Device and method for electrochemical processing in the outline of rotationally symmetrical workpieces

Abstract

Device for electrochemical processing of rotationally symmetrical workpieces (1) in the outline, comprising a first electrode (5) which is advanceable in the direction of the axis of rotation (2) of the workpiece (1) relative to the workpiece (1) in order to produce a preform (13) of a recess (4) open towards the circumference of the workpiece (1), and comprising a second electrode (7) which is rotatable about the axis of rotation (2) relative to the workpiece (1) in order to form the recess (4) in its final dimensions from the preform (13) produced by the first electrode (5), wherein the electrodes (5, 7) are ring electrodes for the simultaneous production of a plurality of recesses (4) distributed over the circumference of the workpiece (1), characterized in that the extension of the second electrode (7) in the direction of the axis of rotation (2) is equal to or greater than the axial extension of the recess (4).

Description

The invention relates to a device for electrochemical machining of rotationally symmetrical workpieces, comprising a first electrode which can be advanced relative to the workpiece in the direction of the workpiece's axis of rotation to produce a preform of a recess open towards the workpiece's circumference, and a second electrode which can be rotatably formed about the axis of rotation relative to the workpiece from the preform produced by the first electrode to form the recess in its final dimensions, wherein the electrodes are ring electrodes for simultaneously producing a plurality of recesses distributed around the circumference of the workpiece. The invention further relates to a corresponding machining method. DE 102 58 920 A1 describes a method for manufacturing impellers with integrally formed blades for turbomachinery by electrochemical machining. An electrode forming the blades is advanced in the direction of the impeller axis and simultaneously rotated about the impeller axis, whereby a linear oscillatory motion is superimposed on the feed motion in the direction of the impeller axis and a circular oscillation is superimposed on the circular feed motion about the impeller axis. In a final stage of the machining process, only a circular feed with superimposed circular oscillation takes place. From EP 0 247 022 A2, a device for the electrochemical processing of a workpiece is known. The workpiece and two identical templates, which serve as tool electrodes, are rotatable relative to each other. German patent application DE 15 40 723 A describes a device for the electrochemical processing of a workpiece. The device can be equipped with two different electrode arrangements: One electrode is designed in the form of a ring electrode, while a second electrode arrangement is formed by electrode teeth projecting from a plate. DE 10 2004 051 854 A1 discloses a device for electrochemical processing which has an electrode arrangement formed by pins projecting from a plate. The invention is based on the objective of creating a new device of the type mentioned above and a corresponding method that enables faster machining of rotationally symmetrical workpieces in the outline compared to the prior art. The device solving this problem according to the invention is characterized in that the extension of the second electrode in the direction of the axis of rotation is equal to or greater than the axial extension of the recess. By using different processing electrodes according to the invention for the formation of a preform and for the final processing, a significant reduction in processing time can be achieved compared to the use of only one electrode, whereby both the formation of the preform and the final processing require less processing time. Advantageously, the first electrode can be designed as a thin disc electrode, while the second electrode extends axially, if necessary, over the entire recess area. The thin electrode can be moved in the side gap at a high feed rate with minimal material removal. The preform can therefore advantageously be already largely approximated to the final dimensions of the recess to be formed, which further shortens the machining step by the second electrode. In a preferred embodiment of the invention, a rotational movement of the first electrode relative to the workpiece can be superimposed on the feed movement of the first electrode in the direction of the axis of rotation, which makes it possible to produce groove-shaped preforms inclined to the axis of rotation. It is understood that the feed or rotary feed movements of the electrodes can be at least partially superimposed with oscillatory movements, which enable more precise machining according to the PECM process. The second electrode is dimensioned so that it can just be inserted into the preform, possibly after rotation around the axis of rotation. The recess can be, for example, a groove running parallel or inclined to the axis of rotation, which preferably ends open on at least one end face of the workpiece. In a particularly preferred embodiment of the invention, the first electrode is connected to the second electrode to form a single unit, which significantly facilitates the handling of the electrodes, especially their successive use. It is understood that the electrodes within the assembly are arranged coaxially to each other and preferably at a distance from each other corresponding to the axial extent of the workpiece. Advantageously, in the latter case, the machining by the first electrode is completed before the second electrode engages the formed preforms. The invention is further explained below with reference to exemplary embodiments and the accompanying drawings relating to one of these embodiments. The drawings show: Fig. 1 a workpiece manufactured according to the invention in a top view showing a section of the workpiece and in a side view; Fig. 2 a first electrode used to manufacture the workpiece of Fig. 1; Fig. 3 a second electrode used to manufacture the workpiece of Fig. 1; Fig. 4 an illustration illustrating the machining of the workpiece of Fig. 1 with the electrodes of Fig. 2 and Fig. 3; and Fig. 5 an illustration illustrating the final machining of the workpiece