Cut-out piece removing method in electric discharge machining and an apparatus therefor

A method and an apparatus for easily and reliably removing cut-out pieces cut out from a workpiece by wire-cut electric discharge machining, in which, upon completion of cutting a piece (41) out, a constraining assembly (63) mounted on the distal end of a piston (62) is brought close to the top surface of the piece under the control of a numerical control unit, and machining fluid is upwardly jetted from a lower nozzle (19) toward the bottom surface of the piece, to thereby hold the piece in the workpiece, with the piece kept away from the lower nozzle and prevented from being detached upwardly from the workpiece. While jetting the machining fluid, a worktable is horizontally moved to cause the cut-out piece to move in unison with the workpiece away from the lower nozzle in the horizontal direction. At a moved position where the machining fluid jet normally no longer acts on the bottom surface of the piece, the table movement is stopped and the machining fluid is downwardly jetted from auxiliary nozzles (70) toward the top surface of the piece, to thereby forcibly drop the piece off the workpiece.

TECHNICAL FIELD 
The present invention relates to a method and an apparatus for removing 
pieces from a workpiece after they are cut out from the workpiece by 
wire-cut electric discharge machining. 
BACKGROUND ART 
In wire-cut electric discharge machining, products of various shapes are 
produced by moving a table mounted with a workpiece, while intermittently 
generating electric discharge between a wire traveling from an upper 
nozzle toward a lower nozzle and the workpiece located between these 
nozzles. In the case of cutting-out, from a single workpiece, a plurality 
of pieces each constituting a product or a core corresponding to a cavity 
portion of the product, the workpiece is moved to a cutting-out machining 
start position for the next piece each time the cutting-out machining for 
one of the pieces is completed. At this time, the cut-out piece and the 
lower nozzle may be rubbed against each other, resulting in damage to the 
cut-out piece or the lower nozzle, in particular, if the workpiece is 
moved under a condition that the cut-out piece is inclined in the 
workpiece due to its own weight. If the cut-out piece as a product incurs 
a frictional scratch, the product quality is deteriorated. 
To obviate these inconveniences, it has been known to remove cut-out pieces 
from a workpiece by means of various methods each time one of the cut-out 
pieces is cut out from the workpiece. For instance, a workpiece is 
horizontally moved while a cut-out piece is held in the workpiece with the 
aid of a supporting plate extending between the bottom surface of the 
workpiece and the upper end surface of the lower nozzle, and the natural 
falling of the cut-out piece from the supporting plate and the workpiece 
is permitted at the end of the supporting plate at a location separated 
from the lower nozzle in the horizontal direction. This method is easy to 
implement, but if the top surface of the supporting plate is soiled or 
scratched, then the movement of the piece on the supporting plate and 
hence the movement of the workpiece may be prevented, possibly causing 
scratches on the piece or undue load onto a table driving mechanism which 
moves the workpiece. 
Another method is known, wherein a piece which is not completely cut out of 
but left slightly linked to the workpiece is tapped off the workpiece with 
a hammer or the like. This method, however, is likely to easily cause a 
flaw on the piece. Further, if the hammer is made smaller so that it can 
remove even such a piece which is small in horizontal section, then it may 
fail to remove a piece having a larger horizontal section or a greater 
thickness. 
Still another method is known, wherein a cut-out piece, which is drawn up 
out of a workpiece using a suction means, such as magnet, suction pad, 
etc. is moved, with the piece attached to the suction means, to a position 
horizontally away from the lower nozzle, and then the sucking action of 
the suction means is released so as to detach the cut-out piece at that 
position. Further, another method is known, wherein a cut-out piece held 
in a workpiece using a similar suction means is moved in unison with the 
workpiece to a position away from the lower nozzle, and then the suction 
of the suction means is released to permit the natural falling of the 
cut-out piece. However, an electromagnetic suction means such as magnet 
cannot be applied to cut-out pieces made of non-magnetic materials. In the 
case of using a suction pad or the like, the provision of a complicated 
piping is required to connect the suction pad or the like to a pressure 
reducing device. Also, a cut-out piece, which has a limited effective 
suction area because of its rugged top surface or other reasons, is likely 
to come off suction means during the movement. When a cut-out piece is 
removed from the workpiece by drawing it up, part of the main body of an 
electric discharge machine to which suction means is installed must be 
reinforced. When a cut-out piece is moved in unison with the workpiece, 
the suction means must be moved in synchronization with the movement of 
the workpiece, resulting in a complicated device configuration. 
