@article{SommerGoetzendorferEsenetal.2021, author = {Sommer, David and G{\"o}tzendorfer, Babette and Esen, Cemal and Hellmann, Ralf}, title = {Design Rules for Hybrid Additive Manufacturing Combining Selective Laser Melting and Micromilling}, series = {Design and Post Processing for Metal Additive Manufacturing}, volume = {14}, journal = {Design and Post Processing for Metal Additive Manufacturing}, number = {19}, doi = {https://doi.org/10.3390/ma14195753}, pages = {1 -- 23}, year = {2021}, abstract = {We report on a comprehensive study to evaluate fundamental properties of a hybrid manufacturing approach, combining selective laser melting and high speed milling, and to characterize typical geometrical features and conclude on a catalogue of design rules. As for any additive manufacturing approach, the understanding of the machine properties and the process behaviour as well as such a selection guide is of upmost importance to foster the implementation of new machining concepts and support design engineers. Geometrical accuracy between digitally designed and physically realized parts made of maraging steel and dimensional limits are analyzed by stripe line projection. In particular, we identify design rules for numerous basic geometric elements like walls, cylinders, angles, inclinations, overhangs, notches, inner and outer radii of spheres, chamfers in build direction, and holes of different shape, respectively, as being manufactured by the hybrid approach and compare them to sole selective laser melting. While the cutting tool defines the manufacturability of, e.g., edges and corners, the milling itself improves the surface roughness to Ra < 2 µm. Thus, the given advantages of this hybrid process, e.g., space-resolved and custom-designed roughness and the superior geometrical accuracy are evaluated. Finally, we exemplify the potential of this particular promising hybrid approach by demonstrating an injection mold with a conformal cooling for a charge socket for an electro mobile}, subject = {Selektives Laserschmelzen}, language = {en} } @article{SommerPapeEsenetal.2022, author = {Sommer, David and Pape, Dominik and Esen, Cemal and Hellmann, Ralf}, title = {Tool Wear and Milling Characteristics for Hybrid Additive Manufacturing Combining Laser Powder Bed Fusion and In Situ High-Speed Milling}, series = {Ultra-Precision Manufacturing Technology for Difficult-to-Machine Materials}, volume = {15}, journal = {Ultra-Precision Manufacturing Technology for Difficult-to-Machine Materials}, number = {3}, doi = {https://doi.org/10.3390/ma15031236}, pages = {1 -- 13}, year = {2022}, abstract = {We report on milling and tool wear characteristics of hybrid additive manufacturing comprising laser powder bed fusion and in situ high-speed milling, a particular process in which the cutter mills inside the powder bed without any cooling lubricant being applicable. Flank wear is found to be the dominant wear characteristic with its temporal evolution over utilization period revealing the typical s-shaped dependence. The flank wear land width is measured by microscopy and correlated to the achievable surface roughness of milled 3D-printed parts, showing that for flank wear levels up to 100 μm a superior surface roughness below 3 μm is accessible for hybrid additive manufacturing. Further, based on this correlation recommended tool, life scenarios can be deduced. In addition, by optimizing the finishing tool start position and the number of afore-built layers, the milling process is improved with respect to the maximum millable angle for undercut surfaces of 3D-printed parts to 30° for the roughing process and to 40° for the entire machining process including finishing}, subject = {Hochgeschwindigkeitsfr{\"a}sen}, language = {de} } @article{SommerEsenHellmann2023, author = {Sommer, David and Esen, Cemal and Hellmann, Ralf}, title = {Static and Dynamic Mechanical Behaviour of Hybrid-PBF-LB/M-Built and Hot Isostatic Pressed Lattice Structures}, series = {Mechanical Properties of Polymeric, Metallic, and Composite Materials}, volume = {16}, journal = {Mechanical Properties of Polymeric, Metallic, and Composite Materials}, number = {9}, doi = {https://doi.org/10.3390/ma16093556}, pages = {1 -- 14}, year = {2023}, abstract = {We report on a comprehensive study