Resiliently mounted, segmented hot forming tool and method for producing a hot formed and press-hardened steel component having a sharply defined transition region

Abstract

A hot forming tool includes a top tool and a bottom tool, both of which can be moved towards each other. When the hot forming tool is closed, a mold cavity is formed between the top tool and the bottom tool, with the top tool and/or the bottom tool being divided into at least two segments. The hot forming tool has one segment designed as a heating segment. The heating segment includes a compensating element on a side thereof opposite the mold cavity, to compensate for a thermal expansion of the heating segment in the press stroke direction.

Claims

1. A method of producing a hot formed and press-hardened steel component, with strength properties that are partially different from each other, said method comprising the following steps: heating a blank made of a hardenable steel alloy in a heating station, with a first region being heated to above an austenitizing temperature, and a second region being heated to below the austenitizing temperature, and forming, between the first region and the second region, a transition region; transferring the resulting heated blank from the heating station into a temperature control station or a hot forming and press-hardening tool, with the temperature control station or the hot forming and press-hardening tool being configured so as to be segmented and having a temperature control segment, with the temperature control segment being disposed in a region of the resulting transition region of the partially differently temperature-controlled blank; temperature controlling the transition region before or during press hardening; and hot forming and press hardening the heated steel blank to form the steel component including a hard region and a soft region, and an in-between transition zone, with the transition zone being smaller in terms of surface area than the transition region, with the transition region between the first region and the second region being produced with a width between 50 mm and 200 mm, and the transition zone between the hard region and the soft region being produced with a width between 1 mm and 50 mm.

2. The method according to claim 1, wherein the heating station is a multiple hearth furnace or a continuous furnace with temperature zones that are different from each other, and wherein the temperature zones are thermally insulated from each other.

3. The method according to claim 2, wherein the temperature zones are thermally insulated from each other by a partition.

4. The method according to claim 1, wherein the temperature control segment covers an area of 50 to 95% of the transition region.

5. The method according to claim 1, wherein the temperature control segment is configured as a heating segment, and wherein the transition region is heated by the heating segment during the hot forming and press-hardening process such that complete hardening does not occur.

6. The method according to claim 5, wherein the transition region is heated by the heating segment during the hot forming and press-hardening process such that with a press-hardened steel component, a material microstructure, which is identical to the soft region, is formed in the transition region that is covered by the temperature control segment.

7. The method according to claim 1, wherein the temperature control segment overlaps the region of the transition region that is heated below AC1 by up to 70 mm.

8. The method according to claim 7, wherein the heating segment overlaps the region of the transition region by up to 60 mm.

9. The method according to claim 8, wherein the heating segment overlaps the region of the transition region by up to 50 mm.

10. The method according to claim 1, wherein the method uses a hot forming tool having a top tool and a bottom tool, both of which are movable towards each other, and having, when the hot forming tool is closed, a mold cavity formed between the top tool and the bottom tool, wherein the top tool and/or the bottom tool is/are divided into at least two segments, with one segment being configured as a heating segment, and the heating segment including a compensating element on a side thereof opposite the mold cavity to compensate for a thermal expansion of the heating segment in the press stroke direction.

11. The method according to claim 1, wherein the hot formed and press-hardened steel component is a motor vehicle component.

12. The method according to claim 1, wherein the second region is heated to less than AC1.

13. The method according to claim 1, wherein the width of the transition zone is between 10 mm and 40 mm.

14. The method according to claim 13, wherein the width of the transition zone is between 20 mm and 30 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other advantages, features, properties and aspects of the present invention are the subject matter of the following description. Preferred design variants are shown in the schematic figures. They are used only to make the invention easier to understand. The drawings show in:

(2) FIGS. 1a and b an inventive hot forming tool in a cross sectional view and side view.

(3) FIGS. 2a and b an alternative design variant to FIGS. 1a and b with heating segment located internally; and

(4) FIG. 3 the inventive method for producing a hot formed and press-hardened steel component with different strength regions.

