EP2993241B1 - Method and press for manufacturing cured sheet metal components, in sections at least - Google Patents

Description

The invention relates to a method and a press for producing sheet metal components that are hardened at least in sections.

In forming technology it is known to carry out sheet metal components made of metal strip material, in particular made of steel, by means of an at least one-stage forming operation in a press. For this purpose, the sheet metal is unwound from the strip and sheet metal blanks of a certain shape are cut from the strip. The forming then takes place in a press with at least one press tool stage.

In the automotive industry in particular, it is common to produce complex geometries and to set certain mechanical properties on the component in addition to the shape. For this purpose, hot forming, also known as press hardening or press hardening, has been widespread for many years for the production of chassis and structural components of motor vehicles.

The DE 10 2008 034 596 A1 describes a method for producing at least partially hardened sheet metal components in two successive tool stages, each tool stage having an upper tool and a Has the lower tool arranged in a press and the upper tool and lower tool are closed by the closing movement of the press and thereby a sheet metal blank heated to austenitizing temperature is hot-formed into a sheet metal component. By holding the sheet metal blank and making contact with the tool halves, the formed sheet metal blank is quickly cooled. In addition, by providing gaps between the tool halves or by using different materials with different thermal conductivity in the upper tool or lower tool, sheet metal components hardened only in sections should be produced.

The DE 10 2009 057 382 A1 describes a method and a press with several tool stages for the hot forming of sheet metal blanks heated to austenitizing temperature for the production of hardened sheet metal components. After hot forming in a cooled forming tool stage, the sheet metal component is to be hardened in a further cooled tool stage and then cold cut. The press should be operated with high throughput, which is why it is proposed to close the tool stages with the upper tool and lower tool as early as possible and to open them as late as possible.

For the state of the art, the JP 2007 136 535 A referenced. A production process in a press with three tool stages is described. A hot forming stage is followed by a trimming stage and a cooling stage or mold hardening stage. Only the cooling stage has a lower tool with an elastic actuator, so that the lower tool can be raised relative to the press table in order to produce the closed state of the cooling tool stage.

The post-publish EP 2 907 881 A2 discloses a hot forming line and method for making hot formed sheet metal products. A heating station and a forming station are proposed. The heating station has a lower tool and an upper tool, between which a metal plate is received for heating. The heating or the heating of a metal plate in the heating station takes place through indirect resistance heating. The entire lower tool carrier can be moved downwards against the force of spring elements, with the movement of the heating station, forming station and cooling station being elastically supported as a result.

The US 2010/0018277 A1 discloses a method in which a blank is hot-formed and the forming begins by an upper, elastically mounted body. Spring-loaded hold-downs in the upper tool press the unformed areas of the blank to be formed against the lower tool before the blank is trimmed at the edge in a final operation.

The object of the invention, based on the aforementioned prior art, is to propose a reliable method that can be implemented on a large industrial scale and a press for producing hardened sheet metal components, which has an increased production throughput and a higher resulting product quality.

The object relating to the method is achieved by the features of claim 1. The dependent claims 2 to 12 represent advantageous design variants.

The object is further objectively achieved by a press according to patent claim 13. The dependent claims 14 to 19 form advantageous design variants.

• Wenigstens abschnittsweises Erwärmen einer Blechplatine auf eine Temperatur von größer als die Austenitisierungstemperatur Ac3,
• Einlegen der erwärmten Blechplatine in eine erste Umformwerkzeugstufe der Presse,
• Warmumformen der Blechplatine zum Blechbauteil in der Umformwerkzeugstufe, wobei dabei die Presse eine Schließbewegung ausführt,
• Zuhalten der Umformwerkzeugstufe für eine erste Haltezeit,
• Abkühlen der umgeformten Blechplatine während der ersten Haltezeit, und
• Transfer der umgeformten Blechplatine in eine zweite Werkzeugstufe,
• wenigstens abschnittsweises Härten der Blechplatine durch Abkühlen in der zweiten Werkzeugstufe innerhalb wenigstens einer zweiten Haltezeit.

A method for the production of a sheet metal component hardened at least in sections is proposed, which is carried out in a press which comprises a press table, a press ram and several tool stages. The following steps are carried out:

• At least in sections heating a sheet metal blank to a temperature greater than the austenitizing temperature Ac3,
• Insertion of the heated sheet metal blank into a first forming tool stage of the press,
• Hot forming of the sheet metal blank into the sheet metal component in the forming tool stage, the press executing a closing movement,
• Holding the forming tool stage closed for a first holding time,
• Cooling the formed sheet metal blank during the first holding time, and
• Transfer of the formed sheet metal blank to a second tool stage,
• Hardening of the sheet metal blank at least in sections by cooling in the second tool stage within at least a second holding time.

In the method, the forming tool stage is moved during the closing movement from an upper reversal point to a lower reversal point of the press by at least one elastic actuator relative to the press, so that the hot forming is ended and the locking begins before the press reaches the lower reversal point, and / or that the closing of the forming tool stage by an elastic actuator is only ended during the upward movement of the press after the lower reversal point of the press has been completely passed, the upper tool and the lower tool having cooling channels, whereby a cooling medium is conducted.

