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

Hybrid components, made of multiple materials, can meet the increasing demands for lightweight construction and functional integration in the automotive and aircraft industry. Hybrid semi-finished components are produced by applying a high-alloy cladding to a low-alloy base material before hot-forming and machining the workpiece. Throughout this process chain, workpiece deviations in the form of material distribution and material properties can occur that influence the component’s lifetime. This paper investigates whether such workpiece deviations can be detected within the process chain by analyzing process signals obtained from subsequent process steps. For this purpose, artificial workpiece deviations were introduced to hybrid semi-finished workpieces made of C22.8/X45CrSi9-3. Then, process signals during forming and machining were analyzed to determine their sensitivity to the artificial deviations. The results revealed that deviations in cladding size can be effectively monitored using signals from both forming and machining. Cladding position deviations can only be detected during machining, while forming signals are more responsive to detecting the introduced hardness deviations of approx. 100 HV0.1.

Laser hot-wire cladding, Cross-wedge rolling, Machining, Monitoring, Workpiece deviations

In the research project “AutoPress”, the IPH – Institut für Integrierte Produktion Hannover gGmbH and Jobotec GmbH are jointly striving to develop an automated process control of screw presses. By retrofitting and applying an optimization algorithm, the energy demand is to be reduced and the component quality increased.

digitalization, forming technology, production technology

The Collaborative Research Center 1153 is investigating a novel process chain for manufacturing high-performance hybrid components. The combination of aluminum and steel can reduce the weight of components and lead to lower fuel consumption. During welding of aluminum and steel a brittle intermetallic phase is formed that reduces the service life of the component. After welding the workpiece is heated inhomogeneously and hot formed in a cross-wedge rolling process. Since the intermetallic phase grows depending on the temperature during hot forming, temperature control is of great importance. In this paper, the possibility of process-integrated contact temperature measurement with thin film sensors is investigated. For this purpose, the initial temperature distribution after induction heating of the workpiece is determined. Subsequently, cross-wedge rolling is carried out and the data of the thin film sensors are compared to the the temperature measurements after heating. It is shown that thin film sensors inserted into the tool are capable of measuring surface temperatures even at a contact time of 0.041 s. The new process monitoring of the temperature makes it possible to develop a better understanding of the process as well as to further optimize the temperature distribution. In the long term, knowledge of the temperatures in the different materials also makes it possible to derive quality characteristics as well as insights into the causes of possible process errors (e.g. fracture of the joining zone).

cross-wedge rolling, thin-film sensors, hybrid components, aluminum, temperature monitoring

The Collaborative Research Center 1153 is investigating an innovative process chain for the production of hybrid components. The hybrid workpieces are first joined and then formed by cross-wedge rolling. Pinion shafts were manufactured to investigate the behavior of the joining zone under increased complexity of the forming process. For this purpose, six types of workpieces produced by three types of joining processes were formed into pinion shafts. The reference process provides a shaft with a smooth bearing seat. It was found that the increased complexity did not present any challenges compared to the reference processes. A near-net shape geometry was achieved for the pinions made of steel.

hybrid components, cross-wedge rolling, hot forming, laser beam welding, LHWD welding

Work-related illnesses and the resulting employee absences can have a major impact on productivity and competitiveness, especially in small and medium-sized enterprises. Particularly in the forging industry, the manual handling of forged parts leads to high physical stress and thus to frequent illnesses of the musculoskeletal system, especially of the hand-arm system. One possibility to counteract this circumstance is the use of ergonomic forging tongs. In the study presented here, the influence of ergonomic forging tongs on the physical stress of forging employees was investigated by simulation and experiment and compared to conventional forging tongs. Within the simulation and the experimental investigation, forging parts and forging tongs were varied. In the simulation, an ergonomics assessment of the forging situation could be evaluated using the Ergonomic Assessment Worksheet. In the experimental study, gripping force measurements and calorie measurements were used to determine the impact of handling the forging tongs on the forging employees. The results show that the use of the new ergonomically optimized forging tongs can lead to a significant physical relief for the forging employees. The knowledge gained from the ergonomically developed concepts can also be transferred in other industries.

