Electrochemical machining

Electrochemical machining (English: Electro Chemical Machining ECM) is a subtractive manufacturing processes particularly for very hard materials, disconnecting assigned and suitable for easy deburring through to manufacture the most complicated spatial forms. A further development of the classic ECM process is the PECM ( Pulsed Electro Chemical Machining ) and the PEM (Precise Electro Chemical Machining). In the next generation PEM method precisions in the micrometer range and thus micro- machining are possible.

Description

Most important feature of the ECM method is the lack of contact between the tool and the workpiece. Therefore no mechanical forces are transferred and material properties such as hardness or toughness has no influence on the process. Of importance are properties such as melting point, thermal and electrical conductivity.

The workpiece is used as anode (positive) and the tool as a cathode (negative) polarized. To generate the requisite current flow, one uses in most cases an external voltage source. In some cases, however, such as in metallography to visualize the microstructure, the electrochemical etching is used. The potential difference in the micron range ( local element ) is used here as an internal power source in order to achieve the desired removal of material.

The shape of the tool before the cathode is the shape of the workpiece. ECM is thus an imaging method. At no tool wear takes place due to the process. Between the tool and workpiece, a gap must be set as a function of the electrical parameters, and on the flow conditions of the electrolyte. The gap width is 0.05-1 mm.

The charge transport takes in the working gap, an electrolyte solution such as aqueous solution of sodium chloride (NaCl, brine ) or sodium nitrate ( NaNO3 ). The resulting electron current releases metal ions from the workpiece. The dissolved metal ions are then at the anode reactions with parts of the split electrolyte. At the cathode, the electrolyte reacts with residual water. The end product falls of metal hydroxide, which settles as sludge and must be removed.

Because of the dependence of the gap between the anode and cathode of electrical and fluid mechanical conditions pre-calculation the shape of the cathode is difficult. Because of the easier to dominant relationships shallow molds are made ( eg turbine blades ) with less preparation effort.

The achievable surface qualities are at Rz = 3-10 microns. The edges are not affected ( only separating method without edge influence zone ). The specific material removal is 1-2.5 mm ³ / A.min. The lowering speed is variable and is between 0 and up to 20 mm / min. The electrolyte should be processed by centrifugation to separate the metal hydroxides of the electrolyte solution. The resulting sludge is further dewatered with filter presses, then to be disposed of as hazardous waste.

ECM is therefore a method for machining electrically conductive workpieces that require a specific material removal. Materials for which the ECM is applied are, for example, carbon steels, austenitic steels, and nickel -based alloys. It goes beyond the limitations of conventional machining.

The manufacturing process is used for:

• Difficult materials
• Complicated shapes
• Operations where no edge zone influence may occur
• Workpieces with internal and hard to reach with conventional tools bore intersections ( deburring )