EP2125263B1 - Method and apparatus for the temperature-controlled shaping of hot-rolled steel material - Google Patents

Abstract

The invention relates to a method for shaping sheet steel. In said method, a blank is produced from the sheet steel, the blank is inserted into a shaping tool, and the shaped workpiece is produced from the blank in a one-stage process by means of the shaping tool. Before being shaped, the blank is heated to such a degree that the steel does not undergo any phase transition and the blank is shaped in the ferritic, pearlitic, or bainitic range without exceeding the eutectoid temperature or the recrystallization temperature. The invention also relates to an apparatus for carrying out said method.

Description

The invention relates to a method and a device for tempered forming of hot-rolled steel material.

It is known to produce suitable components from sheet steel by forming, such as deep drawing. Both hot rolled and hot and cold rolled steel grades are used here.

Such forming processes can be carried out both as a hot forming process and as a cold forming process.

In general, hot working describes deformation in the austenitic region. The maximum temperature of 980 ° C should not be exceeded, if no additional annealing should take place. Furthermore, the transformation must be completed above 750 ° C and the cooling must then take place in still air. For this process, only steels for normalizing can be used as they ensure the strength even after annealing at 950 ° C.

The procedure of this procedure is in Fig. 18 shown. In this case, the mostly cut to final contour board 101 inserted into the first part 102 of the tool 103 and freely deformed. In this case, as shown in step 2 of the figure, the board 101 is arched on the ground. In this process, the board 101 can be fixed only in the rest position before deformation in the tool 103. As soon as the upper part 104 of the tool 103 comes into contact with the circuit board 101, there is an unguided, free deformation ( Fig. 18 above). After this deformation, the circuit board 101 is manipulated into the second tool 105 (FIG. Fig. 18 below). In this step, the edges 106, or radii 107 of the workpiece are compressed. At the same time, if desired, embossing of the welding edge can take place. However, since the indentation is free, a dimensionally pronounced embossing of the edge is difficult to carry out. During embossing, there is an opposite curvature 108 of the component. This material is pushed into the ground and not used for the expression. However, this causes large upsetting paths to meet the dimensional accuracy of the edge and radii. That is, due to the high compression paths, the tool is subject to a high degree of wear. In addition, it must also be taken into account that there must always be two parts in the press in this process. However, this in turn compensates for the reduction of the pressing force due to the high forming temperature.

Typical components that are manufactured in this way are axle bridges of trucks. Here, hot forming is used to reduce the forming force and the bending radii. At the same time, in a second step, the bending edges can be compressed, whereby the component undergoes a higher rigidity.

Such a method is z. B. from the US 2,674,783 known. In this method, in the first step, a form and then finally pronounced this preform in a second operation.

This production has the disadvantage that the workpiece must be manipulated twice. There are different cooling rates. Depending on the tool temperature, the cooling rate in the tool may be higher or lower than static air. As will be described, cooling is of great importance for normalized annealed steels.

Due to the two-stage process, the component temperature decreases increasingly. This has the consequence that the forming forces increase and just when calibrating, i. the process step with the highest forming force, the forming resistance is very high and reduces the advantage of hot forming. Furthermore, care must be taken that the second transformation must be completed above 750 ° C or 700 ° C.

Experiments with preheated tool, ie conditions close to operation, however, show that compared to the cooling in air, the cooling rate due to the hot forming is much higher ( Fig. 19 ).

In all experiments, the temperatures in the component were measured online by means of thermocouples. The thermocouples were inserted into elongated holes with a diameter of 2 mm and formed with. A detailed view of the forming process shows Fig. 20 , Here it can be seen that the first forming stage at about 790 ° C and the second forming stage at about 680 ° C are completed. However, this means below the minimum forming temperature of 750 ° C, or 700 ° C. In Fig. 19 It can also be seen that the conversion of ferrite into austenite either between or during the forming takes place. The exact transformation temperature depends on the alloy composition. The final temperature also indicates that the benefits of hot forming, ie low forming forces, can no longer be asserted in the second forming stage.

The choice of steels for such hot forming processes is limited to normalized annealed steels.

Normalized annealed or rolled steels achieve their mechanical properties both in the initial state (normalized rolling) and in the annealed condition, provided that this is a normalized annealing. The heat treatment takes place above the A3 temperature. That is, annealing occurs in the single-phase austenitic region. If these steels are cold-formed, a heat treatment should be carried out if the degree of deformation exceeds 5%.