of Fig. 1 by the electrode of Fig. 3. A workpiece 1 to be produced by electrochemical processing is designed in its outline as a disk-shaped body of revolution with an axis of rotation 2. Around the circumference of the workpiece 1, recesses 4 in the form of undercut grooves are formed, which are open both to the circumferential surface 3 parallel to the axis of rotation 2 and to the opposing disk surfaces of the workpiece 1. As can be seen in Fig. 1, the groove-shaped recesses 4 are inclined to the axis of rotation 2. For example, radially projecting vanes, in particular turbine wheel vanes, can be positively locked into the undercut recesses 4 of the workpiece 1. The workpiece 1 can consist of a very hard material that is mechanically difficult to remove, but for which electrochemical processes are suitable. An electrode 5, shown in part in Fig. 2, is used for the electrochemical processing of the workpiece 1. In the illustrated embodiment, the electrode 5 is designed as a thin ring disk. The inner radius of the electrode 5 corresponds to the outer radius of the workpiece 1. Projections 6, shaped approximately according to the cross-section of the recesses 4, extend radially from the inside of the electrode ring and directly process the workpiece 1. The cross-sectional dimensions of the electrode projections 6 are smaller than the final dimensions of the recesses 4 that are to be achieved by the electrochemical processing, so that the first electrode only forms preliminary shapes of the recesses 4. A second electrode 7, designed like the first electrode 5 as a ring electrode with an inner radius corresponding to the outer radius of the workpiece 1, serves to achieve the final dimensions. Unlike electrode 5, however, this is not a ring disc that is significantly thinner than the workpiece 1, but rather has a thickness at least equal to that of the workpiece 1. Electrode projections 8, extending radially from the inside and covering the entire thickness of the disc, are inclined to the ring axis according to the course of the recesses 4. The cross-sectional dimensions of the second electrode 7 are also smaller than the final dimensions of the recesses 4 achieved by the electrochemical processing of the workpiece 1. In a device for the electrochemical processing of the workpiece 1, the two electrodes 5, 7 are connected to each other by connecting pieces to form an electrode assembly 10 according to Fig. 4 and are coaxially aligned to each other in the electrode assembly 10. To process the workpiece 1 under electrolyte flow (not shown) between the workpiece and the electrode, the electrode unit 10 is moved in a coaxial orientation to the workpiece 1, parallel to the axis of rotation 2 of the workpiece 1, relative to the workpiece 1 as indicated by arrow 11. Furthermore, the electrode unit 10 is moved relative to the workpiece 1 about the axis of rotation 2 as indicated by arrow 12. With this feed rate, the first electrode 1 leaves behind the preforms 13 of the recesses 4. The feed motion can be superimposed with a vibration or torsional vibration both in the direction of arrow 11 and in the direction of rotation according to arrow 12, meaning that machining can be carried out not only according to the ECM but also the PECM process. Due to the small thickness of the electrode 5, the material removal in the side gap is limited, so that the cross-section of the generated preform 13 does not significantly exceed the corresponding cross-section of the electrode projections 6. At constant feed rates in the directions of arrows 11 and 12, a preform 13 is formed that is slightly curved according to a helical line. The second electrode 7, which is now used in the second step, has correspondingly curved electrode projections 8. In cross-section, the electrode projections 8 are dimensioned such that they can be countersunk into the preforms 13 of the workpiece 1 during a feed movement of the electrode 7 according to arrows 11, 12. After the electrode 7 is inserted into the axially extending preforms 13 through the disc-shaped workpiece 1, the final machining takes place, whereby the electrode 7 only performs rotary feed movements in the direction of arrow 12. The side surfaces 14 and 15 of the electrode projections 8 of the electrode 7 correspond approximately to the shape of the inner surfaces of the recesses 4 to be achieved by electrochemical machining, so that by feeding the electrode 7 in both directions of rotation in the direction of arrow 12, the preforms 13 can be finished until the cross-sectional dimensions and shape of the recesses 4 are achieved. The final machining is preferably carried out using the PECM method, i.e. with a torsional vibration of the workpiece 1 and / or the electrode assembly 10 superimposed on the rotary feed. After each side of the preform 13 has been processed, while a wide gap 16 remains on the other side for rinsing, the processing can be changed by releasing a wide gap 17 on the other side. In one embodiment of the invention, the electrode 7 is divided by an insulating layer such that in a processing cycle only the side of the electrode facing the narrow gap, which is intended for material removal, is subjected to voltage. The slight curvature of the preform 13 produced by the first electrode 5, as described above, could be eliminated by appropriately shaping the second electrode 7, resulting in a recess 4 that is perfectly straight in its longitudinal direction. It is understood that the curvature of the preform 13 could also be corrected by appropriately controlling the path of the electrode 5 as it sinks into the workpiece. In contrast to the example shown, the length of the electrode projections 8 could be smaller than the corresponding length of the preform 13, so that inwardly widening, undercut recesses 4 could be produced by the rotary feed of the electrode 7 according to arrow 12. Beyond simply rotating the electrode 7 back and forth in accordance with arrow 12, the electrode 7 could also be moved in a circular motion according to coordinates X and Y, which are perpendicular to each other and to the direction of arrow 11. It is understood that different control programs can be used for the final processing of the workpiece and, if necessary, surface smoothing by the electrode 7.

