DE102020103977A1 - Method for manufacturing a component by forming a metal strip - Google Patents

Abstract

According to a method for producing a component (1) by reshaping a metal strip (2), a surface coating is applied to the metal strip (2) and preconditioned by a first heat treatment. The preconditioned metal strip (2) is shaped by roll forming and hardened by a second heat treatment.

Description

The present invention relates to a method for producing a component by reshaping a metal strip, a surface coating being applied to the metal strip. The invention also relates to a method for manufacturing a body for a motor vehicle.

Hardened metal components, in particular profile components made of sheet steel, are used in many different ways, for example in body construction for motor vehicles. A problem that occurs during hardening through the use of high temperatures is the scaling of the metal surface. To counteract this, for example, anti-scaling layers are applied to the metal, for example coatings containing zinc or zinc and iron. However, such coatings sometimes prove to be problematic because they tend to form microcracks in the steel substrate, especially when they are processed outside of a very narrow process window. This can lead, for example, to the undesired blooming of zinc.

When using aluminum-containing anti-scaling layers, the problem arises that a low-melting phase leads to the appearance of a liquid phase on the surface of the material at the high process temperatures of the heating. This prevents safe and stable process management. The use of rapid heating technologies, such as inductive heating, is also restricted due to the formation of liquid phases.

In the document EP 2 609 224 B1 describes a method for producing a profile component by continuous roll forming and hardening or partial hardening. The component blank is first formed using a bending process, then heated and then cooled again. Special temperature control during heating and cooling prevents the component from warping.

In the document WO 2009/090555 A1 describes a method for press hardening of components. For this purpose, sheet steel is coated with aluminum or an aluminum alloy and separated. The separated parts are then heated and deformed.

Against this background, it is an object of the present invention to provide an improved concept for producing an at least partially hardened component in which scaling is prevented or reduced and at the same time reliable and stable process management is made possible, in particular with high output in a continuous process.

This object is achieved by the subject matter of the independent claim. Preferred embodiments and advantageous developments are the subject of the dependent claims.

The improved concept is based on the idea of providing a metal strip with a surface coating preconditioned by a first heat treatment and then reshaping and hardening the preconditioned metal strip.

According to the improved concept, a method for producing a component by reshaping a metal strip is specified. A surface coating is applied to the metal strip, and the surface coating is preconditioned by a first heat treatment after it has been applied to the metal strip. After preconditioning, the surface-coated metal strip is deformed by roll forming, in particular incrementally deformed, and hardened by a second heat treatment.

The metal strip can also be referred to as a sheet metal strip and, in particular, be designed as a sheet steel strip.

Here and below, heat treatment of a workpiece can be understood to mean the introduction and heating of the workpiece in an oven or by means of another heat source, or the direct heating of the workpiece, for example by induction. In particular, heating by convection, radiation, contact plates and / or direct current / electron flow is possible. Approaches by means of heating by near-infrared radiation or conduction or direct power lines are also possible.

The surface coating is designed in particular as a scale protection coating and, for example, also as a corrosion protection layer.

The roll forming can also be referred to as roll profiling or roll profiling and can in particular include one or more successive stages, each with different sets of rolls for multi-stage or incremental forming.

The surface coating is in particular a metallic or metal-containing coating, that is to say a coating made of metal or a metal alloy.

The preconditioning by means of the first heat treatment results in a microscopic structure and / or a Alloy composition of the surface coating changed.

Cutting and piercing operations can be performed, for example, before roll forming, during hardening and / or after hardening.

It should be noted that the entire component area does not necessarily have to be heated and hardened, but that certain component areas can also be partially hardened. Depending on the component, for example, soft flanges and hard frame areas or the like can be produced

The method according to the improved concept makes it possible to manufacture hardened metal components without burning or scaling by applying the surface coating. The preconditioning of the surface coating before roll forming and before hardening enables particularly safe and stable process management. In particular, the preconditioning prevents liquefaction or partial liquefaction of the surface coating during the second heat treatment.

This also makes it possible, in particular, to carry out the roll forming and hardening steps continuously, that is to say “inline”, without the metal strip or isolated semi-finished products having to be transferred between different systems. In particular, long furnace times and the like can thereby be avoided. According to at least one embodiment of the method, the preconditioned metal strip is provided as a roll ("coil"), and the preconditioned metal strip is unrolled from the roll, in particular continuously unrolled, during roll forming and during the second heat treatment.