The mechanical characteristics are achieved mainly by the formation of a ferritic-pearlitic matrix. However, this means that the cooling rate must be maintained exactly to ensure the formation of a fine-lamellar perlite. Cooling must be slow, either in still air or in the oven. It is important to ensure that the ferrite and perlite phases are eliminated and that martensite formation is prevented. From 600 ° C, the cooling rate is not critical. The strength of the material is linearly dependent on the Perlitanteil and this in turn of the carbon content. An increase in strength can be achieved for the most part only by a higher carbon content. This means, however, in a further consequence that the weldability decreases. This is recognizable by the increase of the carbon equivalent (see Fig. 15 ).

For normalized annealed steels, a distinction can be made between normalized rolled products and normalized annealed products, and in the case of normalized rolled products, care must be taken that the last hot rolling is above the austenite recrystallization temperature. This is typically around 950 ° C.

The steel recrystallizes completely and the rolling direction is recognizable only due to segregation effects. The recrystallized austenite then converts into ferrite and perlite at a defined cooling rate. In normalized annealed products, boards or components are heated above the A3 temperature and then cooled in a controlled manner. After this heat treatment, the steel recovers the initial properties. Furthermore, following annealing, the board or component can be formed from the heat. However, it must be ensured that the forming must be completed above 750 ° C. At a degree of deformation of not more than 5%, a temperature of 700 ° C applies. The boards or components are to be cooled in still air.

Thermomechanically rolled steels obtain their strength from targeted production during hot rolling. In this case, the final strain is carried out below the recrystallization temperature of austenite. The temperature control of the recrystallization is carried out by additional alloying elements. These elements, and here predominantly niobium, increase the re-crystallization temperature of the austenite, so that a sufficient process window arises between the A3 temperature and the recrystallization temperature.

Since the microstructure can no longer recrystallise after the last pass, it has a large number of germs for the transformation of austenite to ferrite due to the stretched rolling structure. The result is a very fine-grained microstructure consisting mainly of ferrite and too little bainite. Bainite is a very fine lamellar pearlite that can only solidify in imbalance. This is done by a controlled rapid cooling after the last pass. An additional effect is an increase in the toughness of the material.

Solidification in equilibrium requires slow cooling rates, this applies more to normalizing rolled steels. In addition, the alloying elements in precipitated form as carbides, nitrides or carbonitrides prevent grain growth above 1100 ° C. This also has an advantageous effect in the coarse grain zone of the heat-affected zone during welding.

Normalized annealed steels exhibit critical behavior in the manufacture of hot strip at high strengths due to alloy composition. Due to the lower alloy content of TM steels, they can be produced with significantly higher strengths.

While normalized rolled steels are only standardized up to a maximum yield strength of 460 MPa for sheet thicknesses below 16 mm, TM steels are standardized up to a minimum yield strength of 700 MPa at 8 mm (> 8 mm, the yield strength may be 20 MPa lower) , This information can be found in the standards DIN EN 10025-3 for normalizing rolled steels and for thermomechanically rolled steels the standard DIN EN 10149-2 is decisive.

Acid gas resistant steels are made in the same process as thermomechanical steels. Due to their field of application, however, they are shown in the standard API spec 51 or DIN EN 10208-2. These sheets are characterized by extremely low levels of impurities such as sulfur. This causes recombination of the hydrogen to H ₂ , that is, cracking in the vicinity of manganese sulfides, to be prevented. On the other hand, the toughness is greatly improved even at very low temperatures. Furthermore, the low carbon content reduces the formation of center segregation. This prevents the formation of hard phases in the matrix. To increase the strength, the cooling end temperature must be reduced. The result is a steel with a very fine ferritic microstructure.

A comparison of the manufacturing paths in the hot rolling mill is the Fig. 16 refer to. Here is the difference in the final deformation clearly visible. With the cooling conditions from the rolling heat, the microstructure formation during thermomechanical rolling can still be influenced. The different structures of normalized rolled, or annealed and thermomechanically rolled are the Fig. 17 refer to.

The abbreviations in Fig. 16 are T (temperature), TRS (austenite recrystallization temperature), TM (thermomechanical) and ACC (accelerated cooled).

If one compares the microstructure between normalizing rolled and TM rolled, the increased proportion of carbon-rich perlite (dark phase) can be clearly determined. A grain refinement, and thus an increase in the strength, ductility and toughness is only possible by the thermomechanical production.

