EP0230462A1

EP0230462A1 - Process for sparkerosion or electrochemical machining of tapered gears with hypoid tooth profile or similar parts

Info

Publication number: EP0230462A1
Application number: EP86904757A
Authority: EP
Inventors: Laszlo Rabian
Original assignee: Werkzeugmaschinenfabrik Oerlikon Buhrle AG
Current assignee: Rheinmetall Air Defence AG
Priority date: 1985-08-08
Filing date: 1986-08-08
Publication date: 1987-08-05
Also published as: WO1987000782A1; US4772368A; JPS63500442A

Abstract

Dans le procédé ci-décrit où la pièce à usiner (2) est plongée dans l'électrode (1), on évite la liaison de forme entre la pièce à usiner (2) et l'électrode (1) et/ou l'endommagement des flancs de la pièce à usiner, et on obtient la précision et l'état de surface désirés en faisant tourner les flancs négatifs (7) de la dent selon un angle gamma par rapport au centre (4) de l'entredent négatif (5). Cela est combiné avec un premier, un deuxième, un troisième ou même avec un quatrième processus de mouvement et avec l'adaptation constante des paramètres du générateur d'usinage (30) en fonction de la trajectoire restant à parcourir.In the method described above, where the workpiece (2) is immersed in the electrode (1), the form connection between the workpiece (2) and the electrode (1) and/or the damage to the flanks of the workpiece, and the desired precision and surface finish is achieved by rotating the negative flanks (7) of the tooth at an angle gamma with respect to the center (4) of the negative tooth gap ( 5). This is combined with a first, a second, a third or even with a fourth movement process and with the constant adaptation of the parameters of the machining generator (30) according to the trajectory still to be traversed.

Description

Process for EDM or electrochemical machining of bevel gears with curved teeth or similar parts

The invention relates to a method for spark-erosive and / or electrochemical machining, in particular of bevel gears with curved teeth from a workpiece, the workpiece to be machined being in an electrode having its negative shape of a machine operating in a spark-erosive or electrochemical way by means of a screw-shaped machine relative to the electrode Movement is lowered.

Bevel gears with curved teeth are mainly used in vehicle and helicopter transmissions. They are manufactured from high-alloy steels in a soft state on special gear cutting machines in rolling or in part processes with profiled cutting tools. Then they are hardened.

Because of the inevitable hardening delays, they lost their original accuracy. In order to make them usable again for the vehicle transmissions, they are lapped together in pairs on special lapping machines. The most favorable installation position is also determined for each pair of wheels when lapping. In the gear assembly, the installation of the wheel pairs must be brought into this predetermined installation position with ground washers and / or special bearing bushes. One would have liked to avoid this complex handling and would also have liked higher accuracies and surfaces in "more polished quality". Unfortunately, the bevel gears with curved teeth have a very complex tooth geometry. The flank lines in the rolling plane can be spirals, cycloids, hypoids, circular arcs or evolents. The narrow curvatures of the teeth and the narrow tooth gaps only allow grinding tools which are in the order of magnitude of a pencil tip, or only in exceptional cases thin-walled cup wheels. These grinding tools already preclude the possibility of economical grinding even in the case of bevel gears precut or forged with "grinding allowances".

It is known from toolmaking to machine complex three-dimensional workpieces by spark erosion and / or electrochemically. As is known, subsequent hardening and thus the undesired hardening delays are eliminated with this type of processing. The latest state of the art of spark erosion is described in brochure EDM 3374, Robofil / Roboform, from Char illes Technologies SA, 109, rue de Lyon, CH-1211 Geneva 13, dated 05.84 D. Pages 12 and 13 show the possible machining options for the EDM machine and describe them briefly.

For spark erosion machining of bevel gears with curved teeth, the "spiral machining of threads and spiral recesses" is closest. With this type of machining, the workpiece is sunk into the electrode, which has the negative shape of the workpiece, with a relative screwing movement between the workpiece and the electrode. With this type of processing, only those workpieces can be machined where the following conditions are met: - that no closure occurs during screwing in, and

- that the technologically-related working gap width along the entire spiral arch is nowhere undercut during screwing.