This achieves a highly economical manufacturing process, especially for industrial large-scale production, and at the same time improves process and component quality. Specifically, the cycle time for hot forming and hardening of the sheet metal component can be reduced by starting and ending the forming very early and by making maximum use of the holding time for quenching the formed sheet metal component in the individual tool stages. In addition, the elastic actuator (s) can compensate for inaccuracies in the positioning of the upper and lower tool of the forming tool stage, as well as discontinuities in the surface properties and thickness of the sheet metal blank.

The sheet metal blank is further processed into a sheet metal component by hot forming, with both terms also being used in parallel in the following description if it is not about the properties caused by the forming, but rather the process steps, in particular the heat treatment and the press, are explained in more detail.

Within the scope of the invention, the sheet metal blank is brought to a temperature above the austenitizing temperature of the steel alloy used, at least in sections, by heating methods known per se. In the context of the invention, it makes sense to use heating devices with a high heating rate, for example by contact heating with inductively or conductively heated contact masses, direct burner heating or furnace heating with overtemperature in the furnace. A combination of these or with other known types of furnace is also possible, for example when using metal-coated sheet metal blanks.

The austenitizing temperature Ac3 is also referred to as the recrystallization temperature, the level of the austenitizing temperature depending on the exact alloy composition. For the process according to the invention, the use of manganese boron steels has proven successful, which, after being heated by rapid cooling or quenching, experience a continuous hardening by converting the austenitic structure into martensite structure. The mechanical properties yield point Rp0.2 and tensile strength Rm increase with hardness, while the maximum bending angle and elongation A50 decrease.

According to the invention, holding time is to be understood as the period in which the upper tool and lower tool at least the forming tool stage and the second tool stage are closed, i.e. at least in sections are in intimate contact with the formed sheet metal blank or with the sheet metal component.

The term transfer includes any handling operation that brings about the transport of the sheet metal component from one tool level to the next following tool level, including removal from the respective tool level and insertion into the respective tool level.

According to the invention, the reversal point of the press is defined in such a way that the press reaches exactly one open position, the upper reversal point, and precisely one maximally closed position, the lower reversal point, in the work cycle. Of this, depending on the type of press, the maximum that can be achieved for maintenance or retooling operations is to distinguish between the open position of the press, which may be greater than the top dead center.

Edge trimming and / or perforation are preferably carried out during or after the end of hot forming in the forming tool stage, in particular before the press is completely closed. This has the advantage that a subsequent perforation or edge trimming can be omitted in the cold and hardened state of the sheet metal component, thus avoiding tool wear and additional handling processes. Because the punching or trimming takes place before the press is completely closed, the closing movement can be used to drive the cutting means that are necessary for punching or trimming. The trimmed sheet metal component is then transferred to the second tool stage for further rapid cooling, at least in sections.

The second tool stage is also preferably moved relative to the press, at least in some areas, during the closing movement of the press by at least one elastic actuator, so that the locking begins before the press reaches the lower reversal point. However, it is also possible for the locking of the second tool stage to be terminated at least in sections by an elastic actuator only during the upward movement of the press, after the lower reversal point of the press has been completely passed. Most preferably, the second tool stage is mounted in relation to the press by at least one elastic actuator in such a way that the upper tool and lower tool remain closed during a significant time portion of the closing movement and during a significant time portion of the upward movement. A time share of more than 30 percent each in the closing movement and / or in the upward movement of the press is to be regarded as decisive.

Furthermore, the forming tool stage and preferably also the second tool stage can be spring-mounted mechanically, hydraulically or pneumatically by the elastic actuator. The elastic actuators themselves can either have a passive, purely mechanical effect by permanently applying a force counteracting the press force on the upper tool or the lower tool raise. A simple example would be spiral springs or spring assemblies made from other mechanical springs. However, it is also possible for at least one elastic actuator to be actively controlled in order to set an actuating force curve of the actuator that is differentiated during the press movement. The latter makes it possible to distinguish between a level of actuating force that is sufficient for hot forming and a higher level of actuating force required for locking, while protecting the elastic actuator in order to protect the associated actuators. As a result, the overall holding time for carrying out the rapid cooling and hardening of the sheet metal component can also be reduced.

The sheet metal component is transferred according to the invention by a transfer system, comprising a linearly guided transfer bar with grippers, in a transfer time of 1 to 4 seconds, preferably in 2 to 3 seconds, between at least two tool stages. It is thus possible to keep the heat losses during the movement of the sheet metal component between the tool stages as low as possible and ideally to dispense with complicated multi-axis handling devices. It can be provided that the grippers of the transfer system are already brought close to the sheet metal component before the press has reached the upper reversal point. In particular, recesses can be provided in the tool stages for the collision-free implementation of the transfer system or for bringing the grippers close to the sheet metal component, so that the sheet metal component is immediately carried out by the transfer system or the lower tool when the upper tool and lower tool are moved apart, i.e. after the end of the holding time Gripper is removed from the forming tool stage and moved on.

Furthermore, a sheet metal component hardened only in sections can be produced in a particularly simple and reliable manner with the method according to the invention. In the context of the invention, in sections means that the sheet metal component has at least a first section with relatively low strength and yield point with a structure that is preferably unhardened or only slightly hardened, and at least one second section with high strength Rm and yield point Rp0.2 but reduced Has elongation A50 and essentially has a martensitic structure. This means that the first section of the Sheet metal component has a tensile strength between 400 and 800 megapascals (MPa), in particular between 450 and 650 MPa, and predominantly ferrite-pearlite structural components.

