Hot forming and press hardening tool and method for the operation thereof

Abstract

The present invention relates to a hot forming and press hardening tool (1), comprising an upper tool (2) and a lower tool (3) which can be moved towards one another in a press stroke direction (4), wherein a mold cavity (10) is formed between the upper tool (2) and the lower tool (3) in the closed state, and cooling channels (13) for conducting a cooling medium are formed in the upper tool (2) and / or the lower tool (3), wherein at least one cutting tool (7) which can be moved relative to the upper tool (2) is arranged on the upper tool (2), characterized in that the cutting tool (7) has at least one cooling channel for temperature control and / or that the cutting tool (7) has a forming surface (8) oriented in the press stroke direction (4) and a cutting edge (9) lying behind it in the press stroke direction (4) and / or adjacent to the forming surface (8).

Description

[0001] The present invention relates to a hot forming and press hardening tool according to the features in the preamble of claim 1.

[0002] The present invention further relates to a method according to the features in claim 10.

[0003] Hot forming and press hardening technology is well known in the art. For this purpose, steel sheet blanks are used, particularly in the automotive industry, which are heated to a temperature above the austenitizing temperature, i.e., above the Ac3 temperature, which is usually more than 900°C. The blank, heated in this way, is placed in a hot forming tool and formed while hot. The forming properties are particularly good in terms of shaping freedom. Once the forming process has been completed, at least partially, or in particular completely, the component produced in this way is left in the hot forming tool and further quenched. This means that it is brought to a temperature in a particularly short time so that the austenite previously formed due to the austenitizing temperature is at least partially converted into martensite.In this way, tensile strengths Rm of greater than 1000 MPa, in particular even more than 1250 MPa, and particularly preferably more than 1400 MPa, are achieved in the component. For example, a quenching temperature greater than 27 K / s is selected. When a final temperature of, for example, less than 300°C, in particular less than 200°C, is reached, the hard component thus produced is then removed from the hot forming tool.

[0004] It is known from the prior art to process these components mechanically or by cutting. For example, a cutting operation is performed during hot forming and / or after completion of the hot forming or press hardening process.

[0005] For example, such a manufacturing process is known from DE 10 2011 116 714 A1. The forming process is carried out using a forming tool segment. Subsequently, a separating slide is activated, which separates the formed component in the closed hot forming tool.

[0006] The object of the present invention is to optimise the degrees of freedom in shaping as well as the optimisation of the trimming process, especially taking into account thermal losses during the forming process, compared to the state of the art for large-scale production.

[0007] The above-mentioned object is achieved according to the invention with the features in claim 1.

[0008] A process-related part of the problem is solved according to the invention with the features in claim 10.

[0009] The hot forming and press hardening tool has an upper tool and a lower tool. The upper tool and lower tool can be moved towards each other in the press stroke direction. The press stroke direction is essentially vertical. When closed, a mold cavity remains between the upper tool and the lower tool. The previously inserted sheet metal blank or steel sheet blank is then formed into the component in this mold cavity. The closed hot forming and press hardening tool, with its upper tool and lower tool, essentially lies against the formed component over its entire surface. In order to carry out a press hardening process after the hot forming process, cooling channels for the passage of a coolant are formed in the upper tool and lower tool. A coolant is passed through the tool during, or at the latest after, the forming process has been completed in order to quench harden the formed component.

[0010] Furthermore, at least one cutting tool that can be moved relative to the upper tool is arranged in the upper tool.

[0011] According to the invention, the forming of hot forming and press-hardening tools is now characterized in that the cutting tool itself has at least one cooling channel. This cooling channel is, in particular, controlled separately from the cooling channels in the upper and lower tools. With the help of this at least one cooling channel, the cutting tool can be individually temperature-controlled. Appropriate supply and discharge lines are provided on the cutting tool. Thus, according to the invention, it can be ensured that a temperature between 500°C and 700°C is set at the cutting edge of the component during trimming. By further cooling after trimming, the trim edge on the component can then also be press-hardened accordingly.

[0012] Alternatively or additionally, the invention is characterized in that the cutting tool has a forming surface oriented in the press stroke direction and a cutting edge located behind it in the press stroke direction and / or adjacent to the forming surface. The cutting edge is thus formed on the cutting tool itself. A steel sheet blank placed on a hold-down device or on the lower tool is thus initially formed by the forming surface of the cutting tool when the hot forming and press hardening tool is closed in the press stroke direction. In particular, with the tempering of the cutting tool, cooling at the beginning of the forming process is not so severe that press hardening would occur. The cutting movement is preferably only carried out when the hot forming tool is at bottom dead center.Another significant advantage is that the forming surface on the cutting tool itself allows for greater precision with regard to the cutting line or cutting contour to be created. Since the cutting tool is involved, especially in the forming process itself, its geometric position is optimal in terms of precision for the trimming that takes place immediately after the forming process. The cutting tool thus pre-centers the cutting edge.

