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Open Access 2025 | Open Access | Book

Regeneration of Complex Capital Goods

Contributions to the Final Symposium of the Collaborative Research Center 871

Editors: Joerg R. Seume, Berend Denkena, Philipp Gilge

Publisher: Springer International Publishing

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About this book

This open access book compiles the groundbreaking research conducted by the Collaborative Research Center (CRC) 871, centered around the "Regeneration of Complex Capital Goods." This comprehensive work unveils an array of innovative methods developed through CRC 871, designed to revitalize and enhance the functional attributes of these critical assets. From non-destructive characterization of heavily stressed turbine components to the dynamic behavior of regenerated structural elements, each chapter offers a meticulous exploration of diverse facets in the field. The book also addresses the crucial consideration of variability in repair processes and material properties, as well as the comprehensive control of regeneration processes. With insights into simulation-based process design, fast measurement techniques, and resilience-based decision criteria, this volume provides a comprehensive view of the cutting-edge approaches employed. Moreover, readers will find a detailed process chain for condition-based regeneration, offering a practical framework for implementation. Finally, the book sheds light on the importance of targeted public relations in disseminating the invaluable research carried out by Collaborative Research Center 871. This extensive compilation not only showcases the scientific rigor behind maintaining complex capital goods but also demonstrates the collaborative efforts that brought together experts from various fields to push the boundaries of regeneration technology.

Table of Contents

Frontmatter

Inspection and Condition Assessment (Project Area A)

Frontmatter

Open Access

Non-destructive Characterization of Coating and Material Conditions of Heavily Stressed Turbine Components
Abstract
This study presents non-destructive testing techniques for the fast assessment and detailed characterization of turbine blades. Different inspection techniques were developed to realize a flexible and adaptive inspection sequence. In addition to an initial inspection, the advantages of this inspection system with regard to quality assurance measures are also discussed. In this context, the focus is on regeneration. Furthermore, fatigue tests with combined non-destructive testing techniques are presented and the benefit of this new approach for in-situ monitoring of the microstructural evolution is shown.
Maximilian K.-B. Weiss, Sebastian Barton, Hans Jürgen Maier

Open Access

Multiscale Measurement of Blade Geometries with Robot-Supported, Laser-Positioned Multi-sensor-Techniques
Abstract
The regeneration of aircraft engine components requires a thorough assessment of the current condition. Based on this, a suitable repair strategy can be selected. To provide a measurement system, which can be used for the inspection of worn components, various optical measurement methods were combined to create a multi-sensor system. To completely reconstruct complex geometries a 6-axis industrial robot and an additional rotational axis are applied. This robot-assisted multi-sensor system is used to digitise and characterise turbine blades of aircraft engines. The inspection process is non-destructive and different features are measured to acquire a holistic model. The sensors are used to reconstruct the 3-D geometry in different scale ranges and characterise the surface based on reflection properties. Afterwards, the data of each individual sensor are transferred into a uniform coordinate system. To ensure high sensitivity to wear and damage, a model-based system calibration and a data interface for subsequent diagnostics and simulations are essential to provide a reliable assessment of the performance and durability of the inspected components.
Tim Sliti, Markus Kästner, Eduard Reithmeier

Open Access

Exhaust Jet Analysis
Abstract
The aim of project A3 of the Collaborative Research Centre (CRC) 871 is to develop a novel method for automated condition assessment of aircraft engines. The method is based on a combination of numerical simulations, Background Oriented Schlieren (BOS) measurements, and the use of pattern recognition algorithms. The density distribution in the exhaust gas stream of the engine is first measured using the BOS method and then compared with a damage library which was generated numerically through CFD. The automated classification of damage cases can be realized using pattern recognition algorithms. In the third funding period of the CRC, existing reconstruction algorithms used for the calculation of the density distribution in the exhaust gas were improved to increase the accuracy of the BOS measurements. Subsequently, the method was tested experimentally. First, experiments with a model combustion chamber show that 98.5% of all damage cases can be correctly classified by a suitable choice of integral parameters to describe the density distribution in the exhaust gas jet. In a second experimental test, the method was applied to a research engine in order to take realistic impacts into account.
Konstantinos Armanidis, Sebastian Kurth, Viet Nghiem, Joerg R. Seume

