Europaisches Patentamt | | | | 1 1| | | | | 1 1| 1 1| | | | | | | ||

(19) J European Patent Office

Office europeen des brevets (11) EP 0 607 893 B1

(12) E U R O P E A N PATENT S P E C I F I C A T I O N

(45) Date of publication and mention (51) int. CI.6: B23H 9/16, B23H 3/02,
of the grant of the patent: B29C 4 7 / 2 0
23.04.1997 Bulletin 1997/17

(21) Application number: 94100561.3

(22) Date of filing: 17.01.1994

(54) Shaped-tube electrolytic machining p r o c e s s

Elektrolytische Bearbeitung durch STEM-Verfahren
Usinage electrolytique utilisant le procede STEM

(84) Designated Contracting States: (74) Representative: Reinhard - Skuhra - Weise &
BE DE Partner
Postfach 44 01 51
(30) Priority: 19.01.1993 US 5568 80750 Munchen (DE)

(43) Date of publication of application: (56) References cited:

27.07.1994 Bulletin 1994/30 DE-A- 3 726 869 FR-A- 1 290 734
FR-A- 2 167 552
(73) Proprietor: Corning Incorporated
Corning New York 14831 (US) • MACHIN ABILITY DATA CENTER 'MACHINING
DATA HANDBOOK 3 rd. edition' 1980 , THE
(72) Inventor: Willis, Neal Peters JOHNSON & HARDIN CO. , OHIO USA * page
Corning, NY 14831 (US) 11.71 - page 11.75 * * the whole document *

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o Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give
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notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in
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a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art.
Q_ 99(1) European Patent Convention).
LU
Printed by Rank Xerox (UK)Business Services
2.14.2/3.4
 1 EP 0 607 893 B1 2

