part of the hybrid control arm guaranties the same positive fail-safe behavior of a metal component in contrast to the brittle failure mechanics of pure CFRP/GFRP components.</div><div class="htmlview paragraph">To verify the resilience of the hybrid component and especially the bonding surface between steel and LFT quasi-static tests and fatigue tests were conducted. The results are compared with the FE-simulations to validate the simulation technique, which can be used to design metal-LFT structural parts manufactured by hybrid forming for future applications.</div></div>

Effect of hydroforming process on the formability of fiber metal laminates using semi-cured preparation

In this study, the cup part of fiber metal laminates (FMLs) was formed by a method which combines the semi-cured preparation and hydroforming processes. The FMLs in this research were produced by using glass woven fiber prepreg and aluminum 2024-T3. The process parameters were designed by Taguchi method, and the optimized parameters (3 mm pre-bulging height, 15 MPa cavity pressure, 4 MPa pre-bulging pressure and 1.15 mm clearance between blank holder and die) were obtained by range analysis. The part without defect can be obtained using the optimized parameters. The thinning rate of each layer, stress-strain distribution, and the failure modes were analyzed with experiments and numerical simulations. The results show that the middle layer has a great influence on the thinning, stress-strain distribution, and fracture modes in different directions. Numerical simulation can be used for predicting the thinning rate and fracture location. Small-size FML parts can be fabricated directly using the semi-cured hydroforming process, which can improve the production efficiency and expand applications of FMLs.

Influence of process parameters on thinning ratio and fittability of bellows hydroforming

Metal bellows are widely used in piping systems, aerospace, automobile and other industries due to their favourable properties including absorption of expansion, light weight and flexibility. In this paper, the fittability was presented to evaluate the convolution shape precision of the metal bellows. By establishing a finite element model of bellows hydroforming process during the bulging and forming stages, the influence of internal pressure, axial feeding and feeding loading path on the wall thickness variation and fittability of one-convolution bellows was investigated. On that basis, the hydroforming process of multi-convolution bellows was studied, and an experiment was carried out. The results showed that with the increase in internal pressure, the wall thickness of the bellows thinned overall, and the fittability of the root zone of the bellows gradually deteriorated. Some region near the crown zone did not fit the dies well when the internal pressure is small. To improve the fittability of the bellows, the actual axial feeding should be a bit less than the theoretical axial feeding. It is of importance in developing the hydroforming technique and improving the hydroforming quality of bellows.

Deformation behaviors of four-layered U-shaped metallic bellows in hydroforming

Because of the complex constraint effects among layers in multi-layered metallic bellows hydroforming, the stress concentration and defects such as wrinkling and fracture may easily occur. It is a key to reveal the deformation behaviors in order to obtain a sound product. Based on the ABAQUS platform, a 3D-FE model of the four-layered U-shaped metallic bellow hydroforming process is established and validated by experiment. The stress and strain distributions, wall thickness variations and bellow profiles of each layer in the whole process, including bulging, folding and springback stages, are studied. Then deformation behaviors of bellows under different forming conditions are discussed. It is found that the wall thinning degrees of different layer vary after hydroforming, and is the largest for the inner layer and smallest for the outer layer. At folding stage, the wall thinning degree of the crown point increases lineally, and the difference among layers increases as the process going. The displacements of the crown point decrease from the inner layer to the outer layer. After springback, the U-shaped cross section changes to a tongue shape, the change of convolution pitch is much larger than the change of convolution height, and the springback values of the inner layer are smaller than the outer layer. An increase in the internal pressure and die spacing cause the maximum wall thinning degree and springback increase. With changing of process parameters, bellows with deep convolution are easily encountered wall thinning during hydroforming and convolution distortion after springback. This research is helpful for precision forming of multi-layered bellows.

Numerical Optimization of the Blank Dimensions in Tube Hydroforming Using Line-Search and Bisection Methods.

The change from a consolidated manufacturing practice to a new solution is often a complex problem because of the operative limits of technologies and the strict constraints of industrial parts. Moreover, the new process must reflect or enhance the characteristics of the product and, overall, it must be more competitive in performances and costs. Accordingly, the development of a new process is a multilevel and multivariate problem that requires a systematic and hierarchical approach. The present paper focuses on the development of a Tube Hydroforming process capable to replace the current practice for production of T-Joint parts made of AISI 316L for the water pipes market. In particular, the problem must withstand many process and product constraints. Therefore, it was split in three steps focused on specific aspects of the process: identification of process parameters and configuration, numerical optimization of the blank tube dimensions (length and thickness), experimental tests and final improvements. In particular, two numerical methods were implemented in the optimization step: the line–search method to approach to the optimum point and Bisection method to refine the search. These approaches allowed us to identify the optimum process configuration and, in particular, the optimal dimensions of the blank tube that allows one to achieve the product requirements with the minimum cost of material.