The chemical compositions of normalized rolled steel can be found in the standards DIN EN 10149-3 and DIN EN 10025-3. The chemical composition of thermomechanically rolled steel is shown in the standard DIN EN 10149-2. If one compares steel grades with the same minimum yield strength, then the higher carbon contents can be seen in normalized rolled steels.

From the US 5,454,888 is known a method for the production of high-strength steel parts, which are to be thermoformed at 300 ° F to 1200 ° F (149 ° C) warm. The material used should have a ferritic-pearlitic structure. On a special shape is not discussed here. From the EP 0 055 436 For example, there is known a method of reducing springback in mechanically pressed sheet material which is intended to apply counterpressure during forming. The counterpressure piece in this press should in particular control the positioning of the sheet material in the press. However, this document does not disclose forming temperatures or the material to be formed.

For cold forming both steel grades can be used, with thermomechanical steels show better formability at the same yield strengths. An embossing of the edges, or a weld preparation is not possible in the cold forming, since the forces would be too large. For this reason, an economic design of a press for components with complex geometry is no longer present.

The object of the invention is to provide a method which is simple and quick to carry out, with respect to the tool wear is improved and a better controllable Process with lower costs results.

The object is achieved by a method having the features of claim 1.

Further advantageous embodiments are characterized in the subclaims.

It is a further object of the invention to provide an apparatus for carrying out the method with which the forming is carried out simply, quickly and safely, which has low wear, works with a high cycle time and reduces the investment.

The object is achieved with a device having the features of claim 8.

Advantageous developments are characterized in the dependent claims.

In the method according to the invention, the material is indeed heated, but subjected to no phase transformation, that is, the transformation takes place in the ferritic, pearlitic or bainitic region. Neither the eutectoid nor the recrystallization temperature should be exceeded.

For this process, steels can be used, which at temperatures up to max. 700 ° C stable structure possess.

In addition to normalized rolled steels, these include, above all, thermomechanically rolled steels, since they have a stable structure. These steels are also released for stress relief annealing, which occurs approximately in the same temperature range. When using these steels, care must be taken that no recrystallization occurs during the heating and subsequent forming.

Multiphase steels also have martensitic phases in the matrix. However, this martensite is annealed at such high temperatures and thereby changes the mechanical characteristics of the steel grade.

The method according to the invention advantageously makes it possible to reshape without scale. While in known forming processes with temperatures of 900 ° C and higher thick scale layers occur in this case, only thin O-xidhäute formed on the surface of the workpiece. comparing unhardened hot strip with inventively formed components, no difference in surface formation is apparent.

• geführte Umformung
• Stauchen von Material
• Prägen von Schweißkanten
• Bauteilauswurf

This makes it possible to integrate several process steps in a tool, since no annoying scale could interfere with the function. Thus, in the case of the temperature-controlled forming according to the invention, the mentioned two-stage process for the development of sharp radii according to the prior art can be used as a double-acting process. Although this process is performed at lower temperatures than hot working, as only one workpiece is used in the press, compression forces are similarly low. This process allows to combine several process steps in one tool:

• guided forming
• Upsetting material
• Embossing of welding edges
• part ejection

• ein Werkzeug für alle Funktionen;
• geringere Verschleißkosten aufgrund der Prozessparameter und Werkzeugreduktion;
• Erhöhung der Taktzeit, da das Bauteil in einem Arbeitshub gefertigt werden kann;
• Reduzierung der Investition:
  • Kompaktere Ofensysteme nutzbar, dadurch geringerer Ausstoß an CO₂; Presskraft wird nicht erhöht, da sich anstelle von zwei nur ein Bauteil im Werkzeug befindet;
  • Alle Funktionen sind im Werkzeug, das heißt die Presse kann einfach ausgeführt werden.

The cost savings result from the following reasons:

• a tool for all functions;
• lower wear costs due to process parameters and tool reduction;
• Increasing the cycle time because the component can be manufactured in one working stroke;
• Reduction of investment:
  • More compact oven systems can be used, resulting in lower CO ₂ emissions; Pressing force is not increased because there is only one component in the tool instead of two;
  • All functions are in the tool, ie the press can be easily executed.

