Method of producing hollow objects and an arrangement for such method

Abstract

A method of, and arrangement for, producing shaped hollow metal objects by a hot process. A metal hollow semi-finished-product with at least one opening is heated to a forming temperature and placed into a cavity, whose shape corresponds to the desired final external shape of the hollow object. Then the cavity is sealed and water and/or steam is introduced therein. After the final shape of the semi-finished-product is achieved, the semi-finished-product is removed. The cavity is formed by a split mould, whose opening's entry edge has an expanded portion, against which a sealing feature is oriented. The outer surface of the sealing feature is arranged to close against this expanded portion. The sealing feature is also provided with a means of supply of water and/or steam, and a tube through which the water and/or steam is supplied. This tube extends into the interior space of the semi-finished-product, and can be provided with nozzles.

Claims

1. A method of producing a shaped hollow metal object, the method comprising the steps of: a) heating a hollow semi-finished metal product including a central space having an opening to an austenite temperature such that the hollow semi-finished metal product is in an austenite state; b) placing the hollow semi-finished metal product into a cavity of a mould, the cavity having a shape corresponding to a desired findal external shape of the shaped hollow metal object; c) sealing the opening of the hollow semi-finished metal product and the central space via a sealing feature biased by a spring; d) introducing at least one of water and steam into the central space such that the hollow semi-finished metal product heats the at least one of water and steam thereby increasing pressure in the central space so that the hollow semi-finished metal product attains the desired final shape of the shaped hollow metal object via the shape of the cavity of the mould; e) automatically unsealing the opening of the hollow semi-finished metal product when the pressure in the central space generates a counterforce that overcomes a threshold bias force of the spring; and f) removing the shaped hollow metal object from the cavity, wherein steps b)-f) are performed with the respective hollow semi-finished product or shaped hollow metal object being in the austenite state.

2. The method of claim 1, further comprising the steps of reducing a temperature of the hollow semi-finished metal product to be equal to a temperature of the mould via contact of the hollow semi-finished metal product with the mould before removing the shaped hollow metal object from the mould, maintaining thre temperature of the shaped hollow metal object at the equalized temperature for at least 5 minutes, and reducing the temperature of the shaped hollow metal object to ambient temperature via air cooling.

3. The method of claim 1, the mould being a split mould, the cavity including an entry edge having an expanded portion, step c) including pressing a proximal portion of the hollow semi-finished metal product against the expanded portion via an outer surface of a sealing feature, and step d) including introducing the at least one of water and steam through the sealing feature.

4. The method of claim 3, wherein step d) includes introducing the at least one of water and steam via a tube passing through the sealing feature.

5. The method of claim 4, wherein step d) includes evenly distributing pressure in the central space via nozzles circumferentially located on the tube.

6. The method of claim 3, further comprising the step of contacting an inner surface of the hollow semi-finished metal product only at the proximal portion via the outer surface of the sealing feature such that a remainder of the inner surface is uncontacted when step d) is initiated.

7. A method of producing a shaped hollow metal object, the method comprising the steps of: a) heating a hollow semi-finished metal product including a central space having an opening to an austenite temperature such that the hollow semi-finished metal product is in an austenite state; b) placing the hollow semi-finished metal product into a cavity of a mould, the cavity having a shape corresponding to a desired final external shape of the shaped hollow metal object; c) contacting an internal surface of the hollow semi-finished metal product only at a proximal portion of the hollow semi-finished metal product via a sealing feature so as to seal the opening of the hollow semi-finished metal product and the central space, a remainder of the internal surface being uncontacted; d) introducing at least one of the water and steam into the central space such that the hollow semi-finished metal product heats the at least one of water and steam thereby increasing pressure in the central space so that the hollow semi-finished metal product attains the desired final shape of the shaped hollow metal object; e) unsealing the opening of the hollow semi-finished metal product; and f) removing the shaped hollow metal object from the cavity, wherein steps b)-e) are performed with the respective hollow semi-finished product or shaped hollow metal object being in the austenite state, wherein the sealing feature is biased by a spring and step e) includes automatically unsealing the opening when the pressure in the central space generates a counterforce that overcomes a threshold bias force of the spring.

