Dr.-Ing. Jan Langner

Manager process technology
+49 (0)511 279 76-334

Doctoral thesis

The most common method of bulk forming processes is closed die forging with flash. In these processes a surplus of material is used to avoid forging defects such as a missing filling of the cavities. The surplus material is driven through the flash gap and forms the flash. Therefore, the flash gap design has a distinct influence on the material flow within the die and thereby on the cavity filling, the material usage and other process parameters. In indus-try the flash gap is fixed once the dies are manufactured and cannot be changed without additional manufacturing.

A moveable flash gap, which can be changed vertically during the forging operation, was developed within this thesis. It can be used to influence the material flow within the forming process. Thus, the filling of the cavity can be improved. By the use of a variable flash gap in the forging process of a trial part, a maximum increase in the cavity filling of 4.6 mm (17.2 %) was achieved. Furthermore, the influences of different process properties, such as the billet temperature, the trigger force or the height of the moveable flash gap, were evaluated.

To allow the application of a variable flash gap to different forging parts, a guideline was designed. For that purpose, forging parts were classified into characteristic zones. Within the zones the influence of differently designed flash gaps were evaluated using FEA. The result of this evaluation is a recommendation on possible designs of a variable flash gap for differ-ent forging parts, to allow an improvement of the cavity filling.

bulk forming, finite element analysis (FEA), flash gap, material flow, die design


Constantly increasing quality requirements and ever-stricter conditions pose difficult challenges for the foundry industry. They must produce the high-quality components demanded by the market at a reasonable cost. Modern technologies and innovative methods help to master this challenge. Until recently, production, from the design of the aluminum melting furnace to daily process, relied largely on traditional methods and experience. However, important data and information about the melting process—for example, the temperatures and the shape of the aluminum block in the furnace—can hardly be obtained with conventional experimental methods, as the temperatures exceed 700 °C. Therefore, this research project investigates the method of monitoring a melting process by means of optical sensors for the first time. The purpose of this paper is to predict the surface shape of the block during the melting process, as it is not possible to maintain a constant monitoring due to the heat and energy loss during measurement (Einsatz einer Lichtfeldkamera im Hochtemperaturbereich beim Schmelzvorgang von Aluminium. To generate the necessary data, a 3D light-field camera is installed on top of an aluminum melting furnace in order to monitor the process. The basic idea is to find a general method for curve modeling from scattered range data on the aluminum surface in 3D space. By means of the (x, y, z) data from the 3D camera, the aluminum surface is modeled as a polynomial function with coefficient derived using various interpolation and approximation methods. This study presents an attempt to find the optimal polynomial function model that describes the aluminum surface during the melting process by interpolation or approximation methods. The best method for curve fitting will be extended and implemented for surface modeling. 

melting process light-field, polynomial function, interpolation, approximation, aluminum surface

Every year about two billion components are manufactured by forging. Because of the high temperatures and high forming forces required, many components are produced in a segmental manner and later joined together, e.g. by welding. In order to save manufacturing steps – and thus costs and time – a production process is to be developed in which elements of different steels are simultaneously deformed and joined in a single forging. These elements could have very different geometries and thus strongly influence the manufacturability of complex parts. This combination of deformation and joining is called a hybrid process.
In this paper, an investigation on the simultaneous forging and joining of massive bulk and sheet elements is described. The aim is to characterize a first influence of the different forming temperatures on the resulting joint zone of the hybrid process. For this purpose, a series of tests are carried out using a screw press. To find out if there is a correlation between the temperature and the quality of hybrid forgings, the samples are analyzed by means of tensile tests and metallographic analysis. These analyses show the influence of the forming temperature on the joint zone. Based on the knowledge gained, the joint zone can be characterized and evaluated. The main finding is that at higher forming temperatures, the areas of material bonding are significantly stronger than at low temperatures.
The findings obtained contribute to the development of joining by hybrid forging. The results can be used to further investigate the relevant manufacturing processes and component properties of hybrid parts.

forging, forming, hybrid process, massive element, sheet element

In the forging industry, like in many other economic sectors, it is common to simulate forming processes before executing experimental trials. An iterative simulation process is more economic than trials only but still takes a lot of time. A simulation with realistic parameters takes many hours. For an economical production the idea of predicting some main results of the simulation by Data mining was developed. Within this paper, the use of four different Data mining methods for the prediction of certain characteristics of a simulated flange forging process are presented. The methods artificial neural network, support vector machine, linear regression and polynomial regression are used to predict forming forces and the lack of volume. Both are important parameters for a successful simulation of a forging process. Regarding both, forging forming forces and lack of volume after the simulation, it is revealed that an artificial neural network is the most suitable.

