DE102005055494B3 - Production of a metallic flat product, especially a sheet steel blank, used in the construction of chassis components comprises heating the flat product to a deforming temperature using conduction heating directly before deforming - Google Patents

Abstract

Production of a metallic flat product (F), especially a sheet steel blank, comprises heating the flat product to a deforming temperature of 450-700[deg] C using conduction heating directly before deforming.

Description

The The invention relates to a method for producing a component from a metallic flat product, in particular a sheet steel blank, by press forming, in which the flat product by means of conductive warming is heated at least in sections to a forming temperature, before it is inserted into a forming tool and there to the component is press-formed. Processes of this kind are used in particular to make steel or aluminum sheet metal components for body construction.

For the conventional Production of sheet metal components by hot forming are the respectively to be processed flat metal products in the form of a board or a pre-formed component usually heated in an oven to the respective required forming temperature. Then they will have one Transport distance brought into the press forming tool, the length of the local conditions depends.

On the transport route between the furnace removal and the forming In the tool, the heated board or the heated component is usually located in free contact with the ambient atmosphere. Depending on the transport time and Tool temperature it comes to the loss of heat energy from the board or from the component. Also, it may be as a result of Contact with the oxygen of the ambient air to a the quality of the finished product debilitating and the forming process under certain circumstances disabling oxidation of the surfaces of the flat product.

Next Press forming can already produce the flat product in the forming tool hardened and tempered become. For this purpose, known forming tools with cooling devices equipped with the tool surfaces, in the course of the forming process, the previously heated flat product directly touch, full-surface or cooling in sections, so that the flat product accelerates on contact with these tool surfaces chilled becomes. That way you can in the formed of the flat product component generates targeted areas Be that particular in their practical use have adequate strength to meet existing requirements.

For the conductive warming are attached to the respective flat product electrodes, over the an electric current is passed through the product. The electric Resistance of the product itself causes its heating up the desired Temperature.

A method and a device of the type described above is known from DE 102 12 820 C1 known. According to this state of the art, for example, a circuit board, before it is inserted, for example, into a forming tool, is heated by means of conductive heating to forming temperature. For this purpose, electrodes are applied to the board over the surface, between which the heating current flows. In order to form other structural properties and strengths in certain areas than in the other sections of the board adjacent to these areas, adjacently arranged electrodes can be bridged so that there is no current flow through the respective workpiece between these electrodes. Alternatively, a cooling of the respective areas can be provided in order to suppress their heating to the temperature to be set in the other sections. The conductive heating of the board takes place in temporal and spatial proximity to the respective forming tool.

According to the DE 102 12 820 C1 the respective workpiece is heated before entering the respective forming tool, which can be used simultaneously as a tempering tool. It will be a special advantage of the DE 102 12 820 C1 known approach that it is possible due to the small size of the required for the heating of the device facilities to prevent oxidation of the workpiece by air contact easily by the fact that the heating device and the respective forming tool are encapsulated together in a protective atmosphere. In practice, however, shows that the implementation of this measure causes a considerable outlay on equipment, which leads to a high cost, especially in mass production.

The The object of the invention was therefore to provide a method with which it is possible in a simple and practical way, high quality, true to size Manufacture components by a press forming with previous heating.

These Task is inventively by the Teaching of claim 1 solved Service. Advantageous embodiments of this teaching are in the of Claim 1 dependent claims specified.

According to the invention is comparable to that in the DE 102 12 820 C1 described procedure, the heat energy required for a conversion and thus optionally combined compensation process only introduced immediately before the conversion in the processed flat product. Accordingly, in accordance with the invention, the heating of the each workpiece on the forming temperature in such a close-sized temporal and local proximity to the forming process that the risk of oxidation of each processed flat product is reduced to a minimum. Heating under a protective gas atmosphere can therefore be dispensed with. This is especially true when processed as a flat steel sheets, which are provided with a protective against oxidation metallic or organic coating.

