Univ. Prof. Dr. Ing.

Bergs, Thomas

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An Analytical Model for Robot-Based Grinding of Axisymmetric Mold Inserts Using a Rotary Unit

2022 , Tamassia, Eugenio , Hähnel, Sebastian , Pini, Fabio , Grunwald, Tim , Bergs, Thomas , Leali, Francesco

The grinding of mold inserts used for injection molding aims to improve the surface roughness according to precise quality standards. The insert surface must also have a surface topography that facilitates the release of the plastic material at the end of the injection process. In particular, fine machining lines must be parallel to the extraction direction from the mold to avoid the sticking of plastic material and subsequent surface damages compromising the functionality of the finished product. However, this step in the production chain is most often conducted manually. This paper presents an analytical model to grind a truncated cone-shaped mold insert for the mass production of plastic cups. The automated solution consists of a flexible robotic system equipped with a rotating external axis to improve the accessibility of the tool to the surface to be machined. The tool path programming requires the development of an analytical model considering the simultaneous mot ion of the insert and the robot joints. The effectiveness of the developed model is evaluated in terms of final surface quality, grinding lines direction, and total process time. The automated strategy developed can be easily implemented with machine tools and applied to inserts with different axisymmetric geometries.

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Process stabilization through pulsed laser-induced melt pool shaping in dual-beam LMD

2022 , Gipperich, Marius , Gräfe, Stefan , Day, Robin , Bergs, Thomas

Laser Metal Deposition (LMD) is an additive manufacturing process that reaches high deposition rates. Its applications are mainly found in repair, cladding and manufacturing. The two commonly used LMD processes are powder-based (LMD-p) and wire-based (LMD-w). Despite the fact that wire-based LMD uses material more efficiently, its process stability is a major concern. One approach to increase the process stability is superposing a pulsed laser (pw) beam with the conventionally used continuous laser (cw). Previous studies have shown that the metal vapor caused by pulsed laser-induced evaporation in the process zone significantly improves energy absorption. Furthermore, a direct relation between vapor pressure and melt pool form has been demonstrated. In this contribution, we correlate the pw-controlled melt pool geometry to process stability. High-speed camera imaging is employed to evaluate the dynamic melt pool behavior as a function of pw frequency and power. It is shown that irregular melt pool oscillations impairing process stability in conventional LMD-w are reduced if the pulsed laser is added. The melt front is shaped depending on the acting pw-induced pressure. This leads to a more stable interaction between wire and melt pool. Furthermore, the pw pressure changes the welding bead height and width. This cross-sectional geometry has an impact on the resulting waviness in 3D build-up. We also investigate how the waviness influences process stability during multilayer LMD-w. The results demonstrate that the dual beam technology is a promising way to develop more reliable and resource-efficient AM processes.

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Electrochemical Defect Analysis of Additive Manufactured Components

2022 , Sous, Florian , Herrig, Tim , Bergs, Thomas , Karges, Florian , Feiling, Nicole , Zeis, Markus

Due to more freedom in design and flexibility in production, parts produced by additive manufacturing (AM) technologies offer a huge potential for the manufacture of turbomachinery components. Because of the layer by layer built structure, internal defects such as cracks or gaseous pores can occur. These defects considerably reduce the mechanical properties and increase the importance of quality control, especially in the field of turbomachinery. Therefore, in this study, an electrochemical defect analysis (EC-D) of additive manufactured components is introduced, performed, and validated in comparison to a nondestructive X-ray testing of the same part. A test rig was developed, which allows an alternation between electrochemical machining and subsequent optical documentation of each removed layer. The documentation of the surface and the macroscopic defects in the AM-parts are captured by an integrated camera system.

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Tool geometry analysis for plunge milling of lead-free CuZn-alloys

2021 , Baier, Stefan , Kokozinski, Lukas , Schraknepper, Daniel , Bergs, Thomas

Plunge milling is a critical process step in mass manufacturing of rectangular shapes in electrical connector components. These shapes are manufactured by drilling a pilot hole and subsequent plunge milling with a radial offset (pitch) one or more times. The plunged cavity serves as guidance for the final broaching cut. In light of new legislative initiatives, the electronics industry is forced to use lead-free Cu-Zn-Alloys for mass manufacturing of these connectors. The plunging tool is deflected due to the higher cutting forces experienced in machining of lead-free CuZn-alloys in comparison to alloys with lead. This results in an offset of the milled cavity and negatively impacts tool guidance in the subsequent broaching process. Therefore, the geometric tolerances cannot be met. In this paper, the effect of tool geometry and cutting parameters on the workpiece geometry in plunge milling is investigated. The effect of the microstructure of the work-piece materials CuZ n37, CuZn42 and CuZn21Si3P on the tool deflection and cutting force components is examined. The tools used vary regarding the design of the corner in terms of the corner chamfer and the inner shaft thickness. Friction between chips in the tools inner flutes and the cavity walls reduced workpiece accuracy. Improvements were achieved by reducing the width of the cutting corner chamfers, using large inner flutes and applying low cutting parameters.

