Stretch Flanging Process Research Articles

Effects of processes parameters on spring back, wrinkles and cracks in different flanging processes: A Review

Flanging is an important type of sheet metal bending process. In present review, an effort was made to explore the contributions of various researchers to drawn out the cause of defects in the flanging process. Several parameters such as geometrical, material and process parameters affect the formability of the flanging process. In straight flanging process, spring back (due to elastic recovery) is a major problem that affects dimensional and geometrical accuracy of a bent component. Several factors are responsible for springback such as – profile radius of punch and die, bend angle, thickness of sheet, clearance between punch and die, blank-holder force, Young’s modulus, n-value, yield stress, plastic anisotropy of materials, velocity of punch etc. In shrink flanging process, wrinkling is the prime concern that occurs due to the excessive compressive stress in the flange portion. It is mostly affected by mechanical properties of material (R-value, n–value etc.), geometry of the tools and blank, process parameters. In stretch flanging process, the effect of material parameters is found to be less as compared to geometrical parameters for crack initiation and thinning.

Stretch flange forming of steel alloys through FEM simulation

In sheet metal operation flanging is a common process in which one edge of the sheet is bent to the desired angle or the desired contoured shape and the other end keep in control either itself or by blank holder or pad force. Stretch flanging involves stretching the metal circumferentially while the bending line is concave. In the stretch flanging process, the initial flange length is a critical factor. Using commercial finite element software programmed Abaqus, a finite element simulation of the stretch flanging process was performed in this research. The impact of initial flange length on the radial strain, circumferential strain, and flange thickness distribution along the free edge of rectangular-shaped sheet metal blanks is investigated in this work. Aside from maximum radial strain, maximum circumferential strain and maximum thinning in the flange are also explored as effects of initial flange length. With a reduction in initial flange length along the free edge up to the punched centre, circumferential strain and flange thickness drop while radial strain increases. With increasing initial flange length, maximum radial strain, maximum circumferential strain, and maximum thinning are observed to rise. The formability of the stretch flanging process is shown to be considerably influenced by the initial flange length.

EXPERIMENTAL AND FINITE ELEMENT ANALYSIS OF NONAXISYMMETRIC STRETCH FLANGING PROCESS USING AA 5052

This paper deals with experimental and finite element analysis of the stretch flanging process using AA- 5052 sheets of 0.5 mm thick. A parametrical study has been done through finite element simulation to inspect the influence of procedural parametrical properties on maximum thinning (%) within the stretch flanging process. The influence of preliminary flange length of sheet metal blank, punch die clearance, and width was examined on the maximum thinning (%). An explicit dynamic finite element method was utilized using the finite element commercial package ABAQUS. Strain measurement was done after conducting stretch flanging tests. A Mesh convergence examination was carried out to ascertain the maximum percentage accuracy in FEM model. It is found through finite element simulation that the width of sheet metal blanks has a greater impact on the maximum percentage of thinning as compared to preliminary flange length, and clearance of the punch dies.

Stretch-flanging of AA2024-T3 sheet by single-stage SPIF

Flanging is a forming process that is commonly used in many high technology industrial applications such as the manufacturing of thin-walled aircraft structures as wing ribs that are formed using rubber-pad forming during the last forming stages with the aim of increasing the stiffness of the component edges. In addition, the performance of hole-flanged parts manufactured using incremental sheet forming (ISF) processes has been recently addressed, focusing especially in evaluating the formability enhancement, as well as the onset of failure utilising a variety of forming strategies. In this context, this work presents an experimental analysis of formability and failure within the forming limit diagram (FLD) of stretch flanges of AA2024-T3 performed by single point incremental forming (SPIF) for a wide range of process parameters. The numerical modelling of the stretch flanging process in combination with a theoretical framework based on Barlat's anisotropy plasticity criterion, allowed to assess the formability of the material within the triaxiality space, permitting to understand the stress/strain states attained in SPIF and the forming conditions upon which the onset of failure occurs. The results show that this triaxiality space, defined as the accumulative effective strain versus the average stress triaxiality, might be the most appropriated space for analysing the highly non proportional process of stretch flanging by SPIF.

