Note: Descriptions are shown in the official language in which they were submitted.
~2~57~8
EIEC~RODE-~OO~ ~OR EIECTROEROSIVE DRILLING
OF ~IOIES I~ WORKPIECES AND ~ETHOVS O~ EIE~TRO-
E~OSI~E DRI~ G OF HOIES I~ WORKPIEOES BY
SUCH EIECTRODE-~OOII
~IELD OF THE I~E~TION
This invention relates generall~ to electroerosive
machinin~, and more particularly to electrode tools for
electroero~ive drilling of holes in workpiece~ and m~thods
o~ electroerosive hole drilling by such electrode tools.
I~DUS'~RIAL APPLICABI~I~Y
The invention can find application predominantly ~or
machinlng electroconduotive material~ by electrodi~charge
erosion, parbicularly materialo that are ha~r~-tQ-maohin~
otherwl~e (viz~) supe.rhard or viecou~ materials), ~or ob-
taining eub~tantially tubular part~ with complicated cros~-
~ection~. Parts machined by means of ~uch an electrode tool
are emplcyed mo~tly in motor-vehicle produotion, compressor
making, hydraulic and pneumatic engineering.
BACKGROU~D O~ ~Hæ ~EN~IO~
One problem as~ociated with electroero~ive machining
lo evacuation o~ tha produot~ o~ ero~ion. Ef.~ioient evacua-
tion o~ the products o~ ero~ion facilitates obtaining hol-
es with required depth and diameter. It also ma~es po~sible
to obtain ~haped profile~ of part6 machined to a required
preci~ion at one ~st-up; that i~ without any pretreatment
or a~ter-fini~hing~ ~he rate and accuracy of machining fur-
ther depend on the manner in which the energy released
,., ~
,~
~5~8
-- 2 --
from the working end o~ the electrode tool is concentrated.
All the aforementioned depends on the construction of the
elec-trode tool u~ed and the method of màchining employed.
~ here is known a method and devic~ for evacuating the
products of ero~ion and gas bubbles from an interelectrode
gap (cf., Patent of ~est Germany No. 1,139,359; IPC B 23 P,
publi~hed 1958) in which an electrode ~or making holes i9
fa~hioned as a cylinder having an inclined passage there-
in~ide for evacuating the products o~ erosion~ ~he entire
device, including the workpiece being machined, the elect-
rode and the dielectric fluid is acco~modated in a sealed
bath with an overpres~ure produced therein to force the
fluid to move in the electrode-workpiece gap9 entrain the
products of erosion, and di~charge them through the pa~-
a~e in the elsctrode.
However, this con~txuction of the electrode fail~ to
enable maohining deep hole~ of ~mall diameter. 'llhe reason
for the failure i9 in that the considerable sur~ace area
o~ the electrode a8 compared to the inlet area of the
pa~age prevent~ efficient evacuation o~ particles. In
addition, the depth of the hole d~ lled cannot be greater
than the projection of the pas~age in the electrode onto
the vertical centerline of the electrode.
These disadvantages are partially obviated by ~rench
Patent No. 1~178,722; IPC B 23 P, published 1~57 and en-
titled "EDM Device and Method" in which for removing the
products o~ electroerosive machining the electrode tool
has the form o~ a hollow tube in which a dielectric fluid
..
z~
-- 3 --
i~ ~upplied under pre~ure to escape with the product~ of
ero~ion to a bath through an electrode-~or~piece gap.~he
workpiece i~ imparted an 08cillatory mot~on with an am-
plitude causing cavitatio~ in the dielectric fluid, this
motion acting to discharge the product~ of electroero~i~e
machining. ~he workpiece i8 ~imultaneously rotated.
~ owever, thi~ con~truction o~ the electrode ~ails to
allow drilling holes at high magnitudes of di~charge cur-
re~t accompanied by the formation of large-size pa-rticle
~raction of the product of erosion.
An electric pulse discharge causes a vapour fraction
to appear and pitting to take place due to thermoelastic
stresses to ~hlch the electrode is subjected. q'he particl-
e~ of such coarse fraction become larger in size as the
power of di~charge groY~s and duration of the pulse short-
en~. ~herefoxe, an increase in the discharge current re-
~ults in that the coarse fraction fail~ to escape from
the di~charge gap to ~hort-circuit it and lead to the for-
mation on the end of the electrode o~ growths of the pro-
ducts of ero~ion. In view of the foregoing, weak currents
with rather sloping edges are preferable to a~fect the e~-
ficiency of electroerosive process, reliability of the ap-
paratus a~d quality o~ electroerosive machi~ing.
~ n aadition, the above method a~a apparatus ~ail~to
produce deep holes of sub~tantial diameter, since in the
cour~e of electroerosive machining the msterial of the
workpiece in proxlmity to the walla of thë electIode i~
removed at a di~tQnce o~ 1 to 1.5 mm therefrom, whereas
.. . . . . . . . . . .. . . . . .
12~S7;~3
- 4 -
a projection tends to be ~ormed in the center o~ the hole
being dri~led.
'~here is also ~nown a device ~or elactroerosive ma-
chining ~cf~, U.S, Pat. ~o. 2,718~581; Cl. 219-15, publish-
ed 1955) in which in~ide a substantially cylindrical hol-
low electrode there iB dispo~ed symmetrically another hol-
low electrode at one level with the fir~t one. 'rhe second
electrode acts to partially remove the core, while leav-
ing in the center a non-removed portion.
