Consideration of Elastic Tool Deformation in Numerical Simulation of Hydroforming with Granular Material Used as a Medium

2011 ◽  
Vol 473 ◽  
pp. 707-714 ◽  
Author(s):  
Martin Grüner ◽  
Marion Merklein
Keyword(s):  
Numerical Simulation ◽  
Granular Material ◽  
Elevated Temperatures ◽  
High Strength Steels ◽  
High Strength ◽  
Appropriate Technology ◽  
The Body ◽  
Warm Forming ◽  
Forming Process ◽  
Blank Holder

The use of high and ultra high strength steels in modern bodies in white raises steadily since the 1980’s. This trend is caused by the consumers’ wish of low fuel consuming cars with an increased passenger’s safety. The processing of these steels brings new challenges e.g. high flow stresses and a low formability at room temperature or high tool loads. These challenges can be resolved by warm forming at temperatures up to 600 °C reducing the flow stresses and increasing formability. For the production of complex parts that can not be produced by deep drawing hydroforming is an appropriate technology which can also help to reduce the number of parts and thus the weight of the body in white. Nowadays typical fluids used for hydroforming are only temperature stable up to about 330 °C so that it is not possible to combine the benefits of warm forming and hydroforming. Media like gases and fluids tend to leakage during the process which can only be avoided by a sealing or high blank holder forces. A new approach is the use of ceramic beads as medium for hydroforming at elevated temperatures. Building up a heatable tool for hydroforming with granular material used as medium makes it necessary to consider thermal conductivity so that there is a need of thick insulation plates. These insulation plates show high elastic deformations affecting the blank holder forces during the forming process. Measurements of the compressibility of these plates and implementation in numerical simulation allow a significant increase of the prediction accuracy of the model. A comparison of real part geometry and numerical results from models with and without consideration of elastic deformation will be given.

scholarly journals Punch Stretch Test for TRIP690 and DP780 Steel at Elevated Temperatures

2016 ◽  
Vol 854 ◽  
pp. 118-123
Author(s):  
Robert Krupa
Keyword(s):  
Elevated Temperatures ◽  
New Technology ◽  
Temper Embrittlement ◽  
High Strength Steels ◽  
High Strength ◽  
Phase Changes ◽  
Warm Forming ◽  
Forming Process ◽  
Contact Heat ◽  
Sheet Formability

The forming at elevated temperatures for Advanced High Strength Steels (AHSS) opens up a new technology. The phase changes during warm deformation are the key to understanding the warm forming process. The desired microstructure and mechanical properties before and after warm forming have to be known in order to find optimal conditions for achieving good sheet formability and preferred material properties in service. In this work, the TRIP690 and DP780 steels are investigated under punch stretch test conditions in order to evaluate the temperature influence on neck formation and fracture occurrence at ambient and elevated temperatures 200oC, 400oC. Contact heat treatment was used for heating up the circular specimens. It was found that formability of the investigated steels was drastically reduced at a temperature of 400oC and brittle fracture occurred because of temper embrittlement. It is recommended to avoid steel tempering at this critical temperature.

Investigation of EN AW 5754 Aluminum Alloy’s Formability at Elevated Temperatures

2017 ◽  
Vol 885 ◽  
pp. 98-103 ◽  
Author(s):  
Dávid Budai ◽  
Miklós Tisza ◽  
Péter Zoltán Kovács
Keyword(s):  
Elevated Temperatures ◽  
High Strength Steels ◽  
High Strength ◽  
Carbon Composite ◽  
Alloy Sheet ◽  
High Mass ◽  
Mass Reduction ◽  
Forming Process ◽  
Forming Temperature ◽  
Operating Distance