of the mechanical properties of maraging steel body-centred cubic lattice structures fabricated by a hybrid additive manufacturing technology that combines laser powder bed fusion with in situ high-speed milling. As the mechanical properties of additive manufactured components are inferior to, e.g., cast components, surface modifications can improve the mechanical behaviour. Different hybrid additive manufacturing technologies have been designed using additive and subtractive processes, improving process quality. Following this, mechanical testing is performed with respect to static tensile properties and dynamic stress, hardness, and porosity, comparing specimens manufactured by laser powder bed fusion only to those manufactured by the hybrid approach. In addition, the influence of different heat-treatment techniques on the mechanical behaviour of the lattice structures is investigated, namely solution and aging treatment as well as hot isostatic pressing. Thus, the influence of the superior surface quality due to the hybrid approach is evaluated, leading to, e.g., an offset of about 14-16\% for the static testing of HIP lattice structures. Furthermore, the dynamic load behaviour can be improved with a finished surface, heading to a shift of the different zones of fatigue behaviour in the testing of hybrid-built specimens.}, subject = {Isostatisches Heißpressen}, language = {de} } @article{SommerHornungEsenetal.2024, author = {Sommer, David and Hornung, Simon and Esen, Cemal and Hellmann, Ralf}, title = {Surface roughness optimization of hybrid PBF-LB/M-built Inconel 718 using in situ high-speed milling}, series = {The International Journal of Advanced Manufacturing Technology}, volume = {132}, journal = {The International Journal of Advanced Manufacturing Technology}, number = {3-4}, publisher = {Springer Science and Business Media LLC}, issn = {0268-3768}, doi = {http://dx.doi.org/10.1007/s00170-024-13382-5}, pages = {1741 -- 1751}, year = {2024}, abstract = {AbstractWe report on the optimization of the surface roughness of hybrid additive manufactured Ni superalloys, combining a conventional laser powder bed fusion process with in situ high-speed milling. This remarkable hybrid approach has only recently been applied to different steel types and barely to Ni superalloys which opposite to steel appear to be challenging for milling processes, particularly within the powderbed of laser powder bed fusion. Different influencing factors on the surface roughness are varied in this study, following the Taguchi method. Their effect is evaluated with respect to the average surface roughness and the maximum surface roughness. The signal-to-noise ratio for the varied parameters infeed, z-pitch, feed rate, and spindle speed is calculated, determining their relevance on the surface roughness, and defining an optimal parameter combination. As the surface quality is optimized to \$\$\varvec{R_a=0.47\, \mu m}\$\$ R a = 0.47 μ m , the definition of the optimal parameter combination is of the highest relevance for the application of this novel manufacturing approach for Inconel. Using linear regression, the resulting surface roughness of these parameters is predicted, getting validated by the experimental evaluation. Due to a further analysis, including EDX analysis and a quantitative element analysis at different positions of the flank of the milling cutter, wear characteristics as well as the dissipation of the coating of the milling cutter are detected. The flank wear and the resulting breakage of the cutting edge are defined as the main reasons of a rising surface roughness.}, subject = {Hochgeschwindigkeitsfr{\"a}sen}, language = {en} } @inproceedings{SommerHornungEsenetal.2024, author = {Sommer, David and Hornung, Simon and Esen, Cemal and Hellmann, Ralf}, title = {Optimization of mechanical properties of additive manufactured IN 718 parts combining LPBF and in-situ high-speed milling}, series = {Laser 3D Manufacturing XI}, booktitle = {Laser 3D Manufacturing XI}, editor = {Gu, Bo and Chen, Hongqiang}, publisher = {SPIE}, doi = {http://dx.doi.org/10.1117/12.3000952}, year = {2024}, subject = {Hochgeschwindigkeitsfr{\"a}sen}, language = {en} } @inproceedings{SommerSafiEsenetal.2024, author = {Sommer, David and Safi, Abdulrahman and Esen, Cemal