Evaluation Of Formability Research Articles

Comparative evaluation of formability in cup drawing and V-bending using additively manufactured tools

ABSTRACT Additive Manufacturing (AM) is rapidly transforming industrial processes by introducing advanced methods for designing, manufacturing, and prototyping key components across various industries. Its true potential is realized in integrated component repair via reverse engineering, significantly reducing rework, maintenance costs, and time. With growing demand, AM technology continues to evolve, incorporating intelligent printing systems and diverse applications in sectors like automotive, sheet metal forming, healthcare, aviation, and consumer goods. AM also aids in optimizing geometric and process parameters for tools such as dies, punches, and blank holders, enhancing economic batch production. This study focuses on the Finite Element Analysis (FEA) of two commercial operations: bending and deep drawing, using DC04 and AA6060 materials. The analysis identifies geometric precision, thinning, and formability. In steel, increasing the bottom radius from 3 mm to 20 mm results in an 11% difference in thinning, with a maximum of 0.67 mm. For aluminium, thinning varies minimally between 0.68 and 0.75 mm. Increased sheet thickness limits formability in both materials. FDM-printed tools were used for FEA simulation, followed by stress analysis of dies to assess design safety, small batch production, and dimensional conformity.

Experimental correlation between bending crack evolution and load-drop criterion in tight-radius three-point bending test with GPa-grade steels

Determining the bending-fracture limit, also referred to as local formability, is crucial for sheet metal forming. However, this is limited by existing methods such as the VDA-238-100 standard due to limitations in its failure criterion based on the punch load. This study addresses this limitation by proposing a quantitative crack-based failure criterion and investigating its relationship to the load-drop point. Along with surface and cross-sectional optical analyses, an integrated line-scanning system for the VDA-238 test is developed, and advanced high-strength steel (AHSS) grades are analysed with yield strengths ranging from 980 to 1500 MPa in both the rolling and transverse directions. The results showed that, while the load-drop point marks a rapid shift in the crack-propagation direction, the true onset of crack initiation occurs earlier, with different patterns for each AHSS and direction. For all the AHSS and directions tested, a crack depth exceeding 1 % of the sheet thickness occurs at 90 % of the switch-off stroke in the VDA-238 test, suggesting an empirical tendency toward microcrack growth for a more accurate evaluation of the local formability based on early cracks.

Applicability of the formability evaluation method for advanced high strength steels

The use of high strength and ultra-high strength steels has become the main technical solution for reducing vehicle weight and improving safety. It is more complicated to evaluate the formability of advanced high strength steels with different microstructure and deformation characteristics. In this paper, the applicability of existing formability evaluation methods for advanced high strength steels has been verified by experiment and theoretical analysis. The experiment and data analysis of conventional formability evaluation methods, such as strain hardening index, forming limit curve and hole expansion ratio, were carried out on advanced high strength steels, such as dual-phase steel, complex-phase steel, quenched and tempered steel and dual-phase steel with high formability, which are widely used in automotive industry. It is found that due to the complex work hardening characteristics of advanced high strength steels, the work hardening homogenization and forming limit cannot be characterized by a single work hardening index or forming limit diagram, and the standard hole expansion method cannot reflect the quality sensitivity of the formed edge. A new formability evaluation index is proposed and discussed, which can be used to more accurately compare the formability of advanced high strength steels and provide a reference for material evaluation and part selection.