Nowadays, mass reduction is the most often used term in the automotive industry. Car manufacturers are continuously working on getting ever lighter models than the previous ones, because of the global competition and the rigorous emission rules. A light car has many advantages: lower consumption, better handling, longer operating distance, etc. The emission rules forced the car brands to start new researches to find new solutions for mass reduction. The formula is relatively simple, using lighter or less materials or both and the car will be lighter. In the recent solutions there are three different ways: application of high strength steels, aluminum alloys, and carbon-composite elements. Our investigations are focusing mainly on aluminum, because of its high mass reduction potential. The biggest problem with the aluminum is its low formability. The formability of aluminum is lower than the steel, and it causes problems for the manufacturers. To increase the formability of the aluminum is a hot topic in the research and development area. Forming at elevated temperatures is one of the best solutions to increase the formability of aluminum. The relation between the formability and the forming temperature is not linear, furthermore beyond the optimum forming temperature the formability decreases. We need dozens of investigations to describe the perfect relation, but sometimes a good approximation is enough to form sheet products safely. In our work we investigated the EN AW 5754 aluminum alloy sheet at room temperature, 130°C, 200°C and 260°C. From these tests we could obtain FLC curves of the alloy at different temperatures. Using these curves, the process engineers could find the optimum parameters of their forming process.

Comparison of Material Behavior and Economic Effects of Cold and High Temperature Forming Technologies Applied to High-Strength Steels

2005 ◽  
Vol 6-8 ◽  
pp. 101-108 ◽  
Author(s):  
Reimund Neugebauer ◽  
Angela Göschel ◽  
Andreas Sterzing ◽  
Petr Kurka ◽  
Michael Seifert
Keyword(s):  
Elevated Temperatures ◽  
High Strength Steels ◽  
Dimensional Accuracy ◽  
High Strength ◽  
Economic Effects ◽  
Material Behavior ◽  
Spring Back ◽  
Forming Process ◽  
Cold Forming ◽  
Forming Tools

The focus of forming high-strength steel at elevated temperature is to improve its forming properties like elongation and to reduce the power requirements during the forming process in opposite to cold forming. Because of the undefined and large spring-back effects parts made by cold forming are not able to achieve the demanded dimensional accuracy, which is necessary for laser welding operations in car body assembly. The reduction of the spring-back behavior is another advantage of the temperature controlled forming technology. On the other side the forming at elevated temperatures requires increased costs for forming tools and tempering equipment. For a fundamental evaluation of this technology, expenditures for the complete process chain have to be considered.

Mechanical Behaviour of Ceramic Beads Used as Medium for Hydroforming at Elevated Temperatures

2009 ◽  
Vol 410-411 ◽  
pp. 61-68 ◽  
Author(s):  
Marion Merklein ◽  
Martin Grüner
Keyword(s):  
Granular Material ◽  
Elevated Temperatures ◽  
Exhaust System ◽  
High Strength Steels ◽  
High Strength ◽  
Compression Direction ◽  
High Efficient ◽  
Hydroforming Process ◽  
Ultra High Strength Steels

The need of light weight construction for high efficient vehicles leads to the use of new materials like aluminium and magnesium alloys or high strength and ultra high strength steels. At elevated temperatures the formability of steel increases as the flow stresses decrease. Forming high complex geometries like chassis components or components of the exhaust system of vehicles can be done by hydroforming. The hydroforming process by oils is limited to temperatures of approximately 300 °C and brings disadvantages of possible leakage and fouling. Using granular material like small ceramic beads as medium could be an approach for hydroforming of ultra high strength steels like MS W1200 and CP W800 at temperatures up to 600 °C. The material properties of granular material are in some points similar to solid bodies, in other points similar to liquids. For understanding and simulation of the behaviour of the medium a basic characterisation of ceramic beads with different ball diameters is necessary. Powder mechanics and soil engineering give ideas for experimental setups. For the conversion of these approaches on the one hand the behaviour of the ceramic beads itself has to be characterized, on the other hand the contact between a blank and the beads have to be investigated. For the tests three different kinds of spheres with a diameter between 63 microns and 850 microns are used. In unidirectional compression test compressibility, pressure distribution in compression direction and transversal compression direction and the effect of bead fracture are investigated. The tests are carried out at different compression velocities and for multiple compressions. For determination of friction coefficients between blank and beads and determination of shear stress in bulk under compression a modified Jenike-Shear-Cell for use in universal testing machines with the possibility of hydraulic compression of the beads is built up. The gained data can be used for material modelling in ABAQUS using Mohr-Coulomb or Drucker-Prager model.

