EP2855041A1

EP2855041A1 - Method and device for producing shaped sheet metal parts at a low temperature

Info

Publication number: EP2855041A1
Application number: EP13726170.7A
Authority: EP
Inventors: Axel GRÜNEKLEE; Markus ZÖRNACK; Thomas Heller; Ekaterina Bocharova; Seyed Amin MOUSAVI RIZI
Original assignee: ThyssenKrupp Steel Europe AG; Outokumpu Nirosta GmbH
Current assignee: ThyssenKrupp Steel Europe AG; Outokumpu Nirosta GmbH
Priority date: 2012-05-31
Filing date: 2013-05-28
Publication date: 2015-04-08
Anticipated expiration: 2033-05-28
Also published as: US10532395B2; ZA201409111B; CN104379272B; EP2855041B1; BR112014030042A2; JP2015519205A; JP6068627B2; DE102012104734A1; MX2014014544A; IN2014MN02371A; ES2666312T3; US20150082636A1; SI2855041T1; WO2013178615A1; CN104379272A; KR20150016319A

Abstract

The invention relates to a method for producing a shaped sheet metal part from a blank or a semi-finished product (1) made of a material consisting of steel having at least 60 wt.% Fe and a residual austenitic content of at least 5%, wherein the blank or the semi-finished product (1) is partially cooled to a temperature of less than -20 °C prior to the shaping and is shaped at a temperature below -20 °C in a shaping die (2). The problem of providing a method to produce components appropriately designed in terms of load, which enables a highly technical application of low-temperature shaping and is designed in a particularly simple manner, is solved in that a reduction of the material temperature of the blank or the semi-finished product (1) takes place in a cooling device (3) maintained at a temperature below -20 °C.

Description

Method and device for producing formed sheet metal parts at cryogenic temperature

The invention relates to a method for producing a formed sheet metal part from a board or a semi-finished product made of a material consisting of steel mi at least 60 wt. - Fe and a Austenitites content of at least 5%, wherein the board or the semi-finished product before forming at least partially is cooled to a temperature of less than -20 ° C and is formed at a temperature below -20 ° C in a forming tool. In addition, the invention relates to a device for carrying out the method and an advantageous use of the produced

Sheet metal parts . In order to meet the increasing requirements for weight savings, for example in the automotive industry, methods for the production of formed sheet metal parts have been developed, especially under the term

In order to achieve maximum strengths, i.e. yield strengths and tensile strengths, in the press-hardened component, the hot-forming process can be subjected to a press-hardening process

Minimum be reduced. In this case, the board or the semi-finished product usually has to be heated to a temperature above the AC _: - transformation temperature point, so that in

Substantially austenitic microstructure is present in the sheet metal part, in order subsequently to be converted at very high temperature and rapidly cooled. This ensures that the austenitic structure during rapid cooling in Converts martensite, so that very high tensile strengths and yield strengths can be provided. With manganese-boron steels, for example a manganese-boron steel of the type

MBW1500 can be provided by this method tensile strengths in the range of more than 1100 MPa. The known methods for hot forming have been further developed, so that the sheet metal parts can also be provided in regions with enormous yield strengths and tensile strengths and thus a load-friendly design of the

Sheet metal parts can be achieved. The use of a

"Tailored blanks", which is additional costly

Work steps in the form of a joining step, for example, using a laser beam required, or a separate component can thus be avoided. The disadvantage of hot forming but on the one hand the enormous

Energy consumption, which is required for heating the boards or semi-finished products above the ACi transformation temperature, ie usually above 850 ° C. In addition, there are significant problems with

Surface coatings, which for example for

Corrosion protection is required. Conventionally, hot-dip aluminized or However, semi-finished products provided with an Al-Si coating are used, but have no cathodic corrosion protection. Although zinc-containing surface coatings have cathodic protection against corrosion, there is the risk of the zinc melting on the surface

Surface during warming. Uncoated semi-finished products tend to scale, if not under protective gas

is working.

