{ "types" : { "Bookmark" : { "pluralLabel" : "Bookmarks" }, "Publication" : { "pluralLabel" : "Publications" }, "GoldStandardPublication" : { "pluralLabel" : "GoldStandardPublications" }, "GoldStandardBookmark" : { "pluralLabel" : "GoldStandardBookmarks" }, "Tag" : { "pluralLabel" : "Tags" }, "User" : { "pluralLabel" : "Users" }, "Group" : { "pluralLabel" : "Groups" }, "Sphere" : { "pluralLabel" : "Spheres" } }, "properties" : { "count" : { "valueType" : "number" }, "date" : { "valueType" : "date" }, "changeDate" : { "valueType" : "date" }, "url" : { "valueType" : "url" }, "id" : { "valueType" : "url" }, "tags" : { "valueType" : "item" }, "user" : { "valueType" : "item" } }, "items" : [ { "type" : "Publication", "id" : "https://puma.ub.uni-stuttgart.de/bibtex/2a8db9c33dd141c0142c37aec16c3482c/jmichel", "tags" : [ "Aluminium","FluidFlow","HotCracking","Laser","Simulation","Welding","myown","peer" ], "intraHash" : "a8db9c33dd141c0142c37aec16c3482c", "interHash" : "f0ab1e31d3b83b52a60c3373e0a9d2d9", "label" : "Mechanisms of transverse hot crack formation during laser welding of high-strength aluminum alloys at high welding speeds", "user" : "jmichel", "description" : "", "date" : "2025-09-18 13:10:40", "changeDate" : "2025-09-18 13:10:40", "count" : 3, "pub-type": "article", "journal": "Optics & Laser Technology","publisher":"Elsevier BV", "year": "2025", "url": "http://dx.doi.org/10.1016/j.optlastec.2025.113898", "author": [ "Johannes Michel","Jonas Wagner","Frauke Holder","Felix Zaiß","Christian Hagenlocher","Thomas Graf" ], "authors": [ {"first" : "Johannes", "last" : "Michel"}, {"first" : "Jonas", "last" : "Wagner"}, {"first" : "Frauke", "last" : "Holder"}, {"first" : "Felix", "last" : "Zaiß"}, {"first" : "Christian", "last" : "Hagenlocher"}, {"first" : "Thomas", "last" : "Graf"} ], "volume": "192","pages": "113898","abstract": "High-strength aluminum alloys provide favorable material properties for components in modern battery systems, such as battery trays used in electromobility applications. However, laser welding of high-strength aluminum alloys at high welding speeds may result in the formation of transverse hot cracks in the weld seam, potentially causing component failure due to leakage. To determine strategies to avoid transverse hot cracks, the influence of the welding speed during full-penetration laser welding is analyzed both experimentally and theoretically using numerical simulations of the temperature field and the fluid flow. A metallographic analysis of the welded samples showed an increase in the number of transverse hot cracks with increasing welding speeds. The results revealed that a major mechanism for the formation of transverse hot cracks at high welding speeds is a significant reduction of the static pressure at the side of the melt pool, which impairs liquid feeding into the intergranular region. These findings provide fundamental knowledge for the development of optimization strategies to reduce the formation of transverse hot cracks at high welding speeds.", "language" : "English", "issn" : "0030-3992", "doi" : "10.1016/j.optlastec.2025.113898", "bibtexKey": "Michel_2025_Mechanisms_Cracks" } , { "type" : "Publication", "id" : "https://puma.ub.uni-stuttgart.de/bibtex/2853b939fcd9667b6f42a0e7376415ec1/jmichel", "tags" : [ "Aluminium","Embossing","HotCracking","ResidualStress","Welding","myown","simulation" ], "intraHash" : "853b939fcd9667b6f42a0e7376415ec1", "interHash" : "e0e8f74c11b06f561263ecdee9ce9a6c", "label" : "Influence of near-surface embossing on the hot crack formation during laser beam welding of metal sheets from 6000 aluminum alloys", "user" : "jmichel", "description" : "", "date" : "2025-07-07 14:59:20", "changeDate" : "2025-07-07 14:59:20", "count" : 6, "pub-type": "presentation", "year": "2025", "url": "", "author": [ "Maximilian Bachmann","Kim Rouven Riedmüller","Johannes Michel","Christian Hagenlocher","Mathias Liewald","Thomas Graf" ], "authors": [ {"first" : "Maximilian", "last" : "Bachmann"}, {"first" : "Kim