Wire electric discharge machine

Details Wire electric discharge machine Wire electric discharge machine

2000-06-16

2002-02-05

Evans, Geoffrey S. (Department: 1725)

Electric heating

Metal heating

Cutting or disintegrating

C219S069140

Reexamination Certificate

active

06344624

ABSTRACT:

TECHNICAL FIELD
The present invention relates to improvements in a wire electrical discharge machining apparatus which is capable of improving the machining speed and machining accuracy.
BACKGROUND ART
Referring to
FIGS. 5
to
8
, a description will be given hereafter of the configuration and operation of a conventional wire electrical discharge machining apparatus.
FIG. 5
shows an overall configuration of mechanical portions, in which reference numeral
101
denotes a bed as a base of machine, and numeral
102
denotes an X-axis table. The X-axis table
102
is supported by an X-axis guide
103
on the bed
101
, and is driven in the X-direction by an unillustrated X-axis motor through an X-axis ball screw
104
. Numeral
105
denotes a table for fixing a workpiece
25
, which is fixed on the X-axis table 102. Numeral
106
denotes a processing tank for storing a working fluid. Numeral
107
denotes a column for supporting a Z-axis unit
117
, and a lower arm
108
is fixed thereto. A lower guide
109
is attached to a distal end portion of this lower arm
108
. Numeral
118
denotes an upper guide, which is fixed to a distal end portion of the Z-axis unit
117
. Numeral
111
denotes a Y-axis guide on the bed
101
which supports the column
107
. The column
107
is driven in the Y-direction by a Y-axis motor
113
through a Y-axis ball screw
112
. Numeral
114
denotes a wire collector for supporting a roller
115
for collecting a wire electrode, and the collected wire electrode is accommodated in a collecting box
116
. Numeral
120
denotes a wire bobbin, numeral
121
denotes a pad disposed underneath the bed
101
, and numeral
122
denotes a leveling bolt for adjusting inclination.
FIG. 6
is a cross-sectional view illustrating the configuration of the lower guide
109
. The lower guide
109
is fixed to a distal end of the lower arm
108
through an insulating plate
2
, and is mainly comprised of a nozzle
6
, an electric supply die
16
, a lower wire guide holder
12
, a guide supporting plate
23
, and a lower block
3
. The lower block
3
includes a roller
19
which functions to convert the direction of the wire electrode, and has a wire inlet
3
a
and a wire outlet
3
b
which are tapered. A collection pipe
20
is connected at the wire outlet
3
b
. The guide supporting plate
23
incorporates the electric supply die
16
, and also incorporates a withdrawing plate
17
for withdrawing the electric supply die
16
. The electric supply die
16
is fixed by a holding plate
15
. Numeral
18
denotes a lower auxiliary guide, and the lower auxiliary guide
18
, together with the lower wire guide holder
12
, presses a wire electrode
119
against the electric supply die
16
so as to supply electricity to the wire electrode
119
. The nozzle
6
is a portion for jetting the working fluid, and the working fluid is supplied through a pipe
9
as a high-pressure fluid. Numeral
14
denotes a spring, and
13
denotes a holding plate for the nozzle
6
. The nozzle
6
during machining is raised while compressing the spring
14
, is stopped by the holding plate, and is returned downward when the working fluid ceases to be supplied. As a result, when machining is not being effected, the nozzle is lowered, thereby preventing its useless contact with the workpiece. A rectifying plate
22
has the function of rectifying the turbulence of the working fluid inside the nozzle, and a multiplicity of small holes
22
a
are provided therein. Numeral
10
denotes the wiring, which is connected to the guide supporting plate
23
formed of an electrically conductive material, so as to supply machining electric power from an unillustrated machining power supply to the electric supply die
16
. Numeral
24
denotes a lower transporting-current jetting hole, to which a pipe from the outside is connected and which functions to transport the wire electrode
119
in the collection pipe
20
to the collection roller
115
(see FIG.
5
), and is used mainly during the initial setting of the wire electrode
119
. Numeral
26
denotes a machining gap between the workpiece
25
and the wire electrode
119
, and this gap is referred to as the gap between the electrodes. The working fluid jetted from the nozzle
6
is supplied to the gap
26
between electrodes. The principal functions of the working fluid are to discharge the machining sludge produced during machining, to prevent the overheating of the wire electrode, and to prevent the disconnection of the wire electrode during machining.
FIG. 7
is a cross-sectional view illustrating the configuration of the upper guide
118
. An attaching plate
225
fixes the upper guide
118
to the Z-axis unit
117
and is formed of an insulating material. An upper block
226
has a passage
226
a
, and an upper auxiliary guide
229
for guiding the wire electrode
119
is disposed on top of the upper block
226
. An electric supply die
46
is accommodated in the interior of the upper block
226
, and is pressed toward the wire electrode
119
by a pressing plate
230
. The arrangement provided is such that the insertion and withdrawal of the electric supply die
46
are made possible by a withdrawing plate
47
. An upper wire guide holder
236
is fixed to a lower end of the upper block
226
, and a wire guide
236
a
is fixed to a distal end portion of the upper wire guide holder
236
. Further, a housing
234
is provided in such a manner as to cover the upper wire guide holder
236
, and a nozzle
232
is disposed on the outer side thereof. A jet nozzle
233
, which is supported in such a manner as to be vertically movable through a spring
235
, is accommodated inside the housing
234
.
When the working fluid is supplied to a jet pipe
238
, the jet nozzle
233
moves downward by its pressure while pressing the spring
235
, and jets out a jet stream
239
through a jetting hole
233
a
in the jet nozzle
233
. The wire electrode
119
passes through the interior of the jet stream
239
, and is guided to the lower guide located therebelow. During normal machining, the working fluid is supplied from a working fluid pipe
237
, and the working fluid is supplied from a jetting hole
232
a
in the nozzle
232
. In addition, during normal machining, the jet nozzle
233
is retracted upward from the spring
235
. Numeral
221
denotes a cooling hole through which the working fluid is guided into the interior of the upper wire guide holder
236
to cool the wire electrode
119
during machining. Numeral
234
a
denotes a fixing throttle which is used to rectify the disturbance of the working fluid supplied from the working fluid pipe
237
.
The wire electrical discharge machining apparatus is cooled by the working fluid because a large electric current flows across the contacting portions of the wire electrode and the electric supply die, and the temperature of these portions becomes high, possibly resulting in the disconnection of the wire electrode. The cooling working fluid is supplied to the wire passage
226
a
from the cooling hole
221
provided in the upper wire guide holder
236
by making use of the back pressure within the nozzle
232
. The working fluid rises upward from the cooling hole
221
through the interior of the wire passage
226
a
, passes the contacting portions of the wire electrode
119
and the electric supply die
46
, passes the upper auxiliary guide
229
, and is discharged to the outside. Thus, as the working fluid passes, cooling is effected by absorbing Joule heat produced in the contacting portions of the wire electrode and the electric supply die.
Next, referring to
FIG. 8
, a description will be given of the arrangement of the wire electrode and a machining groove during machining. It is assumed that machining is being effected while maintaining a fixed gap in the direction toward the machining/advancing direction in the drawing. Jet streams
240
jet out from the upper and lower nozzles as indicated by the arrows, An come into contact with each other substantially in the vicinity of the center in the vertical dir

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