WO2018153615A1

WO2018153615A1 - Method for producing a component by further forming of a preformed contour

Info

Publication number: WO2018153615A1
Application number: PCT/EP2018/051978
Authority: WO
Inventors: Stefan MÜTZE; Matthias Schneider; Sebastian WESTHÄUSER; Ingwer Asmus Denks
Original assignee: Salzgitter Flachstahl Gmbh
Priority date: 2017-02-23
Filing date: 2018-01-26
Publication date: 2018-08-30
Also published as: KR102386137B1; ES2930811T3; US20200038933A1; RU2743046C1; EP3585531B1; KR20190120205A; DE102017103729A1; EP3585531A1

Abstract

The invention relates to a method for producing a component by further forming of a preformed contour of a blank, wherein the blank which has previously been cut to size at room temperature from a strip or a sheet is subjected to a first shaping operation at ambient temperature after optional further production steps carried out at ambient temperature, such as for example stamping or cutting operations to achieve clearances or apertures, in selected edge regions that have been cold-hardened by the stamping or cutting operations to obtain a preformed contour. Optionally the edge regions that are already intended for shaping, but at least the edge regions that have already undergone the first shaping are thereby heated to a temperature of at least 600°C for a maximum time of 10 seconds and, at any desired time after this thermal treatment, the edge regions are subjected to a second shaping or to further shaping operations at ambient temperature with prior thermal treatments in each case.

Description

A method for producing a component by further molding a

preformed contour

The present invention relates to a method for producing a component by further molding a preformed contour of a circuit board according to the preamble of patent claim 1. The method according to the invention is characterized in

Compared to known methods for producing a component in particular by increased freedom of design during the forming in particular

sheared edge portions of the board.

In the following, a blank or sheet metal blank is understood to mean a blank of a sheet metal, in particular a sheet steel. The metal sheets can

un coated or with a metallic and / or organic

Be provided corrosion protection coating.

In the following, a component is understood to be a component produced from a sheet metal blank by deformation by means of a forming tool at ambient temperature. In this case, all sheet metal materials come into consideration as sheet materials, but especially steel.

Such components are mainly used in automobile construction, but also in the home appliance industry, in mechanical engineering or construction or in the field of the same offer applications.

The intensely competitive automotive market is forcing manufacturers to keep up

Solutions to reduce their fleet consumption while maintaining the highest possible comfort and occupant protection. On the one hand, the weight saving of all vehicle components plays a decisive role, but on the other hand also the most favorable possible behavior of the individual components with high static and dynamic stress during operation as well as in the event of a crash.

The necessary material requirements are tried by the material suppliers

l to take account of the fact that the wall thicknesses can be reduced by providing high - strength and highest - strength steels, while at the same time improving component behavior during production and operation.

These steels must therefore comparatively high requirements in terms of strength, deformability, toughness, energy absorption and corrosion resistance and their processability, for example in the

Cold forming in relation to the fatigue behavior and welding, are sufficient.

Among the above-mentioned aspects, the production of components of higher strength and high strength steels having yield strengths above 400 MPa, advantageously above 600 or above 800 MPa to about 1800 MPa or even above, is becoming increasingly important.

It is known to first cut a sheet metal blank of hot or cold strip at room temperature for the production of a component. As cutting methods are usually mechanical separation methods, such. shearing or punching, but more rarely also thermal separation methods, such as e.g. the

Laser cutting, for use. Thermal separation processes are significantly more costly compared to mechanical separation processes, so that they are used only in exceptional cases.

After cutting the cut board is placed in a forming tool and in single or multi-stage forming steps the finished component, such as. a chassis carrier generated.

In forming, the cut edges, especially when raised or raised, e.g. in collar operations in perforated boards, particularly stressed.

Before forming, various further manufacturing steps, such as e.g. Punching and cutting operations on the board, made.

At the cutting edges various preliminary damages can be present. These are on the one hand due to a work hardening of the material, caused by the mechanical separation, which represents a total transformation to material separation. On the other hand, a notch effect can occur, which is due to the

Topography of the cut surface is created.

Especially with the steel considered here, therefore, occurs in the subsequent

Forming an increased crack probability in the edge regions of these cutting edges.

The aforementioned damage to the sheet edges can lead to premature failure in subsequent forming operations or during operation of the component.

