DE102017223252A1 - Press arrangement and method for producing a hot-formed and press-hardened sheet steel part - Google Patents

Abstract

The invention relates to a press arrangement for producing a hot-formed and press-hardened sheet steel part (7), comprising a heat treatment device (1) in which a sheet steel plate (4) is heat-treated at least in regions to above a material-specific austenitizing temperature Ac3, and with a forming tool (3). in which the heat-treated sheet steel plate (4) is inserted with an insertion temperature (θ) and converted in a forming process stage (U) and cooled to an intermediate temperature (θ) which is greater than a removal temperature (θ) at which the steel sheet part ( 7) can be removed from the press arrangement, and a process-related downstream cooling process stage (K), in which the hot-formed sheet steel part (7) is cooled to the take-off temperature (θ). According to the invention, the cooling process stage (K) is formed with at least one cooling tool (5, 6).

Description

The invention relates to a press arrangement for producing a hot-formed and press-hardened sheet-steel part according to the preamble of claim 1 and to a method for producing such a sheet-steel part according to claim 14.

A hot forming process can be done in a known manner in direct hot forming or indirect hot forming. In the indirect hot working, the cutting / forming operations are already performed before the heat treatment and the hardening of the sheet steel part.

By contrast, in direct hot forming, the cutting and / or forming operations are performed after the heat treatment. Such hot forming is exemplified in DE 10 2009 012 940 A1 known. From the DE 10 2009 050 533 A1 a generic direct hot forming is known in which first a steel sheet to be formed in a furnace is heat treated to a material-specific Austenitisierungstemperatur Ac3. The heat-treated sheet steel blank is placed in a forming tool at an insert temperature and formed therein and cooled to an intermediate temperature greater than a pick-up temperature at which the sheet steel member is removed from the press assembly. The forming tool is followed by a cooling process stage, in which the hot-formed sheet steel part is cooled down to the removal temperature.

In the DE 10 2009 050 533 A1 the downstream cooling process stage is formed in one stage with a cooling tool in which the hot-formed sheet steel part is cooled to the removal temperature. Such a one-step process management is disadvantageous in terms of increasing the efficiency of the hot forming process. In addition, in the DE 10 2009 050 533 A1 at least partially cured in a receptacle by direct heat exchange with a cooling medium. The direct heat exchange takes place in direct contact between component and cooling medium.

From the EP 3 067 128 B1 Another multi-stage process is known in which different tools are mounted under a transfer press on a common plunger and on a common press table. In contrast to the invention, the method uses plate pre-cooling of the board and the board is tempered in order to keep the board temperature above the martensite start temperature.

The object of the invention is to provide a press arrangement and a method for the production of a hot-formed and press-hardened sheet steel part which, in comparison with the prior art, enables further efficiency increases in a simple manner.

The object is solved by the features of claim 1 or 14. Preferred embodiments of the invention are disclosed in the subclaims.

According to the characterizing part of claim 1, the cooling process stage is formed in the simplest variant with only one cooling tool. The hot formed sheet steel part is cooled in the cooling tool to the removal temperature.

In a further embodiment variant, the cooling process stage no longer has only a single cooling tool, but rather the cooling process stage is designed in multiple stages with at least two or more cooling tools. In a first preferred embodiment, the at least two cooling tools can be arranged in process one behind the other in series. In a first embodiment variant, the steel sheet part which has been hot-formed in the forming tool in the cooling tools connected in series can be cooled stepwise to the removal temperature.

In a second embodiment, however, the two cooling tools can not be arranged in series, but rather in parallel to each other, for example in a Y-arrangement or a star-shaped arrangement. In this case, when the first cooling tool is still occupied, a steel sheet part transfer from the forming tool to the still unoccupied second cooling tool can take place. The hot-formed sheet steel part can thus be cooled to the removal temperature either in the first cooling tool or in the second cooling tool positioned parallel thereto. Cycle time reduction by dividing the guard time into several stages.

