DE102007018395B4 - Internal high-pressure forming - Google Patents

Abstract

A hydroforming process in which a tubular workpiece (2) to be formed in a forming tool (1) is preheated from a steel material inside or outside the forming tool (1), the ends (3) of which are in a mold cavity (4) of the closed forming tool (1) received workpiece (2) are sealed and then a gas under pressure in the interior (6) of the workpiece (2) is introduced, wherein the workpiece (2) in a cooled forming tool (1) is inserted, wherein the workpiece (2) deformed in one go by the pressure of the gas and by the temperature of this gas from the inside and the temperature of the forming tool (1) from the outside in the same forming tool (1) consisting of a lower die (11) and an upper die (12) is hardened, characterized in that the gas pressure in the workpiece (2) by relative movement of a press upper part (10) in the closing direction of the forming tool (1) is generated and by a n pressure intensifier (16) is amplified, which is acted upon on its primary side by a fluid pressure, which in turn ...

Description

The The invention relates to a hydroforming process with the features in the preamble of claim 1.

in the Hot forming of sheet materials are two fundamental Method known: first, the press-hardening, d. H. the thermoforming of sheet metal by deep drawing in cooled tools, as well as the Forming of pipes, in particular of aluminum or magnesium by hydroforming in heated tools. With the hydroforming in heated Tools are the shaping possibilities, conditioned by the temperature increase extended. In addition, there is an improved material flow, so that defined by suitable Nachschieben wall thicknesses better are adjustable.

One Hydroforms of preheated workpieces in appropriately heated tools makes high demands to the forming technology. When forming steel pipes, the tools must to at least 450 ° C, better up to 930 ° C be heated. This is due to the resulting scale only using nickel-base alloys or ceramic materials for the tools possible. In addition, heating the tools costs a lot of energy and requires Special presses, as the hot ones Tools opposite need to be isolated from the press.

Furthermore, it is known to undergo hot-formed tubes by hydroforming in a second step of a work hardening process. Here a second forming tool is used ( DE 698 26 234 T2 ), A hardening of the hot-formed tubes is not considered in this process.

It is also state of the art in hydroforming to first heat the forming tool to thereby heat the workpiece. Subsequently, the same forming tool is cooled down again to harden the workpiece ( DE 698 03 588 T2 ), In this procedure, very high energy losses occur due to the constant temperature changes. In addition, it is difficult to ensure the critical cooling rates with sufficient process reliability.

From the DE 102 40 876 A1 For example, a method is known in which a hollow cylindrical metal element is formed in a forming die having a forming surface. The metal element is first heated to a temperature range suitable for quench enhancement. By pressurization by means of a gas, which is introduced into the cavity of the metal element, a wall of the metal element is bulged and / or deformed. The bulged wall comes into intimate contact with the forming surface of the die while simultaneously quenching it. As a result, a reinforcement of the metal element is achieved.

Of the necessary for deformation gas pressure is from a high pressure gas supply source used up, which includes a pressure bomb, which the required Gas volume holds.

Of the Invention is based on the object to show a way how hardened by hydroforming steel tubes under minimization energy costs and reducing tooling costs with high production speed can be.

These Task is with the hydroforming process according to the features of claim 1.

advantageous Further developments of the inventive concept are the subject of the dependent claims.

The Inner hydroforming process according to the invention provides that a tubular workpiece to be formed from a Steel material initially within or outside the forming tool preheated becomes. Then be the ends of the in a mold cavity of the closed forming tool recorded workpiece sealed, causing a gas under pressure in the interior of the workpiece is initiated.

The workpiece is not in a preheated, but in a cooled forming tool inserted. In addition, a cool gas is introduced into the hot workpiece, wherein the workpiece Formed in one go by the pressure of the gas and by the temperature this gas from inside and the temperature of the forming tool of Outside hardened in the same forming tool becomes.

In this method, a hot forming takes place very quickly. This is necessary because the workpiece is cooled very quickly in the tool. Therefore, the period of plastic working is preferably only a few seconds. In particular, the transformation takes place within a maximum of 5 seconds, preferably within 2 seconds. During this period, however, only the hot forming takes place. The onset of contact with the tool hardening, triggered by the cooling of the forming tool as well as by the introduced colder gas, requires locking times, ranging in time from 1 to 20 seconds can move. Preferably, the closing times are less than 10 seconds.

at The compressed gas may be, for example, nitrogen but also to act on compressed air. The required process pressure of the gas is via a relative movement a press upper part in the closing direction of the forming tool generated. By relative movement of the press upper part is a Reduction of a fluid volume, in particular of the gas volume, the directly into the tubular workpiece should be initiated. In particular, there is a pressure intensifier for use. A liquid on the primary side of the pressure intensifier is pressurized by lowering a press upper part. Within the intensifier presses the liquid on a piston on the secondary side again needed for forming Gas biased and pressed into the workpiece to be formed.

