In recent years, deformation induced surface hardening when turning was carried out to enhance the component performance of metastable austenitic steels. To induce such a phase transformation from austenite to martensite in the workpiece surface layer, high mechanical loads and low process temperatures are required. Therefore, cryogenic CO2-snow cooling is an appropriate method to assure low temperatures in the workpiece surface layer. In this context, the influence of the process parameters cutting speed, feed, depth of cut and tool cutting edge inclination on the surface morphology in terms of deformation induced surface hardening and resulting surface roughness was investigated. The results show that the deformation induced surface hardening when cryogenic turning is adjustable via a targeted variation of the investigated process parameters. Thus, the morphology of the surface layer and therefore the properties of the component can be adjusted according to the requirements of the application.

The sealing capabilities of RSS do not only depend on the seal itself but also on the lubricant and the shaft surface. A twist structure on the surface can cause pumping of the fluid during shaft rotation which can result in leakage. In this paper a special, new turning method, which consists of at least two turning steps with feed in reciprocal direction, is presented as an alternative to the conventional manufacturing process. The goal is to create a surface structure with a net pumping rate of zero. Shafts turned with the new proposed method are compared to turned shafts from previous investigations [1]. Criteria for the comparison are the surface pumping rate, leakage and wear behavior of the surface.

The effect of surface modification by cryogenic turning on fatigue behavior of metastable austenitic stainless steel AISI 347 was investigated in stress-controlled fatigue tests at ambient temperature (AT) and 300 °C in air. Five different surface morphologies were manufactured by the variation of turning parameters – with and without cryogenic CO2 snow cooling and feed velocity as well as by the application of polishing for reference surfaces with a very small surface roughness. For a comprehensive characterization of the surface and near surface morphology, X-ray diffraction investigations were performed. Three phases (γ-austenite, α-martensite and ε-martensite) were detected in the near-surface microstructure after cryogenic turning while after turning without cryogenic cooling the only microstructural constituent was γ-austenite. Moreover, residual stress state, micro hardness and surface roughness play an important role in surface morphology. The experimental data on the cyclic deformation behavior and stress-strain response of all surface morphologies are reported. Reference specimens with purely austenitic surface microstructure show the highest plastic strain amplitude during cyclic loading at both AT and 300°C. At elevated temperature these specimens achieved the shortest fatigue life. Martensitic surface layers induced by cryogenic turning result in the reduction of plastic strain amplitude during cyclic loading and significantly enhance fatigue life at both tested temperatures.

In recent years deformation induced surface hardening was carried out to enhance the component performance of metastable austenitic steels. To be able to induce such a phase transformation from austenite to martensite in the workpiece surface layer, high mechanical loads and low process temperatures are required. Therefore, cryogenic CO2-snow cooling is an appropriate method to assure a low heat influence on the workpiece. High mechanical loads can be obtained by high feed. However, this causes relatively rough surfaces due to the process kinematics. In this context, the influence of cutting edge geometry on deformation induced surface hardening and resulting surface roughness is investigated. With a variation of the geometry of the cutting edge, especially the cutting edge radius, mechanical loads and thus the amount of martensite formed were adjustable.

Kurzfassung Unpräparierte Schneiden führen aufgrund mangelnder Stabilität und unregelmäßigen Verschleißes zu instabilen Prozessen und geringen Werkzeugstandzeiten. Eine Stabilisierung der Schneide infolge der Schneidkantenpräparation wirkt dem entgegen. Das Präparationsverfahren mit elastisch gebundenen Schleifscheiben nutzt die weggesteuerte Verfahrbewegung der Werkzeugschleifmaschine, um die Schneidkante zu verrunden. Größe und Form der Verrundung können dabei gezielt gesteuert werden.

Kurzfassung Bauteiloberflächen sind häufig entscheidend für das Einsatzverhalten und die Lebensdauer technischer Systeme. Unter Bauteiloberfläche werden hier auch die Regionen in unmittelbarer Nähe der Grenze zwischen dem Bauteil und der Umgebung verstanden. Im Sonderforschungsbereich 926 der Deutschen Forschungsgemeinschaft werden an der Technischen Universität Kaiserslautern Oberflächenerzeugungs-Morphologie-Eigenschafts-Beziehungen (OMEB) erarbeitet, die es erlauben, vom Fertigungsverfahren und seinen Prozessparametern direkt auf das Einsatzverhalten eines Bauteils zu schließen.

Kurzfassung Die zur Kühlung und Schmierung eingesetzte Kühlstrategie ist für die Produktivität spanender Fertigungsverfahren von hoher Bedeutung. Im Rahmen dieses Beitrags wird eine innovative Kühlstrategie auf der Basis von wässrigen Mono-Ethylenglykol-Lösungen vorgestellt, die zur Steigerungen der Produktivität führen soll. Die Kühlwirkung der neuen Kühlstrategie wird mit einer Trockenbearbeitung und einer kryogenen CO2-Schnee-Kühlung verglichen und zeigt gute Ergebnisse.

The process chain in manufacturing often consists of many steps. As part of current researches the possibility of combining two process steps, turning and hardening, is investigated to optimize the manufacturing time and to decrease the energy consumption of the process. For metastable austenitic steels, deformation induced hardening during turning can be used to achieve surface hardening [1] and thus to increase the wear resistance [2] as well as the fatigue strength [3], by applying high passive forces onto the workpiece. This enables an austenite‐martensite phase transformation, for which it is necessary to maintain low process temperatures, typically below room temperature. Thus, cryogenic coolants are applied [4].