and Hellmann, Ralf}, title = {Additive manufacturing of Nickel-based superalloy: optimization of surface roughness using integrated high-speed milling}, series = {Laser 3D Manufacturing XI}, booktitle = {Laser 3D Manufacturing XI}, editor = {Gu, Bo and Chen, Hongqiang}, publisher = {SPIE}, doi = {http://dx.doi.org/10.1117/12.3000972}, year = {2024}, subject = {Hochgeschwindigkeitsfr{\"a}sen}, language = {en} } @article{SommerHornungEsenetal.2025, author = {Sommer, David and Hornung, Simon and Esen, Cemal and Hellmann, Ralf}, title = {Design Guide for Hybrid-Additive Manufacturing of Inconel 718 Combining PBF-LB/M and In Situ High-Speed Milling}, series = {Journal of Manufacturing and Materials Processing}, volume = {9}, journal = {Journal of Manufacturing and Materials Processing}, number = {3}, publisher = {MDPI AG}, issn = {2504-4494}, doi = {http://dx.doi.org/10.3390/jmmp9030088}, year = {2025}, abstract = {As the correlation between design rules and process limitations is of the upmost importance for the full exploitation of any manufacturing technology, we report a design guide for hybrid-additive manufacturing of Inconel 718. Basic limitations need to be evaluated for this particular hybrid approach that combines laser powder bed fusion (PBF-LB/M) and in situ high-speed milling. Fundamental geometric limitations are examined with regard to the minimum feasible wall thickness, cylinders, overhanging structures, and chamfers. Furthermore, geometrical restrictions due to the integrated three-axis milling process with respect to inclinations, inner angles, notches, and boreholes are investigated. From these findings, we derive design guidelines for a reliable build process using this hybrid manufacturing. Additionally, a design guideline for the hybrid-additive manufacturing approach is presented, depicting a step-to-step guide for the adjustment of constructions. To demonstrate this, a powder nozzle for a direct energy deposition (DED-LB/M) process is redesigned following the previously defined guidelines. This redesign encompasses analysis of the existing component and identification of problematic areas such as flat angles, leading to a new construction that is suitable for a hybrid-additive manufacturing approach.}, subject = {Hochgeschwindigkeitsfr{\"a}sen}, language = {en} } @article{SommerTruetschEsenetal.2025, author = {Sommer, David and Truetsch, Ben and Esen, Cemal and Hellmann, Ralf}, title = {Fractographic Analysis and Fatigue Behavior of Additively Manufactured Ni-Superalloy Components with Post Processing Heat Treatment and Hot Isostatic Pressing}, series = {Advanced Engineering Materials}, volume = {27}, journal = {Advanced Engineering Materials}, number = {12}, publisher = {Wiley}, issn = {1438-1656}, doi = {http://dx.doi.org/10.1002/adem.202500078}, year = {2025}, abstract = {A report is made on a study of mechanical properties and fractographic characteristics of laser powder bed fusion (PBF-LB/M)-built Inconel 718, performing heat treatments and hot-isostatic pressing. For this, tensile components are heat-treated by different processes, as namely stress relief (SR), SR and double aging (SR + DA), and hot-isostatic pressing are conducted. For the mechanical testing, the ultimate tensile strength (UTS) as well as the fatigue behavior are evaluated, examining differences in maximum load behavior, elongation, and the different regimes of fatigue. As changes in material structure can be observed, the sole SR leads to a diminished UTS, while the combination of SR + DA develops an UTS of Rm = 1277 MPa. Within the fatigue behavior, the HIP shows a very balanced material structure with an increased high cycle and very high cycle regime, as the texture gets homogenized during the heat treatment. The metallographic analysis can quantify the material changes, as the density and the hardness are improved by virtue of the heat treatments. Furthermore, the fractographic analysis shows the differences in fracture behavior, arising due to the microstructural changes, as crack initiation points, crack propagation, and forced fractures can be categorized by scanning electron microscopy.