EP1646459B1 - Method for the production of a press-hardened component - Google Patents

Description

The invention relates to a method for producing a press-hardened component according to the preambles of independent claims 1 and 2.

The rigidity and strength of body components are becoming increasingly demanding in vehicle construction. At the same time, however, a reduction of the material thickness is desired in the interests of weight minimization. A solution to meet the contradictory requirements of high-strength and ultra-high-strength steel materials, which allow the production of components with very high strength while maintaining low material thickness. By a suitable choice of process parameters during a conventional hot converter for these materials, the strength and toughness values of a component can be adjusted in a targeted manner.

Such a material is, for example, the precoated boron steel marketed by Usinor under the trader Usibor 1500. The steel is provided with an AISi coating which, among other things, exhibits advantageous corrosion-inhibiting properties in the course of the subsequent heat treatment.

For the production of such a component by means of hot forming a circuit board is first cut out of a coil, which then above the structural transformation temperature of the steel material, above which the material structure is in the austenitic state, heated, placed in the heated state in a forming tool and formed into the desired component shape and cooled with mechanical fixation of the desired Umformzustands, wherein a compensation or curing of the component takes place.

The production of a structural component by hot working is for example off DE 10135647 A1 and DE 100 49 660 A1 known.

Often, the component is subjected to a preforming cut or a trimming step before the actual hot forming. This is for example in the DE 101 49 221 C1 described. However, such a method may cause corrosion problems because a commonly applied tape coating will be damaged during preforming. Conventional preforming and trimming of the components, in particular with precoated high-strength steels such as Usibor 1500 PC, which has an AISi coating, is therefore omitted.

The object of the invention is to specify a press-hardened component as well as a production method for press-hardened components, which enables reliable corrosion protection for precoated, hot-workable steels.

The object is achieved with the features of the independent claims 1 and 2.

A first embodiment of the method according to the invention for the production of press-hardened components comprises the following method steps: a component blank is formed from the precoated semi-finished product by a cold-forming method, in particular a drawing method; the component blank is trimmed on the edge on a part of the production approximately corresponding boundary contour; the trimmed component blank is heated and press-hardened in a hot-forming tool; the press-hardened component blank is coated in a coating step with a corrosion-protective layer.

On the one hand, this embodiment of the invention makes it possible to design the component manufacturing process in such a way that it is possible to dispense with the procedurally complex and costly final trimming of the hardened component. The edge regions are therefore already cut in the uncured state of the component and not only - as usual in hot forming usual - after the heating and hardening process. By pruning the workpiece already in the soft state, significantly lower cutting forces are required than for cold-cutting hardened materials, resulting in reduced tool wear and a reduction in the maintenance cost of the cutting tools. Furthermore, the risk of rapid cracking due to the high notch sensitivity of these materials is significantly reduced when trimming the high strength material in the uncured state.

The pre-coating provided on the semifinished product avoids scaling of the trimmed component blank in the hardening process, and the requirements for an inert atmosphere during curing can be reduced. In addition, the pre-coating prevents decarburization of the material during curing. After the hardening process, according to the invention, a further layer which protects against corrosion is applied, so that the component is completely coated, ie also at the edges.

In a further embodiment of the method according to the invention for producing press-hardened components, the following method steps are carried out: the semifinished product precoated with a first layer is heated and press-hardened in a hot-forming tool; the component blank produced in this way is trimmed at the edge to a boundary contour corresponding to the component to be produced; the press-hardened, cut component blank is coated in a coating step with a second corrosion-protective layer.

In this embodiment, the trimming of the cured component is preferably carried out by means of a laser or water jet cutting method, by which a high-quality trimming of the component edges can be achieved. The subsequent application of the second corrosion protection layer ensures that the component is also protected against corrosion in the area of the trimmed edges.

If the layer is applied to the press-hardened component blank by a hot-dip galvanizing process, a corrosion-protective layer of zinc can be applied in a coating process that can be suitably integrated into a production process.

