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

Publications

Aim: We explore the use of the Open Research Knowledge Graph (ORKG) as such an infrastructure by demonstrating how engineers can utilize the ORKG in innovative ways for communication and (re-)use.

Method: For a use case from the Collaborative Research Center 1153 “Tailored Forming”, we collect, extract, and analyze scientific knowledge on 10 Tailored Forming Process Chains (TFPCs) from five publications in the ORKG. In particular, we semantically describe the TFPCs, i.a., regarding their steps, manufacturing methods, measurements, and results. The usefulness of the data extraction topics, their organization, and the relevance of the knowledge described is examined by an expert consultation with 21 experts.

Results: Based on the described knowledge, we build and publish an ORKG comparison as a detailed overview for communication. Furthermore, we (re-)use the knowledge and answer eight competency questions asked by two domain experts. The validation shows a clear agreement of the 21 experts regarding the examined usefulness and relevance.

Conclusions: Our use case shows that the ORKG as a ready-to-use infrastructure with services supports researchers, including engineers, in sustainably organizing FAIR scientific knowledge. The direct use of the ORKG by engineers is feasible, so the ORKG is a promising infrastructure for innovative ways of communicating and (re-)using FAIR scientific knowledge in engineering sciences, thus advancing this research field.

Tailored forming, scientific knowledge, communication, knowledge graph

It was investigated how a grain refinement can be introduced into a cylindrical rolled piece by means of cross rolling in a flat-jaw design. For this purpose, a non-round shape was rolled in and out again. A theoretical preliminary investigation was used to define a suitable parameter field for experimental evaluation. Metallographic investigations showed that cross-rolling had a positive effect on the microstructure, and IPH will inform the client immediately if it becomes apparent that the estimated costs will be exceeded. The execution of work that leads to the estimated expenditure being exceeded shall only take place after consultation with the client.

Cross-Wedge Rolling, fine grain

A major advantage of flashless precision forging is the saving of resources by avoiding excess material. Especially materials with good flow properties, such as aluminum, sometimes lead to the formation of thin flash. Seals have been developed and experimentally tested to prevent thin flash, i.e. the flow of material into tool gaps. The study presented shows the effectiveness of different sealing materials and the ideal sealing geometry.

thin flash, Sealing concept, precision forging, forming technology, process optimization

This article examines the use of point clouds as a geometric data basis for factory planning and compares different mapping techniques for generating these point clouds. Data and information acquisition is a crucial step in factory planning and thus in developing efficient production processes. In this context, different mapping techniques are analysed: photogrammetry (using drones and action cameras) and LiDAR scans (performed both from drones and from the ground).
The methodology and results of this investigation are discussed in detail, highlighting the advantages and disadvantages of each mapping technique. The focus is on comparing the generated point clouds in terms of completeness, recognisability and geometric tolerance. This comparison provides valuable insights into which technique is best suited for the data acquisition of factory planning. The outlook of this paper includes the further development of recording techniques, particularly with regard to autonomously flying drones. In the future, these could enable more efficient and precise data acquisition for factory planning and thus further strengthen the basis for optimising production processes.

Drone, Photogrammetry, LiDAR, Point cloud, Factory planning, Data acquisition

Around half of the currently 30,000 active wind turbines in Germany will reach the end of their service life by 2030, which is generally defined by the manufacturer as 20 years of operation. The most common strategy for the subsequent use of a wind farm is repowering, provided this is (legally) possible at the respective location. One option for dealing with old turbines is to resell them. At the time of repowering, in Germany after an average of around 17 years, the wind turbines usually still have a remaining operating time of several years before critical parts such as generators fail. 

This article presents a machine learning model for predicting the resale value of used wind turbines. This model can be used to approximately predict the resale value of comparable wind turbines based on certain input parameters such as the power output or the age of the wind turbines. The model was trained using an adjusted data set from an online trading platform for wind turbines. The necessary pre-processing steps such as the removal of extreme outlier values and the addition or replacement of missing or incorrect wind turbinespecific data from a second data source using a self-developed matching algorithm are presented. Finally, the prediction accuracy of different ML algorithms is tested using test data to find the best method for predicting the resale value of wind turbines.