Rouven", "last" : "Riedmüller"}, {"first" : "Johannes", "last" : "Michel"}, {"first" : "Christian", "last" : "Hagenlocher"}, {"first" : "Mathias", "last" : "Liewald"}, {"first" : "Thomas", "last" : "Graf"} ], "abstract": "During laser beam welding of aluminum alloys, the formation of transverse hot cracks in the weld seam represents a critical issue that can substantially impair the mechanical strength and quality of welded joints. These cracks are initiated as a result of thermal deformation, the decrease of the static pressure in the melt pool and the shrinkage during solidification. Particularly, this affects alloys of the 6000 series with elevated concentrations of the alloying elements silicon and magnesium. In [1], authors have demonstrated that applying external mechanical compressive stresses during welding reduces the formation of transverse hot cracks due to an increase of the static pressure in the melt pool. However, since such compressive stresses cannot always be applied externally, it would be desirable to induce these stresses within the sheet metal material. Against this background, near-surface embossing [2] was used in the present study to induce compressive residual stresses in sheet metals. Simulations were first carried out to examine the effects of varying the distances between the embossed patterns and the weld seam area to determine whether the compressive stresses affect the welding zone. Subsequently, several configurations of embossed sheets were produced, analyzed and welded. Finally, the resulting hot cracks were analyzed using metallographic sections and the results were compared with unembossed welded samples. The comparison of embossed and unembossed samples revealed the amount of residual compressive stresses and thus the formation of hot cracks can be reduced depending on the distance and design of the embossing pattern. This proves embossing to be a valid method for inducing compressive residual stresses into sheet metal and thus to reduce the formation of hot cracks during welding.", "eventtitle" : "Conference on Material Forming ESAFORM 2025", "venue" : "Paestum, Italy", "language" : "English", "collection" : "ESAFORM 2025", "eventdate" : "7-9 May 2025", "bibtexKey": "BACHMANN_2025_presentation" } , { "type" : "Publication", "id" : "https://puma.ub.uni-stuttgart.de/bibtex/2e5a0d800dbe296854407a25da82b35d7/jmichel", "tags" : [ "Aluminium","Embossing","HotCracking","ResidualStress","Welding","myown","simulation" ], "intraHash" : "e5a0d800dbe296854407a25da82b35d7", "interHash" : "e0e8f74c11b06f561263ecdee9ce9a6c", "label" : "Influence of near-surface embossing on the hot crack formation during laser beam welding of metal sheets from 6000 aluminum alloys", "user" : "jmichel", "description" : "", "date" : "2025-07-07 14:49:55", "changeDate" : "2025-07-07 14:49:55", "count" : 6, "pub-type": "inproceedings", "booktitle": "Material Forming: ESAFORM 2025","series": "ESAFORM 2025","publisher":"Materials Research Forum LLC", "year": "2025", "url": "http://dx.doi.org/10.21741/9781644903599-133", "author": [ "Maximilian Bachmann","Kim Rouven Riedmüller","Johannes Michel","Christian Hagenlocher","Mathias Liewald","Thomas Graf" ], "authors": [ {"first" : "Maximilian", "last" : "Bachmann"}, {"first" : "Kim Rouven", "last" : "Riedmüller"}, {"first" : "Johannes", "last" : "Michel"}, {"first" : "Christian", "last" : "Hagenlocher"}, {"first" : "Mathias", "last" : "Liewald"}, {"first" : "Thomas", "last" : "Graf"} ], "volume": "54","pages": "1221\u20131228","abstract": "During laser beam welding of aluminum alloys, the formation of transverse hot cracks\r\nin the weld seam represents a critical issue that can substantially impair the mechanical strength\r\nand quality of welded joints. These cracks are initiated as a result of thermal deformation, the\r\ndecrease of the static pressure in the melt pool and the shrinkage during solidification. Particularly,\r\nthis affects alloys of the 6000 series with elevated concentrations of the alloying elements silicon\r\nand magnesium. In [1], authors have demonstrated that applying external mechanical compressive\r\nstresses during welding reduces the formation of transverse hot cracks due to an increase of the\r\nstatic pressure in the melt pool. However, since such compressive stresses cannot always be\r\napplied externally, it would be desirable to induce these stresses within the sheet metal material.