U.S. patent application number 09/795560 was filed with the patent office on 2003-03-27 for method and apparatus for tensioning a wire electrode in a spark-erosion machine.
Invention is credited to Baiardi, Giorgio, Wehrli, Peter.
Application Number | 20030057187 09/795560 |
Document ID | / |
Family ID | 7632844 |
Filed Date | 2003-03-27 |
United States Patent
Application |
20030057187 |
Kind Code |
A1 |
Baiardi, Giorgio ; et
al. |
March 27, 2003 |
METHOD AND APPARATUS FOR TENSIONING A WIRE ELECTRODE IN A
SPARK-EROSION MACHINE
Abstract
A wire tensioning system for a wire-shaped working electrode of
a spark erosion machine and a procedure for the tensioning of the
working electrode. The working electrode at least nearly
circumferentially encompasses a braking roller in a wire entry zone
and/or a tensioning roller in a wire withdrawal zone. A nozzle is
assigned to the braking and/or the tensioning roller such that the
nozzle exerts a tensile force on the working electrode to tension
the wire.
Inventors: |
Baiardi, Giorgio; (Locarno,
CH) ; Wehrli, Peter; (Ascona, CH) |
Correspondence
Address: |
MARSHALL, GERSTEIN & BORUN
6300 SEARS TOWER
233 SOUTH WACKER
CHICAGO
IL
60606-6357
US
|
Family ID: |
7632844 |
Appl. No.: |
09/795560 |
Filed: |
February 28, 2001 |
Current U.S.
Class: |
219/69.12 |
Current CPC
Class: |
B23H 7/108 20130101;
B23H 7/104 20130101 |
Class at
Publication: |
219/69.12 |
International
Class: |
B23H 007/10 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 29, 2000 |
DE |
DE 100 09 556.9 |
Claims
What is claimed is:
1. For use with a spark erosion machine, a wire tensioning system
for a wire shaped metal working electrode comprising: a braking
roller; a tensioning roller; a wire shaped working electrode
partially circumferentially embracing at least one of the braking
roller and the tensioning roller; at least one nozzle for flowing
fluid, the at least one nozzle being assigned to at least one of
the braking roller and the tensioning roller, wherein the fluid
flow through the at least one nozzle exerts a tensioning force upon
the working electrode.
2. A wire tensioning system as defined in claim 1, wherein at least
one of the at least one nozzle is a Venturi nozzle.
3. A wire tensioning system as defined in claim 1, wherein at least
one of the at least one nozzle is an injector nozzle, and the
working electrode passes through a nozzle chamber of the injector
nozzle.
4. A wire tensioning system as defined in claim 1, wherein at least
one of the at least one nozzle is assigned to the tensioning
roller, wherein the at least one of the at least one nozzle is
disposed after the tensioning roller as seen in a direction of
travel of the working electrode, and wherein the tensioning force
exerted by the at least one of the at least one nozzle is directed
away from the tensioning roller.
5. A wire tensioning system as defined in claim 1, wherein at least
one of the at least one nozzle is assigned to the braking roller,
wherein the at least one of the at least one nozzle is disposed in
front of the braking roller as seen in a direction of travel of the
working electrode, and wherein the tensioning force exerted by the
at least one of the at least one nozzle is directed away from the
braking roller.
6. A wire tensioning system as defined in claim 1, further
comprising means for placing a rotational moment on the tensioning
roller.
7. A wire tensioning system as defined in claim 6, wherein the
rotational moment placing means comprises a motor.
8. A wire tensioning system as defined in claim 1, further
comprising means for placing a rotational moment on the braking
roller.
9. A wire tensioning system as defined in claim 8, wherein the
rotational moment placing means comprises a motor capable of
braking the braking roller.
10. A wire tensioning system as defined in claim 1, wherein the
working electrode is wrapped nearly once around the braking roller
such that, the working electrode (2, 2') forms an effective grip on
the braking roller due to friction.
11. A wire tensioning system as defined in claim 1, wherein the
working electrode is wrapped nearly once around the tensioning
roller such that, the working electrode (2, 2') forms an effective
grip on the tensioning roller due to friction.
12. A wire tensioning system as defined in claim 1, further
comprising means for measuring tension in the working
electrode.
13. A wire tensioning system as defined in claim 15, further
comprising: a direction change roller; and a spring securing the
direction change roller to the spark erosion machine, wherein the
measuring means measures the tension in the working electrode by
determining a position of at least one of the direction change
roller and the spring.
14. A wire tensioning system as defined in claim 15, further
comprising a control device which controls fluid flow produced by
the at least one nozzle in response to the tension measured by the
measuring means.
15. A wire tensioning system as defined in claim 1, wherein relief
bores permit energy-poor fluid to escape the wire tensioning
system.
16. A wire tensioning system as defined in claim 1, wherein at
least one of the tensioning roller and the braking roller comprises
cylindrical disks forming a groove in an outer circumferential
surface of the at least one of the tensioning roller and the
braking roller, wherein the groove symmetrically tapers toward a
disk axis.
