Strukturierte und DUPLEX behandelte Werkzeuge für die Trockenbearbeitung beim Rundkneten

Rundkneten ist ein inkrementelles Massivumformverfahren zur Herstellung von Leichtbaukomponenten aus zylindrischen Halbzeugen. Das konventionelle Rundkneten setzt derzeit große Mengen von Schmiermitteln voraus, um sowohl den Werkzeugverschleiß zu minimieren als auch die gewünschte Bauteilqualität einzustellen. Es besteht Interesse den Rundknetprozess in einer trockenen Prozessführung zu realisieren und somit die Prozesskette bei der Weiterverarbeitung der Werkstücke um kostspielige Reinigungsprozesse zu verkürzen. Für eine trockene Prozessführung werden Makrostrukturen durch Fräsen mit Kugelkopffräsern in die Reduzierzonen der Werkzeuge eingebracht, um tribologische Bedingungen einzustellen, die auch bei trockener Prozessführung zu einem stabilen Prozess und qualitativ hochwertigen Werkstücken führen. Um diese Strukturen zu schützen sowie den Werkzeugverschleiß und die Entstehung von Abriebpartikeln zu minimieren, werden Wolfram dotierte, wasserstoffhaltige amorphe Kohlenstoffschichten (a-C:H(:W)) auf die gesamte Umformzone durch reaktives Magnetronsputtern appliziert. Werkstücke, die mit beschichteten Werkzeugen beim Trockenrundkneten hergestellt wurden, weisen zudem vergleichbare oder bessere Werkstückoberflächen auf als unter der konventionellen, geschmierten Prozessführung. Allerdings muss die Schichthaftung auf den Werkzeugoberflächen weiter gesteigert werden, da die Beschichtungen kritisch auf lokale Überbeanspruchungen reagiert. Um einer frühzeitigen Schichtermüdung beim Trockenrundkneten von Stahl effektiv zu begegnen, werden die Werkzeuge nach dem Vergüten zusätzlich plasmanitriert. Im Rahmen dieser Arbeit wird zunächst geprüft, ob eine Übertragbarkeit von plasmanitrierten und anschließend a-C:H(:W) beschichteten Laborproben auf die komplexe Rundknetwerkzeuggeometrie gegeben ist. Zudem werden zwei sogenannte DUPLEX behandelte Werkzeuge gegen Stahl in der trockenen Anwendung getestet und mit den Werkzeugverschleißresultaten der vergüteten Werkzeuge verglichen.3138Bremen5

On the combination of plasma nitrided surfaces and LIPSS

LIPSS are subjected to excessive wear when exposed to direct contact in tribological applications. Therefore, precautions must be taken to increase LIPSS’ hardness and wear resistance while simultaneously preserving their properties like superhydrophilicity. This work shows that a firstly plasma nitrided and subsequently structured surface results in LIPSS of high nano-hardness (14.88 GPa ± 1.05 GPa) who show a super hydrophilic wetting behavior (contact angle of 7°). The results indicate that a previous nitriding could bring LIPSS into tribological applications.Deutsche Forschungsgemeinschaft DFG232

An Investigation into the Wear Behavior of Martensitically Transformed Nitrided Layers

To improve the service behavior of gears, surface heat treatments such as nitriding or induction hardening can be performed. Since these processes are limited in their achievable maximum hardness or depth of hardness, a combination treatment could allow benefits from the advantages of both processes. The aim of this work was to show the correlation between the microstructure resulting from combination treatment and the performance of the surface layer using the example of wear behavior. The investigations focused on the impact of different nitrided states, in the combination treatment of the material EN31CrMoV9, on wear resistance. The wear was evaluated after running the two-disc test gravimetrically and optically. Nitrided-only specimens showed better wear resistance compared to those subjected to induction hardening after nitriding. Substantial differences in weight loss indicate that induction hardening worsens the wear behavior. The variants with the compound layer removed in the nitride-only state as well as in the induction hardened state showed a better wear behavior compared to the respective conditions with a compound layer. This was attributed to the lower surface roughness and the higher hardness due to less retained austenite after combination treatment

Development, characterization and testing of tungsten doped DLC coatings for dry rotary swaging

The extensive use of lubricant during rotary swaging is particularly required for a good surface finish of the work piece and the reduction of tool wear. Abandonment of lubricant would improve the ecological process-balance and could also accelerate for further work piece refinements. Also cleaning of the manufactured components becomes obsolete. Thus, a dry machining is highly innovative, consequently new strategies to substitute the lubricant functions become necessary. To encounter the changed tribological conditions due to dry rotary swaging, low friction, tungsten doped, hard DLC coatings and structured surfaces are the most promising approaches. In this work the development of hard coating by means of reactive magnetron sputtering is presented, a promising layer variant is deposited on a set of tools and then tested and investigated in real use

