Electrolyte , electrochemical machining

Manufacturing engineers wishing to use ECM processes in industry need to address the challenge of proper tool design. The cost of design can be as much as 20% of the cost of an electrochemical machine for complex components. PredictabiUty of overcuts obtained for specific appHcations and the particular electrolytes to be used for the alloy metals that have to be machined must also be considered along with specific controls and limits on the ECM equipment needed. 

Electrochemical machining is a process based on the same principles used in electroplating except that the workpiece is the anode and the tool is the cathode. Electrolyte is pumped between the electrodes and a potential is applied, resulting in rapid removal of metal. 

Finally, metal objects can sometimes be fabricated in their entirety by electrodeposition (electroforming), with much the same considerations as electroplating. Conversely, portions of a metal specimen can be selectively electrolyzed away (electrochemical machining). This technique is especially useful where the metal to be shaped is too hard or the shape to be cut is too difficult for conventional machining. The sample is made the anode, a specially shaped tool the cathode, and electrolyte solution (e.g., aqueous NaCl) is fed rapidly but uniformly over the surface to be machined. Current densities may reach several hundred amperes per square centimeter across the electrolyte gap of a millimeter or so. Excellent tolerances can be achieved in favorable circumstances.16... 

Metal objects with complex shapes can be formed by electrochemical machining (electroerosion), especially important when mechanical machining is not possible. The object is the anode, where dissolution occurs, and the tool is the cathode, having the form of a mould for the object. The cathode has small holes from which jets of electrolyte exit so that there is a layer of electrolyte between anode and cathode (Fig. 15.9). An extremely important example is the manufacture of components such as blades for turbines. 

Electrochemical machining (ECM) is a method of metal machining that aims at producing parts of specified shape, dimensions, and surface finish. The process is based on the removal of metal by electrochemical dissolution ([1-15] and references cited therein). Special machines have been developed to realize this aim. A complete ECM installation (Fig. 1) consists of the machine, the power supply, the electrolyte circulation system (tank, pump, heat exchanger, and sludge removal unit), and the control system (control of current, voltage, feed rate, gap width, and electrolyte temperature, pH value, pressure, and concentration short-circuit protection). 

The electrochemical conversions of solid compounds and materials that are in direct contact with electrolyte solutions or liquid electrolytes (ionic liquids), belong to the most widespread reactions in electrochemistry. Such conversions take place in a wide variety of circumstances, including the majority of primary and secondary batteries, in corrosion, in electrochemical machining, in electrochemical mineral leaching, in electrochemical refining (e.g., copper refining), and in electrochemical surface treatments (e.g., the anodization of aluminum). 

To check the validity for two-dimensional problems, the electrochemical machining process of an iron work-piece was simulated. The applied voltage and the electrolyte conductivity were respectively 10V and... 

Ultrasonic vibrations and vibrations with a low frequency have also been used during electrochemical machining with flowing electrolytes but not with microtool fabrications at a stagnant electrolyte. For all those investigations of microtool fabrications, the times of machining of microtools were considerably high. Transient cavitation phenomena result in the increase in the convective mass... 

During electrochemical machining of a microtool, the radius of curvature is generated at the upper side of the shank because of surface tension of the electrolyte and also at the lower side of the shank... 

N. Qu, X. Fang, W. Li, Y. Zeng, Di Zhu, Wire electrochemical machining with axial electrolyte flushing for titanium alloy. Chin. J. Aeronaut. 26 (2013) 224-229. 

Electrochemical machining (ECM) is a material removal process into which pulsed current is dissipated through a conductive electrolytic solution between the tool and the workpiece (Fig. 2). Such chemical interaction causes material to be removed from the workpiece according to the shape of the tool. ECM is based on thermal effects by extremely quick heating, melting, and vaporizing. The heat sources are the energy... 

Electrochemical machining is a recent innovation, the practice dating back less than twenty-five years. Much of the driving force for its development has come from the aerospace industry with its requirement to machine very hard alloys (e.g. those based on Ti and Fe/Co/Ni/Cr) to produce components able to perform a function reUably but also having minimum weight this specification often leads to components of very complex shape. The alloys which must be employed cause problems in conventional machining because of the low rate of metal removal and the short tool life. Electrochemical machining is, however, based on different properties of the metal independent of its hardness and it is only necessary to find an electrolyte where the alloy will dissolve anodically without passivation when the rate of metal removal may be estimated from Faraday s law. 

The main drawback to electrochemical machining lies in the need to design a tool (cathode) for each new job. Moreover the design process to obtain the correct current density distribution remains a skilled art rather than a science it is often necessary to test the tool and to modify it by trial and error. In addition the need to use large volumes of electrolyte solutions does not fit in well to a mechanical workshop. However carefully they are handled, they lead to corrosion in the environment. 

Investigations of random processes by pulse experiments, which are not limited by diffusion in the electrolyte, are much less common. The increasing interest of industry to introduce pulse techniques, such as pulse plating [22], formation of gradient layers, or pulse electrochemical machining (PECM) [23], will help making these techniques more popular. 

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