Tool wear development in gear skiving process of quenched and tempered internal gears = Entwicklung des Werkzeugverschleißes beim Wälzschälen von vergüteten Innenverzahnungen

Das Wälzschälen ist ein hochproduktives Bearbeitungsverfahren, insbesondere für die Herstellung von hochfesten Innenverzahnungen, wie sie für elektrische Hochleistungsantriebe benötigt werden. Die komplexe Prozesskinematik verursacht jedoch starke Schwankungen der lokal wirksamen Prozesskenngrößen während des Werkzeugeingriffs, sodass insbesondere an das Werkzeug hohe Anforderungen gestellt werden, um eine hohe Standzeit bei geforderter Werkstückqualität zu erreichen. Diese Anforderungen werden bei der Zerspanung von vergüteten Werkstoffen aus dem Vollen noch weiter verstärkt. In der vorliegenden Studie wird der Einfluss verschiedener Schlüsselfaktoren auf die Entwicklung des Werkzeugverschleißes beim Wälzschälen quantifiziert. In mehreren Versuchen werden die Schnittgeschwindigkeit, die Werkstückzugfestigkeit, die Kühlschmierstrategie und die Schnittstrategie variiert, um die Werkzeugstandzeit zu optimieren. Dazu werden Einzelzahnversuche an vergüteten Innenverzahnungen aus 31CrMoV9 (AISI 4340) durchgeführt und die Entwicklung der Verschleißmarkenbreite der Werkzeuge untersucht. Zudem wird das Werkstück hinsichtlich der gefertigten Oberflächenqualität bewertet. Die Ergebnisse zeigen, dass verschiedene Faktorenkombinationen unterschiedliche Auswirkungen auf das Verschleißverhalten der Werkzeuge und damit auf die Standzeit haben können. Die vorgestellten Korrelationen geben Empfehlungen für die praktische Anwendung und tragen zu einem tieferen Prozessverständnis bei

Modelling and prevention of meshing interference in gear skiving of internal gears: Conference Proceedings [Modellierung und Vermeidung von Freiflächeninterferenz beim Wälzschälen von Innenverzahnungen]

Gear skiving is a highly productive process for machining of internal gears which are required in large quantity for electric mobility transmissions. Due to the complex kinematics of gear skiving, collisions of the tool and workpiece can occur during the process. Models exist to check for collisions of the tool shank or collisions in the tool run-out. While these models are sufficient for the process design of external gear skiving, at internal gears meshing interferences between tool and workpiece can appear outside the contact plane on the clearance face of the tool. To test for meshing interference requires comprehensive assessment of workpiece, tool and process kinematics. Currently, this is often done by time consuming CAD-simulation. In contrast, this paper presents an automated geometrical model for the analysis of meshing interference. The test for collisions is thereby performed along the whole height of the tool and especially includes constructive clearance angles and eccentric tool positions. The model is developed for user-friendly implementation and practical applications. The model for avoiding meshing interference in gear skiving is validated on two different process applications. In doing so, influences of the tool and process design on the interference situation are investigated, compared and discussed. Furthermore this new approach enables the prevention of meshing interference or tooth tip collisions in the early tool design by adjusting the process kinematics or the tool design itself. The maximal viable tool height can be quantified and recommendations for improving the clearance face situation are suggested

On the Hopf algebra structure of the AdS/CFT S-matrix

We formulate the Hopf algebra underlying the su(2|2) worldsheet S-matrix of the AdS_5 x S^5 string in the AdS/CFT correspondence. For this we extend the previous construction in the su(1|2) subsector due to Janik to the full algebra by specifying the action of the coproduct and the antipode on the remaining generators. The nontriviality of the coproduct is determined by length-changing effects and results in an unusual central braiding. As an application we explicitly determine the antiparticle representation by means of the established antipode.Comment: 12 pages, no figures, minor changes, typos corrected, comments and references added, v3: three references adde

Gamma-Ray Bursts Trace UV Metrics of Star Formation over 3 < z < 5

We present the first uniform treatment of long duration gamma-ray burst (GRB) host galaxy detections and upper limits over the redshift range 3<z<5, a key epoch for observational and theoretical efforts to understand the processes, environments, and consequences of early cosmic star formation. We contribute deep imaging observations of 13 GRB positions yielding the discovery of eight new host galaxies. We use this dataset in tandem with previously published observations of 31 further GRB positions to estimate or constrain the host galaxy rest-frame ultraviolet (UV; 1600 A) absolute magnitudes M_UV. We then use the combined set of 44 M_UV estimates and limits to construct the M_UV luminosity function (LF) for GRB host galaxies over 3<z<5 and compare it to expectations from Lyman break galaxy (LBG) photometric surveys with the Hubble Space Telescope. Adopting standard prescriptions for the luminosity dependence of galaxy dust obscuration (and hence, total star formation rate), we find that our LF is compatible with LBG observations over a factor of 600x in host luminosity, from M_UV = -22.5 mag to >-15.6 mag, and with extrapolations of the assumed Schechter-type LF well beyond this range. We review proposed astrophysical and observational biases for our sample, and find they are for the most part minimal. We therefore conclude, as the simplest interpretation of our results, that GRBs successfully trace UV metrics of cosmic star formation over the range 3<z<5. Our findings suggest GRBs are providing an accurate picture of star formation processes from z ~3 out to the highest redshifts.Comment: publ. ApJ 809 (2015) 76; 14 figures; replacement to reflect changes to v1 (rounding effects, diff. LF from Bouwens

On the Integrability of large N Plane-Wave Matrix Theory

We show the three-loop integrability of large N plane-wave matrix theory in a subsector of states comprised of two complex light scalar fields. This is done by diagonalizing the theory's Hamiltonian in perturbation theory and taking the large N limit. At one-loop level the result is known to be equal to the Heisenberg spin-1/2 chain, which is a well-known integrable system. Here, integrability implies the existence of hidden conserved charges and results in a degeneracy of parity pairs in the spectrum. In order to confirm integrability at higher loops, we show that this degeneracy is not lifted and that (corrected) conserved charges exist. Plane-wave matrix theory is intricately connected to N=4 Super Yang-Mills, as it arises as a consistent reduction of the gauge theory on a three-sphere. We find that after appropriately renormalizing the mass parameter of the plane-wave matrix theory the effective Hamiltonian is identical to the dilatation operator of N=4 Super Yang-Mills theory in the considered subsector. Our results therefore represent a strong support for the conjectured three-loop integrability of planar N=4 SYM and are in disagreement with a recent dual string theory finding. Finally, we study the stability of the large N integrability against nonsupersymmetric deformations of the model.Comment: 20 pages, 1 figur