Description et al., 3,352,958 to Andrews, 3,793,169 to Joslin,

3,805,015 to Andrews, and 4,088,557 to Andrews.
FIELD OF THE INVENTION In recent years, shaped-tube electrolytic machining
processes have also found application in the manufac-
The present invention relates to a shaped-tube s ture of precision extrusion dies for producing ceramic
electrolytic machining process according to the pream- honeycomb structures. Such structures are particularly
ble of claim 1. useful for automobile catalytic converters.
The manufacture of extrusion dies from these ultra-
BACKGROUND OF THE INVENTION hard materials is an extremely precise process. The
10 extrusion dies are formed with multiple apertures
In Machinability Data Center "Machining Data through which material to be extruded is forced under
Handbook", 3rd edition, 1980, pages 11.71-11.75, a high pressure. In one method of forming the extrusion
conventional STEM (shaped-tube eletrolytic machining) die, mechanical drills are used to provide the extrusion
process is described. The STEM process is a variant of apertures. If the extrusion dies are formed of ultra-hard
the ECM process differing significantly therefrom in the is materials such as, for example, 17-4PH stainless steel
use of acid electrolyte to ensure that the dissolved metal or Inconel® 718 (a registered trademark of International
will go into solution. The STEM process is used to Nickel Co., Inc.), the drilling rate used for aperture for-
machine hard-to-machine materials such as stainless mation is very slow and a great deal of time and effort is
steels. expended in extrusion die formation. If softer die mate-
In the French patent FR-A-2 167 552, a constant or 20 rials are used, the drilling rate is increased, but the life
programmed current ECM process using salt-type elec- span of the resulting extrusion die is correspondingly
trolytes is described wherein a current control is applied shorter.
to correct for relatively minor shifts in hole diameter. Because of these difficulties, apertures are now
In the document FR-A-1 290 734, an electrolytic formed in extrusion dies by electrochemical machining
conduction method for treatment of a workpiece is 25 techniques rather than mechanical drilling. With an
described. electrochemical machining process, the workpiece from
Electrochemical machining is a widely used tech- which the die is to be formed is situated in a fixed posi-
nique for producing holes in difficult-to-machine con- tion relative to a movable manifold. The manifold sup-
ductive parts. Generally, this technique involves using ports a plurality of drilling tubes, each of which are
electrochemical force (as opposed to mechanical force) 30 utilized to form an aperture in the workpiece. The drilling
to disengage or deplate material from a workpiece. tubes operate as cathodes in the electrochemical
A highly specialized adaptation of electrochemical machining process, while the workpiece comprises the
machining, known as shaped-tube electrolytic machin- anode. As the workpiece is flooded with an acid electro-
ing, is used for drilling small, deep holes in electrically lyte from the drilling tubes, material is selectively
conductive materials. Shaped-tube electrolytic machin- 35 deplated from the workpiece in the vicinity of the drilling
ing is a noncontact electrochemical-drilling process that tubes to form the requisite aperture pattern. U.S. Patent
distinguishes itself from all other drilling processes by its No. 4,687,563 to Hayes and European Patent Applica-
ability to produce holes with aspect ratios of up to 300:1 . tion Publication No. 0245 545 to Peters disclose such
Shaped-tube electrolytic machining processes are dis- processes.
cussed in more detail in Machining Data Book, vol. 2, 40 A further difficulty in drilling holes in ultra-hard
pp. 11-71 to 11-75 (3rd ed. 1980); E.J. Weller, Nontradi- materials arises when a series of workpieces is drilled
tional Machining Processes, pp. 109-13 (2nd ed. 1984); using the same electrolytic fluid. As conductive material
and G.F. Benedict, Nontraditional Manufacturing Proc- deplates from the workpiece and accumulates in the
esses, pp. 181-87 (1987). fluid, the fluid's conductivity changes, and, for a given
Advances in jet engine technology have resulted in 45 applied voltage in the drilling process, the resultant cur-
the need to machine super alloys and metals. The char- rent flow through the workpiece will vary. As current
acteristics of these metals and the complex designs changes, hole diameter changes accordingly. This prob-
associated with jet engine hardware have posed lem must be overcome by continuously readjusting
machining problems which are beyond the capability of input voltage to achieve a uniform hole diameter.
conventional machining processes. As a result, shaped- so U.S. Patent No. 3,793,169 to Joslin describes a
tube electrolytic machining processes have found par- process for drilling holes of substantially uniform diame-
ticular applicability in the manufacture of aircraft ter at a high drilling feed rate. To achieve a uniform hole
engines. These processes are especially useful in drill- diameter, Joslin teaches slightly reducing supplied cur-
ing holes through turbine blades, buckets, vanes, and rent as the depth of the hole increases. Current reduc-
struts so that cooling liquid can be circulated through 55 tion is accomplished by "programming" a decrease in
these components during turbine operation. Examples current as hole depth increases, without regard to
of the use of shaped-tube electrolytic machining proc- actual current flows or conductivity levels. At best, this
esses in conjunction with aircraft engine manufacture method for attaining uniform hole diameter is imprecise.
are disclosed in U.S. Patent Nos. 3,352,770 to Crawford A further problem arises when the workpiece to be