Investigation on the Crack and Thinning Behavior of Aluminum Alloy 5052 Sheet in Stretch Flanging Process

Stretch flanging is the important sheet metal-forming process which is widely used in automobile and aerospace sectors. The formability of sheet metal depends on various parameters such as material properties, geometry of the tool setup and process parameters. In the present work, effects of different die radius and sheet width on deformation behavior of sheet are studied by FEM simulation and experiments. The predicted FEM results are presented in the form of edge crack location and its propagation, crack length, forming load and strain distribution in sheet along the die profile radius. This study indicates that crack length increases with increase in the sheet width, while the crack length decreases with increase in the die radius. It is found that the crack propagation in stretch flanging process is affected by the strain distribution in sheet and this distribution of strain depends on many parameters. The crack initiates during deformation of the sheet at the die corner edge and propagates toward the center of the sheet along the die profile radius. Simulation results are compared with the experimental one in terms of crack length and variation in sheet thickness. FE simulation results are found in very good agreement with experimental results. Fractography study is also presented in terms of size, shape of the dimples along with their distribution on the fractured surface.

Effect of punch profile on deformation behaviour of AA5052 sheet in stretch flanging process

Stretch flanging is a type of bending process widely used in automobile and aerospace industries. Forming of the stretch flange is mainly affected by three important parameters: materials of the sheet, the geometry of tools and different process parameters. This work focuses on the effect of punch profile on deformation behavior of AA5052 alloy sheet to form the stretch flange. Six punches of different geometry i.e. cylindrical, two stepped, three stepped, six stepped, conical and hemispherical are used. Results are presented in the form of edge crack in the sheet at edge corner and its propagation towards center, forming load comparison for different punch profile and distribution of radial and circumferential strain in the sheet. It is observed that the punch profile has a considerable effect on the deformation behavior of the sheet. Circumferential strain, radial strain and load requirement to form the flange are found to be minimum in hemispherical punch profile as compared to other punch profiles. Experiments are performed to validate the FE simulation results and results are found in very good agreement in terms of edge crack length. Fractography study shows uniform and large number of small size dimples at the fractured surface for hemispherical and conical punch profile.

Compensation of Contour Distortion in Stretch-Flanging Metal Sheets

Stretch-flanging commonly appears at the concave edge of the panel part. Sheet thickness tends to decrease at the center of flange attributed to the outflow of metal flow, and hence causes a radial shrinking of the material. This shrinking pulls the ends of the flange and makes the adjacent surface overcrown. In this paper the effect of punch profiles on a laboratory scale profile, which assimilates the front fender part adjoining the head light, was investigated for the stretch-flanging process. Both the concave and convex punch profiles were considered. SUS 304 stainless steel sheet of 0.6 mm thick was used as the model metal sheet. DynaForm software was used in simulating the stretch flanging process and followed by experimental verification. The results show that a depression angle of 4.4° and an elevation angle 2.6° can produce lowest crown-contour for the concave and convex punches, respectively. The concave punch also causes less thinning at the flange center which makes it a favorable solution than that of the convex punch.

Some aspects of blank holding force in stretch flanging process

FEM simulation of stretch flanging process was carried out to examine the influence of various blank-holding forces on process parameters. Various blank holding conditions namely without blank holding force condition, elastic blank holder and rigid fixed blank-holder, blank-holding forces with constant intensities and blank-holding forces with variable schemes were utilized for numerical investigations. Finite element commercial software package ABAQUS was used for development of finite element model of stretch flange forming process. Sheet of AA 5052 (aluminum alloy) was utilized both in experimental work and for FEM simulation. FEM simulation results depict great influence of various blank-holding forces on maximum strain in flange, maximum punch load and edge crack and its propagation. Some experiments were carried out for validation of numerical simulation results. A good agreement was obtained between results of FEM simulation and experimental for punch load and final shape. Hence present FEM model is quite capable of accurate prediction of numerical results.

Prevention of crack in stretch flanging process using hot stamping technique

Demand for enhancing of passenger safety as well as weight reduction of automobiles has increased the use of high strength steel sheets. As a sheet metal is a lightweight having high strength is suitable for producing automotive parts such as white body panel. The stretch flanging of the high strength steel sheet is a problem due to high springback and easy to crack. This study uses three methods to stretch flange the sheets; using lubricants, shear-edge polishing and hot stamping. The effectiveness of these methods will be measured by comparing the flange length of each methods can achieved. For stretch flange with lubricant and polished sheared edge, the flange length failed to achieve the target 15 mm while hot stamping improved the formability of the sheet and preventing the occurrence of the springback and crack. Hot stamping not only improved formability of the sheet but also transformed the microstructure into martensite thus improve the hardness and the strength of the sheet after been quenched with the dies.