In the forming tool stage, a cooling temperature of the sheet metal component is preferably set which is higher in a first section of the sheet metal blank than the martensite start temperature Ms required for the transformation of the martensite structure and which is lower than Ms in a second section, with the sheet metal blank in the first section in particular to a cooling temperature of 540 is cooled to 660 ° C. In addition to the cooling temperature, it is important in the second sections to maintain a high cooling rate above 25 Kelvin per second (K / s), in particular above 70 K / s, in order to ensure sufficient hardening of the structure in this section. By cooling the first section of the sheet metal blank to a lesser extent and to a higher temperature compared to the cooling in the second section, it is achieved that a structural transformation in the sheet metal blank from the austenitic state to martensite is prevented, but at the same time a structural transformation from austenite to ferrite and / or pearlite begins.

In order to obtain a particularly elastic and reliably deformable, especially deformable, component in the first section, a cooling temperature of the sheet metal component can be set in the second tool stage, which at the end of the second holding time is between 350 to 500 ° C in the first section and in which The second section is smaller than the martensite finish temperature Mf required for complete transformation of the martensite structure, the sheet metal component in the second section preferably being cooled to less than 200 ° C., in particular to room temperature. This ensures that the steel structure in the first section has enough time at a temperature that is significantly higher than in the first section to complete the structural transformation to ferrite and / or pearlite without bainite or even martensite being produced to any significant extent. In contrast, the temperature control of the second section is intended to achieve a completely martensitic structure, with a tensile strength between 1400 and 2100 MPa, preferably 1450 and 1800 MPa, depending on the steel alloy, in particular depending on the carbon and manganese content, being set.

Furthermore, it can be provided that the sheet metal component is held for a first holding time between 2 and 8 seconds and for a second holding time between 2 and 10 seconds. With the cycle time of the press unchanged, the time available for cooling the formed sheet metal blank and for the associated structural transformations is almost doubled. The difference between the two holding times results primarily from the time required for hot forming in the forming tool stage.

The cycle time of the press with a forming tool stage and a temporally following second tool stage between its upper reversal point and its lower reversal point is preferably between 3 and 11 seconds. This makes it possible to achieve an extremely high output or a high throughput and thus very low production costs. In combination with the production of hardened sheet metal components in sections, there is also the advantage that the component properties and quality do not suffer from the high production cycle. It should be emphasized that the sheet metal components produced have a high degree of dimensional accuracy, in contrast to a one-step hot-forming and press-hardening process for the production of press-hardened sheet-metal components in sections with heated tool areas.

Another aspect of the invention provides that the hardening is only ended in a third tool stage, after which the sheet metal component completely has a cooling temperature below 200 ° C. This has the advantage that the cycle time of the press can be reduced again and at the end of the press a cool sheet metal component that is not critical when touched can be removed. A residual heat distortion is completely excluded, in particular due to the adjustment of the cooling temperatures of the two sections of the sheet metal component.

The cycle time of the press with a forming tool stage and a second tool stage and a third tool stage, therefore in a three-stage chronologically successive process, between its upper reversal point and its lower reversal point is between 3 and 9 seconds. In order to achieve this short press cycle time, the use of a mechanical crank or eccentric press or a servo-electric press is preferred to be provided, whereby in the case of the mechanical press the reversal points are passed through without any significant interruption of the press movement. A holding time due to a press standstill can thus advantageously be dispensed with.

Another aspect of the invention relates to a press for producing sheet metal components that are hardened at least in sections. The press has several tool stages, a press ram and a press table, and is used to carry out the method described above. According to the invention, it is provided that at least one tool stage is a forming tool stage that can be cooled at least in some areas for hot forming of sheet metal blanks, which comprises an upper tool and a lower tool which form a mold cavity in a closed state.

At least one elastic actuator is arranged between the press table and the lower tool so that either the lower tool can be raised relative to the press table and / or the upper tool can be pressurized at a distance relative to the press ram in order to establish the closed state of the forming tool stage before the press is completely closed The upper tool and the lower tool have cooling channels, whereby a cooling medium can be conducted, the cooling channels extending over the entire longitudinal extent of the upper tool and the lower tool, with a cooling source in the form of a heat exchanger being provided outside the forming tool stage as well as an inlet and outlet line from the cooling channels to the heat exchanger.

According to the invention, the sheet metal component is transferred between at least two tool stages by a transfer system which is designed as a linearly guided transfer bar with grippers.

In other words, it is possible for the lower tool and / or the upper tool to be spaced apart from the press table or press ram at least until the lower reversal point of the press is reached. The distance can be adjusted by means of the elastic actuator and is reduced during the hot forming and preferably also during a portion of the holding time when the upper tool and lower tool are closed. An elastic actuator arranged on one side is sufficient to compensate for the position of the upper tool and lower tool with one another and for any discontinuities in the thickness of the sheet metal blank. However, it is also conceivable to provide corresponding actuators on both sides, that is between the upper tool and the press ram and between the lower tool and the press table. If trimming or punching is to take place in the forming tool stage at the same time or after the hot forming, it is also conceivable to provide a cutting means that can be supported on an elastic actuator.

A vertical adjustment path can preferably be set by the elastic actuator, the adjustment path being less than the maximum press stroke path between the upper and lower reversal points of the press, but at least 100 mm. In combination with the speed given by the press drive during the closing movement and during the upward movement of the press, it is thus advantageously possible to extend the holding time through contact between the sheet metal blank, the upper tool and the lower tool.