The testing of the forming behavior of cut sheet edges with regard to their edge crack sensitivity is carried out with a hole expansion test according to ISO 16630. When Lochaufweitversuch a circular hole is introduced into the sheet by shear cutting, which is then widened by a conical punch. The measured variable is the change in the hole diameter relative to the initial diameter at which the first crack occurs at the edge of the hole at the cutting edge.

In order to minimize the above-described edge crack sensitivity in the cold working of sheared or punched sheet edges, e.g. Approaches to altering the alloy composition and material processing (e.g., deliberately setting an optimized texture) or the process technique of cold-cutting the board (e.g., via modifications of cutting gap,

Speed, multiple trimming, etc.).

These measures are either expensive and expensive (e.g., multi-level

Cutting operations, maintenance of 3-D cutting tools, etc.), or they do not yet provide optimal results.

Furthermore, it is known from the published patent application DE 10 2009 049 155 A1 to heat at least the region of the cut edge to a defined temperature and to perform the cutting at this temperature in order to improve the formability of the cut edges and thus the strain hardening in the region of Cut or avoid cutting edge. The disadvantage here are the necessary for heating the sheet high technical and economic effort on the one hand and on the other hand, the forced coupling a heating of the board with immediately subsequent cutting, which makes the production inflexible.

From DE 10 2011 121 904 A1, it is also known to cold-form a sheared sheet and to heat the ka Itverfestigten areas locally by means of a laser before further forming operations with the aim of a pa rtiellen softening. The disadvantage here is in particular the local softening, in terms of the often used highly and extremely strong material, especially in

Stress situations and under oscillating stress represents a discontinuity. In addition, it is unclear exactly where the warming will take place and how the local warming with temperature and time course should take place concretely. Of

Furthermore, it is unclear how and to what extent by the partial softening the forming capacity of the already cold-formed sheet can be improved.

DE 10 2014 016 614 A1 describes a method for producing a component by forming a blank made of steel, in which a cut board after optional punching and / or cutting operations in the areas of

sheared edges of a short temperature treatment (max 10

Seconds) at least 600 ° C is subjected. The heat treated edges are then cold formed at any time after being heated. Although this method basically allows for increased workability of work-hardened, mechanically separated sheet edges compared to other previously known methods, it is still desirable for the reasons mentioned at the outset to achieve an even higher formability of the shear-cut edges.

It is therefore the object of the present invention to provide an alternative method for producing a cold-formed component from a sheet metal sheet sheared at room temperature, preferably in the edge portions of the board subjected to cutting or punching operations during the subsequent cold forming by a conventional Process increased formability and reduced crack sensitivity

distinguished.

The invention solves this problem with the features of the claims and

in particular by a method for producing a component by further molding an already preformed contour of a board, wherein the previously in

Ambient temperature board cut to length from a strip or sheet metal, optionally at ambient temperature

Manufacturing steps, such as Punching or cutting operations to achieve recesses or openings, in selected, by the punching or

Cutting operations cold-strengthened edge regions, to obtain a preformed contour of a first deformation at ambient temperature is subjected, which is characterized in that optionally already provided for forming edge portions but at least the edge portions already subjected to the first deformation for a period of up to 10 seconds to a temperature vo n at least 600 ° C are heated and the edge areas at any time after the heat treatment of a second transformation or further transformations at ambient temperature, each with upstream again

Be subjected to heat treatments.

As ambient temperature, both the room temperature, for example 20 ° C, and the temperature of the forming tool are considered. The temperature of the forming tool can be well above the room temperature.

In experiments it has been shown that the undesirable but unavoidable

Hardening of mechanically cut edges, which becomes even more pronounced in the subsequent deformation of the edge areas, by a

Temperature treatment only the claimed edge areas at least 600 ° C can be significantly reduced or even eliminated. For a very short temperature treatment of a maximum of 10 seconds, in particular from 0.02 to 10 seconds or even from 0.1 to 2 seconds is sufficient. It has now been found that a formability of the material which is exhausted or at least restricted by shear cutting and reshaping of the edge regions is regenerated completely, largely or at least proportionally by the mentioned temperature treatment. As a result, preformed contours may recommence at least 600 ° C after brief heat treatment

Room temperature to be reformed or further formed without there is an increased risk of cracking in the edge regions. Because of the

Tempering the edge portions of the preformed contour not only eliminates unwanted strain hardening but it will

Gefügeschädigungen in the material as well as adverse contour changes such as microcracks removed, so that the previously almost deformed in its formability material after the temperature treatment can be safely re-formed without further thought. The sequence according to the invention of a first forming, of the temperature treatment and of the second forming therefore makes it possible to produce materials of significantly greater deformation potential than conventional ones

Can offer procedures.

