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1

Strategy for Compensation of Thermally Induced Displacements in Machine Structures Using Distributed Temperature Field Control

Pöhlmann Patrick, Müller Jens, Ihlenfeldt Steffen

Journal of Machine Engineering

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2024

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Vol. 24, No. 3

5--16

EN

Thermal deformation is a major source of machining errors in modern machine tools. In addition to optimising the machine structure, correcting the axis position values in the numerical control is a common measure to reduce these errors. Another possibility is to directly influence the temperature field of the machine tool in the process, which requires a complex thermo-elastic modelling approach as well as appropriate thermal actuation and measurement capabilities. This paper presents a strategy for controlling the temperature field based on the eigenmodes of the thermal system. The various aspects of the concept are explained using a finite element model of an exemplary structural component. The basis is the modal analysis of the thermal system, which allows the temperature field to be described by independent discrete states. In addition to the placement of thermal sensors and actuators, this work focuses on the design of a suitable control approach. Transient simulation results are used to clearly demonstrate the performance of this method.

2

Simplification of the rolling contact-related lifetime calculation of profiled rail guides with a polynomial regression

Staroszyk Danny, Müller Jens, Ihlenfeldt Steffen

Journal of Machine Engineering

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2024

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Vol. 24, No. 1

60--73

EN

The calculation of the lifespan of profile rail guides is an essential part in the design process of machines. Conventional lifespan models yield good results when calculating lifespan values under a homogeneous distribution of individual rolling contact forces on the raceways. In the case of an uneven load distribution, significantly too low lifespan values are calculated, resulting in a considerable loss of lifetime potential. The novel and experimentally validated rolling contact-based lifespan calculation (RCBL) takes the transferred force on each rolling element into account, resulting in more realistic lifespan values that can be up to 4 times higher than those obtained through the classical method. The disadvantage lies in the complex calculation of the necessary individual rolling contact forces, which until now has been done by using extensive finite element models, along with the computationally intensive optimization problem of the RCBL. To overcome these disadvantages, a method is introduced that efficiently calculates the individual rolling contact forces, taking into account all relevant system elasticities, and pre-solves the RCBL for a variety of potential superimposed load combinations. The results are subsequently approximated through an analytical multiparametric polynomial function and can be utilized with the conventional lifespan formula for rolling bearings.

3

Enabling federated learning services using OPC UA, linked data and GAIA-X in cognitive production

Friedrich Christian, Vogt Stefan, Rudolph Franziska, Patolla Paul, Grützmann Jossy Milagros, Hohmeier Orlando, Richter Martin, Wenzel Ken, Reichelt Dirk, Ihlenfeldt Steffen

Journal of Machine Engineering

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2024

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Vol. 24, No. 2

18--33

EN

Value creation in production is based on collaboration of different stakeholders and requires the secure and sovereign exchange of knowledge. Today, knowledge has mostly been built up individually and is only exchanged in a proprietary manner. This paper presents an exemplary pipeline for federated services in cross-domain and cross-company value creation networks for cognitive production. On the example of collaboratively training of a federated machine learning model, machine tool lifetime is predicted in industrial manufacturing for high-end operating resources (high-quality cutting tools). From the shop floor to the cloud, all service relevant information is structured using existing digital twin standards and a linked data approach. In particular, the Industry 4.0 Asset Administration Shell (AAS) and OPC UA are used for collecting and referencing operational and engineering data. GAIA-X connectors transfer the service relevant data through a shared data space. The solution enables intelligent analysis and decision-making under the prioritization of data sovereignty and transparency and, therefore, acts as an enabler for future collaborative, data-driven manufacturing applications.

4

Concept of Integrating a Hybrid Thermal Error Compensation Into an Existing Machine Tool Control Architecture

Geist Alexander, Yaqoob Muhammad Faisal, Friedrich Christian, Naumann Christian, Ihlenfeldt Steffen

Journal of Machine Engineering

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2024

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Vol. 24, No. 3

32--36

EN

Thermal error compensation via a numeric control (NC) system is a proven option for upgrading the precision of machine tools. The main advantage is the generally cost-effective application, as no changes to the machine design are necessary. Since modern machine tools are equipped with standard numeric controls along with additional functions and integrated temperature sensors in the machine, compensation methods such as a characteristic diagram (CD) based compensation can be implemented. To increase the applicability and reliability of this CD regression method, a hybrid model approach with a virtual thermo-elastic finite element (FE) machine model and a real-time computable structural model of a machine tool was developed. The structural model uses model order reduction to calculate the current load case in real-time using continuously recorded machine data (motor current, axis position, temperatures). It acts as a virtual monitoring application to check, whether the current machine condition still matches the current CD based prediction. If the current load case is not suitable to the active CDs or any other stored CDs, the generation of new CDs is automatically triggered. In this article, the integration of the hybrid compensation method using an FE model and a structural model of a machine tool is methodically demonstrated. The main focus is on the integration of different software and hardware architectures and their interaction.