Open Access

Adaptable and Component-Protecting Disassembly in the Regeneration Path
Abstract
The disassembly initiates a product’s maintenance and regeneration. In order not to cause any additional damage to the components during disassembly, which would lead to higher repair costs or, in the worst case, to destruction and loss of the components, disassembly must be as gentle as possible on the components. Due to ambiguous causes, such as thermal or mechanical product loads during operation, the unknown product condition is a characteristic uncertainty factor in disassembly. This paper presents approaches and methods on how the disassembly of complex capital goods, which is usually carried out manually, can be automated while still being protective on components and adaptable to varying product conditions. Manual disassembly procedures are substituted using micro impacts induced by a piezo actuator. A learning model predicts optimized process parameters based on varying operational usage scenarios.
Richard Blümel, Annika Raatz

Open Access

Impact of Mixing on the Signature of Combustor Defects
Abstract
Defects in the combustion chamber can negatively influence the performance of an aircraft engine and increase component stress in the turbine. One aim of the Collaborative Research Center 871 is to provide early prediction about the condition of the engine by analysing the signature of the exhaust gas jet. This includes the usage of machine learning techniques and helps to optimise maintenance times and to reduce costs. This topic is linked to the question, how defects in the combustion chamber affect the flow field and how the defect signature is mixed out in the hot gas path. Examples are shown for a simplified ring burning chamber, where several experimental and numerical studies have been done. Additionally, one failure case is described in detail here, where the methodology is applied to a real size gas turbine burning chamber and its subsequent turbine. Furthermore the diffusion theory is generalized to situations with complex geometrical boundary conditions, for instance from the turbine passage channel geometry. This approach is applied on the investigated example case and shows complex thermal diffusion coefficients, being in the order of 10,000–100,000 times larger than the molecular diffusion coefficient. Even these large values allow the determination of burning chamber defects from the exhaust flow pattern.
Panagiotis Ignatidis, Henrik von der Haar, Christoph Hennecke, Friedrich Dinkelacker

Interaction Between Production Processes and the Product's Functional Characteristics (Project Area B)

Frontmatter

Open Access

Near Net Shape Turbine Blade Repair Using a Joining and Coating Hybrid Process
Abstract
Brazing is an established repair technology for turbine blades (air foils and vanes) in the industry and includes multiple process steps that may also require a high degree of manual work. In this study, the development of a near net shape joining and coating hybrid technology for the repair of turbine blades is presented. With this technology, it is possible to shorten the current state-of-the-art process chain for repairing turbine blades. The worn turbine blade receives a repair coating applied by thermal spraying consisting of a nickel based filler metal, a hot gas corrosion protective layer, a bond coat and finally a thermal barrier coating. Subsequently the coated turbine blade is heat treated and a simultaneous brazing and aluminizing process is carried out. The technology presented here brings about technical and economic advantages and allows to shorten the state-of-the-art process chain for repairing turbine blades.
Martin Nicolaus, Kai Möhwald, Hans Jürgen Maier

Open Access

Dexterous Regeneration Cell
Abstract
Complex capital goods such as components from aircraft engines or gas and steam turbines usually have free-form geometry features, individual material deposits, and poor machining accessibility. The recontouring of these components requires increased machine and process flexibility. In sub-project B2, “Dexterous Regeneration Cell”, a dexterous milling repair cell was researched, representing a central component of the real regeneration path in the Collaborative Research Centre (CRC) 871. “Dexterousness” is understood as the ability to carry out a self-optimizing, best possible repair machining. The combination of advanced methods for process design, novel machine tool technologies and adaptive machining functionalities allows the reliable 5-axis recontouring of individual damage cases despite repair-specific variances, influences from upstream processes, and flexibility of the workpiece or tool. In this paper, a force model is created using artificial intelligence to determine variances. Further process knowledge is obtained to minimize shape deviations. Furthermore, the displacement in the recontouring process of turbine blades is carried out with the help of a magnetically guided spindle.
Berend Denkena, Tim Schumacher, Markus Hein