At a certain depth o~ the hole being drilled the pro-
ducts of erosion ~ail to escape from the interior o~ the
inner cylindrical electrode, whereby :~urther drilling be-
come~ impos~ible. 'l'he products o~ erosion are evacuated
with the dielectric fluld through the gap between ~he
wall~ of the outer and inner electrodea.
I-Iowever, the a~oredeecribed device ~u~er~ from a dis-
advantage reaiding in that it enable~ to drill holes o~
only ~mall depth and large diameterO It is also not su~ici~
ently reliable in operation.
A device which bears the cloae~t re~emblance to the
one to be disclo~ed in the present description i9 taught
in ~rench Pate~t No. 2,097,709, IPC B 23 P 1/00, publi~hed
1971 and entitled "Electrode for Electroerosive ~achi~-
ing, Method o~ Using 'l'hereof, and Device ~or Carrying out
the Method". '~he device ha~ an electrode tool provided
with a central electrode enclo3ed by a ~hell? this cent-
ral electrode being fa~hioned a~ a spirally wound rod
havin~ a rectangular or triangular cros~-section and ar-
_ 5 _ ~2/~ranged at the level with the ~hell.
~ he central electrode is spirall~ wound so as to form
bet~een the electrode and the inner surXace of the shell
substantially spiral or helicoidal passages not extending
beyond the longitudinal centerline of the electrode tool.
Inherent in the abo~e conetruction is a disadva~tage
in that the electrode tool ensures hole drilling to a low
depth at a rather low e~iciency of the electroerosi~e ma-
chining proce~s rl'his disadvantage is accounted ~or by the
fact that in the area o~ current~ of considerable magnitude
the large-si~e particle fraction fails to ~eparate from
the central electrod~ and i~ therefore welded thereto due
~o the ~mall intexelectrode gap. On the other hand, it ls
impo~ible to conc~rltr~te the llberated ener~y wlthln a
small portion o~ the electrode,~hich af~ects the ef~iciency
of the electroerosive machining process, since the amoun-t
of the product~ of erosion increase~ ~vith the g~o~th in
the density o~ the energy being liberated. In addition,
the ~pirally wound central electrode accommodated inside
the ~hell of~er~ resi~tance to the ascending flow o~
quid carrying the erosion products. ~his in turn results
in deposition o~ the products of erosion on the faces o~
the 3pirally wound central electrode, build-up of these
products thereon, and clogging o~ the passage in the ele-
ctrode tool~ This makes the device less reliable. In ad-
dition, the above construction o~ the electrode tool makes
it lmpossible to drill holes o~ small dimensi~ns due to
the fact that the spiral shape of the central electrode
~ ~` .
i%45i7~8
-- 6 --
ha3 considerable cross-sectional dimen~ions.
There is ~urther known an electroerosive machinin~
method (cf., U.S. Pat. ~o. 2,902,5~4; Cl. ~19-69) in which
an electrode tool is advanced towa-rd the ~orkpiece being
machined while the working end of the electrode tool is
shi~ted for at least one combined motion in a direction
different from the initial ~eed of the electrode tool. ~he
working end o~ the electrode tool is displaced linearly
toward the workpiece, and thereafter, for obtaining shaped
holes, it is rotated about a center ~omewhat o~et re}a-
tive to the center of the working end of the electrode
tool at a predetermined angle to displace i~ succession
the working end o~ the electrode ~ool. ~his i~ ~ollo~ed
by again rotatin~ the workin~ end o~` the electrode tool
about the oQme center at a ~econd predetermlned angle.
All these ~tages are repea-ted the required number o~ times.
This method, however, fails to ensure the production
of deep holes o~ small diameter. It al~o makes impossible
to obtain ~haped hole~ having acute or reYer~e angle~,
since the working end of the electrode tool i9 returned
to the initial position a~ter the ~irst stage o~ the pro-
cess has been completed without machining the ilmer sur-
~ace o~ the workpiece.
~ he pro~ile o~ the hole being machined depends on
the ~hape o~ the ele¢trode tool, the electrode tool should
pre~erably have a cross-section su~tantially identical to
the profile o~ the hole throughout it~ length. The elect-
rode must al~o move freely in the passage.
~L2~57
-- 7 --
~W~ Y OF ~HE I~E~IO~
It is an object o~ the present in~e~tion to provide
an slectrode tool for and a method o~ electroerosive drill-
ing o~ hole~ in workpiece~ particularly holes o~ variou~
depth and diameter, a~ well a~ through and blind hole~,
Another object of the invention i~ t-o ensure electro-
ero~ive drilling of hole~ having ~haped transverse and
longitudinal sections at one ~et-up without any pretreat-
ment or after-~inishing operation~.
Al~o an object of the invention i8 to increa~e the ef-
ficiency and improve the reliability of the electrode tool7
while maintaining a high quality o~ the hole being drilled~
~ he~e object~ and attending advantage~ are attained
by that in an electrode tool -for ~lectroerosi~ drilling
of hol~ in workpiecee comprl~ing a central eleatrode ~a-
brlcated ~rom an electroconductive material and arranged
coaxially in a ~hell7 accordlng to the invention, the cent-
ral electrode is arranged relative to shell with a gap t~
project away ~rom a working end of the ~hell toward the
workpiece.
Preferably~ the ~hell 1~ -~abricated from metal.