5

Characterization of the machine behaviour during hollow embossing rolling of metallic bipolar half plates

Wagner Martin, Alaluss Mohaned, Kurth Robin, Tehel Robert, Reuther Franz, Ihlenfeldt Steffen

Journal of Machine Engineering

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2023

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Vol. 23, No. 3

167--178

EN

The hollow embossing rolling of thin-walled high precision components like metallic bipolar half plates is characterized by narrow process windows. Here, the knowledge of interaction between forming machine, roll and process is crucial for the process stability and quality of formed bipolar half plates. In this paper, the elastic machine and forming roll behaviour as a major influence parameter is described and analysed on qualitative level and verified by simulation. This investigation involves a review regarding the process sequence, forces for the hollow embossing rolling of metallic bipolar half plates. By varying the load distributions, the elastic deformations of the forming machine and their forming roll are investigated and analysed regarding process influence and potential for process monitoring.

6

Autonomous assembly and disassembly – key technologies and links for the adaptive self-optimization of future circular production

Ihlenfeldt Steffen, Lorenz Marcel, Frieß Uwe, Fritzsche Rayk

Journal of Machine Engineering

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2023

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Vol. 23, No. 2

5--15

EN

European industry and beyond, faces the challenge of becoming carbon neutral within an unprecedented short timeframe. An important approach to achieve this goal is the transformation of the current economy to a circular economy. In this context, the reuse of technical products as well as their recycling are in the foreground. Flexibility and adaptability are crucial for the competitiveness of companies. Therefore, adaptive and autonomous assembly and disassembly systems are the key. Classically automated assembly systems are inflexible due to a mostly rigid and predefined sequence control and are mostly strongly oriented towards economic criteria. Existing autonomous production cells, with their focus on autonomy and failure-free operation, also reach their limits in terms of adaptivity. For this reason, intelligent systems are needed that are able to act autonomously and without interference, as well as to cope with complex and cognitively demanding situations and tasks.

7

Spatial compliance measurement of a clamping table with integrated force sensors

Friedrich Christian, Ihlenfeldt Steffen

Journal of Machine Engineering

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2022

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Vol. 22, No. 1

70--83

EN

Force sensor integration into machine components is a promising approach to measure spatial process forces, especially, when regarding hexapod structures and kinematics. Rigid still-standing hexapod frameworks, such as clamping tables, are particular suitable for this approach, as no dynamic influences need to be taken into account within the measurement model and they allow a measurement in 6 degrees of freedom. On the other hand, the stiffness of rigid frameworks is reduced by force sensor integration significantly. In addition, many approaches apply joints or flexure hinges to reduced lateral forces and improve the measuring quality, which reduce the stiffness even more. In this contribution, the compliance of a clamping table with integrated force sensors and flexure hinges is determined by experimental measurements using a multiline laser interferometer, by analytic calculation, and by finite element simulation. In conclusion, the amount of stiffness reduction by force sensors and flexure hinges is quantified and different methods for compliance determination are compared.

8

Potential of tool clamping surfaces in forming machines for cognitive production

Alaluss Mohaned, Kurth Robin, Tehel Robert, Wagner Martin, Wagner Nico, Ihlenfeldt Steffen

Journal of Machine Engineering

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2022

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Vol. 22, No. 3

116--131

EN

High reproducibility of forming processes along with high quality expectations of the resulting formed parts demand cognitive production systems. The prerequisite is process transparency, which can be improved by increased knowledge of interdependencies between forming tool and forming machine that affects the tool clamping interface behavior. Due to the arrangement as surfaces transmitting process forces, their closeness to the forming process, and yet machine inherent, tool clamping interface provide greater potential for intelligent monitoring. This paper presents a holistic analysis of the interdependencies at the tool clamping interface. Here, the elastic deflection behavior of the press table and slide with their related clamping surfaces, the frictional slip behavior between the interacting machine components and the used clamping devices are described on qualitative level and verified by simulative analysis. Based on the results, available sensor systems are assessed regarding the capability to monitor the identified phenomena inline.