By doing According to the invention, the forming temperatures in the range of 450-700 ° C and thus below the Ac3 temperature can be in terms of their mechanical properties for a variety of applications, such as automotive body construction, create particularly suitable components. This is especially safe Effect achieved when the forming is carried out at temperatures in the range of 500-700 ° C, in particular 600-700 ° C, specifically near 650 ° C, lie. The in this between the conventional cold deformation and the conventional thermal deformation temperature range deformed components have a favorable combination of strength, toughness and stretching up. Their strength can thereby additionally increased be that the respective press-formed component after the press forming an additional, carried out cold Undergoes forming, which adds to it Hardening comes. With the invention it is possible to Forming of high-strength steel sheets in complicated moldings by To ensure reduction of strength and increase of elongation at break. At the same time the forming forces significantly reduced. Thus, in practical experiments a halving the forming forces compared to a be demonstrated conventional forming. The invention allows so the use of presses for a conventional cold forming are provided and because of their limited capacity Conventional procedure not suitable for deformation of high-strength steels are.

With The invention thus has a possibility to disposal, high-strength steel materials, in particular in the field of complex-phase steels, have a low elongation at break, to components with a complex Forming reshape. Due to the tempering of the material according to the invention Before the forming process in particular the elongation at break is increased. there let yourself with the invention also in conventional deformation such steels existing danger of springback so dominate that the transformation and further processing of in reshaped according to the invention Steel sheets can also be made safely if they are made of high strength toughen consist.

Furthermore There is a further advantage of the invention is that in the respective workpiece introduced heat can be used optimally. This is achieved in that between warming and reshaping, to a minimum reduced period only low heat energy losses enter.

These minimized heat loss enable it further, when heating set temperatures in a narrow field so that for example applied to the respective flat product organic and / or metallic coatings by heating not damaged or be affected in their effect. Accordingly, the method according to the invention is particularly suitable for the Forming of flat products containing an organic and / or metallic Have coating.

Also is it possible with the invention only such exactly contoured surface portions of the workpiece To bring forming temperature, to the increased during the forming process be put while the other workpiece sections heated only slightly or not at all become. Furthermore, the procedure according to the invention allows specifically the breaking elongation of the workpiece in certain, during the Press forming particularly high stress areas of the workpiece to increase and thus improving the forming conditions. Another advantage there is a heating according to the invention in that the forming forces overall reduced and the risk of springback after completion the forming process compared to cold forming significantly minimized are.

at in accordance with the invention processed flat product may be a sheet metal blank or a comparable just trained board act. As well However, it also allows the invention, in accordance with the invention to process a flat product, previously in an upstream Step has been preformed to a Bauteilrohform.

Around one possible timely coupling of the heating to achieve the press-forming, it may be expedient the warming immediately before the flat product enters the forming tool perform, so that between the warming and the hot-pressing takes place only the time passes for the Inserting the flat product is needed in the tool.

Even shorter times between heating and forming arise when the flat product is heated to the forming temperature only when it is already in the forming process tool lies.

Especially low process times with minimized times between warming and press forming can be achieved when the heating during the Transports of each processed flat product is carried out in the pressing tool. With regard to a possible short break between warming and reshaping is the heating expediently so performed that the forming temperature is reached exactly when the workpiece in the forming tool is inserted.

The for the Heat needed on forming temperature Time can be reduced by the fact that the respective workpiece before the conducted conductively warming is preheated to forming temperature in an oven to a preheating temperature. The preheating temperature is thereby preferably chosen that they are possible is close to the respectively to be adjusted forming temperature, however so low is they in terms of the risk of oxidation of the workpiece is not critical.

Basically suitable the procedure of the invention especially for such forming processes, in which it during the forming process to a rapid cooling of the previously heated to forming temperature workpiece comes. This fast cooling leads to an increase in Strength and hardness of the obtained component.

At the inventive method the heating takes place each processed flat products conductive by a between at least two to the workpiece flowing electrodes flowing Electricity. Conductive heating has the advantage that the workpiece be brought quickly and concentrated to the forming temperature can.