}, subject = {Rapid Prototyping, Fertigung}, language = {en} } @inproceedings{SommerTruetschEsenetal.2025, author = {Sommer, David and Truetsch, Ben and Esen, Cemal and Hellmann, Ralf}, title = {Microstructural Fracture Behaviour of PBF-LB/M Inconel 718 Components within different HIP Processes}, series = {Lasers in Manufacturing, M{\"u}nchen, Juni 2025}, booktitle = {Lasers in Manufacturing, M{\"u}nchen, Juni 2025}, year = {2025}, abstract = {We report on a study of different hot isostatic pressing (HIP) cycles, improving the mechanical properties of additively manufactured Inconel 718 components. For this, PBF-LB/M built components are post-processed by different HIP sequences, as gas pressure and processing time are varied, leading to differences in microstructure and material characteristics. Static and dynamic mechanical testing are performed, evaluating the changes in mechanical properties with particular focus on the ultimate tensile strength and endurance limit. Furthermore, metallographic analysis is employed to investigate the achieved density and microhardness. Microstructural analysis, showing the grain boundaries, is used to identify generated phases and precipitations of the material matrix. Moreover, the fracture behaviour is classified by grain deformation during mechanical testing. As the HIP leads to microstructural changes of Inconel 718 components, mechanical properties can be improved significantly, enhancing the ultimate tensile strength and simultaneously the endurance limit.}, subject = {Isostatisches Heißpressen}, language = {de} } @inproceedings{SommerPetersEsenetal.2025, author = {Sommer, David and Peters, Maximilian and Esen, Cemal and Hellmann, Ralf}, title = {Influence of in-situ high-speed milling within a hybrid additive manufacturing approach on the fatigue behaviour of Inconel 718 lattice structures}, series = {Lasers in Manufacturing, M{\"u}nchen, Juni 2025}, booktitle = {Lasers in Manufacturing, M{\"u}nchen, Juni 2025}, year = {2025}, abstract = {As lattice structures in various designs are used in additive manufacturing for lightweight components, the mechanical characterisation and fracture behaviour is of upmost importance for their industrial application. In this study, the fatigue behaviour of Inconel 718 lattice structures is evaluated, comparing sole PBF-LB/M to a hybrid additive manufacturing process combining PBF-LB/M with in-situ high-speed milling. At first, the static and dynamic mechanical load behaviour of different packing densities is analysed, determining the compressive strength and the endurance limit. Secondly, hybrid additive manufactured components are compared to PBF-LB/M built parts with respect to these mechanical properties, revealing improved compressive properties and modified regimes of fatigue. In addition, differences in fracture behaviour are qualified by fractographic and surface analysis. Overall, it can be summarized that the mechanical load characteristics, especially the fatigue behaviour, are improved for hybrid additively manufactured components with a superior surface quality of Ra < 1 µm.}, subject = {Hochgeschwindigkeitsfr{\"a}sen}, language = {de} } @article{SommerHornungEsenetal.2025, author = {Sommer, David and Hornung, Simon and Esen, Cemal and Hellmann, Ralf}, title = {In situ high-speed milling and thermal post-processing for the optimization of fatigue behaviour of additive-manufactured IN718 components}, series = {Journal of Materials Research}, volume = {40}, journal = {Journal of Materials Research}, number = {16}, publisher = {Springer Science and Business Media LLC}, issn = {0884-2914}, doi = {https://doi.org/10.1557/s43578-025-01656-x}, pages = {2388 -- 2401}, year = {2025}, abstract = {We report on the optimization of tensile properties and fatigue behaviour of Laser Powder Bed Fusion (PBF-LB/M)-built IN718 components employing an innovative hybrid additive-subtractive technology and various heat treatments. The hybrid approach comprises PBF-LB/M with in situ high-speed milling. Double Ageing, solution and ageing treatment, as well as Hot Isostatic Pressing are used to improve ultimate tensile strength and endurance limit. As a result, the advantages of the hybrid-machined components are clearly demonstrated by their improved mechanical properties. These enhanced properties are associated to changes in microstructure, which are identified as precipitations of IN718. Furthermore, crack initiation and crack growth for high cycle numbers as well as sudden fractures are determined.