(5) The same reference numerals are used to denote identical or similar components in the figures, even if a description is not repeated for the sake of simplification.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

(7) FIG. 1 shows an inventive hot forming tool 1; in the case of FIG. 1b, in a side view; and in the case of FIG. 1a, in a cross sectional view along the section line a-a. The hot forming tool 1 has a top tool 2 and a bottom tool 3, where in this case the top tool is made of three segments 4, 5, 6, which comprise two normal segments 4, 5 and a heating segment 6; and the bottom tool 3 is also made of three segments 7, 8, 9. In this case, too, they also comprise two segments 7, 8 and a heating segment 9.

(8) The heating segments 6, 9 have in each instance two heat sources 10, for example, media lines for conveying a heating medium or also heating coils or the like. The remaining segments 4, 5, 7, 8 have in each instance cooling channels 11.

(9) At the same time the segments 4, 5 of the top tool 2 are attached to a ram table 13 by incorporation of a clamping bed 12. The segments 7, 8 of the bottom tool 3 are attached to a clamping bed 14, which in turn is mounted on a press table 15. The attachment is done, for example, with T-slot nuts.

(10) At this point the invention provides that the heating segment 9 of the bottom tool 3 is floatingly mounted by way of compensating elements 16, where in this case the compensating elements 16 are designed at least partially as springs. In addition, it can be seen very clearly in FIGS. 1a and 1b that the linear guide 17 is centrally disposed and exhibits one degree of freedom of axial motion in the press stroke direction 18. Transversely to the press stroke direction 18, the linear guide 17 is disposed centrally on the heating segment 9, so that the heating segment 9 can expand or contract in all directions transversely to the linear guide 17 owing to the thermal effect.

(11) The hot forming tool 1 is shown in the closed state, so that a mold cavity 19 is produced between the top tool 2 and the bottom tool 3. When the hot forming tool 1 is closed, a formed sheet metal component 20 is in abutting contact with the respective surface of the segments 4, 5 in the mold cavity 19. The compensating elements 16 compensate for any possible varying expansion in the press stroke direction 18 of the heating segment 9 relative to the segment 8 adjacent thereto.

(12) In addition, a gap 21 is provided between the heating segment 9 and the segment 8 as well as between the heating segment 6 and the segment 5, and said gap prevents the heat from being conducted from the heating segment 6, 9 to the segment 5, 8.

(13) In this case the heating segment 6 is not resiliency mounted on the top tool 2. Insulating layers 22 are disposed on the side of the heating segments 6, 9 that faces away from the mold cavity 19, so that the heat is largely prevented from being conveyed to the respective clamping beds 12, 14 due to thermal conductivity. Furthermore, insulating layers 22 are also disposed on the external side faces of the heating segments 6, 9, so that the heat is also prevented from being dissipated to the surrounding environment U.

(14) FIGS. 2a and b show an analogous design variant to FIG. 1 with the differences described below. Based on the drawing in FIG. 2b, the heating segments 6, 9 are disposed internally. In this case, too, the heating segment 6, 9 of the bottom tool 3 is also mounted in a floating or more specifically resilient manner by means of compensating elements 16, so that varying thermal expansion in the press stroke direction 18 is suppressed. In addition, a corresponding insulating layer 22 is disposed between the respective heating segment 6, 9 and, adjacent thereto, the segment 4, 5, 7, 8. Furthermore, it can be seen in FIG. 2a that there is no guide, but rather the compensating elements also assume a guide function; and insulating layers 22 are also disposed relative to the surrounding environment U.

(15) FIG. 3 shows the process flow of the method described according to the invention. First, a blank 100 made of a hardenable steel alloy is provided. In this case said blank already has a precut blank for producing a steel component 101 in the form of a B-pillar for a motor vehicle. The blank 100 is brought into a heating station 102, here, for example, configured as a continuous furnace. The heating station 102 has two different temperature zones 103, 104; in relation to the image plane an upper temperature zone 103 above the AC3 temperature and in relation to the image plane the lower temperature zone 104 with a temperature below AC1. As a result, a first region 105 of the blank 100 is heated to the AC3 temperature or higher; and a second region 106 is heated to a temperature below AC1. Between the first region 105 and the second region 306 there is a wide transition region 107 that is produced, on the one hand, owing to the thermal conduction inside the blank 100 itself, and on the other hand, due to the fact that a partition 108 of the heating station 102 has a certain width, in order to provide a thermal insulation between the temperature zone 103 above AC3 and the temperature zone 104 below AC1.