A conductive heating It also allows, by an appropriate arrangement of the electrodes the heat flow through the workpiece and concomitantly the extent of each on forming temperature heated Section of the workpiece to control specifically. Very cheap proves in this context the possibility of being Arrangement of the electrodes heated to the forming temperature zones of the workpiece so to lay and limit that they are clearly opposite to the adjacent portions of the workpiece are delimited on purpose not heated to forming temperature should be. For example, the fact that the power input in the processed according to the invention Flat products over the entire width takes place, the respective product evenly until be heated just before the contact electrodes, during the Area in which the contact electrode sits on the flat product, clearly less heated becomes.

When especially suitable for For this purpose, electrodes have been found in the known per se Way consist of a copper material. For example, off a sheet metal blank a component are made, in which zones of different strengths are formed, so can accomplish this by using the contact electrodes for current injection be formed and arranged so that they are the part of the flat product, the form the less solid section on the finished molded component should, completely covers. Because of the heat conduction and the shunt effect of the copper remains the board area covered by the electrodes usually until the completion of the conductive warming significantly below 100 ° C, so that while the pressing does not cure, to which it is in the range of the other heated at the forming temperature Sections of the workpiece due to the solid entering upon contact with the tool Cooling comes.

A different possibility, specifically on the component obtained after forming less solid zones form, is the flat product after insertion in the forming tool in at least one section during the Press-forming to keep on the deformation temperature, so that there is no hardening in the section concerned Press tool comes. By the obtained component even after completion of the Pressing process cooled slowly if the initial hardness remains in the area concerned, while in an adjacent, faster through contact with the tool cooled section of the flat product a hardness increase is achieved.

following the invention will be described with reference to an exemplary embodiment Drawing closer explained. Each show schematically:

1 a production line for press-forming sheet metal blanks in a lateral view;

2 a first device for heating a flat product;

3 a second device for heating a flat product.

In the 1 The press-forming production line shown comprises a sheet stock V in which flat products F present in the form of substantially rectangular-shaped blanks made of a thin sheet steel are stacked. The surfaces of the flat product F are provided with a metallic coating, for example by electrolytic galvanizing or hot-dip galvanizing provided zinc layer provided.

In Material flow direction M behind the sheet stock V is a transport unit T1 arranged in the form of a robot with a gripping arm G. The transport unit T1 comprises in the region of its gripping arms G a device which is provided, each of the transport unit T1 the sheet stock V taken flat product F during its transport to a material flow direction M behind the Transport unit T1 arranged press P in the below described Way to conductive to the required forming temperature.

The conventionally formed press P comprises a forming tool U, in which the flat products F in a conventional manner in the them intended form be brought. Complementary or alternative to one Arrangement in the transport unit T1 can also be in the area of the forming tool U of the press P a device for heating each in the press P inserted flat product F be provided.

A arranged in the material flow direction M behind the press P second Transport unit T2 removes the press P the finished formed Flat products X and places them on a stack of parts E from.

The attached for example to the gripping arms G of the transport unit T1 device 1 for conductive heating of each transported flat product has two pairs 2 . 3 of electrodes 2a . 2 B ; 3a . 3b on, each consisting of copper and are connected via supply lines, not shown, to a likewise not shown power supply. The of the electrodes 2a . 2 B . 3a . 3b each output power is controlled by a control and regulating device, also not shown. The width of the electrodes 2a . 2 B of the first electrode pair 2 corresponds to the width B of the narrow sides S1, S2 of the flat product F, while the width of the electrodes 3a . 3b of the other electrode pair 3 only a fraction of the width B of their associated narrow side S2 of the flat product F is.

For heating the flat product F, the one electrode 2a of the electrode pair 2 on the top and the other electrode 2 B placed opposite to the underside of the flat product F and aligned flush with the edge of the narrow side S1 so that it extends over the entire width B of this narrow side S1. The electrodes 3a . 3b of the electrode pair 3 are positioned centrally on the opposite narrow side S2 so that the one electrode 3a at the top and the other electrode 3b aligned flush with the edge of the respective narrow side S2 on the underside of the flat product F.