Open Access

Influence of Complex Surface Structures on the Aerodynamic Loss Behaviour of Blades
Abstract
Operating airfoils under mechanical stress in combination with oxidation and corrosion, abrasion wear, and subsequent regeneration results in complex surface structures that influence the performance of aircraft engines. For predicting this impact on performance the authors propose a reduced order model capable of assessing the effect of surface roughness as a basis for making decisions before or during the regeneration process. The accuracy of this model is increased by using improved roughness sensitive transition and turbulence models created for Reynolds-Averaged Navier–Stokes simulations. Experimental studies are carried out to determine the local and integral effect of complex surface structures on blades and on a flat plate. Direct numerical simulations are also performed to study the effect of complex surface structures on a turbulent boundary layer and contribute to improving the accuracy of prediction, which is achieved by using re-calibrating models and taking into account the effect of skewness and anisotropy of complex surface structures on turbine blade losses.
Hendrik Seehausen, Joerg R. Seume

Open Access

Dynamical Behaviour and Strength of Structural Elements with Regeneration Induced Imperfections and Residual Stresses
Abstract
Repair techniques allow to refurbish blades of jet engines and extend the service life of engine components. However, the mechanical properties of the repaired blades commonly differ from those of the nominal blades. The changes in vibration behaviour and stress distribution resulting from the repair processes could significantly impair the structural integrity of blades. This work addresses this evaluation of repair-specific influences on the structural integrity of blades of blade-integrated disks (blisks). Numerical methods are employed to model and analyse the structural changes of different repair designs. Using Finite Element (FE) simulations, the influences of different repair techniques and designs are systematically evaluated and compared. To further improve the maintenance procedures of blisks, a computational scheme is developed, which features the optimization of repair designs according to the inspected damage of the blade. Since the corresponding optimization tasks involve multiple conflicting objectives, multi-objective optimization is carried out to identify Pareto-optimal repair designs.
Ricarda Berger, Raimund Rolfes

Open Access

Single Crystalline Laser Welding
Abstract
Rising demands on engines in the aerospace industry require high engine inlet temperatures in modern gas turbines in order to increase the efficiency. Single-crystal nickel-based superalloys were developed in order to meet these rising demands and confer high pressure turbine blades with the necessary wear and oxidation resistance at high temperatures. The blades of the high-pressure turbine are subject to significant wear due to the high mechanical strain under extreme conditions, which appears in the form of cracks in the single-crystal substrate material. There are no approaches for the restoration of the original material properties since the repair of cracks and erosions by polycrystalline laser cladding can be applied only to a limited extent. The aim of the subproject is the restoration of defect, single-crystal high-pressure turbine blades. This objective was achieved by developing a novel two-stage laser metal deposition process based on simulation, laser process development, process monitoring and temperature control.
Robert Bernhard, Irene Buchbender, Volker Wesling, Stefan Kaierle

Open Access

Regeneration and Surface Hardening of Titanium Components Using the Example of Titanium Alloy Ti6Al4V
Abstract
In this chapter, two different methods for repairing titanium components are presented. These include patch repair and additive repair using metal inert gas welding and wire-and-arc additive manufacturing. The use of inoculant and flux to affect the weld zone is discussed for both repair methods. Using the titanium alloy Ti6Al4V, it is shown that both flux and inoculant can be used to improve the mechanical properties of the overall joint. In addition, local atmospheric nitriding is presented, which is a method to locally harden the surface of titanium components. Surface hardness of more than 800 HV1 were achieved.
J. Torben Carstensen, Thomas Hassel, Hans Jürgen Maier

Consideration of Variability in the Repair Processes and in Material Properties (Project Area C)

