Coupling of process conditions and material properties across several length scales enables simulative research and optimization of various process chains.
The research topics embedded in this cross-sectional area are assigned to different research groups and are presented below.
Damage Controlled Forming - Caliber Rolling
Based on the increasing demand on light-weighted metal parts with long service time, innovative methods to predict and control damage evolution in metal forming processes need to be developed. With this goal, caliber rolling process is studied on the case-hardening steel 16MnCrS5. Caliber rolling is a hot rolling process to produce semi-finished product and undergoes damage evolution, which can be characterized as nucleation, growth and coalescence of voids. In caliber rolling, several process parameters such as caliber geometry and roll diameter are identified to influence factors the damage evolution and will be investigated in FE simulation. For damage prediction, some existing damage models as well as a further developed damage model will be implemented. Furthermore, rod-shaped metal parts with the same geometry but various damage will be produced by caliber rolling on a universal rolling mill during the research period, which will be subject to further manufacturing processes, e.g. cold extrusion.
For further information, please contact Shuhan Wang.
Image: FE model of caliber rolling, Copyright: IBF
Damage Controlled Forming - Flat Rolling
Flat rolling is a forming process for the production of semi-finished sheet metal products. These products are commonly used in the automotive sector for instance to further process them into structural components. The two main goals of flat rolling are the thickness reduction in order to reach the desired geometry and the improvement of the mechanical properties compared to the raw material, usually cast slabs. The cast slab usually contains voids and pores, which are formed during solidification. The pores can be eliminated by mechanical closure and hot pressure bonding of the voids through favorable process conditions. One of the major factors in this regard is considered to be the so-called load path. It describes the sequence of different states of stress and strain throughout the forming history of the part. The main focus of this project are the determination of the spectrum of accessible load paths and their influence on the pore evolution in simulation and experiments on a universal rolling mill.
For further information, please contact Conrad Liebsch.
Image: Roll gap during hot flat rolling, Copyright: IBF
Cold Rolling Strategies for Producing Magnetic-Optimized Electrical Steel Sheet in Energy-Efficient Electrical Drives
One way to increase the efficiency of electric drives is to optimize the magnetic properties of the electrical steel used in the magnetic core. In order to quantify the influence of process parameters on these final properties and to create a scientific-theoretical basis for the development of low-loss electrical steel, an interdisciplinary DFG research group, FOR 1897, is working on the integrated process chain modeling. The main task of the IBF is to investigate and simulate the cold rolling process. Experimentally, the IBF will test different rolling strategies on the cold and hot rolling mill. A multi-scale model that includes a macroscopic finite element model and a microscopic crystal plasticity finite element model is created to compute the texture evolution, which makes it possible to determine the influence of different rolling strategies and initial states on the local texture development during cold rolling. By linking the sub-models, it enables model-based process design of low-loss electrical sheets for highly efficient electric drives.
For further information, please contact Xuefei Wei.
Image: Multi-scale model for simulating texture evolution during cold rolling, Copyright: IBF, IMM
Simulation of the Process Chain for a Turbine Disc
The production of turbine discs for aerospace applications is characterized by very strict safety requirements including tight windows for the microstructure. The evolution of the microstructure therefor needs to be accounted for during the design of the process chain. Accordingly an online-coupling between StrucSim, a program calculating the microstructure, and the commercial finite element, short FE, Software Simufact was developed. This means that StrucSim is called during the FE Simulation and influencing its results. Subsequently the process chain was reproduced in FE Simulations and calculated using the online-coupling. Thereby the microstructure evolution was calculated for the whole workpiece along the process chain. This technique can be used to optimize processes or process chains regarding productivity or reproducibility in the future.
For further information, please contact Alexander Krämer.