As a result of the second transformation, according to one possible embodiment of the method according to the invention, the desired component can now be obtained.

According to another embodiment of the method alternatively after the second forming any number, in particular two, three or four, further forming steps of the edge regions are carried out at room temperature, each of the further forming steps also a further temperature treatment of the edge regions at least 600 ° C for the Duration of a maximum of 10 seconds, in particular for 0.02 to 10 or 0.1 to 2 seconds, precedes. In this way, a component can be produced in a multi-step process in which the undesired material properties resulting from work hardening, in particular the increased susceptibility to cracking, are adjusted in the material first in each forming step, but are adjusted by the following

Temperature treatment eliminated again or at least significantly reduced.

On the second transformation can therefore according to this embodiment of the method according to the invention as many alternating forming and Connect heat treatment steps, as a result of which eventually the desired component is obtained.

The individual forming and temperature treatment steps of the process according to the invention can be carried out at any time, i. temporally decoupled, done.

The inventive method is particularly applicable to any sheared material edges, in particular punched holes and edges with any contour. Due to the inventively increased Umfor mbarkeit it is possible to produce complex geometries, for which it requires, for example, several forming steps. Demanding components can also be produced in one piece, eliminating the need for additional joining operations.

In the method according to the invention, the heat treatment is preferably carried out over the entire thickness of the board and in the plane direction of the board in a range which corresponds at most to their thickness. The duration of the heat depends on the type of heat treatment process.

The heating itself can take place in any desired manner, for example, conductively, inductively via radiation heating or by means of laser processing. Excellent for the heat treatment is the conductive heating, as it is often used in the automotive industry for example on the example of spot welds.

Advantageously, for example, is a spot welding machine with rather short exposure times for the treatment of punched holes in the board, whereas at longer edge portions to be treated, the inductive method,

Radiation heating or laser processing with longer exposure times come into question.

Thus, the heat input is very concentrated in the scherbeeinflusste n Schnittkantenbereichen and is therefore with a comparatively small

Energy consumption associated, in particular with regard to methods in which the entire board is supplied to a heating or an order of magnitude temporally more complex stress relief is used.

The process window for the temperature to be reached in the cutting edge area is also very large and covers a temperature range from above 600 ° C up to the solidus temperature of approx. 1500 ° C.

The experiments have also shown that the elimination of strain hardening is crucial for a significant improvement in Lochaufweitvermögens. In addition, by the heat treatment, discontinuities such as e.g. Pores, closed and thus positively influenced the topography of the cut edges.

This is independent of whether the heat treatment takes place below or above the transformation temperature Ac1.

If the heat treatment is carried out above Ad, it is converted into so-called metastable phases after treatment in the course of rapid cooling due to the surrounding cold material in the case of convertible steels. The resulting structure then has at least the same or an increased hardness compared to the non-heat treated area. For example, the Vickers hardness increases by up to 1000 HV.

A structural transformation with a usually associated with it

Hardness increase surprisingly has no negative impact on the

Lochaufweitvermögen, regardless of whether a harder compared to the initial structure and thus less tough structure is set, so that too

Treatment temperatures of the cut edges up to the solidus limit are possible.

In any case, it is crucial that the strain hardening introduced by cutting is largely eliminated.

In order to protect the heated cut edge regions from oxidation, an advantageous development of the invention provides for rinsing these areas with inert gases, for example argon or nitrogen. The inert gas purging takes place during the duration of the heat treatment, but can also, if necessary, even shortly before the start and / or in a limited period of time still carried out after the heat treatment.

The forming steps of the method according to the invention can advantageously be carried out with the forming tools already in production, e.g.

cylindrical or conical punches.

Due to the temporal decoupling of the individual forming - and

Temperature treatment steps of the method according to the invention in the industrial application of the method is a particularly high flexibility in

Production process allows. If it appears advantageous from a production point of view, however, the heating of the cut edges can also take place immediately after the first forming step or immediately after an optional further forming step. For this purpose, a heat treatment device of a forming device for cold forming of the board can be connected directly downstream.

The board itself may e.g. be rolled flexibly with different thicknesses or joined from cold or hot strip of the same or different thickness and / or quality. The invention is applicable to hot or cold rolled steel strip from soft to high strength steels, which may be provided with a corrosion inhibiting layer as a metallic and / or organic coating. The metallic coating may, for example, contain or consist of zinc, magnesium, aluminum and / or silicon.