9

Optimization of characteristic diagram based thermal error compensation via load case dependent model updates

Naumann Christian, Glänzel Janine, Dix Martin, Ihlenfeldt Steffen, Klimant Philipp

Journal of Machine Engineering

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2022

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Vol. 22, No. 2

43--56

EN

The compensation of thermal errors in machine tools is one of the major challenges in ensuring positioning accuracy during cutting operations. There are numerous methods for both the model-based estimation of the thermal tool center point (TCP) deflection and for controlling the thermal or thermo-elastic behavior of the machine tool. One branch of thermal error estimation uses regression models to map temperature sensors directly onto the TCP-displacement. This can, e.g., be accomplished using linear models, artificial neural networks or characteristic diagrams. One of the main limitations of these models is the poor extrapolation behavior with regard to untrained load cases. This paper presents a new method for updating characteristic diagram based compensation models by combining existing models with new measurements. This allows the optimization of the compensation for serial production load cases without the effort of computing a new model. The new method was validated on a 5-axis machining center.

10

Integration of OPC UA information models into Enterprise Knowledge Graphs

Weiss Arno, Ihlenfeldt Steffen

Journal of Machine Engineering

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2022

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Vol. 22, No. 2

138--147

EN

Building repositories of data relevant for enterprise operations requires harmonization of formats and semantics. OPC UA’s nodes-and-references data model shares basic elements with well-established semantic modeling technologies like RDF. This paper suggests the use of transformed OPC UA information models on the higher level of Enterprise Knowledge Graphs. It proposes good practice to integrate the separate domains by representing OPC UA servers as RDF-graphs and subsequently attaching them to Digital Twins embedded in Enterprise Knowledge Graph structures. The developed practice is implemented, applied to combine a server’s structure with an existing knowledge graph containing an Asset Administration Shell and released open source.

11

Compliant joints with remote centre of compliance for the improvement of the motion accuracy of a gantry stage

Pöhlmann Patrick, Peukert Christoph, Merx Marcel, Müller Jens, Ihlenfeldt Steffen

Journal of Machine Engineering

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2022

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Vol. 22, No. 2

68--79

EN

Gantry stages, which consist of two parallel acting servo drives, are commonly used in machine tools. One drawback of this concept is the crosstalk between both drives, when a stiff mechanical coupling is present. This can lead to a limited bandwidth of the position control or to high reaction forces. One way to overcome these issues is the usage of joints to create an additional degree of freedom, which allows the drives to move independently. The design of these joints as compliant elements offers advantages compared to common rolling bearings, such as low friction and the absence of backlash. Another benefit is the variability in the design of the compliant joints allowing for adjustments to the position of each joint’s centre of compliance. Thus, the position of the resulting pivot, and the transfer matrix between the motion of the drives and the motion at the gantry stage’s tool centre point, change as well. This paper addresses the placement of the joint’s centre of compliance in order to improve motion accuracy. For this purpose, joints with modular arranged compliant links have been designed. The characteristics of the joints and their effect on the behaviour of the gantry stage are compared using analytical investigations as well as experimental results.

12

Characterization of tool clamping conditions in forging hammers

Wagner Nico, Tehel Robert, Kurth Robin, Ihlenfeldt Steffen

Journal of Machine Engineering

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2022

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Vol. 22, No. 4

95--114

EN

The present work addresses the topic of die clamping at the forging hammer in the context of the definition of a current requirement profile as well as the evaluation of individual influencing variables on the clamping process. In addition to the presentation of survey results for the requirements profile, the first part focus on the sensible minimization of influencing variables to be investigated and on the verification of a possible evaluation method. Based on this, in the second part exemplary influencing variables on the clamping condition are investigated by means of FEM. Thereby it can be shown by way of example, that the heat flow of the forging process and the friction conditions between the clamping elements have a noteworthy influence on the clamping condition of the dies and that deviations in the clamping force can lead to significant damage.