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Approach for multiscale modeling the thermomechanical tool load in gear hobbing

2022 , Troß, Nico , Brimmers, Jens , Bergs, Thomas

In this report, an approach is presented how a geometric penetration calculation can be combined with FE simulations to a multiscale model, which allows an efficient determination of the thermomechanical load in gear hobbing. FE simulations of the linear-orthogonal cut are used to derive approximate equations for calculating the cutting force and the rake face temperature. The hobbing process is then simulated with a geometric penetration calculation and uncut chip geometries are determined for each generating position. The uncut chip geometries serve as input variables for the derived equations, which are solved at each point of the cutting edge for each generating position. The cutting force is scaled according to the established procedure of discrete addition of the forces along the cutting edge over all individual cross-section elements. For the calculation of the temperature, an approach is presented how to consider a variable chip thickness profile. Based on this, the temperature distribution on the rake face is calculated. The model is verified on the one hand by cutting force measurements in machining trials and on the other hand by an FE simulation of a full engagement of a hob tooth.

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Consideration of micro-interaction in the modeling of generating gear grinding processes

2022 , Oliveira Teixeira, Patricia de , Brimmers, Jens , Bergs, Thomas

In grinding, the interaction between workpiece material and abrasive tool rotating at high speed generates high thermo-mechanical loads in the contact zone. If these loads reach critically high values, workpiece material properties deteriorate. To prevent the material deterioration, several models for thermomechanical analysis of grinding processes have been developed. In the most recent of these models, the thermo-mechanical energy is modelled considering the kinematic contact between the grains from the grinding wheel, the gear material and the chip. The consideration of the kinematic contact has the advantage of enabling the use of thermo-mechanical models on different dressing and grinding parameters without the need of extensive experimental investigations. In order to use these modern thermo-mechanical energy models, a penetration calculation model considering the tool topography, based on the grinding parameters and kinematics of the process is required. Such a kinematic topography analysis specifically for the process of generating gear grinding was not developed so far. This work presents a method for the integration of tool topography in an already existing geometric penetration calculation model for the simulation of generating gear grinding process. The method will allow the analysis of micro-interaction characteristics in the contact zone for the process of generating gear grinding.

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Express Wire Coil Cladding as an Advanced Technology to Accelerate Additive Manufacturing and Coating

2022 , Gipperich, Marius , Riepe, Jan , Day, Robin , Bergs, Thomas

Metal shafts are indispensable components in mobility, energy and mechanical engineering. In such applications, the shafts need to withstand severe mechanical loads, friction, high temperature or corrosive media. This is why shafts are often completely made of high-performance alloys. From a technical point of view, coating an inexpensive base shaft with a thin layer of high-performance material is mostly sufficient to ensure its functionality. Adding functional parts such as bearing seats by Additive Manufacturing (AM) is an advantageous approach to increase flexibility and material efficiency. Reliable and economic AM processes need to be developed further, and laser-based processes such as wire-based Laser Metal Deposition (LMD-w) offer high potential to accomplish this. Due to their low deposition rate, however, LMD processes are not economically competitive with high-speed subtractive technologies. Motivated by this challenge, we present an alternative approach for laser-based shaft cladding. Instead of adding the filler wire continuously, wire coils are wound and preplaced on the shaft. In a second step, laser processing while rotating the part generates a metallurgical bond between the wire and the substrate. In this study, several solid and flux-cored wires were analyzed regarding their suitability for this two-step coil winding and LMD process. The resulting surface state and the welded joint quality are evaulated. Metallographic cross sections show low porosity and small heat-affected zones. Thanks to its good scalability, this innovative process can help strongly increase the build-up rate compared to classic LMD-w.

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Knowledge-Based Adaptation of Product and Process Design in Blisk Manufacturing

2022 , Ganser, Philipp , Landwehr, Markus , Schiller, Sven , Vahl, Christopher , Mayer, Sebastian , Bergs, Thomas