In contrast to the above DE 10 2009 050 533 A1 According to the invention, the curing does not take place in a direct heat exchange with a cooling medium. Rather, according to the invention can be dispensed with direct heat exchange and instead of the cooling via the jaws done, which in turn are, for example, water cooled. The heat exchange can therefore be carried out according to the invention via a contact pressure between the board and the jaws. The heat exchange is carried out according to the invention thus not in direct contact between the component and the cooling medium, but under heat technical interposition, for example, a tool jaw.

The main advantages of the invention lie in the lower tool wear of the cooling tools by reducing the friction on active radii as well as thermal influences compared to the forming tool. This results in a long service life. In addition, according to the invention can be dispensed with heated tools, whereby the process robustness is increased. In addition, the output can be increased by coupled or decoupled arrangement of several press stages and the quality and dimensional accuracy of the components can be increased. In addition, maintenance intervals are extended and homogeneous mechanical component properties are achieved by uniform contact pressure in the cooling stages.

With the method according to the invention, special advantages with regard to improved material properties of the steel bleaching part can be achieved. That is, in comparison with the prior art, a lower dispersion of the mechanical properties over the steel sheet part is achieved, as well as a higher ductility and a more uniform hardness formation.

The invention's core involves dividing the hot working process into multiple stages (eg, a forming stage and multiple cooling stages), which significantly reduces process time and increases the yield of sheet steel parts and hence the economy of the process. According to the invention, in the first tool (that is to say forming tool), reshaping to bottom dead center takes place after heating to a steel sheet temperature above the austenitizing temperature, during which process the formed workpiece is transferred by means of a transfer mimic into the cooling process stage in which cooling takes place takes place at component removal temperature, which is preferably 220 ° C or less. As a result, the cycle time-determining holding time in the tool is subdivided into two or more time units and the cycle time is reduced.

The sheet steel plate or the sheet steel part has in the course of the process, over the entire component surface considered, not a consistently constant temperature level. Instead, the temperature level across the component fluctuates very much. Against this background, the process temperatures of the steel sheet part and / or the sheet-metal plate mentioned in the application text are to be understood as temperatures averaged over the component surface.

The material of the sheet steel plate is usually a 22MnB5 low-alloy tempered steel. However, other carbon and manganese steels are also contemplated, for example 20MnB8 or 34MnB8 or 22MnCrB8-2 or 20MnCr9-3. The materials can be used uncoated or coated. Here, for example, an aluminum-silicon coating AS150 or AS80, known under the name Usibor 1500 or MBW 1500, can be used. Alternatively, other coatings or metallic coatings are conceivable. These include both Zn, ZnFe and ZnMg etc. as well as other aluminum-containing coatings (for example, without silicon or with small Fe or Mg contents).

In the above process arrangement, the process parameters mentioned below are of essential importance in order to obtain required component and process properties. First of all, the insertion temperature with which the still unformed sheet steel plate is inserted into the forming tool must be above a material-specific martensite start temperature Ms in order to harden to ensure the sheet steel plate. In addition, it is preferable that the intermediate temperature at which the steel sheet part is cooled after the hot working is in a range of 250 ° C to 600 ° C. In addition, it should be emphasized that in the forming tool a complete transformation (ie mold closure to bottom dead center) takes place and the downstream process stages merely function as a heat sink for the energy dissipation in the downstream process process up to the removal temperature.

In a preferred process control, a complete forming can take place in the forming tool, in which the sheet steel blank is formed to a final contour. The downstream cooling tools thus act only as a heat sink for the energy dissipation until reaching the extraction temperature. In such a process, the cooling tools can act as calibration tools, in which the hot-formed sheet steel part is reshaped, in the event that due to highly abrasive load on the forming tool whose dimensional accuracy is affected during hot forming.

The cooling and forming tools can consist of similar or different materials. With regard to the highly abrasive load of the forming tool, it is advantageous if the forming components of the forming tool are made of a highly wear-resistant material or hot work steel, in particular with high chromium, vanadium, carbon, molybdenum and / or Tungsten content (compared to the cooling tools). In contrast, the cooling tools are exposed to a less severe abrasive load. Against this background, the components of the cooling tools coming into pressure-fitting with the hot-formed steel sheet part can be manufactured from highly heat-conductive materials in comparison with the forming tool. exemplary For example, the punch and the die may consist of similar thermally conductive materials, while a sheet metal holder (due to the larger sheet material flow) consists of an abrasive-resistant material that is less thermally conductive.

