Abstract
The invention relates to a furnace system and a method for the controlled heat treatment of sheet metal components in individual component zones. The invention proposes a furnace system that is suitable for partly heating components made of steel sheet to a temperature above the AC3 temperature. The furnace system has a production furnace for heating the steel sheet parts to a temperature that is close to but below the AC3 temperature, said furnace system further having a profiling furnace with at least one level. The at least one level has an upper and lower part and a product-specific intermediate flange that is introduced into a corresponding receiving area. The product-specific intermediate flange is designed to impose a specified temperature profile on the component with temperatures over AC3 for regions to be hardened and below AC3 for softer regions. Furthermore, the invention relates to a corresponding method for partly heating steel sheet parts to a temperature above the AC3 temperature.
Claims
1. A method for partially heating up sheet steel parts to a temperature above an Ac3 temperature, comprising the steps of: heating a steel part in a production furnace; placing the steel part into a profiling furnace; imparting a temperature profile to a steel part in the profiling furnace, whereby a first area of the steel part is brought to or kept at a temperature above the Ac3 temperature and whereby a second area of the steel part is brought to or kept at a temperature below the Ac3 temperature by a product-specific intermediate flange; removing from the profiling furnace the steel part that has been imparted with the temperature profile and wherein the product-specific intermediate flange actively cools said second area of the steel part.
2. The method according to claim 1, wherein the product-specific intermediate flange actively cools said second area of the steel part by a liquid cooling apparatus of the product-specific intermediate flange.
3. The method according to claim 1, wherein the product-specific intermediate flange actively heats said first area of the steel part.
4. The method according to claim 1, wherein the product-specific intermediate flange actively cools said second area of the steel part by a liquid cooling apparatus of the product-specific intermediate flange and wherein the product-specific intermediate flange actively heats said first area of the steel part.
5. The method according to claim 1, wherein the product-specific intermediate flange actively heats said first area of the steel part by an electric heater of the product-specific intermediate flange.
6. The method according to claim 1, wherein the product-specific intermediate flange actively cools said second area of the steel part by a liquid cooling apparatus of the product-specific intermediate flange and wherein the product-specific intermediate flange actively heats said first area of the steel part by an electric heat of the product-specific intermediate flange.
7. The method according to claim 1, further comprising the steps of: positioning the heated steel part by a positioning system; placing the positioned steel part in a defined position into the profiling furnace.
8. A method for partially heating up sheet steel parts to a temperature above a Ac3 temperature, comprising the steps of: heating a steel part in a production furnace to a temperature above the Ac3 temperature; placing the steel part into a profiling furnace having at least one level, whereby the at least one level has an upper section and a lower section as well as a receptacle for a product-specific intermediate flange and the product-specific intermediate flange installed therein; imparting a temperature profile to a steel part in the profiling furnace, whereby one selected area that is to be hardened of the steel part is kept at a temperature above the Ac3 temperature by the product-specific intermediate flange, while another selected more ductile area of the steel part is brought to a temperature below the Ac3 temperature; removing from the profiling furnace the steel part that has been imparted with the temperature profile wherein said selected more ductile area of the steel part is actively cooled to said temperature below the Ac3 temperature by a liquid cooling apparatus.
9. The method according to claim 8, wherein said selected more ductile area of the steel part is cooled so slowly that the structure change that took place when the steel part was heated to the temperature above the Ac3 temperature is reversed.
10. The method according to claim 8, wherein said one selected area that is to be hardened of the steel part is kept at a temperature above the Ac3 temperature by an electric heater of the product-specific intermediate flange.
11. The method according to claim 8, wherein said one selected area that is to be hardened of the steel part is kept at a temperature above the Ac3 temperature by an electric heater of the product-specific intermediate flange.
Description
BRIEF DESCRIPTION OF DRAWINGS
(1) The following is shown:
(2) FIG. 1 a top view of the furnace system according to the invention;
(3) FIG. 2 a detailed view of the profiling furnace;
(4) FIG. 3 section A-A from FIG. 2.
