METHOD, FURNACE INSTALLATION AND SYSTEM FOR THE HOT STAMPING OF WORKPIECES

Abstract

A system for the hot stamping of workpieces having a furnace installation, in which workpieces can be heated to a forming temperature, and a forming installation, in which the heated workpieces can undergo forming. A transfer device is provided for transferring workpieces from the furnace installation to the forming installation. The transfer device is arranged in a transfer space, which is delimited at least in certain regions by a housing and largely bridges the space between the furnace installation and the forming installation. Also provided is a method for the hot stamping of workpieces.

Description

The invention relates to a system for the hot stamping of workpieces, having

• • a) a furnace installation, in which workpieces can be heated to a forming temperature;
  • b) a forming installation, in which the heated workpieces can undergo forming;
  • c) a transfer device, by means of which workpieces can be transferred from the furnace installation to the forming installation.

Moreover, the invention relates to a method for hot stamping workpieces, in which

• • a) the workpieces are heated to a forming temperature in a furnace installation;
  • b) the workpieces are formed in a forming installation;
  • c) the workpieces are transferred from the furnace installation to the forming installation.

Hot stamping has become established especially as a method for hot forming workpieces made of metal to give component parts, particularly in the automotive industry, and is also familiar under the name press hardening. The workpieces to be formed are heated in a furnace installation, transferred from the furnace installation to a forming installation by means of a transfer device, e.g. a multi-axis robot, and are formed there into the desired component part by a pressing tool.

For example, workpieces made of steel sheet are heated to a forming temperature between about 800° C. and 1100° C. in an “austenitization” process. In practice, the forming temperature for steel sheets made from conventional boron-manganese-steel alloys is 930° C. Such steel sheets are often provided with an aluminum-silicon coating (AlSi). A steel-sheet workpiece of this kind can be a flat steel sheet plate or sheet bar, for example, or even a piece of steel sheet already pre-shaped in a previous step, e.g. by cold deep drawing. The heated workpiece is then formed and simultaneously chilled in the forming installation by means of a cold pressing tool. As a result, the microstructure of the material changes during the forming process, and the component parts obtained have a considerably higher strength and stiffness than component parts which are cold-formed from the workpiece.

On the path of the workpieces from the furnace installation to the forming installation, the workpieces generally come into contact with the surrounding atmosphere and especially with atmospheric oxygen.

However, this can negatively affect the material properties of the workpieces and hence also the resulting component parts in an unwanted way.

Moreover, the abovementioned workpiece cools down. The extent of this cooling depends on implementation parameters, such as time, distance and/or speed, pertaining from the removal of the workpiece from the furnace installation until forming. However, there can be considerable variation in the quality of the component parts obtained during hot stamping if different workpieces come into contact with oxygen and are formed at different temperatures.

In order to heat the workpieces to the required forming temperature, various furnace concepts are known. Currently available commercially there are, in particular, continuous furnaces, in which the workpieces are conveyed continuously through a furnace tunnel by means of a conveying system. Common furnaces in this context are roller furnaces, in which the workpieces are conveyed continuously through the furnace on a roller track. There is nowadays also an established practice of using a plurality of relatively small individual furnaces, in which possibly only a single workpiece or at most a small number of workpieces can be brought to the forming temperature in each case.

It is then the object of the invention to provide a system and a method of the type stated at the outset which take account of these considerations.

This object is achieved, in the case of a system of the type stated at the outset, in that

• • d) the transfer device is arranged in a transfer space, which is delimited at least in certain regions by a housing and largely bridges the space between the furnace installation and the forming installation.

Thus, according to the invention, a transfer space with a dedicated housing is arranged between the furnace installation and the forming installation. The atmosphere in this transfer space can differ from the surrounding atmosphere. In particular, it is possible for an oxygen-free or at least reduced-oxygen working atmosphere to be present there. Moreover, a largely constant temperature can be maintained in the transfer space. In this arrangement, the housing does not need to fully delimit the transfer space. For example, there can be an interspace remaining between wall elements and the bottom of the system without this having a negative effect on the working atmosphere in the transfer space. The housing can also be formed at least partially by flexible housing elements.

