DE10254695B3 - Production of a metallic component, especially a vehicle body component, from a semifinished product made of non-hardened heat-deformable sheet steel comprises cold-forming, trimming, hot-forming and press-hardening processes - Google Patents

Abstract

Production of a metallic component, especially a vehicle body component, from a semifinished product (2, 3) made of non-hardened heat-deformable sheet steel comprises forming a component blank (10) from the semifinished product using a cold-forming process, especially a drawing process. The blank is trimmed at the edge to obtain an edge contour corresponding to the component being produced. The trimmed blank is heated and molded in a hot-forming tool and press-hardened. Preferred Features: The semifinished product is made of air-hardening steel alloy. A deep-drawing process is used to obtain the blank from the semifinished product.

Description

The invention relates to a method for producing a metallic molded component, in particular a Body components, from a semi-finished product of thermoformable sheet steel.

Many components, in particular body parts in the automotive industry, must meet high requirements in terms of rigidity and strength. At the same time, the components should have the lowest possible material thickness in the interest of weight reduction. In order to meet these two requirements, increasingly high-strength and ultra-high-strength steel materials are used, which - depending on the composition and heat treatment - have very high strengths. The production of body parts from these ultra high strength steel sheets is preferably carried out in a hot forming process, in which - as in the DE 24 52 486 A1 and the DE 100 49 660 A1 - heated a board and then molded and cured in a special mold. By a suitable choice of the process parameters during hot forming while the strength and toughness values of the component can be adjusted specifically.

For the production of such a component With the help of hot forming, a circuit board is first turned into a coil cut out, then above the microstructure transformation temperature of the steel material, above which the material structure in austenitic Condition exists, warmed, in the heated Condition inserted in a forming tool and in the desired component shape deformed and under mechanical Fi xierung of the desired Forming state cooled with a remuneration or hardening of the component takes place.

To a made in this way Component dimensionally stable to cut, however, a high expenditure on equipment is required: In particular, for cold cutting hardened materials are very high cutting forces required, resulting in rapid tool wear and high Maintenance costs leads. Furthermore, the cold trimming of such high-strength components problematic, since for example the trimmed when cold Part edges have more or less large burrs, due to the high notch sensitivity of the high-strength materials to a fast cracking lead in the component can.

To avoid this during mechanical trimming the hardened Components occurring difficulties are often alternative Cutting methods used, such as laser cutting or Waterjet cutting. Although, with the help of this method can high-quality trimming of the component edge can be achieved however, these cutting methods work comparatively slowly, because the cycle times here are directly dependent on the length of the cut edge as well depend on the tolerances to be maintained. The final pruning process will set thus a bottleneck in the production of hot-formed components which limits the number of components to be produced per unit of time. Although the overall cycle time of component manufacturing can be reduced if - ever by length the cutting edge - several provided parallel laser or water jet cutting systems However, this is with high additional investments and logistics costs connected and therefore disadvantageous.

From the DE 101 49 220 C1 and the DE 101 49 221 C1 are known methods for producing press-hardened components, in which first a pot-like molding or a passage is formed on a board in the uncured state; At closing, the board is hot formed in a hot forming tool to the finished component and hardened. The component produced in this way can be trimmed in a follow-up operation. However, neither of these two documents discloses the manner in which this trimming process must be carried out in order to minimize tool wear on the one hand and to achieve a short cycle time on the other hand.

The invention is thus the task underlying the process sequence in the manufacture of components from thermoformable sheets to improve that the cycle time - regardless of the length the component outer contour - reduced can be.

The object is achieved by the Characteristics of claim 1 solved.

The basic idea of the invention exists in the consideration, that the Component manufacturing process in one should be designed such that the procedural costly and costly final trimming of the hardened component can be waived. The edge regions are therefore already according to the invention in the unhardened Condition of the component cut off and not first - as usual during hot forming usual - after the heating and hardening process.

The production process according to the invention thus provides that a blank is first cut out of a coil of a hot-workable steel sheet. From this board is then formed by means of a conventional cold forming process, for example by deep drawing, and then trimming the edge regions a component blank, which has both (approximately) the desired three-dimensional shape as well as (approximately) the desired outer contour of the finished component. This component blank is on closing heated to a temperature lying above the forming temperature of the material and transferred in the hot state in a hot-forming tool in which the component is press-hardened. In this process step, the component blank undergoes a comparatively low deformation and at the same time undergoes a targeted heat treatment in the course of which a cross-component or local hardening takes place.