Furthermore, the elastic actuator preferably has an actuating force that increases at least over part of an actuating path from the upper reversal point to the lower reversal point of the press, in particular the actuating force in the closed state of the forming tool stage is at least 20 percent greater, whereby the contact and pressure between the tool stage and the sheet metal component is increased and thus a high heat transfer or the rapid achievement of at least one desired quenching temperature of the sheet metal component is possible.

In order to produce hardened components only in sections, it is furthermore preferred that at least the forming tool step can be heated in some areas by a heat source in order to bring about a reduced cooling rate in the sheet metal component in a first section, with unheated areas having cooling channels for the passage of a cooling medium. Specifically, a temperature close to room temperature, but in any case below 200 ° C, can be set in the unheated area of the tool step. The heat source is in the heated A temperature range between 650 and 450 ° C can be set. Thus, the upper tool and the lower tool are provided to cool the formed sheet metal component during the holding time at different cooling rates and thereby to different quenching temperatures or to keep them at these temperatures. As already described above, a first section with lower tensile strength and at least one second section with high strength can thus be set in the sheet metal component.

Alternatively or preferably in addition, it is also possible that both the forming tool stage and at least the subsequent second tool stage can be heated in certain areas, in particular by a heat source, in order to obtain at least no completely hardened sheet metal component in a first section. The same features and advantages result as was already carried out above in the method for the production of sheet metal components hardened only in sections for the second tool stage.

Furthermore, the unheated area of the second tool stage can have an active cooling source, at least corresponding to a transition section between the first section and the second section of the sheet metal component. The cooling source is used to reduce heat transfer between the sections of the sheet metal blank with different temperatures in order to ensure the narrowest possible transition section. This has the advantage that when designing sheet metal components, especially for the vehicle industry, designers only have to consider a small area to which no mechanical parameters can be directly assigned or for which no mechanical parameters can be guaranteed. It is also ensured that the second area has a homogeneous distribution of the structure and the mechanical properties throughout. The cooling source comprises a heat exchanger arranged outside the press, which is in operative connection with the cooling medium and the cooling channels of at least the forming tool stage.

Finally, it is the first section and the transition section of the sheet metal component that can be fixed in a form-fitting manner by fixing elements, at least in the second tool stage. In the case of a three-stage press with a forming tool stage, the second In the tool stage and the third tool stage, the sheet metal component can preferably also be positively fixed in the third tool stage by means of fixing elements. For the press according to the invention, this results in an equalization of the pressing force in all tool stages and, in particular, it prevents the press table and press ram from being unevenly aligned with one another.

Further goals, advantages, features and possible applications of the present invention emerge from the following description of several exemplary embodiments with reference to the drawings. In this case, all of the features described and / or illustrated in the form of themselves or in any meaningful combination form the subject matter of the present invention, also regardless of their summary in the claims or their reference.

Figur 1

eine erste Ausführungsvariante der erfindungsgemäßen Presse im Querschnitt,

Figur 2a und 2b

eine zweite Ausführungsvariante einer Umformwerkzeugstufe der erfindungsgemäßen Presse im Querschnitt und Längsschnitt,

Figur 3

eine dritte Ausführungsvariante einer erfindungsgemäßen Presse im Längsschnitt,

Figur 4a und 4b

ein Ablaufschema für erfindungsgemäßes Verfahren anhand eines Längsschnitts durch die Umformwerkzeugstufe zu verschiedenen Zeitpunkten des Pressentaktes,

Figur 5

eine Ausführungsvariante einer Umformwerkzeugstufe einer erfindungsgemäßen Presse zur Herstellung abschnittsweise gehärteter Blechbauteile,

Figur 6

eine alternative Ausführungsvariante einer Umformwerkzeugstufe einer erfindungsgemäßen Presse zur Herstellung abschnittsweise gehärteter Blechbauteile im Längsschnitt,

Figur 7a und 7b

eine alternative Ausführungsvariante einer erfindungsgemäßen Presse zur Herstellung abschnittsweise gehärteter Blechbauteile 7a) im Längsschnitt und 7b) im Horizontalschnitt,

Figur 8a und 8b

eine alternative Ausführungsvariante einer erfindungsgemäßen Presse zur Herstellung abschnittsweise gehärteter Blechbauteile 8a) im Längsschnitt und 8b) im Horizontalschnitt,

Figur 9a

einen Zeit-Temperatur-Verlauf der Blechplatine für das erfindungsgemäße Verfahren in einer zweistufigen Presse und separater Kühlstufe und

Figur 9b

einen Zeit-Temperatur-Verlauf der Blechplatine für das erfindungsgemäße Verfahren in einer dreistufigen Presse.

Show:

Figure 1

a first variant of the press according to the invention in cross section,

Figures 2a and 2b

a second variant of a forming tool stage of the press according to the invention in cross section and longitudinal section,

Figure 3

a third embodiment of a press according to the invention in longitudinal section,

Figures 4a and 4b

a flow chart for the method according to the invention based on a longitudinal section through the forming tool stage at different times of the press cycle,

Figure 5

an embodiment variant of a forming tool stage of a press according to the invention for the production of hardened sheet metal components in sections,

Figure 6

an alternative embodiment of a forming tool stage of a press according to the invention for Production of hardened sheet metal components in sections in longitudinal section,

Figures 7a and 7b

an alternative embodiment of a press according to the invention for the production of hardened sheet metal components 7a) in longitudinal section and 7b) in horizontal section,

Figures 8a and 8b

an alternative embodiment of a press according to the invention for the production of partially hardened sheet metal components 8a) in longitudinal section and 8b) in horizontal section,

Figure 9a

a time-temperature curve of the sheet metal blank for the method according to the invention in a two-stage press and separate cooling stage and

Figure 9b

a time-temperature curve of the sheet metal blank for the method according to the invention in a three-stage press.