Evaluation of Tensile Properties and Formability of Al 6061 Alloy Processed by Various Semi-solid Techniques

Evaluation of Tensile Properties and Formability of Al 6061 Alloy Processed by Various Semi-solid Techniques

A Review of Sheet Metal Forming Evaluation of Advanced High-Strength Steels (AHSS)

This paper presents a review on the formability evaluation of AHSS, enhancing necking-based failure criteria limitations. Complementary fracture/damage constitutive modeling approaches specifically tailored to formability evaluation, validated through numerical and experimental methods, are also subjects of research. AHSS are widely processed through sheet metal forming processes. Although an excellent choice when lightweight, high-strength, and ductility are critical factors, their multi-phase microstructure accentuates forming challenges. To accurately model forming behavior, necking-based failure criteria as well as direct fracture models require improvements. As a necking-based failure model, the conventional forming limit diagram/curve (FLD/FLC) presents limitations in estimating direct fracture (surface cracks, edge cracks, shear cracks), as well as deformation histories under non-linear strain paths. Thus, significant research efforts are being made towards the development of advanced fracture constitutive models capable of predicting fracture scenarios without necking, which are more frequently observed in the realm of AHSS. Scientific community research is divided into several directions aiming at improving the forming and fracture behavior accuracy of parts subjected to sheet metal forming operations. In this review paper, a comprehensive overview of ductile fracture modeling is presented. Firstly, the limitations of FLD/FLC in modeling fracture behavior in sheet metal forming operations are studied, followed by recent trends in constitutive material modeling. Afterwards, advancements in material characterization methods to cover a broad range of stress states are discussed. Finally, damage and fracture models predicting failure in AHSS are investigated. This review paper supplies relevant information on the current issues the sheet metal forming community is challenged with due to the trend towards AHSS employment in the automotive industry.

Evaluation of plastic formability of layered metal sheets bonded by adhesives using conical cup testing

Evaluation of plastic formability of layered metal sheets bonded by adhesives using conical cup testing

A novel mechanical attachment for biaxial tensile test: Application to formability evaluation for DP590 at different temperatures

A novel mechanical attachment for conducting in-plane biaxial tensile test is provided in this paper. In this attachment, the conversion of force from an external actuator into two pairs of orthogonal forces is achieved by specially designed trapezoidal blocks. By using trapezoidal blocks with different inclination angles, biaxial tensile tests of six different tensile ratios can be performed. A heating device is designed for the attachment to conduct thermal biaxial tensile tests. The heating device adopts a combination of the induction heating technology and the conduction heating method. With the developed mechanical attachment and the heating device, the forming limit curves (FLC) of DP590 sheets at ambient temperature, 300 °C, 400 °C and 500 °C are determined using biaxial tensile tests. A classical Nakazima test procedure at ambient temperature is carried out to establish a reference FLC for the material, and the reference FLC is further used to evaluate the results from biaxial tensile tests. Furthermore, an anisotropic GTN model based on Yld2000-3d yield criterion is calibrated by inverse identification procedures and applied to predict the localized necking and fracture for DP590 sheets under biaxial tensions.

Formability Evaluation and Strain Distribution at the Limit Dome Height Test of Dual-Phase Steel

Formability Evaluation and Strain Distribution at the Limit Dome Height Test of Dual-Phase Steel

Evaluation of high-temperature formability for Ti-xMo-4Fe metastable beta alloys based on Mo contents

High-temperature formation technology is widely used to fabricate components with metastable β titanium alloys, a material characterized by balanced mechanical properties, including superb formability, corrosion resistance, and high strength. In high-temperature formation, it is crucial to control the formation conditions by linking the changes in those conditions caused by processing variables with microstructures and identifying the optimal conditions for high-temperature formation. As such, in this study, a Ti–Mo–Fe alloy was designed that is different from conventional metastable β titanium by adding molybdenum (Mo) and iron (Fe), which are relatively economical β stabilization elements. The mechanical characteristics of the alloy at room temperature were also examined by varying the Mo content, and a high-temperature compression test was conducted to evaluate its high-temperature characteristics and formability. The high-temperature compression test was performed at five different temperatures (700 °C, 750 °C, 820 °C, 900 °C, and 950 °C) to avoid β-transus and with four different strain rates 1 × 10−3/sec, 1 × 10−2/sec, 1 × 10−1/sec, and 1 × 100/sec. Then, the test results were utilized to create a processing map, which evaluated formability by examining plastic instability and energy distribution efficiency at different temperatures, strain rates, and reduction rates, the processing variables for high-temperature formation. Afterward, their connections with the microstructures were analyzed to determine the optimal conditions for the temperature formation of the newly designed Ti–Mo–Fe metastable β titanium alloy.

