Development of a Pneumatic Bulge Test for High Temperatures and Controlled Strain Rates

2014 ◽  
Vol 1018 ◽  
pp. 245-252 ◽  
Author(s):  
Alexander Braun ◽  
Johannes Storz ◽  
Markus Bambach ◽  
Gerhard Hirt
Keyword(s):  
Finite Element ◽  
Hot Stamping ◽  
High Strength ◽  
Tensile Tests ◽  
Finite Element Simulations ◽  
Bulge Test ◽  
Strain Rates ◽  
Hot Gas ◽  
Pneumatic Bulge Test ◽  
Simulation Input

Due to new material concepts (e.g. boron-manganese steels), hot stamping of sheet metal parts has emerged in order to produce high strength components. Thereby, the design of hot stamping processes by means of finite element simulations requires information about the thermo-mechanical material behaviour up to high strain levels at various temperatures as simulation input. It is known that hot tensile tests are only evaluable until low strain levels. Therefore, a hot gas bulge test for temperatures in the range of 600 °C to 900 °C and strain rates up to 1/s is being developed. In order to design such a hot gas bulge test, the requirements (e.g. forming pressure) are estimated by finite element simulations. The result is a test bench, which already enables a pneumatic forming of specimens at room temperature and pressures up to 200 bar without any unexpected side effects.

Pressure Control for a Hot Gas Bulge Test Using Parallel On-Off Valves

2017 ◽  
Author(s):  
Gunnar Matthiesen ◽  
Hubertus Murrenhoff ◽  
Johannes Storz ◽  
Alexander Braun
Keyword(s):  
Mass Flow ◽  
Elevated Temperatures ◽  
Process Development ◽  
Hot Stamping ◽  
Test Procedure ◽  
Bulge Test ◽  
Detailed Knowledge ◽  
Strain Rates ◽  
Loop Control ◽  
Hot Gas

Weight reduction is an ongoing trend in multiple industries. Especially in the mobility sectors, hot forming of sheet metal parts has become an alternative production process for high strength components. New material concepts, e.g., boron-manganese steels, enable the design of lighter parts at equivalent or even higher strength. During the preliminary process development phase detailed knowledge of the thermo-mechanical material properties of these sheet metals is required at elevated temperatures and high strain rates. Since hot tensile tests can only be evaluated up to comparably low strains, new test designs are needed to supply material parameters at elevated temperatures and higher strain rates. Therefore, the hot gas bulge test has been developed, that allows for such test conditions. In this paper, first the concept of the hot gas bulge test and the developed test bench are described. Opposed to standardized bulge tests, which use hydraulic oil as forming medium, the newly designed test uses gas as medium to account for the hot stamping conditions, i.e., temperatures of up to 950°C. As the forming speed has an increasing influence on the material behaviour at increasing temperatures, a closed loop control of the forming speed was developed. Since there are no proportional pneumatic valves available for the required pressure range, a parallel valve concept was chosen. By combining different valves, the characteristics of a larger proportional valve are imitated. A control algorithm was developed, that maps the required valves conductance into a valve combination to control the mass flow into the pressure chamber. The developed control system is presented and experimental results from the material test procedure are shown. These results reveal that the developed system is capable to track the required mass flow rate for low as well as high forming speeds up to a certain deformation when the deformation of the sheet becomes uncontrollable.

scholarly journals Characterization of High-Strength Packaging Steels: Obtaining Material Data for Precise Finite Element Process Modelling

Metals ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1683
Author(s):  
Fabian Knieps ◽  
Benjamin Liebscher ◽  
Ioana Moldovan ◽  
Manuel Köhl ◽  
Johannes Lohmar
Keyword(s):  
Finite Element ◽  
Flow Curve ◽  
Material Selection ◽  
Biaxial Tension ◽  
Selection Process ◽  
High Strength ◽  
Tensile Tests ◽  
Bulge Test ◽  
Hardening Law ◽  
Stress States

The steadily increasing demand for downgauging to reduce costs in packaging steel applications requires the development of high-strength packaging steel grades to meet strength requirements. At the same time, the demand for a simulative, computer-aided layout of industrial forming processes is growing to reduce costs in tool constructions for downgauging manners. As part of this work, different high-strength packaging steels were characterized for use in a finite element based process layout and validated using application-oriented experiments. Due to a low hardening rate and the occurrence of Lüders bands, high-strength packaging steels show a low amount of elongation in tensile tests, while for other stress states higher degrees of deformation are possible. Thus, common extrapolation methods fail to reproduce the flow curve of high-strength packaging steels. Therefore, a new approach to extrapolate the flow curve of high-strength packaging steels is presented using the tensile test and bulge test data together with a combined Swift–Voce hardening law. Furthermore, it is shown that the use of complex anisotropic yield locus models such as Yld2000-2d is necessary for high-strength packaging steels in order to be able to precisely simulate application-oriented loads in between plane strain and biaxial tension in validation experiments. Finally, the benefit of a material selection process for packaging steel applications guided by finite element simulations based on precisely characterized material behaviour is demonstrated.