A new approach for dry metal forming: CO2 as volatile lubrication in combination with hard and low friction coatings

Nowadays, it is more important than ever to meet the increasing technical and statutory requirements and to develop new process strategies. In sheet metal forming the low consumption of oil lubrication gets an increasingly important role. The aim in sheet metal forming is to reduce the amounts of lubricants. In the long term, the future sheet metal processing should be able to completely dispense without mineral oil-containing lubricants. Two promising approaches for a dry process design are combined in this paper for the first time and the fundamental feasibility of this new hybrid technology is shown. On the one hand, a novel approach for temporary lubrication of deep-drawing processes with CO2 as a volatile medium is used. On the other hand, it is supported by the application of an additional hard coating system such as a silicon nitride (Si3N4) or tungsten doped a-C:H multilayered (Cr/CrNx/a-C:H:W/a-C:H) coating system to further reduce tool wear and wear debris of the formed sheets made of DC04 (mat. no.: 1.0338). The results show a low coefficient of friction and reduced wear. Especially for the carbon coating system, there is minor tool wear at a higher surface pressure. By means of the graphite constituent, even a smoothening of the roughness peaks can be recorded. The next step would be the implementation of this hybrid technology on a tool for deep drawing a rectangular cup

A new approach for dry metal forming: CO2 as volatile lubrication in combination with hard and low friction coatings

Nowadays, it is more important than ever to meet the increasing technical and statutory requirements and to develop new process strategies. In sheet metal forming the low consumption of oil lubrication gets an increasingly important role. The aim in sheet metal forming is to reduce the amounts of lubricants. In the long term, the future sheet metal processing should be able to completely dispense without mineral oil-containing lubricants. Two promising approaches for a dry process design are combined in this paper for the first time and the fundamental feasibility of this new hybrid technology is shown. On the one hand, a novel approach for temporary lubrication of deep-drawing processes with CO2 as a volatile medium is used. On the other hand, it is supported by the application of an additional hard coating system such as a silicon nitride (Si3N4) or tungsten doped a-C:H multilayered (Cr/CrNx/a-C:H:W/a-C:H) coating system to further reduce tool wear and wear debris of the formed sheets made of DC04 (mat. no.: 1.0338). The results show a low coefficient of friction and reduced wear. Especially for the carbon coating system, there is minor tool wear at a higher surface pressure. By means of the graphite constituent, even a smoothening of the roughness peaks can be recorded. The next step would be the implementation of this hybrid technology on a tool for deep drawing a rectangular cup

Development, characterization and testing of tungsten doped DLC coatings for dry rotary swaging

The extensive use of lubricant during rotary swaging is particularly required for a good surface finish of the work piece and the reduction of tool wear. Abandonment of lubricant would improve the ecological process-balance and could also accelerate for further work piece refinements. Also cleaning of the manufactured components becomes obsolete. Thus, a dry machining is highly innovative, consequently new strategies to substitute the lubricant functions become necessary. To encounter the changed tribological conditions due to dry rotary swaging, low friction, tungsten doped, hard DLC coatings and structured surfaces are the most promising approaches. In this work the development of hard coating by means of reactive magnetron sputtering is presented, a promising layer variant is deposited on a set of tools and then tested and investigated in real use

Potential of Nitrided and PVD-MoS₂:Ti-Coated Duplex System for Dry-Running Friction Contacts

Self-lubricating coatings can be used to increase the service life of machine parts which are subjected to high mechanical loads. The present work is concerned with the combination of nitriding and a subsequent Ti-doped MoS2 coating. The focus of the investigations is on the impact of the compound layer on the wear behavior of the coating since the changes in the surface topography due to compound layer growth and pore formation inside the compound layers are expected to have an impact of the adhesion strength and the wear behavior. For this purpose, compound layers with varying thickness and porosity were formed in the surface area of the material EN31CrMoV9 by gas nitriding. A MoS2:Ti PVD monolayer was applied directly on the compound layers. The wear behavior was evaluated using the pin-on-disc test. The MoS2:Ti solid lubricant coatings show good adhesion on the compound layers without any interlayer. Compared with the nitrided reference state, the coating significantly improved the wear behavior of the surface treated material