EP2264193B1 - Production of a partially press-hardened metal sheet component - Google Patents

Description

The invention relates to a method for producing a partially press-hardened sheet metal component according to the preamble of claim 1. The invention further relates to a covering device for producing a partially press-hardened sheet metal component according to the preamble of the independent claim.

The press-hardening of sheet-metal components, in particular of a steel sheet material, is well known from the prior art. Representative is in this regard on the GB 1 490 535 from 1974 directed. In press-hardening, the strength and / or hardness of a sheet material is increased by a heat treatment and final cooling in a press-hardening tool. The increase in strength and / or hardness (hardening) of the sheet material is based essentially on a structural transformation.

In the DE 103 41 867 A1 Among other things, a method for producing a press-hardened sheet metal component is described, which has various areas which have a different degree of hardness. For this purpose, a sheet metal component intermediate form produced in a first method step is heated in an oven to the required hardening temperature and then subjected to a cooling in regions in a press hardening tool. A similar procedure is in the DE 10 2004 038 626 B3 described. A disadvantage is the sometimes very high tooling effort. Another disadvantage is a difficult process management.

The closest prior art forming DE 200 14 361 U1 describes the production of a B-pillar for a motor vehicle in the thermoforming process, wherein, starting from a molding board or a preformed longitudinal profile, this or this austenitized in an oven and then in a cooled tool deformed and hardened (press-hardened). In the oven, large areas of the board or the preformed longitudinal profile can be protected by insulation against the influence of temperature and against structure-changing heating.

The EP 0 632 137 A1 describes another strategy in which the partial heating in the oven takes place through areas covered on the outside.

The prior art is still on the DE 103 05 725 B3 . DE 10 2006 018 406 A1 and EP 2 322 672 A1 pointed.

An object of the invention is to provide an improved method for producing partially press-hardened sheet-metal components, which requires in particular a lower tooling expense. Furthermore, it is an object of the invention to provide a device which can be used to assist in carrying out the method.

This object is achieved by a method according to the features of claim 1 and by a covering device according to the features of the independent claim. Preferred and advantageous developments are the subject of the respective dependent claims.

The inventive method is used to produce a partially press-hardened sheet metal component, wherein the starting sheet material is first formed into a sheet metal part and this forming is followed by a press hardening, for which this sheet metal part is partially heated in an oven and thereafter the press-hardening of the partially heated sheet metal part takes place. According to the invention, for partial heating in the furnace, at least one region of the sheet metal part which is not to be hardened or hardened is covered with two rigid shell molds, which are applied on both sides to the sheet metal part in the relevant area, the inner contour of the shell molds having the spatial contour of the sheet metal part in the area to be covered corresponds or is approximated, and that the thus partially covered sheet metal part is placed as a whole in the oven.

A sheet metal component has a spatial shape design. A partially press-hardened sheet-metal component is a sheet-metal component which has various regions (at least two) in which the sheet-metal material has a strength and / or hardness which can be differentiated from one another. In particular, it is provided that the sheet-metal component produced by the method according to the invention has at least one region in which the strength and / or hardness of the sheet metal material remains substantially unchanged relative to the starting sheet material. In essence, this means that due to various effects, even in such an area quite a slight increase in strength and / or hardening of the sheet material may occur, which, however, in the result significantly below that of the other area or the other area.

An "area" may be determined spatially and / or areally. "Strength" is understood to mean a material property of the sheet material which describes the mechanical resistance which the material of the sheet material brings about for plastic deformation or also for a separation. "Hardness" is understood to mean a material property which describes the mechanical resistance which the material of the sheet metal material opposes to an external mechanical action. Strength and hardness can be correlated according to common material models. Curing can also influence the ductility of the material.

The invention is based on the idea to achieve a partial press-hardening of the sheet metal component by a different, partial heating of the sheet material, wherein the not to be hardened or less hardened area is covered and this covered and / or shielded area in the oven not on the required Hardening temperature can heat and / or the required hardening temperature in this range can not be maintained for a sufficient period of time. Covering virtually results in thermal shielding of the covered area. Simply put, the press-hardened sheet-metal component acquires locally different properties due to the different insertion temperatures in the press-hardening tool, which primarily includes hardness, strength and / or ductility.

