Universiẗat, Diss., 2006--Frankfurt (Main).

Techn. Universiẗat, Diss., 2000--Chemnitz.

Universiẗat, Diss., 2003--Dortmund.

Techn. Hochsch., Diss., 2003--Aachen.

Techn. Hochsch., Diss., 2003--Aachen.

Techn. Universiẗat, Diss., 2004--Dresden.

Jet Electrochemical Machining (Jet-ECM) is a manufacturing technique that applies a free electrolyte jet to generate the desired shapes [1]. Since the principle of the technique is the same as other techniques of Electrochemical Machining where the material removal takes place based on the anodic dissolution of workpiece, the working distance, which is the distance between nozzle’s front surface and the workpiece surface, is one important parameter of the process. The working distance affects the current density and consequently the geometry removal. The control of the working distance can be done based on the data gathered before and during machining by surface measurement [2]. This measurement usually is done by using electrostatic probing to detect a limited amount of points of the initial workpiece surface. Since electrostatic probing is comparatively slow, laser triangulation represents an alternative technique to detect a larger amount of points before machining within significantly shorter time [3]. In addition to electrostatic probing and laser triangulation, the actual working distance can be measured during the machining process to realize constant working distance. This can be done by detecting electrical signals like the actual total current. This method can be combined with pre-machining measurement by laser triangulation in order to ensure the prevention of any collision between the nozzle and the workpiece. In this study, on-machine metrology techniques for measuring the working gap as well as current measurements will be compared. Besides, the advantages and disadvantages of these techniques will be systematized. In further studies, the possibility of combining the techniques will be investigated to enhance Jet-ECM with more accurate measurement techniques.

Due to unique advantages of Jet Electrochemical Machining (Jet‐ECM) such as the absence of mechanical and thermal effects, there is an increasing demand for the implementation of the technology in industrial sectors. However, meeting the stringent quality requirements of the current technological level is a challenge in Jet‐ECM especially for complicated microstructures. Hence, the implementation of an adequate metrology system is necessary to minimise deviations and to enhance the process towards zero‐defect‐manufacturing. The metrology system should be capable of measuring the workpiece before machining in order to enable the machine to adjust the process parameters and to reach the desired micro‐structure. Post‐machining measurements to compare the machined part with the desired shape should be possible as well. This will enhance the machine to make corrections on the workpiece before delivery to the next section in a process chain. However, in order to reach the desired microstructures, the characteristics of workpiece like material properties and previously machined structures on the size and shape of the machined microstructure should be taken into consideration. This is done through the implementation of results of the fingerprint study into the process control. In this study the effects of previously machined single grooves which intersect the secondly machined groove on the size, shape and surface roughness are investigated. The previously machined groove was generated by milling or Jet‐ECM. Since at the intersections the gap size changes and this lead to changes in current and current density, it is expected to observe changes in size and surface roughness. This investigation will show how grooves change at the intersections and whether the mentioned changes are significant. Besides, some suggestions will be provided in order to minimise the effects in Jet‐ECM of intersecting single grooves.

Developing novel electrode materials is a substantial issue to improve the performance of lithium ion batteries. In the present study, single phase Ti–Sn alloys with different Sn contents of 1 to 10 at% were used to fabricate Ti–Sn–O nanotubes via a straight-forward anodic oxidation step in an ethylene glycol-based solution containing NH4F. Various characterization tools such as SEM, EDXS, TEM, XPS and Raman spectroscopy were used to characterize the grown nanotube films. Our results reveal the successful formation of mixed TiO2/SnO2 nanotubes in the applied voltage range of 10–40 V. The as-formed nanotubes are amorphous and their dimensions are precisely controlled by tuning the formation voltage which turns Ti–Sn–O nanotubes into highly attractive materials for various applications. As an example, the Ti–Sn–O nanotubes offer promising properties as anode materials in lithium ion batteries. The electrochemical performance of the grown nanotubes was evaluated against a Li/Li+ electrode at a current density of 504 μA cm−2. The results demonstrate that TiO2/SnO2 nanotubes prepared at 40 V on a TiSn1 alloy substrate display an average 1.4 fold increase in areal capacity with excellent cycling stability over more than 400 cycles compared to the pure TiO2 nanotubes fabricated and tested under identical conditions. This electrode was tested at current densities of 50, 100, 252, 504 and 1008 μA cm−2 exhibiting average capacities of 780, 660, 490, and 405 μA cm−2 (i.e. 410, 345, 305 and 212 mA h g−1), respectively. The remarkably improved electrochemical performance is attributed to enhanced lithium ion diffusion which originates from the presence of SnO2 nanotubes and the high surface area of the mixed oxide tubes. The TiO2/SnO2 electrodes retain their original tubular structure after electrochemical cycling with only slight changes in their morphology.

Manufacturing of components with complex internal features, e.g. for medical applications, aeronautics or automobile industry, is challenging. Those components are often machined in temporarily and locally separated production stages. As results of these separated stages form deviations and positioning errors increase, which lead to additional efforts for the quality assurance. The technology aimed within the project SwitchECM is expected to allow the machining of different complex features of one workpiece in one single production stage and shall simultaneously allow a high precision. For this purpose, a multi-cathode system will be developed, in which separated cathodes can be switched with specific parameters, depending on the requirements of the pre-defined features. This study will show the capability to machine the workpiece with different parameter sets but the same cathode and device as fundamental work for the machining with a multi-cathode system. Therefore the surface and dissolution characteristics for the material 1.4301 were used to design the process. The machining tasks were determined to deburring and edge shaping. In the experiments, the parameters voltage and working time were selected depending on the final geometry. It will be shown that the deburring task can be handled with nearly no edge shaping and the edge shaping task is suitable to adjust different edge geometries.