Image: Turbine disc process chain and position in the engine, Copyright: Leistritz, SMS, IBF
High Manganese Steel Crashboxes
High manganese steels, short HMnS, have a high energy absorption potential due to their extraordinary combination of strength and formability. This qualifies HMnS as potential materials for crash relevant components in the automotive industry. However, the available elongations up to 70% are not reached in the crash of thin walled structures. In order to use HMnS for crash-relevant lightweight structures, various measures have to be taken. These include an adapted alloy design and the adjustment of a tailored microstructure with increased yield strength. Thus, a defined deformation behavior with maximum energy absorption should be achieved. Accompanying the experimental investigation of the optimal material properties, the crash behavior is predicted by multi- scale simulation. Therefore, a physical-based hardening model with input data from ab initio calculations is coupled with the FEM simulation.
For further information, please contact Angela Quadfasel.
Image: Experimental and simulated high manganese steel crashbox, Copyright: IBF
Microstructure Simulation With StrucSim
StrucSim is a program developed at the institute of metal forming to predict the microstructure evolution as well as the flow stress for hot forming processes. The challenge in hot forming processes, especially in multi-stage hot forming processes (process chains), is the description of the interaction between hardening and softening of the material. To overcome this challenge, the microstructure of the material is described by state variables, which develop depending on the process parameters (temperature, time etc.). Thus, quantities as the mean grain size or the recrystallized fraction can be calculated, and the flow stress can be derived for each time point. StrucSim is successfully used in several industrial and scientific projects. The extension of the functionality of the program, as well as the coupling to FE programs, such as Simufact, Abaqus etc. are ongoing work.
For further information, please contact Rajeevan Rabindran.
Image: Simulation of flow stress with StrucSim, Copyright: IBF
Process Chain Modeling of an Aluminium Wrought Alloy in AMAP P1
Within the research cluster "Advanced Metals and Processes", short AMAP, in Aachen, the process chain of an automotive outer skin alloy (AA6016) was investigated within the framework of Project 1 "Process modeling of rolled and annealed aluminum strip with special properties for the automotive industry". A special feature of the project is not only the approach to investigate a process chain in industrial production, in the laboratory and by means of numerical models, but also the consortium of the participating companies. Within Project 1, three major aluminium producers (Aleris, Hydro and Novelis), which would otherwise be in competition with each other, Mubea as the automotive supplier and SMS Group as the mechanical engineering company, are working together. In addition to the industrial partners, the Institute of Physical Metallurgy and Metal Physics, short IMM, and the Institute of Metal Forming, short IBF, of the RWTH Aachen University are also involved.
For further information, please contact Angela Quadfasel.
Image: Process chain and consortium in the AMAP P1 project, Copyright: AMAP
Finite-Element Based Process Design for Fabrication of Metal Composites by Roll Bonding
Roll Bonding enables the production of composites with customized combinations of properties. In roll bonding, the bonding partners are permanently joined together by plastic deformation. The bond formation is a complex process influenced by material properties and process parameters. At IBF an Abaqus subroutine has been developed for computing the formation and failure of the bonds. In a DFG transfer project, this subroutine will be further improved to develop efficient process routes for new material combinations. With this subroutine and the Abaqus process model, Roll Bonding can now be mapped. The bond strength is calculated depending on the surface enlargement. The established bond can also loosen again due to unfavorable load condition after roll gap. The influences of parameters such as temperature and height reduction on the bond strength and the bonding status can now be simulated.
For further information, please contact Zhao Liu.
Image: FE model for simulating bond strength evolution during Roll Bonding, Copyright: IBF, Hydro
Investigation of Skin-Pass Rolling With a Focus on Surface
An important characteristic of rolled aluminium strips for use in the automotive outer skin is the surface quality. The topography of the surface and in particular the number of roughness peaks as well as the volume of closed lubrication pockets influence the success of the subsequent process steps deep drawing and painting.
For further information, please contact Angela Quadfasel.
Image: Sketch of the skin-pass process with mill finish and EDT surface, Copyright: IBF
Void Closure in Open-Die Forging
Large ingots for open-die forging are commonly produced in ingot-casting processes. Despite improvements in the casting qualities, casting defects such as voids, gas porosities and pores cannot be completely avoided. One of the goals of open-die forging is therefore, besides realization of the final geometry as well as a homogeneous deformed microstructure, the closure and healing of the voids, whereby the success depends on the process control. Delivery specifications for forging companies are still based on experienced-based safety factors, which guarantee a safe closure and healing of the voids. The goal of this project is therefore, with the help of finite element methods together with a reliable criteria for void closure and healing, to make the process control shorter and more effective.