8. The method of claim 7, further comprising the steps of reducing a temperature of the hollow semi-finished metal product to be equal to a temperature of the mould via contact of the hollow semi-finished metal product with the mould before removing the shaped hollow metal object from the mould, maintaining the temperature of the shaped hollow metal object at the equalized temperature for at least 5 minutes, and reducing the temperature of the shaped hollow metal object to ambient temperature via air cooling.

9. The method of claim 7, the mould being a split mould, the cavity including an entry edge having an expanded portion, step c) including pressing the proximal portion of the hollow semi-finished metal product against the expanded portion via an outer surface of the sealing feature, step d) including introducing the at least one of water and steam through the sealing feature.

10. The method of claim 9, wherein step d) includes introducing the at least one of water and steam via a tube passing through the sealing feature.

11. The method of claim 10, wherein step d) includes evenly distributing pressure in the central space via nozzles circumferentially located on the tube.

Description

OVERVIEW OF FIGURES IN DRAWINGS

(1) FIGS. 1 and 2 show a schematic depiction of a forming device for making hollow objects prior to the process and with a semi-finished product of the initial and final shapes, respectively.

EXAMPLE EMBODIMENT

(2) A metal hollow semi-finished product P provided with one opening is made of the 25SiCrB material (Tab. 1). This semi-finished product P is heated approximately to its austenite temperature of 950 C. in an electrical furnace. Immediately after that, the semi-finished product P is transferred by means of tongs into a forming device. The forming device comprises a split mould F and a sealing feature U. A cavity D is created by bringing both parts of the mould F together, with their opening's entrance edge being provided with an expanded portion Z, against which the sealing feature U is oriented, whose outer surface B is arranged to close against this expanded portion Z. Bringing the sealing feature U into contact with the expanded portion Z seals the cavity D. In the gap between the expanded portion Z and the outer surface B of the sealing feature U, part of the semi-finished product P becomes trapped which thereby perfectly seals the cavity D. The sealing feature U is provided with a tube T and a means of supply of water by which it extends into the cavity D of the mould and into the semi-finished product P. On its circumference, the tube T is provided with nozzles T. In this case, the forming process in the forming device takes place with the aid of steam which creates internal pressure. The steam is generated by supplying water through nozzles T in the tube T, as a consequence of the contact of water with the heated semi-finished product. By means of the internal pressure, the semi-finished product P is deformed into the final hollow object shape at temperatures in an interval of approximately 920 C. to 500 C. The final shape is obtained by filling the internal contour of the cavity D in the forming device. The sealing feature U is pressed against the mould F via a spring A, which rests on the outer surface B of the sealing feature. When the maximum pressure is exceeded, said spring moves the outer surface B, which is arranged to close against the expanded portion Z of the entrance edge of the opening of the mould F, away from this expanded portion Z and the gap thus provided enables part of the pressurized steam to be released to the surrounding space. Thus, the spring A fulfils the function of a pressure relief valve. After the desired temperature and pressure have been achieved, the cavity D is opened, both parts of the mould F are drawn apart and the resultant hollow object is removed from the forming device and is subsequently cooled to the ambient temperature. After the forming process, when the temperature of the hollow object becomes equal to the temperature of the mould F, which is heated to approximately 250 C., the hollow object having the final shape is removed from the mould F and transferred into a heating device. In this case, the heating device comprises a continuous furnace at the temperature of 250 C. This temperature enables carbon redistribution, austenite stabilization and relieves stress in the microstructure. The hollow object is kept at 250 C. in the furnace for about 6 minutes. In the last step, the hollow object is removed from the heating device and cooled by means of a cooling device in still air to ambient temperature or to room temperature, in this case 20 C. In this case, the cooling device has the form of a cooling conveyor.

(3) TABLE-US-00001 TABLE 1 Chemical composition of the material 25SiCrB (wt. %) C Si Mn Cr Mo Al Nb P S Ni Cu B 0.25 2.0 0.5 0.8 0.03 0.008 0.03 0.01 0.01 0.08 0.07 0.005

INDUSTRIAL UTILITY

(4) This invention can be used in the production of metal parts, namely in the metallurgical industry in making semi-finished products, in particular for the automotive industry.