In other words, before the deformation and hardening steps, there is no separation of semi-finished parts, that is, no complete severing or cutting off of semi-finished parts. Punching or partial trimming in the tool, on the other hand, is also possible inline before the parts are separated.

In particular, there is no transfer of individual components between roll forming and hardening. As a result, no complex transport system and / or storage system is required, whereby the space requirement can be reduced, in particular compared to conventional direct and indirect press hardening.

In particular in comparison to press hardening, in which individual pieces of sheet metal are heated and deformed while cooling, corresponding transfer times and oven times or cooling times and also cooling bearings are saved.

According to at least one embodiment, a content of a component of a base material of the metal strip in the surface coating is increased, in particular in order to increase a melting temperature of the surface coating.

The enrichment of the constituent of a base material due to the first heat treatment and the corresponding diffusion from the base material into the surface coating is generally accompanied by a diffusion of constituents of the surface coating into the base material, for example Al and / or Si.

The melting temperature is increased in particular to a value that is greater than or equal to a predetermined minimum value. Depending on the type of base material of the metal strip, the minimum value can be specified accordingly. If, for example, steel is used, in particular a steel of the types 22MnB5, 34MnB5, 35MnB5, 36MnB5 and so on, the minimum value can be 900 ° C., for example.

The melting temperature can be understood, for example, as the melting temperature averaged over the coating or the intermetallic phases.

The base material, which can also be referred to as the substrate, corresponds in particular to the material of the metal strip before the surface coating is applied.

The enrichment of the constituents of the base material in the surface coating is achieved in particular by setting the process temperature and the process duration of the first heat treatment in such a way that the constituents, i.e. in particular the metal atoms of the base material, diffuse or are transferred into the surface coating.

Whether the desired minimum temperature has been reached or exceeded when the corresponding process parameters are set can be checked and ensured, for example, by sectional image analysis of the crystal structure of the preconditioned surface coating, for example by spectral analysis or X-ray spectroscopy, e.g. energy-dispersive X-ray spectroscopy, EDX.

By increasing the melting temperature, the surface coating is prevented from becoming one during the second heat treatment Forms liquid phase. This enables safer and more stable process management.

When a steel strip is used as the metal strip, the components of the base material correspond in particular to iron atoms which diffuse from the base material into the surface coating through diffusion processes and thus increase the iron content in the surface coating.

During the preconditioning, the coating is enriched with iron atoms from the base substrate via diffusion before roll forming and the second heat treatment. According to the phase diagram of Al-Si-Fe, high-melting intermetallic phases arise during preconditioning. Liquefaction of the surface coating after preconditioning is therefore prevented, at least for process temperatures below 1000 ° C.

According to at least one embodiment, the surface coating contains aluminum or an aluminum alloy, in particular even before the preconditioning. The preconditioned surface coating also contains a higher iron content than before the preconditioning.

The aluminum alloy can be, for example, an aluminum-silicon, AISi, alloy, for example a 90/10 AISi alloy.

The first heat treatment increases, in particular, the melting temperature of the low-melting phase of the AISi alloy.

By using the aluminum alloy, good scale protection is achieved and a relatively large temperature range is made possible for processing the surface-coated metal strip during the second heat treatment. In particular, in contrast to zinc-based anti-scaling coatings, hardening can be possible in a temperature range of several 10 ° C., for example approximately 50 ° C., around the desired temperature value.

The use of the aluminum alloy also enables inductive heating of the surface-coated metal strip during the second heat treatment without the surface coating being heated up rapidly, which can lead to problems such as blooming, burn-off or the formation of an undesirable liquid phase.

According to at least one embodiment, the surface coating contains a primarily aluminum-containing hot-dip coating, for example with 85-90% Al, 5-10% Si and 2-5% Fe.

According to at least one embodiment, the surface-coated metal strip is reshaped by the roll forming after the preconditioning and hardened by the second heat treatment after the roll forming.

In particular, the second heat treatment takes place after the complete completion of the forming by the roll forming.

Subsequent processes such as hot trimming, cold trimming, cutting, bending, punching, and so on are also possible after the second heat treatment or between the first heat treatment and roll forming.

According to at least one embodiment, the roll forming is carried out as cold forming.

In other words, roll forming corresponds to cold rolling or profile cold rolling.

The roll forming can in particular be designed as a multi-stage or incremental process in which the metal strip passes through two or more roller stages connected one behind the other, during which only a slight partial deformation takes place in each case. When the metal strip has gone through all stages, the forming process is complete.

