Dr.-Ing. Malte Stonis

Managing director
+49 (0)511 279 76-119

Doctoral thesis

Defects like folds can arise using forging for the production of long flat pieces made of aluminium. A special defect is the formation of inner folds. These can be seen in the grain flow. Inner folds have a negative effect on the dynamic properties of the forged part. As a production process, forging can be divided into single-directional and multi-directional forging. The formation of inner folds was observed at the single-directional forging. By using the multi-directional forging, a forming operation working from different directions, the forming can be set variably. Thus the development of folds can be prevented. A newly developed method can help in the selection of the forming process and in determining an appropriate tool geometry. Here especially the area is adapted, where the development of inner folds occur. Therefore a calculation model was developed. It integrates a computer-aided identification of the inner folds. Using this model, a correction of the parametrically constructed forging tool is possible.

multidirectional-forging, long flat pieces, aluminium, fibre orientation


Rising and increasingly volatile energy prices resulting from increased power feeds from renewable sources such as solar and wind energy are confronting manufacturers with new challenges. If these companies procure their power supplies at ?uctuating short-term prices from electricity exchanges or through energy purchasing pools, they can in?uence the result-ing energy costs through production control via its actuating variables while energy consumption remains constant. A form of sequencing that decides at short notice which order will be processed next shows particularly high potential. The energy price-oriented sequencing rule that is introduced in this article prioritises orders with a high energy requirement at times when energy prices are low and gives precedence to orders that require less energy at times when energy prices are high, without neglecting the scheduled completion deadline. However, this sequencing rule can only be applied e?ectively under certain preconditions. These are elaborated in this article by means of a simulation study that will con?rm the way the rule functions.

production planning and control, manufacturing control, sequencing, energy costs

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

Interactive assistance systems such as data glasses or headsets as a new human-machine interface enable an increase in process quality and speed through networking within the factory. However, small and medium-sized enterprises (SMEs) are critical to the implementation of these systems. Therefore, this article describes the development of a maturity model for a systematic ability analysis and increase to the implementation of interactive assistance.

industry 4.0, interactive assistance systems, maturity models, implementation support

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 storage planning is an important component of the factory planning and describes an improvement potential in the times of an increasing global competition. The selection of a suitable storage, commissioning and transport system is a big challenge especially for small and medium-sized enterprises. In a research project of IPH – Institut für Integrierte Produktion Hannover a method for companies will be created to determine the necessary level of versatility and automation to choose an optimal system. This article introduces the research project and explains the approach and first results.

storage planning, sct systems, versatility, automation, software demonstrator

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

As a result of the increasing feed-in of renewable energies, the volatility of the electricity price rises. Considering this, manufacturers can save energy costs by applying an energy price-oriented sequencing rule. Since the application of this sequencing rule does not only have an impact on the energy costs, a potential analysis is presented in this article which, in addition to the energy costs, also considers the schedule compliance cost of production orders.

cost accounting, manufacturing control, production planning and control

In production, product-related error costs can be reduced by focusing on human production factors, such as considering human performance fluctuations during the day, when production planning with respect to job-shop scheduling. In this article, the flexible job-shop scheduling problem is extended by considering product-related error costs and logistic costs. Product-related error costs are increased by over stressing the operative workers. Logistic costs are based on work in process and throughput time. This cost-based definition enables a production plan to be simultaneously optimized in respect of both error and logistic costs. The product-related error costs and flexible job-shop scheduling problem are described mathematically and a memetic algorithm is also presented as an approach. Within the memetic algorithm, the evolutionary process is supplemented with a local search procedure to improve the ability of solutions and repair procedures to rectify infeasible solutions. The influence of product-related error costs on the total costs of a production plan within job-shop scheduling is presented.

flexible job shop scheduling, memetic algorithm, human perfor-mance fluctuation, error costs

The measurement of torque via sensors as well as the generation of torque form the basis of many industrial sectors. Within a research project an optical and non-contact measurement method to detect the absolute rotation angle and torque was developed. For comparison with the current state of the art torque sensors a test stand was built and compared to a reference torque sensor. The results of this validation are presented in the present paper.

torque, rotation angle, optical, validation

In order to improve the overall efficiency of production facilities through the use of automated guided vehicle systems (AGVs), the availability of the AGVs has to be high. Failures of AGVs have to be minimized. However, if a failure occurs, a successful disturbance management is crucial. Especially for producing companies, economic losses can occur, if material is not at the right place at the right time. Delays can be a hazard to the adherence to delivery dates. In this research project, a support system is developed that automatically generates strategies for the handling of disturbances.

AGV, expert system, automated guided vehicles, case-based reasoning, CBR

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

In this article, the flexible job-shop scheduling problem is extended by consideration of energy costs which arise owing to the power peak, and further decision variables such as work in process and throughput time are incorporated into the objective function. This enables a production plan to be simultaneously optimized in respect of the real arising energy and logistics costs.

The energy-costs-aware flexible job-shop scheduling problem (EFJSP) which arises is described mathematically, and a memetic algorithm (MA) is presented as a solution. In the MA, the evolutionary process is supplemented with a local search. Furthermore, repair procedures are used in order to rectify any infeasible solutions that have arisen in the evolutionary process. The potential for lowering the real arising costs of a production plan through consideration of energy consumption levels is highlighted.

memetic algorithm, flexible job-shop scheduling, energy-costs, power peak

In the automotive industry, aluminum forged parts must fulfill lightweight and heavy duty performance requirements. The generation of thin flash between die halves and in the small gaps between the die and punch must be prevented during the flashless forging process in completely enclosed dies. However, thin flash formation is neither predictable nor preventable.

A numerical model is developed based on finite element analysis to investigate and predict the generation of thin flash in aluminum flashless precision forging processes. The significance and effects of the main influencing input parameters, including billet temperature, forming velocity, and width of gap, on different resulting parameters are evaluated. Among all resulting parameters in the established numerical model, hydrostatic pressure and the forming force in the main forming direction have been identified as the most suitable for predicting thin flash generation.

aluminum forging, forging in completely enclosed dies, flashless forging, FEA

A combined measurement method for the optical determination of the absolute rotational angle and torque was realized. Absolute codings of the angle as well as proper production technologies for the production of suitable markings on the shaft were investigated and successfully implemented.

The absolute rotational angle could be measured with a resolution of about 0.001° at an accuracy of better than 0.2° (corresponds to 0.05% f. s.). Torque was determined with an accuracy of about 3% f. s..

The conclusion is that the overall aim was achieved.

optical measurement, torque, absolute angle of rotation

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 low energy demand and a fast processing time are required in each industrial process for the production of crankshafts. Crankshafts have a very complex geometry and are forged with a high percentage of flash compared to other forging parts. Recent research showed the feasibility of a flashless forging of crankshafts. One way to forge a flashless crankshaft within three steps is to use cross wedge rolling, multi-directional forging and final forging.

This paper presents the investigation results of the influence of the cross section area reduction in cross wedge rolling on different parameters at multi-directional forging. First, the state of research, the process development and tool design of cross wedge rolling and multi-directional forging are described. Then a parameter study will be presented and the influence of the cross section area reduction on flash generation, billet temperatures, forming degree, forming forces and effective strain are shown. Generally, flash generates because a rotation-symmetric billet is forced into an asymmetric movement. The influence of an increasing cross section area reduction leads to a decreasing amount of flash at the bottom of the crankwebs.

multi-directional forging, cross wedge rolling, crankshaft, parameter study, forming angle

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