(16) After removal from the heating station 102 a temperature controlled blank 109 is made available, in which a first region 105 of said blank is formed above the austenitizing temperature; and a second region 106 is formed below the AC1 temperature. Between said first and second region there is a transition region 107 having a width b107 of 50 mm to 200 mm.

(17) The resulting temperature controlled blank 109 is placed in a hot forming and press-hardening tool 110, which is shown here by way of example by means of the top view of a bottom tool and in which at least one segment is disposed. This segment is designed as a temperature control segment 111 and, in particular, a heating segment. The temperature control segment 111 covers in terms of surface area a large part of the transition region 107 and also overlaps, starting from the transition region 107, a portion of the second region 106, which may be at a temperature below AC1. The temperature control segment 111 makes it possible to control the cooling rate during the press-hardening process and, in particular, to achieve a lower cooling rate, so that in the transition region 107 a martensite formation is largely avoided. Consequently the second region 106 has a soft region 112 compared to a hard region 113. In this case the soft region 112 also extends over a large part of the initially present transition region 107; and a sharply defined transition zone 114 having a width b134 of preferably 10 mm to 35 mm, in particular, between 20 mm and 30 mm is produced. The dashed line shows in the finished steel component 101 the theoretical position of the temperature control segment 111.

(18) In this case the width b114 of the transition zone 114 corresponds to preferably less than half the width b107 of the transition region 107, in particular less than one-third of the width b107 and preferably less than one-fourth of the width b107. Furthermore, it is shown in the hot forming and press-hardening tool 110 that the temperature control segment 111 does not cover an upper portion 107o of the transition region 107, but does cover a lower portion 107u of the transition region 107; and in this case the lower portion 107u of the transition region 107 corresponds to preferably 50 to 95% of the area of the transition region 107. Furthermore, the temperature control segment 111 extends then, starting from the transition region 107, in the direction of the second region 106 with a width of preferably 70 mm, in particular, 60 mm and even more preferred 50 mm. This covered second region 106 is described with the reference numeral 106. This feature ensures that even the interface 115 between the second region 106 and the transition region 107 obtains a homogeneous material microstructure during the press hardening process.

(19) Thus, in the hot forming and press-hardening tool 110 it is possible to achieve by simple and effective measures with a conventional heating station 102 and a modified hot forming and press-hardening tool 110 a sharply defined, highly precise transition zone 114 between different strength regions 112, 113 on a steel component 101.

(20) Furthermore, preferably A-pillars, roof assemblies, rear door windows, or similar motor vehicle components that exhibit, in particular, soft regions over a large area are produced.

(21) The invention being thus described, it will be apparent that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be recognized by one skilled in the art are intended to be included within the scope of the following claims.

LIST OF REFERENCE NUMERALS

(22) 1hot forming tool 2top tool 3bottom tool 4segment to 2 5segment to 2 6heating segment to 2 7segment to 3 8segment to 3 9heating segment to 3 10heat source 11cooling channel 12clamping bed to 2 13ram table 14clamping bed to 3 15press table 16compensating element 17guide 18press stroke direction 19mold cavity 20blank 21gap 22insulating layer 23rear side to 6, 9 100blank 101steel component 102heating station 103temperature zone above AC3 104temperature zone below AC1 105first region to 100 106second region to 100 106covered second region 107transition region to 100 107oupper portion to 107 107ulower portion to 107 108partition 109temperature controlled blank 110hot forming and press-hardening tool 111temperature control segment 112soft region 113hard region 114transition zone to 101 115interface b107width to 107 b114width to 114 Usurrounding environment