Metal deforming – With cleaning – descaling – or lubrication of work or product
Reexamination Certificate
2000-10-19
2001-09-11
Larson, Lowell A. (Department: 3725)
Metal deforming
With cleaning, descaling, or lubrication of work or product
C072S361000
Reexamination Certificate
active
06286350
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for the hot-pressing of workpieces and to a hot-forming machine for carrying out this method.
DESCRIPTION OF THE PRIOR ART
During hot-pressing, first a cylindrical workpiece is usually sheared off from a metal bar heated to forging temperature. As a result of the heating, the workpiece is surrounded by a scale casing, that is to say an oxide layer, which flakes off during the forming of the workpiece. There are basically two possibilities for descaling:
a) The workpiece with scale is introduced into the first or single die of a hot-forming machine, and the scale is broken off from the workpiece there during compression moulding with the aid of a press ram.
b) The workpiece with scale is pre-upset and descaled in a first forming station outside a die and is introduced, in a second forming station, into the first or single die of the hot-forming machine and compression-moulded there.
A multi-stage hot-forming machine, in which the scale is broken off from the workpiece in the die of the first forming station, is described in Japanese utility model No. 2521909. The disadvantage of flaking of the scale within the die is that the scale is for the most part pressed into the workpiece again. This results in a poorer surface quality, thus necessitating more comprehensive cutting finish-machining and more machining outlay, with the result that the amount of material required, and therefore the costs per workpiece, are increased.
The disadvantages are avoided by hot-forming machines in which descaling takes place in a separate first forming action. CH 594 454 describes such a hot-forging press, in which the workpieces are pre-upset outside a die by a press ram, this also being called free upsetting, the scale breaking off from the workpieces and falling down. The descaled and pre-upset workpiece is then transported, by means of a transport gripper, into the second forming station and introduced into the die thereof, in which die the workpiece is compression-moulded.
Although this ensures that the flaked-off scale is not pressed into the workpiece again, an additional forming stage is necessary for this purpose. Moreover, the outside diameter of the pre-upset workpiece varies, since the upsetting force in the case of an empty adjacent forming station, which may occur during normal operation, for example after a conventional dropping of the ends of the metal bar, is greater than when the adjacent forming stations are full. A self-centring transport gripper is therefore virtually indispensable for transporting the workpiece.
A vertical forming machine for forming a workpiece in a closed die is known from JP-A-60030545. A descending slide presses at first an upper outer ram in a die against the workpiece which has been introduced before. Afterwards, an upper inner ram and a lower inner ram are pressed from above and below in the workpiece under pressure control. The ejection of the formed workpiece is finally carried out by means of a lower outer ram. A pre-upsetting of the workpiece outside the die is not provided for.
In view of the disadvantages of the above-described descaling methods known hitherto, the present invention is based on the following object. A method for the hot-pressing of workpieces that have been heated to forging temperature is to be provided, in which descaling of the workpieces takes place outside a die, without an additional forming station being required for this purpose.
SUMMARY OF THE INVENTION
The essence of the invention is that, in a method for the hot-pressing of workpieces, in which a workpiece heated to forging temperature is descaled outside a die by pre-upsetting by means of a press ram and is thereafter pressed to the desired shape in one or more dies, the pre-upsetting and the compression moulding take place in the first or single die by the same press ram in the same cycle of movement of the latter.
By virtue of the invention, a workpiece to be pressed can in a single forming station by a single press ram in one cycle of movement first be pre-upset and descaled outside a die and thereafter be compression-moulded in a die. Since descaling takes place outside a die, that is to say in a freestanding manner, the flaked-off scale is not pressed into the workpiece again, so that the surface quality of the latter is not impaired. Moreover, as compared with the hot-forming machine described in CH 594 454, a forming station can be saved, nor is a self-centering transport gripper necessary, since transport to the next forming station takes place only after compression moulding in the die, after which the workpieces have a well defined outer contour. The hot-pressing method according to the invention thus combines the advantages of both of the known descaling methods described above, without exhibiting their disadvantages.
A preferred exemplary embodiment of a hot-forming machine for carrying out the method according to the invention comprises at least one die, an associated extendable and retractable ejector and a forwardly and backwardly movable press ram. According to the invention, there are means by which the repulsion of the extended ejector by the forwardly moving press ram via a workpiece arranged between ejector and press ram can be delayed in such a way that the workpiece can thereby be pre-upset outside the die.
When a hot-forming machine of this type is in operation, the workpiece is pre-upset outside the die, pushed into the die and compression-moulded there by the forwardly moving press ram in the same cycle of movement, and is finally pushed out of the die again by the ejector. In a multi-stage hot-forming machine, the workpiece is then transferred to the next forming station in a known way.
The means for delaying the repulsion of the ejector and the introduction of the workpiece into the die may be, for example, hydraulic, pneumatic, mechanical or electromechanical means.
Hydraulic or pneumatic delay means comprise, in a preferred exemplary embodiment, a control piston, arranged in a pressure chamber and connected directly or indirectly to the ejector, and means for the supply and discharge of liquid or gas into and out of the pressure chamber. The liquid or gas discharge means are designed in such a way that the liquid or gas discharge from the pressure chamber takes place partially with a delay and delays the repulsion of the control piston and the ejector. They advantageously comprise a liquid or gas discharge line, in which is arranged a throttle or a pressure relief valve, opening only at a particular liquid or gas pressure, or which is opened and closed by means of a control pin.
An advantageous hot-forming machine according to the invention with mechanical delay means comprises a rotatable cam for controlling the extension and retraction of the ejector, the said cam being so shaped and its rotation so coordinated with the forward and backward movement of the press ram that the repulsion of the extended ejector takes place with a delay.
REFERENCES:
patent: 3120769 (1964-02-01), Habetur
patent: 3584498 (1971-06-01), Beche
patent: 3748887 (1973-07-01), Widera
patent: 594454 (1978-01-01), None
patent: 1120848 (1961-12-01), None
patent: 57177845 (1982-11-01), None
patent: 60030545 (1985-02-01), None
patent: 2521909 (1997-01-01), None
Matt Andreas
Schönenberger Raymond
Suter Michael
Hatebur Umformmaschinen AG
Larson Lowell A.
Selitto Behr & Kim
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