WO2013189597A1

WO2013189597A1 - Method and device for producing a press-hardened metal component

Info

Publication number: WO2013189597A1
Application number: PCT/EP2013/001808
Authority: WO
Inventors: Fabian Loges
Original assignee: Steinhoff & Braun's Gmbh
Priority date: 2012-06-22
Filing date: 2013-06-19
Publication date: 2013-12-27
Also published as: EP2864506B1; DE202012007777U1; PL2864506T3; DE102012016075B4; PT2864506T; EP2864506A1; DE102012016075A1; ES2688356T3

Abstract

The invention relates to a method for producing a metal component having at least two regions of differing strength properties within said component, obtained by differing cooling speeds of the different regions, characterized by the following method features: a metallic base body (1), which has at least austenitizing temperature, is provided, a region of the base body (1) is shielded during subsequent heat treatment of the base body (1) until the component temperature of said region has dropped to a predetermined temperature (T2) below the austenitizing temperature, but still above martensite start temperature, wherein an average cooling speed below the cooling speed which is critical for martensite formation prevails in said component region, while the unshielded region is kept to at least the austenitizing temperature, the shielding (3) is removed, the base body (1), having a graded temperature profile, is subjected to a reshaping process by a tool, wherein a cooling speed above that which is critical for martensite formation prevails at least in the previously unshielded region. A device for carrying out the method according to the invention has a shielding device (3) having one or a plurality of contoured cover elements (4) for shielding a predetermined region of a base body (1), preferably of a circuit board, wherein the shielding device (3) is designed to stay in the heating unit (2, 5) during tempering of the base body (1) before reshaping the base body in the reshaping tool.

Description

METHOD AND DEVICE FOR PRODUCING A

Press hardened metal parts

The invention relates to a method and a device for producing a metal component, which is to obtain different strength properties within the same component, according to the preambles of claims 1 and 6, respectively.

In many metal components, for example in the automotive industry, there is a requirement that the components on the one hand have a low weight, on the other hand have specifically adjustable strength ranges. For example, a motor vehicle B-pillar have a hard central area to maintain high stability and on the other hand at the upper and lower attachment points to the body be ductile, so that in an impact introduced energy can be dissipated, if possible without causing tearing. To obtain such components, the different structure formation within a steel material is made use of when choosing different cooling rates. Thus, a high cooling rate leads to the predominant formation of hard martensite, while lower cooling rates favor other microstructures such as bainite or the preferred because of their toughness Ferit and perlite.

A base body, which is subsequently thermoformed in a preferably press-hardening process, can be pushed out of the oven, for example, after being heated to austenitizing temperature with one partial area, which then cools slowly in the air, while the other portion is kept in the oven at austenitizing temperature. The subsequent forming leads at sufficient cooling rate to a hard area (which was left longer in the oven and therefore had Austenitisierungstemperatur) and a

CONFIRMATION COPY softer area, which had already cooled a little further in the air and therefore during further cooling by transformation into the microstructure of Ferit, perlite or bainite passes. A corresponding method with additional use of a buffer furnace as a buffer is described, for example, in EP 2 365 100 A2. This method has the disadvantage that only a softer area can be created, a maximum of two, if the oven is very short, so that the component can protrude on both sides. In addition, the transition zone between soft and hard area in the finished component is often undesirably large. In addition, a buffer oven is shown in EP 2 365 100 A2, which has cooled contact surfaces on which the workpiece can be placed in order to extract heat in some areas. Here, however, the buffer oven must be specially tailored to the workpiece, which is very expensive.

In a further method, therefore, the base body is inserted into the forming tool at a uniform temperature, where it is shaped over differently cooled regions of the tool at different cooling rates. However, this often leads to warping of the components and thus to high reject rates.