Frontmatter

Open Access

Simulation-Based Process Design of Recontouring Technologies
Abstract
Engine manufacturers generate about 50% of their total turnover with maintenance. Damaged parts can either be replaced by spare parts or can be regenerated by e.g. local welding processes. One major step of the manufacturing part of the process chain for regeneration after the material deposition is the removal of excess weld material by cutting, which is called recontouring. Recontouring is often the last process step, which defines the final surface integrity and thus the performance of the repaired parts. Thereby, each component has a batch size of one by reason of individuality. In industrial praxis, the recontouring is done mainly with high manual effort. This results in uncertain and unreproducible repair processes for each component. Hence, a major challenge for recontouring processes is the reduction of the required manual effort by an automated method. In the subproject C1 “simulation-based process design of recontouring technologies”, machining investigations and technological simulations were applied in combination with suitable models for a process adaption in order to reach the required workpiece properties. A special focus was the transition from the undamaged area to the deposited material. Furthermore, a method for effective process planning was developed for the generation of 5-axis milling tool paths. This increases the effectiveness of the process planning by adapting them to the individual shape of the component. The present paper gives an overview of the main results of the investigation of methods for the individual process planning of recontouring technologies based on process simulations. This includes the development of an algorithm for the automatic planning of the recontouring process. A Dexel-based simulation method was developed and experimentally validated which allows the prognosis of the geometrical shape of the material deposition. Based on that, the influence of the resulting material allowance on the recontouring was studied. The aim was the generation of a part quality that satisfies the requirements of the functional review. The evaluation of the part quality was conducted by a Dexel-based technological process simulation of the recontouring process. This allowed the prediction of the workpiece surface as well as the research of the influence of the process parameters on the main residual stresses.
Volker Böß, Berend Denkena, Sven Friebe, Markus Hein

Open Access

Fast Measurement of Complex Geometries Using Inverse Fringe Projection
Abstract
The inspection in confined spaces, for instance inside aircraft engines, is currently performed manually, since the inspection approaches cannot be sufficiently automated. Using a novel sensor system based on the borescopic fringe projection method, such small installation spaces can be inspected with high precision 3D measurements. This provides a basis for a standardization of the inspection processes during maintenance cycles. In order to automate the inspection process, an approach to plan measurement strategies based on ray tracing simulations of the optical measurement is presented. By taking multiple reflections and the corresponding reconstruction failures into account suitable measurement poses are identified. Finally, an in-situ measurement approach to assess the condition of (aero engine) turbine blades and derived damages is presented.
Philipp Middendorf, Markus Kästner, Eduard Reithmeier

Open Access

Regeneration-Induced Variances of Aeroelastic Properties of Turbine Blades
Abstract
Regeneration and wear result in geometric deviations between design intent and reality of turbine blades. These deviations influence the aerodynamic flow field and the aeroelastic behaviour of downstream blades. As an example for the effect of such deviations between modules on blade vibration amplitudes, an experiment is set up to determine the influence of cold streaks, which can occur due to widening of cooling air holes. The vibration amplitude for an off-design point is increased by 20% and for the design point as well. We conclude that the forced response caused by cooling air from the turbine blades must be considered during the design process and for life predictions, especially for higher relative cooling air mass flows. Furthermore, different geometric deviations may occur simultaneously, which can magnify the vibration amplitude even further. A probabilistic process presented here investigates these combined effects. It is shown that a maximum amplitude exists within the given geometric boundaries. Using this information, new safety margins can be set for geometric deviations in the repair or manufacturing process.
Lennart Stania, Joerg R. Seume

Open Access

Prediction of Fatigue Lifetime Using a Wavelet Transformation Induced Multi-time Scaling Method and Xfem
Abstract
Fatigue lifetime prediction due to dynamic crack growth is a significant issue for design and manufacture of engineering components. Damage accumulation in a material on the micro-scale is a main physical mechanism governing crack initiation. For high-cycle fatigue, the number of loading cycles leading to catastrophic fatigue failure can be of the order of millions. The simulation of such processes would be extremely expensive and time-consuming using conventional single time scale methods. In order to overcome this challenging requirement, a wavelet-transformation based multi-time scaling method is successfully adopted in this research to accelerate the prediction of accumulated damage for a large number loading cycles. In this work, the WATMUS technique is coupled with gradient- enhanced damage and the extended finite element method to simulate dynamic crack propagation for a turbine blade.
Jian Sun, Stefan Löhnert, Tengfei Lyu

