DE102006015666B4 - Method for producing a metallic molded component by hot forming with a simultaneous trimming operation - Google Patents

Abstract

Method for producing a metallic molded component (1), in particular a body component, from a semi-finished product (2) made of a hardenable, hot-formable steel sheet, wherein the molded component (1) is produced from the semi-finished product (2) by means of hot forming and wherein the semi-finished product (2) or the molded component (1) is trimmed, characterized in that the trimming takes place in the same process step as the hot forming.

Description

The invention relates to a method for producing a metallic molded component, in particular a body component, from a semi-finished product made from a hardenable, hot-formable steel sheet according to the preamble of claim 1, as for example from DE 102 54 695 B3 emerges as known. The invention further relates to a combination tool for producing a metallic molded component by combined hot forming, hardening and trimming.

In vehicle body construction, high-strength and ultra-high-strength steel materials are increasingly being used, which - depending on their composition and heat treatment - have very high strengths. The production of body components from such high-strength steel sheets is preferably carried out in a hot forming process in which - such as in DE 24 52 486 A1 or the DE 100 49 660 A1 described - a circuit board is heated and then shaped and hardened in a special mold. By appropriately selecting the process parameters during hot forming, the strength and toughness values of the component can be specifically adjusted.

To produce such a component using hot forming, a blank is first cut out of a coil, which is then heated above the structural transformation temperature of the steel material, above which the material structure is in the austenitic state, inserted into a forming tool in the heated state and formed into the desired component shape and is cooled with mechanical fixation of the desired forming state, whereby the component is tempered or hardened.

However, in order to cut a component manufactured in this way to true dimensions, a high level of equipment is required: in particular, very high cutting forces are required for cold cutting of hardened materials, which leads to rapid tool wear and high maintenance costs. Furthermore, cold trimming of such high-strength components is problematic because, for example, the component edges trimmed in the cold state have more or less large burrs, which can lead to rapid crack formation in the component due to the high notch sensitivity of the high-strength materials.

To avoid these difficulties that arise when mechanically cutting the hardened components, alternative cutting methods are often used, such as laser cutting or water jet cutting. Although these methods can be used to achieve high-quality trimming of the component edge, these cutting methods work comparatively slowly because the cycle times depend directly on the length of the cutting edge and the tolerances that must be maintained. The final trimming process therefore represents a bottleneck in the production of hot-formed components, which limits the number of components that can be produced per unit of time.

To avoid such a final pruning process, in the genus DE 102 54 695 B3 suggested trimming the component before hot forming. For this purpose, a component blank is first formed from a circuit board in a cold forming step, which already has (approximately) the desired three-dimensional shape of the finished component. This blank is then trimmed to near-net shape and finally calibrated and hardened in a hot forming tool. Since the component blank already has approximately the desired dimensions at the start of hot forming, only a relatively small adjustment or correction of the component contour is necessary during hot forming. This means that the component edges are only changed insignificantly, so that there is no need for final trimming of the component edges.

When using the in the DE 102 54 695 B3 Using the method described, a final trimming operation of the component after hot forming can be dispensed with. However, this requires the component blank to be preformed, so that the three-dimensional component contour is generated in two forming steps - a cold forming step, followed by a hot forming step. This is accompanied by increased tool costs for two forming tools.

WO 2005/120 741 A2 shows a device for cutting high-strength sheet metal, the method being based on a conventional shearing process in which a workpiece is divided by introducing sufficiently large shear stresses. If these shear stresses are superimposed on tensile stresses, which promote the initiation of workpiece separation. This tensile stress or tensile force component acts transversely to the desired bending line to be created. The tensile stresses are generated by bending stress on the workpiece. The bending stress is selected such that the resulting tensile stress lies on a side of the workpiece facing the cutting tool.

Due to the simultaneous bending stress and shear stress on the work to be separated The formation of a parting plane in the workpiece to be separated is significantly promoted. There is a drastic reduction in cutting forces and an equally drastic reduction in tool wear while at the same time improving the quality of the cut surface.

DE 100 49 660 A1 shows a process diagram that is used to produce a spatially shaped structural part, which consists of a base plate and a smaller, locally arranged reinforcing plate. The base sheet of the structural part is connected in the flat state to the reinforcing sheet at the location predetermined for the later reinforcement point and the parts of the composite sheet patched in this way are then formed together in a forming press using an openable and closable forming tool.

In order to improve the manufacturing process with regard to the process product and result as well as to relieve the burden on the means involved in the process, the patched composite sheet is heated to a temperature above the forming temperature of the material before the joint forming, is formed into the desired shape in the warm state with moderate tool stress and then under mechanical fixation of the desired forming state in the closed forming tool and / or in a subsequent fixing and trimming tool cooled in a defined manner and thereby specifically heat treated.