Current Trends of Hydroforming Process Into Automotive Body Structure and Chassis Applications

2007 ◽  
Author(s):  
Ramakrishna Koganti ◽  
Jason Balzer ◽  
Klaus Hertell
Keyword(s):  
Hot Stamping ◽  
High Strength Steels ◽  
High Strength ◽  
The Body ◽  
Instrument Panel ◽  
Forming Process ◽  
Automotive Body ◽  
Current Trends ◽  
Structural Applications ◽  
Hydroforming Process

Recent low emission, lightweight, safety requirements, automotive manufacturers are implementing lighter and stronger materials and new manufacturing processes into body structural components. Typical widely used forming process in automotive body structures is stamping process. Other forming processes currently used in body structural applications are hydroforming, Rollforming and hot stamping processes. Initially, hydroforming process was used for chassis applications. Few applications of chassis are cross members, engine cradle, instrument panel (IP) beams, and bumper beams. Recently, a few automotive manufacturers are already implemented the hydroforming process into front end structures. Hydroform process gives more part consolidation, and perhaps even weight reduction. However, depending on applications some brackets may be needed to attach other components. Some of the issues related to bracket attachments can be avoided in the design phase. Audi A2, and Chrysler Pacifica have implemented roof rails in the body structures arena. Latest developments are even pushing the hydroforming process into High Strength Steels arena. Pontiac Solstice and Saturn Sky implemented Dual Phase 600 material on the chassis rails. In this paper, current trends of hydroforming process with advanced high strength steels (AHSS) will be discussed. Hydroforming process involves, bending, preforming (low pressure), and final forming (high pressure) with mechanical properties of DP780 material at various stages of the hydroforming process will be discussed.

Springback Investigation in Roll Forming of a V-Section

2014 ◽  
Vol 553 ◽  
pp. 643-648 ◽  
Author(s):  
Akbar Abvabi ◽  
Joseba Mendiguren ◽  
Bernard F. Rolfe ◽  
Matthias Weiss
Keyword(s):  
Elastic Modulus ◽  
Continuous Process ◽  
High Strength Steels ◽  
Shell Element ◽  
High Strength ◽  
Material Model ◽  
The Body ◽  
Roll Forming ◽  
Forming Process ◽  
Advanced High Strength Steels

To have fuel efficient vehicles with a lightweight structure, the use of High Strength Steels (HSS) and Advanced High Strength Steels (AHSS) in the body of automobiles is increasing. Roll forming is used widely to form AHSS materials. Roll forming is a continuous process in which a flat strip is shaped to the desired profile by passing through numerous sets of rolls. Formability and springback are two major concerns in the roll forming of AHSS materials. Previous studies have shown that the elastic modulus (Young’s modulus) of AHSS materials can change when the material undergoes plastic deformation and the main goal of this study is to numerically investigate the effect of a change in elastic modulus during forming on springback in roll forming. Experimental loading-unloading tests have been performed to obtain the material properties of TRIP 700 steel and incorporate those in the material model used in the numerical simulation of the roll forming process. The finite element simulations were carried out using MSC-Marc and two different element types, a shell element and a solid-shell element, were investigated. The results show that the elastic modulus diminution due to plastic strain increases the springback angle by about 60% in the simple V-section roll forming analyzed in this study.