[0013] For this purpose, the cutting tool is designed, in particular, as an elongated tool and is arranged in particular in an edge region of the upper tool. For example, elongated automotive components, such as vehicle pillars, for example, an A-pillar or B-pillar, can be trimmed with the highest precision, at least in a partial area. At the same time, however, not only the cutting geometry but also the material properties in the area of ​​the resulting cut edge on the component are optimized due to the temperature control of the cutting tool and the associated possibility of controlling the microstructure transformation during the press hardening process.

[0014] Furthermore, a cutting edge is preferably formed on the lower tool, which corresponds to the cutting edge of the cutting tool and then performs a trim due to the relative movement of the cutting tool to the lower tool. The lower tool is in particular firmly coupled to a lower press table. The cutting edge of the lower tool can be formed directly and immediately on the lower tool. However, the cutting edge of the lower tool can be designed as an insert or segment. If, for example, the cutting edge of the lower tool were to wear, it can be replaced, thus achieving a highly accurate trim edge.

[0015] The forming surface of the cutting tool itself is, in particular, a rounded edge. Particularly when the cutting tool is arranged on an outer edge region of the upper tool, an edge region of the component to be formed is bent correspondingly to the lower tool according to the principle of deep drawing or bending. The forming surface can be variably designed or change over the length of the cutting tool. The forming surface is therefore not a radius that runs constantly in the longitudinal direction of the cutting tool. Different radii chamfers or forming surfaces can be formed on the forming surface of the cutting tool. This allows a three-dimensional, complexly shaped component to be manufactured and subsequently trimmed. The cutting edge itself does not have to be straight, but can have a variable profile, adapted to the shape geometry of the component to be produced later.

[0016] As the lowering movement continues and the bottom dead center is reached, a mold cavity is formed between the upper and lower tools. After the forming process is complete, the forming surface of the cutting tool is no longer part of the mold cavity. The separating operation then takes place. In this sense, the cutting edge of the cutting tool forms the outer boundary of the mold cavity. By executing the cutting movement, the mold cavity is then limited to the outside with respect to the resulting cutting edge on the component.

[0017] The cutting tool itself is designed as a segment and is mounted in a floating manner on or in the upper tool.

[0018] The cutting tool, in particular, has an elongated extension. This elongated extension is in particular more than 15 cm, particularly preferably more than 20 cm, and especially more than 30 cm long. Thus, a particularly long cutting edge can be trimmed with high precision using the cutting tool according to the invention, both in terms of geometry and the material properties to be adjusted. The elongated extension of the cutting tool can then also essentially correspond to the length of the cutting edge.

[0019] To enable the cutting tool to move relative to the upper tool, it is preferably driven directly by an actuator. The actuator is preferably a hydraulic actuator, in particular a hydraulic actuating cylinder. Preferably, several hydraulic actuating cylinders are provided. These then extend in the direction of movement of the cutting tool.

[0020] If higher cutting forces are required, the cutting tool can preferably be driven by a force transducer, particularly in the form of a wedge valve. The wedge valve itself is then moved by an actuator.

[0021] The direction of movement of the cutting tool itself is essentially transverse to the press stroke direction. In particular, the direction of movement of the cutting tool is oriented at an angle between 40° and 90°, in particular between 50° and 90°, and particularly preferably between 60° and 90°, between the direction of movement of the cutting tool and the press stroke direction of the hot forming tool. The press stroke direction of the hot forming tool is essentially vertical. In simplified terms, the direction of movement of the cutting tool can then be essentially horizontal or run at the angles specified above.

[0022] The cutting tool continues to be mounted in a floating manner on the upper tool. In particular, for example, the predetermined cutting geometry of the resulting cutting edge of the formed component can be determined by the cutting edge of the lower tool. The floating mounting of the cutting tool then allows the cutting tool to shift slightly transversely and / or vertically to its actual direction of movement when executing the cutting movement, thus optimally aligning itself with the cutting edge of the lower tool. This enables a particularly high level of cutting geometry accuracy. For this purpose, for example, the cutting tool itself is spring-loaded in the press stroke direction. The cutting tool can, for example, have an axial degree of freedom in its direction of movement or be axially guided.

