Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
2001-03-21
2003-04-22
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
For bonding with pressure
C219S056210, C219S056220, C219S085160
Reexamination Certificate
active
06552293
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of joining or reflow soldering metallic members by use of electric current having an AC waveform.
2. Description of the Related Arts
Reference is made to
FIGS. 11A-11C
depicting by way of example a fusing process which is one method of joining metallic members together. This process includes electrically and physically joining an insulated wire
2
and a terminal plate
4
made of copper or copper alloy.
First, as shown in
FIG. 11A
, workpieces W consist of the terminal
4
and the insulated wire
2
placed inside a hooked portion or a bent portion
4
a
of the terminal
4
. The workpieces W are interposed between a pair of (e.g., upper and lower) electrodes
6
and
8
in such a manner that the lower electrode
8
provides a support for the underside of the terminal hooked portion
4
a
at a given position while simultaneously the upper electrode
6
is abutted against the top face of the terminal hooked portion
4
a
so that the top face is pressed down by a pressure device (not shown) with a predetermined pressing force F. At the same time, a predetermined voltage is applied across the two electrodes
6
and
8
by a power supply apparatus (not shown).
Then, first, an electric current I flows across the two electrodes
6
and
8
through the terminal hooked portion
4
a
acting as a current path, with the result that Joule heat is generated in the terminal hooked portion
4
a
. Consequently, as shown in
FIG. 11B
, an insulator
2
a
of the insulated wire
2
is melted by the Joule heat and is removed from a conductor
2
b.
After removal of the insulator
2
a
, as shown in
FIG. 11C
, the current I flows across the two electrodes
6
and
8
by way of the conductor (typically, copper)
2
b
of the insulated wire
2
. A pressing force F is continuously applied across the two electrodes
6
and
8
during the current-supplying period, and hence the Joule heat cooperates with the pressing force F to jointly pressure-join and crush the hooked portion
4
a
and the insulated wire conductor
2
b
together for caulking. This allows the insulated wire
2
and the terminal
4
to be firmly electrically and physically joined together. Due to an extremely small resistance of the conductor
2
b
of the insulated wire
2
and the terminal
4
, no nugget (weld joint) will be formed therebetween.
FIG. 12
shows the circuit configuration of a single-phase AC power supply apparatus which has hitherto been used for the above fusing process.
FIG. 13
shows waveforms of a voltage and current appearing in this power supply apparatus.
In this power supply apparatus, a single-phase AC voltage V of a commercial frequency input to input terminals
100
and
102
are fed to a primary coil of a step-down transformer
108
via a contactor composed of a pair of thyristors
104
and
106
. An AC induced electromotive force (secondary voltage) generated in the secondary coil of the transformer
108
is applied via the secondary conductor and the electrodes
6
and
8
are applied to the workpieces W (
2
,
4
) so that a secondary current i
2
having a larger current value than a primary current i
1
flows as the fusing current I through the secondary circuit.
Although the magnitude (effective value) of the fusing current I (i
2
) is determined by the conduction angle, it may also be said that the magnitude depends on the firing angle due to a substantially constant relationship between the firing angle and the conduction angle. In this power supply apparatus, a control unit
110
controls the firing angle (firing timing) &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
).
The control unit
110
accepts a start signal from an external device (not shown) such as a conveyor robot associated with the workpieces W (
2
,
4
), causes the pressure device to commence its pressing operation, executes the above thyristor firing control over a preset current-supplying time after the elapse of a predetermined time (squeeze time), and upon the termination of the current-supplying time, allows the pressure device to release the pressure after the elapse of a predetermined time (hold time).
In the above fusing process, the workpieces W (
2
,
4
) are thermocompressively joined by the Joule heat and the pressing force. However, excessive thermocompressive joining may remarkably impair the shape of the joined parts or may possibly induce breakage thereof or damage thereto. A monitoring device is thus provided for detecting the displacement of the upper electrode
6
in the pressing direction to monitor the degree of thermocompressive joining of the workpieces W (
2
,
4
). Once the displacement of the upper electrode
6
reaches a predetermined value (limit value), the monitoring device issues a current-halting signal, in response to which the control unit
110
brings the supply of current to a halt.
However, since the prior art employs the above thyristor firing control method, its current control ability may be lost after firing or turning on the thyristors
104
and
106
as shown in
FIG. 14
, so that the supply of current cannot be halted until the termination of that half cycle (10 ms in case of 50 Hz). For the duration, the thermocompressive joining of the workpieces W (
2
,
4
) may proceed excessively and render the time lag in halting the supply of current fatal.
SUMMARY OF THE INVENTION
The present invention was conceived in view of the above problems. It is therefore an object of the present invention to provide a metallic members joining method and reflow soldering method in which supply of current (regular supply of current) is ceased at once even in mid course of the AC waveform when situations to halt the supply of current occur prior to the termination of the set current-supplying time in the joining or reflow soldering of the metallic members using the AC waveform current, thereby enabling good quality workpieces work qualities to be obtained.
Another object of the present invention is to provide a metallic members joining method and reflow soldering method in which the regular supply of current is interrupted the instant that a halt signal is received during the supply of current and in which a small electric current of such a magnitude as not to substantially affect the joining and soldering flows is provided depending on the state of supply of current (elapsed time and polarity) upon the receipt of the halt signal, thereby preventing the transformer from undergoing the polarized magnetism or magnetic saturation, to consequently assure the protection or reliability of the power supply unit.
In order to achieve the above objects, according to a first aspect of the present invention there is provided a metallic members joining method in which a pair of electrodes are pressed against metallic members while simultaneously an AC waveform current flows through the pair of electrodes, the metallic members being joined together by making use of Joule heat generated in the metallic members. The method comprises: converting an AC voltage of a commercial frequency by a rectifying circuit into a DC voltage; converting the DC voltage output from the rectifying circuit by an inverter into a pulsed voltage of a high frequency; applying the high-frequency pulsed voltage output from the inverter across a transformer and via the pair of electrodes to the metallic members without rectification on the secondary side of the transformer; segmenting a current-supplying time for a single joining into a plurality of unit current-supplying periods and switching the inverter at the high frequency so as to allow an AC waveform current having a set current value to flow through the secondary side of the transformer with one polarity in each odd-numbered unit current-supplying period but with the other polarity in each even-numbered unit current-supplying period; and when predetermined phenomena or predetermined conditions to halt the reg
Miyachi Technos Corporation
Shaw Clifford C.
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