Formability evaluation based on a constitutive model with stress rate direction dependency considering bifurcation modes

Accurately predicting the fractures that occur in materials during forming not only improves quality, but also reduces the amount of material that is discarded. Therefore, as a key technology for digital transformation to achieve carbon neutrality, it is necessary to improve the accuracy of forming analysis and establish an efficient method for predicting forming limits. Formability assessment is typically performed using ductile fracture criteria or experimental forming limit diagrams (FLDs), which require prior fracture testing. The authors have established a forming evaluation method based on three-dimensional local bifurcation theory as a versatile method that does not require destructive testing. This method can follow abrupt changes in the stress field, such as localized necking, by using a flow rule that takes into account the directionality of the stress rate. In this study, the proposed method is applied to the tensile testing and the forming analysis of a square cup drawing to analytically verify the location and onset time of local bifurcation modes that may lead to fracture.

Formability evaluation of tailor weld blanks of austenitic stainless steel (AISI 304)

ABSTRACT Tailor weld blank (TWB) is preferred in different components of automobiles to reduce weight of the vehicle. However, TWBs have lower formability than sheets because of increased hardness and strength of weld region. Hence, in this work, detailed formability analysis of TWB of AISI304 is done and compared with as-received sheets along with microstructural correlation. Forming limit diagram for as-received sheet, TWBs are determined. Strain hardening exponent value of as-received sheet is 0.381, unweld region and weld region of TWB is observed to be 0.362 and 0.301, respectively. Numerical simulations were also done for predicting the FLC of TWB of AISI304 with the help of PAM STAMP 2 G solver. TWB showed lower formability than as-received sheets. Similarly, predicted FLD for TWB is almost coinciding with the experimental value. Similarly, optical micro-structure studies were also analysed for as-received sheet, unweld region and weld region of TWB, which showed fully austenitic structure with random grain orientations. At the same time, it was found that strain path chosen for FLD determination has a strong influence on microstructure evolution.

Evaluation of the macroscopic formability of metallic materials using a cylinder compression test

Several flow features revealed by hot cylinder compression tests are macroscopically analyzed and compared. Materials including AISI 1025 (100–500 °C), AISI 52100 (900–1200 °C), AA6082 (20–300 °C and 350–550 °C), Ti–6Al–4V (500–800 °C) and AZ61A (250–400 °C) were grouped in terms of formability. The shapes of cylinder-compressed specimens were analyzed and related to formability. The addition of the maximum radius increase near the mid-plane and the averaged minimum radius increase at the two specimen-tool interfaces, i.e., the “cylinder compression evaluation factor” (CCEF), serves as an index of formability. To quantify the effect of temperature on formability, several metrics were used, including the CCEF and temperature softening formability index (TSFI). It has been shown that the CCEF and TSFI have utility for evaluating the formability of tested materials and that temperature softening greatly affects the formability of metallic materials.

Porovnanie charakteristík tvárniteľnosti vysokopevných dvojfázových ocelí skúškou ťahom a LDH skúškou

The paper deals with the issue of formability evaluation of high-strength dual phase steels DP800 and DP1000 with a thickness of 1.6 mm. These steels are used for automotive body deformation zones. The material formability was evaluated by tensile testing with evaluation of mechanical properties, normal anisotropy ratio and strain hardening exponent. The process formability of steels was evaluated by LDH test, which is used for different deformation states modelled by the specimen width. The results of the LDH parameter achieved were correlated with the measured material formability parameters.