Early and efficient harmonization between product design and manufacturing represents one of the most challenging tasks in engineering. Concepts such as simultaneous engineering aim for a product creation process, which addresses both, functional requirements as well as requirements from production. However, existing concepts mostly focus on organizational tasks and heavily rely on the human factor for the exchange of complex information across different domains, organizations, or systems. Nowadays product and process design make use of advanced software tools such as computer-aided design, manufacturing, and engineering systems (CAD/CAM/CAE). Modern systems already provide seamless integration of both worlds in a single digital environment to ensure a continuous workflow. Yet, for the holistic harmonization between product and process design, the following aspects are missing: (i) the digital environment does not provide a complete and data consistent digital twin of the component; this applies especially to the process design and analysis environment, (ii) due to the lack of process and part condition data in the manufacturing environment, an adaptation of product and process design for a balanced functionality and manufacturability is hindered, and (iii) systematic long-term data analytics across different product and process designs with the ultimate goal to transfer knowledge from one product to the next and to accelerate the entire product development process is not considered. This paper presents an exploration concept which couples product design (CAD), process design (CAM), process simulation (CAE), and process adaptation in a single software system. The approach provides insights into correlations and dependencies between input parameters of product/process design and the process output. The insights potentially allow for a knowledge-based adaptation, tackling well-known optimization issues such as parameter choice or operation sequencing. First results are demonstrated using the example of a blade integrated disk (blisk). Early and efficient harmonization between product design and manufacturing represents one of the most challenging tasks in engineering. Concepts such as simultaneous engineering aim for a product creation process, which addresses both, functional requirements as well as requirements from production. However, existing concepts mostly focus on organizational tasks and heavily rely on the human factor for the exchange of complex information across different domains, organizations, or systems. Nowadays product and process design make use of advanced software tools such as computer-aided design, manufacturing, and engineering systems (CAD/CAM/CAE). Modern systems already provide seamless integration of both worlds in a single digital environment to ensure a continuous workflow. Yet, for the holistic harmonization between product and process design, the following aspects are missing: (i) the digital environment does not provide a complete and data consistent digital twin of the component; this applies especially to the process design and analysis environment, (ii) due to the lack of process and part condition data in the manufacturing environment, an adaptation of product and process design for a balanced functionality and manufacturability is hindered, and (iii) systematic long-term data analytics across different product and process designs with the ultimate goal to transfer knowledge from one product to the next and to accelerate the entire product development process is not considered. This paper presents an exploration concept which couples product design (CAD), process design (CAM), process simulation (CAE), and process adaptation in a single software system. The approach provides insights into correlations and dependencies between input parameters of product/process design and the process output. The insights potentially allow for a knowledge-based adaptation, tackling well-known optimization issues such as parameter choice or operation sequencing. First results are demonstrated using the example of a blade integrated disk (blisk).

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Surface Modification of Inconel 718 by Robot-Guided Centrifugal Finishing and Vibratory Finishing

2022 , Ohlert, Marius , Prinz, Sebastian , Barth, Sebastian , Bergs, Thomas

The main task of mass finishing processes is the significant reduction of the surface roughness of a workpiece. Since robot-guided centrifugal finishing has a material removal rate up to Q''w<500mm/h, it is able to reduce the surface roughness in a shorter process time than vibratory finishing. Furthermore, robot-guided centrifugal finishing is a promising manufacturing technology to induce residual compressive stresses even for high-temperature materials, such as Inconel 718. In order to show the potential of robot-guided centrifugal finishing as a surface modification process, experimental tests were carried out. Within the experimental tests, Inconel 718 was machined by vibratory finishing and robot-guided centrifugal finishing. By using robot-guided centrifugal finishing the maximum induced residual compressive stress was 58% higher compared to vibratory finishing. The findings were derived from the difference in terms of transfer of the kinetic energy between the abrasive media and the workpiece in robot-guided centrifugal finishing and vibratory finishing.

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Determination of the Level of Automation for Additive Manufacturing Process Chains

2021 , Horstkotte, Rainer , Bruning, Benedikt , Prümmer, Marcel , Arntz, Kristian , Bergs, Thomas

Industrial manufacturing is confronted with increased cost pressure due to international competition. The use of automation solutions can help to optimally exploit existing potentials and react to market competitors. In particular, increased productivity and shorter cycle times lead to reduced costs and increased capabilities. New manufacturing technologies can also help to achieve an advantage over market competitors. In recent years, additive manufacturing technologies in particular have gained in importance. Laser Powder Bed Fusion (L-PBF) is an additive manufacturing (AM) technology that enables the production of highly complex and individualized metal components. A significant disadvantage of L-PBF is the required post-processing of additive manufactured parts, which is necessary to remove auxiliary structures, separate the workpieces from the substrate plate and obtain high precision as well as low surface roughness. Automation of these post-processes is a crucial factor for increasing productivity and thus for further industrialization of L-PBF. In order to exploit this potential optimally, the level of automation has to be determined. In this paper, a methodology is presented that enables the determination of the level of automation for the additive process chain with L-BPF. The focus is on evaluating the level of automation of individual manufacturing technologies due to consideration of technology-specific requirements and characteristics. The scope of the analysis is not limited to technologies; handling processes are also taken into account. A differentiated e valuation of the level of automation is enabled by the definition of technology-specific and cross-technology sub-tasks.

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