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 3 EP 0 607 893 B1 4

drilled includes a slotted lower surface, in the form of a DETAILED DESCRIPTION OF THE DRAWINGS AND
grid of intersecting slots, as is the case in many drilling THE INVENTION
operations. Holes typically are drilled to meet the inter-
section of the slots. In such workpieces, resultant hole FIG. 1 is a schematic view of a shaped-tube elec-
diameter is reduced as the hole reaches the slotted por- 5 trolytic machining system which is useful for carrying
tion. Such reduced hole diameter is caused by a reduc- out the drilling process of the present invention. The
tion in the electrolyte back pressure experienced as the system includes a work enclosure formed by base 2 and
holes break into the slotted areas. As the hole being cover 4. Positioned within the work enclosure is support
drilled reaches the intersection of slots, electrolyte flows 6 on which workpiece W rests. Workpiece W includes
through the slots and back through previously drilled w slots S in the lower surface thereof. As illustrated, holes
holes, resulting in a loss of electrolyte in the subject H are drilled in workpiece W by passing an electrolyte
hole. This loss of back pressure causes a reduction of through feed manifold 9 into hollow tube electrodes 10.
the current path, and a consequent reduction of current To achieve electrolytic machining, electrode holder 8 is
flow. The reduced current flow slows the deplating rate, provided with cathode contact 40 which is coupled to
which causes the hole diameter to taper where the hole 75 constant current source 32 by connector 38, having
meets the slot. A reduced hole diameter is undesirable ammeter 42. Workpiece W is provided with anode con-
at the interface between a hole and slot because it can tact 36 which is coupled to constant current source 32
cause inconsistencies in material flow through a die pro- by connector 34. As a result, electrolyte E discharged
duced from the workpiece. through hollow tube electrodes 10 deplates metal from
The present invention is directed to overcoming 20 workpiece W, forming holes H. This is shown in more
these deficiencies. detail in FIG. 2, which is an enlarged view of the portion
of the system of FIG. 1 taken within circle 2-2. As illus-
SUMMARY OF THE INVENTION trated, electrolyte E advances through the central pas-
sage defined by hollow tube electrode 10. At end 13 of
The present invention relates to a process for 25 hollow tube electrode 10, electrolyte E contacts work-
shaped-tube electrolytic drilling of holes in workpieces, piece W which increases the depth of hole H. Electro-
particularly those having slotted lower portions. The lyte E then advances upwardly out of hole H as shown
process involves advancing a conductive tube against by the arrows in FIG. 2. This flow of electrolyte E causes
the workpiece while both passing an electrolyte through metal deplated from workpiece W within hole H to be
the tube and into contact with the workpiece and pass- 30 carried out of the hole. In FIG. 1, stationary guideplate
ing a fixed electric current between the tube and the 16 is provided to align hollow tube electrodes 10 so that
workpiece through the electrolyte. The constant current holes H in workpiece W are properly located.
flow through the tube, the fluid, and the workpiece As also shown in FIG. 2, hollow tube electrode 10
causes conductive material from the workpiece to includes metal tube 12 and a coating of dielectric mate-
deplate uniformly throughout the hole. 35 rial 14. End 13 of metal tube 12 is, however, not covered
by dielectric material so that an electrolytic cell is
BRIEF DESCRIPTION OF THE DRAWINGS formed between that portion of metal tube 12 and work-
piece W. Generally, this portion of hollow tube electrode
FIG. 1 is a schematic view of a shaped-tube elec- 10 is sloped such that angle a is preferably 11°. By coat-
trolytic machining system. 40 ing metal tube 12 with dielectric material 14, metal ions
FIG. 2 is an enlarged view of a portion of the sys- present in electrolyte E after removal from workpiece W
tem of FIG. 1 taken within circle 2-2 of FIG. 1. are prevented from depositing on hollow tube electrode
FIG. 3 Is a schematic diagram of a preferred con- 10 where it is coated. This coating also confines drilling
stant current device used to carry out the present inven- to the area around end 13 of metal tube 12. Deposition
tion. 45 can take place on hollow tube electrode 10 only where
FIG. 4 is a magnified (15X) photographic view of metal tube 12 is not coated with dielectric material 14.
holes drilled with a constant DC voltage. However, any deposits can be removed by periodically
FIG. 5 is a magnified (15X) photographic view of reversing the polarity of constant current source 32.
holes drilled, in accordance with the present invention, Such polarity reversal of constant current source 32 is
with a constant applied DC current. so typically carried out for 0.05 to 3.0 sec. after 0.1-30 sec.
FIGS. 6-8 are plots of the average diameter, by row, of operation by hollow tube electrode 10.
of the holes drilled with a constant applied DC voltage Electrolyte E exiting from holes H in workpiece W
where the holes interface with workpiece slots. drains into supply tank 20. Supply tank 20 is provided
FIGS. 9-11 are plots of the average diameter, by with heat exchanger 22 which heats or cools the elec-
row, of the holes drilled, in accordance with the present ss trolyte to maintain a desired temperature. Pump 24 is
invention, with a constant DC current where the holes connected to supply tank 20 for recycling electrolyte
interface with workpiece slots. through filter 26, feedpipe 28, pressure controller 31,
and flow meter 30 into manifold 9.
In operation, the shaped-tube electrolytic machin-