13

Accuracy assessment of articulated industrial robots using the Extended- and the Loaded-Double-Ball-Bar

Marwitz Johann August, Theissen Nikolas Alexander, Gonzalez Monica Katherine, Friedrich Christian, Hellmich Arvid, Archenti Andreas, Ihlenfeldt Steffen

Journal of Machine Engineering

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2022

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Vol. 22, No. 2

80--98

EN

This research paper outlines the methodology and application of geometric and static accuracy assessment of articulated industrial robots using the Extended Double Ball Bar (EDBB) as well as the Loaded Double Ball Bar (LDBB). In a first experiment, the EDBB is used to assess the geometric accuracy of a Comau NJ-130 robot. Advanced measuring trajectories are investigated that regard poses or axes configurations, which maximize the error influences of individual robot components, and, in this manner, increase the sensitivity for a large number of individual error parameters. The developed error-sensitive trajectories are validated in experimental studies and compared to the circular trajectories according to ISO 203-4. Next, the LDBB is used to assess an ABB IRB6700 manipulator under quasi-static loads of up to 600 Newton using circular testing according to ISO 230-4. The stiffness is identified from the loaded circular trajectories. Then, the stiffness is used to perform a reverse calculation to identify the kinematic errors on the path deviations. The concept is validated in a case study of quasi-static loaded circular testing using the LDBB compared to a Leica AT960 laser tracker (LT).

14

Secure data storage and service automation for cyber physical production systems through distributed ledger technologies

Lemme Gordon, Nölscher Kilian Armin, Bei Erhao, Hermeling Christian, Ihlenfeldt Steffen

Journal of Machine Engineering

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2021

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Vol. 21, No. 1

89--97

EN

In this paper, we use the blockchain technology to design a prototype to secure process data from a 3D-printer. Datastreams are gathered from various sources such as OPC UA servers and autonomous retrofit sensor nodes. This is followed by pre-processing for data reduction, storage in a data model, and the generation of a unique hash value over it. The hash values are stored in a blockchain using appropriate consensus methods, taking into account their temporal origin and production identification number. This also includes the context-related influence of sensor signals on the production process Restrictive access regulations using smart contracts make a partially or fully automated machine tool calibration possible. In this context, we show to realize a process partial or full automation through smart contracts. Physical machine tools and virtual simulations are integrated into the block-chain network to document the stability and performance.

15

Towards safe service ecosystems for production for value networks and manufacturing monitoring

Lemme Gordon, Lemme Diana, Nölscher Kilian Armin, Ihlenfeldt Steffen

Journal of Machine Engineering

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2020

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Vol. 20, No. 1

117--126

EN

In a global sales market with networked production steps and increasing complex machine tools, scaling service ecosystems for production provide an adequate solution for handling the generated data. The existing sensor equipment at current and the extension possibility by the System-of-Systems approach for existing machine tools can offer value-added services by the smart handling of production-related data. It is important to make these data validatable and exchangeable, taking into account to different protection goals. The trust of the individual actors in such a volatile value chain and the different (partly cross-border) value creation partners play an important role. The participation of a large number of these actors creates an attractive overall system (ecosystem) with lots of services and network effects. Concerning data security there are numerous aspects, which have not been adequately answered or taken into account in the use of a service ecosystem in the production environment. The paper discusses a distributed ecosystem for production on a distributed ledger-based service ecosystem, in which services can be mapped in the machine tool environment (e.g. calibration). This technology can be used for secure data exchange in order to discuss traceability and unchangeability of data while maintaining data sovereignty.

16

Thermo-elastic structural analysis of a machine tool using a multi-channel absolute laser interferometer

Deutsch Jessica, Albrecht Tom, Riedel Mirko, Penter Lars, Wiemer Hajo, Müller Jens, Ihlenfeldt Steffen

Journal of Machine Engineering

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2020

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Vol. 20, No. 3

63--75

EN

One of the main errors in the machining accuracy of machine tools is the displacement through thermal induced deformation. Modern design and construction methods aim to optimize the heat flow in the machine to achieve minimum displacement. To enable a further improvement it is essential to know the displacement state of the complete machine structure. However, most measurement methods that are used to capture the influence of a thermal load only measure the displacement of the TCP or individual axes. This paper presents a methodology to capture the complex spatial displacement condition of a state of the art machine tool in one measuring cycle using a multichannel laser interferometer. It describes the development of the measurement model as well as the measurement setup in the workspace of the machine. With measurements according to the presented procedure, it is possible to uncover weak points in the structure of a machine tool and to derive warm-up and cooling strategies.