Relationship between Microstructure and Mechanical Properties in Q&P-Steels

2016 ◽  
Vol 879 ◽  
pp. 1933-1938 ◽  
Author(s):  
Richard G. Thiessen ◽  
Georg Paul ◽  
Roland Sebald
Keyword(s):  
Mechanical Properties ◽  
Dual Phase Steel ◽  
High Strength Steels ◽  
High Strength ◽  
The Body ◽  
Advanced High Strength Steels ◽  
Passenger Safety ◽  
Back Scattering ◽  
Body In White ◽  
Expected Increase

Third-Generation advanced high strength steels are being developed with the goal of reducing the body-in-white weight while simultaneously increasing passenger safety. This requires not only the expected increase in strength and elongation, but also improved local formability. Optimizing elongation and formability were often contradictory goals in dual-phase steel developments. Recent results have shown that so-called "quench and partitioning" (Q&P) concepts can satisfy both requirements [1]. Many Q&P-concepts have been studied at thyssenkrupp Steel Europe. Thorough investigation of the microstructure has revealed relationships between features such as the amount, morphology and chemical stability of the retained austenite and the obtained mechanical properties. An evaluation of the lattice strain by means of electron-back-scattering-diffraction has also yielded a correlation to the obtained formability. The aim of this work is to present the interconnection between these microstructural features and propose hypotheses for the explanation of how these features influence the macroscopically observed properties.

Applying 2k Factorial Design to Study on Parameters Affecting Springback of Forming of Advanced High Strength Steel Sheets (AHSS)

2017 ◽  
Vol 872 ◽  
pp. 83-88
Author(s):  
Ramil Kesvarakul ◽  
Chamaporn Chianrabutra ◽  
Watcharapong Sirigool
Keyword(s):  
Elastic Recovery ◽  
Weight Ratio ◽  
High Strength ◽  
Die Design ◽  
Statistical Experimental Design ◽  
Blank Holder Force ◽  
Forming Process ◽  
Blank Holder ◽  
Punch Radius ◽  
Springback Angle

Advanced high strength steels (AHSS) are widely used in the automotive industry due to their appropriate strength to weight ratio. This alloy has unique hardening behavior and variable unloading elastic modulus; however, the unavoidable obstacle of AHSS sheet metal forming is springback. The springback is a result of elastic recovery and residual stress. The aim of this study is to determine the proper process parameters enabling the reduction of the springback defects in AHSS forming process. This work was divided into two parts, regarding to the effects of numerical parameters and process parameter on forming AHSS. In this paper, a U-shape forming was used to examine the springback behaviors, such as springback angle, sidewall curl, and thickness, through an experiment. To achieve this purpose, 2k factorial statistical experimental design has been employed to investigate the parameters affecting the springback of forming in AHSS to find out the main effect in the springback reduction focusing on using as a guideline for die design. It showed that the blank holder force is the most influential parameter. The second is the punch radius. However, the blank holder force and punch radius is not simple to adjust in die design, the die radius becomes the important parameter to be used to reduce the springback angle.

Effect of Stress Relaxation on Springback of Steel Sheet in Warm Forming

2016 ◽  
Vol 725 ◽  
pp. 671-676 ◽  
Author(s):  
Naoko Saito ◽  
Mitsugi Fukahori ◽  
Daisuke Hisano ◽  
Hiroshi Hamasaki ◽  
Fusahito Yoshida
Keyword(s):  
Stress Relaxation ◽  
High Strength Steel ◽  
Room Temperature ◽  
Steel Sheet ◽  
Elevated Temperatures ◽  
High Strength ◽  
Warm Forming ◽  
Sheet Metals ◽  
Stress Relaxation Behavior ◽  
Increasing Temperature

Springback of a high strength steel (HSS) sheet of 980 MPa grade was investigated at elevated temperatures ranging from room temperature to 973 K. From U-and V-bending experiments it was found that springback was decreased with increasing temperature at temperatures of above 573 K. Furthermore, springback was decreased with punch-holding time because of stress relaxation. In this work, the stress relaxation behavior of the steel was experimentally measured. By using an elasto-vicoplasticity model, the stress relaxation was described, and its effect on the springback of sheet metals in warm forming was discussed theoretically.

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