Since the component blank at the beginning the hot forming already approximate has the desired dimensions, is during the hot forming only a relatively small adjustment or correction the component contour necessary. As a result, the component edges are only slightly changed, So that the Necessity of a final Circumcision of the component edges eliminated. Under "component edges" here are both outer boundaries as well as inner border areas (boundaries of breakthroughs of the Component) to understand.

Unlike traditional ones Hot forming process takes place in the production process according to the invention trimming the excess border areas thus before hot forming; at this time is the Component blank in a soft (uncured) state and therefore can with the help of conventional mechanical process are cropped. Thus, on the elaborate and time consuming laser or water jet cutting of the finished press member be omitted, so that the Throughput times compared to conventional process flow can be significantly reduced. At the same time, a high quality cut edge is achieved.

Furthermore, when used the method according to the invention in the hot forming tool only a small deformation of the component; thus can the tool wear of the Hot forming tool can be significantly reduced.

Since the component geometry (almost) completely by Cold forming is produced, the manufacture of the component during the construction phase by conventional forming simulation be secured. this makes possible reduced development costs for Component and tool.

Special advantages can be achieved, if as a cold forming process for near-net shape shaping of the component geometry a (multi-stage) thermoforming process is used (see claim 2). Since in the soft state, a multi-stage formability of the component blank possible is, can too complex component geometries are formed. advantageously, is in the last stage of the thermoforming tool with cutting tools provided so that the Circumcision of the component blank directly takes place in the cold forming tool.

To trim the component blank come preferably mechanical cutting means used (see claim 3). These cutting means can in particular in the form of folding and / or punching tools be integrated into the cold forming, so that the edge trimming not in a separate process step, but as part of the cold forming takes place (see claim 4).

To continue the cycle time of the overall process to be able to reduce it is advantageous to the process step the press hardening of cut as short as possible in order to shorten one possible ensure high throughput of components per hot stamping tool. For this purpose, the finished molded component should be cooled as quickly as possible. In an advantageous embodiment the finished molded component is quenched in a tool, which with the help of a brine (with temperature <0 ° C) as a coolant chilled is (see claim 5); Such a brine has a particularly high thermal conductivity and heat capacity. To this Way can achieve a particularly rapid cooling of the component become.

An additional reduction of the cycle time of the Total process can be reach when the component over several stations (corresponding to several tool sets) chilled becomes. So in a first station, the component is quenched so far, until the martensite temperature has fallen below. The component strength is already sufficient for a further transport to the next Station (or the next Tool). In this second (or a sequence of further) station the component is then cooled down to hand temperature.

In an advantageous embodiment will for the Production of the component a semi-finished product from an air-hardening Steel used (see claim 6). An advantage of air-hardening toughen is that the Quenching of the component in principle no additional cooling (for example, by the hot forming tool) necessary is. In this case, the component blank in the hot-forming tool becomes the final contour and then cooled only in the hot forming tool until sufficient heat resistance, rigidity and associated dimensional stability of the component is reached. Subsequently, the component of the Hot forming tool removed and cooled in the air ready; the Hot forming tool thus stands for the inclusion of another Component blanks ready. In this way, the cycle times in the Production of hardened Shortened components further become. - He follows the air hardening under a protective gas, the result - in addition to this time gain - the further advantage that yourself no scale forms on the component and thus the expensive subsequent descaling deleted (see claim 7).

In such a heating and heat treatment under inert gas, the component remains free of surface contamination and can therefore be subjected to a surface coating advantageously immediately after the hot working and quenching (ie after cooling to a temperature below the Martensisttemperatur) (see claim 8). In the course of this surface coating, in particular corrosion-inhibiting protective layers (eg by galvanizing) can be applied to the component surface. In this case, the residual heat resulting from the hot forming, remaining in the component, can be used directly. Subsequently, a further heat treatment of the component can be carried out by tempering.