It is advantageous if the housing comprises an access, via which one or more workpieces can be introduced into the transfer space. The workpieces then do not pass via the furnace unit, which in this case can optionally be loaded via an inlet remote from the transfer space, but separately into the transfer space and can be handled there by the transfer device.

In this case, it is advantageous if the access is designed as an access lock, by means of which the atmosphere of the transfer space remains separated from the surrounding atmosphere.

It is advantageous if a temperature lock region is formed between the furnace installation and the transfer device. This avoids a situation where the region of the transfer space in which the transfer device is positioned can heat up to such an extent that the transfer device could be damaged. Without such a temperature lock region, too much hot furnace atmosphere could reach the transfer device each time a workpiece was removed from the furnace unit.

The temperature lock region preferably comprises a flow device, by means of which a fluid flow curtain can be produced in front of the furnace installation.

The housing advantageously comprises an outlet, via which a workpiece removed from the furnace installation can be transferred to the forming installation and which can be closed or opened by means of a gate unit. During transfer to the forming installation, it is not possible to avoid a connection between the transfer space and the environment. However, an outlet having a gate unit enables this connection to be kept to as short a time as possible in each case during transfer, and therefore a loss of atmosphere for a change in temperature with effects on the operating conditions occurs only over the period of time required for the transfer of the workpiece to the forming installation.

The transfer device is preferably designed as an articulated-arm robot. This robot is preferably positioned on the ground.

As an alternative, the transfer device can also be designed as a suspended system.

It is advantageous if the volume of the transfer space is as small as possible. To avoid an unnecessary empty volume, it can be advantageous if one or more filler bodies are accommodated in the transfer space.

The abovementioned object is achieved in the case of a method of the type stated at the outset by virtue of the fact that

• • d) the transfer of the workpieces takes place in a transfer space, which is delimited at least in certain regions by a housing and largely bridges the space between the furnace installation and the forming installation.

The advantages thereby achieved correspond to the advantages explained above with reference to the system.

Illustrative embodiments of the invention are explained in greater detail below with reference to the drawings, in which:

FIG. 1 shows a side view of a system for the hot stamping of workpieces, having a transfer space, which connects a furnace installation, which comprises a separate furnace module for each workpiece, and a forming installation;

FIG. 2 shows a view from above of the system in FIG. 1;

FIG. 3 shows a side view of a modified system for the hot stamping of workpieces.

In the figures, 2 designates overall a system for hot stamping, in which workpieces 4 are formed into component parts 6. The workpieces 4 are workpieces made of steel sheet, for example, as explained at the outset.

The system 2 comprises a furnace installation 8, in which the workpieces are heated to a forming temperature. Once a workpiece 4 has reached its forming temperature, it is removed from the furnace installation 8 with the aid of a transfer device 10 and transferred to a forming installation 12. This comprises, in a manner known per se, a cold pressing tool 14, by means of which the workpiece 4 is formed into the component part 6 and chilled in a forming process. After a predetermined dwell time in the pressing tool 14, in which the component part 6 then produced cools to a final temperature, the component part 6 is released and removed from the forming installation 12 with the aid of a removal device 16 and then fed to its further destination, e.g. a mechanical finish machining operation.

It is possible to use multi-axis articulated-arm robots 18 of the kind known per se for handling workpieces both as a transfer device 10 and as a removal device 16; in the present case, therefore, there is a transfer robot 18a and a removal robot 18b.

As can be seen in the figures, the furnace installation 8 comprises a plurality of separate furnace modules 20, each having a dedicated module housing 22 delimiting a furnace space 24 illustrated in dashed lines in each case for one of the furnace modules. In the illustrative embodiment under consideration, two furnace modules 20a, 20b are shown.