To further increase the efficiency, it is preferred if the forming tool and / or the cooling tools are designed such that cutting and / or punching operations can be carried out on the respective sheet steel part.

A process sequence which can be carried out with a press arrangement according to the invention is explained below. First of all, a heat treatment of a still undeformed sheet metal blank to a heating temperature above the austenitizing temperature of the sheet metal material takes place. This can be done conventionally in a gas or electrically heated roller hearth furnace. Alternatively, however, it is also possible to resort to a rapid heating method (inductive, conductive, contact). This becomes particularly relevant when the cycle time decreases by introducing the process and significantly more boards are requested per unit of time. Subsequently, a transfer phase in which the sheet metal blank is transferred into the forming tool. The transfer phase should preferably take less than 10 seconds to counteract excessive cooling. The insertion temperature is chosen above the martensite start temperature of the material to ensure hardenability. Preferably, the forming speed in the forming tool at greater than 60 mm / s, with a minimum surface pressure on the component (after forming in UT) is greater than 3 N / mm ² (except steep areas with an opening angle of less than 5 °) to form completely. The closing time in the forming tool may preferably be between 0.1 s and 5 s at bottom dead center, while the ram return speed may be greater than 50 mm / s.

The following transfer phase for transferring the hot-formed sheet steel part into the cooling process step may be less than 5 seconds, wherein the transfer time consists of gripping, lifting, transfer and depositing. In the cooling tools, the closing speed can be greater than 20 mm / s, while the surface pressure can be set as in the forming tool. The removal temperature may preferably be less than 220 ° C. It should be emphasized that in the first cooling tool, closing in the bottom dead center can not be absolutely necessary and that, if necessary, locking in the following second cooling tool is sufficient.

The press arrangement can be realized both as a press line and as a transfer press. In the press line, the forming tool and the cooling tools can be arranged as individual tools with transfer devices acting therebetween. When executed as a transfer press, however, all upper and lower tools can be mounted on a common press ram and a common press table.

In the execution of the press arrangement as a transfer press results in a forced division of the closing times by the clock time coupling of the individual operations. For example, with three consecutive presses, this would be one third of the hold time. In this case, therefore, could be provided a Zuhaltezeit-division of 6 seconds to about 3x2 seconds.

In the execution of the press assembly as a press line with single presses, a cycle time decoupling can be achieved by varying the press stages (for example, in the above-mentioned Y-arrangement or star-shaped arrangement of the forming and cooling tools). As a result, cooling stages can allow a different from the forming stage clamping time, since the tools can act independently of each other or can be controlled. It is also possible to couple individual cooling stages with each other, without producing a coupling to the forming stage. This can be realized in particular by the arrangement of the forming stage to the cooling stages. Of course, in all cases air cooling is present during part transfer.

Of course, after or in alternation with the cooling stages, it is also possible to arrange trim hole stages (which in turn can be coupled to the cooling stages). With regard to the trimming, a hot trimming in the forming stage can be provided, and a punching at 500 to 550 ° C in the first subsequent stage before the cooling tools component-related can be provided. There is also the possibility of processing edge areas or natural edges.

Due to the division of the operations on several tool stages (that is, forming and cooling tools), these can be designed to load and demand. In detail, this means that a highly wear-resistant material or hot-work steel can be used (in particular with a high proportion of chromium, vanadium, carbon, molybdenum and / or tungsten), in particular for the abrasive tool subject to high abrasive loads. This results in a high dimensional stability of the components over a long production cycle until the next rework. The Wear resistance correlates inversely with the thermal conductivity, which is why the less loaded cooling stages (ie cooling tools) may consist of materials of correspondingly high thermal conductivity in order to effectively dissipate the heat from the component and thus to ensure a shortening of the retention time while increasing component quality. Another approach is the type and design of the cooling used and cooling channel design. This can also be designed for the load case and the resulting component shape. In particular, the cooling stages could have a very near-surface cooling design, since the abrasive wear and the rework cycle are not critical here. The fact that the wear in the cooling stages compared to the reference (single-stage process) is significantly lower, obtained over life significantly better contact pattern in the cooling stages, which leads to an increase in component quality and better mechanical properties (homogeneous hardness, elongation, strength ).

