Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
2002-12-24
2004-03-16
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
For bonding with pressure
Reexamination Certificate
active
06706991
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to a welding method and a welding system for a projection bolt.
2. Description of Related Art
A projection bolt comprises a shank on which screw threads are formed, a flange formed on one end of the shank, and a welding projection formed on the surface of the flange opposite to the shank side, wherein the welding projection is melted to be welded to a plate-shape work. The Japanese Patent No. 2509103 discloses an invention, in which a projection bolt, whose shank is inserted in a receiving hole formed on a movable electrode, is welded to a work, such as a steel plate and the like, when the movable electrode moves forward. The projection bolt is stopped first on the axis of the movable electrode, then is moved along the axis, and the shank of the projection bolt is inserted in the receiving hole.
The prior art described above provides a desired effect as a mechanism for moving a projection bolt and inserting the shank of the bolt in a receiving hole on an electrode. The insertion length for the shank, however, is not accurately controlled in the prior art. As a result, such a case may occur that an inserting rod resets at a stage at which the insertion length is insufficient, or that the projection bolt is inserted excessively enough to make a member holding the bolt interfere with the extremity of the electrode. The former case causes the bolt to come off from the receiving hole, due to the insufficient insertion of the bolt, and the latter case results in damaging the extremity of the electrode or the bolt holding member. These problems occur because the rod for bolt insertion is driven by fluid pressure supplied by an air cylinder and the like. To solve the problems, the behavior of components, such as the electrode, rod and so forth, must be set in a proper manner, particularly for dealing with a matter of how the shank of the projection bolt and the receiving hole on the electrode are allowed to take each relative position.
The prior art described above provides a desired effect as a mechanism for inserting a projection bolt in a receiving hole on an electrode. The prior art, however, lacks a particular consideration for improving the productivity of welding processes. Further, the prior art does not meet satisfactorily a demand that existing equipment is modified in the least extent to achieve the simplification of the equipment and reduction of an equipment cost. For such an operation that a projection bolt is welded to a small steel plate work, the above demand is particularly important. Besides, when the work moves forward to be positioned between two electrodes, a proper arrangement must be made so that the behavior of the work is not hampered. Meanwhile, in the prior art, the shank of the bolt cannot be inserted in the receiving hole of the electrode while the work is kept arranged between both electrodes.
SUMMARY OF THE INVENTION
According to one embodiment of the present invention, a welding method for a projection bolt is the method for welding the projection bolt having a shank, a flange, and a welding projection formed on the surface of the flange opposite to the shank side, to a plate shape work. The method comprises the following steps of: supporting the projection bolt by a holding head provided on a moving-back-and-forth feed rod in a state that the shank of the bolt is projected from the holding head; positioning the projection bolt on the axis of a movable electrode for moving back and forth by moving the feed rod; moving forward the movable electrode having a receiving hole for receiving the shank of the projection bolt and stopping the movable electrode from moving forward at the point that the shank is inserted into the receiving hole; retreating the holding head from the axis of the movable electrode for moving back and forth while the electrode is still; and, after the retreat of the holding head, moving forward the movable electrode again and welding the projection bolt to the work.
According to another embodiment of the present invention, a welding system for a projection bolt is the system for implementing the above welding method, that is, the welding system for welding the projection bolt having a shank, a flange, and a welding projection formed on the surface of the flange opposite to the shank side, to a plate shape work. The system comprises a welding machine on which a movable electrode and a fixed electrode are installed via supporting arms, respectively; a motor provided with a changing mechanism changing rotation into back-and-forth movement for moving the movable electrode; a receiving hole formed on the movable electrode for receiving the shank of the projection bolt; and a moving-back-and-forth feed rod provided with a holding head for holding the projection bolt in a state that the shank of the bolt is projected.
As the motor, an AC (Alternating Current) servomotor is typically employed, and the motor is equipped with the changing mechanism for changing rotation to back-and-forth movement. In general, the basic principle of the changing mechanism is that a screw shaft penetrates in a female screw block, which is rotated to make the screw shaft move back and forth, wherein a ball screw method is employed for reducing mechanical resistance produced upon operating the mechanism. In employing such a changing mechanism, the number of revolutions of the AC servomotor is set precisely according to a command from a controller, so that the extent of back-and-forth movement of the screw shaft can be controlled accurately.
The characteristics of the motor make it possible to determine precisely the stopping position of the movable electrode within a prescribed range. Therefore, the forward movement of the movable electrode is stopped instantly when the movable electrode moves toward the shank of the bolt in wait and the shank has come into the receiving hole in a prescribed length. While the movable electrode is still, the holding head retreats, and the movable electrode holding the projection bolt moves ahead again, pressing the welding projection to the work to be energized, then the welding operation ends.
In the above operation, the control of the mechanism for changing the rotation of the motor into back-and-forth movement and the drive control of the motor are executed properly and accurately, so that the stopping position of the movable electrode can be determined in a precise manner. This fact indicates that if the length of shank insertion in the receiving hole is less than a prescribed length, the holding head cannot be retreated. That is, the shank insertion with an insufficient length makes the shank incline abnormally in the receiving hole when the holding head retreats in the direction perpendicular to the electrode axis, making it difficult to insert the shank into the receiving hole smoothly. On the other hand, if the movable electrode is allowed to move forward to come too close to the holding head, the holding head and the movable electrode come to interfere, damaging each other.
It should be particularly noted in the present invention that the motor provides a control operation most appropriate for controlling the forward movement of the movable electrode. In other words, properly controlled output of the motor is sufficient enough to satisfy motion characteristics required for the movable electrode. If the forward movement of the movable electrode is controlled by a conventional technique, such as an air cylinder, it will be extremely difficult to temporarily stop the electrode within a required range and allow it to move forward again. In that case, the control will have to be made by a special two-stage cylinder. Also, according to the present invention, when the extent of forward movement by the movable electrode needs to be changed according to the replacement of a work or a projection bolt, changing the operation control memory of the motor allows the electrode to make necessary adjustment easily corresponding to the replacement of th
Aoyama Shoji
Aoyama Yoshitaka
Aoyama Yoshitaka
J.C. Patents
Shaw Clifford C.
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