[0023] The present invention relates to a method for producing a hot-formed and press-hardened component. In particular, the production is carried out on the previously described hot-forming and press-hardening tool. The method is characterized by the following process steps: Heating a steel sheet blank to above Ac3 temperature, placing it in the hot forming tool and carrying out the forming operation until the bottom dead center is reached. After reaching the bottom dead center, carrying out the separating operation by moving the cutting tool relative to the upper tool, whereby the cutting edge has a temperature between 500°C and 700°C at the start of the separating operation and / or during the separating operation. Quenching hardening of the formed component and removal.

[0024] This means that a steel sheet blank made of a hardenable steel alloy, for example 22MnB5, is heated to above Ac3 temperature. This is a temperature above the authenticating temperature and is regularly more than 900°C. The thus heated steel sheet blank is then placed in the combined hot forming and press-hardening tool, and the forming operation is carried out. During contact with the tool surfaces, the heated steel sheet blank or the partially formed component cools down as an undesirable side effect. However, this is negligible. In particular, the forming operation is carried out in a time of less than 3 seconds. Particularly preferably, the time between, for example, removal from a heating furnace, insertion into the hot forming tool, and completion of the forming operation is less than 10 seconds.

[0025] The forming operation is understood to mean the execution of the movement in the direction of the press stroke so that the upper tool and lower tool are together at the so-called bottom dead center, i.e., no further relative movement between the upper tool and lower tool occurs, and the sheet steel blank is completely formed into the desired component. According to the invention, part of the forming operation is carried out by the cutting tool itself, in particular the forming surface of the cutting tool.

[0026] While the bottom dead center is being reached or immediately after the bottom dead center is reached, the separating operation is then carried out with the cutting tool according to the invention on at least one component edge to be produced, so that a cutting edge is produced on the formed component. This cutting edge has a length that corresponds in particular to at least 10% of the circumferential length of the formed steel sheet material. The cut is carried out on a component edge and is an edge trim. The material or the substance in the component edge, i.e. at the resulting cutting edge, has a temperature between 500°C and 650°C at the beginning and / or during the separating operation. The temperature can also still be in the aforementioned range after the separating operation has been completed. This is particularly possible because the cutting tool is separately temperature-controlled due to the at least one cooling channel in the cutting movement.Immediately after the cutting operation, cooling of the cutting tool can also produce press hardening of the outer cutting edge. The desired material structure, including the cutting edge area, can thus be reliably produced for large-scale production.

[0027] After completion of the forming operation and / or after completion of the trimming operation, the entire component is then press-hardened in the hot forming and press-hardening tool. Here, an appropriate cooling medium is passed through the upper and lower tools, thus initiating at least partial, and in particular complete, martensite transformation of the formed and trimmed component.

[0028] The cutting operation itself is preferably carried out completely. The separated portion is then removed via a corresponding scrap removal or disposal process. However, according to the invention, it is also possible for the cutting operation to be carried out only partially. This means that at least 50% of the wall thickness of the formed component is cut through. In a later processing step, the remaining wall thickness is then trimmed off in a final cutting operation.

[0029] Further advantages, features, properties, and aspects are the subject of the following description. Preferred embodiments are illustrated in schematic figures. These serve to facilitate understanding of the invention. They show: Figure 1 shows a hot forming and press hardening tool according to the invention in the open state with inserted sheet metal blank, Figure 2 shows the tool in a partially closed state, Figure 3 shows the tool at bottom dead center, Figure 4 shows the tool at bottom dead center with executed trimming movement, Figures 5a to d show an example of the closing of the hot forming tool and execution of a cutting movement, Figure 6 shows a different movement of the cutting tool by means of a direct actuator or a wedge slide, Figure 7 shows the cutting tool according to the invention according to the section line AA from Figure 6 .

[0030] In the figures, the same reference symbols are used for the same components, even if a repeated description is omitted for the sake of simplicity.

[0031] Figure 1shows a hot forming and press hardening tool 1 according to the invention in the open state. This tool has an upper tool 2 and a lower tool 3. The upper tool 1 is designed here as a female die, the lower tool 3 as a male die. Relative to the vertical direction V, the lower tool 3 is thus raised in the press stroke direction 4. However, within the scope of the invention, it is conceivable for the lower tool 3 to be fixedly arranged and for the upper tool 2 to be lowered onto the lower tool 3 or lowered into the lower tool 3.