Investigation of a Bulge Test at High Temperatures and High Strain Rates Using a Finite-Element Simulation Study

2014 ◽  
Vol 622-623 ◽  
pp. 300-307
Author(s):  
Alexander Braun ◽  
Markus Bambach ◽  
Gerhard Hirt
Keyword(s):  
Finite Element ◽  
Simulation Study ◽  
Room Temperature ◽  
High Strain ◽  
Sheet Thickness ◽  
Bulge Test ◽  
Strain Rates ◽  
Membrane Theory ◽  
High Strain Rates ◽  
Hot Gas

In recent years, hot stamping of sheet metal parts has emerged to satisfy the contrary demands of the automotive industry for components with increased strength at reduced weight. To analyse the material behaviour during these processes, a hot gas bulge test at high temperatures and high strain rates is promising, since the bulge test at room temperature has already proven itself as a useful test for the material characterization of sheet metals up to high strains. Therefore, a hot gas bulge test at elevated temperatures and high strain rates is being developed at the Institute of Metal Forming (IBF) in cooperation with the Institute for Fluid Power Drives and Controls (IFAS) at the RWTH Aachen. To verify if the concepts of the membrane theory, which are used for the evaluation of bulge tests at room temperature, are adaptable to such a hot gas bulge test, a simulation study using finite element calculations was conducted. The purpose of this simulation study is is to estimate the errors which occur if the equivalent stress at the bulge pole is calculated by using the membrane theory. In addition to this study several approaches were examined to obtain the sheet thickness at the bulge pole by measuring the bulge height. The study showed that a hot gas bulge test can be described very well by the membrane theory if the sheet thickness, the curvature at the bulge pole and the pressure inside the bulge are exactly known. However, substantial errors can occur if the sheet thickness at the bulge pole is determined by measuring the height of the bulge pole.

scholarly journals Determination of Forming Limits Based on Finite Element Simulations

2021 ◽  
Author(s):  
Fuhui Shen ◽  
Kai Chen ◽  
Junhe Lian ◽  
Sebastian Münstermann
Keyword(s):  
Finite Element ◽  
Damage Mechanics ◽  
Tensile Tests ◽  
Finite Element Simulations ◽  
Experimental Results ◽  
Uniaxial Tensile ◽  
Anisotropic Plasticity ◽  
Forming Limits ◽  
Dog Bone ◽  
Spatio Temporal

Two categories of experiments have been performed to obtain the experimental forming limits of a ferritic stainless steel from uniaxial to equibiaxial tension, including Nakajima tests and tensile tests of flat specimens with different geometries of the central hole as well as the notched dog bone. The plasticity behavior of the investigated material is described using an evolving non-associated anisotropic plasticity model, which is calibrated based on experimental results of uniaxial tensile tests along different loading directions. A damage mechanics model is calibrated and validated based on the global force and displacement response of tensile tests. Finite element simulations of the Nakajima tests and the tensile tests of various geometries have been performed using the anisotropic material model. A novel spatio-temporal method is developed to evaluate the forming limits under different stress states by quantitatively characterizing the plastic strain distribution on the specimen surface. The forming limits have been independently determined from finite element simulation results of tensile specimens and Nakajima specimens using the spatio-temporal evaluation method. The forming limits obtained from numerical simulations of these two types of experiments are in good agreement with experimental results.

Research on the Numerical Simulation of Hot Stamping for High Strength Steel

2014 ◽  
Vol 898 ◽  
pp. 136-139
Author(s):  
Chang Feng Men ◽  
Wen Wen Du ◽  
Cui Hong Han
Keyword(s):  
Numerical Simulation ◽  
Finite Element ◽  
High Strength Steel ◽  
Hot Stamping ◽  
High Strength ◽  
Nonlinear Finite Element ◽  
Weight Percentage ◽  
Finite Element Software ◽  
Simulation Results ◽  
Die Temperature

In order to research on the hot stamping property of high strength steel, the stamping forming of USIBOR1500P is simulated by the nonlinear finite element software Dynaform and Ansys/ls-dyna. The initial data simulated on USIBOR1500P is obtained by the hot tensile test. The simulation results show that the martensite weight percentage and Vickers hardness are in inverse proportion to stamping speed and initial die temperature.

GPU Accelerated Finite Element Simulation for Ultra-High Strength Steel Quenching

2013 ◽  
Vol 842 ◽  
pp. 337-340
Author(s):  
Chao Wang ◽  
Bin Zhu ◽  
Liang Wang ◽  
Yi Lin Wang ◽  
Yi Sheng Zhang
Keyword(s):  
Finite Element ◽  
Latent Heat ◽  
High Strength Steel ◽  
Thermal Contact ◽  
Hot Stamping ◽  
High Strength ◽  
Heat Processing ◽  
Processing Unit ◽  
Ultra High Strength Steel ◽  
Quenching Process

During the hot stamping of ultra-high strength steel (UHSS), the quenching effect of the mold on the sheet plays an important role to achieve the transition from austenite to martensite. Thus a finite element model for the quenching process of UHSS is established in this paper. The key points of the model include contact thermal conduction and the latent heat processing of phase transforming. Finite element program has been developed to calculate the temperature field of the UHSS quenching process, and temperature measurement device was used to get the temperature-time curve of the mold and the sheet to validate the calculation results. It can be concluded that the latent heat and thermal contact resistance have a critical influence on the temperature filed of the sheet during the hot stamping process. Finally, the parallel computation technology based on GPU(Graphics processing unit) was adopted to accelerate the calculation.

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