17. A wire tensioning system as defined in claim 16, wherein the at
least one of the tensioning roller and the braking roller includes
return means for guiding the working electrode into the groove.
18. A wire tensioning system as defined in claim 16, wherein the
cylindrical disks comprise two disks forming the groove
therebetween.
19. A wire tensioning system as defined in claim 1, wherein the
braking roller is located in a wire entry area, the tensioning
roller is located in a wire withdrawal area, and the at least one
nozzle develops the wire tension in at least one of the wire entry
area and the wire withdrawal area.
20. For use with a spark erosion machine, a wire tensioning system
for a wire shaped metal working electrode comprising: a tensioning
roller; a wire shaped working electrode partially circumferentially
embracing the tensioning roller; and a nozzle for flowing fluid,
the nozzle being assigned to the tensioning roller, wherein the
fluid flow through the nozzle exerts a tensioning force upon the
working electrode, and wherein the wire tensioning system does not
include a braking roller.
21. For use with a spark erosion machine, a wire tensioning system
for a wire shaped metal working electrode comprising: a braking
roller; a wire shaped working electrode partially circumferentially
embracing the braking roller; and a nozzle for flowing fluid, the
nozzle being located behind the braking roller as seen in a
direction of travel of the working electrode, wherein the fluid
flow through the nozzle exerts a tensioning force in a direction
away from the braking roller and upon the working electrode,
wherein the wire tensioning system does not include a tensioning
roller.
22. For use with a spark erosion machine, a method for tensioning a
wire-shaped working electrode comprising the steps of: at least
partially circumferentially encompassing at least one of a braking
roller and a tensioning roller with the working electrode; and
exerting a tensile force on the working electrode with fluid
passing through at least one nozzle assigned to at least one of the
braking roller and the tensioning roller.
Description
FIELD OF THE INVENTION
[0001] 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
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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:
F2=F1.times.e.sup..alpha..mu.
[0011] where
[0012] F1 is the basic tensile force generating the basic
tension;
[0013] F2 is the effective tensile force generating the effective
tension;
[0014] .alpha. is the angle of wrap around the circumference;
and
[0015] .mu. is the coefficient of friction.
[0016] 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., F2 becomes independent
of F1 where F1=0).
[0017] In accord with the above, the following can be attained,
among other advantages:
[0018] greater tensile force in the operational position,
[0019] higher reliability
[0020] better operator friendliness
[0021] better possibilities for automation of the electrode
management
[0022] 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.
[0023] 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 outer nozzle chamber.
Also, it is advantageous, if between the nozzle and the braking
and/or tensioning roller to which the nozzle is assigned, no other
additional rollers, such as direction-change rollers or the like,
are to be found. The nozzle should be further in the general
proximity of the roller to which it is assigned.
[0024] Particularly of value, beyond the above, a means is
provided, which applies to the tensioning roller a moment of
rotation and/or an additional means for applying a moment of
rotation to the braking roller. For this purpose, for instance,
corresponding motors can serve, which, respectively, drive or brake
the rollers. For instance, the means can be a tensioning roller
motor, which drives the tensioning roller, and the additional means
a braking roller motor which brakes the braking roller.
[0025] The nozzle which evokes the frictional action is preferably
so designed, that the tensile force exerted by it upon the
electrode wire is directed away from the associated roller. For
example, the nozzle--as seen in the travel direction of the
electrode wire--can be located behind the tensioning roller. It can
further be worthy of consideration, to place the nozzle before the
braking roller, that is to say, in front of the working station.
Particularly advantageous is a design, wherein the nozzle is (seen
in the travel direction of the wire), located behind the braking
roller in the wire withdrawal zone, i.e. behind the operational
position with the workpiece. The nozzle is, in this case, located
relatively distant from its associated braking roller. Of
advantage, the tensioning roller can be totally dispensed with.
This design of the electrode wire tensioning system is of
particular value in the case of relatively fine electrode wires. In
this case, the jet produced by the nozzle generates the effective
tensile force. The basic tensile force in front of the brake roller
must be built up by an additional nozzle or by means of another
auxiliary device such as weight tensioning or an idler roller.
[0026] An electrode wire tension system which exhibits a tensioning
roller and wherein the nozzle is one of the nozzles associated with
the tensioning roller, which is located behind (as seen in
electrode wire travel direction), the tensioning roller is
particularly advantageous. This nozzle further exerts force on the
electrode wire in a direction away from the tensioning roller. In
this design, for instance, the braking roller can be dispensed
with. It is particularly advantageous, nevertheless, if
additionally a braking roller is provided, especially a braking
roller of the above mentioned design, that is, with a tension
producing nozzle assigned thereto. In this case, the basic tensile
force is built up by means of the roller, that is, by the drive
means assigned thereto.