With this type of processing e.g. a cylindrical or conical thread can only be produced with a constant thread pitch. If the thread pitch on the entire spiral changes more than the technologically determined width of the working gap, which is between the electrode and the workpiece, a positive connection will occur when the workpiece is screwed into the electrode. If the thread pitch along the entire thread spiral changes as little as the technologically determined width of the working gap, the thread is partially damaged when the workpiece is screwed into the electrode. It should also be noted here that in all three cases the workpiece and the electrode are equidistant in the end position.

The bevel gears with curved teeth are complex three-dimensional bodies. The pitch of the teeth, the tooth width and the flank normals change along the tooth width according to higher orders. They are therefore briefly described in a practical manner with the partial cone angle o, with the cone distance R, with the tooth width b, with the tooth arch angle as a function of the tooth width ß = f (b), with the module m and with the normal pressure angle ot.

The other data and properties of the bevel gears are determined by the generating machines. The required vibration and noise tolerances require that the geometrical accuracies have to be kept in the order of a few pm. It is not possible to machine bevel edges with curved teeth by screwing them into the electrode, which has the negative shape of the bevel gear, although the electrode would be equidistant from the bevel gear in the end position. Depending on the variation of the above-mentioned parameter of the bevel gear with curved toothing, the tooth flanks are partially or more severely damaged along the tooth width during the insertion of the workpiece into the electrode, and in the less favorable cases even a positive fit occurs.

It is also not possible and could not be economical, firstly because of the narrow change in the surface normal, secondly because of the erosion front concentrated on a very small surface, an electrode with a regularly enlarged working gap and known planetary movements. Way of applying. The invention seeks to remedy this.

The invention, as characterized in the claims, solves the problem of creating a method for spark erosion and / or electrochemical machining of bevel gears with curved teeth or similar parts, in which the electrode is designed so that the negative tooth flanks against the The middle of the negative tooth gaps are screwed in at such a large angle that while the workpiece is being sunk into the electrode with a first spiral screwing movement, according to the gradient curve of the dental arch, between the electrode and the tooth flanks along the entire dental arch, at least there is such a large distance that no material is removed on the tooth flanks; the teeth are only pre-machined, positive locking and / or flank damage can no longer take place, and then the tooth flanks are rotated counterclockwise with a second rotation and clockwise with a third rotation. In the clockwise direction, separately depending on the direction of rotation, finished that the parameters of the machining generator are continuously adjusted during the movements depending on the distance still to be covered in order to obtain the desired surface without structural changes.

The advantages achieved by the invention can essentially be seen in the fact that the electrode with the turned-in negative tooth flanks in interaction with the three relative movements between the workpiece and the electrode and with the ongoing adaptation of the parameters of the machining generator as a function of the distance to be covered Distance allows a more economical alternative fine machining of bevel gears with curved teeth compared to grinding.

Above all, the machining of bevel gears cut or forged with "grinding allowances" and then hardened can be carried out more economically with the method according to the invention than with grinding with the desired accuracy.

However, the method according to the invention also allows the production of bevel gears with curved teeth from hard metals and other materials which are difficult to machine. The method according to the invention also allows the production of negative forms of bevel gears with curved teeth, which are used as very precise forging tools, die casting tools and as electrodes.

The invention is explained in more detail below with the aid of drawings showing only one exemplary embodiment. Show it: 1 shows a perspective view of a typical workpiece, namely an arc-toothed pinion on which only one tooth and the two adjacent tooth flanks are machined for a better overview;

FIG. 2 shows an electrode on the same scale, which has the exact negative shape of the workpiece and on which, according to the invention, the screwing in of the negative tooth flanks against the center of the negative tooth gap is indicated by dash-dot lines;

Figure 3 on the same scale the inventive

Electrode with turned tooth flanks: and

4 shows a spark-erosive machine for processing the workpieces shown in FIG. 1 by means of the electrode of FIGS. 2 and 3.

1, 2 and 3 show an electrode 1 which is suitable for machining a workpiece 2 with the aid of relative movements between the electrode and the workpiece. The electrode and the workpiece are e.g. arranged on a spark erosion or electrochemical machine.