Conventional 22MnB5, low-alloyed manganese-boron steel can be used as sheet metal materials, with an aluminum-silicon coating AS150 or AS80, known as Usibor 1500 or MBW 1500. Alternatively, other base materials or sheet materials are also possible. These include in particular 22MnB8 (as air-hardening variant) and 22MnSiB9-5 as well as higher-strength materials such as Usibor 2000 or MBW1900. Alternatively, other coatings or metallic coatings are conceivable. These include both Zn, ZnFe and ZnMg etc. as well as other aluminum-containing coatings (for example, without silicon or with small Fe or Mg contents).

The reduced cycle times of the process result in an increase in the board requirement from the furnace and this in turn results in a significant increase in furnace length. Therefore, a preferred embodiment provides the application of a rapid heating technology. This can be preceded either by a roller hearth furnace or also be provided alone. The various and potentially conceivable rapid heating technologies include inductive heating in the longitudinal and transverse field as well as contact plate heating or heating with furnace zones with a significant excess temperature> 1000 ° C.

• 1 eine Anlagenskizze, anhand der die in der 2 angedeutete Prozessabfolge zur Herstellung eines warmumgeformten und pressgehärteten Stahlblechteils veranschaulicht ist;
• 2 in einem Blockschaltdiagramm die Prozessabfolge zur Herstellung des Stahlblechteils;
• 3 ein Diagramm, das den zeitlichen Verlauf der Stahlblechteil-Temperatur in der in den 1 und 2 angedeuteten Prozessabfolge zeigt; und
• 4 bis 6 jeweils Ansichten entsprechend der 1 bis 3 gemäß einem weiteren Ausführungsbeispiel.

Hereinafter, embodiments of the invention are described with reference to the accompanying figures. Show it:

• 1 an investment sketch, on the basis of which in the 2 indicated process sequence for producing a hot-formed and press-hardened sheet steel part is illustrated;
• 2 in a block diagram the process sequence for the production of the sheet steel part;
• 3 a diagram showing the time course of the sheet steel part temperature in the in the 1 and 2 indicated process sequence shows; and
• 4 to 6 each views according to the 1 to 3 according to a further embodiment.

It should be emphasized that the figures show only two specific embodiments of the invention, in which the cooling process stage K two cooling tools 5 . 6 which is in series ( 1 ) or parallel ( 4 ) are switched. It goes without saying that the invention is not limited to these embodiments, but rather the cooling process stage K may also have only a single cooling tool or more than two cooling tools.

In the 1 is roughly schematically sketched a press plant, based on the first basic process sequence for the production of a hot-formed and press-hardened sheet steel part 7 is explained. The plant has an example as a heat treatment device 1 a continuous furnace, a forming tool 3 for hot forming and press hardening of sheet steel components 7 and a downstream cooling process stage K in which a first and second cooling tool 5 . 6 arranged in series one behind the other. Furthermore, a storage station 9 provided in the manufactured sheet steel components 7 be stored. It should be noted that the heat treatment facility 1 can work with different technologies, such as induction, conduction, contact plate heating, convection, radiation, etc.

In the 1 are the forming tool 3 as well as the two cooling tools 5 and 6 arranged in a series connection process technology behind one another, as a press line, in which between the forming tool 3 and the two cooling tools 5 . 6 each transfer facilities 11 Act. In the hot forming process, according to the 1 . 2 or 3 First, a still undeformed sheet metal blank 4 made of a hardenable steel in the continuous furnace 1 transferred and there in a heat treatment phase Δt ₁ heated to a process temperature at least partially or in regions above the material-specific Austenitisierungstemperatur Ac3 of the steel used ( 3 ), which may be exemplified at 930 ° C. The thus heated sheet metal blank 4 becomes in a hot state in a transfer phase Δt ₂ ( 3 ) to the forming tool 3 and θ transferred there by an insertion into the forming tool temperature, _a 3 is inserted. The insertion temperature θ is _one with a temperature offset above a material-specific martensite start temperature Ms, in order to harden the steel sheet part to be formed 7 to ensure.

