Research Group Bulk Metal Forming
The bulk metal forming group studies, by means of processes as e.g. forging and ring rolling, numerous different research topics such as increasing the geometry limits and process optimization. Furthermore, models representing bulk metal forming processes are developed, which can be used for process design, prediction and improvement of workpiece properties as well as training courses.
Increasing the Range of Geometries in Open-Die Forging
Open-die forging is an incremental bulk metal forming process, which is mainly used for the production of long and straight workpieces with a simple geometry as round or square. The production of complex geometries by open-die forging usually requires additional manufacturing steps or can only be realized by a high amount of machining. A new manufacturing approach is based on the idea to realize the production of complex workpieces through superimposed manipulator displacements during a forging stroke. Due to the plastic state of stress, already small superimposed stresses are sufficient to control the material flow towards the intended final geometry. This new forging method was successfully realized for the production of curved and twisted workpieces from steel and aluminium using the open-die forging center at IBF. The general approach significantly increases the range of producible geometries in open-die forging.
For further information, please contact Fridtjof Rudolph.
STOFF - Fast Calculation Models for Open-Die Forging
Open-die forging is an incremental forming process, where the initial ingot is forged in up to many hundred forming steps towards the final geometry. The design of new forging process is mainly realized based upon experience or simple geometric correlations. However, by this only a simple geometrical-based process design is possible which does not give any statement about the temperature, the equivalent strain and the grain size. Since FE-simulation of open-die forging is very time consuming and requires a large numerical effort, the IBF developed fast calculation models for open-die forging, which allow the fast calculation of these decisive target values within seconds. Combined with a GUI, a property based design and optimization of open-die forging process can be successfully realized. Furthermore, these models offer a significant potential for teaching purposes as the correlations between forging parameters and resulting workpiece properties can be analyzed in a descriptive way.
For further information, please contact Fridtjof Rudolph.
Online Assisting System for Open-Die Forging
To ensure excellent and homogeneous mechanical properties, industrial open-die forging requires a smooth and controlled forging sequence. However, during the actual forging process it is not possible to measure decisive workpiece properties as the grain size, equivalent strain and the temperature distribution within the workpiece. Therefore, it is not possible for the press operator to evaluate the impact of small deviations from the planned process sequence on the resulting workpiece properties. Thus, the following process sequence cannot be optimized with respect e.g. to the microstructure. Due to this issue, one main research topic in the field of forging at IBF is the development of an assisting system for open-die forging. By applying fast process models for temperature, strain and grain size, the system allows the operator to evaluate the workpiece properties based upon measured and calculated values. This approach follows the vision to develop an autonomous process control for open-die forging. In this context, the IBF open-die forging center will be used as demonstrator.
For further information, please contact Fridtjof Rudolph.
Process optimization in open-die forging using reinforcement learning
In open-die forging, there are often hundreds of different process routes leading to the same final workpiece geometry. However, these differ, for example, in terms of their process duration or the material properties achieved in the final workpiece. Consequently, an optimized process design and in the long term, a closed-loop control of the open-die forging process is essential. Therefore, the use of reinforcement learning (RL) algorithms for the design of optimized open-die forging processes is investigated at the IBF. In initial work RL algorithms have been successfully coupled with fast process models and trained to design pass schedules for efficient forgings (reach desired final geometry, utilize press force and reduce number of passes). Since RL algorithms also offer the advantage of creating individual optimized solutions very quickly after a training process, they shall also be used for controlling the microstructure in open-die forging in the future.
For further information, please contact Niklas Reinisch.
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. In order to design shorter and more efficient process chains, the IBF has therefore used finite element simulations (FEM) and forging tests to develop a reliable criterion for describing void closure during open-die forging. Both the changing load directions during open die forging and the occurring shear are taken into account.
For further information, please contact Moritz Gouverneur.
Parameters influencing material damage in open-die forging
Open-die forging is an incremental bulk metal forming process suitable for the manufacture of components subjected to high mechanical stresses. To ensure damage-free production, the advanced materials used for this purpose require precise process control, such as maintaining a narrow temperature window. However, feedback from industry shows that component failures due to cracks occur regularly and are often not reproducible, so that process variations are suspected to cause these failures. In order to reduce the resulting additional economic effort in the future, the reasons of material damage in open-die forging will be systematically investigated in an IBF research project. The aim is to extend an existing damage criterion for use in open-die forging at higher temperatures by means of a comprehensive inventory, forging simulations and experiments. With this, the process chain can be evaluated and a general understanding of the process can be built up.
For further information, please contact Moritz Gouverneur.
Open-Die Forging of Hollow Shafts
During the last years, the importance of alternative energy sources as wind energy has risen constantly. A higher energy production by wind power plants cannot only be achieved by setting up additional wind parks, but also by an increase in the performance and by this the size of newly built plants. The electric capacity of up to 6 MW requires larger generators which transform the mechanical to electrical energy. This leads to an increased weight of the whole tower construction. One possible approach to realize lightweight construction is to replace the commonly casted hollow generator shaft by a forged shaft with significantly better mechanical properties. Compared to casted hollow shaft, a weight reduction of 50-60% can be realized. For this purpose, the IBF has successfully developed a forging method performed on the open-die forging center, which allows the open-die forging of hollow shafts with an outer and inner contour with respect to an optimized microstructure to ensure good mechanical properties.
For further information, please contact Niklas Reinisch.
Profile Ring Rolling
Profiling of ring rolled components is an important step for the near net shape production, which leads to material savings as well as time saving regarding the machining. Based on the area of application, all four sides of the cross section can be profiled. Dependent on the type of the profile and the geometry of the ring different challenges during the process occur. Examples for these challenges are the reaching of the desired profile filling and conicity in the cross section.
At the Institute of Metal forming strategies for a stable process, which leads to the desired final geometry are developed and investigated numerically as well as experimentally using the IBF ring rolling mill. Therefore, tool and preform design as well as modifications of the actual process strategy are subject of the research.
For further information, please contact Mirko Gröper.
Flexible Radial Ring Rolling for Producing Non-Axially Symmetric Seamless Rings
Minimizing material and milling costs by near-net shape ring rolling today plays an important economical and environmental role. Industrially feasible ring geometries are exclusively rotationally symmetric, even though applications with varying volume distribution around the circumference exist, e.g. eccentric rings with a nearly linear wall thickness distribution. Depending on size, these parts are produced by milling, closed-die forging or casting processes, while disadvantages in terms of material waste, process flexibility or mechanical properties have to be accepted.
This project aims to further develop the ring rolling process to enable production of near-net shape eccentric ring geometries. Especially for large parts this allows for large material savings without restricting process flexibility or product properties.
For further information, please contact Mirko Gröper.
Investigation of Influencing Factors on Ring Rolling Processes
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. 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. 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.
For further information, please contact Laurenz Kluge.
Composite Ring Rolling
Composites offer the opportunity to satisfy locally different requirements of parts by combining materials depending on local loads. Contradicting mechanical, thermal or chemical demands can be fulfilled or by combining high-grade and cheap materials, part costs can be reduced.
Likewise for large, seamless rings it is possible to realize tailor-made product properties by producing composite rings, e.g. by using a hard and abrasion-resistant working surface together with a ductile core. The project composite ring rolling aims to identify and describe the main relationships between process parameters and material properties by simulation and experiment to derive suitable rolling strategies and process windows for successful production of composite rings.
For further information, please contact Laurenz Kluge.