Open Access

Influence of Regeneration-Induced Mistuning on the Aeroelasticity of Multistage Axial Compressors
Abstract
Current developments in turbomachinery favor blade designs which are characterized by low damping. The associated reduction of structural damping, however, creates new problems such as higher vibration amplitudes. Therefore, accurate predictions of these vibration amplitudes and of the fatigue life become increasingly important. Analyzing multistage machinery by only simulating isolated stages can be insufficient. This is particularly the case during repair processes when mistuning, such as that created by wear and repair, magnifies said amplitudes. In this chapter selected current results of the subproject C6 of the Collaborative Research Center (CRC) 871 are presented, building on the earlier research in the subprojects C3 and C6 focussing on mistuning and aeroelasticity, respectively. First, a simulation approach which accounts for structural and aeroelastic interstage coupling under conditions of mistuning is described, followed by an approach for incorporating large mistuning effects into a reduced order model of a single rotor stage. The former model is used to study the effect of intentional mistuning to decrease the sensitivity to additional mistuning due to wear and repair and to allow for smaller safety margins. The aeroelastic models are validated for a 11/2-stage axial compressor.
Lukas Schwerdt, Niklas Maroldt, Lars Panning-von Scheidt, Joerg Wallaschek, Joerg R. Seume

Comprehensive Control of the Regeneration Processes (Project Area D)

Frontmatter

Open Access

Modeling, Configuration and Assessment of Regeneration Supply Chains
Abstract
In contrast to the conventional manufacturing industry, the regeneration of complex capital goods is subject to additional information uncertainty and disturbances throughout the order processing phase. To achieve a high logistics performance despite these constraints, supply chain configurations and appropriate tools are required to address the resulting challenges. Along a roadmap, this report presents measures and tools that support the reduction of information uncertainty, the description of effects of uncertainty within regeneration planning and control and in regeneration logistics as well as a superordinate assessment and configuration of regeneration supply chains. For forecasting a Bayesian Network based approach is presented. The planning quality that is achieved based on these forecasts is assessed using a descriptive model based on the classic milestone trend analysis. To support logistics oriented regeneration supply chain assessment and configuration an extensive simulation model as well as a model for pool stock dimensioning is presented. These tools and models represent the results of the subproject D1 of the CRC871 that had the overall goal to empower regeneration service providers to establish robust regeneration supply chains.
Torben Lucht, Tammo Heuer, Thorben Kuprat, Steffen C. Eickemeyer, Peter Nyhuis

Open Access

Selection of Efficient Regeneration Modes for the Regeneration of Complex Capital Goods
Abstract
In contrast to the production of new parts, for the regeneration of complex capital goods, various modes of regeneration are often available. They reflect, e.g., different repair technologies and/or different personal qualifications. In this paper, we describe solution approaches for the selection of efficient regeneration modes. Thereby, we simultaneously schedule maintenance tasks as they influence mode selection. Using the example of turbine blades of aircraft engines, we explain the problem setting and the need to consider the customer’s business model. For immobile capital goods such as wind turbines, the selection of efficient regeneration modes requires additional decisions concerning the transportation of personnel and material. We explain this adjacent problem setting and solution approaches. In this context, we include stochastic service times and weather conditions as well as the uncertain condition of the good.
Carolin Kellenbrink, André Schnabel, Marleen Hoppmann, Jan Niklas Woidtke, Stefan Helber