\r\nAgainst this background, near-surface embossing [2] was used in the present study to induce\r\ncompressive residual stresses in sheet metals. Simulations were first carried out to examine the\r\neffects of varying the distances between the embossed patterns and the weld seam area to\r\ndetermine whether the compressive stresses affect the welding zone. Subsequently, several\r\nconfigurations of embossed sheets were produced, analyzed and welded. Finally, the resulting hot\r\ncracks were analyzed using metallographic sections and the results were compared with\r\nunembossed welded samples. The comparison of embossed and unembossed samples revealed the\r\namount of residual compressive stresses and thus the formation of hot cracks can be reduced\r\ndepending on the distance and design of the embossing pattern. This proves embossing to be a\r\nvalid method for inducing compressive residual stresses into sheet metal and thus to reduce the\r\nformation of hot cracks during welding.", "venue" : "Paestum, Italy", "collection" : "ESAFORM 2025", "eventdate" : "7-9 May 2025", "eventtitle" : "Conference on Material Forming ESAFORM 2025", "issn" : "2474-395X", "doi" : "10.21741/9781644903599-133", "bibtexKey": "BACHMANN_2025" } , { "type" : "Publication", "id" : "https://puma.ub.uni-stuttgart.de/bibtex/2b357d5772d11474e079011ef5a7b594c/jmichel", "tags" : [ "Aluminium","Cracking","MacroMaterialProcessing","Simulation","Welding","myown" ], "intraHash" : "b357d5772d11474e079011ef5a7b594c", "interHash" : "3bd32eab7941897d45cf2e73a769eeb4", "label" : "Transverse hot cracking in high-speed laser welding of high-strength aluminum alloys", "user" : "jmichel", "description" : "", "date" : "2025-07-07 14:39:44", "changeDate" : "2025-07-07 14:39:44", "count" : 2, "pub-type": "presentation", "year": "2025", "url": "", "author": [ "Johannes Michel","Jonas Wagner","Frauke Holder","Felix Zaiß","Michael Haas","Christian Hagenlocher","Thomas Graf" ], "authors": [ {"first" : "Johannes", "last" : "Michel"}, {"first" : "Jonas", "last" : "Wagner"}, {"first" : "Frauke", "last" : "Holder"}, {"first" : "Felix", "last" : "Zaiß"}, {"first" : "Michael", "last" : "Haas"}, {"first" : "Christian", "last" : "Hagenlocher"}, {"first" : "Thomas", "last" : "Graf"} ], "abstract": "High-strength aluminum alloys offer excellent weight-specific mechanical properties, making them an ideal choice for parts in electromobility applications like battery trays. However, their susceptibility to transverse hot cracking during laser welding at high welding velocities is challenging. This study investigates the mechanisms of transverse hot crack formation by means of numerical simulations of the temperature field and melt flow in the melt pool and validates the results with experiments. The results reveal a critical zone at the side of the melt pool which is characterized by a high static pressure drop at the liquidus isotherm as a result of high melt flow velocities and cooling rates, which affect the intergranular melt flow during solidification. The study provides valuable findings, which enable the optimization of high-speed laser welding of aluminum alloys, to avoid the formation of transverse hot cracks.", "eventtitle" : "Lasers in Manufacturing Conference LiM 2025", "venue" : "Munich, Germany", "language" : "English", "eventdate" : "23 - 26 June 2025", "bibtexKey": "michel2025transversecracks" } , { "type" : "Publication", "id" : "https://puma.ub.uni-stuttgart.de/bibtex/2d63f180b4596242147af20fc8c3909ff/jmichel", "tags" : [ "Ablation","AdditiveManufacturing","AlSi10Mg","Heat-dissipatingStructures","Microstructure","PBF-LB/M","Simulation","Solidification","UltrashortPulse","myown" ], "intraHash" : "d63f180b4596242147af20fc8c3909ff", "interHash" : "65b5dae017fa6d9aac205df60afb2244", "label" : "Adjusting the microstructure of additively manufactured parts with tailored temperature