Andreas Klink

Technological and Economical Capabilities of Manufacturing Titanium- and Nickel-Based Alloys via Electrochemical Machining (ECM)

In this paper technological and economical capabilities of manufacturing titanium- and nickel-based alloys via unpulsed Electrochemical Machining (ECM) are presented. A standardized test to receive typical workpiece material removal properties according to its electrochemical machinability is introduced. First of all the experimental setup of this test is described in detail. The test results for the materials Ti-6Al-4V and Inconel 718 are presented and discussed. Here the feed rate – current density- and surface roughness – current density curves are in focus. With help of these two functions as an example out of many possible applications the capability of blisk manufacturing by electrochemical machining is quantified. Therefore the theoretical machining times for both materials of substituted blisk geometry are calculated. Finally on this basis an economical comparison between ECM and milling as rough estimation is executed.

Process force analysis on sinking-EDM electrodes for the precision manufacturing

Electro Discharge Machining is no longer taken as a “force free” process. Studies are being completed in order to understand how these forces are being exerted on the electrodes and how they might affect the processing of highly precise or high aspect ratio geometries. This paper studies process forces on macro Sinking-EDM with the use of two highly precise piezoelectric axial force sensors which measure single discharge forces simultaneously at the tool and workpiece sides. At the same time, the vibration amplitude and frequency of tool electrodes are measured, along with the analysis of high-speed-camera photographs showing a chronological sequence of gas bubble formation in terms of their dilatation and collapse, allowing a more detailed view into the process. The understanding of the dynamic trends of these process forces allows drawing conclusions about the generation of the pressure field along the working gap and its influence on tool electrode vibration which can decrease the final desired precision of the manufactured workpiece.

Surface integrity in electrochemical machining processes: An analysis on material modifications occurring during electrochemical machining

In contrast to most other manufacturing technologies, in electrochemical machining processes only slight changes in material characteristics in the rim zone of workpieces are stated in the literature. Due to the physical active principle, no thermo-mechanically induced phase changes or the evolution of a so-called white layer were ever observed. Aside of this fact, a not inconsiderable number of smaller modifications in the rim zone were found in the past. The most common effects occurring during electrochemical machining are the generation of a passive layer on the surface by changing the local chemical composition of the material, the selective dissolution of one metallic phase, or the occurrence of flow marks. Consequently, the last two effects also change the surface roughness as the marks and dissolved phases represent ditches in the surface. Therefore, in this article, material modifications occurring during electrochemical machining are presented. Their influence on the surface integrity is exemplarily analyzed for the heat-treatable steel 42CrMo4. In addition, first steps for a correlation of material loadings that promote these changes, the so-called process signature, are made. Based on this, the influence of different machining parameters can be compared to set up rim zone properties purposefully.

Material Loadings during Electrochemical Machining (ECM) - A First Step for Process Signatures

Properties of workpieces, like residual stress in the rim zone, cannot be predicted for manufacturing technologies reproducible in advance. This lack of predictability shall be solved by a new approach, called Process Signatures. These Process Signatures will combine the material loadings forced by the manufacturing process with the change of state variables, e. g. the variation of residual stress in the surface layer. As the Process Signatures shall achieve comparability for different processes with same physical working principle, it is necessary to describe the transition from material loadings to the change of material properties in a uniform way. Consequently an energy based approach is chosen that considers these transitions by the dissipation of the several kinds of energy brought into the manufacturing process and especially in the respective working area.A first step for the development of such Process Signatures is the identification of all process specific material loadings. This paper presents several material loadings generated during the electrochemical sinking process. In a further step the contribution of the individual material loadings to the material removal process are estimated. Finally first approaches for the combination of the main material loadings and the change of material properties are presented.

Comparison of the electrochemical machinability of electron beam melted and casted gamma titanium aluminide TNB-V5

Additive manufacturing technologies are becoming more and more important for the implementation of efficient process chains. Due to the possibility of a near net shape, manufacturing time for finish-machining can significantly be reduced. Especially for conventionally hard to machine materials like gamma titanium aluminides (γ-TiAl), this manufacturing process is very attractive. Nevertheless, for most applications, a rework of these generative components is necessary. Independently of the mechanical material properties, electrochemical machining is one promising technology of machining these materials. Major advantages of electrochemical machining are its process-specific characteristics of high material removal rates in combination with almost no tool wear. But electrochemical machining results are highly dependent on the microstructure of the material regarding the surface roughness. Therefore, this article deals with research on electrochemical machining of electron beam melted γ-TiAl TNB-V5 compared to a casted form of this alloy. The difference between the specific removal rates as a function of current density is investigated using electrolytes based on sodium nitrate and sodium chloride. Moreover, the dissolving behavior of the electron beam melted and casted structure is analyzed by potentiostatic polarization curves. The surface roughness is heavily dependent on a homogeneous dissolution behavior of the microstructure. Thus, the mean roughness as a function of current density is investigated as well as rim zone analyses of the different structures.