Vesirably, an electroinsulating coating is applied to
the metal ~hell at a certain di~tance f`rom the working end
~hereof D
Alternatively1 the shell i~ ~abricated from a dielect-
ric material,
Advisably3 the shell ha~ the ~orm o~ ~ tube, whlle
,
r,
~2~5~7Z8
-- 8 --
the central elec-trode is fashioned as a rod; either the
shell or the central elactrode mus-t preferably ha~e a
cro~s-section conforming to the profile of the hole being
made.
~ he provision of the central electrode projecting a~ay
from the ~orking end of' the shell toward the workpiece
and the arrangement of the central electrode with a gap re-
lati~e to the shell a~sures drilling of deeper holesr
The fabrication of the shell ~rom metal and the failure
to apply voltage thereto f'aoilitate~ the proce~ of elect-
roeroe.ion thanke to shielding o~ -the ~ide ~urface of th~
central electrode with the aim of preventi.ng the di~ipa-
tion of energy and en~urlng a rnore eff`icient ev~cuat:Lon
o~ the product~ of eroeion through the gaps between -the
central electrode and the ~hell, as ~ell as between -the
~hell and the workpiece. Also, the rigidly attached metal
~hell makes hole drilling more accurate, that is without
deviations from -the center.
The application to the metal shell of the same current
potential that i9 f'ed -to the central elec-trode assure~ a
~till ~ore e~f'icient hole drilling becau~e the ~hell per
se becomes involved in the electroerosive machining pro-
cess,
~ he provi~ion of the metal ~hell coated with an elect-
rically insulatin~ material and the application of volt-
age to such a shell gives an even greater increaEe in -the
efficiency and accuracy of hole drilling due to the fact
that the energy is not dissipated from the side surface of
~LZ~57~8
g
the shell7 the energy of any single discharge being re-
lea~ed exclusively in the workpiece-electrode gap, ~r in
the workpiece-3hell gap.
The provi~ion of the shell having Q dielectric coating
applied thereto enables to produce very deep holes of
small cro3s-section by virtue of such a thin-wall shell.
It also makes po~sible to increase the e~ficiency, and rate
of hole drilling, a~ well a~ to improve the accuracy and
sur~ace fini~h of electroerosive machining~ due to the
~act that incidental ~hort-circuiting between the ~ide
~urface of the central electrode and the walls of the hole
being drilled i9 completely eliminated.
~ he tubular shape of the shell and rod-like arrange-
ment o~ the central el~ctrode, along wi~h other distinc-
tivo Peature~, pro~lde f`or ob-taining deep hole~ and inva-
riable cro~s-~eotion o~ the hole in term~ oP its depth.
r~he shape oP the ~hell and central electrode con~orm-
ing to the configuration of the hole being machined make3
it po~sible to produce holes o~ variou~ con~igurations
with invariable cro~s-oection in terms of their depth.
For making ~haped holes o~ complex longitudinal sec-
tional configuration the end of the central electrode pro-
jecting ~rom -the ~hell ~hould pre~erably be bent an angle
, the end of the bent portion preferably being ~paced
~rom the side surface oP the ~hell.
It is ~urther advi~able that in the proposed method
of drilling holss by the above electrode tool in which
the elec-trode tool or the workpiece are advanced toward
- 10 ~lL2~15~72~3
each other the central electrode or the YJorkpiece would be
rotated.
De~irably, in the proposed method of electroerosive
machining o~ hole~ i~ workpiecee by the electrode tool
whereby the electrode tool or the workpiece are advanced
toward each other, the shell and the central electrode tool
are advanced toward the workpiece independently~
The aforementioned method~ en~ure obtaini~g hole~ o~
various depth in workpiece~ of any ~ize and weight.
It i~ also po~sible that in the proposed method o~
electroerosi~e drilling of holes in workpieces by the afore-
de~cribed electrode tool, in which method the electrode
tool or the workpiece are advanced to~ard each other, the
advance of the shell and the advance o~ the central elect-
rode would be independent to be accompanied by rotati~g
either the central electrode or the workpiece.
~ hi8 method allows to drill deep hole~ in lar~e-3ize
part~ or in location~ o~ part~ that are difficultly acces-
~ible ~or electroerosive drilling and for making substan-
tially tubular a~ticle B .
In addition, for obtaining hole pro~iles with reverse
or acute angleR, it i8 advlsable th~t in a modi~ied method
of electroerosive drilling of holes in ~o~kpieces by the
above electrode tool, in which the electrode_to.ol~.or the
~Jork-piece are advanced toward each other, the electrode
tool or the workpiece during their advance travel be de-
v~ated to at least one combined motion in a direction sub-
etantislly perpendicular to their advance travel as the
.. .. ~
L2~L5'7;~3
electrode tool penetrate~ further lnto the ~orkpiece being
machlned~ the electrode tool or the workpiece are prefer-
ably to be moved in a direction opposite to the initial
advance feed to thereby obtain a hole longitudinally eec-
tion~l profile with a reverse or acute angle.
Pr~ferably, for making substantially round hole~ the
central electrode of the electrode tool or the workpiece
are rotated.
Alternatively, for increasing the electroer~ive ma-
chining efficiency the electrode tool or the workpiece are
both rotated independently in the oppo~ite directions.