fields by the combination of powder bed fusion with cw-laser and ablation with ultrashort laser pulses", "user" : "jmichel", "description" : "", "date" : "2024-05-08 21:09:02", "changeDate" : "2024-05-08 21:09:02", "count" : 4, "pub-type": "presentation", "publisher":"SPIE", "year": "2024", "url": "", "author": [ "Johannes Michel","Nico Ulff","Manuel Henn","Brian Simonds","Peter Hosemann","Frederik Zanger","Christian Hagenlocher","Thomas Graf" ], "authors": [ {"first" : "Johannes", "last" : "Michel"}, {"first" : "Nico", "last" : "Ulff"}, {"first" : "Manuel", "last" : "Henn"}, {"first" : "Brian", "last" : "Simonds"}, {"first" : "Peter", "last" : "Hosemann"}, {"first" : "Frederik", "last" : "Zanger"}, {"first" : "Christian", "last" : "Hagenlocher"}, {"first" : "Thomas", "last" : "Graf"} ], "editor": [ "Bo Gu","Hongqiang Chen" ], "editors": [ {"first" : "Bo", "last" : "Gu"}, {"first" : "Hongqiang", "last" : "Chen"} ], "eventtitle" : "LASE Photonics West", "venue" : "San Francisco, California, United States", "language" : "english", "eventdate" : "31 January", "bibtexKey": "michel2024adjusting" } , { "type" : "Publication", "id" : "https://puma.ub.uni-stuttgart.de/bibtex/2c47506f57bff71e5a4b18dd91640762f/jmichel", "tags" : [ "Ablation","AdditiveManufacturing","AlSi10Mg","Heat-dissipatingStructures","Microstructure","PBF-LB/M","Simulation","Solidification","UltrashortPulse","myown" ], "intraHash" : "c47506f57bff71e5a4b18dd91640762f", "interHash" : "65b5dae017fa6d9aac205df60afb2244", "label" : "Adjusting the microstructure of additively manufactured parts with tailored temperature fields by the combination of powder bed fusion with cw-laser and ablation with ultrashort laser pulses", "user" : "jmichel", "description" : "", "date" : "2024-05-08 20:35:51", "changeDate" : "2024-05-08 21:04:50", "count" : 4, "pub-type": "inproceedings", "booktitle": "Laser 3D Manufacturing XI","series": "Proc. SPIE","publisher":"SPIE", "year": "2024", "url": "http://dx.doi.org/10.1117/12.3002302", "author": [ "Johannes Michel","Nico Ulff","Manuel Henn","Brian Simonds","Peter Hosemann","Frederik Zanger","Christian Hagenlocher","Thomas Graf" ], "authors": [ {"first" : "Johannes", "last" : "Michel"}, {"first" : "Nico", "last" : "Ulff"}, {"first" : "Manuel", "last" : "Henn"}, {"first" : "Brian", "last" : "Simonds"}, {"first" : "Peter", "last" : "Hosemann"}, {"first" : "Frederik", "last" : "Zanger"}, {"first" : "Christian", "last" : "Hagenlocher"}, {"first" : "Thomas", "last" : "Graf"} ], "editor": [ "Bo Gu","Hongqiang Chen" ], "editors": [ {"first" : "Bo", "last" : "Gu"}, {"first" : "Hongqiang", "last" : "Chen"} ], "volume": "12876","abstract": "In powder bed fusion with laser beams (PBF-LB/M), the component's quality and mechanical properties are limited by \r\nrestricted process parameter combinations and the geometry of the component. Combining PBF-LB/M with ultrashort laser \r\nablation enables additional control of the heat flow to adjust local solidification. On the one hand it is possible to print \r\nheat-dissipating structures, which can be added and removed during the build process. On the other hand, ablated slits in \r\nthe component can serve as a thermal barrier.\r\nTo investigate the effect of slits and heat-dissipation structures on the local temperature field and solidification conditions, \r\na numerical model was developed. Two different ablation strategies were investigated and compared to conventional \r\nPBF-LB. Numerical investigations of an additively manufactured AlSi10Mg component showed a larger melt pool, a lower \r\ntemperature gradient, and a lower cooling rate if there are slits present next to the current PBF-LB track.\r\nThis approach provides the potential to independently adjust microstructure and mechanical properties, exceeding \r\nlimitations imposed by the component's geometry in conventional additive manufacturing.", "venue" : "San Francisco, California, United States", "language" : "english", "eventdate" : "27 January - 1 February 2024", "eventtitle" : "LASE Photonics West", "doi" : "10.1117/12.3002302", "bibtexKey": "Michel_2024" } ] }