ELID dressing behaviour of fine grained bronze bonded diamond grinding wheels

The application of metal bonded grinding wheels generally results in high wear resistance and profile constancies of the grinding wheels. Especially bronze bonded grinding wheels can efficiently be used for the grinding tasks, as it is easier to modify their chemical composition - and therefore their bond hardness - to suit a specific grinding task. The combination of very small grained diamonds and a metal bond causes great difficulties for conventional dressing. In this paper, an assessment on the capabilities of ELID for dressing of bronze bonded diamond grinding wheels is presented. Distinct types of bronze-bonds with different chemical composition are investigated regarding their electrochemical dissolution and oxidation behaviour during ELID. Iron-based (Fe-Bz) and cobalt-based (Co-Bz) bronze-bond types showed good performance regarding oxide layer formation during the pre-dressing. An extensive oxide layer growth prevents the metal bond from a too fast anodic dissolution. In contrast, pure bronze type (Cu-Bz) showed no closed oxide layer formation resulting in an extensive anodic dissolution of the grinding wheel bond.

Productivity Improvement Through the Application of Hybrid Processes

Many parts require high strength materials, exhibiting high temperatures or where formability should be reduced, requiring new processing technologies. The application of hybrid manufacturing processes can answer the needs. This paper gives first a classification of hybrid manufacturing processes, followed by a description of various productivity improvements. The latter is also demonstrated by various examples in cutting, grinding, forming and chemical & physical processes like EDM, ECM and laser.

Development of a Process Evaluation System for Wire-EDM Applications Using an Intelligent Process Monitoring Tool

In this paper a first approach is presented to investigate the electrical parameters of the EDM process using an intelligent process monitoring tool to evaluate different technologies and generators. Goal is to characterize every single discharge by extracting relevant data from recorded current and voltage signals using an adequate algorithm. For demonstration purposes a steel material is machined using a corresponding technology recommended by the machine tool supplier as well as a recommended technology for hard metal. In a first step the machining quality is evaluated by the cutting rate and surface roughness which is common practice for EDM. These results are then compared to the data extracted by the process monitoring tool. In the future this tool may be able to accelerate the parameter development for a specific task or material significantly. The effectiveness of the process could be determined directly during the process and no longer indirectly by a quality inspection of the machined part. By investigating the course of each discharge the process parameters can be linked to the actual physical parameters and a direct influence could be identified.

Modeling and simulation of the fluid flow in wire electrochemical machining with rotating tool (wire ECM)

Combining the working principle of electrochemical machining (ECM) with a universal rotating tool, like a wire, could manage lots of challenges of the classical ECM sinking process. Such a wire-ECM process could be able to machine flexible and efficient 2.5-dimensional geometries like fir tree slots in turbine discs. Nowadays, established manufacturing technologies for slotting turbine discs are broaching and wire electrical discharge machining (wire EDM). Nevertheless, high requirements on surface integrity of turbine parts need cost intensive process development and – in case of wire-EDM – trim cuts to reduce the heat affected rim zone. Due to the process specific advantages, ECM is an attractive alternative manufacturing technology and is getting more and more relevant for sinking applications within the last few years. But ECM is also opposed with high costs for process development and complex electrolyte flow devices. In the past, few studies dealt with the development of a wire ECM process to meet these challenges. However, previous concepts of wire ECM were only suitable for micro machining applications. Due to insufficient flushing concepts the application of the process for machining macro geometries failed. Therefore, this paper presents the modeling and simulation of a new flushing approach for process assessment. The suitability of a rotating structured wire electrode in combination with an axial flushing for electrodes with high aspect ratios is investigated and discussed.Combining the working principle of electrochemical machining (ECM) with a universal rotating tool, like a wire, could manage lots of challenges of the classical ECM sinking process. Such a wire-ECM process could be able to machine flexible and efficient 2.5-dimensional geometries like fir tree slots in turbine discs. Nowadays, established manufacturing technologies for slotting turbine discs are broaching and wire electrical discharge machining (wire EDM). Nevertheless, high requirements on surface integrity of turbine parts need cost intensive process development and – in case of wire-EDM – trim cuts to reduce the heat affected rim zone. Due to the process specific advantages, ECM is an attractive alternative manufacturing technology and is getting more and more relevant for sinking applications within the last few years. But ECM is also opposed with high costs for process development and complex electrolyte flow devices. In the past, few studies dealt with the development of a wire ECM process to meet t...

EBSD-Analysis of Microstructural Changes Below Wire-EDMed Surfaces

An example for such an application are notched monolithic flexure hinges (cf. Fig. 1), which are analyzed within a larger project for the construction of micro-manipulators at RWTH Aachen University. During the bending of such hinges, the rim zone of the notch is undergoing high tensile strain. In order to predict the operating functionality, the microstructural damage introduced by W-EDM cutting therefore needs to be known in dependence of the cutting parameters.