The heating of the trimmed component blank before hot forming can take place in a continuous furnace (see Claim 9). Alternatively, the heating is carried out inductively (see Claim 10). Such inductive heating is very fast, why in this case an additional Time gain in the total process time can be achieved. Due to the short heating time continues to occur while the warming only a negligible Scaling of the component surfaces why the use of inert gas can be omitted. The inductive warming has special advantages in those applications where not the whole Component, but only selected Be areas of the component to be press-hardened should: Then be selective - by suitable design of the inductors - only the selected, too curing areas heated and subsequently in the hot forming tool hardened, while the rest, unheated Although areas in the hot forming tool to be reshaped, but in the original ductility remain. Alternatively or additionally allows the induction heating an adjustment of the component properties over the sheet thickness ("softer Core - hard Cover layer ") this way you can locally variable strength and stiffness properties on the finished component can be achieved.

For inductive heating can a separate, between cutting device and hot forming tool arranged heating station - analogous to Continuous furnace - intended become. In contrast to a heating in the continuous furnace - in the a certain heating distance is necessary - is inductive heating with a small footprint, resulting in cost savings. The Shape and arrangement of the inductors is based on the shape of the trimmed Component blank or to be heated Areas agreed. Alternatively to heating in a separate heating station can the warming also in the cutting device (directly after the edge trimming) or in the hot forming tool (directly before hot forming). For this purpose, the cutting device or the forming tool with internal Inductors provided, or the component is using external, heated according to shaped inductors, which after edge trimming or before the hot forming in the open cutting device or the open one Hot forming tool introduced and there to the desired Place the component to be placed.

In the following the invention is based on an embodiment illustrated in the drawings explained in more detail. there demonstrate

1 a process diagram of the production process according to the invention of a press-hardened component:

1a : Cutting the board (step I) 1b : Cold Forming (Step II)

1c : Trimming the edges (step III) 1d : Hot Forming (Step IV)

1e Dry cleaning (step V);

2 Perspective views of selected intermediate stages in the manufacture of the component:

2a : a semi-finished product;

2 B a molded blank formed therefrom;

2c a trimmed component blank;

2d : the finished component.

1a to 1e show a schematic representation of the inventive method for producing a spatially shaped, press-hardened component 1 from a semi-finished product 2 , In the present embodiment, as a semi-finished product 2 a circuit board 3 used, which is cut out of a unwound Blechcoil. Alternatively, as semifinished a composite sheet are used, which - as in the DE 100 49 660 A1 described - consists of a base plate and at least one reinforcing plate. Furthermore, as semi-finished a Taylored Blank can be used, which consists of several welded together sheets of different material thickness and / or different material properties. Alternatively, the semifinished product may be a three-dimensionally shaped sheet-metal part produced by any forming process which is to undergo further deformation and a strength / rigidity increase with the aid of the method according to the invention.

The semi-finished product 2 consists of a thermoformable steel. As an example of such a material, mention may be made here of Benteler's air-hardening steel marketed under the trade name BTR 155, which has the following alloy composition, wherein the contents of the alloying partners to be added in addition to the base metal iron are to be understood as percent by mass:
Carbon: 0.18-0.28%,
Silicon: max. 0.7%
Manganese: 2.00 - 4.00%,
Phosphor: max. 0.025%
Sulfur: max. 0,010,
Chrome: max. 0.7%
Molybdenum: max. 0.55
Nickel: max. 0.6%
Aluminum: 0.020-0.060%.

In a first process step I, the board 3 - as in 1a shown - from an abgewi crumbled and straightened section of a coil 5 cut out of a thermoformable sheet metal. The thermoformable material is at this time in a "soft" (ie uncured) state, so that the board 3 easily with the help of conventional mechanical cutting means - for example with the help of a scissors 4 - can be cut out. In mass production, the cutting of the board takes place 3 advantageously with the help of a platinum press 6 which is an automated feeder of the coil 5 and an automatic punching and removal of the cut-out board 3 guaranteed. The board cut out in this way 3 is in 2a shown in a schematic perspective view The cut-out boards 3 be on a pile 7 are stored and stacked in a cold forming station 8th supplied (see 1b ). Here is in a second process step II from the board 3 with the help of the cold forming tool 8th - In the present example, a two-stage thermoforming tool 9 - A component blank 10 shaped. In order to be able to ensure process-reliable, a high-quality shaping of the component geometry, a predetermined, optimized material flow must be targeted during the cold forming process on the board 3 be ensured. To achieve this, rejects the board 3 border areas 11 on top of a (in 2a dashed lines indicated) outer contour 12 of the component to be molded 1 protrude. In these border areas 11 become during the drawing process by hold down 13 controlled forces exerted a targeted flow of material on the board 3 and thus produce a high quality drawing result.