[0027] It is of advantage, if the electrode wire at least nearly
circumferentially wraps around the braking roller and/or the
tensioning roller and finds itself in effective, gripping,
operational contact with the braking roller and/or the tensioning
roller because of frictional forces. The wrap-around angle runs
generally less than 360.degree., particularly between 310.degree.
and 350.degree., and most preferred is 330.degree.. The wrap-around
angle can alternately also be greater than 360.degree.. For
instance, the electrode wire can make multiple wrap-arounds about
the corresponding roller. By that means, with the intervention of
fluid flow through the nozzles a substantial frictional action on
the rollers is achieved, and therewith an exceptional attainment of
force transmission to the tension of the electrode wire occurs,
without damage to the electrode wire or a wire overlapping on the
rollers.
[0028] In a further preferred example, in the case of the wire
tensioning system, additional means are provided for the
measurement of the tension on the electrode wire. Advantageously,
the electrode wire is guided to one or two directional change
rollers. When this is done, at least one of the two directional
change rollers is made elastically resilient by means of a spring
anchorage. The measurement means determines the position of these
directional change rollers, the spring means, and/or further
auxiliary means of the tension of the respectively present
electrode wire. The data so obtained makes it possible, that a
control device can regulate the fluid flow produced from the
nozzles in relation to the wire tension measured and/or in relation
to the set point values.
[0029] In this way, the tensile force activated by the nozzle and
applied to the electrode wire, and therewith also its basic tensile
force, can be influenced. Thus, the effective tensile force
available at the work position, that is the effective wire tension,
can be controlled. Variations in the basic tensile force and
therewith in the resulting effective tensile force have a negative
effect on the quality of metal working.
[0030] Principally, the tensioning roller and/or the braking roller
are preferably constructed as cylindrical disks, whereby,
advantageously, symmetrically within the rim surfaces, a uniform,
circumferential groove is provided, and the groove narrows itself
toward the center of the side surfaces and in the direction of the
disk axis. Such rollers make possible a practically vibration-free
precise electrode wire guidance and thus improve metal working
quality on a workpiece. The rollers are also capable of handling
wires of varying diameters. For example, by means of a V-shaped
groove, the frictional force between the braking rollers (as well
as the tensioning roller) and the electrode wire is increased.
[0031] Advantageously, in the case of the braking roller and/or the
tensioning roller a spiral threaded guide to and/or a threaded
guide return for the electrode wire is provided to maintain the
electrode wire in the desired center groove. For instance, upon an
initial introduction of the electrode wire, this wire could find
itself displaced from the center axis (i.e., from the "V-notch") of
the corresponding roller. With the aid of the guide-in and
guide-back means, the electrode wire is guided to (or back to) the
central circumferential groove. Also the electrode wire, in case it
jumps out of the above mentioned groove during operation of the
machine, is transported back to its proper place. Threaded windings
of this sort can be optionally installed not only in the brake and
tensioning rollers, but also in optional other rollers of the spark
erosion machine. Advantageously, for such a roller, two threadings
are provided, which allow for wire returning in opposite axial
directions.
[0032] Beyond this, such a roller is advantageously built in two
parts, whereby from two parts one interposed groove is formed and
is used for the conducting of the electrode wire.
[0033] Finally, in an advantageous example, in a fluid flow
channel, in which the electrode wire is transported, that is to
say, is carried along, one or more relief borings are provided,
through which energy-poor fluid can be released. These relief
borings are advantageously located at such positions where a
substantial part of the next available kinetic energy has already
been transferred to the fluid, that is, near to a flow accelerating
nozzle. This prevents a situation, in which slow moving, and hence
energy poor fluid interferes too strongly with newly incoming,
energy rich fluid. Further, a sequential, continual increase in
volume flow is avoided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] In the following, the examples are described and explained
in more detail with the aid of the attached schematic drawing
wherein:
[0035] FIG. 1 is a schematic representation of a spark erosion
machine with an exemplary wire tensioning apparatus constructed in
accordance with the teachings of the present invention;
[0036] FIG. 2 is a vertical, longitudinal cross-section view
through a braking apparatus with another exemplary wire tensioning
apparatus constructed in accordance with the teachings of the
invention;
[0037] FIG. 3 is a vertical, longitudinal section view through a
tensioning element of the wire tensioning apparatus of FIG. 2;
[0038] FIG. 4 is an enlarged sectional view of the nozzles shown in
FIGS. 1 and 2;
[0039] FIG. 5 is a schematic representation of another exemplary
wire tensioning apparatus constructed in accordance with the
teachings of the present invention;
[0040] FIG. 6 is a schematic representation of another exemplary
wire tensioning apparatus wherein the tensioning roller is
bypassed; and
[0041] FIG. 7 is a schematic view of the tensioning and braking
rollers used by the spark erosion machines.
DETAILED DESCRIPTION OF PREFERRED EXAMPLES
[0042] In the following descriptions, the same reference numbers
are used for the same, or functionally like components. Further,
the terms "above" and "below" refer to the conventional operational
installation of a wire spark erosion machine, in which braking
means are positioned "above" and tensioning means are positioned
"below."
