Dr.-Ing. 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


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

Globalization enables even small and medium-sized companies to sell their products worldwide. This is also accompanied by an increase in the number of direct competitors. As a result of the steadily increasing competition smaller companies in particular are expanding their direct sales and e-commerce activities. This requires resources for packaging, warehousing and order picking. The high competitive pressure to which The high competitive pressure to which companies are exposed can mean that attention to the requirements of the human resource is pushed into the background of entrepreneurial activity. If this resource is not used sustainably, these companies are often at a competitive disadvantage in the short and long term in that they have to find replacements for employees who are absent at short notice. for employees who are absent at short notice and loses important empirical knowledge through affected employees. This represents a competitive disadvantage for small and medium-sized enterprises in particular. The economic damage must also be damage must also be considered: Expenses for recovery and retraining must be incurred for employees who are ill. Furthermore, jobs are more difficult to fill due to an increasing awareness of health issues if the health of each employee is not taken into account. The research project entitled "Automated camera-based ergonomic evaluation of workplaces" (AkEvAp for short) addresses precisely this point in order to use people as a resource for picking in a sustainable manner.

picking, AkEvAp, ergonomics

Supply chain resilience is massively gaining importance for manufacturing companies in times of severe disruption due to crises. Supplier selection is a key aspect of building a resilient supply chain. Currently, however, there is no holistic method for supplier selection that takes resilience into account. This paper therefore presents a research project that aims to develop an assessment measure for resilience in the context of supplier selection. The aim is to consider the existing resilience from the supplier company’s perspective and the required resilience from the selecting company's perspective.

Logistics, Supplier Selection, Resilience, Supply Chain, Supply Chain Management

Volatile markets and increasing product variance lead to more complex internal material flows. In order to cope with this, a significant increase in the flexibility and adaptability of prevailing intralogistics systems is necessary. (Small-scale) modular conveyor systems can be used to make intralogistics more flexible. Obstacles for the practical use are the low distribution as well as the high investment costs. In order to reduce reservations as well as risks, an evaluation and optimization method as well as an applicationoriented planning tool for modular conveyor system layouts were developed in a research project. It enables both planning service providers and users to evaluate modular conveyor systems and to exploit their potential.

Conveyor Technology, Layout Planning, Optimization, Genetic Algorithm, Software

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

Machine learning is already used in many areas of everyday life and offers far-reaching potential in production. At the same time, the efficient use of resources is becoming increasingly important due to the growing relevance of ESG. By implementing machine learning in production to increase resource efficiency, companies can become more effective and efficient while implementing ESG strategies. SMEs, in particular, face a major challenge when it comes to implementation. In addition to the high complexity of Machine Learning applications, there is often a lack of knowledge about suitable application possibilities as well as a lack of conviction about the benefits that can be derived from them. In the following article, applications of Machine Learning to increase resource efficiency along the internal supply chain as well as their potentials are discussed.

Machine Learning, production, resource efficiency

The realization of a planned layout concept represents a complex subtask within factory planning. In particular, the temporal arrangement of the necessary relocation steps, taking into account existing restrictions, is usually carried out manually according to the current state of the art. Therefore, an easy-to-use method for planning a factory move for reorganization projects was developed in a research project, which can be applied by companies in a practical context.

factory planning, removal planning, project scheduling, optimization, operations research

The use of machine learning has already become es-tablished and is applied in many areas of everyday life. Machine Learning is also becoming increasingly important in the field of production and logistics. However, the complex implementation poses major challenges, especially for small and medium-sized enterprises (SMEs). This leads to the fact that many SMEs refrain from using Machine Learning applications. For this reason, IPH – Institut für Integrierte Produktion and IPRI – International Performance Research Institute are working together on the research project „MLready“ to develop an implementation strategy that will enable SMEs to im-plement and use machine learning easily and efficiently.

machine learning, SMEs, production, ML implementation strategy

Although factory planning is widely recognized as a way to significantly enhance manufacturing productivity, the associated costs in terms of time and money can be prohibitive. In this paper, we present a solution to this challenge through the development of a Software-in-the-loop (SITL) framework that leverages an Unmanned Aircraft System (UAS) in an autonomous capacity. The framework incorporates simulated sensors, a UAS, and a virtual factory environment. Moreover, we propose a Deep Reinforcement Learning (DRL) agent that is capable of collision avoidance and exploration using the Dueling Double Deep Q-Network (3DQN) with prioritized experience replay.

Artificial Intelligence, reinforcement learning, Unmanned Aircraft Systems

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 sequence, forging sequence planning, automation

The realization of reorganization projects represents a complex and independent planning task within the framework of factory layout planning. Only little methodical knowledge exists, which considers the temporal, spatial and organizational restrictions in the creation of a schedule. This paper aims to present the interdependencies in the planning and execution of realization projects and thus to provide a basis for discussion for further investigations in the field of scheduling factory relocations for the reorganization of factory objects.

factory planning, relocation planning, project planning, effect modeling

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

The digital development of spaces within the city of Hannover by means of a digital image makes it possible to cover the usage needs of spaces more efficiently and in line with the requirements. The crea-tion of a digital image, which develops new possibilities for access to public space, requires the use of different sensors such as LiDAR sensors and tracking cameras. In order to select suitable sensors that can be used with UAS, the requirements for the overall system are first defined, which are derived in functional requirements for the sensor technology. Subsequently, the degree of fulfilment of the functional requirements by the different sensors

5G, UAS, digital image, digital twin

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

Additive manufacturing enables the economical production of complex components with a high degree of customization. Therefore, the medical industry is using the advantages of additive manufacturing to produce individualized medical devices. Medical devices are subject to special quality control requirements that additive manufacturing processes do not meet yet. This article deals with the introduction of an in situ process monitoring concept using the example of fused deposition modeling. The process monitoring is carried out by a quality model, which accesses the data of a self-developed sensor concept integrated in the printer. This data is analyzed using a machine learning pipeline to predict process and product quality. Thereby, the machine learning pipeline consist of several sequential steps, ranging from data extraction and preprocessing to model training and deployment. The procedure presented for ensuring print quality forms a basis for the production of safety-relevant components in batch size one and extends conventional quality assurance methods in additive manufacturing.

additive manufacturing, quality monitoring, fused deposition modeling, artificial intelligence