Dr.-Ing. Malte Stonis

Function:
Managing director
Phone:
+49 (0)511 279 76-119
E-Mail:
stonis@iph-hannover.de
vCard:
vCard
Xing:
https://www.xing.com/profile/Malte_Stonis
ResearchGate:
http://www.researchgate.net/profile/Malte_Stonis

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

Publications

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

In recent years, the requirements for technical components have steadily been increasing. This development is intensified by the desire for products with lower weight, smaller size and extended functionality, but also higher resistance against specific stresses.

The superior aim of the Collaborative Research Centre 1153 "Tailored Forming" is to develop potentials for hybrid solid components on the basis of a new process chain by using joined semi-finished workpieces.

This paper presents the approach and first results of selected subprojects for semi-finished workpiece production by composite extrusion presses, for forming the hybrid semi-finished products by means of cross wedge rolling, die forging and extrusion, and numerical failure prediction of the joining zones. This provides an overview of possible lightweight strategies in the area of bulk forming by the use of pre-joined semi-finished workpieces.

tailored forming, semi-finished workpiece production, forming, cross wedge rolling

Different challenges arise in cross wedge rolling hybrid parts depending of the material arrangement (serial or coaxial) which need to be investigated fundamentally first.

In cross wedge rolling of serial components, the controlled forming of the joining zone is the greatest challenge. The forming behaviour of the component halves is different, depending on the flow stress of the materials used. In order to allow the forming process to be carried out in a controlled manner, the forming behaviour was first analysed with regard to the displacement and quality of the joining zone, and then possibilities were determined with which the forming can be effected in a targeted manner. For this purpose, the influencing parameters (workpiece temperature, forming speed, cross-section reduction, shoulder and wedge angle) were determined systematically using the Finite Element method, and the investigations were then verified experimentally. In order to influence the forming behaviour the investigations include structural measures (e.g. unequal tool halves) as well as process-related parameters (e.g. unequal temperature distribution).

Cross wedge rolling of coaxial components has other challenges due to the component construction. The aim is to be able to specifically influence the course of the thickness of the applied coating during the forming. Therefore finite element simulations were carried out to determine the influencing parameters. By a systematic investigation of the test parameters according to the DoE method, the layer thickness before the deformation as well as the cross-section reduction are parameters with the greatest influences on the course of the layer thickness after the deformation gave. The results obtained were subsequently verified in experimental tests.

cross wedge rolling, steel, aluminum, joining zone, coating thickness

The volatility of electricity prices is steadily increasing due to the growing expansion of renewable energies. This is particularly observable at the electricity exchange. Small and medium-sized enterprises (SMEs) in the manufacturing sector can save energy costs due to these fluctuations through targeted load management methods. To increase this potential, SMEs need to use smart meters and obtain their electricity at pricest as close to those at the electricity exchange as possible.

power procurement, electricity exchange, load management, electricity costs

The dismantling of disused industrial facilities such as nuclear power plants or refineries is an enormous challenge for the planning and control of the logistic processes. Existing control models do not meet the requirements for a proper dismantling of industrial plants. Therefore, this paper presents an approach for the control of dismantling and post-processing processes (e.g. decontamination) in plant decommissioning. In contrast to existing approaches, the dismantling sequence and depth are selected depending on the capacity utilization of required post-processing processes by also considering individual characteristics of respective dismantling tasks (e.g. decontamination success rate, uncertainties regarding the process times). The results can be used in the dismantling of industrial plants (e.g. nuclear power plants) to reduce dismantling time and costs by avoiding bottlenecks such as capacity constraints.

dismantling management, logistics planning and control models, nuclear power plant dismantling

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

Hybrid forging combines forming of bulky and sheet metal elements in one process step. During the forming of the bulky and sheet metal elements a joining operation is initiated by the energy provided by the forging operation. Thereby component areas with high loads can be designed using a bulky element whereas areas with lower loads can be designed using a sheet metal element. In consequence, significant weight reductions as well as energy savings within the forging process are achievable. The paper presents the development of a hybrid forging process, using a control arm as demonstration part. By the aid of Finite Element Analysis computations the interactions between the main process parameters and the target value process quality are being derived. It will be shown that the bulky element’s shape has a major impact on further process parameters and that the temperature is crucial for material bonding.