Figure 1 shows a longitudinal section of a press 1 according to the invention with two tool stages, the forming tool stage 2 and a second tool stage 3. An initially unformed sheet metal blank 26 first passes through the forming tool stage 2 and then the second tool stage 3 for forming into a sheet metal component 27. The press 1 has a press ram 6 and a press table 5, two clamping plates 10 being arranged on the press table 5. Each clamping plate 10 furthermore has a plurality of elastic actuators 7 which extend from the clamping plate 10 in the direction of the press ram 6, a tool clamping plate 9 being fixed to the ends of the press ram 6 facing away from the press table 5. The clamping plates 10 are each fixed on the press table 5 via clamping elements 31. In addition, the tool clamping plates 9 are fixed to the ends of the actuators 7 facing away from the press table 5.

A lower tool 12, which comprises the forming tool stage 2 and the second tool stage 3, is fixed to the tool clamping plates 9 via clamping elements 31 ′. Corresponding to the lower tool 12, an upper tool 11 is fixed on the press ram 6, a sheet metal blank 26 being able to be arranged between the upper tool 11 and the lower tool 12. Both the upper tool 11 and the lower tool 12 have cooling channels 17, as a result of which a cooling medium 18 can be conducted. The lower tool 12 also has guide elements 32 ′ which are designed to be insertable into corresponding guide recess 32. The guide elements 32 ′ and guide recesses 32 are designed to correspond to one another and allow the upper tool 12 and the lower tool 11 to be guided with respect to one another. As a result of the floating mounting of the lower tools 12 by the elastic actuators 7, any deviations in position relative to the upper tools 11 transverse to the press movement can be compensated for by means of the guide elements 21 and guide recesses 32. The elastic actuators 7 are in Figure 1 designed as pneumatic spring assemblies, ie they are actuators 7 which can be acted upon by gas pressure and which can be actively controlled. The state of the press at the upper reversal point OP is shown here, whereby it can be seen that the elastic actuators 7 lift the lower tool 12 relative to the press table 5, whereby the path of the closing movement Y of the forming tool stage 2 and the second tool stage 3 is shorter than the press stroke between the upper reversal point OP and the lower reversal point UP of the press 1.

Figure 2a shows a further embodiment of the press 1 according to the invention, the press 1 having two tool stages, but here shown in longitudinal section only the double forming tool stage 2. Behind the forming tool stage 2, the second tool stage 3, which also falls twice, is arranged, which receives the sheet metal blanks 26 that have already been hot-formed in the forming tool stage 2 and cools them down further. The term double means that in the tool stage two components can be thermoformed and cooled at the same time in the press cycle. In contrast to the variant of the Figure 1 are also designed as an elastic actuator 7 mechanical spring assemblies 8, here as a plurality of spiral springs.

Furthermore, the press 1 in the second variant has additional cutting means 33 on the upper tool 11 and cutting means 33 on the lower tool 12, which are used to trim the formed sheet metal blank or the sheet metal component 27 while it is still warm and unhardened. In particular, an edge trimming is carried out here, the upper cutting means 33 ′ being shown by way of example being fixed to the upper tool 11 via elastic actuators 34. The elastic actuators 34, like the actuators 7, can be active or passive. In contrast, the lower cutting means 33 are fixedly and immovably connected to the lower tool 12. A reverse connection of the cutting means 33, 33 'to the forming tool stage 2 is also possible, however. In the image plane on the left it is shown by way of example that the cutting means 33 are firmly but interchangeably connected to the upper tool 11 and lower tool 12. Of course, in practice, the same type of connection can be implemented for both, both for the right and for the left halves of the forming tool stage 2.

Figure 2b shows a cross-sectional view of the second variant of the press 1 through the forming tool stage 2, which is here again arranged on the mechanical spring assembly 8 so that it can move relative to the press table 5. It can be seen here that the cooling channels 17 extend over the entire longitudinal extension of the upper tool 11 and the lower tool 12, whereby (not shown here) an inlet and outlet line of the cooling channels 17 to a cooling source 19, which is located outside the heat exchanger, for example Forming tool stage 2, preferably also outside the press 1, is located.

The Figure 3 shows in a longitudinal section an alternative embodiment of the press 1 according to the invention with a forming tool stage 2 and a second tool stage 3 that follows in the process. It can be seen that elastic actuators 7 in the form of mechanical spring assemblies 8 are arranged on a common press table 5 via a clamping plate 10 . The ends of the elastic actuators 7 facing away from the press table 5 can be coupled to a tool clamping plate 9, which in turn is connected to the lower tool 12 or is an integral part of the lower tool 12. As in the previous Design variants have both the upper tool 11 and the lower tool 12 cooling channels 17 for the passage of a cooling medium 18.