In accordance with the method according to the invention, initially a deformation of the starting sheet material into a sheet metal shaped part takes place, by which is meant a sheet metal part intermediate shape. This can be done in a single-stage or multi-stage deep drawing process. This is preferably a cold forming.

Subsequently, a partial heating of this sheet metal part takes place in an oven. For this purpose, at least one area of the sheet metal part which is not to be hardened or less hardened is covered and thermally shielded. The partially covered and / or shielded sheet metal part is placed as a whole in the oven. Such a furnace is preferably a continuous furnace. In the oven, a protective gas atmosphere may be formed. Furthermore, such an oven may have different temperature zones.

Then, if necessary, after removing the covers, the press hardening of the partially heated sheet metal part in a press-hardening tool. In this press hardening tool, a uniform and / or partially differentiated cooling of the sheet metal material can take place, whereby defined the hardening and / or increase in strength of the sheet material occurs.

The method according to the invention can be supplemented by intermediate steps, further steps and / or further partial steps, some of which are the subject of preferred developments.

The invention provides i.a. the advantage that even existing press hardening plants can be converted easily and at relatively low cost to a partial press hardening. Another advantage is in particular the possibility of partial press hardening coated steel materials, as explained in more detail below.

A sheet metal component produced by the method according to the invention is, in particular, a body component of a motor vehicle (motor vehicle body component). This may be a structural part, such as a B-pillar part, or an attachment part, such as a bumper reinforcement. The sheet metal component may, however, also be, for example, a chassis component, such as, for example, an axle carrier.

According to a preferred embodiment, it is provided that the uncovered and / or shielded region of the sheet metal part is heated in the oven to above 900 ° C. The aim is that, in a steel material, this range will reach the austenitizing temperature required for press hardening and that this range will be maintained in the oven for a sufficiently long time at this austenitizing temperature, e.g. is adjustable in the oven by the residence time of the sheet metal part. On the other hand, the partial covering prevents the austenitizing in the covered and thermally shielded area wholly or at least partially, so that in this area no or only a small quench hardening is possible during press hardening.

According to a preferred development, it is provided that the shaping of the sheet metal part, i. the sheet metal component intermediate form, substantially already corresponds to that of the produced partially press-hardened sheet metal component. In press-hardening, therefore, no further shaping is required or only a very small shaping (for example in the region of component radii), which is indicated by the expression "substantially". This is particularly advantageous with regard to the surface of the sheet metal component to be produced, even if the sheet metal material optionally has a coating.

Preferably, it is further provided that the press-hardened sheet-metal component subsequently no longer has to be trimmed. This can be achieved by a corresponding trimming the sheet metal part, which is less expensive. Furthermore, even before the press hardening, possibly also directly into the output board, holes and recesses can be introduced.

According to a preferred embodiment, it is provided that the starting sheet material is a coated steel sheet. The coating serves as corrosion protection, for example. Such a coating is in particular a zinc-containing coating, which is in particular essentially formed from zinc, and which has preferably already been applied by the manufacturer. Compared to the prior art, the use of zinc-coated starting sheet materials is largely unproblematic. As steel sheet material in particular a steel material of the type 22MnB5 or 16MnB5 is provided.

According to a preferred embodiment, it is provided that the degree of thermal shielding of a relevant area to be covered is adjusted by the choice of the cover, a cover material, its nature and / or its arrangement on the sheet metal part. As cover, e.g. reusable cover devices (as explained in more detail below) into consideration. The degree of thermal shielding may be e.g. be measured in percent. A 100% thermal shield can be considered as a thermal insulation, which substantially prevents heating of the sheet material during the residence time in the oven in the shielded area. A lower thermal shield leads to heating of the shielded area and a corresponding increase in strength and / or hardening of the sheet material during the press hardening, which is well below that of the other, uncovered area. As a result of the degree of thermal shielding, the strength and / or hardness of the sheet metal material that results during press hardening can thus be adjusted in a targeted manner.

According to a preferred refinement, a plurality of regions of the sheet-metal shaped part are covered in such a way that different degrees of thermal shielding result. This makes it possible to produce (in a single pass) a press-hardened sheet-metal component with a wide variety of strength and / or hardness ranges. Such a component may be referred to as a complex press-hardened sheet metal component.