From the Japanese patent application JP 2000/178640 A, however, a method is known in which the components in Low temperature are transformed and thereby very high

Tensile strengths and yield strengths could be achieved by solidification in the material. In the Japanese

Patent application is proposed to cool the components at least partially by liquid oxygen, liquid nitrogen or dry ice or in another way and to reform at temperatures of -50 ° C to -200 ° C. It is proposed to immerse the components for this purpose in the appropriate cooling media to cool them extremely strong. On the one hand, the immersion of the sheet metal parts in liquid nitrogen or oxygen or even dry ice for large-scale use is not readily suitable. In addition, there are dangers for the operating personnel

corresponding plants, which increased to

Safety precautions.

Object of the present invention is therefore, a

To propose a process for the production of load-balanced designed components, which on the one hand a

large-scale use of low-temperature forming

allows and is particularly simple.

The above-indicated object is achieved according to the first teaching of the present invention in that a reduction of the material temperature of the board or the semi-finished product to below -20 ° C takes place in a tempered cooling device.

In contrast to the known state of the art, the board or the semi-finished product is tempered

Cooling device at forming temperature below -20 ° C, preferably at a temperature in the range of -40 ° C to -180 ° C tempered. The low temperatures in combination with a transformation effect. the used one

Resting austenitic steel of board or semi-finished one

Partial transformation of austenite into martensite, so that a significant increase, especially the yield strength is achieved. The tempered cooling device also makes it possible in a simple way the risk by using liquid, frozen cooling media such as liquid

Substantially reduce oxygen, liquid nitrogen or even liquid or solid carbon dioxide (dry ice), so that the industrial use of the low-temperature forming is possible. As tempered cooling devices in the sense of the present patent application devices

understood, in which the boards or semi-finished products

be positioned and brought to cryogenic using appropriately cold cooling media. For this purpose, it is not absolutely necessary for the blanks or semi-finished products to be in direct contact with the cooling medium, for example with liquid oxygen, nitrogen or carbon dioxide.

Preferably, according to a first embodiment of the

present invention, the board or the semi-finished product

removed from the cooling device immediately before the forming process and fed to the forming tool. By the immediate removal of the board or the semi-finished product before the forming process is possible that the board or the semifinished as possible still on forming temperature up to

Forming can be held and insofar also at least at the beginning of the forming process, the desired temperature

having. In addition to using the tempered cooling device, it is possible to use a temperature-controlled forming tool, so that the board or semi-finished product removed from the cooling device can be kept at low temperature in the forming tool for as long as possible.

Moreover, it is possible according to a further embodiment of the present invention as a cooling device that

To use forming tool itself, in which the board or the semi-finished product is cooled and formed. The

Forming tool has for this purpose means for cooling the board or. for tempering the areas in contact with the blank or semifinished product so that an optimal cooling process is achieved. Particularly advantageous in this embodiment of the method according to the invention is that the board or the semi-finished product only has to be introduced into a forming tool and can be formed in this without further removal or transport. As a result, a maximum process control is achieved because the forming temperatures can be easily controlled by the forming tool.

According to a next embodiment of the method according to the invention, the forming tool tempers the board to be reshaped or the semi-finished product to be reshaped only in the

Areas where high yield strength and tensile strength are required. This makes it possible that only by the configuration of the forming tool, the areas of the formed sheet metal part are determined, which increased strength, i. an increased tensile strength and / or

Yield point due to the low temperature transformation should have. Since the forming tool has very low temperatures, the surfaces of the forming tool tend to icing on contact with moist outside air. In this respect, according to a further embodiment of the method according to the invention, the process reliability can be further increased by the fact that the icing of the forming tool, the circuit board and / or the

Semi-finished using deicing means before and during the transformations is prevented.

Is the icing using mechanical

De-icing carried out an existing glaze can be easily removed on the forming tool. In addition, there is a possibility that

additionally or alternatively by using a protective gas, a protective gas atmosphere at the cooled areas of

Forming tool to produce the board or semi-finished so that icing is prevented. By the

Providing a protective gas atmosphere to the cooled areas of the board or the forming tool is achieved that no humidity can condense or freeze out at these points and is reflected at the areas of the board, the semi-finished product or the forming tool. This measure can, for example, with mechanical

De-icing agents are combined.