The Heat of the workpiece to a temperature above Ac3 can outside the forming tool done in a separate continuous furnace. However, it is also possible that workpiece inside the chilled Forming tool to a temperature above the Austenitisierungstemperatur to warm, in particular by electrical resistance heating. Here are the workpieces in the forming tool end brought into contact with electrodes, which are opposite to the Forming tool are isolated. An electric current flows through the workpiece and leads in the shortest possible time Time to a strong temperature rise to a temperature above the austenitizing temperature. In this approach are the heating rates are very high, so that the workpieces for complete austenitization on higher Temperatures are heated have to, as at lower heating rates, as in a continuous furnace prevalence. When electrical resistance heating with high heating rate, temperature ranges around 1050 ° C are desired.

The Gas should have a temperature of less than 40 ° C. The gas can here deliberately cooled down have been, for whatever reason the energy balance as possible should be avoided. Since gas is a relatively poor heat transfer medium and because much less heat from the workpiece is discharged to the gas, as to the forming tool, the plays Temperature of the gas has a less important role than the temperature of the forming tool. Theoretically it is possible that the temperature of the gas is in a range up to 300 ° C. The cheapest is it, when the temperature of the gas corresponds to the ambient temperature and therefore typically in a range around 20 ° C. This temperature is still far below the temperature of the workpiece, which is at a temperature heated has been at least the Austenitisierungstemperatur of the respective Material corresponds. Preferably, the temperature is low Heating rates 30 ° C to 50 ° C above the Austenitizing temperature, d. H. typically in one area of 920 ° C up to 970 ° C. Such workpiece temperatures be in separate ovens generated, wherein the workpiece after removal from the oven and when inserting into the forming tool should still have a temperature of at least 800 ° C. The handling speed the workpieces must be high enough to allow cooling of the workpiece so far it's about to be avoided. When heating the workpiece in the forming tool, in particular by electrical resistance heating, the temperature of the workpiece is immediate before the beginning of the forming process is significantly higher than 800 ° C and can be over 1000 ° C.

With the method according to the invention Is it possible tubular workpieces made of a steel material in one go, d. H. in just a single forming tool both transform, and in the shortest time Time to harden. The tool costs are compared known, heated tools considerably reduced, since standard materials for the tools can be used. There is no special isolation of the tools, ie. H. an additional cooling the press or a press shell required. It also has to no separate tools are provided in which the workpiece cooled in a second step, work-hardened or hardened must become.

The Forming tool has a temperature that is significantly dependent from the cooling medium flowing through the forming tool. Preferably that has cooling medium a temperature of less than 20 ° C, so that the forming tool temperature in an area below 20 ° C is. During the Operation, the temperature of the forming tool can be repeated by repeated Contact with the preheated workpieces increase. Nevertheless, the aim is the temperature of the forming tool in one Temperature range below 50 ° C to keep.

The invention will be explained in more detail with reference to embodiments shown in schematic drawings. The embodiments relate to the 1 and 2 Variants for which no protection is claimed. They serve only to illustrate the inventive idea.

It demonstrate:

1 A first embodiment of a device for hydroforming;

2 A second embodiment for hydroforming and

3 a third embodiment of a device for hydroforming.

1 shows a forming tool 1 in which a workpiece 2 taken from a steel tube. The workpiece 2 has previously been heated in a continuous furnace to a temperature above Ac3. The ends 3 in the mold cavity 4 of the forming tool 1 recorded workpiece 2 are of axial piston 5 closed, which are intended to the interior 6 of the workpiece 2 to close and nachzuführen in the direction of the arrows P.

In the interior 6 of the workpiece 2 is after sealing by the axial piston 5 and closing the forming tool 1 a gas is introduced, which is a pressure accumulator 7 is removed. The accumulator 7 is powered by a compressor with gas flowing through the check valve 8th in the accumulator 7 is initiated. The accumulator 7 is via a pressure control valve 9 shut off. The special feature is that the forming tool 1 is cooled and has a temperature of less than 40 ° C and also the gas from the pressure accumulator 7 a temperature below 40 ° C, whereas the workpiece 2 was previously heated to a temperature above Ac3, before it with high handling speed in the forming tool 1 has been inserted. The plastic deformation within the forming tool 1 takes place very quickly and preferably in a time span of less than 5 seconds. Following the plastic forming a certain holding time in the closed forming tool 1 be provided. The hold time may be greater than the time required for the forming. After completion of the forming process is the formed tubular workpiece 2 hardened.

