Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
1999-12-03
2001-10-16
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C219S069160
Reexamination Certificate
active
06303890
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application corresponds to German Patent Application No. 198 56 099.0, which was filed in Germany on Dec. 4, 1998, and the entire contents of which are hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for the controlled withdrawal movement of a machining electrode in an erosion device, and to a corresponding control device for performing this method.
2. Description of Related Art
In DE-PS-35 25 683 a method is disclosed wherein, when a short-circuit occurs, the machining electrode first moves back along the previously traveled machining path by a predefined, short section inside the already eroded path (first way of withdrawal; from hereon also called the “default” way of withdrawal). If, at the end of this first type of withdrawal, the short-circuit has not been corrected yet, the electrode is moved further away from the short-circuit on a second, straight path. This second path is described by a withdrawal sector whose direction and length have been chosen so that the machining electrode is removed from the short-circuit point as quickly as possible (second type of withdrawal).
A method employing only the “default” way of withdrawal is known, for example, from DE-OS 37 05 475 for an electrical arc device. This publication furthermore describes a “point” way of withdrawal in which the electrode is moved towards a point when a short-circuit occurs. This point is hereby adapted to the current machining site, which means, for example, that it follows it into the depth of the tool when the erosion is performed into it.
DE-PS 38 17 302 describes a further development of the above mentioned process in which the electrode is moved first along the first, then along the second, and then along a third way of withdrawal. The third way of withdrawal follows the second type of withdrawal at the time at which the tip of the withdrawal vector is reached. The third way of withdrawal then takes place parallel to the eroded machining path, in an opposite direction. The withdrawal vector for the second way of withdrawal is also defined so as to have a fixed length and direction (from hereon also called the “fixed vector” way of withdrawal.)
The disadvantage of the known withdrawal strategies is that the machining electrodes are removed either only slowly from the short-circuit point in the initial phase, in particular, they are not moved fast enough from the already eroded machining path (for example, with the “default” way of withdrawal), or there is a risk that the electrodes will damage smaller edges created during the withdrawal movement (for example, with the “fixed vector” and “point” types of withdrawal. These edges are created in such a way, for example, that in the case of a short-circuit the electrode erodes the work piece in such a manner that a curvature corresponding to the electrode curvature is created in the work piece. If the machining electrode is removed only slowly from the short-circuit point, the erosion gap also does not significantly increase at the beginning of the withdrawal movement. The erosion particles causing the short-circuit at this point therefore cannot be flushed quickly enough from the narrow erosion gap, so that the short-circuit continues.
In addition, most of these withdrawal strategies show little consideration of the actual progression of the machining path, resulting in undesired collisions of the machining electrode with the processed work piece. This is the case particularly if the machining path has small, localized directional changes that are not detected by any withdrawal vectors.
OBJECTS AND SUMMARY
An object of the present invention is to improve the aforementioned method and device to the effect that process malfunctions are eliminated as quickly as possible, and at the same time the risk that the machining electrode will collide with work piece surfaces during the withdrawal movement is reduced.
According to one aspect of the present invention, the machining electrode is simultaneously moved backward along both ways of withdrawals, and the direction of the withdrawal vector is adapted at each point to the previously traveled machining path. This combined way of withdrawal is also hereinafter called the “tangent vector” way of withdrawal.
It is advantageous that the simultaneous movement along both ways of withdrawal on the one hand causes a quicker removal of the machining electrode from the work piece surfaces, i.e., the short-circuit is eliminated quicker, and that on the other hand the machining electrode is guided along the actual progression of the machining path, i.e., collisions with the work piece surfaces are avoided. The movement component along the first way of withdrawal hereby prevents, in an advantageous manner, the machining electrode from “getting stuck” on the curvatures which are formed due to the electrode form at the erosion site in the machining path. The second way of withdrawal adds a movement component with which the machining electrode is removed from work piece surfaces as quickly as possible. The particles created during the erosion process are able to aggregate in the previously eroded machining path. If the withdrawal movement again takes place along this eroded machining path, there is a risk that these particles are grated into the flanks or the bottom of the machining path and in this way damage the eroded surfaces of the latter. With the help of the invention, this risk is mostly eliminated.
The simultaneous movement therefore optimizes the time required for eliminating the short-circuit and the risk of collision with a work piece surface or damage of the already eroded surfaces.
But this combination effect is best achieved if the withdrawal vector is adapted to each point of the machining path. This is the best way to avoid that, because of the movement component starting immediately with the onset of the withdrawal, a collision with work piece surfaces occurs along the withdrawal vector. Such a collision can be caused in particular by local curvatures in the machining path. The invention now advantageously adapts the withdrawal vector automatically to such curvatures and hereby prevents such a collision.
Such an adaptation can be characterized, for example, in that it considers (only) larger directional changes in the machining path that is being traveled in a backward movement. The adaptation seen in the direction of the machining path that is being traveled in a backward direction also may be performed in an anticipating manner, so that only directional changes expected within a very short or a specific time are being considered. This adaptation may be accomplished with simple or more complicated mathematical calculations, such as a projection of components of the withdrawal vector on the machining path, etc.
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patent: 38 17 302 C1 (1988-05-01), None
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patent: 195 16 990 C2 (1996-11-01), None
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patent: 4-289026(A) (1991-03-01), None
AGIE SA
Burns Doane Swecker & Mathis L.L.P.
Evans Geoffrey S.
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