Experimental investigations on the forming mechanism of a new incremental stretch-flanging strategy with a featured tool

In conventional stretch-flanging process by incremental sheet forming (ISF), serious thinning is a major challenge due to the ISF deformation mechanism of stretching, bending, and considerable shearing in the area far from the flange edge. To solve this problem, a new flanging tool for ISF is proposed, accompanied with the suitable tool path strategy. In order to obtain a better understanding of this new stretch-flanging approach, experiments have been conducted to study the geometric accuracy, thickness distribution, forming force, and fracture behavior of typical circle and square flange features. Besides, the effect of tool radius on the new stretch-flanging process is also investigated. Results show that the forming strategy which the tool moves horizontally in the X–Y plane is the most suitable one for the new flanging tool. Thicker but shorter flange with a more uniform thickness distribution can be obtained by the proposed stretch-flanging approach. Tool radius also has an important influence on the diameter of the final hole, the forming depth, and the fracture limit strains in the new stretch-flanging process.

Effect of process parameters on deformation behavior of AA 5052 sheets in stretch flanging process

Aluminum alloys are widely used in manufacturing of aircrafts and in automotive industry. In this paper aluminum alloy 5052 of 0.5 mm thickness was utilized to investigate deformation behavior in stretch flanging process. The effect of process parameters such as initial flange length, punch-die clearance and blank-holding force were investigated using FE simulation and experimentation. The results show that the circumferential strain and radial strain increases with increase in initial flange length and blank-holding force and decreases with increase in punch-die clearance. Experimental investigations were also carried out to validate FE simulation results. A very good agreement was obtained between FE simulation results and experimental in terms of punch load and edge crack location and propagation.

Prediction of crack location and propagation in stretch flanging process of aluminum alloy AA-5052 sheet using FEM simulation

The stretch flanging process is significantly affected by various geometrical, material and process parameters. The punch-die clearance and initial flange length are main parameters which have major effects on the edge crack location and strain distribution along die profile radius in the flange. Non-axisymmetric stretch flanging process of AA-5052 sheet metal blanks was carried out by numerical simulation to predict the deformation behavior of flange, location and propagation of crack in flange and to investigate the effect of punch die clearance, flange length, die and punch profile radius and friction in the stretch flanging process. The experimental investigations were made to validate the simulations results. The results reveal that the crack length increases with the increase in the flange length. It is found that the flange length has a significant effect in circumferential direction as compared with the radial direction. The punch die clearance has the most significant effect in crack propagation in comparison with flange length. The circumferential strain is found to be larger in the case of punch having the profile radius less than the die profile radius, which leads to faster edge crack propagation. A close agreement is found between simulation and experimental results in terms of location of edge crack and forming load.

Influence of Blank Holding Force on Stretch Flange Forming of Aluminum Alloy

The effect of blank holding force on the stretch flanging process was investigated using finite element simulation and experimental analysis. Finite element model was used to study the effect of blank holding forces on punch load and forming kinematics. An aluminum alloy 5052 sheet of 0.5mm thickness was employed for this work. Blank holding force has a great effect on punch load and significant influence on forming kinematics. Validation of FEM results were obtained by conducting experiments. A very good agreement was obtained between FEM simulation results in terms of punch load and final shape which shows the accuracy of present finite element model.

Finite Element Analysis of Non-axisymmetric Stretch Flanging Process for Prediction of Location of Failure

Stretch flanging is an important sheet metal forming process which is applied in automotive industry. In this paper, finite element simulation of stretch flanging process of AA 5052 has been carried out. It is found that both punch-die clearance and initial flange length has great effect on strain distribution and edge cracking along die profile radius. A good agreement has been obtained between results of simulation and experimental results, in terms of edge crack, punch load and punch stroke. From this investigation, finite element simulation is found to be quite useful in predicting deformation behavior of stretch flange quite efficiently.

Computer simulation and experimental validation of stretch flanging

The axisymmetric stretch flanging process is a common secondary operation in sheet metal stamping. The process is characterized by a uniaxial state of stress at the edge of the flange. An approximate analysis, based on the assumption that the state of stress throughout the flange is mainly uniaxial, is used to model the stretch flanging (second step) process. The approximation is derived from the total strain membrane theory of plasticity which incorporates strain hardening and normal anisotropy of the material. Under such conditions, flangeability is controlled by the tensile elongation of the metal and is limited by localized necking or fracture of the flanged edge. The analysis includes a stretching limit criterion to determine the flanging limit of the material. The influence of prestretching (first step) on flangeability is modeled using the membrane shell theory with axisymmetric deformation to solve the contact condition in stretch forming. Inputs to the model are a desired flange profile, material properties, and sheet thickness. The output includes the feasibility of the flanging operation, any requirements for prestretching and the size of the trim radius needed to successfully flange the profile. The model is verified by experimental results.