forming technology, ergonomics

Forgings are produced in several process steps, the so-called forging sequence. The design of efficient forging sequences is a very complex and iterative development process. In order to automate this process and to reduce the development time, a method is presented here, which automatically generates multi-stage forging sequences for different forging geometries on the basis of the component geometry (STL file). The method was developed for closed die forging. The individual modules of this forging sequence design method (FSD method) as well as the functioning of the algorithm for the generation of the intermediate forms are presented. The method is applied to different forgings with different geometrical characteristics. The generated forging sequences are checked with FE simulations for the quality criteria form filling and freedom from folds. The simulation results show that the developed FSD method provides good approximate solutions for an initial design of forging sequences for closed die forging in a short time.

forging, forging sequences, CAD, automated process design, closed die forging

Process Optimization through Thin Flash Prevention. Due to the good flow properties of aluminum, the material tends to flow into tool gaps during flashless precision forging and produce the so-called thin flash. For the industrial implementation of flashless precision forging processes, an innovative prediction method for thin flash as well as sealing concepts are to be developed in cooperation with an industrial partner. Simulative studies show that local form filling does not correlate with high pressure or an increased potential for thin flash.

thin flash, FEM-simulation, sealing concepts, precision forging, forming technology

A new process chain for the manufacturing of load-adapted hybrid components is presented. The "Tailored Forming” process chain consists of a deposition welding process, hot forming, machining and an optional heat treatment. This paper focuses on the combination of laser hot-wire cladding with subsequent hot forming to produce hybrid components. The applicability is investigated for different material combinations and component geometries, e.g. a shaft with a bearing seat or a bevel gear. Austenitic stainless steel AISI 316L and martensitic valve steel AISI HNV3 are used as cladding materials, mild steel AISI 1022M and case hardening steel AISI 5120 are used as base materials. The resulting component properties after laser hot-wire cladding and hot forming such as hardness, microstructure and residual stress state are presented. In the cladding and the heat-affected zone, the hot forming process causes a transformation from a welding microstructure to a fine-grained forming microstructure. Hot forming significantly affects the residual stress state in the cladding the resulting residual stress state depends on the material combination.

laser hot-wire cladding, cladding, hot forming, residual stress, tailored forming

In the non-circular rolling, the feasibility of rolling several mutually offset, locally non-round shaped elements into a cylindrical semi-finished product are investigated. One sub-area of the investigations is the rolling of two elliptical sections.

From three different calculation concepts for the determination of the tool engraving, one was chosen for a simulative parameter study. The main influencing variables, including the length and width of the engraving and a process window, were identified.

forming technology, manufacturing technology, FEM

In order to make the production of complex geometries as efficient as possible, several forming stages are generally used. In these, the billet is first heated homogeneously and then forged via several preliminary and intermediate stages as well as final forming. Previous investigations have shown that significant material savings can be achieved by using inhomogeneous, rather than homogeneous, billet heating. A limiting factor in the practical implementation of inhomogeneous heating is the temperature gradient between the hot and warm regions of the billet.

This study therefore investigates the influence of the length of the temperature gradient on the blank size required to achieve form filling for a given finished part geometry. For this purpose, a simulative parameter study was carried out with three temperature transitions of different lengths and two different finished part sizes.

It was shown that, depending on the finished part size and the length of the temperature gradient, between 3.31% and 17.49% material can be saved compared to a homogeneously heated billet. The length of the temperature gradient thus has a significant influence on the material savings potential.

bulk forming, inhomogeneous heating, resource efficiency, FEA

Process monitoring strategies allow wear-related conditions of forging dies to be detected and predicted. The prediction of the wear condition allows intelligent maintenance strategies. This allows residual tool life to be fully utilized, scrap to be reduced and downtime to be calculated. The content of this article is an economic analysis for calculating the payback period of a process monitoring system.

forging, process monitoring, economic efficiency

During flat die rolling, two die plates pass each other and form the cylindrical semi-finished product enclosed within. Non-circular rolling examines the rolling of multiple, locally nonround geometries such as eccentrics. With the aid of statistical experimental design, a simulative parameter investigation has been carried out, main influencing variables have been recognised and process windows identified.