[0043] FIG. 1 provides an overview of a spark erosion machine 1
possessing a wire tensioning apparatus constructed in accordance
with the teachings of the present invention. The wire tensioning
apparatus of FIG. 1 exhibits--as seen in the wire travel
direction--in front of the work position of the spark erosion
machine, a braking apparatus 5 as well as a--as seen in the wire
travel direction--tensioning apparatus 10 located after the work
position of the spark erosion machine. The electrode wire, that is,
the wire shaped machining electrode 2, which is to be tensioned by
the wire tensioning apparatus (hereafter electrode wire 2), is
first found on a supply spool 3, wherein the electrode wire 2 is
wrapped in several layers over and beside one another about the
core of the supply spool 3. From the supply spool 3 the unwinding
electrode wire 2 runs vertically upwards to an idler roller 4 which
is preloaded against the travel direction of the electrode wire 2.
This idler roller 4 is resiliently secured by a spring means 32
which in turn is anchored to the spark erosion machine 1. This
idler/spring arrangement serves, among other things, as a
compensation element (electrode wire storage) as well as a
measuring instrument for the wire tensioning.
[0044] The electrode wire 2 then runs over the upper quarter of the
idler roller 4, and is directed about 90.degree. to the right (in
FIG. 1) in a horizontal direction to the braking apparatus 5.
[0045] This braking apparatus 5 is enclosed in a housing-like guide
block 6a and possesses a braking roller 7, which is rotatably
mounted in bearings in the guide block 6a and is further driven by
a braking motor. On the periphery of the braking roller 7 a
V-shaped groove is provided, in which the electrode wire 2 is
accommodated. The electrode wire 2 runs in a counter clockwise
direction around the braking roller 7, and wraps about the braking
roller 7 with an angle of about 270.degree. so that the electrode
wire 2, because of frictional forces, is in effectively gripping
contact with the braking roller 7.
[0046] From the braking roller 7, the electrode wire runs
vertically downward through an upper guide head 6b (which is
connected with the guide block 6a) to the characteristic working
position 8 with the workpiece 9, and from there on further through
an under guide head 6c to a tensioning apparatus 10.
[0047] This tensioning apparatus 10 is similar to the braking
apparatus 5 in that it is housed in a guide block 6d and possesses
therein a tensioning roller 11, which is rotatably supported in
bearings, and which is driven by a tensioning roller motor. On the
circumference of this tensioning roller 11 is provided a groove, in
which the electrode wire 2 can be accommodated. Electrode wire 2
runs in a counter clockwise direction also about the tensioning
roller 1. The electrode wire 2 wraps around the tensioning roller
11 with a wrap angle of about 270.degree., so that the electrode
wire 2, because of frictional forces, is in an effectively gripping
contact with the tensioning roller 11. From the tensioning roller
11, the electrode wire 2 runs horizontally to the left in the
direction of two counter rolling rollers, which form a clamping
pair 12. From these clamping rollers 12, the electrode wire
proceeds to an electrode wire recycling removal arrangement. In an
alternative, but not shown example, instead of the clamping roller
pair, essentially a guide roller is provided. In the area of the
electrode wire recycling is placed an electrode wire cutting
apparatus 14, which cuts the electrode wire into small pieces. The
pieces of the cut-up electrode wire 2 are collected in a
container.
[0048] In the guide block 6d--as seen in the travel direction of
the electrode wire--behind the tensioning roller 11 a tension
nozzle is 13 is provided. This will be more completely described in
connection with FIG. 4. A fluid flows through the tension nozzle 13
in the direction of the electrode wire 2 travel, from which nozzle
the same fluid will be ejected downward. The fluid can, for
instance, be air, or, for example, the dielectric fluid used in
spark erosion machining for rinsing and cooling. By the ejection of
the fluid, a fluid flow is created in a direction away from the
tensioning roller 11. The electrode wire 2 runs centrally placed,
directly through the tensioning nozzle 13, and because of the
friction between the fluid and the electrode wire 2 surface, is
carried along by the produced fluid flow.
[0049] In other words, by means of the tensioning nozzle 13, a
tensile force F4(a), which is directed away from the tensioning
roller 11 is exerted on the electrode wire 2, which the electrode
wire 2 brings into a frictional gripping with the tensioning roller
11. The basic tensile force is also exclusively generated by the
nozzle 13.
[0050] Alternative to this exclusive force generation approach, the
tensile force can be increased, in that the clamping roller pair 12
can be driven with the aid of an associated motor, to thus subject
the electrode wire 2 is subjected to a further tensile force F4(b).
Then, the electrode wire 2 behind the tensioning roller 11, as seen
in the direction of the wire travel, is subjected to a combined
basic tensile force of
[0051] F4=F4(a)+F4(b). The clamping roller pair 12 is controllable,
that is, it can be automatically opened and closed. The clamping
roller pair 12 becomes activated, when a greater basic tension is
required, which cannot be attained by the nozzles alone.
[0052] In the case of the above mentioned alternative example
without a clamping roller pair, the basic tensile force is
continually and exclusively produced by the nozzle 13.