The furnace space 24 is accessible from the outside via an opening 26 in the module housing 22, which can be opened or closed by means of a module door 28. In the furnace space 24 there is a workpiece carrier (not shown specially), which supports an individual workpiece 4 or a workpiece group comprising two or more workpieces 4 during heating. The workpiece carrier ensures the satisfactory positioning of the workpiece or workpieces 4 relative to the furnace module 20. In particular, the workpiece carrier can be manufactured from reaction-bonded silicon-infiltrated silicon carbide.

The furnace modules 20a, 20b illustrated are ones in which only a single workpiece 4 can be heated in each case. This fundamentally reflects the ideal case but it cannot always be implemented, taking into account the space required for this purpose and the throughput rate of the system 2.

If the intention is to heat a workpiece group comprising two or more workpieces 4 in a furnace module 20, therefore, the module housing 22 is in each case of correspondingly taller construction and the workpiece carrier provides a plurality of carrier levels. In this case, the module housing 22 can have a respective opening 26 at the height of each of these carrier levels and can comprise a module door 28 for each of these openings 26. As an alternative, it is also possible to move a plurality of carrier levels up to a single opening 26 in a furnace module 20.

The furnace modules 20 of a system 2 do not have to be of identical construction. It is also possible for there to be different furnace modules 20, the dimensions of which, in particular the volume of the furnace space 24 and the cross section of the opening or openings 26, are each matched to different types of workpieces 4 or to a different number of workpieces 4 to be accommodated.

Each furnace module 20 operates independently and, for this purpose, includes at least one dedicated heating device 30. The heating device 30 can be an electric heating unit having a heating coil, for example. As an alternative, IR radiators or gas burners or similar established heating technologies can also be considered.

In the case of a modification (not shown specially), a muffle, which closely surrounds the workpiece carrier, can additionally be arranged in the furnace space 24 of a furnace module 20. The muffle can ensure uniform temperature distribution and can protect the furnace space 24 and, in said space, particularly components of the heating device 32 from impurities such as scale or coating component parts, which can fall off the workpieces 4 in the furnace module 20. It is possible to accomplish protection of heating components without a muffle by means of encapsulation of the relevant component parts; with a muffle, this is not necessary and, as a result, this outlay on construction can be eliminated and it may be possible to reduce costs.

If a protective gas atmosphere is required, the consumption of protective gas is reduced since the muffle has a smaller volume than the furnace space 24. Moreover, the furnace walls do not have to be freed from oxygen and water to the same extent as is otherwise customary.

Each furnace module 20 is supplied via a bundle of lines 32 with electric or fluid operating supplies necessary for operation. These include especially the supply of energy or fuel to the heating device 30, for which purpose the bundle of lines 32 accordingly comprises an electric lead and/or a fuel line. In special cases, a special furnace atmosphere, in which the workpieces 4 are heated and which is different from the surrounding atmosphere, can be produced in the furnace modules 20. In this case, the bundle of lines 32 also comprises fluid lines, via which an atmospheric gas is blown into the furnace space 24 or via which the furnace atmosphere can be extracted. The individual lines of the bundle of lines 32 lead to the individual sources of supply, which are not shown specially here.

A process control system (not shown specially) monitors the correct operation and the parameters of the individual furnace modules 20. For this purpose, each furnace module 20 is fitted with corresponding sensors, which monitor the operating parameters of the furnace module 20 and send corresponding output signals to said process control system. To this end, the bundle of lines 32 comprises not only the supply lines mentioned but also corresponding data lines.

If a fault occurs in a particular furnace module 20, e.g. if the heating device 30 of a particular furnace module 20 fails, this furnace module 20 can be selectively detected. The faulty furnace module 20 can then be segregated from the working process and serviced separately without significantly affecting the rest of the sequence of the forming process or even leading temporarily to a stoppage of the sequence.

