Electric heating – Capacitive dielectric heating – Bonding
Reexamination Certificate
2000-05-18
2002-11-26
Walberg, Teresa (Department: 3742)
Electric heating
Capacitive dielectric heating
Bonding
C219S777000, C219S778000
Reexamination Certificate
active
06486456
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fusing processing method making use of Joule heat and a pressurization force in order to crimp a workpiece.
2. Description of the Related Art
An exemplary fusing work is illustrated in
FIGS. 3A
to
3
C. This work provides electrical and physical connections between a covered wire
10
and a strip-like terminal
12
made of e.g., copper or copper alloy.
Referring first to
FIG. 3A
, a workpiece is inserted between a pair of (e.g., upper and lower) electrodes
14
and
16
, the workpiece consisting of the terminal
12
and the covered wire
10
embraced in a hooked portion or a bent portion
12
a
of the terminal
12
. The undersurface of the terminal hooked portion
12
a
is carried by the lower electrode
16
at a fixed position, with the upper electrode
14
abutting against the top surface of the terminal hooked portion
12
a
so that the latter is pressed downward with a predetermined pressurizing force F by a pressure device not shown. At the same time, a predetermined voltage is applied to the two electrodes
14
and
16
by a power supply apparatus not shown.
Then, current I first flows, through the terminal hooked portion
12
a
providing a current path, between the pair of electrodes
14
and
16
, to generate Joule heat at the terminal hooked portion
12
a
. As a result of this, an insulator
10
a
of the covered wire
10
melts by Joule heat and peels off a conductor
10
b
as illustrated in FIG.
3
B.
Once the insulator
10
a
is removed, current I is allowed to flow, through the conductor
10
b
(typically, made of copper) of the covered wire
10
, between the two opposing electrodes
14
and
16
as illustrated in FIG.
3
C. During the current-supplying period as well, the pressurization force F is still continuously applied to the two electrodes
14
and
16
, and hence Joule heat and pressurization force F act, in cooperation, to cause the terminal hooked portion
12
a
and the covered wire conductor
10
b
to be integrally pressure welded or pressure squashed for crimping. This enables the covered wire
10
and the terminal
12
to be electrically and physically joined together in a rigid fashion. Due to an extremely small resistance of the conductor
10
b
of the covered wire
10
and the terminal
12
, no nugget will be generated therebetween.
FIG. 6
illustrates a circuit configuration of a single-phase AC power supply apparatus that has hitherto been used for the fusing work as described above.
FIG. 7
illustrates waveforms of the voltage and current delivered from the power supply apparatus.
In this power supply apparatus, a single-phase AC voltage V of a commercial frequency fed to input terminals
100
and
102
is applied to a primary coil of a step-down transformer
108
by way of a contactor that is comprised of a pair of thyristors
104
and
106
. An AC induced electromotive force (secondary voltage) generated at the secondary coil of the transformer
108
is applied through the secondary conductor and the electrodes
14
and
16
to the workpiece W (
10
,
12
) so as to allow a secondary current i
2
having a larger current value than that of a primary current i
1
to flow as the fusing current I through the secondary circuit.
The magnitude (effective value) of the fusing current I (i
2
) is determined depending on a conduction angle. Due to the presence of a substantially fixed relation between a firing angle and the conduction angle, it may be said that the magnitude depends on the firing angle. This power supply apparatus provides a control of firing angles (firing timings) &thgr; of the thyristors
104
and
106
by way of a firing circuit
112
, to thereby control the effective value of the fusing current I (i
2
).
FIG. 8
illustrates a configuration of a DC inverter power supply apparatus that has hitherto been used in the fusing work.
FIGS. 9A and 9B
depict waveforms of the voltage and current output from the power supply apparatus.
This power supply apparatus comprises an inverter circuit
120
to which a DC voltage E is applied at a predetermined voltage level by a rectifying circuit not shown. The inverter circuit
120
includes switching elements and serves to issue high-frequency AC pulses in such a manner as to chop up the DC input voltage E at a high-frequency switching in response to a control pulse CP from a inverter control unit
128
. The AC pulses output from the inverter circuit
120
are fed to a primary coil of a step-down transformer
122
so that AC pulses similar to those at primary side are acquired in the secondary coil. The secondary pulsed alternating current is converted into a direct current by a rectifying circuit
126
consisting of a pair of diodes
124
a
and
124
b
, with the secondary direct current i
2
being fed as a fusing current I to the workpiece W (
10
,
12
) by way of the electrodes
14
and
16
.
In such a conventional fusing processing method using the single-phase AC power supply apparatus, the ratio is small of the effective current-supplying time (the time during which current actually flows) to the gross current-supplying time, so that a current peak value needs to be increased in each current-supplying cycle if it is desired to supply a sufficient thermal energy for the fusing work. However, the increased current peak value tends to result in an increased instantaneous peak value of Joule heat generated in the workpiece, which may possibly cause undesirable deformations or damages as a result of heat shock to which the workpiece W may be subjected. In the example of
FIGS. 3A
to
3
C, immediately after the commencement of current supply (i.e., at the stage of FIG.
3
A), the bend of the hooked portion
12
a
of the terminal
12
may crack in the vicinity of its top due to the heat shock.
On the contrary, in the conventional fusing processing method using the DC inverter power supply apparatus, the ratio of the effective current-supplying time is large and its heat generating efficiency is high, so that a sufficient thermal energy can be supplied to the workpiece even at a relatively low current peak value, and thus any heat shock can be suppressed. However, this method is problematic in that since the fusing current I can flow between the two electrodes only in the same direction (polarity), the amount of heat generation may differ from place to place due to Peltier effect appearing between the electrodes
14
,
16
and the workpiece W, whereupon the deformations and wears at the extremities of the electrodes are apt to concentrate in one electrode (typically, in the electrode
14
at positive side), which may result in a cumbersome maintenance and a rise in cost.
SUMMARY OF THE INVENTION
The present invention was conceived in view of the above problems. It is therefore the object of the present invention to provide a fusing processing method capable of preventing any heat shock on a workpiece to improve the work quality and evening out the wears and degradations of the electrodes to improve the maintenance (workability, costs).
According to an aspect of the present invention, in order to attain the above object, there is provided a method of fusing a workpiece in which a pair of electrodes are pressed against the workpiece while simultaneously a current flows through the pair of electrodes to the workpiece to generate Joule heat, the method comprising the steps of converting an AC voltage of a commercial frequency into a DC voltage by means of a rectifying circuit; converting the DC voltage output from the rectifying circuit, into a pulsed voltage of a high frequency by means of an inverter; passing the high-frequency pulsed voltage output from the inverter through a transformer, to apply it via the pair of electrodes to the workpiece without any rectification at secondary side of the transformer; and segmenting a current-supplying time for a single fusing processing into a plurality of current-supplying periods, to output the high-frequency pulses with one polarity from the inverter in odd-numbered cu
Moro Kyoji
Mukai Ren
Miyachi Technos Corporation
Van Quang
Walberg Teresa
Wenderoth , Lind & Ponack, L.L.P.
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