[0053] The tensioning roller motor drives the tensioning roller 11,
and produces at that point, a rotational moment Mz in a counter
clockwise direction in FIG. 1. Because of the friction between the
electrode wire 2 and the tensioning roller 11 an effective tensile
force F3 is exerted on the electrode wire 2 in the area in front of
the tensioning roller 11. Further, by means of the idler roller 4,
seen in the direction of the travel of the electrode wire, in an
area lying in front of the braking roller 7 a tensile force F1 is
exerted on the electrode wire 2, which force is directed away from
the brake roller 7. The basic tensile force F1 is enhanced by a
nozzle 13a, which, as shown in FIG. 1, is placed in front of the
braking roller 7 at the brake apparatus 5, as seen in the direction
of the wire travel. This nozzle 13a is designed similarly to the
nozzle 13, 13' shown in FIG. 4 and engenders on the electrode wire
a force directed away from the braking roller 7. This force arises
since this nozzle 13a pulls in fluid through its pressurized fluid
intake port, and this fluid is ejected in the direction of a
funnel-shaped, through opening, whereby a fluid flow directed away
from the braking roller 7 is brought about.
[0054] Based on the above related reinforcement effects,
consideration can be given to a situation wherein the basic
tensioning force F1 proceeds from the nozzle 13a alone, that is,
additional tensioning means such as the idler roller 4 can be
dispensed with.
[0055] The motor of the braking roller drives the roller 7 and
produces thereon a braking moment Mb in clockwise direction.
Because of the friction between the electrode wire 2 and the
braking roller 7, accordingly the electrode wire 2, in the area
after the braking roller 7, is subjected to an effective tensioning
force F2.
[0056] The two effective tensioning forces F2 and F3 act in
opposite directions, whereby, in the work position 8 of the spark
erosion machine 1, the necessary wire tension for the machining
work on the workpiece 9 is produced. More detailed explanations as
to the construction and for the establishment of the wire
tensioning follow later.
[0057] The exemplary wire tensioning apparatus shown in FIGS. 2 and
3, is constructed in accordance with the teachings of the present
invention, and exhibits a brake apparatus 5' (FIG. 2), and a
tensioning apparatus 10' (FIG. 3). The wire tensioning apparatus is
built into a spark erosion machine, which is constructed in similar
manner to the spark erosion machine depicted in FIG. 1.
[0058] According to FIG. 2, the braking apparatus 5' is placed in a
housing-like guide block 6a'. An electrode wire 2' is introduced
through a guide tube 16' into a channel system 17'. This channel
system 17' is formed in the guide block 6a' and continues in guide
block 6b' which is coupled with guide block 6a'. The channel system
17' in FIG. 2 comprises essentially the five following channel
sections arranged behind one another in the electrode wire travel
direction, namely, 18a', 18b', 18c', 18d', 18e'. That is, in more
detail, the channel includes a first, straight line running channel
section 18a', a second curved section 18b' circumferentially
encompassing a braking roller 7', and then a third, a fourth and a
fifth channel section 18c', 18d', 18e', which are respectively
straight line sections, although placed in a zig-zag formation. The
second and the third channel sections 18b', 18c' are respectively
connected to relief borings 19a', 19b'.
[0059] The braking roller 7' is supported on ball bearings in the
guide block 6a'. This roller 7' possesses on its circumference a
V-shaped groove, in which the electrode wire 2' can lie.
[0060] The electrode wire 2 wraps about the braking roller 7' with
a wrap angle of about 330.degree., so that the electrode wire 2'
finds, because of the friction forces, an effective gripping
contact with braking roller 7'. Between the third and the fourth
channel sections 18c', 18d', an upper electric current supply 20'
is placed, and between the fourth and fifth channel sections 18d',
18e', an upper wire guide 21' is located. By means of the described
arrangement, it is assured that the electrode wire 2' always leaves
the braking roller 7' at the same place, whereby the wrapping angle
of 330.degree. is maintained.
[0061] Further, a nozzle 22a' is provided, which communicates
through a boring 23a' with the second channel section 18b', which
circumferentially surrounds the braking roller 7'. Besides this,
additional nozzles 22b', 22c', 22d' are to be found in the areas of
the first, third, and fifth channel sections 18a', 18c', 18e'. The
following nozzles 22a', 22b', 22c', 22d', which are progressively
arranged in a sequential manner, serve a main function of easing
the changes of direction of the electrode wire as it is initially
threaded through the system, and are preferably constructed like
the tensioning, injection nozzle 13, 13' depicted in FIG. 4.
[0062] Referring to FIG. 3, the tensioning apparatus 10' is placed
in a housing-like guide block 6d'. Through this guide block 6d' and
through a guide head 6c' coupled with the guide block 6d' is formed
a continuous guide channel 24' for the electrode wire 2'. This
channel comprises essentially the five sequential channel sections
25a', 25b', 25c', 25d', 25e' located, one after the other in the
direction of travel of the electrode wire 2'.
[0063] The channel 24 is made up, in other words, of a first
channel section 25a', which possesses an inlet funnel 26'. This
section 25a' opens in an essentially straight line direction into a
second and third channel section 25b', 25c' which, respectively are
straight line sections.
[0064] The channel continues with a fourth section 25d', encircling
a tensioning roller 11' and connecting into a fifth section 25e'
which opens into a guide tube 26a'.