A further alternative according to EP 1 180 470 B1 is therefore not to heat certain areas into the austenite by partially covering the base body with a cover placed thereon in the furnace during the first heating before the forming process. This can also be done by partial heat removal during the heating process according to DE 10 2006 018 406 B4. However, both methods have disadvantages when, for example, coated materials are used. For example, in the case of an AISi coating, thorough heating is required so that alloying and optimum bonding of the layers takes place. If this is not the case, the aluminum coating adheres to the following Forming process often on the tool, resulting in a high tool wear.

From DE 102 08 216 C1, a method is known in which regions of an end component, which are to have a higher ductility later, are quenched to a cooling-stop temperature which is above the martensite start temperature. Then these areas are kept isothermal and later cooled together with the entire component in the hardening process. To quench the later ductile areas they must be subjected to a cooling medium and sealed off from the other areas. The process is therefore complicated. In addition, the result is not uniform, since the cooling medium itself is subject to a change in temperature. Homogeneity problems can therefore occur.

Finally, DE 10 2010 048 209 B3 describes a method in which a board heated to austenitizing temperature is intermediately cooled in a subarea which receives a mixed structure of martensite and bainite in the following forming process. The intermediate cooling, which is preferably carried out by integrated cooling plates in the forming tool itself, however, is expensive. In addition, the martensite and bainite mixed structure obtained in the subregion is not optimal for many applications due to the high bainite content.

The invention is therefore based on the object of specifying a method and a device which avoid the disadvantages of the previously known processes and in particular enable the production of components with more complicated contours between the regions of different strength properties. This object is achieved by a method having the features of claim 1 and a device having the features of claim 6. Claim 15 relates to a shielding device as an inventively essential component of the device according to claims 6 to 14.

In the method according to the invention, a metallic base body, in particular a sheet steel plate, which may also be coated, is heated to at least austenitizing temperature or made available at this temperature. In a subsequent process step, a region of the base body, which can also be composed of several subregions, is shielded against the action of heat by a shielding device accompanying the workpiece, while the base body continues to be subjected to heat. Thus, the unshielded area of the body is kept at Austenitisierungstemperatur while the shielded area controlled below the Austenitisierungstemperatur but above martensite starting temperature drops, wherein in this component area an average cooling rate below the martensite critical cooling rate prevails, so that the structure of this area after the subsequent forming consists mainly of ferrite and perlite, regardless of the subsequent cooling rate during forming. The cooling of the shielded areas should be done slower than a self-given cooling in air. After the removal of the shield, which may consist of several sub-elements, the base body, which then has a graded temperature profile obtained by the shield, subjected to a forming process by a tool, in particular a hot forming with thereby resulting press hardening. In this case, at least in the previously unshielded region of the base body, a cooling rate above the critical for martensite cooling rate is maintained, ie the cooling of the body is so fast that in the previously unshielded area a structure of predominantly martensite is formed. During the forming do not have different cooling rates for the different areas are set. In particular, both areas of the base body can be cooled at a cooling rate greater than the critical cooling rate for martensite formation, since a martensite transformation can only occur in the previously unshielded area because of the partial cooling of the shielded area or shielded areas.

This method avoids all the disadvantages of those known in the art. Thus, both coated and uncoated materials can be used as the base body, since the starting temperature above the austenitizing temperature results in a previous alloying of the entire base body, whereby the forming tools are spared. Also, components with complicated contours for the different strength properties can be created, as they can be imaged by the design of the shield. Thus, it is possible, for example, to produce a component for a B-pillar with a hard center, a soft upper and lower connection region to the body and a circumferential soft flange, which considerably facilitates the subsequent shape cutting along the entire component in the flange region. In addition, complicated temperature control devices for the forming tool are unnecessary because the deformation can be done with a uniform cooling rate over the entire body, which also avoids the risk of warping of the components when removed from the mold.