According to the invention, the electrode 1 is designed such that the negative tooth flanks 3 are screwed in against the center 4 of the negative tooth gaps 5 with a large angle y. The angle / is selected such that while the workpiece 2 is sunk into the electrode 1 with a first spiral screw movement, which takes place according to the gradient curve of the dental arch, there is a distance between the screwed-in negative tooth flanks 7 and the tooth flanks 8 am entire dental arch. This distance is so large that material can no longer be removed from the tooth flanks 8. Thus, the teeth 9 are only pre-processed. Form locking or flank damage can no longer take place. The tooth flanks 8 are then finished with a second clockwise rotation and a third counterclockwise rotation, separated in time depending on the direction of rotation.

During the movements, the parameters of the machining generator, such as ignition voltage, pulse shape, pulse current, pulse duration, pause, mean current value, working voltage, flushing pressure, flushing quantity, are continuously adapted depending on the distance still to be covered in order to achieve the desired surface without structural changes to obtain.

According to the invention, the electrode 1 can also carry out the following alternative processing. With the first spiral screw movement, the workpiece 2 is moved into the electrode 1 only to a depth at which the gap at the tooth head 9 and at the tooth base 10 is reduced to such an extent that material removal could also begin at these points under roughing conditions .

This depth is referred to as the neutral position, because in this position neither the tooth flanks 8 nor the tooth base 10 nor the tooth head 9 can be damaged under roughing conditions.

Then, from this neutral position, the tooth flanks 8, processed according to the direction of rotation, are processed in a clockwise direction with a second movement sequence, which can be composed of screwing and rotating movements as desired. The workpiece 2 is returned to the neutral position with a third movement sequence. and finished with a fourth movement in the counterclockwise direction.

The order of processing clockwise and counterclockwise can also be reversed. Here, the parameters of the machining generator have to be continuously adapted as a function of the distance traveled, in order to obtain the desired surface without structural changes.

In order to achieve shorter machining times according to the invention, the electrode 1 is expediently composed of a large number of parts which are electrically insulated from one another. Each electrode part is electrically connected to the spark erosion or electrochemical generator by its own cable. This enables multichannel machining with significantly shorter machining times.

When machining bevel gears with curved teeth from the full piece or with too much material addition, it is expedient to use several electrodes 1 according to the invention in order to machine a workpiece with high accuracy. These electrodes can have the same or different spatial dimensions to have.

FIG. 4 shows an electrical discharge machine 11 with which the workpiece 2 of FIG. 1 is produced. The workpiece can also be produced by an electrochemical machine tool. According to FIG. 4, the dielectric container 13, in which the workpiece 2 is mounted, is fastened on the machine table 12. The container 13 is drawn cut open for better illustration. The workpiece 2 is immersed in dielectric, which is a liquid. To improve the rinsing ratio During the electrical discharge machining, the workpiece is arranged on a suction cup 14, which sucks the dielectric through the working gap, which separates the electrode 1 and the workpiece 2 from one another during machining and is indispensable for spark machining. The dielectric is conveyed via the suction openings 15 and via lines, not shown, to a pump, not shown, and is pumped back into the container 13 after it has been cleaned. During processing, a gas escapes from the dielectric, which is removed by the symbolically drawn gas extraction system 16. The machine head 23, to which the electrode 1 is fastened as a tool for machining the workpiece, is slidably attached to the electrical discharge machine 11. Its displacements take place via the electric drive motor 27, which receives the control commands from the NC or CNC control system 29. The tachogenerator 28 transmits the rotations of the drive motor 27 to the control system 29. The control system receives the information about the executed movements of the machine head 23 via the linear scale 17 and measuring sensor 18 for the Z-axis 21 The Z-axis is used for the feed and lift-off movements of the electrode 1. The electrode 1 can also move in the C-axis, whose circular directions of movement are represented by the arrows 20. These movements are carried out by the control system 29 by means of the electric drive motor 25. The tachometer generator 26 transmits the information about the executed rotations of the drive motor to the control system 29. The measuring system 23 transmits the executed movements of the electrode 1 in the C-axis to the control system 29. The spark erosion generator 30 generates the necessary for the current processing Ignition voltage, working voltage, pulse shape, pulse duration, pause between the pulses, pulse current, average current and gives the electrical machining parameters to the electrode 1 via the slip rings 22 and to the workpiece 2 via the machine table 12. The values of these electrical machining parameters change continuously during the machining of the workpiece 2 by the electrode 1. Furthermore, the Values of the pressure and the amount of the liquid dielectric. The control system 29 always controls the spark erosion generator 30 in such a way that these electrical parameters are optimally adapted to the path still to be covered during the entire machining process. The control system also controls the flushing system, not shown, so that the dielectric liquid is optimally adapted to the conditions prevailing in the working gap during the machining process, the distance still to be covered being taken into account.