data mining, artificial neural network, linear and polynomial regression, support vector machine

This paper describes the production process of serially arranged hybrid steel parts, produced by combining a laser welding process with a subsequent cross wedge rolling process. The presented results are only a first approach in order to get first insights in the forming behaviour of laser welded and cross wedge rolled parts. The investigated material combination is C22 (1.0402) and 20MnCr5 (1.7147). This innovative process chain enables the production of hybrid parts. To evaluate the developed process chain, the weld and the joining zone is analysed before and after cross wedge rolling. Main results are that the joining process using laser welding enables a strong bonding between the two materials with a higher hardness in the joining zone than for the individual materials. After the forming process, the bonding of the joining zone is still present, while the hardness decreased but remains higher than of the materials themselves.

tailored forming, laser welding, hybrid parts, cross wedge rolling

The melting process in an aluminum melting furnace cannot be monitored by contact sensors, since the furnace is not accessible due to the high temperatures (more than 700 °C). Therefore, monitoring the melting process by means of optical sensors is investigated for the first time in this research project. This article deals with an innovative optical measuring system that is able to monitor the melting bridge despite the red-hot furnace walls. For this purpose, a light-field camera is installed on top an aluminum melting furnace in order to monitor the process and to control a targeted heat input into the melting furnace using a rotatable burner. The light-field camera used can capture a 3D point cloud with only one image. To achieve this, a separate field of lenses is placed between the image sensor and the main lens, projecting a virtual intermediate image onto the actual image sensor for further data processing. In addition, a self-developed image analysis program serves to monitor the height variation of the aluminum block and any melting rest on the melting bridge of the furnace.

Thus, the energy efficiency of the aluminum melting process could be increased by 15 % and the melting time reduced by almost 20 minutes by means of online monitoring.

light-field camera, process monitoring, image processing, melting process, energy efficiency

Lot sizing is an important task of production planning and control: basis of lot sizes are order change costs and costs for storage. Models for lot sizing do not consider lot size dependent maintenance costs. However, for a forging company the tool wear is very important, because the tooling costs represent a major part in the production cost. In this article, the deter-ministic lot size model of Andler is extended with lot size dependent maintenance costs. For this purpose, the correlation between lot size and the tool wear is ?rst derived in order to develop a lot size dependent wear function. The linking of a lot size dependent wear function with maintenance costs results in a lot size dependent maintenance cost function, which can be integrated into existing lot size models with a customized total cost function. The validation of the extended lot size model consists of two parts. In the ?rst part, the functionality of the extended lot size model is validated. In the second part, a sensitivity analysis of the lot size is carried out with regard to lot size dependent costs and unit costs.

lot sizing, tool wear, forging industry, sensitivity analysis

In this paper, investigations about the displacement of the joining-zone of serially arranged semi-finished hybrid parts durig cross-wedge rolling are presented. The investigated material combinations are steel-steel (C22 and 41Cr4) and steel-aluminum (20MnCr5 and AlSi1MgMn). The rolling process is designed using FEM-simulations and the cross-wedge rolling process was experimentally investigated afterwards. Research priorities are investigations of the displacement of the joining-zone depending on the main parameters of cross wedge rolling. It could be shown that the forming behaviour of serially arranged hybrid parts made of steel-steel and steel-aluminum can be described using FEM. The deviation of the simulated displacement of the joining-zone compared to the trials is only about 3 %, which is a good approximation.

cross-wedge rolling, steel, aluminum, joining-zone

The investigation of thin flash generation in a precision forging process of an aluminum long part using finite elements analysis (FEA) and corresponding forging trials is described in the presentation. Thin flash generation leads to bad handling and positioning in subsequent process steps and therefore tolerance defects. For investigation purpose, the forging processes were varied by use of different preforms with equal volumes but different mass distributions, while the geometrical parameters of the final part were not varied. 