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ing system shown in FIG. 1 circulates electrolyte ment of constant current power supply 32. Unregulated
through the system until holes H of sufficient depth are forward power supply 104 converts supplied three-
formed in workpiece W. As hole H deepens, the struc- phase AC voltage to a DC signal. This type of power
ture formed by manifold 9, electrode holder 8, and hol- supply, which rectifies the AC input signal to a DC sig-
low tube electrodes 10 is advanced toward workpiece W 5 nal, is well known in the art, and any such rectifier can
in the direction of arrow A by a constant feed servosys- be used to carry out the present invention. The rectified
tem (not shown). As a result, ends 13 of hollow tube power signal is applied to the drilling apparatus at con-
electrodes 10 are maintained in a position suitable for tact 40. Current transducer 106, connected to the work-
optimal deplating of metal from workpiece W. Generally, piece W at contact 36, senses DC current flow exiting
the rate at which these components are advanced along 10 the circuit consisting of the hollow tube electrodes, elec-
the path defined by arrow A is substantially equal to the trolyte, and workpiece, and generates a proportional
rate at which the workpiece material is dissolved. The output signal when a change of current is detected. The
system of Figure 1 is provided with a mechanism (not output signal is induced by passing the DC supply cur-
shown), as is well known in the art, to control operation rent through a magnetic flux field which will result in an
of constant current source 32, the constant feed servo- 15 induced voltage should current change. The principle
system and the electrolyte circulating system. upon which the transducer operates is the Hall effect
The shaped-tube electrolytic machining process of which is well known in the art. Such transducers are
the present invention can he used to drill holes in a vari- also well-known in the art and consist of a substantially
ety of conductive materials, such as 304 stainless steel, torroidal permanent magnet 107, through which the cur-
321 stainless steel, 414 stainless steel, inconel alloy 20 rent-carrying conductor passes. The generated feed-
718, inconel alloy 625, inconel alloy X-750, and inconel back signal is proportional to the change in current, and
alloy 825. Holes as deep as 610 millimeters can be pro- is applied via feedback line 109 to a monitor board 102,
duced with length-to-diameter (i.e. aspect) ratios of up which preferably includes one or more operational
to 300:1 and diameters ranging from 0.5 to 6.4 millime- amplifiers (not shown) for generating difference signals
ters. Oval and other shapes should have a minimum 25 in response to system current changes sensed by cur-
width of 0.5 millimeters and a major-to-minor axis ratio rent transducer 106.
of 3:1. To set the constant current level of the system, an
The electrolyte is a solution which contains an acid operator enters a desired level into computer 108 via a
selected from the group consisting of nitric acid, sulfuric keyboard (not shown). Computer 108, is any computer
acid, hydrochloric acid, and mixtures thereof. Generally, 30 that can be programmed to deliver a correction signal in
the electrolyte has a volumetric acid concentration of response to a signal representing a change in current
16-18 vol. %. The electrolyte is applied to workpiece W flow. The computer will generate a reference signal pro-
at a temperature of 18-32°C due to the effect of heat portional to the desired current, the reference signal
exchanger 22 and at a pressure of 344-551 KPA which being applied to the monitor board 102. The feedback
is imparted by the discharge pressure from pump 24, as 35 signal from the current transducer 106 and the fixed sig-
regulated by pressure controller 31. The content of nal supplied by computer 108 each are applied to an
metal particles in the electrolyte is a maximum of 45- input of a single operational amplifier on monitor board
2500 milligrams per liter. Generally, conductivity 102. Differences in the two signals trigger the opera-
increases with the concentration of metal and acid in the tional amplifier to generate an output signal to be
electrolyte. Higher acid concentrations result in 40 applied to the voltage regulator 110. The difference sig-
increased metal removal from workpieces; however, nal is used to activate or deactivate one or more transis-
accelerated chemical attack on the electrodes may tors in the voltage regulator 110 and change the applied
occur. Increased concentration of acid in the electrolyte current. Voltage regulation board 110 preferably
also increases the hole size. Increases in electrolyte includes five emitter-follower transistors which can be
temperature have the same effect as concentration 45 selectively actuated by output signals from monitor
increases. board 102 to adjust input voltage and, therefore, DC
Constant current source 32 is preferably a direct current flow through the electrode, the electrolyte, and
current power supply. It has a voltage of 1-1 5 volts, a for- the workpiece.
ward on time of 0.1-30 seconds, and a reverse time of To summarize, the problem of inconsistent hole
0.05-3 seconds. A preferred current value during drilling so diameter resulting from sudden supply current changes
is approximately 166 Amps, and an acceptable range of as the holes reach the slotted portions of the workpiece
current has been found to be 160-170 Amps. Generally, is solved by controlling DC current in accordance with
the cross-sectional area of the hole being drilled the present invention. Specifically, DC current is main-
becomes larger as current increases. However, it is not tained at a constant level despite sudden changes in
desirable to operate at the upper limit of the voltage 55 conductivity resulting from loss of electrolyte as slots
range, because the resulting heat generated may dam- are encountered. As a reduction in current flow is
age the coating of dielectric material 14 and will accel- sensed, input voltage is automatically adjusted upward
erate the build up of metal ions on the electrode. to restore current flow to an desired level.
FIG. 3 is a detailed drawing of a preferred embodi- Hollow tube electrodes 10 are generally fabricated

