ELECTRODE FOR ELECTROCHEMICAL MACHINING, METHOD OF ELECTROCHEMICAL MACHINING WITH SAID ELECTRODE, A BEARING AND A METHOD OF DETERMINING A PROFILE USING SAID ELECTRODE

Abstract: The invention relates to an electrode for electrochemical machining, said electrode comprising a plurality of electrode segments separated by insulating material. As desired, different voltages are applied to each of the electrode segments giving control over the amount of material locally removed from the metal piece. The invention also relates to a method of electrochemical machining.

Description: Electrode for electrochemical machining, method of electro¬ chemical machining with said electrode, a bearing and a method of determining a profile using said electrode The present invention relates to an electrode for electrochemical machining. Such electrodes are known in the art and consist of a solid electrode body which has a form complementary to the desired'form of the metal piece to be electrochemically machined. The object of the present invention is to provide an electrode which allows for controlled and flexible electro¬ chemical machining. To this end the electrode according to the invention is characterized in that the electrode comprises a plurality of electrode segments, which are separated from each other by an electrically insulating layer, the electrode segments hav¬ ing a electrically non-insulated end for facing a metal piece to be electrochemically machined. Such an electrode allows the application of different voltages to different electrode segments relative to the metal piece to be machined. Thus the amount of material removed from the metal piece can be locally controlled. The invention also relates to a method of electro¬ chemically machining a metal piece. This method is characterized in that an electrode according to the invention is used to machine the surface of the metal piece, by applying different current densities to each of the electrode segments of the electrode, depending on the amount of material to be removed at a particular site of the metal piece facing a corresponding non-insulated end of the electrode segment. Thus a method is provided in which not only constant voltages can be applied to each of the electrode segments resulting in local removal of material from the metal piece, but also a time-dependent variation of the applied voltage thus giving ample control over the electrochemical machining process. The invention also relates to a bearing comprising a bearing ring, characterized in that the bearing ring is elec¬ trochemically machined in accordance with the invention. Furthermore, the invention relates to a bearing com- prising a cylindrical rotating body, characterized in that the cylindrical rotating body is electrochemically machined in accordance with the invention. Finally the invention relates to a method of measur¬ ing the profile of a metal piece, being characterized in that an electrode comprising a plurality of electrode segments according to the invention is put above the surface of the metal piece, forming a gap which is filled with an electrically conducting fluid, and the resistance over the gap is measured for each of the segments. The invention will now be elucidated with the aid of the drawing, illustrating the invention by way of example. Fig. 1 is a cross section of an electrode according to the invention. Fig. 2 is a side view of the electrode and half of a cylindrical rotating body. Fig. 3 shows the current density as experienced by cylindrical rotating body of Fig. 2. Fig. 1 shows an electrode 1 for electrochemical machining, which electrode comprises electrode segments 2' to 2" which are separated on the sides of the electrode segments by an electrically insulating layer 3 1 to 3 1 ". The electrode 1 is covered with an electrically insulating layer, leaving the end of each electrode segment free of electrically insulating material for machining the metal piece to be electrochemically machined and contact means (not shown) for applying a voltage to each of the electrode segments 2. Fig. 2 shows a side view of a part of the electrode 1 shown in Fig. 1. The metal piece to be electrochemically machined is here a cylindrical rotating body, roller 4 (par- tially shown) , for a cylindrical roller bearing, which cylin¬ drical roller 4 is spaced from the electrode 1 forming a gap 5 through which electrolyte is passed. As shown in Fig. 2, non- insulating ends 6 1 to 6" (uneven shown) of the electrode seg¬ ments 2 face the cylindrical roller 4 and lie in one plane. More specifically the plane is a flat surface. This means that such an electrode 1 is easy and cheap to manufacture and this geometry is possible due to the fact that the voltage over the gap 5 can be chosen for each electrode segment 2 separately. To electrochemically machine the cylindrical roller 4, it is rotated around the axis indicated with numeral 7 and the non-insulated ends 6 of the electrode segments 2 form a narrow blade. Cylindrical rollers 4 in a cylindrical roller bearing are more strained at the surfaces of the cylinder near the ends of the cylindrical roller 4. To spread the load over the full cylindrical surface the roller 4 must be of a slightly smaller diameter near the ends of the roller 4. To this end the voltage applied to the electrode segments 2 is increased towards the outer electrode segments 2' and 2" respectively . Thus the current density and hence the amount of material removed from the cylindrical roller 4 is increased near its ends. The resulting profile 8 shown in Fig. 2 is highly exag¬ gerated. Usually the difference in diameter between the centre and the ends of the roller 4 is in the order of microns or tens of microns. As the electrode 1 and the metal piece are moved par¬ allel to each other, while different voltages are applied to the electrode segments 2, and the intersections of the insulating layers 3 and the non-insulated ends 6 of the elec- trode segments 2 are, over at least part of their lengths, inclined to the direction in which the electrode l and the metal piece move parallel to each other result in a smooth variation of the current density (as shown in Fig. 3) over the length of the cylindrical roller 4. Thus it is possible to obtain a smooth curvature of the metal piece with a limited number of electrode segments 2. Thus for a smooth variation it is preferred that the electrode 1 is characterized in that the intersection of the insulating layer 3 and the non-insulated end 6 of the elec- trode segment 2, over at least part of its length, is inclined to the nearest side walls of the electrode 1, and that the insulating layers 3 of the different electrode segment sides meet each other. The particular design of the electrode 1 according to the invention enables the workpiece form to be measured and hence can produce an accurate form irrespective of the initial form of the workpiece. ith the currently used, single piece conforming electrodes, the initial workpiece form must be carefully controlled and the machining time and current care- fully matched to the required form. Measurement of the workpiece form is achieved by measuring the resistance of the gap local to each segment 2 of the electrode l. The resistance is proportional to the local gap width 5, so by comparing the local resistance measurements of adjacent segments 2, the workpiece profile can be determined. As desired the electrode may be moved relatively to the metal piece. Thus the invention allows the determina¬ tion of the profile of a metal piece.

