No description available.

No description available.

In the study, a self-developed electrolytic micro-machining tester is employed to investigate the effects of the supply voltage and the highest position of the workpiece relative to the tool on the geometry of the tungsten rod. The peripheral surface of the iron needle (tool) is insulated by an insulator and its tip with a diameter of 50£gm is exposed to the electrolyte as a cathode. The tungsten rod (workpiece) with 200£gm in diameter reciprocates as an anode. Both the cathode and the anode are dipped into an aqueous electrolyte of 2wt % sodium hydroxide to proceed electrochemical machining. Experimental results show that since the length and the diameter of the workpiece are varied during the machining process, it is necessary to manually adjust the highest position and the gap between the workpiece and the tool in each reciprocating motion to achieve a uniform tungsten rod. Moreover, because of the higher removal rate of the workpiece at the higher supply voltage, it is hard to control the geometry of the workpiece. On the contrary, the geometry of the workpiece can be controlled at the lower supply voltage. Finally, the workpiece is first machined at the higher supply voltage, and then the supply voltage is switched to the lower one to achieve a uniform tungsten rod with 2£gm in diameter and 200£gm in length, or 100 in aspect ratio.

This thesis presents numerical and experimental investigations into Electrochemical Machining (ECM). The aim is to develop a computer program to predict the shape of a workpiece machined by the ECM process. The program is able to simulate various applications of EC machining which are drilling, milling, turning and shaped tube electrochemical drilling (STED). The program has been developed in a MATLAB environment. In this present work, EC-drilling, EC-milling and EC-turning are analysed as three-dimensional problems whereas STED is simulated in two-dimensions. Experiments have been carried out to verify the accuracy of the predicted results in the cases of EC-milling and EC-turning. The ECM modeller is based on the boundary element method (BEM) and uses Laplace's equation to determine the current distribution at nodes on the workpiece surface. In 3D, the surfaces of the tool and the workpiece are discretised into continuous linear triangular element types whereas in 2D, the boundaries of the tool and workpiece are discretised into linear elements. The ECM modeller is completely self-contained, i.e. it does not rely on any other commercial package. The program contains modules to automatically discretize the surfaces/boundaries of the tool and workpiece. Since the simulation of the ECM process is a temporal problem, several time steps are required to obtain the final workpiece shape. At the end of each time step, the shape of the workpiece is calculated using Faraday's laws. However, the workpiece's shape changes with progressing time steps causing the elements to become stretched and distorted. Mesh refinement techniques are built in the ECM modeller, and these subdivide the mesh automatically when necessary.The effect of time step on the predicted 3D shape of a hole in EC-drilling is investigated. The effect of discontinuity in the slope between neighbouring elements is also studied. Results obtained from the ECM modeller are compared with 2D analytical results to verify the accuracy that can be obtained from the ECM modeller. Milling features ranging from a simple slot to a pocket with a complex protrusion were machined in order to determine the feasibility of the EC milling process. These features were machined on a 3-axes CNC machine converted to permit EC milling. The effect of tool geometry, tool feed rate, applied voltage and step-over distances on the dimensions, shape and surface finish of the machined features were investigated. A pocket with a human shape protrusion was machined using two different types of tool paths, namely contour-parallel and zig-zag. Both types resulted in the base surface of the pocket being concave and the final dimensions of the pockets are compared with the design drawing to determine the effect of tool path type on the accuracy of machining. The ECM modeller was used to simulate the machining of a thin-walled turned component. The machining parameters, i.e. initial gap, rotational speed, and applied voltage, were specified by the collaborating company. Since only a small amount of material had to be removed from the thin-walled component, the tool was held stationary i.e. a feed in the radial or longitudinal direction was not required. By taking advantage of the axi-symmetric nature of a turned component, only a sector of the component was analysed thereby reducing the computing time considerably. The accuracy of the modeller was verified by comparing the predicted time to machine the thin-walled component with the actual machining time. The initial investigations in STED were both experimental and numerical in nature and they studied the effect of applied voltage, tool feed rate and electrolyte pressure on the dimensions of the holes. Later investigations were numerical and an iterative methodology has been developed to calculate a set of feed rates which could machine a specified turbulator shape.