non-round, eccentric, flat jaw tools, preforms, intermediate forms, FEM

In manual solid forming, hand-guided forging tongs are used when processing forged parts. During the forging process, employees are physically stressed by high forging part weights and transmitted impacts. This physical stress leads to employee health limitations and increases absenteeism rates. Ergonomic forging tongs have been developed at IPH that lead to a relief of the forging employees.

ergonomics, forging tongs, forming technology, prevention

The results of the wear investigations will allow multidirectional processes in hot forging to be optimized in the future in a low-wear and economical manner. The determined, wear-inducing process parameters within the design guideline represent elementary basic knowledge which can be applied in a process-specific manner. In principle, the economic potential of multi-directional forging processes using of multi-directional forging processes using sliding dies depends on the application and the desired component geometries. Multi-directional forging processes forging processes offer great potential for savings and can be process design using the results obtained, they can achieve high tool life and have a positive influence on the competitive situation of companies. As a result costs for explicitly selected niche components with significantly higher with significantly increased complexity can be reduced in the future with manageable investment costs in the future. In addition to the process-specific optimization of the process parameters, in the future options for mold design adaptation with regard to local cooling or local cooling or thermal insulation of the slide-wedge wedge mechanics, in order to be able to use the systems in automated series automated series production.

Slide tools, process design, economic efficiency, solid forming

The Tailored Forming process chain is used to manufacture hybrid components and consists of a joining process or Additive
Manufacturing for various materials (e.g. deposition welding), subsequent hot forming, machining and heat treatment. In
this way, components can be produced with materials adapted to the load case. For this paper, hybrid shafts are produced by
deposition welding of a cladding made of X45CrSi9-3 onto a workpiece made from 20MnCr5. The hybrid shafts are then
formed by means of cross-wedge rolling. It is investigated, how the thickness of the cladding and the type of cooling after
hot forming (in air or in water) afect the properties of the cladding. The hybrid shafts are formed without layer separation.
However, slight core loosening occurres in the area of the bearing seat due to the Mannesmann efect. The microhardness
of the cladding is only slightly efected by the cooling strategy, while the microhardness of the base material is signifcantly
higher in water cooled shafts. The microstructure of the cladding after both cooling strategies consists mainly of martensite.
In the base material, air cooling results in a mainly ferritic microstructure with grains of ferrite-pearlite. Quenching in water
results in a microstructure containing mainly martensite.

laser hot-wire cladding, cross-wedge rolling, hybrid components, cladding

In the automotive and mechanical engineering industries, forged parts are used in many applications. The dies for the forged parts are subject to high wear during forging due to high forming forces and temperatures. In order to enable economical production operation, methods to reduce the wear in warm forging have been investigated. One promising method is the use of Diamondlike-Carbon (DLC) wear-resistant coatings.

Warm Forging, Coating, DLC, Wear

Due to the increased integration of functions, many components have to meet high and sometimes contradictory requirements. One way to solve this problem is Tailored Forming. Here, hybrid semi-finished products are manufactured by a joining or cladding process, which are then hot-formed and finished. For the design of hybrid components for a possible later industrial application, knowledge about properties of hybrid components is required. In this paper it is investigated how the respective process steps of the Tailored Forming process chain change the surface and subsurface properties of the applied cladding layer. For this purpose, shafts made of unalloyed steel are provided with a high-alloy austenitic steel X2CrNiMo19-12 cladding by laser hot-wire cladding. Subsequently, hot forming is carried out by cross-wedge rolling and the finishing by turning and deep rolling. After each process step, the subsurface properties of the cladding such as microstructure, hardness and residual stress state are examined. Thus, the influence of different process steps on the subsurface properties in the process chain of manufacturing hybrid shafts can be analyzed. This knowledge is necessary for the specific adjustment of defined properties for a required application behavior.

Cross-Wedge Rolling, Tailored Forming, Hybrid

Reducing the planning and development time for efficient staging sequences in closed die forging offers companies in the forging industry a high potential for responding to competitive to respond to competitive challenges and remain competitive.The digitization of development processes opens up innovative support options for companies.

forging sequence desing, forming technology, digitization, process development, CAD

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