New developments of formability evaluation methods for hot stamping

Formability is an essential material property that needs to be considered when selecting materials for hot stamping applications. Due to the difficulties of achieving rapid cooling before deformation and the failure of lubricant systems, however, it is challenging to use conventional Nakajima and Marciniak tests to evaluate the formability of materials under hot stamping conditions. Recently, biaxial test methods have shown great potential to overcome this challenge. In this paper, recent developments of the biaxial test methods for formability evaluation are reviewed, including testing machines, specimen designs, specimen heating methods, testing procedures, and limit strain determination methods. Compared to the Nakajima or the Marciniak tests, the biaxial test method can provide better simulation for hot stamping conditions and it can be a promising method for evaluating the formability of sheet metals under hot stamping conditions. However, more developments such as the standardisation of the specimen designs and the limit strain determination methods, are still needed for the wide use of the biaxial test method.

Characterization of AZ31B, AZ61A and AZ80A magnesium alloys with an emphasis on temperature compensation for their application to a hot forging

Flow characterization of AZ31B, AZ61A, and AZ80A alloys is conducted using a hot cylinder compression test. The effects of friction and temperature on their flow behaviors are studied. The numerical results show that the effect of friction on the compression load-stroke curve (CLSC) is negligible, whereas the effect of temperature on flow behavior is substantial. A general method for temperature compensation during the hot cylinder compression test using the general C-m flow model was presented. With the flow behaviors by the temperature compensation scheme, formability evaluation using the macroscopic instability index (MII) showed that AZ80A exhibited distinct macroscopic instability during the test, as revealed by its CLSCs. The three materials were used for hot-forging of an automotive, magnesium alloy bracket. The validity of the methodology was verified for AZ31B. The overall shapes and the overlapping defects of predictions and experiments were compared. The three magnesium alloys were numerically and experimentally compared in terms of their flow behaviors and formabilities during the fabrication of real automotive parts.

Experimental and numerical evaluation of formability in three-layer metallic sheets with various layer arrangements

Multi-layer metallic sheets are composed of two or more metallic layers connected to each other to achieve desirable features based on the various properties of the constituent layers. This study attempted to predict the forming limits and deformation behavior of three-layer metallic sheets. Additionally, the effects of the layer arrangement on the forming limit diagram (FLD), stress triaxiality, and limiting dome height (LDH) were investigated using a finite element numerical approach. To this end, three-layer metallic sheets made of aluminum (AA3004), stainless steel (SUS304), and copper (Cu1011) bonded by polyurethane as the bonding layer were employed. The numerical results were validated using the experimental results of Nakajima stretch-forming tests. The numerical results were in good agreement with the experimental data. The results indicate that the formability of the three-layer sheet increased by placing the AA3105 layer as the inner layer in contact with the punch, the Cu1011 layer in the middle, and the SUS304 layer as the outer layer. Therefore, the formability of the Al-Cu-SUS sheet was higher than that of the other layer arrangements. Moreover, the results show that the material properties, particularly the tensile strength, play a key role in controlling the FLD of the three-layer sheets.

Microstructural Variation and Evaluation of Formability According to High-Temperature Compression Conditions of AMS4928 Alloy

Ti-6Al-4V alloys are used in various industrial fields such as aircraft parts due to its excellent specific strength and mechanical properties. A high-temperature forming technology has been applied because it is difficult to process complex shapes. During the high-temperature forming process, the microstructure changes significantly due to temperature, strain rate, reduction ratio, and other process variables, and mechanical properties of high-temperature molded products are changed accordingly. Therefore, in this study, a high-temperature compression test was performed on AMS4928, which is one of Ti-6Al-4V alloys used as a material for aircraft parts, and the severe plastic deformation and dead zone were confirmed in connection with the processing map. The changes in microstructure were comparatively analyzed. In addition, it was confirmed that there was a difference in formability due to grain refinement by dynamic recrystallization, and optimal high-temperature forming conditions were derived by linking and analyzing the formability and microstructural factors.