Claims

Device for electrochemical processing of rotationally symmetrical workpieces (1) in the outline, comprising a first electrode (5) which is advanceable in the direction of the axis of rotation (2) of the workpiece (1) relative to the workpiece (1) in order to produce a preform (13) of a recess (4) open towards the circumference of the workpiece (1), and comprising a second electrode (7) which is rotatable about the axis of rotation (2) relative to the workpiece (1) in order to form the recess (4) in its final dimensions from the preform (13) produced by the first electrode (5), wherein the electrodes (5, 7) are ring electrodes for the simultaneous production of a plurality of recesses (4) distributed over the circumference of the workpiece (1), characterized in that the extension of the second electrode (7) in the direction of the axis of rotation (2) is equal to or greater than the axial extension of the recess (4). Device according to claim 1, characterized in that a rotational movement of the first electrode (5) relative to the workpiece (1) can be superimposed on the feed movement of the first electrode (5) in the direction of the axis of rotation (2). Device according to claim 1 or 2, characterized in that the feed or rotary feed movements of the electrodes (5, 7) can be at least partially superimposed with oscillatory movements. Device according to one of claims 1 to 3, characterized in that the second electrode (7) can be inserted into the preform (13), optionally by rotation about the axis of rotation (2). Device according to one of claims 1 to 4, characterized in that the recess (4) is a groove running parallel or inclined to the axis of rotation (2), which preferably ends openly on at least one end face of the workpiece (1). Device according to one of claims 1 to 5, characterized in that the extension of the first electrode (5) in the direction of the axis of rotation (2) is smaller than the axial extension of the preform (13) of the recess (4). Device according to one of claims 1 to 6, characterized in that the first electrode (5) is connected to the second electrode (7) to form a unit (10). Device according to claim 7, characterized in that the electrodes (5, 7) are arranged coaxially to each other within the assembly (10) and preferably at a distance corresponding to the axial extent of the workpiece (1). Method for electrochemical machining of rotationally symmetrical workpieces (1) in the outline, wherein a preform (13) of a recess (4) open towards the circumference of the workpiece (1) is produced with a first electrode (5) by advancing the electrode in the direction of the axis of rotation (2) of the workpiece (1) relative to the workpiece (1), and a final machining of the preform (13) produced by the first electrode (5) is carried out with a second electrode (7) by rotating the electrode about the axis of rotation (2) relative to the workpiece (1), wherein the electrodes (5, 7) are ring electrodes for the simultaneous production of a plurality of recesses (4) distributed over the circumference of the workpiece (1), characterized in that the extent of the second electrode (7) in the direction of the axis of rotation (2) is equal to or greater than the axial extent of the recess (4).

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