It is envisaged that the covering takes place by means of at least two shell molds, which are applied on both sides of the sheet metal part in the area concerned. It is further provided that an inner contour of such a shell shape corresponds to the spatial contour of the sheet metal part in the area to be covered or this is approximated. A mold shell is rigid. On a sheet metal part several shell molds of different design can be arranged.

According to a preferred embodiment, it is provided that such a mold shell is essentially formed from a heat-resistant fiber material. Preferably, this fiber material is pressed and in particular compression molded used. A heat-resistant fiber material is in particular a rock wool, a silicate wool, an asbestos material or an asbestos substitute material.

According to a preferred embodiment, it is provided that a mold shell is formed from a ceramic material. Preferably, a mold shell is formed from a ceramic foam material.

According to a preferred embodiment, it is provided that a mold shell is formed from a metallic material. In particular, a mold shell is formed from a sheet metal material. In such a shell mold, it may be e.g. to act a section of an identical sheet metal part, one of which is placed in the area to be covered on the sheet metal part and placed under.

According to a preferred embodiment, it is provided that a mold shell is formed from a composite material. Such a composite material may e.g. may be formed of a plurality of the aforementioned materials, e.g. are arranged in a sandwich structure.

According to a preferred embodiment, it is provided that a mold shell does not essentially rest directly on the sheet metal molding. Rather, a spacing or a spacing gap is provided between the surface of the sheet metal part and the inner surface of the mold shell to allow a relative thermal movement to each other and the surface of the sheet metal part and possibly their coating to protect against damage. By means of such a spacing, the degree of thermal shielding can also be changed. However, the mold shell and the sheet metal part can touch one another in a punctiform manner, which is indicated by the phrase "essentially".

According to a preferred development, it is provided that a heat-resistant material is arranged at least in sections between a mold shell, in particular a metallic or ceramic shell mold, and the sheet metal molded part. Such a material may be, for example, one of the abovementioned materials or a material composite formed therefrom, which is available, for example, in the form of a flexible mat or a flexible braid. The covering device according to the invention serves to cover a region which is not to be hardened or less hardened during the heating of a partially press-hardened sheet metal part in an oven. It is a reusable cover, which can reduce costs. The covering device comprises an upper part and a lower part and at least two rigid shell molds, which can be applied on both sides of the sheet metal part in the area concerned, wherein the inner contour of the shell molds corresponds to the spatial contour of the sheet metal part in the area to be covered or this is approximated

It is preferably provided that the covering device is designed as a unit which is designed to completely receive the area of the press-hardening sheet-metal shaped part which is not to be hardened or less hardened.

According to a preferred embodiment, it is provided that the covering device comprises at least one mold shell according to the above statements, the rigid, i. dimensionally stable, is formed.

According to a preferred development, it is provided that the covering device has at least one means for automated attachment and / or removal on or from the press-hardening sheet-metal shaped part. This will be explained in more detail below in connection with the figures.

The method according to the invention is preferably carried out using at least one covering device according to the invention.

Fig. 1

ein erfindungsgemäßes Verfahren in einer schematischen Übersicht;

Fig. 2

am Beispiel einer B-Säule einen erfindungsgemäß abzudeckenden Bereich, in einer perspektivischen Ansicht;

Fig. 3

eine wiederverwendbare Abdeckeinrichtung in einer schematischen Schnittansicht und Detailansicht; und

Fig. 4

eine alternative Ausführungsmöglichkeit einer Abdeckeinrichtung in einer schematischen Schnittansicht.

The invention will be explained in more detail by way of example with reference to FIGS. Show it:

Fig. 1

a method according to the invention in a schematic overview;

Fig. 2

the example of a B-pillar according to the invention to be covered area, in a perspective view;

Fig. 3

a reusable cover device in a schematic sectional view and detail view; and

Fig. 4

an alternative embodiment of a covering device in a schematic sectional view.

Fig. 1 shows the inventive method for producing a partially press-hardened sheet metal component according to a preferred embodiment in a schematic overview. The illustrated method comprises six steps I to VI, wherein further steps and / or sub-steps may be provided, such as a Entgraden or cleaning, which are not listed in detail.

