Producing a partially hardened formed part

Abstract

A process of producing a partially hardened metallic formed part comprises: heating a semi-finished product of hardenable hot-formable steel sheet to a hardening temperature; hot-forming the heated semi-finished product in a combined hot-forming cutting device into a three-dimensional formed part; cutting the formed part in the combined hot-forming cutting device; pressure-hardening the formed part in the hot-forming cutting device into a hardened formed part such that a first partial region is hardened by rapid cooling and that a second partial region of the formed part is heat-treated so as to comprise a greater ductility and a lower strength than the first partial region, wherein the operation of cutting the formed part takes place at least in one of the first and second partial region. A combined hot-forming cutting device can be used to produce a metallic formed part.

Claims

1. A process of producing a partially hardened metallic formed part, comprising: heating a semi-finished product of hardenable hot-formable steel sheet to a hardening temperature; hot-forming the heated semi-finished product in a combined hot-forming cutting device into a three-dimensional formed part, wherein the combined hot-forming cutting device comprises an upper tool part and a lower tool part which are closed for hot-forming the semi-finished product; cutting the formed part in the hot-forming cutting device; and pressure-hardening the formed part in the hot-forming cutting device into a hardened formed part such that a first partial region is hardened by rapid cooling and a second partial region of the formed part is heat-treated so as to obtain a greater ductility and a lower strength than the first partial region; wherein at least the second partial region of the formed part is subjected to an air flow at least one of during and after the upper tool part and lower tool part are being opened; wherein, after the air flow, the second partial region still has the greater ductility and the lower strength than the first partial region; and wherein cutting the formed part takes place in at least one of the first partial region and of the second partial region.

2. The process according to claim 1, wherein the cutting takes place while the tool part is being closed and prior to the pressure hardening.

3. The process according to claim 2, wherein, after the upper and lower tool parts have been closed, the semi-finished product is held at a temperature between 300° C. and 600° C. in the second partial region.

4. The process according to claim 2, wherein the upper and lower tool parts are kept closed for a period of 0.5 seconds to 360 seconds.

5. The process according to claim 1, wherein the first partial region of the formed part is subjected to another air flow at least one of during and after the upper tool part and lower tool part are being opened.

6. The process according to claim 2, wherein at least one of the upper tool part and the lower tool part comprises a first tool portion which, during the hot-forming and pressure hardening, contacts the first partial region of the formed part, wherein the first tool portion is cooled to a first temperature such that the first partial region of the formed part is hardened, and further wherein at least one of the upper tool part and of the lower tool part comprises a second tool portion which, during the hot-forming and pressure hardening, contacts the second partial region of the semi-finished product, wherein the second tool portion is heated to a second temperature which is higher than the first temperature of the first tool portion such that the second partial region of the formed part obtains a greater ductility than the first partial region.

7. The process according to claim 6, wherein the first tool portion is cooled at least one of prior to, during and after the hot-forming.

8. The process according to claim 7, wherein the first tool portion is cooled by a cooling medium flowing through a first cooling channel arrangement of the first tool portion.

9. The process according to claim 6, wherein the heating of the second tool portion is conducted by heating a plurality of heating cartridges received in cavities of the second tool portion.

10. The process according to claim 6, wherein the second tool portion is at least temporarily cooled at least one of prior to, during and after the hot-forming.

11. The process according to claim 10, wherein the second tool portion is cooled by an air-containing fluid flowing through a second cooling channel arrangement of the second tool portion.

12. The process according to claim 11, wherein at least some channels of the second cooling channel arrangement end in a forming face of the second tool portion, such that the air-containing fluid flowing through the at least some channels is blown, as the air flow, against the semi-finished product respectively formed part.

Description

SUMMARY OF THE DRAWINGS

(1) Example embodiments of the invention will be explained below with reference to the Figures.

(2) FIG. 1 shows an example hot-forming cutting device for producing a metallic formed component in a first embodiment.

(3) FIG. 2 shows a detail of the hot-forming cutting device according to FIG. 1 in an enlarged illustration.

(4) FIG. 3 is a plan view of a starting component.

(5) FIG. 4 shows a formed part in the form of a B-column produced from a starting component according to FIG. 3.

(6) FIG. 5 shows an example process for producing a metallic formed part.

(7) FIG. 6 is a diagrammatic illustration of an example hot-forming cutting device for producing a metallic formed part in a second embodiment.