Electrochemical machining (ECM) is a non-conventional manufacturing process, which uses electrochemical dissolution to shape any conductive metal regardless of its mechanical properties and without leaving behind residual stresses or tool wear. Therefore, ECM can be an alternative for machining difficult-to-cut materials, complex geometries, and materials with improved characteristics, such as strength, heat-resistance or corrosion-resistance. Notwithstanding its great potential as a shaping tool, the ECM process is still not fully characterised and its research is an on-going process. Various phenomena are involved in ECM, e.g. electrodynamics, mass transfer, heat transfer, fluid dynamics and electrochemistry, which occur in parallel and this can lead to a different material dissolution rate at each point of the workpiece surface. This makes difficult an accurate prediction of the final workpiece geometry. This problem was addressed in the first part of the present thesis by developing a simulation model of the ECM process in a two-dimensional (2D) environment. A finite element analysis (FEA) package, COMSOL multiphysics® was used for this purpose due to its capacity to handle the diverse phenomena involved in ECM and couple them into a single solution. Experimental tests were carried out by applying ECM on stainless steel 316 (SS316) samples. This work was done in collaboration with pECM Systems Ltd® from Barnsley, UK. The interest of studying ECM on stainless steels (SS) resides on the fact that the application of ECM on SS typically results in various different surface finishes. The chromium in SS alloys usually induces the formation of a protective oxide film that prevents further corrosion of the alloy, giving the metal the special characteristic of corrosion resistance. This oxide film has low electrical conductivity; hence normal anodic dissolution often cannot proceed without oxide breakdown. Partial breakdown of the oxide film often occurs, which causes pits on the surface or a non-uniform surface finish. Therefore the role of the ECM machining parameters, such as interelectrode gap, voltage, electrolyte flow rate, and electrolyte inlet temperature, on the achievement of a uniform oxide film breakdown was evaluated in this work. Experimental results show that the resulting surface finish is highly influenced by the over-potential and current density, and by the characteristics of the electrolyte, flow rate and conductivity. The complexity of experimentally controlling these parameters emphasised the need for the development of a computational model that allows the simulation of the ECM process in full. The simulation of ECM in a three-dimensional (3D) environment is crucial to understand the behaviour of the ECM process in the real world. In a 3D model, information that was not visible before can be observed and a more detailed realistic solution can be achieved. Hence, in this work a computer aided design (CAD) software was used to construct a 3D geometry, which was imported to COMSOL Multiphysics® to simulate the ECM process, but this time in a 3D environment. This enhanced simulation model includes fluid dynamics, heat transfer, mass transfer, electrodynamics and electrochemistry, and has the novelty that an accurate computational simulation of the ECM process can be carry out a priori the experimental tests and allows the extraction of enough information from the ECM process in order to predict the workpiece final shape and surface finish. Moreover, this simulation model can be applied to diverse materials and electrolytes by modifying the input ECM parameters.

This master thesis deals with the efficiency improvement proposal of the deburring technology of the edge of the holes intersection inside of the given part. In the introductory chapter it deals with the introduction of Česká zbrojovka a.s. company, where the creation of this thesis took place. The definition of the fire guns, some of the special products of the CZUB a.s. company and the description of the given part are following. The third chapter contains the description of the current manufacturing process. In the second part the proposals of the possible technologies are listed along with their current state. In the end a technical-economic evaluation is accomplished.

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.

No description available.

The manufacturing of components with complex internal features, e.g. for automobile industry, aeronautics or medical applications, is a significant challenge. Such components are often machined in temporarily and locally separated stages of production. Due to these separated stages, the form deviations and positioning errors increase, which leads to additional efforts for the quality assurance. The technology that shall be developed within the project SwitchECM is supposed to enable machining of components with differing complex features in one single production stage and shall simultaneously allow for high precision. For this purpose, a multi-cathode system will be developed, in which every single cathode can be switched with specific parameters. The specific switching parameters shall be adjusted according to the requirements of the pre-defined features. For the manufacturing of different pre-defined features with one multi-cathode system the usage of pulsed direct current as well as continuous direct current shall be possible. Hence, removal experiments were carried out on 1.4301 stainless steel using a PEMCenter 8000 with varying feed rates and voltages at a pulsation frequency of 200 Hz. With this comparatively high frequency and a pulse duration of 4 ms pseudo direct current experiments are realized. The results are compared to experiments with a more common pulse frequency of 50 Hz. The mass removal analyses show, in which degree the transferability of experimental results from pulsed current to pseudo direct current or rather direct current is feasible.