If the layer is applied to the press-hardened component blank by a thermal diffusion method, a readily controllable method can be used, with which preferably a layer of zinc or a zinc alloy can be applied, which is also suitable for complex component geometries and edge layering is. The layer thickness can be adjusted selectively between a few microns and over 100 microns. A thermal load of the component is low. Components can be used regardless of their size, dimensions, Configuration, complexity and weight are coated. A cleaning prior to the coating step with a dry cleaning, in particular blasting of the press-hardened component blank with glass particles or zinc particles, can be omitted, since the precoating substantially prevents scaling of the component blank during hot forming. This saves a process step; In addition, it is avoided that a small, but possibly disturbing component distortion occurs by blasting the components with particles.

In a pre-coating with an aluminum-containing layer, preferably of AlSi, and a zinc-containing coating, a good adhesion between the two coatings results. In addition, there is good protection of the material against hydrogen embrittlement, against which zinc in particular can protect the material. The second layer applied to the first layer of the precoat provides edge coating and coating of those areas where the first layer of the precoat e.g. was chipped in the pre-forming or cracked due to excessive friction.

If the component blank is cleaned of residues after the coating step, for example with ultrasound, and passivated, a surface is formed which gives a good primer for coatings, in particular primers of paints or coatings themselves.

Advantageously, the component blank is tempered after the coating step. It is particularly advantageous if the component blank is coated with a zinc-containing layer, since an oxide is formed on the surface, which is suitable as a primer.

A press-hardened component, in particular a body component, from a semifinished product of unhardened, hot-workable steel sheet, which has been produced according to at least one embodiment of the method according to the invention, is particularly suitable for mass production with corresponding series production and combines a favorable weight reduction of the component with excellent corrosion protection.

Further advantages and embodiments of the invention can be taken from the further claims and the description.

In the following the invention with reference to an embodiment shown in a drawing is explained in more detail.

Fig. 1

ein Verfahrensschema des erfindungsgemäßen Verfahrens eines pressgehärteten Bauteils mit 1a: Zuschneiden der Platine (Schritt I); 1b; Kaltumformung (Schritt II); 1c: Beschneiden der Ränder (Schritt III); 1d: Warmumformung (Schritt IV); 1e: Beschichtung (Schritt V); 1f: alternatives Verfahren zu Beschichtung (Schritt V');

Fig. 2

perspektivische Ansichten ausgewählter Zwischenstufen bei der Herstellung eines Bauteils mit 2a: ein vorbeschichtetes Halbzeug; 2b: ein daraus geformter Bauteil-Rohling; 2c: ein beschnittener Bauteil-Rohling; 2d: ein beschichteter Bauteil- Rohling;

Fig.3

einen alternativen Verfahrensablauf zur Herstellung eines pressgehärteten Bauteils mit 1a: Zuschneiden der Platine (Schritt I), 1 b: Warmumformung (Schritt II'); 1 c: Beschneiden der Ränder (Schritt III'); 1d: Beschichtung (Schritt IV').

Showing:

Fig. 1

a process diagram of the method according to the invention of a press-hardened component with 1a: cutting the board (step I); 1b; Cold forming (step II); 1c: trimming the edges (step III); 1d: hot working (step IV); 1e: coating (step V); 1f: alternative method of coating (step V ');

Fig. 2

perspective views of selected intermediate stages in the production of a component with 2a: a precoated semi-finished product; 2b: a component blank formed therefrom; 2c: a trimmed component blank; 2d: a coated component blank;

Figure 3

an alternative process sequence for the production of a press-hardened component with 1a: Cutting the board (step I), 1 b: hot forming (step II '); 1 c: trimming the edges (step III '); 1d: coating (step IV ').

The FIGS. 1a to 1e schematically show an inventive method for producing a spatially shaped, press-hardened component 1 from a semifinished product 2. In the present embodiment, a board 3 is used as a semifinished product 2, which is cut out of a developed coil 5. Alternatively, as a semifinished product 2, a composite sheet are used, as for example in the DE 100 49 660 A1 is described and which consists of a base plate and at least one reinforcing plate. Furthermore, as semifinished product 2 also 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 2 may be a three-dimensionally shaped sheet-metal part produced by any forming process which is to undergo further deformation and a strength and / or rigidity increase with the aid of the method according to the invention.

