Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Z051093
ELECTRIC DISCHARGE MACHINE WITH
MULTIPLE TOOL ELECTRODES
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an electric discharge
machine, more particularly to an electric discharge
machine incorporating multiple tool electrodes.
2. Description of the Related Art
Electric discharge (or electric-spark) machining is
a metal removal process in which materials that conduct
electricity are removed by electric sparks. Machining
of a stationary workpiece is accomplished without any
grinding or cutting operation so that the workpiece is
not subjected to external forces which may cause
undesired deformation thereto. Electric discharge
machines possess a high degree of precision and can be
used for relatively long periods. These machines are
preferred if accurate machining is desired.
Figure 1 is an illustration of a conventional
electric discharge machine. The electric discharge
machine comprises two major parts: a main machine
assembly (90) and a power supply box (80). Normally,
the main machine assembly (90) is fitted with a movable
ram (11), an electrode clamping tool (12) carried by
the movable ram (11), and a tool electrode (13)
coaxially secured to the electrode clamping tool (12).
The metal workpiece (14) is provided immediately below
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the tool electrode (13) and is held in a stationary
position by a magnetic base (15) of a workbench on the
main machine assembly (90). The movable ram (11) is
drivingly coupled to a servomechanism (not shown). As
material removal progresses, the movable ram (11)
advances the tool electrode (13) toward the workpiece
(14) to maintain a constant spark gap. The discharge
current can be controlled via the power supply box
(80).
During use, the desired depth of material removal is
first set. When machining has reached the set depth,
current to the servomechanism is cut-off and machining
of the workpiece (14) is stopped. An alarm signal is
then generated to indicate that machining has been
accomplished. The workpiece (14) is then removed and
replaced with a new workpiece.
The main machine assembly (90) also includes various
operating circuits and control keys, and a lighting and
dielectric fluid supply system. The power supply box
(80) contains the necessary power supply control and
detector circuits, and several control keys.
Figure 2 illustrates the electrical connection
between the power supply box (80) and the main machine
assembly (90). Electrical wires (801) transmit power
and control signals from the power supply box (80) to
the main machine assembly (90). Electrical wires (802)
transmit the required discharge current from the power
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supply box (80) to the tool electrode (13) and to the
workpiece (14). The power supply box (80) has an
electrical plug (803) for connection with a primary AC
electrical outlet.
The conventional electric discharge machine has the
following characteristics and limitations:
1. The tool electrode and the workpiece are spaced
by a small spark gap. The spark generated melts the
small point on the surface of the workpiece that it
strikes and forms a crater thereat. This is how the
electric discharge machine achieves its machining
objective.
2. The surface of the workpiece is gradually eroded
through the use of this method and excessive amounts of
current tend to roughen the surface of the workpiece.
Therefore, in order to obtain a high degree of
accuracy, machining of the workpiece must be
accomplished at a very slow pace.
3. Since the desired depth of material removal is
set beforehand, manual supervision is unnecessary
during machining. When machining has been accomplished,
the electric discharge machine automatically stops and
an alarm signal is then generated to indicate that the
machined workpiece can be removed and replaced with a
new workpiece.
4. The conventional electric discharge machine can
machine only a single workpiece at a time. Machining a
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batch of workpieces thus requires a long total
machining time. To reduce the total machining time,
additional electric discharge machines must be
provided. This solution is, however, quite costly.
SUMMARY OF THE INVENTION
The main objective of the present invention is to
provide an electric discharge machine having multiple
tool electrodes to permit simultaneous machining of a
plurality of workpieces, thereby reducing total
machining time without entailing high equipment costs.
Accordingly, the preferred embodiment of an electric
discharge machine of the present invention comprises: a
main machine assembly including a movable ram member,
an electrode clamping assembly carried by the movable
ram member, a plurality of tool electrodes secured to
the electrode clamping assembly, and a workbench, each
of the workpieces being secured on the workbench
immediately below one of the tool electrodes; and a
power supply box including a discharge current
supplying means to supply discharge current
independently to each of the tool electrodes. The
discharge current supplying means can be formed as a
plurality of electrode sockets provided on the power
supply box or as a plurality of independent power
supply devices. The present invention thus provides an
electric discharge machine having a plurality of tool
electrodes in a single main machine assembly to permit
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simultaneous machining of a plurality of similar or
different workpieces to reduce the total machining time
without incurring huge equipment costs.