FEA, hybrid forging, bulge forming, sheet metal forming

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 forming angle 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 multidirectional forging are described. Then the parameter study will be presented and the influence of the forming angle ? 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 a rising forming angle leads to a higher amount of flash at the bottom of the crankwebs.

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

To reduce production costs of forged parts, different approaches are possible. Especially for valuable materials like titanium, material costs represent a large part of the production costs. Therefore, reducing the initial material can decrease the total costs significantly. In order to identify the potential for improvements, an existing forging sequence was investigated.

For a titanium hip implant, a new forging sequence was developed. To reduce the initially needed material, cross wedge rolling as a preforming operation and die forging with flash brakes was investigated. The influence of the different stages on the final result was analysed and presented in detail. To increase the prediction accuracy of the newly developed flash-reduced forging sequence and to decrease iteration loops of die designs, feasible simulation parameters considering the boundary conditions of the forging environment were investigated. This is done using Finite Element Analysis (FEA), considering form filling, process stability, die stress and press forces. Using cross wedge rolling and die forging with flash brakes, the newly developed forging sequence reduces the flash rate significantly from 69 % to 32 %.

cross wedge rolling,forging, flash-reduced, finite element simulations, flash brakes

In this article, image processing of a binary single track code for determining torque is presented. The aim of the research is to determine the absolute angular position of a shaft and the applied torque. For capturing an image of the binary code two independent imaging modules are used, both allowing for measuring the angular position and rotational speed. Combining both imaging modules, torque can be determined. Position markings are directly applied on the shaft using a laser to ensure a simple integration of the system into any application. The selected technological approach is based on a contactless measurement method using angle differences. The concept of image processing as well as first research results are presented for determining the angular position twice and, thus, the torque applied to the shaft.

image processing, single track code, torque

In multistage hot forging processes, the preform shape is the parameter mainly influencing the final forging result. Nevertheless, the design of multistage hot forging processes is still a trial and error process and, therefore, time consuming. The quality of developed forging sequences strongly depends on the engineer’s experience. To overcome these obstacles this paper presents an algorithm for solving the multi-objective optimization problem in designing preforms. Cross wedge rolled preforms were chosen as subject of investigation. An evolutionary algorithm is introduced to optimize the preform shape taking into account the mass distribution of the final part, the preform volume and the shape complexity. A crucial factor in preform optimization for hot forging processes is the amount of flash. Therefore, an equation for improving the amount of flash is derived. The developed algorithm is tested using two connecting rods with different shape complexities as demonstration parts.

preform optimization, forging, evolutionary algorithms, cross wedge rolling

In order to enable small and medium-sized enterprises to use cross-wedge rolling in the future, existing barriers have been eliminated. For this purpose, a method was developed to enable the design of cross wedge tools using software support. For two demonstrator components, hip implant and common rail, cross-wedge rolling processes were designed. With the cross-wedge rolled preforms, flash-reduced forging sequences could be designed for both demonstrator components. In order to be able to roll the parts industrially at low cost, a cross wedge rolliing machine was designed, manufactured and built at the forging company. The complete process chain of the hip implant was successfully tested.

cross wedge rolling, forming machine, ressource efficiency, hip implant, common rail

In multistage hot forging processes, the preform shape is the parameter mainly influencing the final forging result. Nevertheless, the design of multistage hot forging processes is still a trial and error process and therefore time-consuming. The quality of developed forging sequences strongly depends on the engineer's experience. To overcome these obstacles, this paper presents an algorithm for solving the multi-objective optimization problem when designing preforms. Cross wedge rolled (CWR) preforms were chosen as subject of investigation. An evolutionary algorithm is introduced to optimize the preform shape taking into account the mass distribution of the final part, the preform volume and the shape complexity. The developed algorithm is tested using a connecting rod as a demonstration part. Based on finite element analysis, the implemented fitness function is evaluated, and thus the progressive optimization can be traced.

preforming optimization, hot forging, evolutionary algorithms, cross wedge rolling