The semifinished product 2 consists of an unhardened, hot-forming steel sheet. A particularly preferred material is a boron-containing tempering steel, e.g. Usibor 1500, Usibor 1500 P or Usibor 1500 PC, which are distributed by the company Usinor under these trade names.

In a first process step I, the board 3 ( Fig. 1a ) are cut out of a unwound and straightened portion of a coil 5 from a precoated, thermoformable sheet. Preferably, the coating is a coating of aluminum or an aluminum alloy, in particular a silicon-containing aluminum alloy AlSi. The thermoformable material is at this time in an uncured state, so that board 3 easily using conventional mechanical cutting means 4, for example, a scissors, can be cut out. In mass production, the cutting of the board 3 is advantageously carried out with the help of a platinum press 6, which ensures an automated feed of the coil 5 and an automatic punching and removal of the cut-out board 3. The cut out in this way board 3 is in 2a shown in a schematic perspective view.

The cut-out blanks 3 are deposited on a stack 7 and fed in stacked form to a cold-forming station 8 (FIG. Fig. 1b ). Here, in a second process step II from the circuit board 3 by means of the cold forming tool 8, for example a two-stage deep drawing tool 9, a component blank 10 is formed. In order to be able to ensure a high-quality shaping of the component geometry, the board 3 has edge regions 11 which protrude beyond an outer contour 12 of the component 1 to be molded. As part of this cold forming process (process step II), the component blank 10 is formed close to the final contour. The term "close-to-net shape" should be understood to mean that those parts of the geometry of the finished component 1 which are accompanied by a macroscopic flow of material are completely formed in the component blank 10 after the cold-forming process has been completed. After completion of the cold forming process, only slight conformations of shape are required to produce the three-dimensional shape of the component 1, which require a minimum (local) material flow; the component blank 10 is in Fig. 2b shown.

Depending on the complexity of the component 1, the near-net shape shaping can take place in a single deep-drawing step, or it can take place in several stages ( Fig. 1b ). Subsequent to the cold forming process, the component blank 10 is in a Cutting device 15 is inserted and cut there (process step III, Fig. 1c ). The material is still in the uncured state at this time, so trimming can be accomplished by conventional mechanical cutting means 14 such as cutting knives, folding and / or punching tools.

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

Through the cold forming process and the trimming (process steps II and III) is made of the board 3 a near net shape trimmed component blank 17 of both in terms of its three-dimensional shape and with respect to its edge contour 12 'little of the desired shape of the component 1 deviates. The cut edge portions 11 are removed in the cutting device 15; the component blank 17 ( Fig. 2c ) is removed with the aid of a manipulator 19 from the cutting device 15 and fed to the next process step IV.

In a particularly advantageous alternative, the process steps II and III are integrated in a single processing station, in which the forming and cutting is carried out fully automatically. The removal of the component blank 17 from the processing station can be automated or there may be a manual removal and stacking of the component blanks 17.

In the following process step IV ( Fig. 1d ), the trimmed component blank 17 is subjected to hot working in a hot forming area 26, in the course of which it is formed and hardened to a final shape of the component 1. The trimmed component blank 17 is inserted by a manipulator 20 in a continuous furnace 21, where it is heated to a temperature which is 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. For a preferred material of a boron-containing steel, in particular Usibor 1500P, a favorable range is between 900 ° C and 1000 ° C. The atmosphere of the continuous furnace can be rendered inert by the addition of a protective gas, but the precoating of the blanks 3 already prevents at least a full-surface scaling of the blank surface.

The uncoated interfaces of the edge contour 12 'of the trimmed component blanks 17 represent only a very small area ratio of the component blank 17, so that adhesion of a layer applied later is virtually unaffected. A suitable inert gas for inertization is e.g. Carbon dioxide or nitrogen.