The electrode 1 is advanced in the direction of the workpiece 2 and works the tooth flanks 8 of the teeth out of the full material. The finished workpiece 2 has been drawn in FIG. 4 because of the better overview. The movements in the Z and C axes are controlled in the manner described in connection with FIGS. 1, 2 and 3.

Claims

PATENT CLAIMS

1. A method for spark-erosive and / or electrochemical machining, in particular of bevel gears with curved toothing from a workpiece, the workpiece to be machined being recessed into an electrode of its negative shape in a machine operating on a spark-erosive or electrochemical path by means of a helical movement relative to the electrode is characterized in that the electrode (1) used is one in which its tooth flanks (3) are screwed in against the centers (4) of their tooth gaps (5) at an angle v which prevents material from being removed from the tooth flanks to be formed (8 ) of the workpiece (2), the tooth flanks (8) of the workpiece (2) are then finished by at least two mutually opposite rotary movements, and that during all movements on the machine, the spark generator (30 ) the ignition voltage, pulse shape, pulse duration, the pause between two Im pulses, pulse current, mean current value, working voltage and furthermore the pressure and the amount of the rinsing liquid used in the machining are continuously adapted depending on the distance still to be covered, the adaptation being carried out by means of a control system (29) of the machine tool (11) .

2. The method according to claim 1 dadurchge ¬ indicates that the electrode (1) and the workpiece (2) are moved to each other with a first spiral rotary movement according to the slope curve of the dental arch, and then a second clockwise rotation and then a third rotary movement Execute counterclockwise relative to each other.

3. The method according to claim 2 d a d u r c h g e ¬ k e n n z e i c h n e t that the third rotary movement is followed by a fourth counterclockwise movement between electrode (1) and workpiece (2).

4. The method according to claim 1 dadurchge ¬ indicates that with the first spiral rotary movement in the workpiece (2), the electrode (1) is only moved to a predetermined depth at which the gap on the tooth head (9) and on the tooth base (10) of the workpiece (2) is reduced to such an extent that material abrasion could also begin at these points under roughing conditions, and that then the tooth flanks (8), separated in time depending on the direction of rotation, with a second movement sequence in the Clockwise after any curve with a third sequence of movements after any curve the electrode (1) is returned to the predetermined depth, the workpiece (2) being finished by means of a fourth sequence of movements after any curve in the counterclockwise direction.

5. Device for performing the method according to one of the preceding claims, characterized in that the temporally successive movements between the on the EDM machine (11) attached electrode (1) and the workpiece (2) by the control system (29) ge ¬ are controlled and the spark erosion generator (30) the ignition voltage, pulse shape, pulse duration, the pause between two pulses, pulse current, mean current value, working voltage the current state in the working gap between the electrode (1) and the workpiece (2) adjusts.

6. Device according to claim 5 d a d u r c h g e k e n n z e i c h n e t that the electrode (1) consists of a plurality of parts which are electrically insulated from each other, each electrode part is electrically connected to the spark erosion generator (30) with its own cable.

7. Device according to claim 5 d a d u r c h g e k e n e z e i c h n e t that several electrodes are used to carry out successive machining steps on the workpiece (2), each of the electrodes having the same or different spatial dimensions.