Figur 1:

den Verfahrensablauf eines zweifach wirkenden erfin- dungsgemäßen Prozesses;

Figur 2:

den Aufbau eines zweifach wirkenden erfindungsgemäßen Werkzeug;

Figur 3:

die Umformkräfte in Abhängigkeit der Temperatur;

Figur 4:

den Temperaturverlauf beim erfindungsgemäßen Verfah- ren bei einer Starttemperatur von 700 °C;

Figur 5:

den Temperaturverlauf beim erfindungsgemäßen Verfah- ren bei einer Starttemperatur von 500 °C;

Figur 6:

die Oxidationsrate von Eisen in Luft;

Figur 7:

die Verfestigung bei 180°-Faltung von TM-Stahl;

Figur 8:

den Härteverlauf bei Vergütungsstahl (V) und thermo- mechanisch gewalztem Stahl (TMBA);

Figur 9:

die mechanischen Kennwerte von thermomechanisch ge- walztem Stahl in Abhängigkeit der Glühtemperatur;

Figur 10:

die Herstellung von Bauteilen nach einer ersten Aus- führungsform des erfindungsgemäßen Verfahrens;

Figur 11:

die Herstellung von Bauteilen nach einer zweiten Aus- führungsform des erfindungsgemäßen Verfahrens;

Figur 12:

die Herstellung von Bauteilen nach einer dritten Aus- führungsform des erfindungsgemäßen Verfahrens;

Figur 13:

die Herstellung von Bauteilen nach einer vierten Aus- führungsform des erfindungsgemäßen Verfahrens;

Figur 14:

eine Gegenüberstellung von thermomechanisch gewalztem Stahl gegenüber normal geglühtem Stahl;

Figur 15:

die Streckgrenze und das Kohlenstoffäquivalent für verschiedene Herstellverfahren und Stahlsorten;

Figur 16:

die Herstellung von warmgewalztem Stahl;

Figur 17:

das Gefüge aufgrund der unterschiedlichen Herstellung von warmgewalztem Stahl;

Figur 18:

den Verfahrensablauf eines zweistufigen Prozesses nach dem Stand der Technik;

Figur 19:

den Temperaturverlauf beim Warmumformen nach dem Stand der Technik bei einer Starttemperatur von 940°C im Vergleich zu einer Luftabkühlung;

Figur 20:

den Temperaturverlauf beim Warmumformen nach dem Stand der Technik bei einer Starttemperatur von 940 C.

The invention will be explained with reference to a drawing, in which:

FIG. 1:

the procedure of a dual-acting inventive process;

FIG. 2:

the structure of a dual-acting tool according to the invention;

FIG. 3:

the forming forces as a function of the temperature;

FIG. 4:

the temperature profile in the process according to the invention at a starting temperature of 700 ° C;

FIG. 5:

the temperature profile in the process according to the invention at a starting temperature of 500 ° C;

FIG. 6:

the oxidation rate of iron in air;

FIG. 7:

solidification at 180 ° folding of TM steel;

FIG. 8:

the hardness curve for tempered steel (V) and thermo-mechanically rolled steel (TMBA);

FIG. 9:

the mechanical characteristics of thermomechanically rolled steel as a function of the annealing temperature;

FIG. 10:

the production of components according to a first embodiment of the method according to the invention;

FIG. 11:

the production of components according to a second embodiment of the method according to the invention;

FIG. 12:

the production of components according to a third embodiment of the method according to the invention;

FIG. 13:

the production of components according to a fourth embodiment of the method according to the invention;

FIG. 14:

a comparison of thermomechanically rolled steel versus normally annealed steel;

FIG. 15:

the yield strength and the carbon equivalent for different production processes and grades of steel;

FIG. 16:

the production of hot-rolled steel;

FIG. 17:

the structure due to the different production of hot-rolled steel;

FIG. 18:

the procedure of a two-stage process according to the prior art;

FIG. 19:

the temperature curve during hot forming according to the prior art at a starting temperature of 940 ° C compared to an air cooling;

FIG. 20:

the temperature curve during hot forming according to the prior art at a starting temperature of 940 C.

Fig. 1 and 2 show the structure of the tool. Depending on the type of applications, the tool parts can be carried out cooled.

In the upper part 7 are the stamp 2, which generates the shape of the component and the Prägeleisten to the expression of small radii and, if necessary, the welding preparation. Of the Stamp 2 is connected via a spring assembly 4 with the upper part 7. This spring package may consist of steel springs and hydraulic spring / damper systems or gas springs. In the lower part 11 are the die insert 3 and the die 6 itself. The spring assembly 5 for controlling the die insert 3 may also consist of steel springs and hydraulic spring / damper systems or gas springs.