A CDM-based unified viscoplastic constitutive model of FLCs and FFLCs for boron steel under hot stamping conditions

Forming limit curves (FLCs), which are constructed using the limit strains at localised necking, are the most widely used tools for the evaluation of the formability of sheet metals. Fracture forming limit curves (FFLCs) are more recently developed, complementary tools for formability evaluation which are instead constructed using the limit strains at fracture. Since the formability depends strongly on forming conditions such as strain state, temperature and strain rate, models for predicting FLCs and FFLCs are essential for the optimisation and further application of hot forming processes in which these forming conditions vary significantly with both position and time. However, no model has so far been developed to predict FFLCs either alone or in conjunction with FLCs for sheet metals such as boron steel under hot stamping conditions. In this study, a set of unified viscoplastic constitutive equations for the prediction of both FLCs and FFLCs based on continuum damage mechanics (CDM) has been formulated from a set of recently developed constitutive equations for dislocation-based hardening, in combination with two novel coupled variables characterising the accumulated damage leading to localised necking and fracture. The novel variables take into account the effects of strain state, temperature and strain rate on the formability of sheet metals. The material constants in the CDM-based constitutive equations have been calibrated using experimental data comprising true stress-true strain curves and limit strains of a 22MnB5 boron steel obtained at a range of temperatures and strain rates. Investigation of the effect of varying selected parameters in the coupled damage variables on the resulting computed FLCs and FFLCs has demonstrated the flexibility of the model in enabling curves of different shapes and numerical values to be constructed. This indicates the potential of the CDM-based constitutive model for application to other materials for warm or hot stamping processes.

Post-rolling annealing of a multilayered Brass/IFS/Brass composite: An evaluation of anisotropy, formability, and mechanical properties

The multilayered Brass/IFS/Brass composite was produced through the cold roll bonding (CRB) process and was then subjected to annealing treatments at different temperatures. The microstructure, texture, anisotropy, formability, and mechanical properties of the composite were investigated as a function of annealing temperature. The results revealed that the annealing of the composite at 500 and 650 °C led to full recrystallization in Brass and IFS layers, respectively; this resulted in significant changes in the mechanical properties of the composite. Formation of equiaxed, recrystallized grains instead of elongated, rolled grains led to a decrease in preferred orientation intensity, and consequently, lower anisotropy. In addition, the occurrence of recrystallization and formation of (111) || RD fiber in the fully recrystallized IFS layer were the parameters effective on the higher formability of the annealed composites. Annealing of the composite also led to a decrease in strength and increase in the elongation of the composite. Annealing at 500 and 600 °C was more effective on these variations due to the full recrystallization of the Brass and IFS layers. Moreover, the annealing of the composite resulted in the variation of the fracture from a brittle to a ductile mode.

Evaluation of hole expansion formability of high strength AA7075 alloy under varying temper conditions

There has been a widespread increase in the use of aluminum alloys in automotive industries for meeting ever-growing light-weighting requirements. However, edge formability is a critical manufacturing challenge that restricts their widespread use. Edge formability of sheet metal is determined using a hole expansion test (HET) and is evaluated by the hole expansion ratio (HER). The present study investigates the effect of temper conditions on the edge formability of AA7075 alloy sheets. Hole expansion tests were conducted in different temper such as W-temper (super saturated solid solution followed by water quenching), under aged (UA), and peak aged (PA) conditions. Two different hole preparation techniques, a punching and a drilling process, were used to prepare samples with varying edge conditions. The results demonstrate that the W-temper has the highest edge formability irrespective of hole edge conditions. Researchers have reported that uniaxial stress state prevails at the hole edge during the HET. Consequently, uniaxial tensile tests were conducted on for each temper condition and various tensile properties such as yield stress (YS), ultimate tensile strength (UTS), ratio of yield stress to ultimate tensile strength (YS/UTS) were determined to evaluate edge formability. Furthermore, microstructural and failure analysis of the failed specimens were performed to explain the deformation behavior during the HET.