Prof. Dr.-Ing. Bernd-Arno Behrens

Function:
Managing partner
Phone:
+49 (0)511 279 76-119
E-Mail:
info@iph-hannover.de
vCard:
vCard
ResearchGate:
http://www.researchgate.net/profile/Bernd-Arno_Behrens

Publications

In the forging industry, which is dominated by SMEs, the tool life of forging dies is usually determined on the basis of empirical values and subjective decisions. In order to avoid considerable logistical and economic expenses as a result of unplanned downtimes and die failure, the tool life is often set many times lower and a waste of existing residual tool life is caused. One possibility to determine the remaining tool life of forging tools is a combined measuring method, which is to be developed at the Institut für Integrierte Produktion Hannover (IPH) gGmbH.

Forming technology, tool life, process monitoring

The manual handling of forged parts is physically demanding for forging employees. These physical stresses are reflected in damage to the hand-arm system and back and lead to forging employee absenteeism. In order to protect the health of forging employees, the aim is to reduce the basic stress caused by the dead weight of the forging tongs by using lightweight forging tongs.

forging tongs, ergonomics, lightweight design

The production of hybrid components involves a long process chain, which leads to high investment costs even before machining. To increase process safety and process quality during finishing, it is necessary to provide information about the semi-finished parts geometry for the machining process and to identify defect components at an early stage. This paper presents an investigation to predict variations in dimension and cavities inside the material during cross-wedge rolling of shafts based on measured tool pressure. First, the process is investigated with respect to the variation in diameter for three roll gaps and two materials. Subsequently, features are generated from the hydraulic pressures of the tools and multi-linear regression models are developed in order to determine the resulting diameters of the shaft shoulder. These models show bet-ter prediction accuracy than models based on meta-data about set roll gap and formed material. The features are additionally used to successfully monitor the process with regard to the Mannesmann effect. Finally, a sensor concept for a new cross-wedge rolling machine to improve the prediction of the workpiece geometry and a new approach for monitoring machining processes of workpieces with dimensional variations are presented for upcoming studies.

Cross-Wedge Rolling, Forming, hybrid, tailored forming

Warm forged components have better surface properties and higher dimensional accuracy than hot forged components. Diamond-like-carbon (DLC) coatings can be used as wear protection coatings, which are anti-adhesive and extremely hard (up to 3500 HV), to increase tool service life. In the first funding period of the research project at the IPH – Institut für Integrierte Produktion Hannover gGmbH and the Institute for Surface Technology (IOT) of the Technical University of Braunschweig in cooperation with the Fraunhofer Institute for Surface Engineering and Thin Films (IST), the influence of different coating types and process temperatures on tool wear was investigated. The result is, that DLC coatings can reduce tool wear in some cases significantly, but that their service life is strongly dependent on the temperature. Coating-integrated temperature measurement could not be realised at that point, due to adhesion challenges. During the second funding period, the effect of multilayer DLC coatings on tool wear was investigated. Also, an additional method of the temperature measurement on the engraving surface using thin film sensors was developed in order to correlate the local process temperature and local layer wear. In this work, the development of and the results gathered by the thin film temperature sensors are presented, which enable for more accurate temperature measurements than commonly used thermocouples. Their functionality and durability under high loads were investigated and showed to be promising.

DLC2, warm forging, forging, wear, forming

Solid formed components are subject to ever higher load requirements while at the same time striving for resource efficiency.
ciency at the same time. An ultrafine-grained microstructure can improve the strength and ductility of the component. This makes it possible to design smaller and lighter components and to exploit lightweight construction potential. One possibility
process for producing an ultrafine-grained microstructure is cross wedge rolling.

 

Cross wedge rolling, Fine-grained structure, Lightweight construction

In a research project at the Institute for Integrated Production in Hanover, the process parameters for cross-wedge rolling are to be determined with which an ultrafine microstructure can be achieved in cylindrical blanks. The aim is to achieve grain sizes of the rolled part in the range of 500 nm.