The suitability of coated steel strips can be explained by the possibility of limiting the treatment of the edge area to a distance to the edge, which corresponds to a fraction of the board thickness, since in this area the predominant part of the damaging work hardening during shear cutting is present. Thus, for sheet thicknesses of a few millimeters thickness, the range up to a distance to the edge of a few tens of micrometers may already be sufficient, so that

For example, the effective corrosion protection of a metallic

corrosion-inhibiting layer is not or only insignificantly influenced. As higher-strength steels, all single-phase as well as multi-phase steel grades are used. These include microalloyed, higher-strength steel grades as well as bainitic, ferritic or martensitic grades as well as dual phases,

Complex phases and TRIP steels. For example, steels having the following alloy composition in% by weight are used:

C 0.01 - 0.2%

Si 0.2 - 4.0%

Mn 0.5 - 4.0%

Al 0.02 - 0.1

Ti 0.0-0.2

V 0,0 - 0,3

Nb 0.0 - 0.1

with optional addition of Cr, Ni, Mo, B, balance iron, inclusive

melting impurities.

The inventive method has the advantage over the known measures for reducing the edge crack sensitivity that by the

Heat treatment only the shard-influenced edge areas are microstructured changed and the strength is usually not reduced, but increased. The insensitivity to edge cracks in the sense of a larger Lochaufweitvermögens can be improved by a factor of 3 or even more than 4.

In the industrial application of the method according to the invention can be due to the significantly increased formability of the critical shear influences

Edge regions of sinkers on the one hand, the Committee can be lowered on formed components and on the other hand, previously necessary joining operations, for example, by now feasible collar operations in the formation of e.g. Saved from storage locations.

The inventive method also allows due to the improved formability of the cut edges areas more complex component geometries and thus greater design freedom when using the same materials. In addition, the fatigue strength of the cold-formed component is expected due to the setting, although possibly compared to

Initial state harder but more homogeneous structure not reduced, but especially in pronounced two-phase structures such. Dual phase structures increased.

Due to the short temperature treatment time of a maximum of 10 seconds, the inventive method can be integrated in a series production, which specifies a clocking in the range of 0.1 to 10 seconds, as Zwischenfertig ungsschritt. In particular, the production of sheet metal components in the automotive sector in several successive steps thus represents a predestined

Scope of the method according to the invention.

The invention further relates to the use of a steel circuit board for the production of a component, wherein the previously cut at room temperature from a strip or a sheet metal plate after optional further at

Room temperature carried out manufacturing steps, such. Punching or

Cutting operations to achieve recesses or breakthroughs, in selected by the punching or cutting operations work hardened

Edge regions for receiving a preformed contour of a first deformation at room temperature is subjected, and wherein the first deformation

subjected edge regions for a maximum of 10 seconds, preferably from 0.02 to 10 seconds or from 0.1 to 2 seconds, to a temperature of at least 600 ° C are heated and the edge portions at any time after the heat treatment of a second transformation at

Room temperature to be subjected

Optionally, the band or sheet, from which the board used for the production of the component is cut, preformed in a pre-treatment step and then cut from the already preformed band or sheet, the board, if this makes sense in terms of manufacturing technology.

Alternatively, the preforming can also be done only on the already cut board. According to a preferred embodiment, the cutting takes place by shear cutting, wherein the term shear cutting includes both open and closed cuts, ie both cutting and punching operations.

Further features, advantages and details of the invention will become apparent from the following description of Figure 1, which shows a schematic representation of the individual steps of the method according to the invention.

The left-hand image of FIG. 1 shows the optional preforming of a circuit board already cut by shear cutting. The second image from the left in FIG. 1 shows the punching of a hole in the board (step 1). The cut edges of the hole are then optionally subjected to a heating according to the invention (step 1a). The method according to the invention furthermore includes the

subsequent forming of the board in their edge areas to a

preformed contour, for example, to an incomplete collar (step 2).

Because the resulting preformed contour in her scherberträchtigten

Edge regions has a high strain hardening, which in further

Forming could possibly lead to defects in the material, the edge areas are then used to eliminate or reduce the

Cold work hardening of the inventive temperature treatment of at least 600 ° C for a period of up to 10 seconds subjected (font 3).

Due to the temperature treatment, the component is also in the claimed edge areas to a considerable extent its formability back, so that in the next step, a new, further transformation can take place (step 4).

