Metal deforming – With cutting – Severing a discrete piece from stock – work – or product
Patent
1994-10-27
1996-06-11
Crane, Daniel C.
Metal deforming
With cutting
Severing a discrete piece from stock, work, or product
470 40, 470129, 470140, 470904, B21J 508, B21K 146, B21K 158
Patent
active
055244718
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns an apparatus for making screws, rivets or similar objects, wherein a metal wire is passed through a stationary cropping bushing forwardly to a movable cropping bushing present in a receiving position, following which the movable cropping bushing is moved away from the receiving position substantially transversely to the axial direction of the wire to release a blank from the wire.
In the making of e.g. screws it is known to use an upsetting process wherein a blank is retained in a die, one end of the blank being formed by a punch or a tool.
Before a bland can be placed in such a die, the blank is provided by e.g. cutting from a wire. This typically takes place by a so-called cropping process wherein a wire is moved through a cropping bushing into a cropping tool. Release of a blank from the wire then takes place by briefly moving the cropping tool transversely to the longitudinal direction of the wire. This cropping tool is often open such that a so-called open cropping is performed.
The resulting blank is then to be moved by means of some form of transport mechanism to a position outside the die where further shaping is to take place. Here, a punch can move the blank into the die and then perform a pre-upsetting operation, the die being closed at the other end by a bottom stop, e.g. in the form of an ejector pin.
A relatively complicated transport mechanism is necessary for moving the released blank from the cropping position and forwardly for insertion into the die. The cropping tool itself may form part of the transport mechanism, but in that case it must be removed from the position in front of the die while the punch moves the blank into the die, which limits the production rate.
In addition to the complicated transport mechanism, this technique has the drawback that the mentioned open cropping does not provide an optimum quality of the resulting blanks, unless a complicated holding mechanism retains the wire in the tool during the cropping process. The disuniform quality of the blanks impedes optimum control of the subsequent steps in the forming process.
It is also known to use so-called closed cropping in other connections, wherein the employed cropping tool has the shape of a closed cropping bushing, which gives a much better quality of the resulting blanks. The use of this principle in traditional screw machines requires a complicated transport mechanism and also another ejector pin to eject the blank from the cropping bushing. This entails that an additional process step is introduced, which reduces the production rate.
From DE-C-933 430 a device is known in which after release of a blank from the wire the movable cropping bushing together with the released blank is moved further on to a discharge position where a punch is adapted to move the blank partly into the die and to compress the blank sufficiently to upset it by cold flowing in the region between the die and the movable cropping bushing.
SUMMARY OF THE INVENTION
One advantage provided by the invention is that the closed cropping gives an optimum quality of the resulting blanks, another being a high production rate because of the avoidance of extra process steps for transporting the blank from the cropping position and forwardly for insertion into the die where the blank is optimally aligned with respect to the die, which minimizes wear.
This is achieved according to the invention in that at least two movable cropping bushings are provided, arranged in a manner such that movable cropping bushings can be present simultaneously in the cropping or receiving position and the discharge position opposite the die, respectively. In this way it will be possible to achieve a particularly high production rate, since wire can be inserted into the one cropping bushing while a blank at the other bushing is moved into the die and is pre-upset.
In a special embodiment a plurality of movable cropping bushings are arranged in a rotatable cropping table capable of assuming a plurality of positions which cor
REFERENCES:
patent: 102418 (1870-04-01), Morgan
patent: 311969 (1885-02-01), Fischer
patent: 2396995 (1946-03-01), Friedman
patent: 3635389 (1972-01-01), Shibata
patent: 4052763 (1977-10-01), Dunkin
Crane Daniel C.
Enkotec A/S
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