Application of the propo~fed method enables to make
holes in variou~ electroconductive material~ with any va-
riable-in - depth pro~ile of longitudinal ~ection.
q'he u~e of the method al~o make~ it po~6ible to cont-
rol the curvature and ~ize of such variable profiles of
the hole 8 made.
~ he re~er3e or acute angle is understood to mean an
angle obtained in the workpiece during the ~ovement of the
electrode tool having a bent projecting portion of the cent-
ral electrode to an angle of ~ C 90 in a direction oppo-
~ite or reverse to the initial advance t~lereof toward the
orkpiece accompanied by simultaneous motions of the elect-
rode tool in a direction'perpendicular'to the'advance feed.
~RIEF D~SCRIP~ION 0~ THE DRA~INGS
~ he invention will now be described i~ greater detail
with refer~nce to variou~ preferred embodiment~ thereof
~2~572~3
- 12 ~
taken in con3unction with the accompanying drawing~, in
which:
Fig, 1 illustrate~ an electrode tool for elec-troero-
~ive drilling of holes in workpiece~ according to the in-
vention;
~ i.g. 2 ~how~ a construction of the electrode tool ~or
electroero~ive drilling o~ hole~ when voltage i~ applied
to a shell fabricated from metal,
~ ig. 3 i~ a con~truction of the electrode tool ~or
electroerosive drilling of holes in workpiece~ in which
an electroin~ulating coating i~ applied to a metal ~hell;
~ ig. 4 ~hows an alternative modi~ication of the elect-
rode tool ~ccordin~ to the invention in which ~he ~hell i~
mad.e ~rom ~ dielectric material;
~ ig. 5 ill~strate~ an alternative construction o~ the
electrode tool according to the invention in whlch the
~hell and the central electrode are ~a~hioned as polyhe-
dron~;
~ ig. 6 -,~ one more modi~ied con~truction o~ the elect-
rode tool according to the invention in which the ~hell and
the central eleotrode are star-shaped;
~ ig, 7 lllu~trate~ one more po~ible embodi~ent of
the electrode tool f'or electroero~ive drilling of hole~
according to the in~ention in which the ~hell and the cent-
ral electrode are of' polyhedral ~hape with any de~ired
angles;
~ ig. 8 i~ another alternative con~truction o~ the ele-
ctrode tool ~or electroero~ive drilling of holes accord-
ing to the invention;
1~57~8
-- 13 --
~ ig. 9 show~ a construction of the electrode tool for
electroero~ive drilling o~ hole~ in workpieces in whi.ch
a voltage i~ applied to the metal shell;
~ lg. 10 show~ an electrode tool according to the ln-
vention in which an electroinsulating coating i~ applied
to a metal ~hell;
Fig~ 11 illustrate~ a construcbion o~ the electrode
tool according to the invention in which the shell is ~ab-
rieated ~rom a dielectric material;
~ ig. 12 .~ho~ one po~sible con~truction of the elect-
rode tool according to the invention for drilling holes
o~ slotted con~iguration with invariable sections in terms
o~ the depth o~ ~uch holes;
~ i~. 13 i~ a view ~rom above o~ the electrode tool
~hown in l~ig. 12;
Fig. ~4, 15 and 16 show long~itudinal sections of' the
pro~iles of substantially ~lotted holes obtained at di~-
feren~ angles o~ bend o~ the projecting portion o~ the.
central electrode, the pro~iles being variable in ~hape
in terms o~ the hole depth;
~ ig. 17 illustrate~ a variable pro~ile of a ~ub~tan-
tially ~lotted hole with a reverse or acute angle;
Fig~ 18, 19 and 20 show ~ubstantially round shaped.
pro~ile~ of hole~ obtained by the bent projecting portion
o~ the eentral electrode; and
Fig. 21 ~how~ a round shaped pro~ile o~ hole~ w~h a
reverse or acute angle.
~57;~3
- 14 -
BEST MODE OF CA~RYIl~G OU~ ~HE I~VE~TIO~
An electrode tool for electroerosi~e drilling o~ holes
în workpieces according to the invention comprises a cent-
ral electrode 1 (~ig. 1) made from an electroconductive
material on which there is rnounted a substantially hollo~J
adapter 2 having a nipple 3 and securecl to the central
electrode 1 by mean~ o~ a sleeve 4 and a seal 5~
On the ~ide opposite to the arrangement o~ the sleeve
4 the adapter 2 ha~ fitted thereon a shell 6 so as to
embrace the central electrode 1 with a gap indicated by
AB, the central electrode projecting away from a working
end of the ~hell 6 toward the workpiece 7 being machined
a length indicated by BC.
A non workin~ end o~ the central electrode 1 i~ con~
nected to a mean~ 8 enouring at,tachment, feed and adju~t-
ment o~ the electrode tool.
The eleotrode tool operates in the ~ollowing manner.
~ he working end of the central elec-trode 1 i8 plaCea
in front of the workpiece 7 and connected to a negative
terminal of a pul~ed power source (rlo-t sho~n), whereas
the workpiece 7 i~ connecte~ to a po~itive terminal o~
thi~ power ~ource. After the working end o~ the central
electrode 1 of -the electrode tool is brought clo~er to the
workpiece 7, particularly to a di~tance su~icient for
a ~park to be initiated therebetween, electroerosion of
the material of the workpiece 7 take~ place in the area o~
the projec-tin~ portion o~ the central electrode 1. A~ a
, . . .