Figure 4a shows the respective operating position of the press 1 and the corresponding forming tool stage 2 based on different times of the press cycle 11 and the lower tool 12 includes and the hot forming takes place. The lower tool 12 is still fully raised by the elastic actuators 7 at this point in time. The closing movement Y of the press 1 is continued continuously. The travel W7 is the portion of the press stroke which, starting from the upper reversal point UP of the press, moves the upper tool 11 and the lower tool 12 towards one another until the forming tool stage 2 is completely closed with the formation of a mold cavity 13.

In Figure 4b the time at which the press 1 is in the upper reversal point OP is shown on the left, but the press 1 is now shown on the right at the time at which the lower reversal point UP is being passed or the distance A between the lower tool, which can be set by the actuators 7 12 and press table 5 is minimal. The press stroke W1 is the distance which the press 1 covers from its upper reversal point OP to its lower reversal point UP.

Figure 5 shows a variant of a forming tool stage 2 of the press 1 according to the invention for producing hardened sheet metal components 27 in sections. The forming tool stage 2 comprises an upper tool 11 and a lower tool 12, each of which has an unheated area 22 and a heated area 21. Cooling channels 17 for the passage of a cooling medium 18 run through the unheated area 22, the cooling channels 17 being connected in such a way that the cooling medium 18 can be fed from the forming tool stage 2 to the outside in a cooling source (not shown), for example a heat exchanger. In this embodiment variant, the heated areas 21 are designed as molded inserts 15 and with the unheated Areas 22 firmly but interchangeably connected. Heating cartridges heated by gas burners or electrical resistance serve as the heating source 14. The forming tool stage 2 can be coupled via the clamping plate 10 on the press ram 6 and additionally via the tool clamping plate 9 and elastic actuators 7 on the press table 5 or on the clamping plate 10 fixed thereon.

In contrast to the aforementioned variant in Figure 5 are in Figure 6 a segmented upper tool 11 and lower tool 12 designed for the production of hardened sheet metal components in sections. A heated area 21 is arranged as a separate mold segment 16 separated from the unheated area 22 by an insulation 20 in the upper tool 11 and in the lower tool 12. This is used for more energy-efficient use of the heating sources 14 and cooling sources. After the mold closing time t ₂ and the first holding time t _{2 '} in the forming tool stage 2, a temperature profile is established in the sheet metal component with a first section at a relatively high temperature and a second section at a lower temperature. This prepares the structural transformation into martensite in the second section and into ferrite and / or pearlite in the first section. Between the first and second section there is a narrow transition section 30 with later relatively undefined mechanical properties.

It is of course possible to provide more than one heated area 21 in the forming tool stage 2 as well as in the second tool stage 3.

Finally in the Figures 7a and 7b a further variant of the entire press 1 for producing hardened sheet metal components 27 in sections is shown. First, in Figure 7a a longitudinal section through the press 1 is shown. It comprises the forming tool stage 2 according to Figure 6 as well as a second, regionally heated tool stage 3 with fixing elements 24 for, in particular, form-fitting reception of the sheet metal component (not shown) and areas 21 heated by heat sources 14 in the form of a further molding segment 16. The molding segment 16 can be of identical design in the forming tool stage 2, or at least with regard to the material, the material quality, the The thermal capacity or the temperature resistance can be designed to be stronger or more robust than in the second tool stage 3.

Furthermore, a transfer bar 25 and in the forming tool stage 2 gripper recesses 25 ', which serve to ensure that when removing the sheet metal component 27, grippers (not shown), which are connected to the transfer bar 25, can approach the sheet metal component as early as possible are indicated by dashed lines. without colliding with the lower tool 12 during the upward movement Z.

In terms of time, the second tool stage 3 is followed by a further tool stage 4, which here primarily serves to further cool down the sheet metal component. Like the unheated area 23 of the second tool stage 3, it has fixing elements 24, as a result of which the sheet metal component can be fixed precisely in position for further cooling. The cooling itself can be done by cooling sources not shown, for example by air ventilation, air or cooling medium shower or by immersion according to the German patent DE 10 2005 028 010 B3 take place in that part of the third tool stage 4 with the sheet metal component 27 can be immersed in the cooling medium.

How Figure 7b clarified, in this embodiment variant each tool step is designed to be doubly falling and has two tools in each of the forming tool step 2, the second tool step 3 and the third tool step 4. The transfer bar for transporting the sheet metal blank or the sheet metal component into or out of the tool stages 2, 3, 4 is not shown. A heating device 35 is indicated in which the sheet metal blanks 26 are heated to Ac3 temperature at least in sections.

In the Figures 8a and 8b an alternative embodiment of the entire press 1 for the production of hardened sheet metal components 27 is shown in FIG Figure 8a as a longitudinal section and in Figure 8b as a horizontal section through the lower tools 12. In contrast to Figure 7 Here, the third tool stage 4 'is arranged separately in another press 36, which has the advantage that the final cooling can be decoupled from the high press cycle and more space in the press 1 for the forming tool stage 2 and second tool stage 3 remains. As an example, a triple-falling forming tool stage 2 and a triple-falling second tool stage 3 and a heating device 35 in front of the press 1 are shown.

In the third tool stage 4 ', one of the sheet metal components 27 produced is shown, the first section 28 and the second section 29 as well as the transition section 30 with the above-described different mechanical properties adapted to the use of the component and different structural structures. Of course, as shown here, the sheet metal component 27 can also be used in the embodiment variant according to FIG Figure 7 manufacture in this way.

Finally shows the Figures 9a and 9b Time-temperature curves of the sheet metal blank 26 or sheet metal components 27 assigned to the last two embodiment variants during the implementation of the method according to the invention.