It should be emphasized that the sheet steel plate or the sheet steel part 7 During the course of the process, when viewed over the entire component surface, there is no consistently constant temperature level. Instead, the temperature level across the component fluctuates very much. Against this background, the process temperatures of the steel sheet part and / or the sheet-metal plate relevant here are to be understood as temperatures averaged over the component surface.

In addition, it should be emphasized that with segmental or partial heating (tailored tempering) of the board different warm board areas or platinum zones are generated. In this case, the process temperature of the board is not averaged over all different board areas but rather only the hottest board area is used for averaging the process temperature of the board (ie, averaged process temperature only over the hottest board area), while disregarding the cooler board areas.

During the hot forming phase Δt ₄ takes place in the forming tool 3 a press hardening or cooling of the sheet steel part 7 to an intermediate temperature θ _Z , which in the 3 exemplarily at about 600 ° C. The hot-formed sheet steel part 7 will then be in another transfer phase Δt ₄ in the first cooling tool 5 transferred and there in a first cooling phase Δt _5.1 to a cooling temperature θ _K ( 3 ) is cooled. After that, the cooled to the cooling temperature Δ _K steel part 7 in another transfer phase Δt ₆ in the second cooling tool 6 transferred and there in a second cooling phase Δt _5.2 cooled down to the withdrawal temperature θ _E of about 220 ° C.

Based on the following 4 to 6 is sketched according to a second embodiment, a further press plant, in which the two cooling tools 5 . 6 not linearly one behind the other with the forming tool 3 are positioned in series, but rather the cooling tools 5 . 6 are arranged in parallel to each other. In this way, in the hot forming process with still occupied first cooling tool 5 a sheet steel part transfer from the forming tool 3 into the still empty second cooling tool 6 respectively.

When in the 4 The system sketch shown thus results in a process sequence in which after the hot forming phase Δt ₃ in the forming tool 3 the molded sheet steel part 7 in a transfer phase Δt ₄ either in the first cooling tool 5 or in the second cooling tool 6 is transferred. In the first cooling tool 5 or in the second cooling tool 6 the cooling phase takes place Δt ₅ in which the hot-formed sheet steel part 7 is cooled to the removal temperature θ _E.

LIST OF REFERENCE NUMBERS

1

Heat treatment facility

3

forming tool

4

sheet metal blank

5

first cooling tool

6

second cooling tool

7

Steel sheet metal part

9

deposit station

11

transfer device

Δt ₁

Heat treatment phase

Δt ₂

transfer phase

Δt ₃

Warmumformphase

Δt ₄

second transfer phase

Δt ₅ , Δt _5.1 , Δt _5.2

cooling phases

Δt ₆

third transfer phase

K

Cooling process stage

U

Forming process stage

θ _a

insertion temperature

θ _E

removal temperature

θ _K

cooling temperature

θ _z

intermediate temperature

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102009012940 A1 [0003]
• DE 102009050533 A1 [0003, 0004, 0011]
• EP 3067128 B1 [0005]

Claims (14)