Preferably, the shielding takes place contactlessly, at least over the predominant area of the area to be shielded, ie the base body should touch the shielding at as few points as possible. It is particularly advantageous if the base body is mounted on supports, kiln furniture, furnace carriers or the like and the shield is completely contactless with respect to the base body, since then the Shielding is cheaper and almost wear-free. However, the shielding device is workpiece accompanying and not furnace bonded. Preferably, the shielding takes place at least partially via radiation shielding, so that the heat radiation in the shielded areas can not penetrate to the base body. This is preferably even the predominant type of shielding. In order not to leave the temperature profile in the shielded areas of the main body to itself, the shield can be subject to an active temperature control, which is realized by a targeted temperature / cooling of the cover. This serves in particular to protect the shield itself, in order to avoid its excessive heating by the radiant heat of the body, the furnace and / or by the heat application of the rest of the body. Since the surface of the shield may preferably be made of aluminum, it is prevented that it melts. But the introduction of heat energy is possible if, for example, the shield for the desired temperature drop is too strong and even slower cooling is desired.

A device according to the invention is also claimed which has at least one heating unit, or a series main oven, for example a roller hearth furnace, a (multi-layer) chamber furnace or a reciprocating furnace, and a forming tool, in particular a press-hardening tool or a forming press. The heart of the device and therefore claimed separately in claim 15 is a shielding device which has one or more contoured cover elements for shielding the predetermined area of the base body and is designed both in terms of its material and in terms of their functional design so that they in the heating unit can be inserted and stay there with the body, while the body is tempered before forming. The cover (s) are preferably slidably or pivotably attached to the shielding means so as to be according to necessity and intended use can be moved over, under and / or around the area of the body to be shielded. In this case, a shielding device does not have to allow different possibilities of movement of the cover elements, since a shielding device designed especially for its geometry is usually produced for each workpiece to be produced, as there is also a separate press hardening mold for each workpiece. Therefore, the furnace itself does not have to be adapted to the workpiece, but only the shielding device accompanying the workpiece. The cover or the elements are preferably held pivotably or displaceably on a guide element of the shielding. In particular, they can be arranged to be closed and reopened in the manner of a mold. This can be done for example via a rotary knob and a toothed rail, which translates the operation of the rotary wheel in a lateral and opposite movement and extension of the cover.

The device according to the invention and the shielding device can also be used advantageously in processes if the main body has not yet reached complete austenitizing temperature before being taken into the shielding device, ie thorough heating of the main body has not yet been completed. This can be, for example, at a temperature just below Austenitisierungstemperatur, eg Austenitisierungstemperatur minus 30 K. The shielded areas of the body then reach despite austenitisierung temperature despite ongoing heating, while adjusting itself in the unshielded areas. As a result, reduced cycle times can be realized because the Temperierungsphasen be shortened. Without disadvantage, this can be used for uncoated base materials and also for coated base materials whose coating does not require alloy, eg zinc-based coating systems. If the production does not allow a direct adaptation of the shielding device in the series main furnace, a self-sufficient heating unit can be provided into which the shielding device can be integrated. As a result, the heating to austenitizing temperature and the maintenance of the temperature in the unshielded areas of the body, while the shielded areas are already undergoing a targeted cooling, can be decoupled from the main heating unit, which makes sense even if the timing in the different areas takes different lengths.

Arranged by a cover element or cover elements of constant thickness and at a constant distance from the surface of the base body, a transition region in which the material properties pass from those of one area to that of the other area is formed on the separating contour of the cover element in the finished workpiece. The methods of the prior art resulted in a mostly relatively large transition region. By contrast, a very small transitional area of, for example, only 15 to 25 mm can be achieved via the shielding device according to the invention with a sharp-edged contour of the cover elements. However, if a wider transition range is desired, this can also be adjusted with the device according to the invention by varying the thickness of the cover element - and thus the shielding effect - in the direction of the transition zones. A thus targeted adjustment of temperature and strength gradients after final shaping and cooling in the forming tool can also be done by varying the distance of the cover to the main body in the shield. The variation of the distance and the thickness of the cover can also be used together.

