Application of the contour method to determine axial residual stresses in cold extruded steel rods

Residual stresses in cold extruded parts play an important role in both component lifetime and succeeding in manufacturing performance. When a cold extruded part is used directly, the lifetime of the part depends on the residual stresses induced during cold extrusion. On the other hand, if the part is exposed to post operations such as machining, residual stresses may cause distortions. Despite their importance, there are only a few residual stress measurement methods to assess axial residual stresses in full cylindrical thick components of massive forming. As high-energy X-ray and neutron diffraction methods are less available and considerably expensive, the contour method may be an alternative providing the accurate assessment of residual stresses without requiring specialized facilities. In the present work, residual stresses in cold extruded rods are determined via the contour method for various extrusion ratios. The finite element analyses for the same conditions are also carried out to provide the comparison to the contour method. The results indicate that the contour method can be a valuable candidate for the measurement of axial residual stresses in cold extruded thick components.

Substructures in the Keplerian disc around the O-type (proto-)star G17.64+0.16

We present the highest angular resolution (∼20 × 15 mas–44 × 33 au) Atacama Large Millimeter/sub-millimeter Array (ALMA) observations that are currently possible of the proto-O-star G17.64+0.16 in Band 6. The Cycle 5 observations with baselines out to 16 km probe scales < 50 au and reveal the rotating disc around G17.64+0.16, a massive forming O-type star. The disc has a ring-like enhancement in the dust emission that is especially visible as arc structures to the north and south. The Keplerian kinematics are most prominently seen in the vibrationally excited water line, H2O 55, 0−64, 3 ν2 = 1 (Eu = 3461.9 K). The mass of the central source found by modelling the Keplerian rotation is consistent with 45 ± 10 M⊙. The H30α (231.9 GHz) radio-recombination line and the SiO (5-4) molecular line were detected at up to the ∼10σ level. The estimated disc mass is 0.6 − 2.6 M⊙ under the optically thin assumption. Analysis of the Toomre Q parameter in the optically thin regime indicates that the disc stability is highly dependent on temperature. The disc currently appears stable for temperatures > 150 K; this does not preclude that the substructures formed earlier through disc fragmentation.

Verzugsarme Kaltmassivumformung*/Low distortion cold massive forming – Development of a new technology for the reduction of residual stresses

Eigenspannungen, die während des Herstellungsprozesses in Bauteile eingebracht werden, sind oft Ursache von Verformungen und beeinträchtigen zudem die Ermüdungs- und Korrosionsbeständigkeit. In diesem Beitrag wird daher die Entwicklung einer neuen Technologie vorgestellt, die es ermöglicht, die Eigenspannungen bei kaltfließgepressten Teilen zu verringern. Zudem wird eine Wärmebehandlung numerisch simuliert, um zu zeigen, wie mit dieser Technologie Verformungen vermieden werden können. &nbsp; Residual stresses stored in components during the manufacturing process often cause distortions besides negatively affecting fatigue and corrosion resistance. This paper reveals a new technology for residual stress reduction in cold extruded parts. The studied system can be implemented in conventional cold forging production and does not cause changes in the processing times. A heat treatment process is numerically simulated to show how distortions can be avoided by this technology.

Masers as probes of the gas dynamics close to forming high-mass stars

Imaging the inner few 1000 AU around massive forming stars, at typical distances of several kpc, requires angular resolutions of better than 0″.1. Very Long Baseline Interferometry (VLBI) observations of interstellar molecular masers probe scales as small as a few AU, whereas (new-generation) centimeter and millimeter interferometers allow us to map scales of the order of a few 100 AU. Combining these informations all together, it presently provides the most powerful technique to trace the complex gas motions in the proto-stellar environment. In this work, we review a few compelling examples of this technique and summarize our findings.

Evaluation of Tribological Properties of AlMg4.5Mn0.7 in Massive Microforming Using the Barrel Compression Test

Tribology is one of the major issues in forming processes. It is influenced by many factors such as workpiece and tool material, lubrication, process parameters, geometric scale etc. Especially in microforming processes, friction plays an important role due to an increased surface to volume ratio and the domination of open over closed lubricant pockets. A simple and sensitive method to quantify the friction factor under realistic conditions of massive forming is the barrel compression test. The friction factor is calculated out of the friction-dependent barreling of cylinder samples while being compressed between two parallel tool surfaces.In these investigations, the barrel compression test was applied to determine the friction factor between cylindrically shaped samples made of the aluminium alloy AlMg4.5Mn0.7 (EN AW 5083) and polished surfaces made of the tool steel 1.3343. The specimen diameter was varied between 0,5 mm and 10 mm. The focus of investigations was the size-dependence of the friction factor under the variation of the parameters such as forming degree, lubrication conditions, and die velocity. In addition to the calculation of the friction factor, surfaces were evaluated by microscopy and roughness measurements.