4
 7 EP 0 607 893 B1 8

from titanium because of its resistance to electrolytic hole 204 and slot 206 has a smaller diameter than the
action. The layer of dielectric material 14 must be remainder of hole 204. This narrowing can cause incon-
smooth, have an even thickness, be concentric with the sistencies in the flow of materials during extrusion.
tube, be tightly adhered to metal tube 12, and be free of
pin holes or foreign material. Straightness is essential to 5 Example 2
achieve satisfactory hole quality. Suitable dielectric
materials include polyethylene, polytetrafluoroethylene, The procedure of Example 1 was repeated and the
ceramics, and rubbers. A particularly preferred dielec- interface (i.e., 202) of all holes drilled was measured
tric coating material is ALKANEX™. with the results for each row being averaged and plotted
Holes are formed in a solid workpiece (having slots 10 in FIG. 6. This figure shows the wide variation in the
in the bottom surface thereof) like that of workpiece W in sizes of the hole interfaces. In addition, FIG. 6 indicates
FIG. 1 by the process described above. After holes H of that the initially drilled holes (i.e, holes 1, 37 and 19)
suitable length are formed in workpiece W, a constant have substantially the same area. However, the size of
feed servosystem (not shown) withdraws the portion of subsequent, proximately drilled holes have reduced
the apparatus constituted by feed manifold 9, electrode 15 areas, because previously drilled holes create a greater
holder 8, and hollow tube electrodes 10 away from number of paths for electrolyte flow. For example, the
workpiece W and out of holes H. Generally, holes H electrolyte used to drill the holes in row 20 tends to flow
extend through workpiece W. As a result of the drilling through the slots and back up through the holes in row
process, holes H have a surface roughness of 0.8-1 .0 19 when the holes in row 20 reach the slot at the lower
m. This is accomplished with a drilling speed (i.e., a rate 20 portion of the workpiece. This reduces the current flow
at which hollow tube electrodes 10 advance into holes path and produces a smaller diameter at interface 202
H) of 0.4-5.0mm per minute. in row 20.
As stated previously, as deplated material accumu-
lates in the electrolyte, the conductivity of the electrolyte Example 3
increases accordingly. This change in conductivity 25
results in a decrease in DC current flow through the The procedure of Example 1 was repeated with the
tube, the electrolyte and the workpiece for a given results for each row of holes being averaged and plot-
applied voltage. To maintain uniformity in hole diameter ted, as shown in FIG. 7. This figure showed that this
from workpiece to workpiece, the current must be kept example achieved substantially the same results as
constant, and the applied voltage raised for each sue- 30 Example 2.
cessive workpiece drilling operation. In a preferred
embodiment, the applied DC voltages for a series of Example 4
four successive workpieces are as follows:
The procedure of Example 1 was repeated with the
First workpiece drilled: 8.3 to 8.5 V 35 results for each row of holes being averaged and plot-
Second workpiece drilled:8.6 to 8.8 V ted, as shown in FIG. 8. This figure shows that Example
Third workpiece drilled: 8.8 to 9.0 V 4 achieved substantially the same results as Examples
Fourth workpiece drilled:9.0 to 9.2 V 2 and 3.

By upwardly adjusting supply voltage as conductiv- 40 Example 5

ity decreases, drilling can be accomplished under iden-
tical conditions from workpiece to workpiece. The procedure of Example 1 was repeated except
that it was carried out at a constant current of 166 amps
EXAMPLES (instead of a constant voltage as in Examples 1-4). The
45 resulting drilled holes (enlarged by 15X) are shown in
Example 1 FIG. 5.
FIG. 5 shows that interface 202 is not smaller than
Two pieces of 6.35 mm x 29.083 mm x 203.2 mm hole 204 when constant current operation is utilized.
USN # S45000 stainless steel were clamped together
for drilling with a shaped-tube electrolytic machining so Example 6
apparatus generally like that shown in FIG. 1. Such drill-
ing was carried out where the two pieces mate at a con- The procedure of Example 5 was repeated and a
stant voltage of 9 volts, an electrode feed rate of .889 plot of the average interface hole diameter, by row, was
mm per minute, and an electrolyte pressure of 448 KPA. made, as shown in FIG. 9. FIG. 9 shows that the aver-
This was carried out by drilling 37 separate rows of 145 55 age interface diameter of the 37 rows of drilled holes is
holes. After drilling was completed, the clamped pieces substantially uniform and that constant current opera-
were separated, and the drilled holes photographed. tion does not encounter any adverse drilling sequence
FIG. 4 is one such photograph which has been enlarged effect.
by 15X. As this figure shows, interface 202 between