BEST MODE FOR CARRYING OUT THE INVENTION
(5) FIG. 1 shows a top view of the furnace system according to the invention. A first robot 61 positions a part 5 onto a roller conveyor that transports the part 5 through the production furnace 10. The production furnace 10 is a conventional universal furnace that is heated up by natural gas burners 9 to a temperature below the Ac3 temperature of the material in question. The conveying speed for the parts 5 through the production furnace 10 is selected in such a way that the parts 5 almost reach the temperature that prevails in the production furnace 10. The production furnace 10, however, can also be heated up to a temperature above the Ac3 temperature, even above a coating-dependent diffusion temperature. In the case of the steel sheets 5 that are commonly employed, the Ac3 temperature is, for instance, 800 C. [1472 F.], whereas the diffusion temperature of AlSi coatings is approximately 950 C. [1742 F.]. When this type of coated steel sheets 5 are employed, the steel sheets 5 can be heated up to at least 950 C. [1742 F.] in the production furnace 10 and kept at this temperature for at least 300 seconds. The throughput speed of the parts 5 through the production furnace can be selected accordingly. Downstream from the production furnace 10 in the transport direction, there is a positioning system 20 that places each part 5 in a defined flat position. A handling system 22 picks up the part 5 and places it in a defined position into the profiling furnace 40. Inside the profiling furnace 40, there is an upper section 41 and a lower section 42 as well as a receptacle 44 for a product-specific intermediate flange 45 and the product-specific intermediate flange 45 itself. The intermediate flange 45 has an area with a heater 46 on one side and an area 48 that can be cooled on the other side. In addition, it is also possible to provide the profiling furnace 40 only with means 46 for controlled heating or else only an area 48 that can be systematically cooled. In this context, such an area 48 can have cooling openings through which a cooling medium such as water or oil flows. However, it is likewise possible to employ familiar means such as heat pipes or inserts made of highly heat-conductive materials such as, for example, copper alloys, for purposes of very systematic cooling. Examples of heaters 46 that can be used are all known types of heaters such as electric heating cartridges or electric heating radiators. Electric heaters have the advantage that they can be regulated very quickly and precisely. The area 30, which is supposed to be very hard after undergoing a subsequent press-hardening process, is heated up to a temperature above the Ac3 temperature by means of the heater 46. Another area 50, which is supposed to have a higher elongation at break after the subsequent press-hardening process, is kept at a temperature below the Ac3 temperature by means of the systematic cooling 48 of this area. Especially when AlSi-coated metal sheets that had been heated in the production furnace to at least 950 C. [1742 F.] are heat-treated, they can be after-treated in the product-specific intermediate flange 45 in such a way that the selected area 30 that is supposed to be very hard after the subsequent press-hardening process is kept at a temperature above the Ac3 temperature. Another area 50, which is supposed to have a higher elongation at break after the subsequent press-hardening process, is brought to a temperature below the Ac3 temperature so slowly by the systematic cooling 48 that the structure change of the part 5 that took place when it was heated up to the temperature above the Ac3 temperature is reversed. Here, the typical temperature gradient for the often-employed 22MnB5 steel is, for example, less than 25 K/s. At such a temperature gradient, the austenitic structure does not become a martensitic structure, but rather, it becomes a pearlite/ferrite structure. The martensitic structure is particularly hard, whereby the ductility of this structure is lower than that of the softer, non-martensitic structure. The temperature is regulated in at least one closed control circuit. At the end of the holding time needed to heat up the area 30 to the desired temperature above the Ac3 temperature, the part 5, which has now been imparted with a temperature profile, is removed from the profiling furnace 40 by means of the handling system 22. In the embodiment shown, the handling system 22 is configured as a rake. However, any other suitable handling systems can likewise be used. The handling system 22 once again places the part 5 onto the positioning system 20. However, it is likewise conceivable to place the part 5 onto another transfer station after it has been imparted with a temperature profile. A second robot 60 then takes over the part 5 in order to place it into the die 70 of a press so that it can be press-hardened. Normally, however, the part 5 can be placed directly into the pressing die 70 without being repositioned, since there is no longer any relative to movement in the profiling furnace 40 and thus no reorientation of the part 5.
(6) FIG. 2 shows a top view of the profiling furnace 40 in a detailed view. It is possible to see a part 5 that is located on the positioning system 20 in front of the profiling furnace 40. Another part 5 is inside the profiling furnace 40. Areas 30 of the part 5 that are supposed to be very hard after the press-hardening process are in the places of the product-specific intermediate flange 45 that can be heated by the heaters 46. This heater is an electric heating element that is supplied via connectors 47 with electricity made available by a regulator (not shown here). Another area 50 of the part 5 that, after the press-hardening process, is supposed to have a higher elongation at break than the hard area 30, is located in an area 48 of the product-specific intermediate flange 45 that can be systematically cooled. For this purpose, cooling medium is fed in via the connections 49 in the area 47.
(7) FIG. 3 shows the section A-A from FIG. 2 through the profiling furnace 40. The profiling furnace 40 has an upper section 41 and a lower section 42 as well as a receptacle 44 for a product-specific intermediate flange 45 and the product-specific intermediate flange 45 itself. Heaters 46 that are supplied with power via connectors 47 can be seen in the product-specific intermediate flange 45. In this manner, the part 5 in the area 30 can be systematically heated up to a temperature above the Ac3 temperature. Likewise visible is the handling system 22, which is situated in front of the profiling furnace 40. The arrows indicate that the handling system 22 can move a part 5 vertically and horizontally, so that a part 5 located on the positioning system 20 (not shown here) can be placed into the product-specific intermediate flange 45 inside the profiling furnace 40 by means of the handling system 22.
(8) Instead of the above-mentioned robot, it is likewise possible to employ any other suitable handling system. In the embodiment shown in the figure, only a profiling furnace 40 with one level is described. However, it is likewise possible to have more than one level in the profiling furnace 40, whereby each level has an upper section and a lower section as well as a receptacle for a product-specific intermediate flange, so that several parts 5 can be imparted with a temperature profile in parallel or partially in parallel. By the same token, several profiling furnaces 40 can be provided in order to increase the capacity of the furnace system 1.
LIST OF REFERENCE NUMERALS
(9) 1 furnace system 5 sheet steel part, part 9 gas burner 10 production furnace 20 positioning system 22 handling system 30 hard area 40 profiling furnace 41 upper section 42 lower section 44 receptacle 45 product-specific intermediate flange 46 heater 47 connector 48 cooled area 49 cooling-water connection 50 extensible area 60 second robot 61 first robot 70 pressing die 70
(10) Although the invention has been described with a certain degree of particularity, it should be understood that those skilled in the art can make various changes to it without departing from the spirit or scope of the invention as hereinafter claimed.