[0032] This movement takes place in the press stroke direction 4. Upper tool 2 and lower tool 3 each have cooling channels 5.

[0033] An inserted steel sheet blank 6, hereinafter also referred to as a sheet blank, is placed on the lower tool 3. Cutting tools 7 according to the invention are arranged on the left and right sides of the upper tool 2. Each cutting tool 7 is arranged in the region of an outer edge of the upper tool 2. The cutting tool 7 has a forming surface 8 directed in the press stroke direction 4.

[0034] According to Figure 2 Here, the lower tool 3 has been raised in the press stroke direction 4. The blank bends around the forming surface 8 of the cutting tool 7 in the press stroke direction 4, then follows the Figure 4 described cutting edge 9. By further moving together in the press stroke direction 4, the Figure 3The position shown is assumed. This is then the bottom dead center. Thus, the upper tool 2 and lower tool 3 are completely closed in the press stroke direction 4. This results in a mold cavity 10, and within the mold cavity 10, a blank (not shown in detail) rests almost completely on the surface. The cutting tool 7, in particular the forming surface 8 of the cutting tool 7, no longer rests against the blank (not shown in detail).

[0035] Immediately upon reaching or immediately after reaching the bottom dead center, the cutting tool 7 then executes a movement in the direction of movement 11. This direction of movement 11 is arranged at an angle α of preferably 40° to 90° with respect to the press stroke direction 4.

[0036] The cutting edge 12 of the cutting tool 7 corresponds to a cutting edge 9 of the lower tool 3. As a result, a piece of sheet metal projecting beyond it is cut off, and thus severed, due to the cutting movement 11 or shearing movement.

[0037] A cooling channel 5 is arranged in the cutting tool 7 itself. The temperature of the cutting tool 7 can then be adjusted based on this at least one cooling channel 5. The cutting tool 7 can, for example, have residual heat, so that until the start of the cutting process, the sheet metal blank resting against the cutting tool 7 is only insignificantly cooled, but in particular, is not partially hardened, at least in this area, so that the cutting process can be performed in the soft or unhardened area.

[0038] Figures 5a to d show the process of Figure 1 to Figure 4 again in a detailed view. According to Figure 5aA steel sheet blank 6 is placed on the lower tool 3. The lower tool 3 is then moved into the upper tool 2 in the press stroke direction 4, so that the forming process begins, shown in Figure 5b The outer part of the steel sheet 6 is then bent. This occurs in particular due to a contact with the forming surface of the cutting tool 7. Figure 5c The forming process is complete. Upper tools 2 and lower tools 3 have moved into each other and are at bottom dead center. The outer part of the steel sheets, in this case the formed component, protrudes outward from the mold cavity 10.

[0039] According to Figure 5d, the cutting tool 7 is then moved in the direction of movement 11 and separates the outer part of the formed component. This occurs due to a corresponding cutting movement when the cutting edge 12 of the cutting tool 7 passes the cutting edge 12 of the lower tool 3, thus executing the cutting movement.

[0040] Figure 6 shows, on the left side of the image plane, a cutting tool 7 directly driven by an actuator 15, also shown in the Figures 1 to 4This can be a hydraulic cylinder, for example. The actuator 15 moves the cutting tool 7 directly in the direction of movement 11. For this purpose, the cutting tool 7 is floatingly mounted on the upper tool 2. In the press stroke direction 4, the cutting tool 7 can be spring-mounted, for example, via spring elements 16, so that a certain amount of play in the press stroke direction 4 is possible. During a subsequent cutting movement, it is thus possible that the cutting edge 12 of the lower tool 3 in particular is passed with corresponding precision. When the bottom dead center is reached, the cutting tool 7 can rest on a lower slide rail 17, which can be fastened, for example, to a part of the lower tool 3, so that it is guided on the slide rail 17 and on the upper side by spring mounting.

[0041] If increased forming forces are necessary, the movement in the direction of movement 11 can be translated using a wedge slide 18, allowing higher forces to be applied to execute the cut. This is the case, for example, if the cutting edge extends into the image plane over more than 20 cm, especially more than 30 cm. The wedge slide 18 itself can also be driven by an actuator 15. However, due to the translation between the wedge slide 18 and the cutting tool 7, a higher cutting force can be applied.

[0042] Within the scope of the invention, both drives can also be combined, especially if, for example, two cutting tools 7 are coupled to the upper tool 2 and one cutting tool 7 only needs to apply low cutting forces due to a short cutting edge on the component. However, another cutting tool 7 requires increased cutting force, for example, with a cutting edge of more than 20 cm, in particular more than 30 cm.