DISCLOSURE OF THE INVENTION 
An object of the present invention is to provide a method and an apparatus 
for removing cut-out pieces, which make it possible to easily and reliably 
remove pieces cut out of a workpiece by wire-cut electric discharge 
machining, without damaging the cut-out pieces or the lower nozzle. 
To achieve the above-mentioned object, according to one aspect of the 
present invention, there is provided a method for removing a cut-out piece 
in electric discharge machining in which a piece is cut out from a 
workpiece. The method of the present invention comprises the steps of: (a) 
upwardly jetting fluid toward a bottom surface of a piece cut out of a 
workpiece; and (b) horizontally moving the cut-out piece in unison with 
the workpiece while jetting the fluid. The cut-out piece is permitted to 
naturally drop off the workpiece when it reaches a horizontal moved 
position at which the jetted fluid no longer acts thereon. 
Preferably, the method of the present invention further includes the step 
of downwardly jetting the fluid toward a top surface of the cut-out piece 
when the cut-out piece reaches the horizontal moved position at which the 
jetted fluid no longer acts thereon. Preferably, the method of the present 
invention is applied to an electric discharge machine having a nozzle for 
upwardly jetting machining fluid toward the workpiece, and a table for 
horizontally moving the workpiece. When a piece has been cut out of the 
workpiece, the jetting of the fluid in the step (a) is performed by means 
of the nozzle, and the movement of the cut-out piece in the step (b) is 
performed by means of the table. 
According to another aspect of the present invention, there is provided a 
cut-out piece removing apparatus for use in a wire-cut electric discharge 
machine in which a piece is cut out from a workpiece. The apparatus of the 
present invention comprises fluid jetting means for upwardly jetting fluid 
toward a bottom surface of the piece cut out of the workpiece; drive means 
for horizontally moving the cut-out piece in unison with the workpiece; 
and control means for starting operations of the fluid jetting means and 
the drive means upon completion of cutting out of the piece from the 
workpiece. 
Preferably, the cut-out piece removing apparatus, which is mounted on an 
electric discharge machine having a lower wire guide, further includes 
second fluid jetting means for downwardly jetting the fluid toward the top 
surface of the cut-out piece at a location horizontally away from the 
lower wire guide, under the control of the control means. Preferably, the 
cut-out piece removing apparatus further includes constraining means, 
having a constraining member which is movable between a retreated position 
away from the lower wire guide and a constraining position which is close, 
right above the lower wire guide, to the top surface of the cut-out piece, 
for preventing the cut-out piece from being upwardly detached from the 
workpiece. Preferably, a nozzle mounted on the electric discharge machine 
for upwardly jetting machining fluid toward the workpiece is used as the 
fluid jetting means; a table mounted on the electric discharge machine for 
horizontally moving the workpiece is used as the drive means; and a 
control unit mounted on the electric discharge machine for controlling 
operations of the electric discharge machine is used as the control means. 
As described above, according to the present invention, the fluid is jetted 
upwardly toward the bottom surface of a cut-out piece to thereby retain 
the cut-out piece in the workpiece, and the cut-out piece is horizontally 
moved in unison with the workpiece. Thus, the piece drops off the 
workpiece when the cut-out piece reaches a position, horizontally away 
from the lower wire guide, where an upward force produced by the jetted 
fluid no longer acts upon the piece. This allows the piece to be easily 
removed from the workpiece simply by horizontally moving the cut-out piece 
while jetting the fluid. In addition, since the piece is held in the 
workpiece away from the lower wire guide by means of the jetted fluid 
during the travel of the cut-out piece, there is no contact between the 
cut-out piece and the lower wire guide, thus causing no damage to the 
piece or the guide due to contacting. Unlike the prior art in which a 
supporting plate is employed, the cut-out piece is supported by the jetted 
fluid, so that there is no chance of damage to the cut-out piece during 
the travel of the cut-out piece or of undue load applied to the main body 
of the electric discharge machine. Since the piece is completely cut out 
of the workpiece before the cut-out piece is removed from the workpiece, 
there is no need to tap the cut-out piece off, allowing cut-out pieces of 
various dimensions to be removed without failure. Unlike the prior art 
which uses electromagnetic suction means, the present invention can be 
also applied to cut-out pieces made of non-magnetic materials. Further, 
unlike the prior art of a pressure-reduction type, the prevent invention 
is capable of reliably removing cut-out pieces of various shapes, 
including pieces with rugged top surfaces. In contrast to the 
pressure-reduction type prior art which requires a pressure reducing 
device and piping, the present invention can be implemented using an 
arrangement with a simple configuration, and there is no need to move a 
suction means in synchronization with workpiece movement. To implement the 
present invention, for instance, a machining fluid jetting nozzle, a 
worktable, and a control unit of an electric discharge machine can be 
utilized, which are originally used for electric discharge machining.