-15-
result, a crater or hole 9 is formed in the workpiece
7 through which and in conjunction with the gap AB
between the central electrode 1 and the shell 6,
as well as a gap DE between the shell 6 and the
workpiece 7, the erosive fraction which is in a
suspended state can be easily evacuated. A combina-
tion of such features as the arrangement of the central
electrode 1 with the gap AB relative to the shell
6 and projection of the central electrode 1 away
from the working end of the shell 6 in a direction
toward the workpiece 7 being machined facilitates
a more efficient evacuation of the products of erosion
from the machining zone, thereby ensuring increased
capacit~ of the apparatus, improving the quality
oE machining, and providing for extended depth of
holes at small diameters thereof.
The shell can be fabricated from metal
and, optionally,electric current may be applied to
this shell 6. It is possible that the electric
current would not be applied to the shell 6. In
this case the shell 6 serves for shielding the side
surface of the central electrode 1 with the aim of
preventing dissipation of energy and for more effi-
cient discharge of the erosive fraction through the
gaps AB and DE. In addition, the shell 6 rigidly
secured on the adapter 2 assures a more accurate
drilling of holes without deviation from the center.
,,
57~3
-16-
In order to make the process of electroero-
sive drilling of holes more efficient, the shell
6 (Fig. 2) is connected to the negative terminal
of the pulsed current source, i.e., the same potential
is applied thereto as to the central electrode 1,
which involves the shell 6 in the process of electro-
erosive drilling of holes. Initially, erosion of
the material of the workpiece 7 takes place in the
area of the central electrode 1 to result in the
formation in the workpiece 7 of the small crater
9. Thereafter, the electrode tool is advanced toward
the workpiece, whereby a progressive movement of
the central electrode 1 to -the thus forMed crater
9 results in that the distance be-tween the workpiece
7 and shell 6 is reduced to cause a spark between
the workpiece 7 and the she~l 6. In this manner
the wor~cing end of the shell 6 becomes engaged in
the process of electroerosive machining to result
in a large hole 10 (Fig. 2).
By feeding or advancing the electrode tool
at a predetermined rate toward the crater or hole
being made an electroerosive machining process is
set to maintain the following sequence of actions
for drilling the hole by the parts of the electrode
tool: first, electroerosion by the central electrode
1, and thereafter by the shell 6~ In other words,
a successive automatic self-adjustment for deep-hole
11 ~4~5~
-16a-
drilling is effected, where subsecluent to making
a small hole a large hole is drilled.
In order to increase the efficiency and
accuracy o~ electroerosive drilling of holes of
substantial depth, an insulating coating 12 is applied
to a shell 11 fabricated from metal (Fig. 3) at a
certain distance from the working end thereof when
the electric current is applied to the shell 11.
The need for applying such a coating is accounted
for by that during the progressive movement of the
electrode tool to a greater depth side surface of
the shell 6 (Figs. 1, 2) is bro-
.~
~LZ~S7;~:8
17 -
ught into actioll to result in a leak of energy, and con-
sequently in a failure to main~ain the shape of the charge
pulse in the course of drilling hole 9 throughout their
d~pth and release a higher den~ity energy on the end face
part of the shell 6~
A distinctive fea-ture of operation of the shell 11
(~ig. 3) having an insulating coating 12 resides in that
the energy o~ every single discharge is liberated in ex-
clu~ively one gap, particularly, either in the workpiece 7
- central electrode 1 system, or in the workpiece 7 - shell
11 system. This increases the density of the energy libe-
rated and results in greater efficiency of the apparatu~.
For obtaini~ hole~ of ~mall diallle-ter it i~ nece~sary
that the walls of the shell 6, ll (Figs. 1, 2 and 3) be
~uf~icientlg thin, which is practically impo~ible -to at-
tain when the~ are fabricated from metal. To satis~y the
requirement~ o~ small diameter, these walls are pre~erabl~
made ~rom a dielectric material~
The use of a dielectric shell indicated by 13 in ~ig.4
make~ it pos~ible to completely eliminate short circuitin~
between the side eur~ace of the central electrode 1 and
the walls o~ -the hole being made, which assuree a trouble-
~ree operation o~ -the electrode tool and enables to drill
the hole by a quite definite end face portion of the cent-
ral electrode 1 projecting from the dielectric ~hell 13.
In turn, this allo~Ys to mai-ntain the shape of discharge
pul~e throughout -the length o~ the hole, that is to ef-
fect a controllable or progr~able electroero~ive hole
7~:8
8 -
drilling~ All the aforedescribed promote~ the efficiency,
speed9 accur~cy and surfac~ finish o~ the hole~ drilled,
a~ well a~ enables to obtain very deep ho1es of small dia-
meterO
Holes are drilled by such an electrode tool in a mann-
er similar to what ha~ been de~cribed with re~erence to
the electrode tool having the metal shell 6 (Fig. 1),when
an electr~c current is not applied thereto.
In the course of carrying out the aforedescribed ~e-
thod~ of electroerosive hole drilling b~ mean~ of elect-
rode tools of the proposed construction~ an i~creased ef-
ficiency of electroero~ive machining is attained when,
for making substantially round holes, rotation i9 i~p~rt-
ed to the central electrode 1 apart from advancing it to-
ward the workpiece.
