FIELD OF THE INVENTION

[0001] The invention relates generally to a system and method for hot stamping components. In particular, the system includes a station for the provision of blanks, a furnace station for heating the blanks to the deformation temperature, and a press having a tool that is designed for press hardening / hot stamping technology.

BACKGROUND

[0002] Steel continues to be the material of choice when it comes to modern and cost- effective vehicle bodies. In terms of material, new steels that combine high strength with good formability have been developed in response to the demands of the automotive industry for lightweight construction materials. In particular, the multiphase steels are used extensively in hot stamping processes in which a steel blank is heated into the zone of full austenitization (typically 920 °C). The heated blank is subsequently inserted into the forming tool while still hot, and is rapidly cooled during the pressing operation. From a relatively soft, ferritic- pearlitic initial structure, hard martensite with strengths of at least about 1500 MPa is obtained. The forming behaviour is controlled by means of the boron content and the strength is controlled by means of the carbon content. Typically, a boron-alloyed steel with 0.24% carbon is employed.

[0003] Advantages of the press hardening method include the low forming resistance and the better formability of steel at this temperature, as well as the high strength and good dimensional stability of the obtained component. In general, the use of hot stamping methods and new steel materials results in high-strength but low-weight vehicle bodies.

[0004] Due to the increasing use of hot stamping technology in the automotive industry, the press-hardening machinery is becoming faster. Machines that achieve five strokes per minute have been in use for some time already, and newer machines that achieve seven strokes per minute are known. As a result of the reduced cycle length, the efficiency of the hot stamping method is increased. However, the heating of the supplied blanks via heating furnaces has hitherto been the limiting factor. Since the blanks have to be heated to a processing temperature of over 900 °C, heating furnaces which are configured as continuous furnaces are used. Over a 30 m length of such a continuous furnace, the blank is heated by 30 °C per metre. Accordingly, the pass-through speed of the blanks and the length of the heating furnaces limits the cycle length of the hot stamping system.

[0005] It would be beneficial to provide a system and method that improves and/or overcomes at least some of the above-mentioned disadvantages. SUMMARY OF EMBODIMENTS OF THE INVENTION

[0006] It is an object of the invention to provide a hot stamping system, which is optimized for processes with higher cycle durations. That is to say, the cycle rate is increased such that more strokes per minute are achievable.

[0007] According to an aspect of at least one embodiment of the invention, provided is a system for hot stamping of components, comprising: a station for providing steel blanks; a tempering container for storing the steel blanks and for pre-heating the steel blanks to a preheating temperature; a furnace station for receiving the pre-heated steel blanks from the tempering container and for further heating the steel blanks to a predetermined deformation temperature; and a press having a tool that is designed for hot stamping technology, the press for receiving the heated steel blanks from the furnace station and for hot stamping the components.

[0008] Through the use of a tempering container, a part of the heating process is performed prior to introducing the blanks into the furnace station. As a result, the furnace station is shortened and the pass-through process can thereby be adapted to the faster cycle rates of the presses.

[0009] In at least one embodiment the blanks are heated in the tempering container to a temperature of at least 100 °C. As a result, the furnace station can be shortened by several metres, since the blanks are introduced into the furnace station already with a starting temperature higher than the ambient atmosphere. [0010] In at least one embodiment the furnace station is a continuous furnace and is directly connected to the tempering container.

[0011] The direct connection between the tempering container and the continuous furnace has the advantage that the blanks do not cool down in the course of the process, e.g. during transfer between the tempering container and the continuous furnace. [0012] In at least one embodiment the system is designed such that the continuous fumace for the system, given a target temperature above 900 °C, is shortened by at least 5 m.

[0013] Through the shortening of the length of the continuous furnace, the time needed for the heating of the blanks is shortened and the blanks can be removed from the press at a faster rate.

