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

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

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

Flat die rolling is a solid forming operation, in which two engraved tool plates run past each other and thereby form a cylindrical semi-finished product. The non-circular rolling can be used as a preform optimising process, where it should be possible to form local non-circular sections, for example ellipses or eccentrics, into a cylindrical semi-finished product. The material flow should be exclusively in radial direction. Initial simulations show that the requirements can be met.

non-circular rolling, cross wedge rolling, flat dies, preforms and intermediate forms, FEM

Multi-stage forging process chains are often used for the efficient production of complex geometries. Typically, these consist of homogeneous heating, one or more preform stages, and the final forging step. By inhomogeneously heated billets, the process chains can be simplified or shortened. This shall be achieved by setting various temperature fields within a billet, resulting in different yield stresses. These can influence the material flow, leading to easier production of complex parts. In this study, the influence of inhomogeneously heated billets on the forming process is investigated by means of FEA. For this purpose, two process chains including inhomogeneous heating and three homogeneously heated reference process chains are developed and compared. Each process chain is optimized until form filling and no defects occur. Target figures for the assessment are necessary forming force, the amount of material necessary to achieve form filling and die abrasion wear. For process chains with inhomogeneously heated billets, the results showed a small time window of about 5 s for a successful forming in terms of form filling. Forming forces and die abrasion wear increase for inhomogeneously heated billets due to higher initial flow stresses. However, the flash ratio decreases when billets are heated inhomogeneously. Depending on their size, inhomogeneously heated billets show up to 11.8% less flash than homogeneously heated billets. This shows a potential for the use of inhomogeneous heating to make forging processes more efficient. Subsequently, experimental tests will be carried out to verify the results of the simulations.

Inhomogeneous heating, Forging, FEA, Resource efficiency, Preform operation

To increase the economic efficiency in the production of geometrically complicated forgings, material efficiency is a determining factor. In this study, a method is being validated to automatically design a multi-staged forging sequence initially based on the CAD file of the forging. The method is intended to generate material-efficient forging sequences and reduce development time and dependence on reference processes in the design of forging sequences. Artificial neural networks are used to analyze the geometry of the forging and classify it into a shape class. Result of the analysis is information on component characteristics, such as bending and holes. From this, special operations such as a bending process in the forging sequence can be derived. A slicer algorithm is used to divide the CAD file of the forging into cutting planes and calculate the mass distribution around the center of gravity line of the forging. An algorithm approaches the mass distribution and cross-sectional contour step by step from the forging to the semi-finished product. Each intermediate form is exported as a CAD file. The algorithm takes less than 10 min to design a four-stage forging sequence. The designed forging sequences are checked by FE simulations. Quality criteria that are evaluated and investigated are form filling and folds. First FE simulations show that the automatically generated forging sequences allow the production of different forgings. In an iterative adaptation process, the results of the FE simulations are used to adjust the method to ensure material-efficient and process-reliable forging sequences.

Automatic process design, Forging, FEA, Resource efficiency, CAD

A method is presented that enables the complexity of a forging to be determined automatically on the basis of the CAD file of the forging. An automated evaluation of the forging complexity is necessary for a digitized and automated design of stage sequences in order to be able to determine important design parameters such as the flash ratio or the number of stages.

CAD, forming technology, algorithms

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