Электрохимическая обработка металлов

Process for shaping conductive metals

Electrochemical machining (ECM) is a method of removing metal by an electrochemical process. It is normally used for mass production and for working extremely hard materials, or materials that are difficult to machine using conventional methods. Its use is limited to electrically conductive materials. ECM can cut small or odd shaped angles, intricate contours or cavities in hard and exotic metals, such as titanium aluminides, Inconel, Waspaloy, and high nickel, cobalt, and rhenium alloys. Both external and internal geometries can be machined. In the ECM process, a negatively charged (cathode) cutting tool is advanced into a positively charged (anode) workpiece. Pressurized electrolyte is injected at a set temperature into the area being cut, at a feedrate equal to the rate of "liquefication" of the anode material. The gap between the tool and the workpiece varies within 80–800 micrometers (0.003–0.030 in.) As far back as 1929, an experimental ECM process was developed by W. Gussef, although it was 1959 before a commercial process was established by the Anocut Engineering Company. B. R. and J. I. Lazarenko are also credited with proposing the use of electrolysis for metal removal. High surface quality may be achieved. No direct contact between tool and work material so there are no forces and residual stresses. The surface finish produced is excellent. Less heat is generated.

The saline (or acidic) electrolyte poses the risk of corrosion to tool, workpiece and equipment. It cannot be used for soft materials.

The needed current is proportional to the desired rate of material removal, and the removal rate in mm/minute is proportional to the amps per square mm. Typical currents range from 0.1 amp per square mm to 5 amps per square mm. Thus, for a small plunge cut of a 1 by 1 mm tool with a slow cut, only 0.1 amps would be needed. However, for a higher feed rate over a larger area, more current would be used, just like any machining process—removing more material faster takes more power. Thus, if a current density of 4 amps per square millimeter was desired over a 100×100 mm area, it would take 40,000 amps (and much coolant/electrolyte).

ECM machines come in both vertical and horizontal types. Depending on the work requirements, these machines are built in many different sizes as well. The vertical machine consists of a base, column, table, and spindle head. The spindle head has a servo mechanism that automatically advances the tool and controls the gap between the cathode (tool) and the workpiece. CNC machines of up to six axes are available. Copper is often used as the electrode material. Brass, graphite, and copper tungsten are also often used because they are easily machined, they are conductive materials, and they will not corrode.

The tool and workpiece are separated by a very small gap, i. e. no contact in between them is made. The tool and material must both be conductors of electricity. Needs high capital investment. Systems consume much power. A fluid is used as a medium between the tool and the work piece (conductive for ECM and dielectric for EDM). The tool is fed continuously towards the workpiece to maintain a constant gap between them (ECM may incorporate intermittent or cyclic, typically partial, tool withdrawal).

Electrochemical grinding (ECG) is similar to electrochemical machining (ECM) but uses a contoured conductive grinding wheel instead of a tool shaped like the contour of the workpiece.