The heated trimmed component blank 17 is then inserted by means of a manipulator 22 in a hot-forming tool 23, in which the three-dimensional shape and the edge contour 12 'of the trimmed component blank 17 are brought to their desired level. Since the trimmed component blank 17 already has near net shape dimensions, only a slight adaptation of the shape is necessary during hot forming. In the hot-forming tool 23, the trimmed component blank 17 is finished and rapidly cooled, resulting in a fine-grained martensitic or bainitic material structure is set. This step corresponds to a hardening of the component blank 18 and allows a targeted adjustment of the material strength. Details of such a curing process are eg in the DE 100 49 660 A1 described. It can be cured both the whole component blank 17, as well as only locally at selected locations of the component blank 17 hardening be made. Once the desired degree of hardening of the component blank 18 has been reached, the hardened component blank 18 is taken out of the hot forming tool 23 with a manipulator and optionally stacked until further processing. Because of the hot-forming process upstream near-net shape trimming of the component blank 10 and the shape adjustment of the edge contour 12 'in the hot forming tool 23, the component 18 after completion of the hot forming process already the desired outer contour 24 of the finished component 1, so that after the hot forming no time-consuming trimming the edge of the component is necessary.

In order to achieve a rapid quenching of the component blank 18 in the course of hot forming, the component blank 18 can be quenched in a cooled hot forming tool 23. Since the surface is not scaled by the layer 33 of the precoating, a subsequent cleaning can be omitted.

Since laser cutting of the hardened component blank 18 does not have to take place, the cycle times in the production method are advantageously short. In the process, now the cooling of the component blank 18 is a possible bottleneck. To defuse this, air-hardening or water-hardening materials for the components 1 can be used. The component blank 18 then only needs to cool down until sufficient heat resistance, rigidity and the associated Dimensional accuracy of the component blank 18 is reached. Then, the component blank 18 can be removed from the tool 23, so that the further heat treatment process takes place in the air or in water outside of the tool 23, which then very quickly after a few seconds again for receiving further component blanks 17 is available.

In a further process step V ( Fig. 1e ), the press-hardened component blank 18 is coated in a coating process with a corrosion of the component 1 preventing layer 34. For this purpose, drums 31 are charged with the press-hardened component blanks 18 and a zinc-containing powder, preferably a zinc alloy or a zinc-containing mixture, closed and introduced into a coating installation 30. There, the component blanks 18 are heated slowly at about 5-10 K / min with slow rotation of the drums 31 to about 300 ° C. In this thermal diffusion process, the zinc or zinc alloy is distributed substantially homogeneously over the entire surface of the component blanks 18 and bonds to the surface. In the case of an aluminum-containing precoating of the sinkers 3, an excellent adhesion is formed between the precoating, in particular AlSi, and the zinc-containing layer 34. At the same time, the uncoated cut edges are coated with the zinc-containing layer 34.

Depending on the composition of the powder, the time and the temperature, a uniform layer thickness arises on the component blanks 18, which can be set arbitrarily between a few μm and more than 100 μm, preferably between 5 μm and 120 μm. The layer 34 is weldable and gives a tensile strength that can be more than 1300 MPa for a component 1 made of BTR 165. In the thermal diffusion method There are practically no residues or emissions into the environment.

The coating process is concluded with a passivation process in an adjacent passivation station 35, in which the drums 31 are discharged from the coating installation 30, cooled in a cooling station 36, ultrasonically freed of residues of the coating powder in a cleaning station 37 and in a tempering station 38 at a temperature of about 200 ° C for about 1 h, wherein the layer 34 is passivated. Optionally, suitable passivating additives may also be added. Then the finished corrosion-protected components 1 can be removed from the drum 31.

In an alternative embodiment (process step V ', Fig. 1f ), the zinc-containing layer 34 is applied to the press-hardened component blank 18 by a hot-dip galvanizing process in a coating area 40. Component blanks 18 are suspended in a submersible housing 41, which transports the component blanks 18 through a plurality of stations of the coating area 40. In a flux station 42, the component blanks 18 are hung in a suitably tempered flux bath, preferably with zinc chloride at about 360 ° C, then dried in a drying station 43, preferably at 80 ° C and then in a galvanizing bath 44 at about 400 ° C. 450 ° C immersed and galvanized. Then the finished components 1 can be removed from the submersible housing 31.