The invention is based on the object of proposing a method for producing molded components from hot-formable sheets, in which the tool costs for forming the three-dimensional component contour are reduced and at the same time a final trimming of hardened areas following hot forming is minimized or eliminated entirely. Furthermore, a tool should be provided that is suitable for carrying out this method.

The object is achieved according to the invention by the features of claims 1 and 6.

The molded component is then trimmed in the same process step as hot forming. Selected edge areas of the component are cut off during the hot forming process or immediately after the hot forming. For this purpose, a combination tool is advantageously used in which the component is both formed and selectively cooled (press-hardened) as well as trimmed (at least in areas).

To produce the press-hardened, trimmed component, an appropriately sized, possibly already pre-formed semi-finished product made of hardenable, hot-formable steel sheet is heated and inserted into the combination tool. In this combination tool, the semi-finished product is formed into the desired three-dimensional shape while warm and cooled to a defined extent while mechanically maintaining the forming state. Preferably, the trimming of the component edges in the combination tool follows immediately after the three-dimensional contour has been formed. The residual heat from the hot forming is used: the trimming is expediently carried out at a temperature between 400° C and 700° C. At these temperatures, the final strength or final hardness of the press-hardened component has not yet been reached, so that the trimming takes place in one while still in a soft state. As a result, the trimming operation can be carried out without high tool wear using a conventional mechanical cutting tool arranged in the combination tool; There is no need for subsequent laser or water jet cutting of the finished component.

The combination tool includes an upper tool and a spring-loaded die, which protrudes beyond the cutting punches arranged on the edge in the closing direction when the tool is open. When the upper tool is lowered onto a heated semi-finished product placed in the die, the three-dimensional component shape is formed between the die and the upper tool; At the same time or immediately afterwards, the edge of the component is trimmed using the cutting punches when the die is lowered by the press force and laterally protruding component edges are sheared off between the die edge and the cutting punches.

The invention is explained in more detail below using an exemplary embodiment shown in the figures.

• 1 ein Verfahrensschema des Herstellungsprozesses eines pressgehärteten Bauteils:
• 1a Zuschneiden eines Halbzeugs;
• 1b Erhitzen, Warmumformung und Beschneiden der Ränder;
• 2 eine schematische Darstellung eines Kombinationswerkzeug zum Warmumformen und Beschneiden:
• 2a Einlegen des Halbzeugs in das geöffnete Kombinationswerkzeug;
• 2b Umformung;
• 2c Beschneiden.

Show:

• 1 a process diagram of the manufacturing process of a press-hardened component:
• 1a Cutting a semi-finished product;
• 1b Heating, hot forming and trimming the edges;
• 2 a schematic representation of a combination tool for hot forming and trimming:
• 2a Inserting the semi-finished product into the opened combination tool;
• 2 B reshaping;
• 2c Trimming.

1a and 1b show a schematic representation of a method for producing a spatially shaped, press-hardened (ie hot-formed and specifically cooled) molded component 1 from a semi-finished product 2. In the present exemplary embodiment, a circuit board 2 'is used as the semi-finished product 2, which consists of an unwound sheet metal coil made of hardenable, hot-formable steel sheet is cut out. Alternatively, a composite sheet can be used as a semi-finished product, which - as in the DE 100 49 660 A1 described - consists of a base sheet and at least one reinforcing sheet. Furthermore, a tailored blank can be used as a semi-finished product, which consists of several sheets of different material thickness and/or different material properties welded together. Alternatively, the semi-finished product can be a three-dimensionally shaped sheet metal part produced by any forming process, which is to undergo further forming and a local or cross-component strength increase using the method according to the invention. The semi-finished product can be provided with a corrosion protection layer made of a metal or an alloy, in particular also with a protective layer made of an intermetallic compound.

In a first process step, the circuit board 2' - as in 1a shown - cut out from an unwound and straightened section of the coil 5 made of hot-formable sheet metal. At this point, the hot-formable material is in a “soft” (ie unhardened) state, so that the circuit board 2′ can be easily cut out using conventional mechanical cutting means - for example using lifting scissors 4. In large-scale production, the blank 2' is advantageously cut to size with the aid of a blank press 6, which enables the coil 5 to be fed automatically and the cut blank 2' to be automatically punched out and removed.

The cut boards 2 'are placed on a stack 7 and are fed in stacked form to a hot forming station 8 (see 1b) . In this hot forming station, the semi-finished product 2 is subjected to a combined hot forming and trimming operation, in which the semi-finished product 2 is brought into the three-dimensional molded component 1, hardened across components or locally and trimmed at least in sections. For this purpose, the semi-finished product 2 is first inserted by a manipulator 9 into a continuous furnace 10, where it is heated to a temperature that is above the structural transformation temperature into the austenitic state; Depending on the type of steel, this corresponds to heating to a temperature between 700°C and 1100°C. Advantageously, the atmosphere of the continuous furnace 10 is inerted by a targeted and sufficient addition of a protective gas in order to prevent scaling of uncoated interfaces of the semi-finished products 2 or - when using uncoated sheets - of the entire semi-finished product surface.

