The invention relates to an ECM machine for electrochemically machining metallic workpieces by anodic dissolution of the workpiece by means of an electrolyte and an applied dc voltage.
The principle of ECM machining (ECM=Electro Chemical Machining) is based on the fact that a direct current is applied between a mold and the workpiece, which is to be machined. This direct current is sufficient to bring about a uniform, anodic dissolution of the workpiece in a region in the vicinity of the latter. In the gap between the workpiece and the mold (cathode) a suitable electrolyte solution flows continuously at a high rate. A copying of the contour of the mold is achieved by moving the workpiece forwards in a controlled manner. The ECM method works without the action of a mechanical force between the workpiece and the mold, which is not subjected to any wear. A very high copying accuracy and repetition accuracy is achieved and it is possible to produce complicated spatial shapes. For this reason, ECM is a particularly advantageous method for machining materials with a high heat resistance, which, because it is difficult to machine and work them with other methods, are subjected to limits. One application example is the machining of integrally bladed rotors for flow machines, which frequently are also called blisks. Here the blades, roughly worked by suitable methods, are finished using an ECM machine and appropriately molded mold cathodes. The blades are wound in themselves and, in a threading motion, which depends on the shape of the blades, must be moved into the spaces between the blades.
An ECM machine, suitable for this purpose, is known from the EP 0 292 213 B2. For this machine, two revolving tables are used, which are orthogonal to one another and the axes of rotation of which extend horizontally and are orthogonal to one another. At one revolving table, there are the mold cathodes, which can be rotated by the revolving table about the axis of the table and can be moved independently and linearly with respect to one another. At the other revolving table, at the end of a rotating shaft, there is a mold mount, at which the rotor, which is to be machined, is disposed. Because of the arrangement of the axes of rotation of the tables relative to one another, the blades, with their free end faces in the machining position, are perpendicular to the revolving table carrying the cathodes. This means that the longitudinal axis of the blades is aligned with the axis of rotation of the cathode revolving table. The shaft, carrying the rotor, furthermore can be moved linearly along a linear axis, extending parallel to the axis of rotation of the cathode revolving table, to the cathode revolving table.
For various reasons, such a machine has limitations. On the one hand, because of the configuration selected, the movability of the cathodes and of the workpiece with respect to one another is limited. On the other, because of the structure selected, with the two revolving tables and the freely bearing shaft carrying the rotor, there is only a limited static and dynamic stiffness of the system, resulting in a reduced working accuracy. Due to process forces and thermal expansion, there may be deformations, which, even if they are slight, result in shape defects in the workpiece. The machining possibilities are limited by the size and geometry of the parts.