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Abstract. The innovative forming processes Linear Flow Splitting (LFS) and Linear Bend Splitting (LBS) were developed to facilitate the continuous production of branched profiles with tailored sheet thickness by inducing severe plastic strain. In contrast to most SPD processes the stress state in LFS and LBS is very complex and plastic deformation is confined to limited volumes which results in steep strain gradients and consequently ultrafine grained (UFG) gradient microstructures. Even though the processes have been commercialized, the increased lightweight potential that originates from the local grain refinement remains mostly idle since it is neither fully understood nor easily assessable yet. The present work shows the state of the art for the LFS and LBS processes and compares the microstructures and distribution of mechanical properties for different steels processed with different LFS parameters. The data is used to identify characteristic manufacturing induced properties that are insensitive to processing parameters. Based on the experimental results a material flow model for the processing zone is proposed which is discussed with respect to the current understanding of plasticity at severe strains.Keywords: Surface Severe Plastic Deformation, Work Hardening, Linear Flow Splitting, Linear Bend Splitting, Gradient Microstructures IntroductionThe use of Severe Plastic Deformation (SPD) as top down approach to refine microstructures of metals and alloys to the submicron range has been investigated extensively during the last decades [1][2][3]. Aside from the scientific interest in fundamental research on plasticity phenomena at large strains, there is also a strong technological interest in these processes which is driven by the exceptional mechanical properties that are associated with the presence of ultrafine grained (UFG) microstructures [1]. Even though high strength materials are needed for a wide range of commercial applications where lightweight design is mandatory, the commercial success of SPD processes is rather limited so far [4]. The main reason for this are most likely the high processing costs of the predominantly discontinuous SPD processes but there is also a strong competition from materials based on modern alloy design and thermo-mechanical processing [5]. However, the Linear Flow Splitting (LFS) and Linear Bend Splitting (LBS) processes that are reviewed in the present paper demonstrate that UFG microstructures by SPD and commercial success in mass markets are no antagonisms. The LFS and LBS processes also referred to as split profiling and split bending have an exceptional position in the field of SPD. In contrast to conventional SPD processes their primary objective is not the generation of UFG microstructures while retaining the initial shape of the workpiece but the production of branched profiles from plain sheet metal [6][7][8]. However, since LFS and LBS induce severe strains under high hydrostatic compressive stresses they generate UFG microstructures by the same mechanisms [9]...

Das Massivumformverfahren Spaltprofilieren befindet sich auf dem Übergang von der Forschung unter Laborbedingungen in die industrielle Anwendung. Dadurch rücken Fragestellungen zur Prozesssicherheit bei hohen Produktionsgeschwindigkeiten und variierenden Schmierzuständen in den Mittelpunkt wissenschaftlicher Untersuchungen. Neben den zu erwartenden Änderungen der Geometriegrößen sind vor allem werkstoffseitige Beeinflussungen von Interesse. In diesem Artikel wird daher zunächst eine quantitative Beschreibung des Einflusses von Bandgeschwindigkeit, Bandzug und Schmiermenge auf die Profilgeometrie gegeben. Hierbei wird bewertet, inwieweit eine Beeinflussung der Bauteilgeometrie durch Variieren der Prozessgrößen erfolgt. Des Weiteren werden die bei unterschiedlichen Prozessbedingungen zu beobachtenden Gefügecharakteristika, Härteverläufe und Texturen der spaltprofilierten Halbzeuge dargestellt. Durch Verwendung statistischer Methoden, insbesondere der uni‐ und multivariaten Regressionsanalyse, wird abschließend auf Basis der experimentellen Ergebnisse eine analytische Beschreibung zur Vorhersage sich einstellender Bauteilgeometrien hergeleitet. Diese eröffnet die Möglichkeit einer gezielten Steuerung der Bauteilgeometrie durch die identifizierten Einflussgrößen.