BEST MODE OF CARRYING OUT OF THE INVENTION 
Referring to FIGS. 1 and 2, the wire-cut electric discharge machine is 
provided with a machine main body 10 which is basically constructed in a 
known manner, and a numerical control unit 30 for controlling operations 
of various sections of the machine main body 10 in accordance with a 
program stored beforehand in a computer memory. 
The machine main body 10 includes a Z-axis unit 12 vertically movable 
relative to an upper column 11 of the main body, an automatic wire 
extension unit 13 fixed to the Z-axis unit 12 via a stay 14 and having a 
wire cutting function, an upper wire guide 15 having an upper nozzle 16 
and mounted to the Z-axis unit 12, and a lower wire guide 18 having a 
lower nozzle 19 facing the upper nozzle 16 and mounted to the distal end 
of a lower arm 17. Preferably, the upper wire guide 15 is arranged to be 
vertically movable in unison with the Z-axis unit 12 and horizontally 
movable relative to the unit 12. The upper nozzle 16 and the lower nozzles 
19 are respectively connected to a machining fluid supply system (not 
illustrated) of the machine main body 10, and are each designed to jet the 
machining fluid toward a workpiece 40 when an associated one of solenoid 
valves in the machining fluid supply system are opened. A table 20 of the 
machine main body 10, on which the workpiece 40 is mounted, is operatively 
coupled to an X-axis and Y-axis motors (not shown). 
In the machine main body 10 which operates under the control of the 
numerical control unit 30, a wire electrode 50 passing through the 
workpiece 40 is delivered by a wire delivery unit (not shown) from the 
upper wire guide 15 to the lower wire guide 18, and the table 20 is driven 
by the X-axis and Y-axis motors, so that the workpiece 40 mounted on the 
table 20 is moved along a specified machining track on the XY plane. 
During that time, a machining voltage is applied from a machining power 
source (not shown) to a machining gap between the workpiece 40 and the 
wire electrode 50 to thereby perform electric discharge machining, while 
the machining fluid is jetted form the upper nozzle 16 and the lower 
nozzle 19 to the gap, whereby a plurality of pieces (products or cores) 41 
are cut out in succession from the workpiece 40, for example. 
Next, an apparatus, which constitutes the principal part of the present 
invention, for removing the cut-out pieces 41 from the workpiece 40 each 
time cutting-out machining of one of the pieces 41 is finished, will be 
explained. 
This cut-out piece removing apparatus has a first fluid jetting means for 
upwardly jetting the fluid toward the bottom surface of the cut-out piece 
41, a drive means for horizontally moving the cut-out piece 41 in unison 
with the workpiece 40, and a control means for controlling the operation 
of these two means. To simplify its configuration, the cut-out piece 
removing apparatus, according to an embodiment of the present invention, 
utilizes the lower nozzle 19 and the table 20 of the machine main body 10 
and the numerical control unit 30, as the first fluid jetting means, the 
drive means, and the control means, respectively. 