[0065] In this construction the first, the second, and the third
channel sections, (i.e., 25a', 25b' and 25c'), are so arranged,
that the electrode wire 2' lies securely against an electric
current supply source 29'.
[0066] The tensioning roller 11' is supported in the guide block
6d' on rotatable bearings. The roller 11' possesses on its
circumference a V-shaped groove in which the electrode wire 2'
lies. The wire 2' wraps around the tensioning roller 11' with a
wrapping angle of about 330.degree., so that the electrode wire 2',
because of frictional force, has an effective grip thereon.
Furthermore, between the first and the second channel sections
25a', 25b', a lower wire guide 28' is located, and between the
second and the third channel sections 25b', 25c' a lower current
supply source 29' is placed. By means of the described arrangement,
assurance is given that the electrode wire 2' always contacts the
tensioning roller 11' at a predetermined location, whereby the
wrap-around angle of about 330.degree. is maintained. The wire
guides 21' and 28' arrange for an exact guidance of the electrode
wire in relation to the workpiece.
[0067] In the case of the tensioning apparatus 10', a plurality of
nozzles are installed at various sections of the transport system,
arranged as a sequential nozzle-set. A first nozzle 30a' is to be
found at a boring 31' communicating with the fourth channel section
25d', which circumferentially encircles the tensioning roller 11'.
An additional nozzle 30b' is provided in the area of the third
channel section 25c'. Further, in the fifth channel section 25e', a
tensioning nozzle 13' is placed, which, in connection with FIG. 4,
will be discussed in more detail below. The remaining nozzles,
30a', 30b' correspond to the tensioning nozzle 13' in construction
and service.
[0068] Now turning to FIG. 4, the tensioning nozzles 13, 13' shown
respectively in FIGS. 1 and 3, are preferably constructed as double
chamber, injection nozzles, having the two chambers 85, 95
essentially coaxial to one another. In this way, a forward
discharge funnel forms the inner chamber 85, the outer wall 91 of
which is likewise funnel shaped and tapers itself toward the
front.
[0069] The so created funnel is encapsulated in a hollow cylinder
93, forming, likewise, a funnel-shaped, through-flow passage 94 and
sealed against the hollow cylinder 93 by packing 92. The outer wall
of the discharge funnel 85, and the inner wall of the
funnel-shaped, through passage 94, mutually border at the outer jet
chamber 95. Chamber 95 is further connected with a fluid inlet
boring 96 to a pressurized fluid inlet channel of the respective
guide block 6d, 6d', and by this means, a supply of pressurized
fluid is made available to the nozzle.
[0070] The corresponding electrode wire 2, 2' runs essentially
along the central axis of the nozzle 13, 13' (i.e., through the
center of the inner chamber 85). The wall of the inner chamber
extends itself slightly beyond the outer nozzle chamber 95 in the
direction of travel of the electrode wire. Sealing rings 97 take
care for a leak free insertion of the tension nozzle 13, 13' in the
corresponding recess of the guide block 6d, 6d'.
[0071] The tension apparatuses shown in FIGS. 1 and 2 operate as
follows:
[0072] In an automatic insert mode of the spark erosion machine 1,
the introduced electrode wire 2, 2' is transported through the
illustrated wire tensioning apparatus, powered by the flow impulse
of the corresponding nozzles through which jets of fluid flow,
namely, nozzles, 22a', 22b', 22c', 22d', 30a', 30b' 13', 13 within
the channel system 17', which includes the guide channel 24'. In
this operation, the electrode wire 2, 2', is entrained, i.e.
carried along by the fluid, which flows through the channel system
17' and accordingly the guide channel 24'.
[0073] The electrode wire 2, 2' then, is by this method transported
through the channel system 17', that is the guide channeling 24'.
For a fluid, water of low conductivity serves as the operational
liquid, which is regularly employed in spark erosive cutting as a
dielectric medium. The relief borings 19a', 19b', 27a', 27b', are
located in such positions as where the fluid already has received a
substantial part of the next available kinetic boost, --that is to
say, somewhere near the third channel section 25c', just before the
nozzle 30b', or in the vicinity of the circular channel sections
25d', 118b', as seen in the fluid flow direction, directly in front
of the nozzles 30a', 22a'.
[0074] This positioning of the relief borings prevents the
energy-poor fluid from interfering with the energy-rich fluid too
strongly.
[0075] In the operation mode of the spark erosion machine, the
electrode wire tension is built up and adjusted. At all
times,--particularly in the work position 8, 8' at the workpiece
9--this tension should exhibit the specified value with the
greatest possible exactness. In the present case, the setting of
the desired wire tension is performed by means of the tension
nozzles 13, 13', the idler roller 4, as well as the three motors,
namely the motor for the clamping roller pair 12, the motor for
driving the spool, then the braking roller motor for driving the
braking roller 7, 7', and the tensioning roller motor which drives
the tensioning roller 11, 11'. At the same time, the tensioning
nozzles 13, 13' arrange for a certain basic tension of the
electrode wire 2, 2' in the stretch between the nozzles and the
tensioning roller 11, 11', while the nozzles accept fluid through
the pressure fluid inlet borings 96, and eject this fluid in the
direction of the funnel shaped through-flow opening 94. The
injected fluid, as has been explained above, can be air or, for
instance, the dielectric fluid used for the spark erosion.