Process development, cross wedge rolling, material properties,Ultra fine microstructure

This paper presents concepts for shock and vibration reduction of a forging tongs. In the forging industry, hand-operated forging tongs are often used for the machining of forged parts. Here, the employees are exposed to high loads from shocks and vibrations of the forming machines. A simulation model that has been created evaluates concepts for reducing the shocks and vibrations during forging

Ergonomics, forging, shock and vibration reduction

Handling hot steel parts weighing several kilos is physically demanding. A new type of forging tongs is designed to reduce stress at work, prevent pain and reduce sick leave.                             

forging, ergonomic, stress reduction

The aim of subproject B1 of the Collaborative Research Center (CRC) 1153 is to determine the formability of novel hybrid semi-finished products by means of incremental forming cross wedge rolling. Main aspect is the forming of hybrid semi-finished products made of steel, aluminium and hard material alloys. In order to reduce the component weight, the use of hybrid semi-finished products makes it possible to manufacture less stressed segments of a previously monolithic component from a light metal. To increase wear resistance, a component area (e.g. a bearing seat) can be coated with a hard material. In addition, process variables (e.g. temperature and force) are to be measured in contact between work piece and tool in the future. There are primarily two material arrangements for the semi-finished products used: coated (coaxial - demonstrator shaft 1) and joined at the front (serial - demonstrator shaft 3). One challenge is the heating of the semi-finished products necessary for forming, since the hybrid semi-finished product has different flow resistances due to the different materials and may have to be heated inhomogeneously in order to enable uniform forming.

cross-wedge rolling, forming, hybrid work pieces, tailored forming, hybrid semi-finished products

To this day, the design of preforms for hot forging processes is still a manual trial and error process and therefore time consuming. Furthermore, its quality vastly depends on the engineer’s experience. At the same time, the preform is the most influencing stage for the final forging result. To overcome the dependency on the engineer’s experience and time-consuming optimization processes this paper presents and evaluates a preform optimization by an algorithm for cross wedge rolled preforms. This algorithm takes the mass distribution of the final part, the preform volume, the shape complexity, the appearance of folds in the final part and the occurring amount of flash into account. This forms a multi-criteria optimization problem resulting in large search spaces. Therefore, an evolutionary algorithm is introduced. The developed algorithm is tested with the help of a connecting rod to estimate the influence of the algorithm parameters. It is found that the developed algorithm is capable of creating a suitable preform for the given criteria in less than a minute. Furthermore, two of the five given algorithm parameters, the selection pressure und the population size, have significant influence on the optimization duration and quality.

preform optimization, genetic algorithm, cross wedge rolled, adaptive flash

The Hybrid Forging Process satisfies the needs of modern structural and material lightweight engineering by combining forming and mechanical joining operations within one process. This paper presents an analytical approach for the prediction of symmetrical joining bonds of bulk material and sheet metal. Finite element simulations verify that the analytical approach provides a threshold value for the sheet metal thickness at which the bending elongation is reduced significantly. Furthermore, the analytical approach emphasizes that surpassing the threshold value leads to a saturation of the bending elongation reduction and only marginal benefit is achieved by increasing the sheet metal thickness.

hybrid forging, bonding, joining, elastomechanics, lightweight, multi-material manufacturing

Components manufactured by hybrid forging in progressive dies have a high potential for lightweight construction. The example of a suspension arm shows the advantage of hybrid forged parts creating new possibilities for structural and material lightweight construction. Additionally, it is demonstrated that the heat subjected to hybrid forged parts during the subsequent hardening process does not threaten the potential of material lightweight construction.

progressive compound, hybrid, forging

The Collaborative Research Centre 1153 (CRC 1153) “Process chain for the production of hybrid high-performance components through tailored forming” aims to develop new process chains for the production of hybrid bulk components using joined semi-finished workpieces. The subproject B1 investigates the formability of hybrid parts using cross-wedge rolling. This study investigates the reduction of the coating thickness of coaxially arranged semi-finished hybrid parts through cross-wedge rolling. The investigated parts are made of two steels (1.0460 and 1.4718) via laser cladding with hot-wire. The rolling process is designed by finite element (FE)-simulations and later experimentally investigated. Research priorities include investigations of the difference in the coating thickness of the laser cladded 1.4718 before and after cross-wedge rolling depending on the wedge angle, cross-section reduction, and the forming speed. Also, the simulations and the experimental trials are compared to verify the possibility of predicting the thickness via finite element analysis (FEA). The main finding was the ability to describe the forming behavior of coaxially arranged hybrid parts at a cross-section reduction of 20% using FEA. For a cross-section reduction of 70% the results showed a larger deviation between simulation and experimental trials. The deviations were between 0.8% and 26.2%.

cross-wedge rolling, hybrid forming, FEA, coating thickness

Within the Collaborative Research Centre (CRC) 1153 “Tailored Forming “the manufacturing of hybrid bulk components is investigated. Therefore, a process chain consisting of joining, forming, milling and quality control has been established by multiple subprojects.Within subproject B1 of the CRC forming of hybrid parts by the incrementally forming cross-wedge rolling (CWR) process is investigated. The superior aim is to determine process limits and capabilities, when forming parts consisting of different materials joined by varying technologies.