As part of this cold forming process (process step II), the component blank 10 formed close to the final contour. By "near net shape" is to be understood that those parts of the geometry of the finished component 1 , which are associated with a macroscopic material flow, after completion of the cold forming process completely into the component blank 10 are formed. After completion of the cold forming process (process step II) are thus for the production of the three-dimensional shape of the component 1 only small form adaptations are necessary, which require a minimum (local) material flow; the component blank 10 is in 2 B shown.

Depending on the complexity of the component geometry, the near-net shape shaping can take place in a single deep-drawing step, or it can be multi-stage - for example in the in 1b shown two-stage deep drawing press 9 - respectively.

Subsequent to the cold forming process, the component blank is 10 in a cutting device 15 inserted and cut there th (process step III, 1c ). As the material of the component blank 10 is still in a "soft", ie uncured state at this time, this trimming process using mechanical cutting means 14 (Especially with cutting blades, folding and / or punching tools) done.

For the pruning process can - as in 1c shown - a separate cutting device 15 be provided. Alternatively, the cutting means 14 in the last stage 9 ' of the thermoforming tool 9 be integrated so that in the last deep drawing stage 9 ' in addition to the final shaping of the sheet metal blank 10 also the marginal circumcision takes place.

By Kaltumform- and the trimming process (process steps II and III) is thus from the board 3 an endkontaunaher trimmed component blank 17 made, both in terms of its three-dimensional shape and with respect to its edge contour 12 ' differs only slightly from the desired component shape. The cut edge areas 11 be in the cutting device 15 dissipated; the component blank 17 ( 2c ) is using a manipulator 19 from the cutting device 15 removed and fed to the next process stage.

In the following process stage IV ( 1d ) becomes the clipped component blank 17 subjected to hot forming, in the context of which he is to the final component shape 1 is shaped and cured. For this purpose, the trimmed component blank 17 from a manipulator 20 in a continuous furnace 21 where it is heated to a temperature above the structural transformation temperature in the austenitic state; Depending on the grade of steel, this corresponds to heating to a temperature between 700 ° C and 1100 ° C. Advantageously, the atmosphere of the continuous furnace 21 rendered inert by a targeted and sufficient addition of a protective gas to a Verzundern not coated ter interfaces 12 ' the trimmed blanks 17 or - if uncoated sheets are used - on the entire blank surface. As protective gas, for example, carbon dioxide and / or nitrogen can be used.

The heated trimmed component blank 17 is then using a manipulator 22 in a hot forming tool 23 inserted, in which the three-dimensional shape and the edge contour 12 ' of the trimmed component blank 17 be brought to their final, desired level. Because the trimmed component blank 17 already has near-net shape dimensions, only a slight adaptation to the shape is necessary during hot forming. In the hot forming tool 23 becomes the pruned blank 17 preformed and rapidly cooled, whereby a fine-grained martensitic or bainitic material structure is adjusted. This process step corresponds to a hardening of the molded component 1 and allows a targeted adjustment of the material strength. Details and various embodiments of this curing process are for example in the DE 100 49 660 A1 described. This can be a cross-component hardening of the entire mold component 1 respectively; alternatively, by a suitable shape of the hot forming tool 23 For example, insulating inserts, air gaps, etc.) selected areas of the component are recessed from the curing, so that the curing of the molded component 1 only done locally.

Is the desired curing state of the molded component 1 achieved, so is molded component 1 from the hot forming tool 23 taken. Due to the hot forming process upstream endkontontahen circumcision of the component blank 10 as well as the shape adaptation of the outer boundary 12 ' in the hot forming tool 23 has the mold part 1 after completion of the hot forming process already the desired outer contour 24 so that after the hot forming no time-consuming trimming of the component edge is necessary.

To quickly quench the mold component 1 to achieve in the course of hot forming, the mold component 1 is in a hot-working tool cooled by brine 23 deterred. Such a brine has a high thermal conductivity and heat capacity. Depending on the salts added, the brine can be cooled to temperatures well below the freezing point of water.