The cut-out piece removing apparatus further includes a constraining means 
for preventing the cut-out piece 41 from being upwardly removed from the 
workpiece 40 by an upward acting force of the jetted fluid, the 
constraining means including a cylinder-piston assembly 60 and a 
constraining assembly 63. As shown in FIGS. 2 and 3, the cylinder-piston 
assembly 60 includes an air cylinder 61 fixed to one end of the stay 14 
which in turn fixed to the Z-axis unit 12, and slantingly and downwardly 
extending from the stay end toward the lower wire guide 18, and a piston 
62 disposed in the cylinder 61 for advancing and retreating motion. This 
cylinder 61 has first and second cylinder chambers (not shown). The 
constraining assembly 63 extending horizontally is fixed to the distal end 
of the piston 62. The piston 62 is arranged to advance slantingly and 
downwardly when pressurized air is supplied to the first cylinder chamber 
of the cylinder 61 from a pressurized air source (not shown) through a 
first solenoid valve (not shown) which is controlled by the control unit 
30, and retreat slantingly and upwardly when pressurized air is supplied 
to the second cylinder chamber through a second solenoid valve (not 
shown). As the piston 62 advances or retreats, the constraining assembly 
63 is moved between a retreated position (shown by the solid line in FIG. 
2) away from the lower wire guide 18 and a constraining position (shown by 
the dotted line) which is close, at right above the guide 18, to the top 
surface of the piece 41 with a gap of, e.g., approximately 1 mm. 
The constraining assembly 63 has a square plate 64 fixed at its one end 
portion to the distal end of the piston 62 and extending horizontally, and 
a square frame 65 disposed thereunder. The frame 65 is mounted, through 
guide rods 66 and springs 67 fitted on those rods, to the plate 64 for 
movement toward or away from the plate. The frame 65 has a net 68 made of 
stainless wire. The bottom surface of the frame 65 is covered with a 
synthetic resin sheet (not shown). 
The cut-out piece removing apparatus further includes three auxiliary 
nozzles (second fluid jetting means) 70 for downwardly jetting the fluid 
toward the top surface of the piece 41 to cause the cut-out piece 41 to be 
detached from the workpiece 40. Each of the auxiliary nozzles 70 is fixed 
to the plate 64 of the constraining assembly 63, and is connected to the 
machining fluid supply system of the machine main body 10 via a tube 71 
provided at its middle with a solenoid 72 which operates under the control 
of the numerical control unit 30. 
In the following, a cut-out piece removing operation of the electric 
discharge machine will be explained. 
Upon completion of cutting-out machining for one of the pieces 41, the 
supply of the machining fluid to the upper and lower nozzles 16 and 19 is 
interrupted, the wire 50 is cut by the automatic wire extension unit 13, 
and then the Z-axis unit 12 is moved upward to the retreated position. At 
the end of the cutting-out machining, the cut-out piece 41 separated from 
the workpiece 40 rests on the lower nozzle 19 in a manner slightly 
inclined in the workpiece (the degree of inclination of the piece 41 is 
emphasized). 
When the Z-axis unit 12 reaches the retreated position, the first solenoid 
valve associated with the cylinder 61 is opened under the control of the 
control unit 30, which functions as the control means of the cut-out piece 
removing apparatus, so that pressurized air is supplied to the first 
cylinder chamber of the cylinder 61 to cause the piston 62 to advance. 
Thereafter, when the constraining assembly 63 moves from the retreated 
position shown by the solid line in FIG. 4A to the constraining position 
shown by the dotted line in FIG. 4A, the supply of the pressurized air is 
cut off, causing the assembly 63 to be retained in the constraining 
position. As a result, the net 68 of this assembly is disposed at a 
location close to the top surfaces of the workpiece 40 and the cut-out 
piece 41. Then, the machining fluid at approximately 15 atmospheres is 
jetted upwardly from the lower nozzle 19, which functions as the first 
fluid jetting means, toward the bottom surface of the cut-out piece 41. As 
shown in FIG. 4B, the cut-out piece 41, which receives at its bottom 
surface with an upwardly acting force, is urged upward and is moved in the 
upward direction away from the lower nozzle 19. The piece is prohibited 
from being upwardly detached from the workpiece 40 because of the presence 
of the net 68 located near the top surface of the piece. When the cut-out 
piece 41 collides with the net 68, the net 68 moves up to absorb an impact 
force. As a result, the cut-out piece 41 is retained in the workpiece 40 
in a state away from the lower nozzle 19, and the machining fluid fills 
the gap between the bottom surface of the piece and the lower nozzle 19. 