The method begins in step I with the provision of a sheet of hardenable steel sheet material. This board is formed in step II in the cold state to form a sheet metal part. The forming takes place in particular by deep drawing. In step III, individual areas of this sheet metal part, ie at least one area covered, which should not be cured in a subsequent press hardening or only to be less hardened. In step IV, the partially covered sheet metal part, together with the covers, is placed in an oven. In the oven, the uncovered areas are heated to austenitizing temperature (> 900 ° C, sometimes up to 950 ° C) and kept at this temperature level over a defined period of time. Depending on the cover, the covered areas are not heated at all or only slightly heated, as long as the residence time in the furnace is not too long and / or the temperature in the furnace is not too high. Subsequently, the partially heated sheet metal part is removed from the oven and inserted after removing the covers in a press hardening tool. The press hardening tool is arranged in a closing device, in particular a press. In step V, the press-hardening tool is closed by means of the closing device, whereby the heated sheet-metal molding portions are quenched and hardened in the cooled press-hardening tool (quench hardening). This quench hardening in the press hardening tool takes place under a simultaneous shaping or shape retention, for which purpose the press hardening tool remains closed under the action of force. In step 6, the press-hardened sheet metal component is removed from the press-hardening tool to be subsequently processed further.

Fig. 2 shows the inner reinforcement part 10 of a B-pillar for a motor vehicle body. This is a press-hardened sheet metal component made of a steel sheet material. The inner reinforcement part 10 has a longitudinal web 13, which merges at its lower longitudinal end into a transverse web 12, which is provided for connection to a side sill, and which merges at its upper longitudinal end into a transverse web 11, which is provided for connection to a roof construction is. The longitudinal web 13 has two connection points 14 and 15 for the door hinges of a vehicle door.

In the hatched area 17, which comprises the lower connection point 15, the press-hardened inner reinforcement part 10 should have a lower strength and / or hardness, possibly also ductility, than in the other areas. To achieve this, the press-hardened internal reinforcement part 10 is produced by the process according to the invention, as explained above. The specified range 17 is for explanation only. Also, several such areas may be provided.

To cover the area 17, a covering device according to the invention can be used, such as one below in connection with FIG Fig. 3 is explained by way of example.

Fig. 3a shows a reusable cover 20 in a schematic sectional view. The cover device 20 is designed as a multi-part unit, in which the inner reinforcement part 10 is received in the region 17 and protrudes by way of example on the right side. The covering device 20 comprises a lower part 21 and an upper part 22, which are each rigidly formed. The lower part 21 has a sandwich structure which is formed from an outer shell 23 and an inner shell 24. The upper part 22 also has a sandwich structure, which is likewise formed from an outer shell mold 25 and from an inner mold shell 26.

The outer shell molds 23 and 25 are formed for example of a metal material or a ceramic material, which in particular with regard to the shielding of thermal radiation in the furnace and the mechanical strength and stability of the Cover device 20 is advantageous. The inner mold shells 24 and 26 are formed, for example, of a heat-resistant and heat-insulating fiber material, as explained above. On the thickness and / or nature (eg density) of the inner shell molds 24 and 26, inter alia, the thermal shield can be adjusted.

According to a preferred embodiment, the inner mold shells 24 and 26 are flexible and are supported by the outer mold shells 23 and 25. Alternatively it can be provided that the inner shell molds 24 and 26 are formed dimensionally stable, which is e.g. can be achieved by an in-molding Pessen the fiber material in conjunction with additives. The inner shell molds 24 and 26 may themselves be constructed in multiple layers. Here, e.g. As a result, a very good thermal insulation can be achieved by a different fiber orientation in the individual layers. The outer shell molds 23 and 25 may be fixedly connected to the inner shell molds 24 and 26. Alternatively, the inner shell molds 24 and 26 can be loosely inserted into the outer shell molds 23 and 25, whereby a slight interference effect is possible by a slight oversize. A modular design proves to be particularly advantageous in case of repair of the thermally highly stressed cover 20.

The upper part 22 and the lower part 21 are hingedly connected to each other via at least one hinge 28. In the example shown, the covering device 20 can be opened like a scissors around an unspecified hinge point for attaching and removing, or for inserting and removing the internal reinforcement part 10. The opening can e.g. by applying a force F on the actuator arm 29, which is located on the left side of the hinge 28 and which belongs to the upper part 22. The closing of the cover 20 is preferably carried out automatically, in particular by gravity. This makes it very easy to automate the attachment and / or removal of the cover 20. The hinge 28 is heat resistant and has e.g. designed as a ceramic bearing.