By means of the individual furnace modules 20, it is possible for each workpiece 4 to pass through a customized heating process, which can be controlled separately for each workpiece 4 by means of the process control system.

The furnace modules 20 form a furnace unit 34, which, in modified versions that are not shown specially, can also comprise more than two furnace modules 20 or even just a single furnace module 20.

The transfer device 10, i.e. the transfer robot 18a in the illustrative embodiment under consideration, is arranged in a transfer space 36, which largely bridges the space between the furnace installation 8 and the forming installation 12.

The transfer space 36 is delimited by a housing 38 having housing walls 40, wherein the furnace modules 20 project through a housing wall 40 into the transfer space 36 in such a way that the openings 26 thereof can be reached by the transfer device 10. The housing walls 40 are thermally insulated and can optionally be cooled by means of a separate device.

The atmosphere prevailing in the transfer space 36 can be different from that in the area of the system 2 surrounding the transfer region 36. In a modified version that is not shown specially, there are furthermore means with which a separate working atmosphere can be built up and/or maintained in the transfer space 36.

In continuous operation, the atmosphere in the transfer space is heated by the hot workpieces 4 coming from the furnace installation 8 and, where applicable, by the escaping hot furnace atmosphere until a largely constant operating temperature is established. If appropriate, a temperature control device can be provided in addition, by means of which a particular operating temperature can be produced and/or maintained in the transfer space 36.

In the illustrative embodiment under consideration, a temperature lock region 42 is formed between the furnace installation 8 and the transfer device 10. For this purpose, a flow device 44 is provided, by means of which a fluid flow curtain 46 can be produced in front of the furnace unit 8. In practice, an inert gas, e.g. nitrogen, is used as a fluid here. By means of the fluid flow curtain 46, a temperature barrier is formed between the furnace modules 20 and the transfer device 10. This prevents the transfer device 10 from coming into contact with the hot atmosphere of the furnace modules 20, which is released when the module doors 28 are opened. By appropriate control of the fluid flow curtain 46, negative effects on the workpiece 4, such as, in particular, cooling, are reduced when the workpiece 4 reaches the flow curtain 46. This can be accomplished by changing the direction of flow and/or the speed of flow, for example.

The housing 38 of the transfer space 36 furthermore comprises an access 48, via which workpieces 4 are introduced into the transfer space 36. In the illustrative embodiment under consideration, the access 48 comprises a magazine carrier 50, which can accommodate a plurality of workpieces 4 to be processed. In a modified version that is not shown specially, there is also the possibility for just a single workpiece 4 to be introduced from the outside into the transfer space 36 by the access 48 at any one time.

Moreover, the housing 38 comprises an outlet 52, via which a workpiece 4 removed from a furnace module 20 can be transferred to the forming installation 12. The outlet 52 can be closed or opened by a gate unit 54.

As a further illustrative embodiment, FIG. 3 shows a system 2′ in which components and component parts corresponding to components and component parts in the system 2 shown in FIGS. 1 and 2 bear the same reference signs. Here, there is no furnace lock region 42 with a flow device 44. In a modified version that is not shown specially, however, a furnace lock region 42 can be provided in a corresponding manner to that in system 2.

In contradistinction to system 2, the transfer device 10 is not designed as an articulated-arm robot 18 but as a suspended system 56 with a traversing telescopic arm 58, which can be moved on rails 62 with the aid of a drive 60 and can be pivoted about a vertical axis. The rails 62 are arranged on the roof of the transfer space 36. At its lower end, the telescopic arm 58 carries a gripping unit 64, by means of which workpieces 4 can be gripped.

In system 2′, the access 48 is designed as an access lock 66, ensuring that the atmosphere of the transfer space remains separate there from the surrounding atmosphere. A corresponding access lock can also be provided in the system 2 shown in FIGS. 1 and 2.