The forging processes were analyzed by FEA with focus on the value of the form-filling simultaneity depending on the preform geometry. Afterwards, corresponding forging trials were carried out for validation.The results of the experiments and the FEA showed good agreement concerning the part areas were thin flash generation was predicted by FEA and actually occurred in experiments.Preforms with higher values of form-filling simultaneity showed less thin flash generation while preforms with lower values of form-filling simultaneity showed significantly increased thin flash generation.

forging, aluminum, FEA, thin flash generation, prediction

Plasma-transferred arc welding (PTA) is a flexible welding process to coat metallic materials with a wide variety of material combinations. At the University of Hanover, this process is currently being qualified for the production of hybrid semi-finished parts for bulk forming products. The technology provides many answers to the questions about cost-effective manufacturing methods in the field of high-performance components. The process shown is a combination of a welding and cross wedge rolling (CWR) process, which is intended to create homogeneous coatings from steel with high carbon equivalents (CEV>0.5). Weak points due to inhomogeneities in later components must be avoided when the parts are used in tribological applications, so the production process has to be very reliable. Therefore it is necessary, that important properties of the joining zone between the material partners such as the coating thickness and metallic microstructure are well known and can be controlled.

The deformation of the weld seams and the microstructure is optically examined. It is shown, that it is possible to convert the original casting structure of the welded layer into a forming structure. The investigations provide a first overview of the possibilities to influence the coating quality by forming processes in the production of welded hybrid semi-finished steel parts.

tailored forming, plasma-transferred arc deposition welding, hybrid parts, cross wedge rolling

High temperatures up to 1280 °C and high pressures during the forming opperation lead to strong tool wear in forging processes. Increasing tool wear can lead to very high costs. By experiments conducted at the Institut für Integrierte Produktion in Hanover the correlation between tool wear and lot size in hot forging processes was verfied. The findings will help companies to optimise maintenance procedures and therefore reduce cost in the future.

forging, steel, tool wear, lot size

A main target in automotive engineering research and development is currently to reduce fuel consumption and CO2 emissions. Therefore in this project lightweight design was combined with material design in order to produce more efficient structural components. The joining process for tubes of steel and aluminum by laser brazing was investigated to create a joint area that is highly formable. These steel-aluminum joints were afterwards hydroformed, at which steel and aluminum parts were formed in a single step. This process is called "IHU-THT" and can provide lightweight components with excellent mechanical properties.

FEA, hydro forming, tailored forming

Most of today’s technical parts and components are made of monolithic materials. These mono-material components produced in established production processes reach their limits due to their respective material characteristics. Thus, a significant increase in production quality and efficiency can only be achieved by combining different materials in one part. Bulk forming of previously joined semi-finished products to net shape hybrid components that consist of two different materials is a promising method to produce parts with locally optimized characteristics. This new production process chain offers a number of advantages compared to conventional manufacturing technologies. Examples are the production of specific load-adapted forged parts with a high level of material utilization, an improvement of the joining zone caused by the following forming process and an easy to implement joining process due to the simple geometries of the semi-finished products.

This paper describes the production process of hybrid steel parts, produced by combining a plasma-transferred arc deposition welding process with a subsequent cross wedge rolling process. This innovative process chain enables the production of hybrid parts. To evaluate the developed process chain, coating thickness of the billet is analysed before and after cross wedge rolling. It could be shown, that the forming process leads to an improvement of the coating, meaning a more homogeneous distribution along the main axis.

process chain, plasma-transferred arc deposition welding, hybrid parts, cross wedge rolling

For lighter and less consuming car engines the uncercut forging of a steel piston the process has to be designed at first. Therefore the process had been set up in FEA simulations and developed until the final forging sequence was found.

FEA, forging, forge, undercut, multidirectional

The most common method of bulk forming processes is closed die forging with flash. In these processes a surplus of material is used to ensure a complete filling of the cavity of the forging die. The surplus material is driven out of the die through the flash land, thus the design of the flash land has a major influence on the filling of the die. All dimensions of the flash land are typically fixed during the manufacturing process of the die and can not be changed within the forging process. By use of a moveable flash gap that can be actively changed during the forging process the material flow can be altered. This permits to improve the filling of the cavity. In this paper a moveable flash gap for a hot forging process is described and the influence of such a system on the filling of the die cavity is determined. This is done by a comparison to a conventional forging process with a fixed flash land. Furthermore, the results of experimental trials are compared to results of corresponding FEA simulations. Additionally, the influence of the initial billet temperature is investigated. Experimental trials showed that the moveable flash gap has a distinct influence on the material flow. The higher the flash ratio, the bigger is the influence of the moveable flash gap. The moveable flash gap is designed as a flash brake of a height of 2 mm. Its usage lead to differences in height of the parts up to 4.5 mm, which correspond to 16.6% of the parts height, compared to parts forged with a fixed flash land. If the forging temperature is decreased from 1200 °C to 1000 °C, the influence of the moveable flash gap is reduced. The average differences in height are about 0.5 mm (about 3%).