BRIEF DESCRIPTION OF THE DRAWINGS
Other features and advantages of the present
invention will become apparent in the following
detailed description of the preferred embodiments with
reference to the accompanying drawings, of which:
Figure 1 is an illustration of a conventional
electric discharge machine;
Figure 2 illustrates the electrical connection
between a main machine assembly and a power supply box
of the conventional electric discharge machine shown in
Figure 1;
Figure 3 is an illustra-tion of the preferred
embodiment of an electric discharge machine with
multiple tool electrodes according to the present
invention;
Figure 4 is a first example of electrical connection
between a main machine assembly and a power supply box
of the electric discharge machine shown in Figure 3;
and
Figure 5 is a second example of electrical
connection between the main machine assembly and a
power supply box of the electric discharge machine
shown in Figure 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
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Referring to Figures 3 and 4, the first preferred
embodiment of an electric discharge machine with
multiple tool electrodes according to the present
invention is shown to comprise a main machine assembly
(91) and a power supply box (81). The main machine
assembly (91) is fitted with a movable ram (11'), an
electrode clamping assembly (12') carried by the
movable ram (11') and tool electrodes (131-134) secured
to the electrode clamping assembly (12'). [Figure 3
shows four tool electrodes (131-134) secured to the
electrode clamping assembly (12'), although more may be
provided thereon depending upon the construction of the
electrode clamping assembly (12')]. Metal workpieces
(141-144) are each disposed immediately below a
respective one of the tool electrodes (131-134) and are
provided on a workbench (15') of the main machine
assembly (91). The movable ram (11') is drivingly
coupled to a servomechanism (not shown).
Electrical wires (801') transmit power and control
signals from the power supply box (81) to the main
machine assembly (91). The power supply box (81) is
provided with a plurality of electrode discharge
current supply sockets ~811-818). Four of the sockets,
(811-814), are electrically connected to the tool
2S electrodes (131-134). [The remaining sockets (815-818)
are provided to supply discharge current to additional
tool electrodes]. The electrode sockets (811-814)
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supply the required discharge current from the power
supply box (81) to the tool electrodes (131-134) and to
the workpieces (141-144). The power supply box (81)
further has an electrical plug (803') for connection
with a primary AC electrical outlet.
The spark gaps between the tool electrodes (131-134)
and the respective workpieces (141-144) are preferably
equal, so that machining of the workpieces (141-144)
can be accomplished at an equal pace. Equal machining
pace is desirable especially if the wor~pieces are of
the same type, and the desired machining is the same
for all workpieces.
The preferred embodiment can also be used even if
the specifications of the workpieces are different,
such as different machining depths are required.
Assuming that depths of 0.05 mm and 0.03 mm are
required, those workpieces which require a machining
depth of 0.05 mm are first machined up to a depth of
0.02 mm. Machining of all the workpieces is then
performed at an equal pace for the remaining depth of
0.03 mm. Machining of all the workpieces thus ends at
roughly the same time, and the electric discharge
machine generates an alarm signal to indicate that the
machined workpieces can be removed and replaced with a
new set of workpieces.
Figure 5 is a second preferred embodiment of an
electric discharge machine with multiple tool
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electrodes according to the present invention.
Electrical wires (801") are provided to transmit power
and control signals from a power supply box (82) to the
main machine assembly (91) of the electric discharge
machine. The operation of the second preferred
embodiment is substantially similar to that of the
first preferred embodiment and will not be detailed
further~ The main difference between the first and
second preferred embodiments lies in the construction
of the power supply boxes, (81) and (82). The power
supply box (82) comprises a plurality of independent
power supplies (821-826). Each of the independent power
supplies (821-826) has an electrical plug (804-809) for
connection with a primary AC electrical outlet. Four of
the power supplies, (821-824), are electrically
connected to the tool electrodes (131-134) and the
workpieces (141-144), supplying the required discharge
current. The remaining power supplies (825-826) are not
connected to the tool electrodes (131-134) but instead
supply the required power to drive the servomechanism
and other parts of the main machine assembly (91).
The present invention thus provides an electric
discharge machine which has a plurality of tool
electrodes in a single main machine assembly. This
permits simultaneous machining of a plurality of
similar or different workpieces. This is in contrast
with conventional electric discharge machines which
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permit machining of only one workpiece at a time.
While the present invention has been described in
connection with what is considered the most practical
and preferred embodiments, it is understood that this
invention is not limited to the disclosed embodiments,
but is intended to cover various arrangements included
within the spirit and scope of the broadest
interpretation so as to encompass all such
modifications and equivalent arrangements.