It is preferably provided that the inner mold shells 24 and 26 do not rest directly on the inner reinforcement part 10. Rather, a spacing in the form of a spacing gap 30 is provided between the surface of the inner reinforcement part 10 and the inner shell molds 24 and 26. this shows Fig. 3b which has an enlarged section of the Fig. 3a reproduces. Such a spacing gap 30 may, inter alia, enable a relative thermal movement and protect the surface of the inner reinforcement part 10 from damage. The spacing gap 30 can be very small and is preferably less than the sheet thickness of the inner reinforcement part 10.

Fig. 4 shows an alternative embodiment of a covering device 20a in a schematic sectional view. The main difference to the possibility of execution of Fig. 3 is that the inner, formed from a fiber material mold shells 24 and 26 are included. For this purpose, inner support shells 41 and 42 are provided, which bear against the inner reinforcement part 10 directly or even spaced. These inner support shells 41 and 42 are formed, for example, of a metal material or a ceramic material and may, like the outer shell molds 23 and 25 also, be one or more parts.

In a simple embodiment of the in Fig. 4 shown covering means 20a, the outer shell molds 23 and 25, and the inner support shells 41 and 42 are formed by component cutouts, which are spaced apart by an insulating material.

Claims (13)

1. A method for producing a partially press-hardened sheet metal component (10), especially a bodywork component, wherein the starting sheet metal material is firstly formed into a sheet metal formed part and this forming procedure is followed by a press hardening procedure, for which the sheet metal formed part is partially heated in a furnace and thereafter the partially heated sheet metal formed part is press hardened, characterised in that
   for partial heating in the furnace, at least one region (17) of the sheet metal formed part which is not to be hardened or is to be hardened to a lesser extent is covered by two rigid mould shells which are applied on both sides of the sheet metal formed part in the region (17) concerned, the internal contour of the mould shells corresponding to or approximating the spatial contour of the sheet metal formed part in the region (17) to be covered, and in that the partially covered sheet metal formed part is brought in its entirety into the furnace.
2. A method according to claim 1,
   characterised in that
   the uncovered region of the sheet metal formed part is heated in the furnace to above 900°C.
3. A method according to claim 1 or claim 2,
   characterised in that
   the shaping of the sheet metal formed part already corresponds to that of the sheet metal component (10) to be produced.
4. A method according to any one of the preceding claims,
   characterised in that
   the starting sheet metal material is a coated steel sheet.
5. A method according to any one of the preceding claims 1 to 4,
   characterised in that
   one mould shell is formed from a heat-resistant fibre material.
6. A method according to any one of the preceding claims 1 to 4,
   characterised in that
   one mould shell is formed from a ceramic material.
7. A method according to any one of the preceding claims 1 to 4,
   characterised in that
   one mould shell is formed from a metallic material.
8. A method according to any one of the preceding claims 1 to 4,
   characterised in that
   one mould shell is formed from a composite material.
9. A method according to any one of the preceding claims,
   characterised in that
   one mould shell does not rest directly on the sheet metal formed part.
10. A re-usable cover device (20, 20a) for covering a region (17) which is not to be hardened or is to be hardened to a lesser extent during the heating of a sheet metal formed part which is to be partially press-hardened in a furnace,
    comprising
    an upper part (22) and a lower part (21) and at least two rigid mould shells which can be applied on both sides of the sheet metal formed part in the region (17) concerned, the internal contour of the mould shells corresponding to or approximating the spatial contour of the sheet metal formed part in the region (17) to be covered.
11. A cover device (20, 20a) according to claim 10,
    characterised in that
    the upper part (22) and the lower part (21) are articulated together by at least one hinge (28).
12. A cover device (20, 20a) according to claim 10 or claim 11, comprising at least one mould shell according to any one of claims 5 to 8.
13. A cover device (20, 20a) according to claim 10, claim 11 or claim 12,
    characterised in that
    it comprises means (29) for automated application to the sheet metal formed part to be press-hardened and for removal from the sheet metal formed part to be press-hardened.

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