Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
2002-04-15
2004-11-30
Stoner, Kiley (Department: 1725)
Electric heating
Metal heating
For bonding with pressure
C219S093000, C219S119000
Reexamination Certificate
active
06825436
ABSTRACT:
BACKGROUND ART
As for a nut for fixing an automobile wheel, a box nut is used in order to prevent entry of water, mud or the like or to improve the external appearance. This box nut has a bowl-shaped cap welded to the nut. The present invention belongs to the technical field that relates to the welding of such nut.
In the prior art, a cap and a nut are abutted together and in this state they are held by a chuck, and with the cap and nut integrally held standby on the axis between both electrodes, the latter advance to press the cap and nut and a welding current is passed to complete the welding. Particularly, electric resistance welding is performed by holding a nut on the flat end surface of the fixed electrode by a chuck, fitting thereon a cap held also by a chuck, and advancing the movable electrode into this state. Such system is disclosed in FIG. 3 of Japanese Unexamined Patent Publication Hei9-85464.
With the prior art described above, since the cap and nut, which are not welded together, are held by the chuck, iron scraps from somewhere or the like entering the holding dogs of the chuck causes a misalignment in the relative position between the cap and nut, resulting in the two parts being welded in the deviated state. Since the cap and nut held by the chuck are kept standby and the electrodes are advanced thereto, even the slightest misalignment in the relative position between the electrodes, cap and nut leads to the failure of the cap and nut to be correctly held by the electrodes, so that the cap and nut are nonalignedly welded or the cap is driven out when abutted against the nut. Further, with the chuck system, it is necessary to greatly increase the precision of the chuck mechanism, requiring that a correspondingly high installation be prepared. As the number of parts handled by the chuck mechanism increases, the movable parts, such as jaws and shaft, wear, incurring a lowering in operating precision.
DISCLOSURE OF INVENTION
According to an embodiment of the present invention, a box nut welding method is characterized in that one electrode is provided with a recess for receiving and holding a bowl-shaped cap and the other electrode is provided with a recess for receiving and holding a nut, the arrangement being such that the open end of the cap and the end surface of the nut held by the respective electrodes are pressed against each other by the advance of the electrode, whereupon a welding current is passed, thereby welding the cap and nut. Since the cap and nut are respectively held in the recesses of the electrodes, both parts assume the correct relative position when both electrodes on the same axis approach each other to abut both parts against each other; thus, a box nut of satisfactory welding precision is obtained. Since the cap and nut are received in the recesses of the electrodes, the relative position between the electrodes and the parts held therein can be accurately set, so that welded parts of high precision as described above can be obtained. Further, since the cap and nut are held directly by the electrodes, the need for employing a chuck mechanism as used in the prior art is eliminated, freeing the operator from the foregoing problems caused by the use of a chuck.
The cap and nut are moved axially of the electrodes after their axes may be positioned coaxial with the axis of the electrodes, and then they are received and held in the recesses of the electrodes. That is, the loci of the cap and nut are moved to the recesses of the electrodes after the cap and nut are coaxial with the axis of the electrodes, so that the loci of both parts assume the simplest form; therefore, the process for holding the parts in the electrodes is simply and reliably effected, ensuring that reliable operation is attained.
The cap and nut may reach the recesses of the electrodes as they are held by respective feed members that perform square motions. Both parts reach the recesses of the electrodes as they are held by the feed members, in which case the loci of the feed members are provided by square motions, thus making it easier to attain a reliable operation including movement of both parts to the electrode recesses after both parts are positioned on the electrode axis. That is, it is required that the feed members provide a locus for returning to the parts-receiving position and a locus for moving to the advance-ready position after parts have been received. These requirements are reliably achieved by the square motions.
A guide pin adapted to fit into the threaded hole in the nut may be installed in the recess of the nut holding electrode. As for the holding of the nut by the electrode, installing such guide pin can prevent the nut from abnormally tilting during pressing for welding, so that correct abutment of the nut against the cap is ensured. As for the cap, if the cap is bowl-shaped, the cap is pressed against the nut end surface with the uniformity of entire open end of the cap during pressing against the nut in a manner analogous to a phenomenon in which a ball freely rolls in the electrode recess. That is, the cap has a self-aligning action imparted thereto.
According to another embodiment of the invention, a box nut welding device is characterized in that one electrode is provided with a recess for receiving and holding a bowl-shaped cap and the other electrode is provided with a recess for receiving and holding a nut, both electrodes being disposed on the same axis, the device having a cap feeding mechanism for carrying the cap to the recess of the electrode subsequent to the positioning of the cap coaxial with the electrode axis, and a nut feeding mechanism for carrying the nut to the recess of the electrode subsequent to the positioning of the nut coaxial with the electrode axis. Since the cap and nut are respectively held in the recesses of the electrodes, both parts assume the correct relative position when both electrodes on the same axis approach each other to abut both parts against each other; thus, a box nut of satisfactory welding precision is obtained. Since the cap and nut are received in the recesses of the electrodes, the relative position between the electrodes and the parts held therein can be accurately set, so that welded parts of high precision as described above can be obtained. Further, since the cap and nut are held directly by the electrodes, the need for employing a chuck mechanism as used in the prior art is eliminated, freeing the operator from the problems caused by the use of a chuck.
Driving means may be combined so that the feed members of the cap feeding mechanism and nut feeding mechanism perform square motions. Both parts reach the recesses of the electrodes as they are held by the feed members, in which case the loci of the feed members are provided by square motions, thus making it easier to attain a reliable operation including movement of both parts to the electrode recesses after both parts are positioned on the electrode axis. That is, it is required that the feed members provide a locus for returning to the parts-receiving position and a locus for moving to the advance-ready position after parts have been received. These requirements are reliably achieved by the square motions.
A guide pin adapted to fit into the threaded hole in the nut may be installed in the recess of the nut holding electrode, the guide pin having a means for allowing the box nut to escape from the electrode recess after welding. As for the holding of the nut by the electrode, installing such guide pin can prevent the nut from abnormally tilting during pressing for welding, so that correct abutment of the nut against the cap is ensured. Where the guide pin is provided with an escape means, such as a compressed air spout or a push-out rod, the completed box nut is allowed to escape from the electrode. Particularly, since the cap is internally acted on by an escape force, the force necessary for escape is reliably transmitted to the box nut and the reliability of escape itself is increased. As for the cap, if the cap is bowl-shaped, the cap is pr
Aoyama Shoji
Aoyama Yoshitaka
Stoner Kiley
Tran Len
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