Patent
1983-10-03
1985-07-09
Combs, E. Michael
10 86F, B23G 700, B21D 5324
Patent
active
045272999
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method for the forming of an internal thread in a hollow body, principally a hollow body formed from a metal plate which is bent around a longitudinal axis to form a tube slotted along its length.
Hitherto known methods of cutting internal threads in articles of a certain length are effected by machining by means of a tap. This demands a certain wall thickness in order for the article to retain adequate strength and, moreover, calls for considerable cleaning of tools and components after the cutting of the thread. A further disadvantage is the long production time, which again in turn means a high cost of manufacture.
Tools for forming an internal thread by means of a thread-forming tap, which is turned in through a hole, are already known within the art. However, these methods are limited to relatively thin workpieces such as plates, in which there is formed a so-called trumpet hole. As soon as the thickness of the workpiece exceeds the diameter of the thread, use must normally be made of thread-cutting taps.
The object of the present invention is to overcome the drawbacks and disadvantages of known methods of thread forming, and this is achieved by a method whereby a workpiece in the form of a tube is introduced over a mandrel which is positioned between a number of clamping jaws in which there is located a yielding dowel, said dowel being pressed in towards the mandrel for fixing the tube, after which the clamping jaws are moved in against the tube on the mandrel and clamp the tube completely together, this taking place before or after the mandrel is drawn out of the tube, whereupon a thread-forming tap rotated in the direction of the thread is turned into the tube to produce the internal thread by deformation, after which the tap is screwed out and the clamping jaws separated to release the tube.
There is thus achieved the possibility of producing a thread by deformation in a tube having a length which can be up to several times the diameter of the thread. By this deformation there is formed a perfect thread while retaining the material's structure and strength. Moreover, the workpiece is hardened by the deformation, thus ensuring a considerable retention of shape even when said workpiece is produced of spring steel. This method enables tubular nuts to be produced both more quickly and inexpensively and with hitherto unknown strength characteristics and shape retention.
In order to achieve the best possible operating conditions, it is expedient, as presented in claim 2, to introduce cutting oil both to the front and possibly to the inside of the tube, hereby also enabling the length/diameter ratio of a workpiece threaded by this method to be considerably increased.
Finally, as presented in claim 3, a method can be used by which the tube is fed in onto a spindle with a thread-forming tap which begins at the shank of the tap, so that the formation of the thread is effected by a single screwing out of the tap. This saves considerable time, in that in opposition to the normal procedure, where the tap must be turned in, its direction of rotation reversed and then turned out again, the tap needs to be turned only one way.
The invention will now be described in greater detail with reference to the accompanying drawing, where
FIG. 1 shows the tube introduced into a tool before the formation of the thread,
FIG. 2 shows a section seen in the direction II--II in FIG. 1, and
FIG. 3 shows the tube introduced over a second embodiment of the thread-forming tap.
FIGS. 1 and 2 show an example of one embodiment of a tool for the execution of the method in accordance with the invention.
The tool consists of two clamping jaws 1, 2, which can slide towards and away from each other while guided by a guide 3, said guide 3 comprising a spindle upon which the jaws can slide against spring pressure from springs 4. The inside faces of the clamping jaws are provided with a recess for the workpiece 9 which is to be securely clamped. Moreover, in said recesses are located one or more dowels 5 which, are
REFERENCES:
patent: 1839476 (1932-01-01), Golrick
patent: 2441580 (1948-05-01), Mageoch
patent: 3668726 (1972-06-01), Shinjo
Aktieselkabet J.H. Holm Holding
Combs E. Michael
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