}, subject = {Hochgeschwindigkeitsfr{\"a}sen}, language = {en} } @article{SommerTruetschEsenetal.2025, author = {Sommer, David and Truetsch, Ben and Esen, Cemal and Hellmann, Ralf}, title = {Effect of Hot Isostatic Pressing and Sequenced Heat Treatment on the Mechanical Properties of Hybrid Additive Manufactured Inconel 718 Components}, series = {Journal of Manufacturing and Materials Processing}, volume = {9}, journal = {Journal of Manufacturing and Materials Processing}, number = {11}, publisher = {MDPI AG}, issn = {2504-4494}, doi = {https://doi.org/10.3390/jmmp9110378}, year = {2025}, abstract = {We report on the effect of hot isostatic pressing combined with solution and ageing treatment in different sequences on the mechanical properties of Inconel 718 specimens, which in turn have been fabricated by a hybrid additive manufacturing approach. The latter combines conventional laser powder bed fusion and in-situ high speed milling, yielding superior surface quality as being quantified by Ra about 1 μm. In a comparative study between hybrid additively manufactured parts and those built without milling, we find that, in general, any combination of heat treatment leads to a higher ultimate tensile strength and an improved endurance limit, while, however, hot isostatic pressing affects these figures of merit most. In addition, metallographic analysis reveals increased density and hardness for hot isostatic pressed parts due to precipitation hardening. These improvements of the mechanical properties are found to be even more pronounced when the printed parts are manufactured by the hybrid additive approach, i.e., for parts with improved surface conditions.}, subject = {Isostatisches Heißpressen}, language = {en} } @article{SommerPetersEsenetal.2026, author = {Sommer, David and Peters, Maximilian and Esen, Cemal and Hellmann, Ralf}, title = {Enhancing mechanical properties of double-periodic lattice structures using hybrid-additive manufacturing}, series = {The International Journal of Advanced Manufacturing Technology}, volume = {142}, journal = {The International Journal of Advanced Manufacturing Technology}, number = {7-8}, publisher = {Springer Science and Business Media LLC}, issn = {0268-3768}, doi = {https://doi.org/10.1007/s00170-025-17373-y}, pages = {4065 -- 4071}, year = {2026}, abstract = {We report on a study of the mechanical properties of hybrid-additive manufactured Inconel 718 double-periodic lattice structures. For this, a hybrid approach, combining Laser Powder Bed Fusion (PBF-LB/M) and in-situ high-speed milling, is employed. Within this technique, the PBF-LB/M process is interrupted after several layers, as the milling process starts, enabling a machining of inlaying structures.}, subject = {Hochgeschwindigkeitsfr{\"a}sen}, language = {en} } @article{SommerHornungEsenetal.2025, author = {Sommer, David and Hornung, Simon and Esen, Cemal and Hellmann, Ralf}, title = {Design Guide for Hybrid-Additive Manufacturing of Inconel 718 Combining PBF-LB/M and In Situ High-Speed Milling}, series = {Journal of Manufacturing and Materials Processing}, volume = {9}, journal = {Journal of Manufacturing and Materials Processing}, number = {3}, publisher = {MDPI AG}, issn = {2504-4494}, doi = {https://doi.org/10.3390/jmmp9030088}, year = {2025}, abstract = {As the correlation between design rules and process limitations is of the upmost importance for the full exploitation of any manufacturing technology, we report a design guide for hybrid-additive manufacturing of Inconel 718. Basic limitations need to be evaluated for this particular hybrid approach that combines laser powder bed fusion (PBF-LB/M) and in situ high-speed milling. Fundamental geometric limitations are examined with regard to the minimum feasible wall thickness, cylinders, overhanging structures, and chamfers. Furthermore, geometrical restrictions due to the integrated three-axis milling process with respect to inclinations, inner angles, notches, and boreholes are investigated. From these findings, we derive design guidelines for a reliable build process using this hybrid manufacturing. Additionally, a design guideline for the hybrid-additive manufacturing approach is presented, depicting a step-to-step guide for the adjustment of constructions. To demonstrate this, a powder nozzle for a direct energy deposition (DED-LB/M) process is redesigned following the previously defined guidelines. This redesign encompasses analysis of the existing component and identification of problematic areas such as flat angles, leading to a new construction that is suitable for a hybrid-additive manufacturing approach.