As already mentioned above, cold forming followed by the second heat treatment offers advantages especially compared to press hardening, in which a workpiece is heated and deformed while cooling. In this way, transfer times and oven times or cooling times and cooling storage can be saved. The combination of preconditioning, cold forming and second heat treatment in this order enables a particularly efficient inline process.

In addition, an increased component quality can be achieved through cold forming, namely an improved surface quality and / or lower achievable dimensional tolerances.

According to at least one embodiment, the second heat treatment includes moving a device for heating the metal strip and the preconditioned metal strip relative to one another, in particular along a rolling direction of the metal strip.

In other words, when the device is stationary or moving, the metal strip is unrolled for heating at a defined distance from the device. Alternatively, the belt can stand still, while the heating device is moved with respect to the belt.

This enables the hardening to be controlled individually, so that hardened and unhardened areas of the component can be achieved, for example.

According to at least one embodiment, the metal strip is inductively heated during the second heat treatment.

In other words, the second heat treatment is designed as inductive heating or inductive hardening.

This has the advantage that only the preconditioned metal strip itself is heated, while the system and bypass are largely not heated. This leads to corresponding energy savings.

For inductive heating, the metal strip can be passed through one or more inductors or coils, for example.

According to at least one embodiment, the metal strip is partially, that is not completely, hardened by the second heat treatment. In particular, not all component areas are heated and hardened, but only certain areas such as radii, flanges and so on.

According to at least one embodiment, a part of the reshaped and hardened metal strip is separated from the metal strip.

The separated part then corresponds, for example, to the component. The component can be, for example, a prefabricated component or a semi-finished component. In particular, further processing steps can be carried out on the component, for example surface treatments or machining steps, in order to produce a prefabricated component.

The part can be separated from the metal strip, for example, by means of laser cutting.

According to at least one embodiment, the metal strip and / or the severed part of the metal strip is cut and / or perforated.

According to at least one embodiment, the surface coating is designed as a scale protection layer for the second heat treatment.

In addition, the surface coating can, for example, serve as a corrosion layer for the component by offering passive corrosion protection through its barrier effect.

According to the improved concept, a method for manufacturing a body for a motor vehicle is also specified. For this purpose, a component is produced according to a method for producing a component by reshaping a metal strip according to the improved concept and installed as part of the body.

The motor vehicle is preferably designed as a motor vehicle, in particular as a passenger vehicle or truck, or as a passenger bus or motorcycle.

Further features of the invention emerge from the claims, the figures and the description of the figures. The features and combinations of features mentioned above in the description as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures can be used not only in the specified combination, but also in other combinations without departing from the scope of the invention . Embodiments of the invention that are not explicitly shown and explained in the figures, but emerge and can be generated from the explained embodiments by means of separate combinations of features, are therefore also to be regarded as covered and disclosed. Designs and combinations of features are also to be regarded as disclosed, which therefore do not have all the features of an originally formulated independent claim. In addition, designs and combinations of features, in particular through the statements set out above, are to be regarded as disclosed that go beyond the combinations of features set forth in the back-references of the claims or differ from them.

Exemplary embodiments of the improved concept are described below. The exemplary embodiments explained below are preferred embodiments of the invention. In the exemplary embodiments, the described components of the embodiments each represent individual features of the invention which are to be considered independently of one another and which also further develop the invention in each case independently of one another. Therefore, the disclosure is intended to include combinations of the features of the embodiments other than those shown. Furthermore, the described embodiments can also be supplemented by further features of the invention that have already been described.

In the figures, the same reference symbols denote functionally identical elements.

The FIGURE (FIG. 1) shows a flow chart of an exemplary embodiment of a method according to the improved concept.

The figure shows an exemplary embodiment of a method for manufacturing a body 3 shown for a motor vehicle according to the improved concept. The procedural steps S1 until S3 correspond to an exemplary embodiment of a method for manufacturing a component 1 by forming a metal strip 2 according to the improved concept.

In step S1 of the process becomes the metal band 2 for example provided as a role. The metal band 2 is in particular a sheet steel strip, for example made of a 22MnB5 steel.

The surface coating can be applied, for example, using various known methods, for example by means of hot-dip finishing, as is shown schematically in FIG. 1 with regard to S1.

The surface coating can in particular contain an aluminum alloy, for example an AISi alloy, for example an aluminum alloy with an approximately ten percent silicon content, or consist of this alloy.