In embodiments in which the desired deformation is not yet obtained by the second deformation, the material stresses generated by the second deformation can be at least partially eliminated by a subsequent temperature treatment of at least 600 ° C. for a maximum of 10 seconds, after which a third Forming step can take place. Should the desired result not be reached as a result of the third forming step, the steps of the temperature treatment of at least 600 ° C for a maximum of 10 seconds, followed by a subsequent forming step at room temperature, as often as may be repeated.

The features of the invention disclosed in the preceding description, in the figure 1 and in the claims can, both individually and in any combination for the realization of the invention in its various

Embodiments be essential.

Claims

claims

1. A method for producing a component by further molding a

Preformed contour of a board, wherein the previously cut at room temperature from a strip or a sheet metal circuit board for optional further, carried out at ambient temperature manufacturing steps, such as. Punching or cutting operations to achieve recesses or perforations in selected edge portions cold work hardened by the punching or cutting operations to obtain a preformed contour of a first transformation at ambient temperature;

characterized in that optionally already for forming

provided edge regions but at least the edge portions already subjected to the first deformation for a maximum of 10

Seconds to a temperature of at least 600 ° C and the edge areas at any time after this

Heat treatment of a second deformation or further transformations at ambient temperature, each with upstream heat treatments are subjected.

2. The method according to claim 1, characterized in that the strip or sheet, from which the board used for the production of the component is cut, in a pretreatment step before the first

Forming is preformed.

3. The method according to claim 1 and 2, characterized in that the component is obtained by the second deformation.

4. The method according to any one of the preceding claims, characterized

characterized in that after the second forming any number of further forming steps of the edge regions are carried out at ambient temperature, each of the further forming steps preceded by a further temperature treatment of the edge regions at least 600 ° C for a maximum of 10 seconds.

5. The method according to at least one of the preceding claims, characterized in that subjected to the first forming

Edge regions are heated to a temperature of at least 600 ° C for a period of 0.02 to 10 seconds.

6. The method according to at least one of the preceding claims, characterized in that subjected to the first forming

Edge areas for a period of 0.1 to 2 seconds to a temperature of at least 600 ° C are heated.

7. The method according to at least one of the preceding claims, characterized in that subjected to the first forming

Edge areas are heated to a temperature of 600 ° C to solidus temperature.

8. The method according to at least one of the preceding claims, characterized in that subjected to the first forming

Edge regions are heated to a temperature from the transition temperature Ad to the solidus temperature.

9. The method according to at least one of the preceding claims, characterized in that the heating to a temperature of at least 600 ° C inductively, conductively, by means of radiation heating or by means of

Laser radiation takes place. 0. The method according to at least one of the preceding claims, characterized in that the board has an organic and / or metallic coating.

11. The method according to claim 10, characterized in that the metallic coating Zn, Mg, Al and / or Si contains.

12. The method according to at least one of the preceding claims, characterized in that the heat treatment of the board, starting from the edge, takes place in a region which corresponds at most to the thickness of the board.

13. The method according to at least one of the preceding claims, characterized in that the area around the point of the heat treatment for protection against oxidation during, and optionally before and / or after the

Heat treatment is purged by means of an inert gas.

14. The method according to at least one of the preceding claims, characterized in that a steel with the following alloy composition in wt .-% is used:

C 0.01 - 0.2%

Si 0.2 - 4.0%

Mn 0.5 - 4.0%

Al 0.02 - 0.1

Ti 0.0-0.2

V 0,0 - 0,3

Nb 0.0 - 0.1

with optional addition of Cr, Ni, Mo, B, balance iron, including impurities caused by melting.

Use of a steel circuit board for the manufacture of a component, wherein the circuit board previously cut to size from a strip or a sheet at room temperature is subjected to optional further production steps carried out at room temperature, e.g. Punching or cutting operations to achieve recesses or perforations in selected edge portions cold work hardened by the punching or cutting operations to obtain a preformed contour of a first transformation at room temperature, and wherein the first formed

Edge areas for a maximum of 10 seconds on one

Temperature of at least 600 ° C are heated and subjected to the edge portions at any time after the heat treatment of a second transformation at room temperature.

16. Use according to claim 15, characterized in that the edge portions subjected to the first deformation are heated to a temperature of at least 600 ° C for a period of 0.02 to 10 seconds.

17. Use according to claim 15 or 16, characterized in that the edge portions subjected to the first deformation are heated to a temperature of at least 600 ° C for a period of 0.1 to 2 seconds.