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Thin film sensors are used to record temperatures, forces and tool wear in machining processes in the immediate vicinity of the contact zone between tool and workpiece. On the one hand, this makes it possible to precisely calibrate analytical models for describing boundary layer conditions. On the other hand, the parameters recorded in-process can be used to implement a so-called soft sensor for controlling the process parameters in order to specifically adjust the properties of the subsurface layer of the workpiece.

Electronic devices are progressively fabricated on flexible substrates allowing new fields of applications. A maskless and very flexible structuring process is offered by ablation using ultra-short pulse laser irradiation. Usually, certain areas of a functional thin film coating are locally removed to yield the needed device structures. Micro laser patterning quality is not only influenced by the beam properties (beam profile, fluence) but also by pulse overlap, scan repetitions and many other factors such as substrate and coating material. This makes process parameter optimization a challenging task. In this paper, we present a systematic approach to efficiently find suitable parameters for laser-induced ablation of thin films on susceptible polymer substrates. As an example, we use a sputtered NiCr coating with a thickness of 100 $nm$ on a polyimide film made by spin coating of PI-2611 precursor (@ 2000 $rpm$ > ca. 8 ${\mu}m$, HD microsystems). Irradiation is conducted using a fs-laser with infrared wavelength of 1030 $nm$ and a pulse length of 212 $fs$. The energy per pulse is varied in the range of 0,29 ${\mu}J$ to 4,83 ${\mu}J$, yielding fluence values between 70 $mJ/cm^2$ and 1,11 $J/cm^2$. Ablation threshold fluence for a 100 $nm$ layer of NiCr was found to be ${\phi}_{th}$ ($N_P$:1)=0,50 $J/cm^2$ and the incubation factor was evaluated to be ${\xi}$=0,53. A clear distinction must be made between the material ablation at the surface of a bulk material and the selective removal of a thin film. In the second case effects such as flaking occur in practice and influence the ablation characteristic. We then investigate different varieties of thin film removal including dot-, line- and areal-ablation. The methodology is presented using a practical example, but can be applied to selective ablation of a wide range of thin film systems., Comment: 11 pages, 23 figures

Currently a high amount of lubricants is used in aluminum forming processes to ensure a long tool lifetime and a high product quality. These technological and economical goals are traded for a negative environmental impact caused by the usage of lubricants. One approach to reduce the environmental impact is the utilization of dry forming of aluminum. Therefore, alternative methods for a tribological optimization need to be implemented like the deposition of tool coatings. Diamond like carbon (DLC) coatings are well known for their exceptional tribological properties. However, state of the art DLC coatings fail due to rapid formation of aluminum adhesions. In this paper, the nanoscopic roughness of DLC coatings will be presented as a critical property for preventing the formation of aluminum adhesions and enabling dry forming of aluminum. For this purpose, an amorphous hydrogenated carbon (a-C:H) coating will be deposited, subsequently polished and characterized to validate the impact of the material selection and surface treatment on the coating roughness. For an evaluation of the tribological properties, polished and unpolished a-C:H coatings will be tested in application oriented strip drawing and industry-oriented deep drawing tests. These tests demonstrate the capability of smooth a-C:H tool coatings to enable dry forming of aluminum with a reduced environmental impact.

Das Plasmantrieren ist ein wichtiges Verfahren zur Erhöhung der Verschleißfestigkeit metallischer Werkstoffe, insbesondere auch austenitischer Stähle. Eine entscheidende Rolle für den Härteanstieg spielt die Gitteraufweitung durch eindiffundierte Stickstoffatome, die zur Bildung der sogenannten s‐Phase (""extended austenite"") führt. Im Rahmen einer Masterarbeit am Institut für Oberflächentechnik der Technischen Universität Braunschweig wurde ein Modell zur Vorhersage der s‐Phasendicke für Plasmanitrierprozesse von vier austenitischen rostfreien Stählen entwickelt. Das Modell wurde durch eine Reihe von Kontrollversuchen validiert. Es zeigt aufgrund des geringen relativen Fehlers von weniger als 6 % eine sehr gute Annäherung an die experimentell ermittelten Werte.

It is known that surface patterns and coating systems can affect the flow behavior of forming tools. In this context, we report about the surface modification of forming tool steels for aluminum sheet metal forming process. Microstructures with variable spatial periods and depths are fabricated on tool steel samples using the direct laser interference patterning method. A picosecond-pulsed infrared laser source with a two-beam interference setup is applied for producing line-like structures. In addition, a diamond like carbon (DLC) coating system is deposited on the structured surfaces. To improve the adhesion tendency of the DLC coating, also different plasma nitriding parameters are examined. According to the results, a broad spectrum of different coating-structure combinations can be efficiently processed, which can optimize the tribological properties of the forming tool for aluminum forming applications.