The embodiment of the 2 shows a variant in which the gas pressure required for the forming by relative movement of a press upper part 10 in the closing direction of the forming tool 1 results. The forming tool 1 consists of a lower cast 11 and a superstar 12 , The press top 10 is with the upper die 12 connected and lifts this to open the forming tool 1 on or lowers this to close. When the upper part 12 already in the closed position, the press upper part can 10 but still further lower and thus relative to the upper Gesenk 12 move. This is a piston 13 a piston-cylinder arrangement 14 in a cylinder 15 urged, in which a gas pressure is built up. The gas can turn from a compressor into the piston-cylinder arrangement 14 be introduced. A check valve 8th prevents a backflow of the gas. Via a pressure control valve 9 can the gas from the piston-cylinder arrangement 14 in the interior 6 of the workpiece 2 be initiated. Also in this embodiment, the forming tool 1 with cooling channels 16 provided to the forming tool 1 to cool to the desired temperature.

The embodiment of the 3 is different from the one of 2 characterized in that in the piston-cylinder arrangement 14 a liquid is present when lowering the press top 10 relative to the upper Gesenk 12 in a pressure intensifier 16 is directed. A piston 17 the pressure booster is the primary side of the liquid from the piston-cylinder assembly 14 applied and compressed on the secondary side that for forming the workpiece 2 required gas. The gas is on the secondary side 18 of the pressure intensifier 16 , The secondary side 18 is powered by a compressor with gas. A check valve 8th in turn prevents a backflow of the gas to the compressor. The introduction of the gas into the workpiece 2 in turn is via a pressure control valve 9 controlled or regulated. The structure of the forming tool 1 corresponds to the one of 2 ,

LIST OF REFERENCE NUMBERS

1

forming tool

2

workpiece

3

The End

4

mold cavity

5

axial piston

6

inner space

7

accumulator

8th

check valve

9

Pressure control valve

10

Press top

11

lower die

12

upper die

13

piston

14

Piston-cylinder arrangement

15

cylinder

16

Pressure intensifier

17

piston

18

secondary side

P

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Claims (9)

Hydroforming process in which a in a forming tool ( 1 ) to be formed, tubular workpiece ( 2 ) of a steel material inside or outside the forming tool ( 1 ) is preheated, the ends ( 3 ) in a mold cavity ( 4 ) of the closed forming tool ( 1 ) picked workpiece ( 2 ) are sealed and at closing a gas under pressure in the interior ( 6 ) of the workpiece ( 2 ), wherein the workpiece ( 2 ) in a cooled forming tool ( 1 ) is inserted, wherein the workpiece ( 2 ) in one go by the pressure of the gas and by the temperature of this gas from the inside and the temperature of the forming tool ( 1 ) from the outside in it, from a lower die ( 11 ) and an upper die ( 12 ) existing forming tool ( 1 ), characterized in that the gas pressure in the workpiece ( 2 ) by relative movement of a press upper part ( 10 ) in the closing direction of the forming tool ( 1 ) and by a pressure intensifier ( 16 ) is reinforced, which is acted upon on its primary side by a fluid pressure, which in turn from a relative movement of the press upper part ( 10 ) in the closing direction of the forming tool ( 1 ) results. Hydroforming process according to claim 1, characterized characterized in that the gas is introduced at a temperature below 40 ° C. becomes. Hydroforming process according to one of claims 1 or 2, characterized in that the deformation of the workpiece ( 2 ) in a period of up to 5 seconds. Hydroforming process according to one of claims 1 to 3, characterized in that the temperature of the forming tool ( 1 ) is in a range of 4 ° C to 50 ° C. Hydroforming process according to one of claims 1 to 4, characterized in that the workpiece ( 2 ) is heated to a temperature which is above the austenitizing temperature. Hydroforming process according to one of claims 1 to 5, characterized in that the workpiece ( 2 ) is heated by electrical resistance heating before forming within the cooled forming tool. Hydroforming process according to one of claims 1 to 6, characterized in that the workpiece ( 2 ) has a temperature of at least 800 ° C immediately before the beginning of the hot working. Hydroforming process according to one of claims 1 to 7, characterized in that nitrogen is used as the gas. Hydroforming process according to one of claims 1 to 8, characterized in that compressed air is used as the gas.

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