A targeted influencing of the component strength of the component to be produced can also take place, in particular, by the fact that the cover element or the covering element Elements have an active temperature control, in particular an active cooling. In addition, the extraction temperature can be adjusted specifically. In particular, by such a controllable and controllable time-dependent temperature control in the shielding significantly higher insertion temperatures of the shielded and thus already partially cooled areas of the body when inserted into the forming tool can be selected, thereby reducing both an abrasive and an adhesive tool wear and significantly improves the formability becomes. Increased degrees of deformation are thus also possible in the areas which should have softened properties after the deformation.

In order to control and, if appropriate, purposefully influence the cooling process during the residence of the base body in the shielding device, it is advantageous if it has an integrated temperature sensor which can be integrated in particular in the cover elements. In addition, the current temperature of the recorded body is to be determined in these areas. If a coupling of the temperature sensor with the active temperature control of the cover, a time-dependent temperature control can be automatically controlled and controlled.

Further advantages and details emerge from the claims and the figures, which i.a. contain preferred embodiments of the invention and are described below; show it:

1 shows schematically a ZTU diagram of the cooling processes according to the invention, FIG. 2 shows an example board before the forming process, FIG. 3 schematically shows different process stages, 4 shows a perspective view of a heating unit with shielding device shown in front,

5 the decoupling of process steps through the use of a self-sufficient heating unit,

Fig. 6, the shielding device according to the invention in different views and partly different scales.

In the diagram of Fig. 1, the various processes of cooling and thus microstructure of the metal component over time, but offset from one another. The unshielded region of the component undergoes a temperature profile along the curve A, in that it is kept at above austenitizing temperature after being heated to at least the austenizing temperature and during the further heat application. The essential cooling of this area takes place only in the forming tool at a cooling rate above the critical for martensite cooling rate (27 to 30 K / s), whereby a targeted martensite takes place. Thus, strength characteristics result in this range of about Rm 1300 MPa - 1650 MPa, Rp0.2 1000 MPa - 1250 MPa, hardness 400 - 520 HV and ε> 15%. The further region of the main body or the other regions which are shielded during the application of heat undergo a temperature profile along the curve B and are cooled on removal from the shielding to a temperature below the Austenitisierungstemperatur but still above the Martenitstarttemperatur and have this cooling in one Experience speed below the martensite critical cooling rate. As a result, in the subsequent rapid cooling in the forming tool no predominantly martensitic structure more achieved, but it is a microstructure with high ferrite and / or Perlitanteil formed. For example, after forming, these areas have strength properties of the order of magnitude Rm output properties - 1300 MPa, Rp0.2 output properties - 1000 MPa, hardness 100 - 400 HV and ε> 15%.

(Note to Fig. 1: In order to illustrate the structure formation, curves A and B are shown in the same diagram.) However, both areas of the base body and later metal component remain exposed to heat for an identically long time, only area B is shielded and area A is not The timeline for the curve A therefore begins practically further to the left in the area of the graph which is no longer shown.)

Fig. 2 shows a base body 1 after removal from the shielding and in front of a further not shown in detail forming. The main body 1 here has the form of a circuit board with locally graded temperature profiles, namely a temperature range T1 and a temperature range T2, wherein T1 is greater than T2, since the region T1 was not shielded. Based on this board 1, the method according to the invention or the device according to the invention is also illustrated in the following figures.

FIG. 3 shows, at the first position, the homogeneous heating of the blank 1 in a heating unit 2, in this case a series furnace of the production line, where appropriate a permeation of a coating takes place when it has been applied. In front of the furnace 2 is a shielding device 3 in the open state, in this case with two cover elements 4. At the second position, the shielding device 3 is moved over the board 1 in the furnace 2 for setting the desired temperature in the covered board area. Position 3 shows the removal of the shielding device 3 including the circuit board 1 from the furnace 2. In the fourth position, the shielding device again shown open and releases the board 1 with graded temperature ranges, as shown in Fig. 2, for the subsequent forming process.