}, subject = {Hochgeschwindigkeitsfr{\"a}sen}, language = {en} } @article{SommerTruetschEsenetal.2025, author = {Sommer, David and Truetsch, Ben and Esen, Cemal and Hellmann, Ralf}, title = {Fractographic Analysis and Fatigue Behavior of Additively Manufactured Ni-Superalloy Components with Post Processing Heat Treatment and Hot Isostatic Pressing}, series = {Advanced Engineering Materials}, volume = {27}, journal = {Advanced Engineering Materials}, number = {12}, publisher = {Wiley}, issn = {1438-1656}, doi = {https://doi.org/10.1002/adem.202500078}, year = {2025}, abstract = {A report is made on a study of mechanical properties and fractographic characteristics of laser powder bed fusion (PBF-LB/M)-built Inconel 718, performing heat treatments and hot-isostatic pressing. For this, tensile components are heat-treated by different processes, as namely stress relief (SR), SR and double aging (SR + DA), and hot-isostatic pressing are conducted. For the mechanical testing, the ultimate tensile strength (UTS) as well as the fatigue behavior are evaluated, examining differences in maximum load behavior, elongation, and the different regimes of fatigue. As changes in material structure can be observed, the sole SR leads to a diminished UTS, while the combination of SR + DA develops an UTS of R m  = 1277 MPa. Within the fatigue behavior, the HIP shows a very balanced material structure with an increased high cycle and very high cycle regime, as the texture gets homogenized during the heat treatment. The metallographic analysis can quantify the material changes, as the density and the hardness are improved by virtue of the heat treatments. Furthermore, the fractographic analysis shows the differences in fracture behavior, arising due to the microstructural changes, as crack initiation points, crack propagation, and forced fractures can be categorized by scanning electron microscopy.}, subject = {Nickellegierung}, language = {en} } @article{SommerHornungEsenetal.2025, author = {Sommer, David and Hornung, Simon and Esen, Cemal and Hellmann, Ralf}, title = {Evaluation of the Impact of Heat Treatment Processes and Surface Conditions on the Mechanical Properties of PBF-LB/M-Built Inconel 718 Components}, series = {Materials Science Forum}, volume = {1155}, journal = {Materials Science Forum}, publisher = {Trans Tech Publications, Ltd.}, issn = {1662-9752}, doi = {https://doi.org/10.4028/p-9gR9cI}, pages = {11 -- 17}, year = {2025}, abstract = {A study of the mechanical properties of hybrid additive manufactured IN718 components is presented, optimising mechanical properties due to an in-situ high-speed milling and different heat treatment processes. At first, the impact of different heat treatment processes is investigated, as the changes in microstructure during the process lead to different mechanical properties. Static and dynamic mechanical load behaviour is tested, quantifying microstructural changes by means of the Ultimate Tensile Strength (UTS) and the endurance limit. Furthermore, sole PBF-LB/M- and hybrid built components are compared, investigating the effect of a surface finish on the static and dynamic load behaviour, as superficial cracks and melting errors diminish the UTS and the endurance limit of PBF-LB/M-built components. Within these experiments, a change of fatigue behaviour for the heat-treatedstates can be observed, compared to the as-built state of the PBF-LB/M, as the development of different phases during heat treatment leads to an improvement of the endurance limit for, e.g., solution and ageing treated components. Additionally, the improvement of the surface quality to Ra = 2 µm leads to a significant increase of the dynamic mechanical load behaviour of hybrid-built components, as superficial cracks and surface defects are reduced.}, subject = {Hochgeschwindigkeitsfr{\"a}sen}, language = {en} }