Then, the table 20 is moved in the horizontal direction, so that the 
cut-out piece 41 is moved together with the workpiece 40 in the horizontal 
direction away from the lower nozzle 19, with the lower nozzle 19 jetting 
the machining fluid. During that time, the cut-out piece 41 and the lower 
nozzle 19 are kept out of contact from each other by the machining fluid 
jet, whereby the cut-out piece 41 smoothly moves horizontally along the 
net 68 in the direction opposite from the lower nozzle while keeping in 
contact with or away from the net 68. 
Subsequently, when the table 20 is horizontally moved over a predetermined 
amount of table movement (30 to 60 mm), which corresponds to a 
predetermined piece moved position where the machining fluid jet normally 
no longer acts on the bottom surface of the cut-out piece and which was 
experimentally predetermined, the table movement is stopped. In addition, 
the solenoid valve 72 associated with the auxiliary nozzles 70 is opened, 
so that the machining fluid is jetted downward from the auxiliary nozzles 
70 toward the top surface of the cut-out piece 41, as shown in FIG. 4C. As 
a result, the cut-out piece 41 is forcibly dropped from the workpiece, 
being subjected to the downward machining fluid jet at the table stop 
position where the upward working force of the machining fluid jet is 
normally rendered substantially ineffective, and hence the natural falling 
of the piece from the workpiece is normally permitted. Next, the solenoids 
respectively associated with the auxiliary nozzles 70 and the lower nozzle 
19 are closed, to thereby stop the supply of the machining fluid jet from 
those nozzles. Further, the second solenoid associated with the cylinder 
61 is opened to supply the pressurized air to the second cylinder chamber 
of the cylinder 61, causing the piston 62 to retreat. When the 
constraining assembly 63 moves from the constraining position to the 
retreated position, the pressurized air supply is cut off so that the 
assembly 63 is retained in the retreated position, whereby the cut-out 
piece removing operation is completed. Whereupon, the table 20 is 
positioned in the start position for the cutting-out machining of the next 
piece, and then the automatic wire extension is performed. 
The present invention is not limited to the aforementioned embodiment, and 
various modifications thereof may be made. 
For instance, in the embodiment, the cylinder-piston assembly 60 slantingly 
mounted is used as part of the constraining means for preventing the 
cut-out piece 41 from being upwardly detached from the workpiece 40 by the 
upward machining fluid jet. Alternatively, a similar cylinder-piston 
assembly may be installed vertically, and its piston may be rotatively 
driven by a motor. In this case, the piston is moved downward until the 
constraining assembly mounted on the distal end of the piston reaches the 
height slightly above the top surface of the cut-out piece, and then the 
piston is turned until the constraining assembly reaches the location 
right above the top surface of the cut-out piece. 
In stead of the aforementioned vertical cylinder-piston assembly, an 
assembly rotary mechanism consisting of a rotary shaft mounted at its 
distal end with the constraining assembly, and a supporting section fixed 
to the Z-axis unit and supporting the rotary shaft may be used. In this 
case, the Z-axis unit is moved down in place of the piston. 
The constraining means comprised of the cylinder-piston assembly 60 and the 
like is not an essential element of the present invention. In case that no 
constraining means is provided, the discharge pressure of the machining 
fluid jetted from the lower nozzle 19 is so adjusted that the pressure 
falls within an appropriate range. 
In the aforesaid embodiment, to simplify the configuration of the 
apparatus, the lower nozzle 19, the table 20 and the numerical control 
unit 30, which are originally used for electric discharge machining, are 
respectively employed as the first fluid jetting means, the cut-out piece 
drive means and the control means for the cut-out piece removal operation 
effected after the electric discharge machining. However, these means may 
be provided separately. The first fluid jetting means, in particular, may 
be provided independently of the lower nozzle 19. In this case, the first 
fluid jetting means may be arranged to be movable, so as to cause a 
cut-out piece to drop at a farther point from the lower nozzle. Although 
the machining fluid is used, in the embodiment, as the fluid for cut-out 
piece removal, various other types of liquids or gases such as pressurized 
air may be used instead.