The heated semi-finished product 2 is inserted with the aid of a manipulator 11 into a combination tool 12, in which the three-dimensional shape of the molded component 1 is generated. In the combination tool 12, the heated semi-finished product 2 is formed and quickly cooled, whereby a fine-grained martensitic or bainitic material structure is set. This process step corresponds to hardening of the molded component 1 and enables the material strength to be specifically adjusted. Details and various configurations of this hardening process are, for example, in DE 100 49 660 A1 described, the disclosure content of which is hereby incorporated into the present application. Immediately after the hot forming and during the process for targeted cooling, the formed molded component 1 is trimmed in the combination tool 12. The trimming takes place at a point in time at which the three-dimensional component shape has already been fully formed (at least locally), but at which there is still so much residual heat in the molded component 1 that the hardening of the molded component 1 has not yet been completely completed; During trimming, the area of the component 1 to be trimmed is still in a “soft” or at least in a “not completely hardened” state, so that the trimming can be done with the help of a conventional mechanical tool, for example a cutting insert 20, 20 'in the combination tool 12 , can be carried out.

The combination tool 12 includes an upper tool 13, which is attached to a press ram 14 of a forming press 15 (see 2a) . Furthermore, the combination tool 12 includes a die 17, which is mounted on a press table 16 of the forming press 15 via force elements 18. The force elements 18 are hydraulic, pneumatic or mechanical springs 18 ', with the help of which a counterforce is built up against the upper tool 13 mounted on the press ram 14. Upper tool 13 and die 17 have functional surfaces 13 ', 17' between which the semi-finished product 2 is formed. Cutting punches 19 with cutting inserts 20 are arranged on the edge 21 of the die 17, with which the molded component 1 is trimmed after forming or during the forming process. The cutting punches 19 can surround the die 17 in a ring shape, so that the entire outer edge of the mold component 1 is trimmed; alternatively, the cutting punches 19 can also only be used in selected areas of the matrix edge 21 can be arranged. For cutting out recesses, holes, etc. in the interior of the component, you can still use it - as in 2a indicated by dashed lines - column-shaped cutting punch 19 'with cutting inserts 20' can be provided, which are guided in recesses 22 of the die 17.

The functionality of the combination tool 12 during the combined forming, press hardening and trimming is shown in the 2a until 2c explains:

2a shows the combination tool 12 in the open state. In this state, the die 17 is pressed so far in the direction of the upper tool 13 by the force elements 18 that the functional surface 17 'of the die 17 in the closing direction 23 of the press 14 is offset 25 relative to the cutting inserts 20, 20' of the cutting punches 19, 19'. are offset.

The semi-finished product 2 heated in the hot forming station 8 is inserted into the opened combination tool 12. Since the die 17 is raised relative to the cutting punches 19, 19 'due to the pressure force of the force elements 18, the semi-finished product 2 rests on the die 17 without touching the cutting tools 20, 20'. When the press ram 14 is lowered, the semi-finished product 2 is formed between the upper tool 13 and the die 17. Due to the pressure force of the force elements 18 counteracting the press pressure, the die 17 remains in the in 2a raised position shown; The die 17 is therefore not lowered (or only insignificantly) by the press pressure during the forming process. Is the three-dimensional shape of the molded component 1 completely formed ( 2 B) , the upper tool 13 presses the die 17 back against the pressure force of the force elements 18 towards the press table 16 when the press ram 14 is lowered further. When the die 17 is submerged, the edge 24 of the formed molded component 1 is guided along the cutting tools 20 arranged on the die edge 21 and cut off in the process; Likewise, the cutting punches 19 ' arranged inside the die penetrate into the molded component 1 and cut out corresponding recesses or holes from the molded component 1 when the die 17 is lowered further ( 2c ). The cut or cut sheet metal areas 24' are disposed of as waste.