5
 9 EP 0 607 893 B1 10

Example 7 the electrolyte (E) has a temperature of 18-32°C

during said drilling.
The procedure of Example 5 was repeated with a
plot of the interface hole diameter for 37 rows of holes 6. The process according to any one of the claims 1-
set forth in FIG. 10. This figure shows that Example 7 5 5, characterized in that
achieved substantially the same results as Example 6. the tube electrode (10) is made of metal,
and/or metal tube exteriorly coated with a dielectric
Example 8 material (14) except at its end (13) where the elec-
trolyte (E) is discharged against the workpiece.
The procedure of Example 5 was repeated with a 10
plot of the interface hole diameter for 37 rows of holes 7. The process according to claim 1 further character-
set forth in FIG. 11. This figure shows that Example 8 ized by one or several of the following steps of
achieved substantially the same results as Examples 6
and 7. (a) collecting the electrolyte (E) after it has con-
15 tacted the workpiece (W) during said drilling,
Claims (b) recycling the collected electrolyte (E) to the
metal tube electrode (10) for reuse during said
1. A shaped-tube electrolytic machining process for drilling,
drilling a hole (H) of uniform diameter in a conduc- (c) filtering the elctrolyte (E) during said recy-
tive workpiece (W) by advancing a conductive tube 20 cling.
(10) toward the workpiece (W) while passing an
acid electrolyte (E) through the tube (10) into con- 8. The process according to any one of the preceding
tact with the workpiece (W), and passing an electric claims, characterized by further comprising
current between the tube (10) and the workpiece
(W) through the electrolyte (E), characterized in 25 simultaneously drilling a plurality of holes (H).
that
the electric current is maintained at a fixed 9. The process according to any one of the preceding
value by sensing the electric current, comparing the claims, characterized by further comprising
sensed electric current against a reference signal,
and adjusting the fixed electric current in response 30 repeating said drilling on one or more addi-
to the comparison, whereby conductive material tional workpieces (W) using the same electro-
from the workpiece (W) is deplated uniformly lyte (E).
throughout the hole (H).
Patentanspruche
2. The process according to claim 1, characterized in 35
that 1. STEM-Verfahren zum Bohren eines Lochs (H) mit
the direction of the current during said drill- einheitlichem Durchmesser in ein leitendes Werk-
ing is periodically reversed to prevent build-up of stuck (W) durch Vortreiben einer leitenden Rohre
deplated conductive material on the tube (10). (10) in das Werkstiick (W) und gleichzeitiges
40 Durchlassen eines Saureelektrolyts (E) durch die
3. The process according to claim 1 or 2, character- Rohre (10) in Beriihrung mit dem Werkstiick (W)
ized in that sowie Durchlassen eines elektrischen Stroms Zwi-
the drilling speed is 0.4 to 5.0 mm/min. schen Rohre (10) und Werkstiick (W) durch das
and/or wherein the fixed electric current has a value Elektrolyt (E),
of 160-170 amps. 45 dadurch gekennzeichnet, daB
der elektrische Strom durch Erfassung des elektri-
4. The process according to claim 1 or 2, character- schen Stroms, Vergleichen des erfaBten elektri-
ized in that schen Stroms mit einem Bezugssignal und
the hole (H) has a surface roughness of 0.8 Einstellen des festen elektrischen Stroms anspre-
to 1.0 m after said drilling, and/or wherein the hole so chend auf den Vergleich auf einem festen Wert
(H) has a length to diameter ratio of up to 300:1 . gehalten wird, so daB das leitende Material von
dem Werkstiick (W) in dem Loch (H) einheitlich
5. The process according to claim 1 or 2, character- abgetragen wird.
ized in that
the electrolyte (E) contains an acid selected 55 2. Verfahren nach Anspruch 1, dadurch gekennzeich-
from the group consisting of nitric acid, sulfuric net, daB die Richtung des Stroms wahrend des
acid, hydrochloric acid, and mixtures thereof, Bohrens periodisch umgekehrt wird, urn den Auf-
and/or wherein the electrolyte (E) has a volumetric bau von abgetragenem leitenden Material auf der
acid concentration of 16-18 vol. %, and/or wherein Rohre (10) zu verhindern.