~ or rnaintaining the length BC (Figs. 1, 29 3 and 4)
of the projecting portion of the central electrode 1 in-
Yariable in the course of its wear due to continuou~ ope-
ration the shells 6, 11 and 13, as well as the central
electrode 1 aIe advanced -toward the workpiece independent-
ly,
Hereinafter, preferred configurations of the shell and
central electrode for producing holes of ~arious shape~
~ill be considered. ~or making ~ubatantially cylindrical
holes having an in~ariable longitudinal section the cent-
ral electrode 1 (Fig~., 2, 3 and 4) is preferably fa~hion-
ed a~ a rod~ while the shell~ 6~ 11 and 13 may be fashion-
ed a6 tubes. By means of such an electrode tool it i6
- 19 _ :l24l5i72l 3
possible to fabricate tubular part~ ~rom substantially
cylindrical workpieces3 as well a~ to make cylindrical
hole~ in large-size parts or in part locations where ac-
ces~ is difficult. r~he ~hell in thi~ case may be made o~
metal, or fabricated from a metal coated with a dielect-
ric material, or entirely from a dielectric material~
~ or making shaped hole~ with invariabla pro~ile thro-
ughout the depth thereo~ in terms of their longitudinal
and txanaver~e sections the ~hell and the ¢entral elect-
rodee have preferably cro~s-~ections conforming to the
pro~ile of the hole~ made. ~or example, it is pos~ible
to ~ashion the ~hell 14 (Fi~. 5) and the central electrode
~5 in the ~orm o~ a polyhedron witll obtu~e (or ri~ht) an-
gleo to obtain hole~ 16 o-~ faceted con~i~ur~tion,
It i~ al~o poe~ible to ~ashion the shell 17 (~ig. 6)
and ths electrode 18 as a ~tar to produce qtar-~haped
holes 19.
~ ig. 7 represent~ a case of fashioning a central elect-
rode 20 and shell 21 for producing a hole 22 in the form
of a polyhedron with any desired angles.
Drillin~ the ~haped hole~ 16, 19 and 22 (Fig~. 5, 6
and 7) by means of the aforede~cribed constructions of the
electrode tools iq carried out exclusively by virtue o~
the forward movement of the electrode tool, the central
electrode 15, 18, 20 and the shell 14, 17, 2~ being moved
independently from each otherO
~ et ~s consider an alternative modi~ication ~ the
electrode tool having a bent central el~ctrode.
-20-
Such an electrode tool for electroerosive
drilling of holes comprises a central electrode 23
(Fi.g. 8) fabricated from an electroconductive material
and having mounted thereon a substantially hollow
adapter 24 provided with a nipple 25, the adapter
24 being secured to the central electrode 23 by means
of a sleeve 26 and a seal 27.
On the side opposite to the arrangement
of the sleeve 26 the adapter 24 has fitted thereon
a shell 28 so as to embrace the central electrode
23 with a gap AB, the central electrode 23 projecting
away from a working end of the shell 28 toward the
workpiece 29, whereas the pro~ecting portion of the
centra]. electrode 23 is curved or bent an angle ~ ,
the end of the bent portion of the central electrode
23 being spaced a certain distance from the side
surface of the shell 28. The angle ~ can be varied
within a range of O~ ~ ~ 180.
The non-working end of the central electrode
23 is connected to a means 30 ensuring attachment,
feed and adjustment of the electrode tool.
This modification of the electrode tool
operates as follows.
The working end of the central electrode
23 is placed in front of the workpiece 2g and is
connected to a negative terminal and the workpiece
29 to a positive terminal of a pulsed source of
; electric current (not shown). After the working
` ~.;;~
~2~
-21-
end of the central electrode 23 of the electrode
tool is brought closer to the workpiece 29, partic-
ularly close enough for a spark to be initiated
therebetween, electroerosion of the material of the
workpiece 29 takes place in the area of the projecting
portion of the central electrode 23. As a result,
a crater or hole 31 is formed in the workpiece 29
through which and in conjunction with the gap AB
between the central electrode 23 and the shell 28,
as well as gaps CD and EF between the shell 28 and
the workpiece 29 the erosive fraction in a suspended
state can be easily evacuated. A combination of
such features as the arrangement of the central
electrode 23 ~ith the gap AB relative to the shell
28 and the projection of the central electrode 23
away from the working end o the shell 28 toward
the workpiece 29 being machined, as well as the
configuration of the central electrode 23 bent the
angle 4~ provide for efficient evacuation of the
products of erosion from the machining zone, thereby
ensuring a higher efficiency of the machining process~
The shell 28 can be fabricated from metal.
Electric current may optionally be applied to this
shell 28. It is possible that the electric current
would not be applied to the shell 28. In this case
the shell 28 serves for shielding the side surface
of the central electrode 23 with the aim of preventing
21a-
dissipation of energy and for a more efficient
discharge of the erosive fraction through the gaps
AB, CD and EF. In addition, the shell 28 which is
rigidly fixed on the adapter 24 assures a more ac-
curate drilling of holes without deviation from the
center.
In order to make the process of electroero-
sive drilling still more efficient, the shell 28.
(Fig. 9) is connected to the negative terminal of
the pulsed current source, i.e., the same potential
is applied thereto as to
~1 2~5~2~3
22
the centr~l electrode 23. This involves the shell 28 in
the process of electroerosive machining o~ hole~. Initial-
ly, erosion of the rnaterial of the workpiece 29 take~ place
in the formation in the workpiece 29 of a crater 31r r~here-
a~ter, the electrode tool i8 adv~nced toward the workpiece
299 whereby a progressive movement of the central elect-
rode 23 to the thus formed crater 31 re~ults in that the
distance between the workpiece 29 and the shell 28 is re-
duced to cause a spark between -the workpiece 29 a~d the
~hell 28. In this manner the working end of the shell 28
becomes engaged in the proces~ of electroerosive machin-
ing to re~ult in a cr~ter 32.