Claims: CLAIMS 1. Electrode for electrochemical machining, charac- terized in that the electrode (1) comprises a plurality of electrode segments (2) , which are separated from each other by an electrically insulating layer (3) , the electrode segments (2) having a electrically non-insulated end (6) for facing a metal piece to be electrochemically machined. 2. Electrode according to claim 1, characterized in that the intersection of the insulating layer (3) and the non- insulated end (6) of the electrode segment (2) is, over at least part of its length, inclined to the nearest side walls of the electrode (1) . 3. Electrode for electrochemical machining, charac¬ terized in that the non-insulating ends (6) of the plurality of electrode segments (2) lie substantially in one plane. 4. Electrode according to claim 3 , characterized in that the plane is a flat surface. 5. Electrode according to claim 2 to 4 , characterized in that the non-insulating ends (6) of the electrode segments (2) form a narrow blade. 6. Electrode according to claim 2 to 5, characterized in that the insulating layers (3) of different electrode seg- merit sides meet each other. 7. Method of electrochemical machining a metal piece, characterized in that an electrode (1) according to any of the claims 1 to 6 is used to machine the surface of the metal piece, by applying different current densities to each of the electrode segments (2) of the electrode (1), depending on the amount of material to be removed at a particular site of the metal piece facing a corresponding non-insulated end (6) of the electrode segment (2) . 5. Method of electrochemical machining according to claim 7, characterized the electrode (1) and the metal piece are moved parallel to each other while voltage is applied. 9. Method of electrochemical machining according to claim 8, characterized in that the intersection of the insu¬ lating layer (3) and the non-insulated end (6) of the elec- trode segment (2) is, over at least part of its length, inclined to the direction in which the electrode (1) and the metal piece move relatively to each other. 10. Method of electrochemical machining according to one of the claims 7 to 9, characterized in that the metal piece is a bearing ring. 11. Method of electrochemical machining according to on of the claims 7 to 9 , characterized in that the metal piece is a cylindrical rotating body. 12. Bearing comprising a bearing ring, characterized in that the bearing ring is electrochemically machined accord¬ ing to claim 10. 13. Bearing comprising a cylindrical rotating body, characterized in that the cylindrical rotating body is elec¬ trochemically machined according to claim 11. 14. Method of measuring the profile of a metal piece, characterized in that an electrode (1) comprising a plurality of electrode segments (2) according to any of the claims 1 to 6 is put above the surface of the metal piece, forming a gap (5) which is filled with an electrically conducting fluid, and the resistance over the gap (5) is measured for each of the segments.

Inventors: WARDLE FRANK PETER, WARDLE, FRANK, PETER
Applicants: SKF IND TRADING & DEV, WARDLE FRANK PETER, SKF INDUSTRIAL TRADING & DEVELOPMENT COMPANY B.V., WARDLE, FRANK, PETER
Application year: 1996
Main classification: B23H3
IPC codes: B23H1, B23H3, B23H7