Preferably, the cooling of the forming tool, the

Board and / or the semifinished product by a protective gas, wherein preferably the protective gas by in the forming tool

provided flow channels in the corresponding areas to be cooled of the forming tool, the board and / or the

Semi-finished product flows. Moreover, in the method according to the invention, particularly small wall thicknesses of the board or of the semifinished product can be used. These are preferably 0, 5 mm to 1.80 mm, more preferably 0.7 mm to 1.20 mm. In particular, by the use of the tempered forming tool is a corresponding deformation of the board or semi-finished with these small thicknesses particularly advantageous because they can be brought very quickly to low temperature in the forming and thus with a relatively low cycle time load-adapted, formed sheet metal parts can be produced which the higher-load areas have significant increases in strength. Particularly preferred is a board or a semi-finished formed, which or. which has a surface coating, wherein as a surface coating optionally a zinc-containing surface coating is used. In the case of low-temperature forming, the surface coating is not damaged, so that cathodic corrosion protection can be readily used by using a zinc-containing surface coating without adversely affecting the forming process

Strength values and is also due to the OberflächenbeSchichtung particularly good against corrosion

protected. Of course, in addition to an ink

containing surface coating also readily an organic coating can be used, which is deformable at the correspondingly low temperatures. According to a second teaching of the present invention, the above object is achieved by a device for

Implementation of the method solved by a

Forming tool is provided, which has a receptacle for inserting a circuit board or a semi-finished product and

Means are provided for at least partially cooling the board or semi-finished product to a temperature below -20 ° C in the recording. The device according to the invention makes it possible, the board or the semi-finished in

To cool forming tool to forming temperature and reshape without further transport step. As a result, maximum efficiency is achieved by a

Removal of the board or semifinished product between the

Tempering and forming step from the forming tool no longer needs to be done.

The forming tool preferably has means for de-icing the cooled areas of the forming tool, the blank and / or the semifinished product, in order to ensure a permanent, process-reliable operation. The funds can do this

For example, mechanical means such as brushes or scrapers, which can remove already existing icing again. According to a further embodiment of the invention

Device has the forming tool at least in the areas in contact with the board or the semi-finished in contact areas flow channels through which a cooling medium flows for local cooling of the board or the semi-finished product. The cooling medium used is preferably an anhydrous cooling medium, for example dry ice or liquid nitrogen.

For example, the flow channels to the board or to the semi-finished product, so that these the corresponding areas of the inserted in the forming tool board or the inserted semi-finished product to low

Cool temperatures and at the same time a protective gas atmosphere is formed, which prevents the icing of the areas. In addition, however, the flow channels can also run only in Umfortnwerkzeug, so that no cooling media, such as oxygen, nitrogen or carbon dioxide leak in the area of the forming tool.

According to another teaching of the present invention, the above object is achieved by the use of a

Sheet metal part, which was produced by the process according to the invention, as a structural part of a motor vehicle, wherein the structural part areas with different

Strengths solved. As already stated above, it is possible by the low-temperature forming also large differences in strength in formed

To achieve sheet metal parts. The increase in yield strength and tensile strength is due to the

Restaustenitgehaltes the material achieved by converting the Austentenitgehaltes in matensitic structure. By choosing the low temperature can increase the

Strength increase must be achieved, taking into account that with decreasing temperature, the brittleness of the material increases and thus the degree of deformation are limited.

Moreover, since, as already stated, a surface coating which protects against corrosion, in particular a coating containing zinc, does not suffer any damage in the method according to the invention, it is particularly advantageous to use the Sheet metal part as a pillar, carrier, large-area component, floor panel, tunnel, front wall or wheel arch of a

Motor vehicle to use. All sheet metal parts are usually a more or less strong

Corrosion attack in the motor vehicle exposed and therefore require a corrosion-protective surface coating. In addition, load-oriented, i.

Areas with different strengths

Sheet metal parts the opportunity to save costs, because no more expensive tailored blanks, which consist of several sheets, must be used. The one-piece

Sheet metal parts also have no strength debilitating

Weld on. Furthermore, a component reduction and thus a cost reduction can be achieved because it can be dispensed with separate reinforcements.

According to a further embodiment of the use according to the invention, the sheet metal part as A-, B-, C- column of a

Used motor vehicle, wherein at least the region of the roof connection of the A, B, C column has a higher strength than the region of the column base of the A, B, C column.