By ad~ancing the electrode tool at a predetermined
rate toward the crater or hole bein~ drilled ~n elec-tro-
ero~ive machlning prooe~s is ~et to maintain th~ follow-
ing sequence of actions for drilling the hole by the parts
of the electrode tool- first by the central electrode
23, and there~ter by the shell 28. In other word~, a
~uccessive automatic self-adjustment for deep-hole drill-
e~ected.
In order to increa~e the e~lciency and accuracy of
electroero~ive machini~g of deep holes, an eleatroinou-
lating coating 34 i~ applied to a metal shell 33 (~ig.10)
at a certain di~tance ~rom the working end thereo~ for the
cas~ whe~ an electric current is supplied to thi~ shell 33.
~he need ~or applying such a coating i~ accounted for
by that during the progres~ive movement o~ the electrode
tool to a greater depth side surface of the shell 28
124L57;~:8
-- 23 --
(~ig. 8) is brou~ht into erosive action to re~ult in a leak
o~ energy~ and con~equently in a failure to maintain the
shape of the charge pulse in the cour~e o~ drilling holes
througShout their length or depth7 or to relea~e a higher
density energy on the end face o~ the shell 28~
A di9tinctive feature o~ operation o~ the shell 33
(~ig. 10) having an insulating coat~ng 34 resides in that
the energy o~ every single discharge is emanated onl~ in
one gap, particularly, either in the workpiece 29 ~ ce~tral
electrode 23 ~y~tem, or in the workpiece 29 - shell 33 ~ys-
tem. ~hi~ increa~es the denoity of energy liberated and re-
~ult~ in ~re~ter e~iciency of the electroeroeive machin-
in~ proces~.
~ or producing nnrrow ~lotted hole~ lt i~ neae~ary
that ~he wal].s o~ the ~hells 28, 33 (~igs. 8, 9 and 10)
be thinner, which is practically impossible to attain when
they are $abricated ~rom metal. For this purpose these
shell~ are preferably made ~rom a dielectric material.
~ he u~e o~ a dielectric sh~ll 35 (~ig. 11) makes it
possible to completely eliminate a ~hort circuit between
the side surface o~ the central electrode 23 and the wall~
o~ the hole being made, which asaures a trouble-~ree opera-
tion of the electrode tool and enables to drill the hole
by the projecting bent portion o~ the central electrode
23. In turn~ thi~ allows to sustain the shape o~ the di~-
charge pulse throughout the length o~ the hole 7 that is to
e~ect a controllable or programmable electroerosive hole
drilling in the workpiece 29. All the a~oredescrib~d pro-
~LX~L57~3
- 2~ -
motes the e~ficiency, increa~e~ the speed, and improve~
the accuracy of hole drilling. It al~o enables to obtain
deep narrow slotted holes.
Hole~ are drilled by the aboYe electrode tool in a
manner similar to what has been de~cribed with reference
to the electrode tool having the metal ~hell ~8 ~ig. 8)
when an electric current is not applied thereto.
In the course of carrying out the aforedescribed me-
thod~ o~ electroeroeive machining of holea by mea~s of
electrode tool~ of the above con~truction and for making
sub~tantially round hole~ rotation i~ imparted -to the~cent-
ral electrode 23 apart for advancing i~ progre~slvoly ~o-
~ard the workplecc.
All the a~`orede~cribed method~ can be u~ed ~or electro-
erosive machinin~ of holes of substantially cylindrical
~hape and variou~ depth, as well as for making blind or
throu~h hole~
~ et us con~ider modi~ication~ for producing holes ha~-
ing variable transver~e and longitudinal sections in term~
of depth of such hole~.
The ~hape of tran~ver~e and longitudinal`~ection~ o~
a hole made depend~ ~ub~tantially on the angle Cv of bend-
ing of the projecting portion of the central electrode 1
'~he angle ~ may be varied within a range 0< ~ ~180.
BJ presetting the required angle ~ o~ bending of the
projecting portion of the central electrode it is possible
to control the size and the pro~ile o~ transverse and lon-
gitudinal section~ o~ the hole being ~achined.
, .
728
-25~
The method of electroerosive machining
of holes with variable profile of transverse section
in terms of the depth of the hole is carried out
by means of the projecting portion of the central
electrode bent an angleO~ in the following manner.
As the electrode tool moves axially toward
the hole being made, it penetrates progressively
to this hole. In such an instance, the hole takes
the form of a slot having invariable cross-section
in terms of depth (cf. Figs. 12 and 13). For drill.ing
a hole with a changing in terms of depth profile
cross-section, the electrode tool or the workpiece
29 (Fig. 8) are imparted, along with the axial
advancement, at least one complex motion in a direc-
tion substantially perpendicular to the direction
of such advancement. Therewith, the rate of such
perpendicular travel of the electrode tool or the
workpiece 29 may be either greater, or less, or the
same as the rate of axial feed of the electrode tool
or the workpiece 29. Depending on the ratio between
the rates of movement of the electrode tool or the
workpiece 29 in the two mutually perpendicular direc-
tions, a hole with varying shape in terms of its
depth is formed having a required profile and pre-
determined transverse and longitudinal dimensions.