A press arrangement for producing a hot-formed and press-hardened sheet steel part (7), comprising a heat treatment device (1) in which a steel sheet (4) is at least partially heat treated above a material-specific austenitizing temperature Ac3, and a forming tool (3) in which the heat-treated Sheet steel plate (4) with an insertion temperature (θ _a ) inserted and in a forming process stage (U) formed and cooled to an intermediate temperature (θ _Z ), which is greater than a removal temperature (θ _E ), in which the sheet steel part (7 ) can be removed from the press arrangement, and a process technology downstream cooling process stage (K) in which the hot-formed sheet steel part (7) is cooled to the removal temperature (θ _E ), characterized in that the cooling process stage (K) with at least a cooling tool (5, 6) is formed, and that in particular the hot formed sheet steel part (7) in d em cooling tool (5, 6) is cooled to the removal temperature (θ _E ). Press arrangement according to Claim 1 , characterized in that the cooling press stage is formed in several stages with at least two or more cooling tools (5, 6), and that in particular the cooling tools (5, 6) are arranged in process one behind the other in series, and the hot-formed sheet steel part (7) in the cooling tools ( 5, 6) is gradually cooled down to the removal temperature (θ _E ). Press arrangement according to Claim 2 , characterized in that the at least two cooling tools (5, 6) in the multi-stage cooling process stage (K) process technology downstream of the forming tool (3), so that in a still occupied first cooling tool (5) a steel sheet part transfer in an unoccupied second cooling tool (6) can take place. Press arrangement according to Claim 3 , characterized in that the hot-formed sheet steel part (7) either in the first cooling tool (5) or in the second cooling tool (6) to the extraction temperature (θ _E ) cools. Press arrangement according to one of the preceding claims, characterized in that in the forming tool (3) a complete deformation takes place in which the sheet steel plate (4) is formed to a final contour, and that in the downstream cooling process stage (K) the cooling tools ( 5, 6) additionally act as a calibration tool, in which the hot-formed sheet steel part (7) is reshaped, and indeed for the case that due to highly abrasive load of the forming tool (3) the dimensional stability is impaired during hot forming. Press arrangement according to one of the preceding claims, characterized in that in the forming tool (3) takes place a defined surface pressure, so that not only reshaped in the forming tool (3), but is also held with a holding time, wherein the holding time depending on the Sheet thickness of the sheet metal blank and / or results in dependence on the tool assembly, and / or that the holding time in the different tool levels by the orientation of the forming tool (3) to the cooling tools (5, 6) results, and that in particular in a series arrangement of a Forming tool (3) and a cooling tool (5) the holding times in the forming tool (3) and in the cooling tool (5) are identical. Press arrangement according to one of the preceding claims, characterized in that the cooling and forming tools consist of identical or different materials, and / or that forming forming tool components of a highly wear-resistant material or hot work steel, in particular with high chromium, vanadium, carbon , Molybdenum and / or tungsten content are made, in comparison to the cooling tools (5, 6), and that with the hot-formed sheet steel part (7) coming into pressuring components of the cooling tools (5, 6) compared to the forming tool ( 3) are made of highly thermally conductive materials. Press arrangement according to one of the preceding claims, characterized in that the insertion temperature (θ _a), by which the steel sheet metal plate (4) in the forming tool (3) is inserted, is located above a material-specific martensite Ms to a hardenability of the steel sheet part (7) to ensure and / or that the intermediate temperature (θ _Z ), on which the steel sheet part (7) is cooled after hot working, in a range of 250 ° C to 600 ° C. Press arrangement according to one of the preceding claims, characterized in that the forming tool (3) and / or the cooling tools (5, 6) are designed so that cutting and / or punching operations on the sheet steel part (7) can be carried out, in particular in the first and / or second operation stage. Press arrangement according to one of the preceding claims, characterized in that the press arrangement is realized as a press line, wherein the forming tool (3) and the cooling tools (5, 6) as individual tools with Intermediate transfer means (11) are arranged. Press arrangement according to one of Claims 1 to 9 , characterized in that the press arrangement is realized as a transfer press, in which all the upper and lower tools of the forming tool (3) and the cooling tools (5, 6) are mounted on a common press ram and a common press table. Press arrangement according to one of the preceding claims, characterized in that the material of the sheet steel part (7) is a low-alloy, carbon and manganese-containing tempering steel with a metallic scale protection coating or coating which is aluminum or zinc-containing. Press arrangement according to one of the preceding claims, characterized in that the forming tool (3) is not necessarily, that is not necessarily, cooled or tempered, and / or that the at least one cooling tool (5, 6) has a cooling device for cooling its active surfaces in that the cooling takes place in particular by means of a boring cooling, in which cooling channels are flowed through below the tool-active surfaces coolant and the coolant is out of contact with the board or the sheet steel part (7). Process for producing a hot-formed and press-hardened sheet-steel part (7) in a press arrangement according to one of the preceding claims.

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