In step S2 becomes the metal band 2 subjected to a first heat treatment to precondition the surface coating. The first heat treatment can, for example, by means of a hood annealing 4th or inline after the hot dip finishing.

The first heat treatment increases the melting temperature of the low-melting phase of the AISi alloy, for example to over 900 ° C. This is achieved by the diffusion of iron atoms from the substrate of the metal strip through the heat treatment 2 in the AISi alloy, so that the iron atoms accumulate in the surface coating.

In step S3 becomes the metal band 2 after preconditioning it is shaped by roll forming and hardened by a second heat treatment.

The step S3 contains in particular sub-steps S3a , S3b , S3c and optionally S3d.

The steps of roll forming and hardening by the second heat treatment are performed in the step S3 in particular inline, that is, with continuous unwinding of the metal strip 2 from the role provided.

In a partial step S3a becomes the preconditioned metal strip 2 using one or more role levels 6th cold formed. In the case of multiple role levels 6th the cold forming takes place in particular incrementally.

In step S3b becomes the formed metal strip 2 by means of a device for heating 7th , for example one or more induction coils through which the metal strip 2 is passed through, heated to achieve hardening.

In particular, in the case of a steel strip, the metal strip is heated to 880 to 950 ° C., in particular to a temperature above the austenitizing limit temperature, which can also be referred to as the Ac3 temperature.

Then the hardened metal band can 2 optionally actively or passively cooled, for example by means of an optional cooling device 8th . The cooler 8th can cool the metal band with the help of water, for example.

In step S3c becomes the metal band 2 cut, for example by means of a laser 9 .

The cut part is in the optional step S3d further edited. For example, contours or holes can be made around the prefabricated component 1 to create.

In step S4 becomes the prefabricated part 1 in the manufacture of a body 3 of a motor vehicle installed.

As described, a high-strength hardened component, for example for use in a vehicle body, can be produced by roll forming by means of the improved concept, scaling being avoided by a surface coating and a stable process control being made possible at the same time.

The improved concept enables continuous inline hardening. For this purpose, a preconditioned surface coating is used in particular to protect against scaling. After that, roll forming is carried out with an in-line hardening.

For example, a preconditioned aluminum-containing coating can be used as the surface coating, which is adjusted with regard to the melting temperature of its low-melting phase by means of a prediffusion process before the deformation or before the hardening.

The inline hardening is made possible according to the improved concept without liquid phase formation, so that a significantly increased process stability results.

Further advantages are the avoidance of long diffusion times or oven times, the avoidance of roller caking in the oven and, in the case of inductive hardening, increased energy efficiency.

List of reference symbols

1

Component

2

Metal band

3

body

4th

Hood glow

6th

Role level

7th

Device for heating

8th

Cooling device

9

laser

S1, S2, S3, S4

Procedural steps

S3a, S3b, S3c, S3d

Sub-steps

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 2609224 B1 [0004]
• WO 2009/090555 A1 [0005]

Claims (10)

A method for producing a component (1) by reshaping a metal strip (2), a surface coating being applied to the metal strip (2), characterized in that the surface coating is preconditioned after application to the metal strip (2) by a first heat treatment ; and - after the preconditioning, the metal strip (2) is reshaped by roll forming and hardened by a second heat treatment. Procedure according to Claim 1 , characterized in that - the preconditioned metal strip (2) is provided as a roll; and - the metal strip (2) is unrolled from the roll during the roll forming and during the second heat treatment. Method according to one of the preceding claims, characterized in that a content of a component of a base material of the metal strip (2) in the surface coating is increased. Method according to one of the preceding claims, characterized in that - the surface coating contains aluminum or an aluminum alloy; the preconditioned surface coating has a higher iron content than the surface coating before the first heat treatment. Method according to one of the preceding claims, characterized in that the metal strip (2) is reshaped by the roll forming after the preconditioning and is hardened by the second heat treatment after the roll forming. Procedure according to Claim 5 , characterized in that the roll forming is carried out as cold forming. Method according to one of the preceding claims, characterized in that the metal strip (2) is inductively heated during the second heat treatment. Method according to one of the preceding claims, characterized in that a part (1) of the reshaped and hardened metal strip (2) is separated from the metal strip (2). Method according to one of the preceding claims, characterized in that the surface coating is designed as a scale protection layer for the second heat treatment. Method for manufacturing a body (3) for a motor vehicle, wherein a component (1) is installed as part of the body (3), characterized in that the component (1) is manufactured according to a method according to one of the preceding claims.

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