Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
2001-02-28
2003-04-01
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C226S195000, C242S422200
Reexamination Certificate
active
06541728
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to spark-erosion machines, and more particularly to a method and apparatus for tensioning a wire shaped metal working electrode in a spark-erosion machine.
BACKGROUND OF THE INVENTION
As used herein, the word “wire tensioning” relates principally to the drawing force exerted on the metal working electrode under the assumption of a constant electrode diameter.
An example of a wire tensioning system and procedure in accord with the generic type is disclosed by DE 196 07 705 A1. In this instrument the wire shaped metal working electrode (hereinafter “electrode wire”) is withdrawn from a supply reel and guided over several directional change rollers to a braking roller. The electrode wire circumferentially embraces the braking roller, then runs over further directional change rollers to a clamping roller-pair, and from this to a container for waste recycling. For the automatic startup threading of the electrode wire about the braking roller, DE 196 07 705 A1 further proposes to furnish injector nozzles to produce jets of a through-flowing fluid. This arrangement is so constructed, that during the introduction of the electrode wire, a fluid flow tangential to the braking roller is produced, so that the electrode wire is guided about the circumference of the braking roller.
The establishment of the wire tensioning is done with the aid of three motors, which drive the supply spool, the braking roller, and the clamping roller-pair. In this combination of drivers, the clamping roller-pair motor determines the desired transport speed of the electrode wire. The braking roller generates, with the aid of the thereby caused friction effects, the specified electrode wire tensioning especially in the working area within the confines of the workpiece to be machined. When the electrode wire is brought to the electrically conductive workpiece, there occurs an electrical discharge, and a material removal occurs in accord with the known technology of spark erosion machining. By means of a relative motion between the electrode wire and the workpiece, the desired shaping can be achieved. In any case, where the spark erosion process is concerned, forces are generated, for instance from electromagnetic and electrostatic fields, which lead to a deviation in path of the electrode wire. In order to reduce this deviation, the wire electrode is tensioned, as has been explained above.
It is desirable to make available an improved wire tensioning system and a better procedure for tensioning of an electrode wire than can be supplied by the present conventional systems as described above.
ADVANTAGES OF THE DISCLOSED APPARATUS
In accord then, with this purpose, a wire tensioning system is disclosed for an electrode wire, or the like, of a spark erosion machine, in which the electrode wire circumferentially and frictionally embraces a braking roller placed in the wire entry zone and/or also so embraces a tensioning roller placed in the wire withdrawal zone. Further, the braking and/or the tensioning roller is provided with attendant fluid through-flow nozzles which are so designed that they engender in the wire entry zone and/or the wire withdrawal zone a pulling force on the electrode wire for the generation of a basic tension.
The procedure, then, is for the tensioning of an electrode wire, or the like, in a spark erosion machine, wherein the electrode wire, at least partially frictionally and circumferentially embraces a braking roller in the wire entry zone and/or so embraces a tensioning roller in the wire withdrawal zone. Additionally, an electrode wire is further placed under tension by means of one of the fluid through-flow nozzles associated with the braking roller and/or the tensioning roller, for the generation of a basic tension in the electrode wire entry zone, and preferably also in the electrode wire withdrawal zone.
In this procedure, under the concept of “braking roller”, an optional roller is placed in the electrode wire entry zone. That is, as one looks in the wire travel direction, the braking roller is located in front of the operational position of the spark erosion machine (i.e., the position in which the workpiece is situated). Preferably, however, the roller is proximal to an upper electrode wire guide-head of a cutting erosion machine. Conversely, the “tensioning roller”, is to be found (again looked at in the direction of the electrode wire travel), following the operational position of the spark erosion machine, that is, in the electrode wire withdrawal zone, preferentially proximal to the lower electrode wire guidance head of a cutting spark erosion machine.
The fluid through-flow nozzles associated with the braking and the tensioning rollers, fulfill the purpose of generating a basic tension of the electrode wire in both the wire entry and wire withdrawal zones, and do so before the braking roller and following the tensioning roller, as seen in the travel direction of the electrode wire. This is carried out in that the nozzle jet engenders a tensile force counter to that of the braking or tensioning roller on the already introduced electrode wire. In this way, the electrode wire comes into a frictionally conditioned effective engagement to grip the braking and/or the tensioning roller. The effective tensioning in the operational position of the spark erosion machine, in which position the workpiece lies (that is, the tension, as seen in the travel direction of the electrode wire, immediately behind the brake roller and directly in front of the tensioning roller), is built up in accord with the cable-friction principle under which the braking and/or the tensioning roller operates.
In this way, in a particularly advantageous manner, the effect can be of value. The value lies in the fact that already a relatively small tensile force, or tensile force change, effected by the nozzles, is sufficient to attain the necessary effective tension. In other words, this means essentially exerting influence on the effective tension. The electrode wire embraces, namely, the braking and/or the tensioning roller. Because of the basic tension generated by the accelerating/decelerating action of the nozzle jets, the wire remains in an effective grasping contact with the respective roller, because of frictional forces between the electrode wire surface and the roller periphery. In accord with the cable friction formula in accord with Euler, the following equation is valid:
F
2
=
F
1
×
e
&agr;&mgr;
where
F
1
is the basic tensile force generating the basic tension;
F
2
is the effective tensile force generating the effective tension;
&agr; is the angle of wrap around the circumference; and
&mgr; is the coefficient of friction.
In accord with this formula, the effective tensile force is essentially proportional to the basic tensile force. If the product of the wrap angle and the friction coefficient is large enough, then the system is self restraining (i.e., F
2
becomes independent of F
1
where F
1
=0).
In accord with the above, the following can be attained, among other advantages:
greater tensile force in the operational position,
higher reliability
better operator friendliness
better possibilities for automation of the electrode management
It is advantageous, if the nozzle is designed as a venturi nozzle, bringing about a flow of fluid, and thereby making use of the tensile force on the electrode wire. The fluid especially preferred is that operating fluid which is itself designed for spark erosion. Preferably, the nozzle is an injector nozzle. This can, for instance, be constructed as a two-chamber nozzle with two, chambers placed essentially coaxially to one another.
Advantageously, the electrode wire is penetratively run through one of the chambers of the injector nozzle. The outer nozzle chamber, is preferably connected to a pressure fluid supply. Particularly advantageous is a situation in which the inner nozzle chamber structure—as seen in the travel direction of the electrode wire—is extended to protrude beyond the out
Baiardi Giorgio
Wehrli Peter
Agie SA
Evans Geoffrey S.
Marshall Gerstein & Borun
LandOfFree
Method and apparatus for tensioning a wire electrode in a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for tensioning a wire electrode in a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for tensioning a wire electrode in a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3037507