(8) FIG. 7 is a diagrammatic illustration of an example hot-forming cutting device for producing a metallic formed part in a modified embodiment.

DESCRIPTION

(9) FIGS. 1 to 7 will be described jointly below.

(10) FIGS. 1 and 2 show a cross-section through a hot-forming cutting device 2 for producing a three-dimensional metallic formed part. The starting material for producing a three-dimensional formed part 20 is a semi-finished product 19, more particularly a blank of steel sheet which can also be referred to as a form cut or planar component.

(11) The semi-finished product 19 can be produced from strip material of steel sheet. The strip material can be obtained by rolling after previously having been heated, which is also referred to as an hot (rolled) strip, and/or the strip material can be cold-rolled, with the final removal of thickness being achieved by rolling without prior heating, which is also referred to as a cold (rolled) strip. The semi-finished product to be formed can comprise a uniform sheet thickness along its length and/or along the width of the component respectively. It is also possible for the semi-finished product to comprise regions of different thicknesses which can be produced in different ways, for example by flexible rolling (Tailor rolled blanks), strip profile rolling or by welding individual sheet plates with different sheet thicknesses (Tailor welded blanks).

(12) In the case of flexible rolling, strip material with a substantially uniform sheet thickness is rolled by changing the roll gap during the process of producing the strip material with a variable sheet thickness along the length of the material. The portions with different thicknesses produced by flexible rolling extend transversely to the longitudinal direction and to the direction of rolling respectively. In the case of strip profile rolling, sheet metal material, i.e., strip material or individual sheet metal elements, having a substantially uniform thickness is rolled through a roll profile into sheet metal material with a variable thickness along the width of the material. The portions with different thicknesses produced by strip profile rolling extend along the longitudinal direction of the sheet metal material. In the case of strip profile rolling, which is also referred to as roll profiling, individual regions of the sheet metal material are quenched towards the outside.

(13) The hot-forming cutting device 2 is suitable for further processing blanks 19, produced by any method, into the formed part 20. The specific design of the hot-forming cutting device 2 depends on the contour of the formed part to be produced. The device 2 shown here serves to produce a formed part for the B-column of a motor vehicle. A profile cut part 19 for producing the B-column is shown in a plan view in FIG. 3. The three-dimensional B-column 20 produced from a planar profile cut part 19 is shown in FIG. 4. In a cross-sectional view the B-column has an approximately hat-shaped profile.

(14) The hot-forming cutting device 2 shown for producing the B-column comprises a plurality of upper tool parts 3, 4, 5 and a plurality of lower tool parts 6, 7, 8 between which the planar semi-finished product is inserted and is shaped into a three-dimensional formed part by moving of the upper tool parts 3, 4, 5 relative to and towards the lower tool parts 6, 7, 8. The lower tool parts 6, 7, 8 are fixed on carrier elements 9, 10.

(15) Furthermore, the hot-forming cutting device 2 comprises a plurality of cutting tools 11, 12 which are designed so as to cut and shape the formed part 20. The cutting tools 11, 12 each comprise a blade 31, 32 and a counter blade 33, 34 which cooperate while the device is being closed for cutting off the projecting part of the formed part. The blades and counter blades, which can also be referred to a cutting punch and cutting die, can be produced from a hardened material. It can be seen that the blades 31, 32 are each arranged in lateral recesses of the lower tool part 7 and are fixedly connected thereto. This is achieved, for example, by threaded connections as indicated by the boreholes 22 in the tool part 7, with other commonly used types of connection also being possible.

(16) The upper tool parts 3, 4, 5, and the lower tool parts 6, 7, 8 each comprise tool portions 13, 14, 15; 16, 17, 18 which are located close to the surface and which, when closing the tool, come into contact with the semi-finished product. By closing the upper tool parts relative to the lower tool parts, the planar sheet bar positioned therebetween is formed into a three-dimensional formed part 20. Relative to the form-giving (shaping) tool portions, the cutting tools 11, 12 are arranged such that the cutting operation takes place when the semi-finished product 19 has already been largely formed into the formed part 20, but before the device 2 has been fully closed, i.e., before the formed part 20 has been pressure hardened upon having complete surface contact with the tool parts.