Hot forming of the molded part 1 As a rule, he goes with a scaling of the component surface, so that the molded part 1 in a further process step (process step V, 1e ) in a dry cleaning station 25 (for example, by shot peening) must be descaled.

By the in 1a to 1e process shown with the near-net shape trimming of the component blanks 10 in the soft state, a significant reduction in the cycle time over the conventional procedure it is sufficient, in which the finished, hardened molded component 1 only after the hot forming by cutting (laser) is cut to the desired size. If the method according to the invention is used, the molding component has 1 after completion of the hot forming process (process step IV) already the desired final outer contour 24 on, so that the Hartbeschneidung - which formed the bottleneck in the conventional process - is eliminated.

In the process sequence according to the invention now provides the cooling of the finished molded molded part 1 in the hot forming tool 23 the bottleneck of the overall process: When hardened in the tool 23 namely, the total cooling time required with good design of tool-integrated cooling depending on the sheet thickness, workpiece size and final temperature about 20 to 40 seconds, with the majority of cases in the range between 25 and 30 seconds. A shortening of the cycle time can be achieved here by the use of air-hardening steels as materials for the molded components 1 Who can do this? In this case, the mold part needs 1 in the hot forming tool 23 only to be cooled to a sufficient heat resistance, rigidity and associated Maßhältigkeit the mold component 1 is reached; then the molded part can 1 from the tool 23 are removed, so that the further heat treatment process in the air outside the tool 23 takes place, and the hot forming tool 23 for receiving a next component blank 17 ready. In this way, the residence time of the mold component 1 in the hot forming tool 23 be reduced to a few (<10) seconds, resulting in a further shortening of the overall cycle time.

Additional savings or reductions in cycle time can be achieved, if not just the heating of the component blanks 17 , but also the hot forming takes place in a protective gas atmosphere; in this case, the forming tool 23 , as in 1d indicated by dashed lines, in the protective gas atmosphere 26 of the continuous furnace 21 integrated. As a result, a scale-free Preßhärtungsprozeß is realized, so that the otherwise previously necessary subsequent dry cleaning of the components 1 (Process step V) can be omitted.

Alternatively to the heating of the component blanks 17 in the continuous furnace 21 the heating can be done inductively.

Claims (10)

Method for producing a metallic molded component ( 1 ), in particular a body component, from a semi-finished product ( 2 . 3 ) from an uncured thermoformable steel sheet with the following process steps: - from the semifinished product ( 2 . 3 ) is by a cold forming process, in particular by a drawing process, a component blank ( 10 ) shaped (process step II); - the component blank ( 10 ) is on the edge of a molded part to be produced ( 1 ) approximately corresponding edge contour ( 12 ' ) (process step III); - the trimmed component blank ( 17 ) is heated and stored in a hot forming tool ( 23 ) and simultaneously press-hardened (process step IV). Method according to Claim 1, characterized in that for shaping the component blank ( 10 ) from the semifinished product ( 2 . 3 ) a deep drawing process is used. Method according to claim 1 or 2, characterized in that the component blank ( 10 ) by means of a mechanical cutting method ( 14 . 15 ) is cropped. Method according to claim 3, characterized in that the trimming of the component blank ( 10 ) as part of the cold forming. Method according to one of the preceding claims, characterized in that the hot forming tool ( 23 ) is cooled with a brine. Method according to one of the preceding claims, characterized in that the semifinished product ( 2 . 3 ) consists of an air-hardening steel alloy. Method according to the preceding claims, characterized in that the heating and hot working of the trimmed component blank ( 17 ) in a protective gas atmosphere ( 26 ) he follows. Method according to claim 7, characterized in that - the molding component ( 1 ) is cooled after the hot forming (process step IV) to a temperature below the martensite temperature - and that the molded component ( 1 ) immediately afterwards with a surface coating, in particular a corrosion protection layer is provided. Method according to the preceding claims, characterized in that the heating of the trimmed component blank ( 17 ) in process step IV in a continuous furnace ( 21 ) he follows. Method according to one of claims 1 to 8, characterized in that the heating of the trimmed component blank ( 17 ) is carried out inductively in process step IV.