• Die Ablage der auf Wunsch endgeometrienahen Platine 1 erfolgt zum einen auf das Unterteil 11 des Werkzeuges und zum anderen auf den Matrizeneinsatz 3. Berührt nun das Oberteil 7 die Platine 1, so wird durch beidseitigen Kontakt von Oberteil 7 und Matrizeneinsatz 3 die Platine 1 geklemmt und die Umformung erfolgt geführt und nicht frei. Des weiteren kann sich dadurch auch keine Wölbung im Werkzeug einstellen. Bei der weiteren Verformung (Schritt 2) wird nun der Matrizeneinsatz 3 durch den Stempel 2 verdrängt. Dabei sind die Kräfte der Federpakete von Stempel 2 zu Matrizeneinsatz 3 so abgestimmt, dass in der Platine 1 keine Abdrücke erzeugt werden. Im Schritt 3 wird der Bauteil zur Gänze umgeformt, wobei der Stempel 2 dabei den unteren Totpunkt erreicht hat. Gleichzeitig stützt sich nun der Matrizeneinsatz 3 in der Matrize 6 ab, sodass die Prägekräfte nicht über das Federpaket 5 übertragen werden müssen. In weiterer Folge wird nun das Federpaket 4 im Stempel 2 verdrängt und die Ausprägung durchgeführt (Schritt 4). Nach dem Öffnen des Werkzeuges dient die Federkraft des Matrizeneinsatzes 3 zum Ausstoßen des Bauteiles, das heißt das Werkzeug nimmt wieder die Position in Schritt 1 ein.

The production of a component by means of a double-acting process can be explained as follows:

• The storage of the desired endgeometrienahen board 1 takes place on the one hand on the lower part 11 of the tool and on the other on the die insert 3. Now touches the upper part 7, the board 1, so by both sides contact of the upper part 7 and die insert 3, the board 1 is clamped and the forming is done and not free. Furthermore, this can also adjust any curvature in the tool. In the further deformation (step 2), the die insert 3 is now displaced by the punch 2. The forces of the spring assemblies of stamp 2 are matched to die insert 3 so that in the board 1 no prints are generated. In step 3, the component is completely transformed, wherein the punch 2 has reached the bottom dead center. At the same time, the die insert 3 is now supported in the die 6, so that the embossing forces do not have to be transmitted via the spring assembly 5. Subsequently, the spring package 4 is now displaced in the punch 2 and the expression is carried out (step 4). After opening the tool, the spring force of the die insert 3 is used to eject the component, that is, the tool assumes the position in step 1 again.

The production of a component with tight radii and / or weld preparation therefore takes place in a stroke or step of the tool. A processing of the welding edge allows the further use of components for component production without a machining intermediate machining of the edge.

Depending on the starting material, the boards can be heated between 500 ° C and 700 ° C. Fig. 3 shows the necessary forming forces as a function of the temperature on an identical component. From this diagram it can be seen that hot forming at 900 ° C halves the pressing forces compared to tempered forming. However, since the final temperature drops to 700 ° C in the two-stage hot forming process, the forming forces increase to 1.5 times (-..- line). Considering further that two components are in the press, it can be assumed that the press must be designed similarly to the tempered forming. In addition, the increased friction at 900 ° C is clearly visible. While at lower temperatures, the force decreases after the first forming, the Umformwiderstand at 900 ° C remains approximately constant, which suggests increased friction due to the present Zunders in Zargenbereich. This phenomenon occurs in step 2 in Fig. 18 during the forming.

The temperature profile of the tempered forming according to the invention is the example of a transformation of 700 ° C in Fig. 4 seen. On the one hand shows that the production of the component was carried out in one step, the second occurs while a maximum temperature loss of only about 120 ° C. Compared to hot forming, it can be seen that a reduction of the initial temperature of approx. 240 ° C results in a reduction of the final temperature of only 100 ° C.

Another example is in Fig. 5 seen. In this case, the board temperature at the beginning of the forming was 500 ° C. The evaluation shows that in the region of the bottom and the frame, the temperature loss is less than 100 ° C, while in the region of the edge, ie at the point where the Prägeleisten attack, a reduction in the forming temperature of more than 150 ° C occurs. Due to the heat conduction in the component, however, an immediate increase in the temperature is still the opening of the press. Fig. 6 shows the dependence of the oxidation rate of iron on air as a function of the temperature. If one selects the oxidation rate at 600 ° C as a reference, the rate increases sevenfold at 700 ° C and 230 times at 950 ° C. This makes the advantage of tempered deformation according to the invention clearly. The drastic reduction of oxide formation on the component surface reduces the wear of the tool. The second cost effect is the increase in the cycle time, since the intermediate cleaning of the tool can be many times less, or eliminated.

