Volume 75, Issue 3

Instead of quenching medium, quenching equipment and quenching parameters, an adapted surface structure of the heat treated component shall be investigated as influencing factor on rewetting during liquid quenching. Steel cylinders and aluminium cylinders have been quenched in water baths and oil baths. Fine surface structures by machining with turning tools with small flange radii have caused a significant relative surface increase compared to flat samples and thereby a significant decrease in rewetting duration of the whole sample (from rewetting start to finish). This is beneficial regarding quenching homogeneity. Local surface structures applied by ultrashort laser pulses have also influenced on rewetting, if resulting fins are arranged in axial cylinder direction and possess a sufficient axial length.

On the basis of economic and ecological constraints a reduced weight and/or minimized volume of automobile components is more and more focused in industrial and scientific activities in recent years. Apart from the application of new materials with considerably lower density a change of component design can be used to succeed in aims regarding lightweight construction. But aspects of a production-oriented design, especially for heat treated drive train components, have to be considered, too. This topic applies in particular to the final heat treatment because serious distortion problems can arise due to reduced stiffness and asymmetric mass distribution of a component. In the previous research work, the distortion behavior of gear base bodies as essential part of a gear was analyzed and a first design guideline for gear base bodies resulting in tolerable distortion was developed. In the ongoing research work, the basic approaches used for the determination of this guideline for gear base bodies will be applied to a complex gear with strong asymmetric mass distribution. One of the first questions of this work concerns the influence of the teeth on base body distortion. In this paper results of comparitive experiments between a complexed shaped gear with and without teeth will be presented.

The influence of different mechanical and chemical pre-treatments for heat-treated AISI M3:2 tool steel (~ DIN S 6-5-3) on the coating adhesion of a CrAlN coating is investigated. Surface topography and residual stresses before and after the PVD coating process are examined. Nitriding and grinding with toric grinding pins results in compressive residual stresses in the subsurface, whereas polishing leads to tensile stresses. After the deposition process a decrease of the residual stresses in the substrate material is observed, whereas the stresses in the nitrided surface are not affected. The resulting residual stresses and roughness profiles are correlated with the adhesion of the PVD coating showing a clear dependency on the substrate pre-treatments. Additionally, interactions between the residual stresses in the subsurface and the resulting stress gradient in the PVD coating could be determined by depth profiles. Based on these findings an optimized grinding process can therefore make the additional process step of nitriding obsolete and can provide an improved coating adhesion for an enhanced wear resistance.

The present work focuses on the effect of thermo-mechanical processing on the mechanical properties and microstructural evolution of AA6082 and AA7075 aluminum alloys using a novel forming process, i. e. integrating solution heat treatment, hot forming and tool quenching. Different tool temperatures ranging from 24 °C to 350 °C were applied to investigate their influence on mechanical strength and ductility. By using various tool temperatures, this study aims to provide insights needed for tailoring the mechanical properties of two different high-strength aluminum alloys. Further it is shown, how the different resulting cooling rates affect the final property distribution. Upon processing, uniaxial tensile tests were carried out at room temperature to characterize the mechanical properties of the investigated conditions. Microstructural investigation was further conducted by using scanning electron microscopy to reveal the prevalent deformation and strengthening mechanisms. Results obtained by mechanical testing reveal that reduction in tool temperature finally results in the realization of parts with higher strength upon aging. Tool temperatures above 200 °C deteriorate the strength of both alloys, however, improve ductility. Most importantly, the thermo-mechanical process used in the present work has only minor impact on the grain size of both alloys. However, the process appears to have a strong influence on the final morphology and size of precipitates. Elevated tool temperatures and, thus, lower cooling rates, make both alloys prone to the formation of coarse precipitates eventually deteriorating strength.

Mounting on a body during the powder bed process is a way to save manufacturing time and costs while still producing individual and complex components. However, components in the powder bed process are always manufactured with an allowance in order to compensate for inaccuracies in the process by means of subsequent production steps. Accordingly, hybrid components must also be reworked. This publication presents the results of investigations into the influence of the transition from conventional to an additive microstructure during the machining of hybrid samples. For this purpose, samples of 316L, IN718 and Ti-6Al-4V were printed on the corresponding conventionally produced samples. The first half of the samples were machined directly after being manufactured in the LPBF process, while the second half passed a heat treatment step before being machined. The machining tests were performed in orthogonal cutting with variation of uncut chip thickness and cutting speed. The chip formation, the cutting and passive forces, the surface roughness, the microstructure and the hardness are analyzed and compared. The measurement of the process forces showed a difference between the conventional and the additive areas for all materials examined, even after heat treatment. In contrast, the roughness profiles as well as the microstructure and the measured hardness of the conventional and the additive area could be approximated by heat treatment.