Open Access

Resilience-Based Decision Criteria for Optimal Regeneration
Abstract
Complex capital goods, such as jet engines, are critical to the functioning of modern societies. These sys- tems are exposed to various threats that cannot be prevented entirely. Thus, the concept of resilience – encompassing reliability as well as robustness and recovery in the presence of a disruptive event – is combined with efficient reliability methods to support decision making for complex capital goods. As fundamental step, the current work addresses the generation of a functional model from a physical model based on sensitivity analyses. The developed resilience analysis framework is applied to this model in order to derive conclusions supporting decision maker while incorporating monetary and technical aspects. A combination with the concept of survival signature allows efficient reliability analysis in repeated model evaluations. A novel methodology is developed by amalgamating the non-intrusive stochastic simulation method and the concept of survival signature leading to an significant reduction of the computational effort when considering mixed uncertainties.
Julian Salomon, Matteo Broggi, Michael Beer

Open Access

Interaction of Combined Module Variances and Influence on the Overall System Behaviour
Abstract
Within the Collaborative Research Centre 871, geometrical variances caused by repair procedures and deterioration are evaluated for the turbomachinery of a high-bypass aircraft engine. Part of this evaluation is the investigation of the influence of isolated and combined geometric variances on the overall aircraft engine performance. For this purpose, a virtual twin of a research aircraft engine is developed in sub-project D6. This virtual aircraft engine is based on the Pseudo Bond Graph approach, which allows for transient manoeuvres and the effects of interactions to be simulated with a higher degree of accuracy compared to conventional methods. After validation of the model, a design of experiments is performed to analyse the sensitivities between the variances of modules and engine performance. Within the sensitivity analysis, it is shown that the evaluated steady-state and transient performances are mainly influenced by the high-pressure modules, especially by the mass flow and efficiency variances. Furthermore, it is shown that the sensitivities strongly depend on the operating points. However, significant interactions are found which can be attributed to both the high-pressure and low-pressure modules.
Jan Goeing, Jens Friedrichs

Open Access

Process Chain for Condition-Based Regeneration
Abstract
The regeneration of complex capital goods is dominated by manual labor and experience-based decisions about machining measures. The functional condition, which describes how well a part performs its task, is unknown before and after regeneration. Instead, the target geometries for the regeneration are based on continuity constraints and subjective assessments. In this study, a new type of process chain for condition- based regeneration is developed that selects the machining measures based on the achievable functional condition, the production effort as well as customer requirements. This allows a targeted and efficient decision on a regeneration process based on the customer requirements for the functional condition. A proof-of-concept process chain was successfully built to demonstrate the feasibility of this novel approach. It was shown that the concept is realizable with currently available technologies and that the functional assessment has minor influence on the regeneration time.
Nicolas Nuebel, Joerg R. Seume, Berend Denkena

Open Access

Target-Group Based Public Relations for the Collaborative Research Center 871
Abstract
This report describes the public relations work of the Collaborative Research Centre (CRC) 871 in its third and final funding period together with its partners. The public relations work aimed at two target groups: The expert audience and the general public with a focus on pupils. The expert audience includes research and industry, which were informed via symposiums, exhibitions and events. The general public, and in particular the target group of pupils, was informed about the contents of CRC 871 by events and newly developed interactive and multimedia learning materials. Furthermore, it is described how the public relations work was adapted to the restrictions of the Corona pandemic. For that adaptation, a new concept was developed and implemented in cooperation with the Faculty of Mechanical Engineering at Leibniz University Hannover, which primarily uses virtual media to make the contents of CRC 871 accessible to a broad public, even beyond the end of CRC 871.
Claudia Schomaker, Gunnar Friege, Philipp Gilge, Joerg R. Seume

Open Access

Introduction
Abstract
This volume on the results of the research of the Collaborative Research Center 871 (CRC 871) contains selected papers presented at the Final Symposium of the CRC 871, which took place from March 31 through April 1, 2022 at Leibniz University Hannover, Germany.
Joerg R. Seume
Metadata
Title
Regeneration of Complex Capital Goods
Editors
Joerg R. Seume
Berend Denkena
Philipp Gilge
Copyright Year
2025
Electronic ISBN
978-3-031-51395-4
Print ISBN
978-3-031-51394-7
DOI
https://doi.org/10.1007/978-3-031-51395-4

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