For further information, please contact Paul Hibbe.
Image: Comparison of void closure in experiment and FEM, Copyright: IBF
Investigation of Influencing Factors on Ring Rolling Processes
The research project entitled "Analysis of the influencing factors on material damage in ring rolling processes" was successfully completed. The results obtained are briefly summarized below:
Ring rolling is a hot forging process for the production of seamless rings. Today, the goal of minimizing the material input and the machining ratio through near-net-shape ring rolling is of considerable economic and ecological importance, since not only the costs, but also the energy input are decisively determined by the amount of material used. In some cases, non-reproducible defects are found in the rolled rings under obviously identical conditions. These defects can include cracks in the component, but also a coarse and/or unevenly distributed microstructure. Since the occurrence of cracks in particular obviously happens randomly, the ring must be planned with large oversize in order to reduce cost- and time-intensive failures of entire rings to a minimum. In general, these oversizes are based on empirical values and are larger than actually necessary. In this research project, therefore, influencing factors on material damage in ring rolling processes were investigated. In a first step, comprehensive data recording was carried out in the companies of the project's advisory board. Fluctuating process parameters were identified and quantified. Subsequently, the data determined in this way has been applied to FEM simulations of upsetting, piercing and ring rolling processes in order to reproduce the influences of the fluctuating parameters on the material damage using damage models. In particular, the speed of ring-growth and the mandrel roll geometry turned out to be decisive values for the material damage during ring rolling. Based on the results of the research project, it is now possible to better adapt the selection of the system, the tool and the process kinematics to the product to be achieved and accordingly to save material and energy costs in the form of smaller oversizes and less reworking time and scrap.
Image: Crack on the edge of a ring rolled workpiece, Copyright: IBF
The project (IGF No. 19316) was supported by the "Verein der Eisenhüttenleute" (VDEh) and supported by the AiF within the framework of the Programme for the Promotion of Industrial Community Research (IGF) by the Federal Ministry of Economic Affairs and Energy on the basis of a decision of the German Bundestag.
Local Heat Treatment of Strain-Hardened Steels
Current lightweight design strives for high strength steels, which at the same time offer sufficient formability. To tailor the properties of low alloy steel accordingly, strain hardening combined with a subsequent local heat treatment presents a promising alternative. This approach can be used to locally increase the formability of semi-finished parts as well as to adapt the property distribution of the sheet metal at best to the function of the final part. In the joint research project of the Institute of Metal Forming and the Fraunhofer Institute for Laser Technology, a crash box serves as an example part. Local softening strategies, which increase the energy absorption capacity, are developed, at first, by means of FE simulations. Dynamic impact tests of real crash boxes confirm that the deformation path can be reduced by 28 % compared to a globally heat-treated crash box and thus weight can be saved.
For further information, please contact Laura Conrads.
Image: Locally and globally heat-treated crash boxes after crash test, Copyright: ILT
FE Simulation of Multi-Stage Bending Processes
The stamping and bending technology is used for the production of complex bending parts, for example for the electric industry. The process design is mainly based on expert knowledge and experimental testing. Aim of the cooperation project with Phoenix Feinbau GmbH & Co. KG is the development of precise FE models to describe multi-stage bending processes and the springback behavior of the produced parts. One key aspect is the identification of material data of high-strength spring steels by means of an inverse modeling approach under bending conditions. Experimental investigations are further carried out to implement the FE boundary conditions correctly. The validated FE models are then applied to examine and evaluate different influencing factors on the final parts in stamping and bending processes.
For further information, please contact Marvin Laugwitz.
Image: Bending center of a stamping and bending machine, Copyright: Phoenix Feinbau GmbH & Co. KG