FIGS. 3a to 3d schematically show an alternative process flow for producing a spatially shaped, press-hardened component 1 from a semifinished product 2, in particular from a pre-coated circuit board 3. Just as in the embodiment of FIGS. 1a to 1e will be here in one too first process step ( Fig. 3a ) Cut the board 3 in the platinum press 6 from a pre-coated, hot-forming sheet. Subsequently, the coated board 3 is subjected to a hot-forming step ( Fig. 3b ). For this purpose, the board 3 is inserted by a manipulator 20 'in a continuous furnace 21', in which the board 3 is heated to a temperature which is above the transition temperature in the austenitic microstructure state. Subsequently, the heated board 3 is inserted into a hot forming tool 23 ', in which from the circuit board 3, a component blank 10' of the desired three-dimensional shape is formed; In the process, the component blank 10 'is cooled down so rapidly that it experiences a (component-wide or local) hardening. The continuous furnace 21 'and the hot forming tool 23' may be in a protective gas atmosphere 26 ', however, by pre-coating the boards 3 is a full-scale scaling of the boards 3 avoided.

Then, the hardened component blank 10 'is transferred to a cutting device 15' ( Fig. 3c ), in which the component blank 10 'is trimmed at the edge to produce a blank 18' with edge contour 12. The trimming is preferably carried out with a laser 14 '. The cut edge portions 11 'are disposed of. In the subsequent process step the 3d figure is the press-hardened and trimmed blank 18 '- analogous to the process stage V or V' of FIGS. 1e or 1f - coated in a coating system 30.

The press-hardened, coated component 1 is particularly suitable as a body component in vehicle construction, which are produced in large quantities. The method according to the invention enables advantageous process control with short cycle times, all process steps have industrialization potential. Despite the use of a precoated material is a use of a conventional pre-forming possible. By the subsequent application of an additional corrosion protection, a conventional forming and trimming is possible even with high-strength materials, so that - when using the manufacturing process according to FIG. 1 - The costly laser cutting can be replaced at high volumes costly. Sheet metal components can be protected by this manufacturing method already in the development by conventional forming simulation on their production. In addition, a favorable combination of the corrosion protection properties of the precoating 33 on the one hand with those of the layer 34 with the advantage of edge coating, in particular AlSi layers 33 in conjunction with zinc layers 34. In a vehicle, in turn, which is joined by such components, the fuel consumption is through reduced the weight of the components, since they can be much thinner than conventional sheet metal parts, while the passive safety is increased because the components have a very high strength.

Claims (7)

1. Method for the production of press-hardened components, more particularly press-hardened components of the body of an automobile, consisting of a semi-finished product (2) made of non-hardened sheet steel adapted for hot working,
   characterized in that
   the following method steps are executed

   - using a cold working method, especially a drawing method, to form a component blank (10) from the semi-finished product (2) pre-coated with a first layer (33),

   - trimming the edge of the component blank (10) to an edge contour (12') that approximately corresponds to the component (1) to be produced;

   - heating the trimmed component blank (17) and press-hardening the same in a hot-working tool (23);

   - coating the press-hardened component blank (18) with a second, anticorrosion coating (34) in a coating step.
2. Method for the production of press-hardened components, in particular a car body component, from a semi-finished product (2) made of non-hardened sheet steel adapted for hot working,
   characterized in that
   the following method steps are executed

   - heating the blank (2) pre-coated with a first layer (33) and press-hardening the same in a hot-working tool (23);

   - trimming the edge of the press-hardened component blank (10') thus formed to a contour corresponding to the edge contour (12) of the component (1) to be produced;

   - coating the press-hardened component blank (18') with a second, anticorrosion coating (34) in a coating step.
3. Method of claim 1 or 2,
   characterized in that
   the second coating (34) is applied onto the press-hardened component blank (18, 18') by means of a galvanizing process.
4. Method of claim 1 or 2,
   characterized in that
   the second coating (34) is applied onto the press-hardened component blank (18, 18') by means of a thermal diffusion process.
5. Method of at least one of the preceding claims,
   characterized in that
   the second coating (34) is deposited both onto the pre-coating (33) and on uncoated parts of the component blank (18, 18').
6. Method of at least one of the preceding claims,
   characterized in that
   after the coating step, residuals from the coating step are cleaned from the coated component blank (18, 18').
7. Method of at least one of the preceding claims,
   characterized in that
   the coated component blank (18, 18') is tempered after the coating step.

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