To keep the operating volume of the transfer space 36 as small as possible, filler bodies 68, of which just three filler bodies 68 are shown by way of example in FIG. 1, can be accommodated in the transfer space 36.

Systems 2 and 2′ operate as follows:

Workpieces 4 are introduced into the transfer space 36 through the access 48. The transfer device 10 picks up a workpiece 4 from the magazine carrier 50 and puts the workpiece 4 down in a furnace module 20. While this workpiece 4 is being brought to its forming temperature, the transfer device 10 loads the second furnace module 20 with another workpiece 4.

Once the first workpiece 4 has reached its forming temperature, the transfer device 10 removes the workpiece 4 and transfers it through the opened gate unit 54 at the outlet 52 to the forming installation 12, where the workpiece 4 is formed into a component part 6 and is then conveyed onward by the removal device 16.

During this process, the transfer device 10 picks up another workpiece 4 and puts the latter down in the now free furnace module 20. Such a cycle is then repeated, wherein the furnace modules 20 are correspondingly loaded and emptied in alternation.

In the illustrative embodiments explained above, the furnace installation 8 comprises furnace modules 20 into which the transfer robot 18a must reach in order to remove a workpiece 4. As an alternative, it is also possible to implement a module concept in which the workpiece 4 has already been removed from the furnace space 24 before the transfer robot 18a picks up the workpiece 4. This can be achieved by means of a kind of drawer-type solution, for example, in which a carrier drawer can be moved out of the furnace space 24 together with the workpiece 4, ensuring that the transfer robot 18a receives access to the workpiece 4 outside the furnace space 24.

In a modified version that is not shown specially, the furnace installation 8 can also be designed as a continuously operating roller furnace of the kind already discussed at the outset.

In the illustrative embodiments explained above, the transfer device 10 with all the essential components and component parts is arranged within the transfer space 36. In another modified version that is not shown specially, provision can be made for only the moving components of the transfer device 10 to be situated in the transfer space 36. In the case of the transfer robot 18a, these moving components are, for example, formed by the robot arm, which does not bear a specific reference sign. A functional connection between the component parts outside and inside the transfer space 36 can be formed through a housing wall 40.

Claims

1. A system for the hot stamping of workpieces comprising: wherein

a) a furnace installation, in which workpieces can be heated to a forming temperature;

b) a forming installation, in which the workpieces which have been heated can undergo forming;

c) a transfer device for transferring workpieces from the furnace installation to the forming installation;

d) the transfer device is arranged in a transfer space, which is delimited at least in certain regions by a housing and largely bridges a space between the furnace installation and the forming installation.

2. The system as claimed in claim 1, wherein the housing comprises an access via which one or more workpieces can be introduced into the transfer space.

3. The system as claimed in claim 2, wherein the access is designed as an access lock, by means of which the atmosphere of the transfer space remains separated from the surrounding atmosphere.

4. The system as claimed in claim 1, wherein a temperature lock region is formed between the furnace installation and the transfer device.

5. The system as claimed in claim 4, wherein the temperature lock region comprises a flow device, by means of which a fluid flow curtain can be produced in front of the furnace installation.

6. The system as claimed in claim 1, wherein the housing comprises an outlet, via which a workpiece removed from the furnace installation can be transferred to the forming installation and which can be closed or opened by means of a gate unit.

7. The system as claimed in claim 1, wherein the transfer device is designed as an articulated-arm robot.

8. The system as claimed in claim 1, wherein the transfer device is designed as a suspended system.

9. The system as claimed in claim 1, wherein one or more filler bodies are accommodated in the transfer space.

10. A method for hot stamping workpieces the method comprising the steps of: wherein

a) heating the workpieces to a forming temperature in a furnace installation;

b) transferring the workpieces from the furnace installation to a forming installation,

c) forming the workpieces in the forming installation;

d) the transferring of the workpieces takes place in a transfer space, which is delimited at least in certain regions by a housing and largely bridges a space between the furnace installation and the forming installation.