forging, die design, material flow, FEA, flash land, flash gap

Flash-reduced forging is a promising alternative for the forging of complex heavy-duty parts. The use of flashless preforming operations is one possible approach in achieving this. Avoiding flash in preforming by keeping dies completely closed during the forging operation is the main challenge in flashless forging, especially when the parting line of the die is located at the center of the part. In order to do this, an advanced closing mechanism that completely locks the dies mechanically without the use of any spring mechanism was developed.

closed-die forging, closing mechanism, flashless forging, forging process, preforms

The most common bulk forming process is closed die forging with flash. One goal of the industry is to reduce flash. For geometrically difficult parts like crankshafts flash reduction can be achieved by flashless preforming and flash-reduced final forging. The corresponding process design is challenging and defects like an insufficient cavity filling often occur in final forging. A controlled, moveable flash gap enables the alteration of the material flow, increasing the filling of the cavity again. In this paper, the flashless preforming for crankshafts and the influence of a controlled flash gap on cavity filling are described.

Forging, die design, material flow, FEA, flash land

In common forging processes for geometrically complicated parts such as crankshafts, an excess on material (flash) is technically needed to produce a good part, which results often in a material utilization between 60 % and 80 %. But the material costs in forging represent up to 50 % of the total production costs. By decreasing the flash ratio, the material usage and production costs in forging operations can be reduced significantly. For a crankshaft, the development of a new forging sequence was necessary, to achieve the reduction of flash. This development was performed for an industrial two-cylinder crankshaft, based on finite element analysis (FEA) simulations. The new forging sequence consists of three flashless preforming operations, an induction reheating followed by a multidirectional forging and the final forging. By use of this forging sequence the flash ratio was reduced from about 54 % to less than 10 %. Due to the huge reduction of the flash ratio, material as well as energy can be saved from now on, thus increasing the competitiveness of the company.

hot forging, FEA simulation, reduction of flash, multidirectional forging, resource efficiency

The more complicated a forging geometry is, the more flash is necessary to achieve a form filling and a part free of defects. Most small and medium sized enterprises (SME) forge many different parts in small and medium batch sizes and cannot afford the high effort to design more efficient forging processes. In the paper the development of a resource efficient forging process chain for crankshafts is summarized. The forging sequence consists of flashless preforming steps and a flash reduced final forging. The tools were designed to work on industrially used fast moving mechanical presses. The last of the four flashless preforming steps is a multidirectional forming of the crank webs and a pin offset. To keep the forging forces on a low level and enable a stable forging process, an induction reheating of the preform before multidirectional forging was designed. The crankshaft was successfully forged with a reduced flash ratio of less than 10 %.

forging, flash, induction heating, preform, crankshaft

Pistons for combustion engines are usually made of aluminum. But increasing requirements on efficiency and performance can be met by use of steel pistons that will probably spread in the automotive industry in the next years. The pistons are forged and an expensive machining process is necessary to finish them. In the usually unidirectional forging process it is not possible to pre-forge some areas, such as the pin bores as they represent an undercut. By the help of a multidirectional forging operation it is possible to forge undercuts. This process is distinguished by a pre-forging of the pin bores and an improved material usage. Furthermore, the following machining operation will be simpler due to an easier positioning of the part. Currently, the forging tools are under development. Once they are finished they will be tested in an industrial environment on an eccentric press. The tools and parts will be analyzed concerning the quality of the parts, the die wear and the economic efficiency of this new process.

piston, steel, forging, pin bore, undercut, multidirectional

Using hybrid forging techniques, both bulk or sheet metal can be formed and joined in a single step, rendering subsequent joining processes unnecessary. Moreover, using sheet metal rather than bulk material means that material-savings can be made and/or more economical forming units can be used.

hybrid, forging, sheet metal forming, joining technology, steel, adhesive bond

Research projects