FIG. 4 shows the process stage 3 from FIG. 3 in a perspective view, while in FIG. 5 an autonomous heating unit 5 is provided separately from the furnace 2 for decoupling the process for forming different temperature ranges in the board. Schematically 5 heating elements 6 can be seen in the self-sufficient heating unit and the underlying arranged shield 3. This is shown in more detail in the various views of FIG. 6 with the board 1 received therein. In particular, section B-B shows that the cover elements 4 comprise the board 1 in the areas to be shielded above and below and thus reduce heat radiation from both sides.

It is particularly advantageous in the device according to the invention that the shielding device 3 can be integrated into existing furnace systems or coupled to them. If integration into the series main furnace 2 can not be achieved or if this is not desired, the method can nevertheless be carried out with a self-sufficient heating unit 5. This can also be designed as a heating cooling unit, in particular if the cover elements 4 of the shielding device 3 should have an active temperature control, preferably an active cooling, in order to even more effectively influence the temperature grading of the component 1 before the deformation and thus the strength properties of the finished metal component to be able to.

Claims

claims

1. A method for producing a metal component having at least two regions of different strength properties within the same component obtained by different cooling rates of the different regions, characterized by the following process characteristics:

a metallic base body (1) having at least austenitizing temperature is provided,

- An area of the base body (1) is shielded during a subsequent heat application of the base body (1) until the component temperature of this range has dropped to a predetermined temperature (T2) below the Austenitisierungstemperatur but still above the Martensitstarttemperatur, in this Component area, an average cooling rate below the martensite critical cooling rate prevails, while the unshielded area is still maintained at least austenitizing temperature,

- the shield (3) is removed,

- The base body (1) with a graded temperature profile is subjected to a forming process by a tool, wherein at least in the previously unshielded area a cooling rate above the critical for martensite cooling rate prevails.

2. The method according to claim 1, characterized in that the waste of

Temperature of the body (1) in the shielded area slower as the material-specific cooling characteristic of the body (1) is carried out in ambient temperature.

Method according to one of the preceding claims, characterized in that the shield takes place without contact at least over the predominant surface of the region to be shielded.

Method according to one of the preceding claims, characterized in that the shielding takes place at least partially, preferably even predominantly over radiation shielding.

Method according to one of the preceding claims, characterized in that during the shielding in the covered area a preferably controlled active temperature control, in particular cooling takes place.

Apparatus for carrying out the method according to any one of claims 1 to 5, comprising a heating unit (2, 5) and a forming tool, characterized by a shielding device (3) with one or more contoured covering elements (4) for shielding a predetermined area of a Basic body (1), preferably a circuit board, wherein the shielding device (3) for staying in the heating unit (2, 5) is designed during a temperature of the base body (1) prior to forming in the forming tool.

Apparatus according to claim 6, characterized in that the cover (4) on the shielding device (3) displaceable and / or is pivotally mounted and under, over and / or around the shielded area of the base body (1) is arranged to be movable.

Device according to one of claims 6 or 7, characterized in that the shielding device (3) at least two on at least one guide element (7) slidably and / or pivotally held cover elements (4).

Apparatus according to claim 8, characterized in that the cover elements (4) via the guide element (7) are arranged in the manner of a form closable and apparently

Device according to one of claims 6 to 9, characterized by a self-sufficient heating unit (5), in which the shielding device (3) is integrally formed.

Device according to one of claims 6 to 10, characterized in that the distance of the cover (4) to the base body (1) and / or the thickness of the cover (4) changes to the regions of different temperature of the base body (1) separating contour , in particular the thickness decreases.

Device according to one of claims 6 to 11, characterized in that the cover (4) has an active temperature control.

13. Device according to one of claims 6 to 12, characterized in that the shielding device (3) has a particularly integrated Tem- having peratursensorik for determining the current temperature of the recorded base body (1) in at least one area.

14. The apparatus of claim 12 and 13, characterized by a coupling of the temperature sensor with the active temperature control.

15. Shielding device (3) according to one of claims 6 to 14.