Starting from a sheet metal blank 26 heated at least in some areas to austenitizing temperature Ac3, a transfer takes place within 2 seconds from the heating device 35 to the forming tool stage 2 of the press 1. Then the closing movement of the press and the tool begins until the forming tool stage 2 is completely closed and the sheet metal blank 26 to the sheet metal component 27 is hot forged. The first holding time t _{2 '} then begins to cool the sheet metal component while the press 1 executes the lower reversal point UP and the upward movement begins. During the upward movement, the forming tool stage 2 is opened with a delay, the sheet metal component 27 having cooled down to different cooling temperatures T _1.1 and T _1.2 due to the different temperatures and / or tool material properties. Another transfer follows within the transfer time t ₃ from the forming tool stage 2 to the second tool stage 3. The sheet metal component 27 is then cooled further while the second tool stage 3 is closed and the component 27 is held in a fixed position. The temperature difference between the cooling temperature T _2.1 and T _2.2 in the sections 28, 29 of the sheet metal component 27 is in turn determined by different cooling rates through the heated and unheated areas 21, 23 of the second tool stage 3 ( Figure 8b ) set.

The transfer then follows within the transfer time t _{5 of} the sheet metal component 27 into the third tool stage 4, 4 ', the Figures 9a and 9b distinguish. Figure 9a corresponds to the variant of the press according to Figure 8 and Figure 9b with the variant according to the Figure 7a and 7b . It can be seen that the cooling at the cooling time t ₆ in Figure 9a lasts longer than in Figure 9b , since the last process takes place with press 1 linked to the cycle time. The cooling temperatures T _3.1 and T _3.2 have come very close and are below 200 ° C in both sections.

Reference number:

• 1 - press
• 2 - forming tool stage
• 3 - Second tool level
• 4, 4 '- Another tool level
• 5 - press table
• 6 - press ram
• 7 - actuator
• 8 - Mechanical spring package
• 9 - mold clamping plate
• 10-10 clamping plate
• 11 - upper tool
• 12 - lower tool
• 13 - mold cavity
• 14 - heating source
• 15 - mold insert
• 16 - shape segment
• 17 - cooling duct
• 18 - cooling medium
• 19 - source of cooling
• 20 - insulation
• 21 - Heated area
• 22 - Unheated area for 2
• 23 - Unheated area for 3
• 24 - fixing element
• 25 - transfer bar
• 25 'gripper recess
• 26 - sheet metal blank
• 27 - sheet metal component
• 28 - First section on 27
• 29 - Second section on 27
• 30 - transition section to 27
• 31 - clamping element
• 32 - guide recess
• 32 'guide element
• 33.33 'cutting means
• 34 - actuator
• 35 - heating device
• 36 - press

• D - thickness to 27
• A - press stroke
• W7 travel
• t ₁ - transfer time
• t ₂ - mold closing time
• t _{2 '} - first hold time
• t ₃ - transfer time
• t ₄ - mold closing time
• t _{4 '} - second holding time
• t ₅ - transfer time
• t ₆ cooling time
• A - distance
• Ac3 austenitization temperature
• Ms - martensite start temperature
• Mf - martensite finishing temperature
• OP - top dead center
• UP - lower dead center
• RT - room temperature
• T _1.1 - cooling temperature
• T _1.2 - cooling temperature
• T _2.1 - cooling temperature
• T _2.2 - cooling temperature
• T _3.1 - cooling temperature
• T _3.2 - cooling temperature
• Y closing movement
• Z- upward movement

Claims (19)

1. Method for manufacturing a sheet metal component (27), cured in sections at least, in a press (1), which comprises a press table (5), a press ram (6) and several die stations (2; 3; 4), characterised by the following steps:

   - heating, at least in sections, of a sheet metal plate (26) to a temperature of greater than the austenitisation temperature Ac3,

   - laying of the heated sheet metal plate (26) in a first forming die station (2) of the press (1),

   - hot forming of the sheet metal plate (26) to form the sheet metal component (27) in the forming die station (2), wherein here the press (1) carries out a closing movement,

   - keeping shut the forming die station (2) for a first holding time (t₂'),

   - cooling the formed sheet metal plate (26) during the first holding time (t₂'), and

   - transfer of the formed sheet metal plates (26; 27) into a second die station (3), wherein the sheet metal component (27) is conveyed by a transfer system, as a linearly guided transfer bar (25) with grippers, in a transfer time (t3, t5) of 1 to 4 seconds between at least two die stations (2; 3; 4),

   - curing, at least in sections, of the sheet metal plate (26) by cooling in the second die station (3) within at least one second holding time (t₄'),