Finally, a further advantageous use results from the fact that the sheet metal part is used as a longitudinal member in the front region of a motor vehicle and the longitudinal member has a front region which has a lower strength than the rear region. The front portion of the longitudinal member in the front area with lower strength is to deform in the event of an impact and thus absorb the impact energy. The rear area of the

On the other hand, the longitudinal member should, as far as possible, not be subject to deformation and thus protect the passenger compartment. Corresponding solutions have so far only by

Use of patches, tailored blanks or additional reinforcement components can be realized. The inventive use of the sheet metal part also makes it possible in a simple way to provide a one-piece sheet metal part, which in addition to a very good cathodic protection against corrosion

at the same time a simplified and economic

Production of a longitudinal member with areas

different strengths possible.

In addition, the invention is based on

Embodiments will be explained in more detail in conjunction with the drawings. The drawing shows in Fig. 1 ne principle of a

Embodiment of the method

Production of a formed sheet metal part,

FIG. 2 shows an alternative embodiment to that shown in FIG. 1 illustrated method,

Fig. 3a), b) embodiment of a

Forming tool for performing the

Method,

Fig. 4 shows another embodiment of a

Forming tool for performing the

Process for the preparation

formed sheet metal part and Fig. 5, 6 and 7 embodiments of advantageous

Uses of a corresponding

produced Biechteils. In Fig. 1, a schematic diagram of the method for producing a formed sheet metal part is first shown, in which a circuit board 1 is to be formed in a forming tool 2. The forming tool 2 is as simple

Deep drawing tool shown. However, the forming tool 2 stands for any forming tools, as they are for

Production of formed sheet metal parts from flat boards or already preformed or cut semi-finished products can be used. The board 1 consists of a steel with at least 60 wt. -% Fe and a retained austenite content of at least 5%. Typical representatives of these steel grades are, for example, high-manganese steels but also TRIP steels. In these steels, especially in the

Residual austenitic steels (TRIP steels) are observed to be austenitic at very low temperatures during forming

Partly in martensitic structure

umwandein and thus in addition to the deformation resistance, a further yield strength and increase in strength is achieved. It was found that this effect continues at

sinking temperatures rises significantly, so that the

Solidification process, which in addition to the classic workhardening effect still a so-called TRIP effect, can lead to very high yield strengths and tensile strengths. For example, with an RA-K 40/70 steel (TRIP steel), the yield strength can be increased from 410 MPa to over 800 MPa. In the in Fig. 1 shown

Embodiment of the method, the circuit board. 1

first in a cooling device 3 to a temperature of below -20 ° C, preferably at a temperature of. - 40 ° C to -190 ° C cooled. This can be done in the

Cooling device Cooling media such as liquid

Nitrogen, dry ice or even liquid oxygen

be used without any risk to the safety of operators of the device. The tempered

Cooling device, for example, have closed circuits of the correspondingly cool cooling media, which heat, for example, via direct metal contact to the

Transfer board or semi-finished product. Reaches the board, which has a wall thickness of preferably 0, 5 mm to 1, 8 mm, more preferably 0.70 mm to 1.20 mm, the

Forming temperature is removed from the cooling device 3 and fed to the forming tool 2 shortly before the forming process. The deformation then takes place directly, so that the temperature rise due to the removal from the

Cooling device is limited. Preferably, the

Forming tool 2 even be tempered, so that a significant increase in temperature of the board is prevented in the forming tool.

As shown in FIG. 1, the cooling device 3 provides a discontinuous operation of the cooling of the board 1 available. In contrast, the in Fig. 2 illustrated cooling device 3 'a continuous

Pass the board 1 or the semi-finished product 1 through the

Cooling device 3 ', so that the board 1 and. the semifinished product 1 at the outlet of the cooling device 3 'was brought to deformation temperature. The board 1 resp. the semifinished product 1 is then inserted immediately after leaving the cooling device 3 'in the forming tool 2 and reshaped. As already stated above, the forming tool 2 is merely here Represented as a thermoforming tool.

Basically, AHU / hydroforming tools and any other forming tools are conceivable, which cause a deformation and thus a solidification in the sheet metal part suitable.

