Evelina Vogli

Aspects of Die Design for the Electromagnetic Sheet Metal Forming Process

Within the electromagnetic sheet metal forming process, workpiece velocities of more than 300m/s can occur, causing typical effects when forming into a die, which will be described and discussed in the present paper. These effects make numerous demands regarding the die design. In order to analyze these requirements, experimental as well as numerical investigations have been carried out. Thereby, special focus is put on the possibilities to accomplish these requirements, which are discussed in the following.

Effect of Plasma Treatment on Adhesion of DLC Layers to Steels

Diamond like carbon layers play a key role in industrial applications. However the layers quality deteriorates often due to insufficient interfacial adhesion. In this research work a prior plasma treatment of steel substrates was employed aimed to improve the interfacial adhesion of DLC-layers to steel substrates. Three different kinds of steels were employed and their microstructures as well as their compositions before and after plasma treatment were analyzed. The interfacial adhesion of DLC layers on the non-nitrided and nitrided steels was observed and the influence of the steel microstructure on the interfacial adhesion was studied.

Nanostructured Bionic PVD-Coatings for Forming Tools

It is very important to minimize wear and friction in forming processes in order to avoid adhesion between work piece and tool. For the realization of these requirements, the PVD-coating system CrAlN was deposited and tested on substrates made from high speed steel 1.3343 by means of a reactive sputter process. The coatings were deposited as single- and multilayers with a metallic Cr-interlayer. Prior to realizing the appropriate coating design, the substrates were pre-structured. For this purpose natural surfaces were used as a pattern and tested in this research work. The skin of an insect serves as a model and its fine structures were reproduced on the substrate surface by milling. The generated specimens were analyzed with a scanning electron microscope, nanoindenter and ball on disc tester to compare the performance of the coating systems.

Deposition of Multi-Functional Coatings by Physical Vapour Deposition

Multifunctional coatings open new dimensions due to a combination of properties like high friction and wear resistance, electrical attributes, heat or corrosion protection in one system. In this study multifunctional coatings for in-situ temperature measurements on cutting inserts as well as multilayer coatings have been investigated. Corresponding metallurgical analyses together with mechanical tests are presented.

Influence of Substrate Nitriding on Adhesion, Friction and Wear Resistance of DLC (Diamond-Like Carbon)-Coatings

Since diamond like carbon layers feature excellent mechanical and tribological behavior under defined environmental circumstances, they are well established in a wide field of industrial and automotive applications in the last decade. However, the pretreatment of the substrate plays also an important role in supporting and enforcing the excellent properties of the coatings. This work analyses the effect of the plasma nitrided cold working steel substrate (80CrV2) on the adhesion, friction and wear resistance of DLC-coatings and compares it to the performance of DLC-coatings applied on a non-hardened substrate material. Therefore the grinded and polished specimens were nitrogen-hardened in an Arc-PVD (Physical Vapor Deposition)-device before the DLC-coating was applied in a Magnetron Sputter-PVD-process. In order to measure the hardness of the thin film coating, a nanoindenter was used. The adhesion was tested with a scratch tester and the wear resistance was measured by using a Ball-on-disc-tester. A 3D-profilometer and a SEM (Scanning Electron Microscope) were utilized to analyze the scratches and wear tracks on the samples. With these results correlations between the substrate nitriding and the mechanical and tribological performance of the DLC-coating were made.

Near-Net-Shape and Dense Wear Resistant Thermally Sprayed Coatings

Deep drawing of high strength steels imposes high tribological requirements on forming tools. Thermal spraying is regarded as a promising technology to improve the tool’s performance and the service life of the forming tool, as long as ambitious demands of the coating process are matched. In order to qualify a thermal spraying process for a surface technology in deep drawing it is crucial that the coating obtains an extremely dense structure and a smooth, near-net-shape surface. The study presented considers two different approaches to achieve those goals. The application of fine-scaled powders (<10

Desirability-Based Multi-Criteria Optimisation of HVOF Spray Experiments

m) spraying through HVOF technique offers the opportunity to deposit dense coatings with very smooth surfaces. In contrast, it is also feasible to achieve very smooth and dense coatings by combining conventional powders with a subsequently densification procedure

Thermisch gespritzte Cu-Schichten

The reduction of the powder grain size is of key interest in the thermal spray technology to produce superfine structured cermet coatings. Due to the low specific weight and a high thermal susceptibility of such fine powders, the use of appropriate process technologies and optimised process settings are required. Experimental design and the desirability index are employed to find optimal settings of a high velocity oxygen fuel (HVOF) spraying process using fine powders (2 − 8 μm). The independent factors kerosene, hydrogen, oxygen, gun velocity, stand-off distance, cooling pressure, carrier gas and disc velocity are considered in a 12-run Plackett-Burman Design, and their effects on the deposition efficiency and on the coating characteristics microhardness, porosity and roughness are estimated. Following an examination of possible 2-way interactions in a 25 − 1 fractional-factorial design, the three most relevant factors are analysed in a central composite design. Derringer’s desirability function and the desirability index are applied to find optimal factor settings with respect to the above characteristics. All analyses are carried out with the statistics software “R”. The optimisation of the desirability index is done using the R-package “desiRe”.

Wear-resistant and low-friction diamond-like-carbon (DLC)-layers for industrial tribological applications under humid conditions

Kurzfassung Die elektromagnetische Blechumformung besitzt ein großes Potenzial zur Realisierung anspruchsvoller Fertigungsaufgaben. Um die Vorteile dieses Verfahrens auch bei Werkstoffen mit einer geringen elektrischen Leitfähigkeit nutzen zu können, kommen Treiberschichten mit guter elektrischer Leitfähigkeit zum Einsatz. Mit diesem Hintergrund wurden thermische Spritzverfahren auf ihre Anwendbarkeit zur Abscheidung von Kupfer als Treiberschicht untersucht.