Only by combining temperature control and material selection is it possible to implement the process according to the invention.

Compared to cold forming, much more complex geometries are possible. This is caused by a Nachfördern the material during the forming. As a result, substantially lower outer and inner radii can be produced while maintaining the starting cross-section of the starting material. Therefore, it is possible that with the same mechanical properties of the material larger loads are transmitted, since the surface resistance torques can be greatly increased. With the same load, the wall thickness can be reduced accordingly and thus weight can be saved.

In conventional cold forming, the material is thinned out in the deformation area.

As already mentioned, the cooling rate has only a small influence on the mechanical properties of the material after forming, while with the use of normalizing rolled steels, the cooling rate is an essential function for achieving the mechanical properties.

If the annealing conditions for forming are maintained, the yield strength increases due to accelerated aging effects. Furthermore, precipitations can still form.

Short term temperatures, e.g. occur during flame straightening, if they are carried out according to the delivery condition of the starting material, can be carried out analogously to the starting material.

Due to the selected temperature range for forming all materials can be used, which retain their properties by a tempered heat treatment. This also applies to normalizing rolled steels, if special processing requires the use of these steels.

Preference is given to using thermomechanical steels, since the already good formability at room temperature is improved by the tempered forming and the process can be supplemented by upsetting processes.

In comparison to cold forming, only moderate hardening effects occur in tempered forming, since the deformation is in the range of the recovery of the material, and as a result the solidification can be reduced without incubation time. A Homogenization of internal stresses is the result. A reduction in solidification is in Fig. 7 seen.

The tempered forming according to the invention does not limit the further processing with respect to welding or surface coatings. This method makes it possible to produce complex components with high strengths without restriction to subsequent processes. Due to the hot forming, for example, only normalizing rolled steels can be used. As already described, these are much more critical to welding due to their alloy composition. In addition, due to the high temperature, the surface needs to be cleaned considerably more expensively.

The fundamental prejudice against the use of thermomechanical steels is their sensitivity to high temperatures, as they occur, for example, in welding. However, modern TM steels also have very good mechanical properties after welding due to their alloy composition. This is achieved, inter alia, by the addition of micro-alloying elements. Finely dispersed precipitates of micro-alloying elements in conjunction with nitrogen or carbon impede the formation of coarse grain in the heat-affected zone, as grain boundary growth becomes difficult to adhere to. As a result, the softened zone becomes very narrow, as in Fig. 8 shown on the right side (WEZ = heat affected zone, SG = weld metal). In both cases, the drop in hardness is the same, with the softening zone being much narrower in the thermomechanically rolled steel. This is due to the fact that no softening of the material occurs below AC1 (eutectoid temperature), ie the grain size does not change. Above AC1 there is a transformation into austenite followed by the above mentioned coarse grain formation.

With tempered steel (V), the softening zone is designed to be much wider, since it also undergoes transformations below the ACl. In this case, tempering effects occur and thus change the mechanical properties of the material. In addition, due to the higher carbon content, there is an increased carburization in the transition region from the melt to the heat-affected zone. This is particularly critical under dynamic loading as it acts like a metallurgical notch.

The invention will be further described by means of embodiments, wherein a specific choice of material is not made here, so that in the method according to the invention all materials already described can be processed.

The method allows, so to speak, the use of standardized steels, provided that the annealing conditions are maintained analogous to stress relief annealing. During production, however, a recrystallization must be avoided during the forming, as this is accompanied by a reduction in strength. Steels are used which have a strong tendency to start, e.g. due to martensitic phases, a loss of strength is to be expected.

example 1

An example of the use of a thermomechanically rolled steel for tempered forming is shown in FIG Fig. 9 shown. The samples were heated to the respective temperature within 15 minutes. In all cases, a complete warming could be ensured. Subsequently, the samples were cooled in air, in water or between two cooled copper plates. The Evaluation shows that up to a temperature of 700 ° C the mechanical properties are at least equal to the initial values. An increase in the yield strength is due to accelerated aging. Above 700 ° C, a change in the structure occurs, the formation of austenite begins. A softening of the thermomechanically rolled steel is the result.