[0076] Thereby, as seen in the direction of wire travel, behind the
tensioning apparatus 10, 10', especially proximal to the fifth
channel section 25e', and the guide tube 26a', a fluid flow,
directed away from the tensioning roller 11, 11', is activated,
whereby a come-along effect is exerted upon the electrode wire 2,
2'. In other words, the electrode wire 2, 2' is also sucked through
by the low pressure evoked by the tensioning nozzle 13, 13'. On
this account, a tensioning force F4(a), directed away from the
tensioning roller 11, 11', is exerted against the electrode wire 2,
2'. The so produced basic tension in the area (as seen in the
electrode wire travel direction) behind the tension roller 11, 11',
can be increased, alternatively, by the use of a larger
cross-section electrode wire, since, an additional, likewise
tensioning force F4(b) away from the tension roller 11, 11'
produced by the drive of the spool motors associated with the
clamping roller pair 12, can be exerted on the electrode wire 2,
2'. Then, a combined basic tensioning force of F4=F4(a)+F4(b)
exists. As mentioned above, the electrode wire 2, 2'
circumferentially wraps around the tensioning roller 11, 11' and,
because of the existing base tensioning force F4, the electrode
wire 2,2' is brought into effective gripping contact with the
tensioning roller 11, 11' also because of the cable-friction-force
principle. The basic tensioning force F4 engendered by the tension
nozzles 13, 13' and alternatively that of the clamping roller pair
12, brought upon the electrode wire, is also increased, in accord
with the cable friction formula, wherein validity is found in:
F3=F4.times.e.sup..alpha..mu.
[0077] where:
[0078] F3 is the effective tensile force;
[0079] .alpha. is the angle of wrap; and
[0080] .mu. is the coefficient of friction.
[0081] The effective tensioning force F3, in front of the
tensioning roller 11, 11', as seen in the travel direction of the
electrode wire, that is (especially at the work position 8, 8' with
the workpiece 9, is thus, especially because of the relatively
great wrap-around angle of 330.degree.), substantially greater than
the base tensioning force F4.
[0082] In order to fulfill the so-called compensation condition,
this being:
Mz=(F4-F3).times.R
[0083] where R is the radius of the tensioning roller 11, and Mz is
a rotational moment, directed counterclockwise on the roller, the
rotational moment Mz is brought about by the operation of the motor
of the tensioning roller 11, 11'.
[0084] With the aid of the braking roller 7, 7', an effective
tensile force F2 is brought about which is contrary in direction to
F3, and thereby the electrode wire 2, 2' is tensioned as desired in
the work position 8, 8' of the machine.
[0085] Contributing to this purpose, the braking roller 7, 7' is
driven by its associated braking roller motor at a corresponding
rotational speed, whereby the moment Mb, in clockwise direction, is
exerted upon the braking roller 7, 7'. The tension action between
the braking roller 7, 7' and the electrode wire 2, 2' rests again
on the cable friction.
[0086] Seen in the travel direction of the wire, in this case, in
the area in front of the braking roller 7, 7', there is exerted on
the electrode wire 2, 2' a basic tension force F1. The basic
tension force F1 is clearly less than the desired working tension
force F2.
[0087] The basic tension force F1 is produced in an area, which, as
seen in the direction of wire travel, lying in front of the braking
roller 7, 7', the idler roller 4, as explained, is secured by the
spring 32 to the spark erosion machine. The idler roller 4 serves,
besides this function, as a compensation element (wire storage).
The basic tension force F1 is reinforced by the nozzle 13a, which,
as shown in FIG. 1 (again, as seen in the direction of travel of
the electrode wire), is placed in front of the braking roller 7
(for example, at the braking roller 5' in FIG. 2 in the area of the
first channel section 18a'). This activates, as has been explained
above, a force directed away from the braking roller 7, 7' onto the
electrode wire 2, 2'. Because of the above mentioned reinforcement,
considerations can be made, to the effect that, the basic tensile
force F1 can be produced alone from the nozzle 13a, that is,
further tensioning means such as the idler roller 4 may be done
away with. In the area between this nozzle 13a and the supply spool
3, the wire hangs practically without tension (wire storage). In
this case, a measuring instrument measures the convexity/concavity
of the of the wire, with which data the wire supply spool motor can
be controlled. This solution is employed when very small effective
forces are required.
[0088] Changes in the electrode wire tensioning are compensated for
as follows:
[0089] As has been explained, the idler roller 4 (which, as seen in
the direction of the wire travel), lies in front of the braking
roller 7, 7', and is resiliently fastened to the spark erosion
machine 1 by a spring means 32. As a result of this arrangement,
there exists a connection between the spatial position of the idler
roller 4 and the basic tension force F1 effective on the electrode
wire 2, 2'.