[0043] Figure 7 shows a sectional view along section line AA from Figure 6. The cutting tool 7 can be seen, which has a corresponding length L. This length L corresponds to the length L of the cutting edge to be produced on a component and can, for example, be more than 20 cm, in particular more than 30 cm long. The cutting tool 7 is mounted in the upper tool 2 in the press stroke direction via spring means 16. The cutting tool 7 can also have an upper slide rail 19 between the spring means 16 and the upper tool 2. The cutting tool 7 is mounted on corresponding slide rails 17 on a lower tool 3 and rests on these. Further axial guide elements 20 can be provided. Reference symbol:

[0044] 1 -Hot forming and press hardening tool 2 -Upper tool 3 -Lower tool 4 -Press stroke direction 5 -Cooling channels to 2, 3 6 -Steel sheet blank 7 -Cutting tool 8 -Forming surface to 7 9 -Cutting edge to 7 10 -Mold cavity 11 -Movement direction to 7 12 -Cutting edge to 3 13 -Cooling channel to 7 14 -Outer part 6 15 -Actuator 16 -Spring element 17 -Sliding rail 18 -Wedge slide 19 -Upper sliding rail 20 -Axial guide element L -Length V -Vertical direction α -Angle

Claims

1. Hot forming and press hardening tool (1), comprising an upper tool (2) and a lower tool (3), which are movable towards one another in a press stroke direction (4), wherein a mold cavity (11) is formed between the upper tool (2) and the lower tool (3) in the closed state, and cooling channels (5) for conducting a cooling medium are formed in the upper tool (2) and / or lower tool (3), wherein at least one cutting tool (7) movable relative to the upper tool (2) is arranged on the upper tool (2), characterized in that the cutting tool (7) has at least one cooling channel (13) for temperature control and / or that the cutting tool (7) has a forming surface (8) oriented in the press stroke direction (4) and a cutting edge (9) located behind it in the press stroke direction (4) and / or adjacent to the forming surface (8).

2. Hot forming and press hardening tool (1) according to claim 1, characterized in thatthe cutting tool (7) is arranged in an edge region of the upper tool (2).

3. Hot forming and press hardening tool (1) according to claim 1 or 2, characterized in that a cutting edge (12) is formed on the lower tool (3), which carries out a cutting movement with the cutting tool (7).

4. Hot forming and press hardening tool (1) according to one of the preceding claims, characterized in that the forming surface (8) is a rounded edge, wherein in particular the forming surface changes in the longitudinal direction of the cutting tool (7).

5. Hot forming and press hardening tool (1) according to one of the preceding claims, characterized in that the cutting tool (7) is designed as a segment, in particular has an elongated extension of more than 15 cm, in particular more than 20 cm and in particular more than 30 cm.

6. Hot forming and press hardening tool (1) according to one of the preceding claims, characterized in thatthe cutting tool (7) is driven directly via an actuator (15) or that the cutting tool (7) is driven via a force translator (18), in particular in the form of a wedge mechanism.

7. Hot forming and press hardening tool (1) according to one of the preceding claims, characterized in that the direction of movement of the cutting tool (7) is oriented at an angle to the press stroke direction between 40° and 90° inclusive, in particular between 50° and 90°, particularly preferably between 60° and 90°.

8. Hot forming and press hardening tool (1) according to one of the preceding claims, characterized in that the cutting tool (7) is floatingly mounted on the upper tool (2).

9. Hot forming and press hardening tool (1) according to one of the preceding claims, characterized in that that the cutting tool (7) is spring-elastically mounted in the press stroke direction (4).

10. Method for producing a hot-formed and press-hardened component, in particular on a hot-forming and press-hardening tool (1) according to the features in claim 1, characterized by the following process steps: - heating a steel sheet blank to above Ac3 temperature, - placing it in a hot forming and press hardening tool (1) and carrying out the forming operation - reaching the bottom dead center, - after reaching the bottom dead center, carrying out the separating operation by moving the cutting tool (7) relative to the upper tool (2), wherein the cutting edge has a temperature of 500°C to 700°C at the start of the separating operation and / or during the separating operation - quench hardening of the formed component at least in sections and removal.

11. Method according to claim 10, characterized in that the cutting operation is carried out completely or that the cutting operation is carried out to at least 50%, based on the wall thickness of the formed component.

12. Method according to claim 10, characterized in that in the trimmed edge, a tensile strength Rm greater than 1350 MPa is achieved by cooling and press hardening after trimming.

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