Configuration of holes in this case depends
also on the selected anglec~ . For example, when
this angle o~ is 90, the hole configuration will be
.
-25a~ 5 7~8
as one shown ln Fig. 14; for the angle o~ c 9o it
will be llke one illustrated in Fig. 15, whereas
for the angle G~90 the hole
,, ~,
~S7;~8
- 26 -
con~iguration will be as shown in Fig. 16.
~ or obtaining a hole with an acute or reverse angle
u~e is made of the central electrode 23 the end of which
is bent at an angle ~ <90 (~ig. 17).
Sub~equent to penetration of the electrode ~ool to the
workpiece 29, thi~ electrode tool or the workpiece 29 are
made to move in a direction perpendicular to the direction
of feed accompanied by simultaneou~ movement of the elect-
rode tool or the workpiece in a direction rever~ed rela-
tive to the feed path. Depending on the required pro~ile
o~ the hole being made and on the transverse and longitu-
dlnal dimen~ion~ thereo~, a required ratio between the
ra~c of ~eed o~ the elec~rod~ ~ool or ~he workpiece 29 ln
the nlutually perp~ndicular direotiono i~ ~elected.
For producing ~ubstantially round ~haped pro~i~e~ o~
the holee being made varying in their shape in term3 o~
their depth and featuring an acute angle, apar~ from the
aforedescribed operations o~ the method, the electrode
~ool or the workpiece 29 are rotated. t~he ~ection~ of hol-
e~ thu~ obtained are repre~ented in ~igs 18, 19 a~d 20;
~ig. 21 illuetrating a hole with an acute or revereed
a~gle profile.
t~he rota~ion of the central electrode 23 (~ig~ 8~ of
the electrode tool relative to the workpiece 29 is e~ecut-
ed ~or obtaining ~ubstantiall~ round ~haped profilee of
hols~ being made in large-size workpisce~ and in dif~icul-
ty acce~sible locatio~ o~ workpieces.
~ he workpiece 29 i6 normally rotated relative to the
~2~ 728
-- 27 ~
electrode tool for drilling hole~ in small-~ize workpiece~
In-order to increa~e the ef~iciency of the electroero-
si~e machining it i~ al~o po~sible to rotate both the work-
piece 29 and the central electrode 23 o~ the electrode tool
independently in the opposite direction~O
A11 the a~orede~cribed stage~ o~ the propo~ed method
o~ electroero~ive machining are repeated, i~ necessary,
a required number of times, the electrode tool being set
to operation a single time.
It is to be noted that all the movements between the
workpiece and the electrode tool can be viewed as relative
movements. ~or example, con~idered hereinbefore were the
ca~e~ where for carrying out the proposed method of elect-
roero~ive ma¢hining o~ hole~ the workpiece remairled ~-ta-
tionary, whlle the ~orward travel toward the workpiece be-
ing maohined wa~ imparted to the electrode tool. For ob-
taining ~ubstantially cylindrical holes the central eleot-
rode i~ also rotated. Such a method is pre~erable ~or treat-
ing large-~iæe workpiece~ or ~or making holes in part lo-
cations that are dif~iculty acce~slble ~or machiningO Al-
ternatively, the workpiece may be advanced toward the ele-
ct~ode tool, the latter remaining stationary relative to
the workpi.ece being mac~ined. It al~o need~ to be noted
that even in the case o~ a ~tationary electrode tool the
movement i~ imparted to the ~hell or the central electrode
~or maintainlng the length o~ the projecting portion o~
the certral electrode as it wears out during electroero-
~ive machining.
~572l3
-- 2~ --
For makLng cylindrical holes the workpiece is addi-
tionally rotQted ~ith the electrode tool remaining statio-
nary.
Such a method is more preferable for machining ~mall-
size workpiece~, as well a~ for producing workpieces in
the form of tubular rod-like parts.
It is also possible during the forward feed o~ the
electrode tool or the advance o~ the workpiece to the
electrode tool to impart rotation to both the central ele-
ctrode snd the workpiece in the oppo~ite directions~ Such
a method i9 preferable ~or increasing the e~iciency of
machining -through accelerating the rate o~ the electroero-
~ive hole drilling, e~pecially when it i~ impo~sible to
increa~e the rotational ~peed o~ the central electrode or
th0 rotational ~peed o~ the workpiece.
It i~ al~o to be noted that during elec-troero~ive
machlning of hole~ by the proposed electrode tools it i~
pos~lble to ~elect such a mode of operation in which the
rate o~ wear of the projecting portion of the central ele-
¢trode and the ~hell would be equal. Such operation obvi-
ates the need for independent motion of the ~hell and the
central electrode relative to each other.
In v.iew of the aforede~cribed, the propo~ed construc-
~ion~ of the electrode tool and modi~ication~ of the me-
thod ~or electroerosive drilling o~ hole~ in wor~pieces
provide for machining of both blind and ~hrough holes o~
various depth and diameter, as well as holes o~ complex
co~iguration in the tran~verse or longitudinal ~ection~O
~z~s~
- 29 -
The pr~posed electrode tool and method for electroero~ive
machining as~ure high efficienc~ and re:Liability of the
electrode tool along with high quality of' holes made at one
~et-up without pre-treating or af`ter-~iniehing operation~