In this paper, the investigation of cross-wedge rolling of serially arranged hybrid parts made of steel and aluminum is described. The focus of the research presented in this publication is the displacement of the joining zone of hybrid parts due to the cross-wedge rolling process. Therefore, finite element simulations have been developed, that allow the investigations of hybrid solid components. After simulation of various variations of the cross-wedge rolling process, i.e.  differently shaped tools and forming velocities, experimental trials were carried out with identical parameter sets. A comparison of simulation and experiment, showed that the simulation model is capable of describing the cross-wedge rolling process of hybrid parts. The standard deviation of the displacement of the joining zone between simulation and experimental trials is 8.8% with regard to all investigated cases.

tailored forming, cross-wedge rolling, material forming, aluminum, steel

Within the Collaborative Research Centre 1153 “Tailored Forming“ a process chain for the manufacturing of hybrid high performance components is developed. Exemplary process steps consist of deposit welding of high performance steel on low-cost steel, pre-shaping by cross-wedge rolling and finishing by milling.
Hard material coatings such as Stellite 6 or Delcrome 253 are used as wear or corrosion protection coatings in industrial applications. Scientists of the Institute of Material Science welded these hard material alloys onto a base material, in this case C22.8, to create a hybrid workpiece. Scientists of the Institut für Integrierte Produktion Hannover have shown that these hybrid workpieces can be formed without defects (e.g. detachment of the coating) by cross-wedge rolling. After forming, the properties of the coatings are retained or in some cases even improved (e.g. the transition zone between base material and coating). By adjustments in the welding process, it was possible to apply the 100Cr6 rolling bearing steel, as of now declared as non-weldable, on the low-cost steel C22.8. 100Cr6 was formed afterwards in its hybrid bonding state with C22.8 by cross-wedge rolling, thus a component-integrated bearing seat was produced. Even after welding and forming, the rolling bearing steel coating could still be quench-hardened to a hardness of over 60 HRC. This paper shows the potential of forming hybrid billets to tailored parts. Since industrially available standard materials can be used for hard material coatings by this approach, even though they are not weldable by conventional methods, it is not necessary to use expensive, for welding designed materials to implement a hybrid component concept.

tailored forming, cross-wedge rolling, hard material coatings, PTA

The Institute for Integrated Production Hannover develops process technologies for the simultaneous forming and joining of dissimilar materials. In the future, they should enable, for example, sheet-metal solid parts and steel-aluminum connections. This expands the possibilities for cost-efficient multi-material construction methods in the automobile.

forging, hybrid, progressive compound

Tool wear is of great economic relevance for forging companies. In addition to the maintenance costs, wear-related rejects are also produced. In the course of the research project “Processes for lot sizing planning in consideration of abrasion”, a method was developed for the determination of component-specific cost functions depending on the tool wear. The method allows the determination of a lot size, that leads to a most cost saving production.

lot sizing planning, tool wear, method, software demonstrator, forging tools

Bulk-formed components are used in many applications in automotive and plant engineering. The conditions under which the components are manufactured, often at more than 800°C and thousands of tons of forming force, lead to high die wear. One way to reduce wear is to use suitable protective coatings. Initial basic investigations showed that the use of hard Diamond-like Carbon (DLC) wear-resistant coatings can significantly reduce the tribological effects on the die surface. With new methods such as the use of multilayer layer coatings and temperature measurement on the die surface by use of thin layer sensors, the potential of wear protection for semi-hot massive forming is to be investigated and expanded.

DLC, hot forging, wear

The melt level and oxide layer quantity in an aluminum melting furnace cannot be monitored by contact sensors, since the melting bath is not accessible due to the high holding temperature (above 600°C). Therefore, the method of monitoring the melting bath by means of optical sensors is investigated for the first time. For this purpose, suitable optical measuring systems can be applied which will be able to record the melting bath. The height change of the melt is to be elaborated by means of image analysis and any oxide layer on the bath surface is to be detected.

aluminum melting furnace, metling bath monitoring, oxide layer

Material efficiency and the development time of a forging sequence are decisive criteria for increasing the economic efficiency in the production of complex forgings. SMEs can often only interpret forging sequences in a shortened form due to insufficient capacities and high competitive pressure. Therefore, a generally valid method is to be developed that automatically generates multi-stage, efficient forging sequences based on the mass distribution of any forged part.

automated process design, die forging, resource efficiency