The state of the art industrial manufacturing process to produce shafts as counter surfaces for radial shaft seal rings is plunge grinding. This process consists of three major steps. The blank is turned to a slight diameter-oversize followed by the heat treatment and the hard-finishing by plunge grinding. The geometric surface structures of the resulting shafts in general exhibit a stochastic distribution. These surface characteristics contribute to a reliable and stable sealing functionality. And the surface and subsurface hardness generally leads to a higher wear resistance of the shaft.Motivated by economic benefits and in order to achieve a compact production process for at least ten years, turning is investigated as an alternative manufacturing process. However due to the resulting lead structure on the shaft surface and the associated risk of leakage it has not become prevalent yet. In this paper turned shafts of the metastable austenitic steel AISI 347 (1.4550, X6CrNiNb1810) are investigated as alternative material for counter surfaces of radial shaft seal rings and compared to turned shafts of carburized AISI 5115 (1.7131, 16MnCr5). In addition to surfaces dry turned at room-temperature, cryogenic turned AISI 347 counter surfaces are analyzed. By applying cryogenic cooling, the formation of deformation-induced alpha'-martensite in the surface layer is possible during the turning process. Endurance tests in radial shaft seal ring test rigs are performed and complemented with detailed investigations of microstructure, micro-hardness and surface topography. The results are compared to results of state of the art ground AISI 5115 shafts. (C) 2015 Elsevier B.V. All rights reserved.

The use of cryogenic cooling in material removal processes has been reported by several researchers. The objectives were enhanced tool life and an expanded range of machinable materials. In this paper, a novel application of cryogenic cooling is presented: its use achieve direct surface hardening of metastable austenitic steels during cutting. Metastable austenite can transform into martensite due to plastic deformation if a sufficiently low temperature is maintained. In order to use this effect during cutting, cryogenic conditions must be maintained at all times. With this approach, cutting and hardening can be combined in one process.

Metastable austenitic steels offer the opportunity of a surface hardening during machining due to a deformation induced martensite formation, substituting downstream hardening-processes. To maintain the necessary low process and workpiece temperatures for a phase transformation from austenite to martensite, cryogenic cooling using CO2-snow was examined in this study. The influence of workpiece diameter, coolant flow rate as well as pre-cooling and pre-surface hardening on the obtainable phase content of martensite in the surface layer was investigated.

In terms of production costs and manufacturing time there is a permanent effort to shorten the process chain by combining different process steps. For metastable austenitic steels there is the opportunity of an integrated surface hardening during machining. This leads to an increase of the wear resistance and fatigue strength of highly loaded components. For this purpose, high deformations combined with low temperatures during the material removal process are needed. To achieve this an insert with a chamfered cutting edge is used to enlarge the passive forces. The central challenge is to keep the temperatures in the cutting zone at a sufficient low level during turning AISI 347. Cryogenic coolants like liquid nitrogen (LN2) or carbon dioxide (CO2) offer an opportunity to keep the process temperature at low values. In this context, the influence of different cryogenic cooling strategies are compared with dry cutting. Additionally, the cutting parameters feed f and cutting speed vc are varied. To detect cause and effect relationships measurements of the passive force, workpiece surface temperature, formed martensite content and micro hardness are performed.

Kurzfassung Edelstähle finden dank ihrer chemischen Zusammensetzung vermehrt Anwendung in korrosiver Umgebung. Wird funktionsbedingt eine gehärtete Oberfläche benötigt, ist die Fertigung infolge hoher Werkstoffkosten und einer langen Prozesskette kostenintensiv. Die metastabilen Austenite als Untergruppe der Edelstähle bieten hierbei eine Möglichkeit einer integrierten Randzonenhärtung während der spanenden Bearbeitung mit kryogener Kühlung. In diesem Beitrag werden die Einflussfaktoren auf diese verformungsinduzierte Aufhärtung während des Drehens erläutert und das Potenzial dieser neuartigen Methode beleuchtet.

This work is motivated by cryogenic turning which allows end shape machining and simultaneously attaining a hardened surface due to deformation induced martensitic transformations. To study the process on the microscale, a multivariant phase field model for martensitic transformations in conjunction with a crystal plastic material model is introduced. The evolution of microstructure is assumed to follow a time‐dependent Ginzburg‐Landau equation. To solve the field equations the finite element method is used. Time integration is performed with Euler backward schemes, on the global level for the evolution equation of the phase field, and on the element level for the crystal plastic material law. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Radnabenanordnung, beinhaltend folgende Merkmale: – Ein Bremsscheibentrager (21, 24) mit wenigstens einem hulsenartigen Abschnitt (24), – ein zum Drehen vorgesehenes Lagerteil (11) einer Walzlagerung, – fur ein Zentrieren des Lagerteils (11) und des hulsenartigen Abschnitts (24) zueinander umfassen das Lagerteil (11) und der hulsenartige Abschnitt (24) jeweils eine sich einander gegenuberliegende Mantelflache, und – wenigstens eine der Mantelflachen ist von der Kreiszylinderform abweichend derart gestaltet, dass sich die beiden Mantelflachen lediglich in einer begrenzten Anzahl von wenigstens drei in Umfangsrichtung verteilt angeordneten Punkten beruhren.