An optional embodiment of the forming tool is shown in FIGS. 3a), b) shown in Perspective, schematic view. The in Fig. 3a) has an upper Umformwerkzeughä1fte 4a, in which flow channels 5 are arranged, which produce a cooled portion 6 of the board, which then at

Low temperature is formed. For this purpose, a cooling medium, for example liquid nitrogen or liquid oxygen or else deep-frozen carbon dioxide flows through the

Strömungskanä1e and thereby cools the board in this area from strong.

When forming takes place in the strongly cooled areas much stronger solidification by the TRIP effect as i non-cooled areas, so that the produced sheet metal part 7 has a region 7a, which due to the strong TRIP effect significantly higher yield strengths and

Has tensile strengths. To prevent the icing of the forming tool from FIG. 3a)

prevent it, it is advantageous when opening the

Tool the upper mold half 4a, which the

Having flow channels and thus is particularly cold, even during the opening of the tool, the cooling medium through the Strömungskanä1e leads. As a result, icing of the

Tool surfaces thereby preventing a training a protective gas atmosphere 8 in the region of the highly cooled surfaces of the forming tool takes place.

In Fig. 4 is now an embodiment of a

Forming tool shown, which has a closed circuit with respect to the cooling medium. The

For this purpose, forming tool 9 shown schematically has in the region of the punch or. the die coolant channels 10, through which a correspondingly low-temperature

Coolant flows. The board 1, which is arranged between the two halves of the forming tool 9 and having these surface contact, is in the range of

Contact surfaces cooled with the cooled stamp very strong and brought to forming temperature of less than -20 ° C. Should any areas be present that should not be brought to the appropriate temperature, means are provided in the stamp 11, which allow local heating of the board 1 in addition. These funds can

be configured for example as a heating cartridge or similar heat-emitting means. In addition, means for mechanical deicing on the forming tool 9 are provided and shown schematically. The mechanical deicing means 12 consist of a holder for receiving a scraper 12a, which cleans the surface of the punch 9 ', for example, when the forming tool 9 is opened. It is also conceivable to use brushes instead of the scraper 12a. The

shown forming tool 9 can be an inserted board 1 in a relatively short time due to the large

cooling surface contact to the forming temperature below -20 ° C and thus provide a simple, economical manufacturing process. The Fig. FIGS. 5, 6 and 7 show typical embodiments of advantageous uses of the formed sheet metal part 1. In FIG. 5, for example, the use of the sheet metal part as a B-pillar 13 of a motor vehicle 14 is shown schematically. The B-pillar 13 should preferably have a high yield strength and tensile strength roof connection area 13b and one with lower strength but with a

having greater elongation at break equipped pedestal 13a. With the method according to the invention, this B-pillar can be prepared in an economical manner by the upper

Area of the B-pillar 13 in the forming tool is strongly cooled down and. subsequently transformed. This gives the upper area a much higher yield strength and

Tensile strength compared to pedestal 13a. The same applies in principle for the other columns, the illustrated A-pillar 15 and the C-pillar 16th

Fig. 6. shows two longitudinal members of a front region of a vehicle body, which have two different functions in one component. The longitudinal members 17 serve

on the one hand, in the event of an impact, first of all

To absorb on rallenergie and at least partially deform and on the other hand in the rear area

lying passenger compartment to protect against further deformation. For this purpose, the longitudinal members 17 are usually such

designed so that the front area is easier to reshape and the rear area is formed as stiff as possible. With the method according to the invention, a longitudinal member 17 can now be produced such that its front region 17a. has a lower strength than the rear portion 17b, wherein in the forming tool, the rear portion of the longitudinal member 17b is strongly cooled. This will achieve that the yield strength and tensile strengths of the two areas differ significantly. Thus, for example, in the high yield strength portion of the side member 17, as in the other uses previously as well

Yield strength of more than 800 MPa provided so that this area is particularly strong. The area 17a, on the other hand, is made soft in the same operation, since this area of the forming tool is not tempered. The use of possible tailored blanks, which additionally require work steps to provide a similar strength profile, can therefore be dispensed with.