[0014] In at least one embodiment the tempering container is heated with the waste gas of the continuous furnace. Through the return of the waste heat of the continuous fumace into the tempering container, an advantageous solution from an energy viewpoint is obtained. The need for higher power levels, as would otherwise be required with a shortened furnace to maintain the same target temperature, is avoided. On the contrary, the use of energy is reduced in that the waste heat is passed into the tempering container and is used there to preheat the blanks.

[0015] It is additionally of advantage that the method for the hot stamping of components comprises the following steps:

• provision of blanks,

• introduction of the blanks into a tempering container

• heating of the blanks in the tempering container

• introduction of the preheated blanks into a continuous furnace

• pressing in a press hardening / hot stamping tool.

[0016] Advantageously, if the blanks are heated to a higher temperature in the tempering container, then the length of the continuous fumace may be decreased. The higher the temperature in the tempering container, the shorter the minimum length of the continuous fumace.

[0017] It is additionally of advantage that the waste heat of the continuous fumace is utilized to heat the tempering container in order to obtain an optimal utilization of the energy and, at the same time, to shorten the cycle time.

BREIF DESCRIPTION OF THE DRAWINGS

[0018] The invention will now be described by way of example only, and with reference to the attached drawing. It should be understood that the drawing is not necessarily to scale. In certain instances, details that are not necessary for an understanding of the disclosure or that render other details difficult to perceive have been omitted.

[0019] Fig. 1 is a simplified diagram showing a system according to an embodiment of the invention. DETAILED DESCRIPTION OF THE DRAWINGS

[0020] Referring to Fig. 1, a hot stamping system 1 includes a tempering container 2, which is connected to a furnace station 3. The furnace station 3 is in turn connected to a press 6. The furnace station 3 supplies heat into the tempering container 2 via a waste gas return line 4. In the tempering container, blanks 5 are represented schematically. The blanks 5 are prepared by a blank-providing station, which is represented in the drawing only schematically as an arrow on the left-hand side, and are delivered to the tempering container 2. The blanks can here be simple portions of steel bands supplied on rolls, or can exist in a form already pre-trimmed by a trimming station. The blanks 5 are inserted into the tempering container 2. Present in the tempering container 2 is an apparatus in which the blanks can be stored at a distance apart, so that the individual blanks can be easily removed again. In the present example the tempering container is designed such that the residence time of the blanks in the tempering container is sufficient to preheat them to the preheat temperature of over 100 °C, most advantageously to 180 °C. Optionally, the blanks are preheated in the tempering container to even higher temperatures, if such higher temperatures can be obtained via the waste gas return line. [0021] According to the "first in - first out" principle, the blank that has resided for the longest time in the tempering container 2 is removed first, followed by the blank that has resided for the second longest time in the tempering container 2, and so on. It is thereby ensured that the removed blank is already at the preheat temperature. The preheated blank 5 is introduced into the furnace via a direct connection of the tempering container 2 to the furnace 3. In the furnace 3, the blank 5 passes through the entire furnace length between the tempering container 2 and the press 6. At the end of the furnace 3, the blank 5 is removed and immediately inserted into the pressing tool 7 of the press 6.

[0022] The design of the tempering container 2 for blanks 5 can be shown on the basis of an example. An exemplary continuous furnace in the furnace station 3 has a length of 30 m and obtains a predetermined exemplary deformation temperature of 920 °C. The downstream press has currently five strokes per minute. Should it be desired to operate the machine at 7 strokes per minute, this means an increase of about 20% in the cycle frequency. It therefore follows that the blanks 5 must arrive at the press 20 % quicker out of the furnace station 3, and the continuous fumace must therefore be shortened by about 6 m. With a heating rate of 30 °C per 1 m of fumace length, this means that the tempering container must be set to 180°C in order to feed a continuous furnace length of about 24 m.

Reference symbols

1 hot stamping system

2 tempering container

3 furnace station 4 waste gas return line

5 blank

6 press

7 pressing tool