The subsequently between the electrode pairs 2 . 3 flowing stream heats the flat product F in a section A that extends between the electrode pairs 2 . 3 extends and in the region of the electrode pair 2 the entire width B of the flat product F occupies, from which it extends in the direction of the second electrode pair 3 tapered to its width b. In this way it is achieved that the flat product F is heated to forming temperature only in section A, while the adjacent zones Z1, Z2 are kept at a temperature at which it in the course of the subsequent compression of the flat product F and the associated rapid cooling to no formation of hardness structure in the flat product F comes.

If the flat product F is to be uniformly brought to the forming temperature over its entire width, then this is done instead of the electrode pair 3 a pair of electrodes 4 attached to the flat product F, whose electrodes 4a . 4b each extend over the entire width B of the flat product F. Like the electrodes 3a . 3b is aligned flush with the edge of their associated narrow side S2, the one electrode 4a to the top and the other electrode 4b of the electrode pair 4 attached to the underside of the flat product F. If, in this case, an area Z3 of the flat product F emanating from the opposite narrow side S1 is to be recessed from the heating to the forming temperature, then the electrodes are used for this purpose 2a . 2 B of the electrode pair 2 positioned at a corresponding distance from the respective narrow side S1. The current flow between the electrode pairs 2 . 4 in this way does not detect the zone Z3, which in this way is kept at a temperature of less than 100 ° C.

In the forming tool, the flat product F then becomes a component pressed, from the subsequently for example, the B-pillar an automobile body is made.

1

contraption

2, 3, 4

Pairs of electrodes 2a . 2 B ; 3a . 3b ; 4a . 4b

2a, 2 B

electrodes

3a, 3b

electrodes

4a, 4b

electrodes

A

on Forming temperature warmer Section of the

flat product F

B

width the narrow sides S1, S2 of the flat product F

e

parts stack

F

flat product

G

claw arm the transport unit T1

M

Material flow direction

P

Press

S1, S2

narrow sides of the flat product F

T1, T2

transport units

U

forming tool

V

sheet stock

X

finished deformed flat products

Z1, Z2

at the section A adjacent zones of

flat product F

Z3

Not heated to forming temperature zone of

flat product F

Claims (12)

Method for producing a component from a metallic flat product (F), in particular a sheet steel blank, by press forming in which the flat product (F) is heated at least in sections to a forming temperature by means of conductive heating immediately before the press forming process, before it is placed in a forming tool and is press-formed there to the component, characterized in that the forming temperature is 450-700 ° C. Method according to claim 1, characterized in that that the conductive warming immediately before the flat product (F) enters the forming tool carried out becomes. Method according to claim 1, characterized in that that the conductive warming is performed in already inserted in the forming tool flat product (F). Method according to claim 1, characterized in that that the conductive warming during the Transport of the flat product (F) from an upstream processing device performed to the forming tool becomes. Method according to one of the preceding claims, characterized characterized in that the flat product (F) before the conductive heating in preheated in a stove becomes. Method according to one of the preceding claims, characterized characterized in that the conductive heating to at least one certain portion (A) of the flat product (F) is limited. Method according to one of the preceding claims, characterized in that the flat products (F) are an organic and / or have metallic coating. Method according to one of the preceding claims, characterized in that the electrodes used for the conductive heating ( 2a . 2 B . 3a . 3b . 4a . 4b ) consist of a copper material. Method according to claim 8, characterized in that the electrodes ( 2a . 2 B ) are placed along the boundaries of a region of the flat product (F) whose temperature is to be kept below the deformation temperature. Method according to one of the preceding claims, characterized characterized in that the flat product (F) after insertion into the Forming tool in at least one section during the press forming continue is kept at the deformation temperature. Method according to one of the preceding claims, characterized characterized in that the flat product (F) before the press forming is preformed in an upstream step. Method according to one of the preceding claims, characterized in that the press-formed from the flat product (F) Component after press forming an additional, cold carried out forming is subjected.