(17) There are provided tempering devices 23, 24, 25; 26, 27, for tempering the tool portions close to the surface; tempering in the context of the present disclosure in particular refers to setting the respective tool portion to a certain temperature which can be cooling and/or heating. It is proposed that at least one of the upper or lower tool parts 3, 4, 5, 6, 7, 8 comprises two different tempering devices such that a first tempering device of the tool part is designed for cooling and a second tempering device for heating the respective tool part.

(18) This will be explained exemplary with reference to the upper tool part 3 whose tempering device 23 comprises a first tempering part 23A which serves for specifically cooling the associated first tool portion 13A to a first temperature T1, and a second tempering device 23B which serves to heat the associated second tool portion 13B to a second temperature T2 which is higher than the first temperature T1. The first temperature T1 for the first tool portion 13A is set such that the formed part 20, is hardened in this region, during the pressing process between the upper tool parts 3, 4, 5 and the lower tool parts 6, 7, 8. Due to the first tool portion 13A cooled to the first temperature T1, the component 19, starting from the hardening temperature, is cooled so rapidly with a critical cooling speed that a material structure comprising a high degree of hardness and high strength respectively is achieved.

(19) In contrast, the second tool portion 13B is heated to the second temperature T2 which can range between 300° C. and 600° C., for example. By heating the second tool portion 13B, the formed part 20, in this region, is provided with a higher degree of ductility and a lower strength than in the hardened first region. In accordance with the required structure properties of the formed part 20, the lower tool parts 6, 7, 8 are designed to correspond to the upper tool parts 3, 4, 5. That is, the first tool portion 17A of the lower tool part 7, which is positioned opposite the cooled first tool portion 13A of the upper tool part 3, is also cooled, whereas the second tool portion 17B of the lower tool part 7 arranged opposite the cooled second tool portion 13B of the upper tool part 3 is also heated.

(20) The first tempering devices 23A, 27A of the upper tool part 3 and of the lower tool part 7 each comprise a cooling channel assembly with several cooling channels which can be passed through by a cooling medium. The cooling channels extend in such a way through the upper tool part 3 and the lower tool part 7, respectively, that the tool surface coming into contact with the partial region 21B of the semi-finished product to be cooled, respectively, of the component 19 produced therefrom, is cooled. The cooling medium can be water, for example.

(21) The second tempering devices 23B, 27B, which serve to heat the second tool portions 13B, 17B, can be used in the form of heating cartridges which are inserted into suitable hollow spaces of the second tool portions. The heat of the heating cartridges is thus transferred to the second tool portions 13B, 17B and from there to the semi-finished product, respectively the component 19 produced therefrom, which is positioned between the tool portions 13B, 17B.

(22) It can be seen that the cutting tool 11 is arranged in the region of the heated second tool portions 23B, 27B of the upper and lower tool parts 3, 7. The operation of cutting the formed part 20 thus takes place in a partial region 21B which, due to having been heated, comprises a greater ductility than in the cooled partial regions 21A. This is advantageous in that in this heated region, the cutting tool 11, 12 is subjected to a small amount of wear only. However, it is understood that one or several further cutting tools can be provided also in those tool portions which are designed for pressure hardening the formed part, which, however, is not critical for the wear of the cutting tool in that the cutting operation during the pressure application stroke, in terms of time, takes place prior to the tool parts 3, 4, 5, 6, 7, 8 fully coming into planar contact with the component, and thus prior to the formed part being hardened.

(23) The holding time for the formed part 20 between the fully closed tool parts 3, 4, 5, 6, 7, 8 can range between 0.5 seconds and 360 seconds. After the holding time has been reached, the formed part 20 comprises its end contour and the required structure, and can be removed from the device after the tool parts 3, 4, 5; 6, 7, 8 have been opened again.

(24) The process of producing a partially hardened metallic formed part 20 with a hardened first partial region 21A and a ductile second partial region 21B thus comprises the following process steps, as diagrammatically illustrated in FIG. 5: first, heating the semi-finished product 19 which is produced from a hardenable hot-formable steel sheet, at least in the first partial region 21B to a hardening temperature (stage S10). This can be achieved by induction heating for example or in a furnace. Subsequently, the semi-finished product 19 is hot-formed in the combined hot-forming plus cutting device 2 into a three-dimensional formed part 20 (stage S20). Once the semi-finished product has been at least largely formed into the formed part 20, the formed part 20 is cut in the hot-forming plus cutting device 2 (stage S30). In a further process stage (S40), the formed part 20 is pressure hardened in the hot-forming cutting device 2 in such a way that a first partial region 21A is hardened by rapid cooling, and that a second partial region 21B of the formed part 20 is produced with a greater ductility and lower strength than the first partial region 21A by being heated. Subsequently, the component 19 is cut in the hot-forming cutting device 2, at least in the second partial region 21B, by the cutting tool 11, which, time-wise, can occur prior to the hardening. In order to prevent the heated tool parts from overheating, it is possible to provide a further process stage in that said tools parts are temporarily or permanently cooled.

