Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
2000-08-22
2001-12-04
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
For bonding with pressure
C219S091210
Reexamination Certificate
active
06326580
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for joining a coated wire to a terminal member by supply of current.
2. Description of the Related Art
Coated wires are electric wires each made of a conductor coated with an insulator such as polyimide, polyurethane, enamel or vinyl. Hitherto known is a resistance welding apparatus capable of welding such a coated wire to a terminal member by mere supply of current without subjecting the coated wire to chemical or mechanical pretreatment. This type of resistance welding apparatus comprises a welding head that includes an intermediate electrode interposed between the coated wire and an upper electrode abutting against the coated wire, the intermediate electrode forming an electric bypass leading to a lower electrode abutting against the terminal member.
In such a configuration, the insulator of the coated wire shuts out the current at the initial stage of the supply of current, so that the current flows from the upper electrode through the intermediate electrode bypassing the lower electrode. As a result, the upper and intermediate electrodes (especially, the contact portion between the two electrodes) generate heat by Joule effect, which in turn apply thermal energies to the coated wire. Finally, the insulating film of the coated wire melts and the interior conductor or bare wire become exposed. After the exposure of the coated wire conductor in this manner, the workpieces (coated wire and terminal member) form a part of the electrically conductive path, allowing current to flow between the upper electrode and the lower electrode. The current passing though the workpieces causes the work contact portions to generate heat by Joule effect and fuse and metallurgically join together. Thus, by merely passing current through the welding head, the coated wire insulator is automatically removed so that the coated wire conductor is resistance welded to the terminal member.
Such a conventional resistance welding apparatus has managed (controlled) the main current flowing through the welding head (especially, the upper electrode) and the current-supplying time to have certain values without distinguishing the current used for the melting removing of the coated wire insulator from the current used for the workpiece resistance welding.
However, in spite of a series of steps associated with the same coated wire within the continuous current-supplying time, melting and removing of the insulator and the conductor resistance welding are intrinsically different steps, which are naturally to be given separate optimum current values. In addition, the current-supplying time should also consist of two stages for separate control.
Any means has not been found so far that monitors the current-supplying time (first current-supplying time) required for melting and removing of the insulator, which has made it difficult to manage the current-supplying time (second current-supplying time) for resistance welding to have a desired set value. For this reason, the second current-supplying time and thus the joint quality were influenced by any possible variance of the first current-supplying time. More specifically, too long a first current-supplying time results in too short a second current-supplying time, which impedes the acquisition of a sufficient welding strength. Inversely, when the second current-supplying time becomes too long as a result of short first current-supplying time, there has arisen a drawback that the workpiece joining portions, especially, the coated wire conductor may excessively fuse, which is apt to cause a defective welding due to occurrence of spatters.
SUMMARY OF THE INVENTION
The present invention was conceived in view of such conventional problems. It is therefore the object of the present invention to provide a joining apparatus ensuring an optimum control, in a single current-supplying sequence, of both the current consumed for the removal of the coated wire insulator and the current consumed for the joining of the coated wire conductor, to thereby achieve an improved joint quality.
Another object of the present invention is to provide a joining apparatus capable of executing, at an accurate timing, a switching from the current dedicated to the removal of the coated wire insulator to the current dedicated to the joining of the coated wire conductor.
A further object of the present invention is to provide a joining apparatus having an improved stability in the generation of heat by the electrodes for melting the coated wire insulator.
Yet another object of the present invention is to provide a joining apparatus ensuring an enhanced current-supplying efficiency in the major current supplying after the removal of the coated wire insulator.
Still another object of the present invention is to provide a joining apparatus allowing the flow of stabilized current for the removal of the coated wire insulator by use of heater electrodes.
In order to attain the above objects, according to a first aspect of the present invention there is provided a joining apparatus for joining coated wires each consisting of a conductor covered with an insulator, the apparatus comprising first and second electrodes arranged to clamp the coated wires laid one on top of the other or the coated wire and a terminal member laid one on top of the other, to apply a pressure thereto from both sides; a power supply circuit having first and second output terminals electrically connected to the first and second electrodes, respectively, the power supply circuit supplying a main current to an electrically conductive path extending between the first and second output terminals; a third electrode having a portion in intimate contact with a fore-end of the first electrode, the third electrode electrically connected to the second output terminal of the power supply circuit; current monitoring means monitoring a current flowing through the second electrode and detecting a timing when a current value of the current has reached a predefined level; and current control means providing a control of the power supply circuit so as to allow the main current to be substantially coincident with a first current set value for melting and removing of the insulator during a first current-supplying time starting from the initiation of the supply of current and ending by the detection of the timing, the current control means providing a control of the power supply circuit so as to allow the main current to be substantially coincident with a second current set value for joining the conductor and the terminal member together during a second current-supplying time starting from the detection of the timing and ending by the termination of the supply of current.
In the joining apparatus, the main current is constant current controlled to have a current value suitable to melt and remove the coated wire insulator in the first period that is basically defined as an unfixed period, whereas the current flowing through the second electrode is monitored while allowing the first and third electrodes to generate heat for the melting and removing of the insulator. Then, at the timing when the monitored current has reached a predetermined level (skip level), the supply of current of the first period is terminated and simultaneously the supply of current of the second period is commenced. The second period can be a predefined, certain period, during which the main current is constant current controlled to have a current value suitable to join the coated wire conductor to the terminal member, thereby ensuring a stable and satisfactory joining of members to be welded together.
According to another aspect of the present invention, a system is also possible that monitors the current (bypass current) flowing through the third electrode. In such a case, an appropriate skip level may be set for the amount of drop in the current value of the bypass current. As an alternative, the current flowing through the second electrode in the second period may be the object
Miyachi Technos Corporation
Shaw Clifford C.
Wenderoth , Lind & Ponack, L.L.P.
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