In the combination tool 12, the heated semi-finished product 2 is formed in quick succession and the molded component 1 formed therefrom is trimmed. Furthermore, the formed molded component 1 is cooled in the combination tool 12, the molded component 1 being mechanically fixed in the desired forming state during this cooling time . In order to enable targeted cooling of the formed molded component 1 in the combination tool 12, the tool parts are provided with cooling channels (not shown in the figures) which are included in a cooling circuit. During targeted cooling, cross-component hardening of the entire molded component 1 can take place; Alternatively, through a suitable design of the combination tool 12 (e.g. insulating inserts, air gaps, etc.), selected areas of the molded component 1 can be spared from hardening and thus remain in the “soft” state. At the same time or slightly offset in time from the cooling of the molded component 1, the trimming described above is carried out by the cutting tools 20, 20 '. or In order to minimize the wear of the cutting inserts 20, 20 ', the component edges or recesses 24 are expediently trimmed at a time when the molded component 1 is still “soft”. The trimming time is adjusted relative to the forming time by adjusting the offset 25 between the die 17 and the cutting punch 19, 19 'or by the lowering speed of the press ram 14. In order to ensure a low-wear trimming operation, the offset 25 (depending on the lowering speed of the press ram, the temperature of the inserted semi-finished product 2, the component shape, etc.) is set to such a level that the component edges 24 of the molded component 1 adjacent to the cutting tools 20, 20 'are in a "soft" or "not completely hardened" state, when they hit the cutting tools 20, 20'. If different areas of the molded component 1 are to be trimmed in different phases of hardening, the offset 25 can be varied locally; Likewise, by locally varying the offset 25, it can be achieved that selected edge areas are trimmed at an early point in time, at which other areas of the molded component 1 are not yet completely formed.

The entire component edge 24 can be trimmed by suitable geometric design of the cutting inserts 20, 20'. Alternatively, only selected areas of the component edge 24 can be trimmed. Advantageously, all those areas of the molded component 1 that are in a hardened structural state after completion of the combined hot forming/trimming/cooling are trimmed in the combination tool 12; This ensures that the molded component 1 does not need to be subjected to final trimming in these areas using a laser or water jet tool. However, unhardened areas of the molded component 1 can also be removed after the molded component 1 has been removed from the Combination tool 12 can be re-trimmed, since trimming these areas can be carried out with a conventional (mechanical) cutting tool without much wear.

The hot-formed and (at least partially) trimmed molded component 1 is removed from the combination tool 12 with the aid of a manipulator 28 and placed on a shelf 29 (see 1b) .

While a process has so far been described in which the forming and trimming are carried out together in a combination tool 12, the two steps can also take place in separate tools. In particular, the semi-finished product 2 can first be inserted into a first (forming) tool in which the three-dimensional contour of the molded component 1 is formed and targeted cooling to a first temperature T1 takes place. The molded component 1 is then transferred to an adjacent second (fixing) tool, in which the molded component 1 is trimmed and further cooled with mechanical fixation. The two adjacent tools (forming and fixing tools) are arranged within the forming press 15 in the manner of step tools and are connected by a transfer device known per se, which synchronously lifts the components out of the adjacent tools when the press is opened and places them in the next tool or in the shelf 29 arranged outside the press passes on.

Advantageously, not only the heating of the semi-finished products 2, but also the hot forming/trimming is carried out in a protective gas atmosphere. In this case the combination tool is 12, as in 1b indicated by dashed lines, integrated into the protective gas atmosphere 27 of the continuous furnace 10. This results in a scale-free press hardening process, so that subsequent dry cleaning of the mold components 1 can be omitted.

In addition to the in 2 The elements shown can be provided with hold-down devices in the combination tool in order to ensure controlled pulling in of the semi-finished product at the edge.

Claims (6)

Method for producing a metallic molded component (1), in particular a body component, from a semi-finished product (2) made of a hardenable, hot-formable steel sheet, wherein the molded component (1) is produced from the semi-finished product (2) by means of hot forming and wherein the semi-finished product (2) or the molded component (1) is trimmed, characterized in that the trimming takes place in the same process step as the hot forming. Procedure according to Claim 1 characterized in that the trimming takes place immediately after the hot forming. Procedure according to Claim 1 or 2 characterized in that the trimming takes place in the same tool (combination tool 12) as the hot forming. Method according to one of the preceding claims, characterized in that the trimming takes place at a temperature between 400°C and 700°C. Method according to one of the preceding claims, characterized in that the molded component (1) is cooled in the combination tool (12) after hot forming in such a way that press hardening takes place. Combination tool for producing a metallic molded component (1), in particular a body component, by combined hot forming, hardening and trimming, starting from a heated semi-finished product (2) made of a hardenable hot-formable steel sheet, the combination tool (12) - one on a press ram (14) attached upper tool (13), a die (17) mounted on a press table (16) via force elements (18), and at least one cutting tool (20, 20') fixed on a cutting punch (19, 19 '), - the cutting punch (19, 19') is arranged on the edge (21) or in a recess (22) of the die (17), an area of the functional surface (17') of the die (17) adjacent to the cutting punch (19, 19') in Open state of the combination tool (12) is offset by an offset (25) relative to the cutting punch (19, 19 '), and the offset (25) between the cutting punch (19, 19') and the die (17) is set in such a way is that a component edge (24) of the hot-formed component (1) opposite the cutting punch (19, 19') is in an unhardened or incompletely hardened state when this component edge (24) of the component (1) is in contact with the cutting punch (19, 19') comes into contact.

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