Finally, FIG. 7 shows an example of an end wall 18, which is preferably also produced by the method according to the invention. The end wall 18 is usually

large area and has a relatively small thickness. In order to form individual attachment regions 19, for example with a higher yield strength and tensile strength, so that no reinforcements in the form of patches, tailored blanks or separate components are more necessary. In addition, by targeted temperature control of the

Forming tool not only be achieved that specific areas of the end wall 18 a significantly different

Umformverha11en in the event of an impact show, but also local areas with corresponding. Yield strength, and

Tensile strengths are provided, which are used to hold aggregates, such as brake booster,

Air conditioning etc. serve, so that the end wall 18 can be designed load-appropriate without additional measures. In the in Figs. 5-7 illustrated typical uses of the sheet metal part formed according to the invention can be particularly readily cathodic corrosion protection based on a zinc-containing surface coating and / or an organic surface coating

be provided because it can be dispensed with hot forming.

Claims

Patent claims

A method for producing a formed sheet metal part from a board or a semi-finished product of a material consisting of steel with at least 60 wt .-% Fe and a Austenitgehalt of at least 5%, wherein the board or the semi-finished product before forming at least partially to a temperature of is cooled to less than -20 ° C, and is formed at a temperature below -20 ° C in a forming tool,

d a d u r c h e k e n e s, there is a reduction in the material temperature of the printed circuit board or semifinished product to below -20 ° C. in a tempered cooling device.

Method according to claim 2,

The board or the semifinished product is directly in front of the board

Forming process removed from the cooling device and fed to the forming tool.

Method according to claim 1,

characterized in that as the cooling device, the forming tool is used, in which the board or the semi-finished product is cooled and then formed. Method according to claim 3,

In the case of the forming tool, the forming tool, the blank to be reshaped or the semi-finished product to be reshaped are only in the regions

tempered, in which a high yield strength and

Tensile strength is required.

Method according to claim 3 or 4,

The icing of the forming tool, the blank, and / or the semi-finished product using de-icing means before and during forming is prevented.

Method according to one of claims 3 to 5,

d a d u r c h e c i n e s, the icing using mechanical

Deicers and / or using a

Protective gas to generate a protective gas atmosphere is prevented at the cooled areas.

Method according to one of claims 3 to 6,

The cooling of the forming tool, of the blank and / or of the semifinished product is effected by a protective gas, the protective gas preferably being provided by means provided in the forming tool

Flow channels flows.

Method according to one of claims 3 to 7,

characterized in that the wall thickness of the board or the semi-finished product is 0, 5 mm to 1, 80 mm, preferably 0, 7 mm to 1.20 mm. Method according to claims 1 to 8,

That is, a board or semi-finished product is formed which has a surface layering layer and optionally a zinc surface coating layer

containing surface coating will use.

Device for carrying out a method according to one of Claims 3 to 9,

a forming tool (4, 9) is provided which has a receptacle for inserting a printed circuit board (7) or a

Semi-finished product (7) and means (5, 6, 10) for

at least partially cooling the circuit board (7) or the semifinished product (7) to a temperature below -20 ° C are provided.

Device according to claim 10,

That is, the forming tool has means (12, 12a) for de-icing the cooled regions of the forming tool (9), the blank (7) or the semi-finished product (7).

Device according to claim 10,

d a d u r c h e k e n e z e i c h n e, d a s s the forming tool (4, 9) at least in the with the

Board (7) or the semi-finished product (7) in contact areas flow channels (6, 10), through which a cooling medium for local cooling of the board or the semifinished product flows. Use of a sheet-metal part, which was produced by a method according to one of claims 1 to 9, as a structural part of a motor vehicle, wherein the structural part has areas with different strengths.

Use according to claim 13,

The sheet metal part is used as a pillar (13, 14, 15), support (17), large-area component (18), floor panel, tunnel, end wall or wheel arch of a motor vehicle.

Use according to claim 13 or 14,

The sheet metal part is used as a B pillar (13) of a motor vehicle, at least the region of the

Roof connection (13b) of the B-pillar has a higher strength than the area of the B-pillar base (13a).

Use according to one of claims 13 to 15,

The sheet metal part is used as a longitudinal member (17) in the front region of a motor vehicle and the longitudinal member (17) has a front region (17a) which has a lower strength than the rear region (17b).