[0090] If one then employs, for instance, a sensor, in order to
determine on a continuous basis the respective actual position of
the idler roller 4, from the transmitted data, one can determine
the respective, effective basic tensile force F1 then present.
[0091] With consideration of additional values--(for instance the
rotational moment Mb produced by the motor of the braking roller,
or the radius of the braking roller R, etc.)--then a central
controller (not shown) can determine the available effective
tension at the work position 8, 8'. Should this value deviate from
the optional value, then the controller can correspondingly make
correction by regulation of the braking motor and/or the tensile
roller motor and/or the tension nozzle 13, 13' and/or the clamping
motor. In this way, the basic tension is kept essentially
constant.
[0092] In an additional example, depicted in FIG. 6, the area of
the tension apparatus 10 is so designed, that its housing can be
circumvented without any wrapping of the tensioning roller in a
kind of by-pass operation. Thus the effective tension, respectively
according to need, (kind of wire, effective force), can be adjusted
in various ways. This solution is especially of use, when very
small effective forces are required. In this case, the fluid nozzle
and/or the clamping roller pair are directly responsible for the
effective force. Under certain circumstances, a series or a set of
nozzles is necessary, in order to achieve the optimal electrode
wire tension. The fluid nozzle is constructed similarly to the
nozzle as shown in FIG. 4. The nozzle takes in fluid through its
pressure fluid intake port and ejects this in the direction of a
funnel shaped opening. By this means, referring to FIG. 6, again a
fluid flow directed away from the braking roller is effected, which
carries with it the electrode wire 2'", so that this wire is
tensioned in the work position at the workpiece. This arrangement
is particularly employed when very small effective forces are
required. The tensioning apparatus possesses, as is shown in FIG. 3
in dotted lines, an additional nozzle 30c'" and an additional
directional change roller 30d'". The nozzle 30c'" produces, during
a time of electrode wire 2'" insertion, a fluid flow which passes
by the roller 11' on the left. The electrode wire 2'" moves also
from the third channel section 25c' over the change of direction
roller 30d'" direct to the fifth channel section 25e'.
[0093] FIG. 5 shows a schematic representation of another exemplary
wire tensioning apparatus constructed in accordance with the
teachings of the present invention, which is preferable and
appropriate for fine electrode wires. This apparatus possesses
principally a braking mechanism 5", however, no tensioning
apparatus.
[0094] In this case, the braking apparatus 5" is constructed like
the braking apparatus shown in FIG. 5, and is integrated into a
spark erosion machine, which machine, essentially resembles the
machine 1 shown in FIG. 1. However, instead of a tensioning
apparatus, principally a tensioning nozzle 13" is provided, and,
indeed lies in a zone which (seen in wire travel direction), is
behind a work position 8" with a workpiece 9". Under certain
circumstances, a series, or a set of nozzles are required to
achieve the required wire tension. The tension nozzle 13" is
constructed in the same manner as that nozzle shown in FIG. 4, and
produces a force F on the wire electrode 2", which force is
directed away from a braking roller 7". The roller 7" is supported
on bearings in a housing-like guide block 6a". This is achieved,
since the nozzle 13" takes in fluid through its pressure fluid
boring, and ejects this in the direction of a funnel-shaped,
through opening. By this means a fluid stream moving in a direction
away from the braking roller 7" is effected, which takes with it
the electrode wire 2". In this way, in the work position 8" at the
workpiece 9" the electrode wire is under tension. This arrangement
is also put to use where very small effective forces are
required.
[0095] FIG. 7 shows a schematic view of a tensioning roller or a
braking roller as the roller would be used in a spark erosion
machine as described in the foregoing. This roller is constructed
in two parts, which comprise two, coaxial disks, bound together.
The disks are essentially cylindrical disks 40a, 40b. The left disk
40a has a conical chamfer on its right circumferential rim. The
right disk, in reverse, has a conical chafer on its left
circumferential rim. In this way, the combined disks 40a, 40b form
a circumferential V-shaped guide groove between them. In this
grooving, the inner edge 43b of the chamfer 41b of the right disk
40b lies nearer to the central axis of rotation of the disks than
does the inner edge 43a of the chamfer 41a of the left disk
40a.
[0096] As a result, electrode wires of relatively large diameter
may run between the surfaces of 41a and 41b. On the other hand,
fine electrode wires, of relatively small diameter, run within the
offset between the chamfer 41b of the right disk 40b and the right
sidewall 42a of the left disk 40a. Additionally, both disks 40a and
40b are provided with a circumferential, threaded winding 44a and a
winding 44b.
[0097] The two threaded windings are counter oriented. Should, for
any reason, the electrode wire 2 jump out of the above mentioned
V-shaped groove 45 between the chamfers 41a and 41b, that is,
between the chamfer 41b and the sidewall 42a (if fine wire), the
electrode wire will then be transported back from the respective
winding 44a, 44b into the center V-notch.
[0098] Although certain examples of apparatus constructed in
accordance with the teachings of the invention have been disclosed
herein, the scope of this patent is not limited to those examples.
On the contrary, this patent covers all apparatus and/or methods
falling within the properly constructed scope of the appended
claims.
* * * * *