6
 11 EP 0 607 893 B1 12

3. Verfahren nach Anspruch 1 oder 2, dadurch piece d'usinage conductrice (W) en avangant un
gekennzeichnet, daB tube conducteur (10) vers la piece d'usinage (W)
die Bohrgeschwindigkeit 0,4 - 5,0 mm/min betragt, tandis qu'un electrolyte acide (E) est passe a tra-
und/oder der teste elektrische Strom einen Wert vers le tube (1 0) en entrant en contact avec la piece
von 160 bis 170 Ampere aufweist. 5 d'usinage (W) et qu'un courant electrique est passe
entre le tube (1 0) et la piece d'usinage (W) a travers
4. Verfahren nach Anspruch 1 oder 2, dadurch I'electrolyte (E), caracterise en ce que le courant
gekennzeichnet daB, electrique est maintenu a une valeur fixe par detec-
das Loch (H) eine Oberflachenrauhigkeit von 0,8 - tion du courant electrique, comparaison du courant
1,0 m nach dem Bohren aufweist und/oder das 10 electrique detecte par rapport a un signal de refe-
Loch (H) ein Lange/Durchmesser-Verhaltnis von rence et ajustement du courant electrique fixe en
bis zu 300:1 aufweist. reponse a la comparaison, de la matiere conduc-
trice etant detachee de la piece d'usinage (W) de
5. Verfahren nach Anspruch 1 oder 2, dadurch maniere uniforme sur tout le trou (H).
gekennzeichnet, daB is
das Elektrolyt (E) eine Saure ausgewahlt aus der 2. Procede suivant la revendication 1, caracterise en
Gruppe bestehend aus Salpetersaure, Schwefel- ce que le sens du courant pendant le forage est
saure, Salzsaure und Mischungen davon aufweist periodiquement inverse pour empecher une accu-
und/oder das Elektrolyt (E) eine volumetrische Sau- mulation de matiere conductrice detachee sur le
rekonzentration von 16-18 Volumenprozent auf- 20 tube (10).
weist und/oder das Elektrolyt (E) eine Temperatur
von 18 - 32°C wahrend des Bohrens aufweist. 3. Procede suivant I'une des revendications 1 et 2,
caracterise en ce que la vitesse de forage est de
6. Verfahren nach einem der Anspriiche 1 bis 5, 0,4 a 5,0 mm/minute et/ou en ce que le courant
dadurch gekennzeichnet, daB 25 electrique fixe a une valeur de 160-1 70 Amps.
die Rohrenelektrode (10) aus Metall hergestellt ist
und/oder die Metallrohre auBen mit einem dielektri- 4. Procede suivant I'une ou I'autre des revendications
schen Material (14) mit Ausnahme ihres Endes (13) 1 et 2, caracterise en ce que le trou (H) presente
beschichtet ist, wobei das Elektrolyt (E) gegen das une rugosite de surface de 0,8 a 1,0 m apres ledit
Werkstiick entladen wird. 30 forage et/ou en ce que le trou (H) a un rapport entre
la longueur et le diametre allant jusqu'a 300/1 .
7. Verfahren nach Anspruch 1, gekennzeichnet durch
einen oder mehrere der folgenden Schritte: 5. Procede suivant I'une des revendications 1 et 2,
caracterise en ce que I'electrolyte (E) contient un
(a) Sammeln des Elektrolyts (E), nachdem es 35 acide choisi parmi le groupe comprenant de I'acide
mit dem Werkstiick (W) wahrend des Bohrens nitrique, de I'acide sulfurique, de I'acide chlorhydri-
in Beriihrung gekommen ist, que et leurs melanges et/ou en ce que I'electrolyte
(E) a une concentration en acide volumetrique de
(b) Recyceln des gesammelten Elektrolyts (E) 16-18% en volume, et/ou en ceque I'electrolyte (E)
fur die Metallrohrenelektrode (10) zur Wieder- 40 a une temperature de 18-32°C pendant le forage.
benutzung beim Bohren,
6. Procede suivant I'une quelconque des revendica-
(c) Filtern des Elektrolyts (E) wahrend des tions 1 a 5, caracterise en ce que I'electrode en
Recycelns. tube (10) est faite en metal et/ou est un tube en
45 metal exterieurement revetu d'une matiere dielectri-
8. Verfahren nach einem der vorhergehenden Ansprii- que (14) a I'exception de son extremite (13) ou
che, gekennzeichnet durch den Schritt des gleich- I'electrolyte (E) est dechargee contre la piece d'usi-
zeitigen Bohrens einer Vielzahl von Lochern (H). nage.