The method described above for the production of components by means of tempered forming can be carried out by different tool designs. Furthermore, the functions of springs, hydraulic dampers and gas pressure dampers can also be taken over by the press itself. Depending on the number of pieces and the accuracy of the components, water cooling can be carried out in the tools. In contrast to curing in water-cooled tools, in this case, no such cooling rates must be achieved. The cooling is intended to protect the tool and its functions from thermal stress.

All methods have the simplification in common that in one step both the deformation, as well as the embossing of the side edges takes place. An additional ejector, which could destroy the contour, or the surface of the component is not necessary in any execution. At the same time, lateral clamps on the die insert prevent the component from sticking to the punch. These clamps open automatically when opening the tool or can be controlled with hydraulic or gas.

Example 2

The procedure is in Fig. 10 shown.

Step 1:

At the beginning of the forming, the board 1 between the punch 2 and die insert 3 is clamped. This can prevent slippage of the board. In conventional methods, the forming is done due to the omission of a die insert, i. the board is not guided. In classic hot forming, chipping scale can affect the operation of the die insert. Spring 4 and spring 5 are on bias.

Step 2:

The forming takes place in the clamped state. Spring 4 is on bias, spring 5 is displaced by the punch 2.

Step 3:

The punch and die insert reach the bottom dead center. If no welding processing of the edges or thickened corner areas is necessary, step 4 can be skipped. Spring 1 is displaced to preload, spring 2 by stamp and the die insert 3 is based on die 6 from.

Step 4:

In order to save costs, in this step, the processing of the welding edge with processing punch 7 with stamping strips 8, regardless of the welding process and the necessary angle. At the same time, the radii of the corners can be reduced both inside and outside become. In addition, the wall thickness in this area is increased. Spring 4 is displaced by the stamping strips spring 5 remains in position.

Step 5:

The die insert 3 also serves to eject the component and can accommodate the next board in this position.

Advantages:

• no free forming by die insert;
• Embossing takes place only when the component is in the lower dead center, ie It is not moved by the embossing material into the ground - smaller compression path than in the prior art (see Fig. 18 );
• simple tool design, i. only one spring system in the stamp necessary;
• low tooling costs;
• no additional path-dependent control in the tool necessary.

Example 3

The procedure is in Fig. 11 shown.

Step 1:

Board 1 is clamped between die 6 and 2 stamp. Depending on the component, a die insert may support the clamping (not shown). F1, F2 and F3: see note in Fig. 11 ,

Step 2:

The components are freely deformed when leaving the Matrizeneinsatzes. F1, F2 and F3 without change.

Step 3:

The stamp 2 is retracted, this is done by the control of F1. Stamping strips 8 come into contact with the frame 9. F2 and F3 remain unchanged.

Step 4:

System moves to step 9 on Contact with Overhead 9.

Step 5:

The edges 10 of the component touch the Matrizenboden. This causes a storage of the material in the soil. F1, F2 and F3 analogous to step 3.

Step 6:

Top 7 moves down, F3 is completely displaced. F2 is proportionately displaced by this amount. This causes a displacement of the material in the corners, without a high friction occurs in the frame area.

Step 7:

Embossing of the component by completely displacing F3.

Advantages:

• Material storage in the soil;
• low wear in the frame;
• slight compression over the frame necessary.

Example 4

The procedure is in Fig. 12 shown.

Step 1:

Board 1 is clamped between die 6 and 2 stamp. Depending on the component, a die insert may support the clamping (not shown). F1 and F2: see note in Fig. 12 ,

Step 2:

The components are freely deformed when leaving the Matrizeneinsatzes. F1 and F2 without change.

Step 3:

The bottom area is clamped between punch 2 and 9 Vorwölber. F1 and F2 without change.

Step 4:

F1 is displaced by the downward movement of the upper part 7, so that the stamping strips 8 press the component into the die 6 in the corner area. F2 remains unchanged.

Step 5:

Stamp 2 and Prägeleisten 8 simultaneously go down and emboss the component. This F2 is displaced.

Advantages:

• simple tool design, i. only one spring system in the stamp necessary;
• low tooling costs;
• no additional path-dependent control in the tool necessary;
• Stockpiling of material in the floor area through protrusions.

Example 5

The procedure is in Fig. 13 shown.

Step 1:

Board 1 is clamped between die 6 and 2 stamp. Depending on the component, a die insert may support the clamping (not shown). F1 and F2: see note in Fig. 12 ,

Step 2:

The components are freely deformed when leaving the Matrizeneinsatzes. F1 and F2 without change.

Step 3:

The bottom area is clamped between punch 2 and 9 Vorwölber. F1 and F2 without change.