   wherein the forming die station (2) during the closing movement is moved from an upper return point (OP) to a lower return point (UP) of the press (1) by means of at least one resilient actuator (7) relatively to the press (1), such that the hot forming is ended and the keeping-shut starts, before the press (1) reaches the lower return point (UP) and/or that the keeping-shut of the forming die station (2) on the part of the resilient actuator (7) is ended only during the upward movement of the press (1) after the lower return point (UP) of the press (1) has been completely traversed.
2. Method according to claim 1, characterised in that in the forming die station (2) an edge trim and/or a perforation is carried out, in particular before the press (1) is completely closed.
3. Method according to claim 1 or 2, characterised in that the second die station (3) is moved at least in sections during the closing movement of the press (1) by at least one resilient actuator (7) relatively to the press (1), such that the keeping-shut starts before the press (1) reaches the lower return point (UP) and/or the keeping-shut of the second die station (3) at least in sections by a resilient actuator (7) is ended only during the upward movement of the press (1) after the lower return point (UP) of the press (1) has been completely traversed.
4. Method according to any of the preceding claims, characterised in that the forming die station (2) and preferably also the second die station (3) is mechanically, hydraulically or pneumatically spring-mounted by the resilient actuator (7).
5. Method according to any of the preceding claims, characterised in that the sheet metal component (27) is conveyed through the in a transfer time (t₃, t₅) of 2 to 3 seconds between at least two die stations (2; 3; 4).
6. Method for manufacturing a sheet metal component (27) which is cured in sections according to any of the preceding claims, characterised in that in the forming die station (2) a cooling temperature (T_1.1; T_1.2) of the sheet metal (27) component is set which in a first section (28) is greater than the Martensite starting temperature Ms required for the Martensite structure transformation, and which in a second section (29) is less than Ms, wherein the sheet metal component (27) is cooled in the first section (28) in particular to a cooling temperature (T_2.1) of 540 to 660°C.
7. Method according to claim 6, characterised in that in the second die station (3) a cooling temperature (T₂) of the sheet metal component (27) is set which at the end of the second holding time (t₄') in the first section (28) is between 350 and 500°C and in the second section (29) is less than the Martensite finish temperature Mf necessary for the complete Martensite structure transformation, wherein the sheet metal component (27) is cooled in the second section (29) preferably to less than 200°C, in particular to room temperature (RT).
8. Method according to at least one of the preceding claims, characterised in that the sheet metal component (27) is held for a first holding time (t₂') between 2 and 8 seconds and for a second holding time (t₄') between 2 and 10 seconds.
9. Method according to at least one of the preceding claims, characterised in that the cycle time of the press (1) having a forming die station (2) and a second die station (3) between its upper return point (OP) and its lower return point (UP) is between 3 and 11 seconds.
10. Method according to one of claims 1 to 8, characterised in that the curing is ended only in a third die station, wherein thereafter the sheet metal component has in its entirety a cooling temperature (T_3.1, T_3.1) of below 200°C.
11. Method according to claim 10, characterised in that the cycle time of the press (1) having a forming die station (2) and a second die station (3) and a third die station (4) between its upper return point (OP) and its lower return point (UP) is between 3 and 9 seconds.
12. Method according to claim 1, characterised in that the grippers of the transfer system are already brought close to the sheet metal component for the press has reached the upper return point.
13. Press (1) for manufacturing a sheet metal component (27), cured at least in sections, having several die stations (2; 3; 4), a press ram (6) and a press table (5), for carrying out the method according to any of claims 1 to 12, wherein at least one die station (2, 3, 4) is a forming die station (2), which can be cooled at least in regions, for the hot forming of sheet metal plates (26), which comprises an upper die (11) and a lower die (12) which in a closed state form a mould cavity (13), wherein between press table (5) and lower die (12) is arranged at least one resilient actuator (7), such that either the lower die (12) can be raised relatively to the press table (5), and/or the upper die (11) can have pressure applied to it at a distance (A) relatively to the press ram (6) in order to create the closed state of the forming die station (2) before the press (1) is completely closed, characterised in that the upper die and the lower die of the forming die station have cooling channels for the passage of a cooling medium and the cooling channels extend across the entire longitudinal extension of the upper die and the lower die, wherein externally to the forming die station is provided a cooling source in the form of a heat exchanger as well as a feed line and discharge line from the cooling channels to the heat exchanger, wherein furthermore a transfer system is assigned to the press, which transfer system is in the form of a linearly guided transfer bar (25) with grippers, in order to convey the sheet metal component (27) between at least two die stations (2; 3; 4) of the press (1).
14. Press (1) according to claim 13, characterised in that by means of the resilient actuator (7) a vertical actuating path (W7) can be set, wherein the actuating path (W7) amounts to less than the maximum press lift path (W1) between the upper and lower return points (OP, UP) of the press (1), however at least 100 mm.
15. Press (1) according to claim 13 or 14, characterised in that the resilient actuator (7) has an actuating force which increases at least across a part of an actuating path (W7) from the upper return point (OP) to the lower return point (UP) of the press (1), in particular, the actuating force is at least 20% greater in the closed state of the forming die station (2).
16. Press (1) for manufacturing a sheet metal component (27), cured in sections, according to any of claims 13 to 15, characterised in that at least the forming die station (2) can be heated in regions by a heating source (14), in order in a first section (28) to effect a reduced cooling speed in the sheet metal component (27), wherein unheated regions (22) have cooling channels (17) for the passage of a cooling medium (18).
17. Press (1) according to any of claims 13 to 16, characterised in that both the forming die station (2) as well as at least the subsequent second die station (3) can be heated in regions, in particular by a heating source (14), in order in a first section (28) to obtain a sheet metal component (27) which is at least not completely cured.
18. Press (1) according to claim 17, characterised in that the unheated region (22) of the second die station (3) at least corresponding to a transition section (30) between first section (28) and second section (29) of the sheet metal component (27) has an active cooling source (19).
19. Press (1) according to claim 18, characterised in that the first section (28) and the transition section (30) of the sheet metal component (27) can be fixed at least in the second die station (3) in form-fitting manner by means of fixing elements (24).

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