9. Verfahren nach einem der vorhergehenden Ansprii- so 7. Procede suivant la revendication 1, caracterise en
che, gekennzeichnet durch den Schritt des Wieder- outre par une ou plusieurs des etapes suivantes
holens des Bohrens an einem oder mehreren
Zusatzlichen Werkstiicken (W) unter Benutzung (a) une recolte de I'electrolyte (E) apres qu'il a
desselben Elektrolyts (E). ete en contact avec la piece d'usinage (W) pen-
55 dant le forage,
Revendications (b) un recyclage de I'electrolyte recolte (E) vers
I'electrode en tube metallique (10) pour une
1. Procede d'usinage electrolytique a tube profile pour reutilisation pendant le forage,
forer un trou (H) de diametre uniforme dans une (c) un filtrage de I'electrolyte (E) pendant le

7
 13 EP 0 607 893 B1 14

recyclage.

8. Procede suivant I'une quelconque des revendica-

tions precedentes, caracterise en ce qu'il comprend
en outre un forage simultane de plusieurs trous (H). s

9. Procede suivant I'une quelconque des revendica-

tions precedentes, caracterise en ce qu'il comprend
en outre une repetition dudit forage sur une ou plu-
sieurs pieces d'usinage (W) supplementaires en w
utilisant le meme electrolyte (E).

15

20

25

30

35

40

45

50

55

8
EP 0 607 893 B1
LU O T

C
a

Q I
i— r
LU |
-1 LU i

3
 EP 0 607 893 B1

F I G . 4

F I G . 5

11
 EP 0 607 893 B1

FIG. 6 HOLE DIAMETER AT BREAKTHROUGH

Die N u m b e r 65140

0.060-

0.059-

0C 0.058-
LU
I- 0.057-
UJ
0.056-
<
0.055-
Q
0.054-
LU
-I
0.053-
o
0.052-

0.051 -

0 . 0 5 0 -■ i i I I I r—
37 32 2!7
7 22 17 12 7 2

Top Hole Number Bottom

FIG. 7 HOLE DIAMETER AT BREAKTHROUGH

Die N u m b e r 65141

0.060-

0.059-

OC 0.058 -
LU
h- 0.057-
LU
2 0.056-
% 0.055-

0.054 -
m
0.053-
O
x 0.052-

0.051 -

0.050 ■
27 22 17 12 7
Hole Number Bottom

12
 EP 0 607 893 B1

FIG. 8 HOLE DIAMETER AT BREAKTHROUGH

Die Number 65139

37 32 27 22 17 12 7

Top Hole Number Bottom

FIG. 9 HOLE DIAMETER AT BREAKTHROUGH

Die Number 65137

27 22 17

Top Hole Number

13
 EP 0 607 893 B1

FIG. 1 0 HOLE DIAMETER AT BREAKTHROUGH

Die N u m b e r 65134

0.060 -

0.059-

CC 0.058 -

P 0.057-
UJ
^ 0.056-

^ 0.055-

0.054 -
yj
0.053 -
0
1 0.052 -

0.051 -

0.050-
27 22 17

Top Hole Number Bottom

FIG. 1 1 HOLE DIAMETER AT BREAKTHROUGH

Die Number 65136

0.060 - -

0.059-

0.058 \
DC
LU
I- 0.057-
III
0.056-
<
0.055-
Q
0.054 -
LU
0.053-
o
X 0.052-

0.051 -

0.050 - - —i 1
37 32 27 22 17 12 :7

Top Hole Number Bottom

14