Step 4:

The stamp 2 holds its position by controlled displacement of F1. The upper part 7 moves downwards, so that the stamping strips 8 press the component in the corner area into the die. F2 remains unchanged.

Step 5:

Stamping bars move to the final dimension of the component and the punch remains in a constant position F1 controls the relative movement to the stamping bar so that the punch position remains constant. F2 remains unchanged.

Step 6:

Stamping of the component by extending the stamp by means of F1. F2 is displaced by this.

Advantages:

• Upper part only needs one spring system;
• low tooling costs;
• Stocking in the ground area independent of the crushing height of the stampingists.

In the invention, it is advantageous that a method and a device are provided, with which a guided deformation, including the upsetting of material, embossing of welding edges and the component ejection within a tool can be performed reliably, quickly and safely, wherein due to the process control, in particular the low temperatures, less wear occurs, the cycle time is increased and more compact furnace systems are available. In addition, the scale formation is reduced, which reduces post-processing and gives the opportunity to produce complex components from higher-strength TM steels.

As a sheet steel for the boards, bare sheet metal but also coated sheet metal can be used.

Suitable coatings are electrolytic or the most diverse hot dip galvanizing, optionally with an alloying step, zinc-aluminum or aluminum-zinc layers, aluminum layers but also nano-layers, etc.

Claims (10)

1. Method for shaping steel sheet, wherein a plate is produced from the steel sheet, the plate is inserted into a shaping tool and the shaped workpiece is produced from the plate with the shaping tool in a single-stage process, wherein the plate is heated prior to shaping, wherein the heating is carried out to an extent where the steel does not undergo any phase transition, and the shaping takes place in the ferritic, pearlitic or bainitic range without the eutectoid or recrystallization temperature being exceeded, characterised in that the side edges of the shaped workpiece are stamped or compressed with stamping ledges for stamping small radii and/or for increasing the wall thickness in this area and/or welding pre-processing.
2. Method according to claim 1, characterised in that the steel used is a steel which has a stable structure at temperatures of up to maximally 700°C.
3. Method according to any one of the preceding claims, that a normalized-rolled steel, a normalized steel or a thermo-mechanically rolled steel are used as the steel material.
4. Method according to any one of the preceding claims, characterised in that the steel is heated to a temperature of 400°C to 800°C, preferably to 600°C to 750°C.
5. Method according to any one of the preceding claims, characterised in that the plate is inserted between an upper shaping tool part and a lower shaping tool part, wherein the upper part comprises a punch that produces the shape of the component, and the stamping ledges for stamping small radii and, if so desired, a welding pre-processing are additionally present, and the lower shaping tool part comprises a die insert as well as the die itself, wherein, by the upper part touching and the contact of the upper part and the die insert on both sides, the plate is clamped and the shaping carried out, wherein, if shaping is continued, the die insert is displaced by the punch and the component is shaped completely, until the punch has reach the bottom dead centre, the die insert supporting itself in the die and stamping being carried out subsequently.
6. Method according to any one of the preceding claims, characterised in that bare or coated steel sheet is used as the steel sheet for producing the plates.
7. Method according to claim 6, characterised in that electro-galvanized steel sheet, galvanized steel sheet (hot-dip galvanized steel sheet), a hot-dip coated steel sheet with a hot-dip coating of zinc and aluminium, or aluminium and zinc and optionally other metals, or a coating substantially of aluminium and silicon, or a coating of zinc alloyed with the steel in an alloying step, is used as the coated steel sheet.
8. Apparatus for the temperature-controlled shaping of a steel plate, wherein the plate is inserted into a shaping tool and the shaped workpiece is produced from the plate with the shaping tool, in particular apparatus for carrying out the method according to any one of the preceding claims, characterised in that the apparatus comprises an upper part (7) and a lower part, wherein a punch (2) that produces the shape of the component is disposed in the upper part, and stamping ledges for stamping small radii and, if required, a welding pre-processing are additionally present, wherein the punch is connected with the upper part (7) via a spring assembly (4), and a lower part (11) is additionally present in which a die insert (3) and the die (6) itself are disposed, wherein a second spring assembly (5) is present for controlling the die insert (3).
9. Apparatus according to claim 6, characterised in that the spring assemblies (4, 5) consist of metal springs, in particular steel springs, hydraulic springs, damping system or gas-pressure springs.
10. Apparatus according to claim 6 or 7, characterised in that there is a bulger (9) at the bottom of the die.

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