Renewable energies, wind turbines, resale values, machine learning, data science

The article addresses a method for generating project schedules for factory relocations based on a planned layout concept in reorganisation projects. The layout is modelled in a cell grid with cells of uniform edge length. The factory objects are arranged in this grid for both the actual and the target layout state. Further input parameters relate to the required time and personnel resources according to several operations. A two-stage optimisation algorithm is presented, which first checks a given solution for layout feasibility and then generates and solves a project scheduling problem on this basis. Accordingly, elements of the facility layout problem are integrated into a resource constrained project scheduling problem. The process steps of generating and evaluating of the project schedule are further embedded in a genetic algorithm, which successively improves the solution. The project schedules for relocation are evaluated through a combination of the resulting project duration and the downtimes of all factory objects. The aim of the optimisation is to minimise both objective values considering a weighting factor. The article concludes by validating the method using a practical example.

factory planning, relocation planning, reorganisation, project scheduling, project planning

Increasing the service life and process reliability of systems plays an important role in terms of sustainable and economical production. Especially in the field of energy-intensive bulk forming, low scrap rates and long tool lifetimes are business critical. This article describes a modular method for AI-supported process monitoring during hot forming within a screw press. With this method, the following deviations can be detected in an integrated process: the height of the semi-finished product, the positions of the die and the position of the semi-finished product. The method was developed using the CRISP-DM standard. A modular sensor concept was developed that can be used for different screw presses and dies. Subsequently a hot forming-optimized test plan was developed to examine individual and overlapping process deviations. By applying various methods of artificial intelligence, a method for process-integrated detection of process deviations was developed. The results of the investigation show the potential of the developed method and offer starting points for the investigation of further process parameters.

Process monitoring, Wear, Hot forming, Predictive maintenance, Quality management

Wear due to thermal and mechanical stresses is one of the major causes of forging die failure. The assessment of die condition and the associated die life is usually based on experience. This paper presents a method to objectively predict the remaining life of a forging die. With this method a prediction based on optical measurements can be calculated. Practical tests show the possible applications. In addition, force measurements are performed and analyzed to determine how wear affects the force distribution in the die. The assessment based on optical measurements allows objective statements about the remaining tool life of forging dies. The analysis of the force measurements shows potential for predicting tool life but needs further investigation.

You can view the article here.

Process monitoring, wear, optical measurements, force measurement

A continuously growing number of product variants increases the demands on the flexibility of intralogistics transportation. One way to achieve greater flexibility is the use of cellular automated guided vehicles, which can be variably interconnected depending on the size of the product to be transported. This article explains the characteristics of cellular automated guided vehicles and the relationships between influencing variables of the cellular transport system and economic and logistical target variables.

Intralogistics, automated guided vehicles, cellular transport units

The resilience of a supplier is a fundamental factor in the design of supply chains. In supplier selection, resilience is not yet fully taken into account in the evaluation process. As part of a research project, the aim is to create a basis for this and thus integrate resilience as an evaluation criterion into the supplier selection process. The article aims to create an understanding of the various success factors of resilient supply chains.

Resilience, sustainability, supply chain management, risk management

Twelve interviews were conducted with IT system users and providers in order to investigate the adaptability of IT systems in manufacturing companies. A methodical evaluation of the interviews made it possible to identify factors that influence the service life of IT systems. The evaluation shows that, in addition to the technical characteristics, human and organizational aspects in particular are decisive for the long-term use of IT systems.

Information management, people and technology, software

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

By creating ultrafine-grained microstructures, the properties of a material can be improved. Ultrafine-grained microstructure has high strength combined with high ductility. This paper describes how a rolling process can be used to influence the microstructure of a material. The process is investigated by simulation and process windows are determined using statistical design of experiments for practical testing.

Grain refinement, flat-jaw rolling, non-circular rolling, finite element method

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