17

Stiffness evaluation of a hexapod machine tool with integrated force sensors

Friedrich Christian, Kauschinger Bernd, Ihlenfeldt Steffen

Journal of Machine Engineering

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2020

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Vol. 20, No. 1

58--69

EN

Today, in-process force measurement is required by many manufacturing applications, such as process monitoring, quality assurance, or adaptive process control. A very promising force measurement approach bases on sensor-integration into the machine structure and is particularly suitable for hexapod structures and kinematics, where it allows a measurement in 6 degrees of freedom. On the other hand, a sensor integration also affects the machine. Especially for strain-gauge-based force sensors, a stiffness reduction is predicted, as their measuring principle requires a deformation. The practical consequences of these influences are investigated in this contribution. In particular, this work presents extensive experimental studies of the stiffness change caused by sensor integration for a single hexapod strut as well as for the complete hexapod machine tool. The results are evaluated in comparison to compliances of other components, such as the kinematic joints, and to stiffness changes resulting from sensor-integration into the end-effector or the application of a commercial force/torque sensor at the end-effector. In conclusion, the studies support the approach of structure-integrated force measurement for parallel kinematics, as the stiffness loss is rather small in many cases.

18

Fast evaluation of the volumetric motion accuracy of multi-axis machine tools using a Double-Ballbar

Kauschinger Bernd, Friedrich Christian, Zhou Ruiqing, Ihlenfeldt Steffen

Journal of Machine Engineering

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2020

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Vol. 20, No. 3

44--62

EN

The proof of manufacturing accuracy requires continuous verification and crosscheck of the motion accuracy of machine tools. Machining in 5 to 6 axes intensifies the problem of measurement and evaluation of volumetric motion accuracy in up to 6 degrees of freedom (DOF) in the whole workspace. Although, there are many known, even standardized, measuring methods, they are either expensive, time-consuming, not applicable in an operational state of the machine under shop floor conditions, or their significance is limited to only 1 or 2 feed-axes. Appropriate methods to be run regularly, fast and cost-efficient by the machine operator as a performance test are still desired. The article presents a new approach that meets these requirements. It is based on a Double-Ballbar (DBB) with enlarged measuring range and volumetric measuring paths of up to 6 DOF with all feed-axes moving simultaneously during continuous measurement, instead of plane circular paths according to ISO 230-4. After an explanation of the proposed method, the developed DBB device is introduced, including its mechanical and sensor design, the data interface, and results of experimental investigations on the measuring accuracy. Furthermore, relevant problems regarding the design, optimization, and programming of appropriate 6 DOF measuring paths are discussed and experimental results are presented that show the advantage compared to other measuring paths.

19

Compliant joints for the improvement of the dynamic behaviour of a gantry stage with direct drives

Pöhlmann Patrick, Peukert Christoph, Merx Marcel, Müller Jens, Ihlenfeldt Steffen

Journal of Machine Engineering

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2020

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Vol. 20, No. 3

17--29

EN

Gantry stages, which consist of two parallel acting servo drives, are commonly used in machine tools. One drawback of this concept is the crosstalk between both drives due to the structural coupling that can cause stability issues and therefore limits the bandwidth of the position control. This paper deals with the development of compliant joints to solve the coupling between the drives. When compared to solutions containing bearings, the advantages of such flexible elements are low friction and the absence of backlash. To adjust the properties of the joints, packages of spring-steel-sheets are used as compliant links. One design aspect of the flexible joints is a low stiffness relating to the rotation around one specific axis, but a high stiffness relating to the other degrees of freedom. With this method, the dynamic behaviour of the gantry stage is modified and the bandwidth of the controllers can be increased. Additionally, by releasing the mechanical coupling of the drives, the reaction forces the actuators have to provide can be reduced. Both systems with flexible and with rigid connecting elements, are analysed by measured frequency response functions.

20

Simulation-based investigation for heat transfer behavior of steel reinforcements in concrete machine frames and their thermal effects

Glänzel Janine, Geist Alexander, Ihlenfeldt Steffen

Journal of Machine Engineering

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2019

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Vol. 19, No. 3

17--30

EN

The determination of the thermal-elastic behavior is one of the main aspects in the design phase of new machine frames. Prototypically simulation models are used for preliminary investigations, which are based on finite element approaches and usually work with simplified material laws. By the manufacturing of machine frames of concrete steel reinforcements are used to ensure the operation reliability due to the high sensitivity of concrete to tensile stresses. Because of different thermal conductivity and specific heat capacity of steel and concrete the reinforcement has a not negligible influence on the total thermal behavior of the system, which cannot be covered with conventional material laws, e.g. from material libraries. Preliminary investigations show, that a volume fraction more than 1 % of the reinforcement of the total volume can cause a relative error up to ten percent in the temperature field. To reflect the real behavior of reinforced concrete for a machine bed, the influence should be exanimated for two different approaches. Next to the real illustration of the geometry of the reinforcement in the FE-model, decoupled simulation approaches are used on reduced models, which should approach numerically the material behavior of the reinforcement.