(25) A formed part 20 in the form of a B-column produced in the hot-forming cutting device 2 in accordance with said process is shown in FIG. 4. Said B-column or formed part 20 comprises regions 21B with a greater ductility and a lower strength which are darkened in the drawing; there is also shown a hardened region 21A having an increased strength and a lower ductility. At least part of the regions 21B have been hot-cut. It is understood that this embodiment is only shown by way of example and that the concrete embodiment of the formed part 20 depends on the respective technical requirements.

(26) FIG. 6 shows a hot-forming with cutting device 2 in a modified embodiment which largely corresponds to the embodiment according to FIGS. 1 and 2, so that, as far as common features are concerned, reference is made to the above description. Identical details or details corresponding to one another having been given the same reference numbers as those given in FIGS. 1 and 2.

(27) A difference featured by the present embodiment is that only one upper tool part 3 and one lower tool part 6 is provided, with more than one upper and lower tool part also being possible. The upper tool part 3 and the lower tool part 6 each comprise a first tool portion 13A, 17A which, for the purpose of pressure hardening the formed part 20, is cooled, wherein, for the sake of simplicity, the cooling channels are not shown. Furthermore, the upper tool part 3 and the lower tool part 6 each comprise a second tool portion 13B, 17B, which are each provided with tempering devices 23B, 27B for heating the component 19. In the present embodiment, the tempering devices 23B, 27B are provided in the form of heating plates whose temperature T2 can be set via suitable temperature control means. The heated second tool portions 13B, 17B are insulated relative to the cooled first tool portions 13A, 17A by an insulating material 37, 38 or an air gap.

(28) Furthermore, a cutting tool 11 can be seen in the region of the second tool portions 13B, 17B of the upper and lower tool parts 3, 7. The blade 31 is firmly connected to the upper tool part 3, for example by a threaded connection, and the counter blade 33 is associated with the lower tool part 7, respectively firmly connected thereto. In the edge region of the tool part 7, which edge region laterally adjoins the counter blade 33, a recess 35 is provided which serves as a free space for the cut-off edge of the component 19. Furthermore, a second cutting tool 12 can be seen in the edge region of the cooled first tool portion 13A, 17A of the upper and lower tool parts 3, 7. The blade 32 is fixedly connected to the upper tool part 3, whereas the counter blade 34 is connected to the lower tool part 7. A recess 36 is provided laterally adjacent to the counter blade 34 which recess 36 serving as a free space for sheet blank waste.

(29) In the present embodiment, the operation of cutting the formed part 20 takes place both in a tool portion 13A, 17A cooled for the purpose of hardening the formed part as well as in a tool portion 13B, 17B heated for the purpose of ensuring ductility.

(30) FIG. 7 shows a hot-forming cutting device 2 in a further modified embodiment which largely corresponds to the embodiment according to FIG. 6, and to FIGS. 1 and 2 respectively, so that, as far as common features are concerned, reference is made to the above embodiment. Identical details or details corresponding to one another have been given the same reference numbers as in FIG. 6 and FIGS. 1 and 2 respectively.

(31) A special feature of the present embodiment is that the second tool portions 13B, 17B are each provided with a cooling device. The cooling device comprises a channel assembly 39, 40 with a plurality of channels which extend through the second tool portions 13B, 17B and which end in the shaping surface. To that extent, the cooling device comprises two functions, i.e., cooling the second tool portions 13B, 17B in order to avoid overheating, as well as directing an airflow against the component for cooling same after the device has been opened again. The cooling medium is air.

(32) Overall, the device and the process carried out therewith are advantageous in that formed parts can be hot-formed, cut to shape and pressure hardened in one single process stage. There is produced a near-end-contour formed part with the required material properties.