DE102017103729A1 - Method for producing a component by further shaping a preformed contour - Google Patents

Abstract

The invention relates to 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 Breakthroughs, in selected by the punching or cutting operations work hardened edge portions to obtain a preformed contour of a first deformation at ambient temperature is subjected.
At the same time, the edge areas intended for forming are at least heated to a temperature of at least 600 ° C. for at least 10 seconds, and the edge areas are heated at any time after this heat treatment of a second deformation or further transformations subjected at ambient temperature, each with upstream heat treatments.

Description

The present invention relates to a method for producing a component by further shaping a preformed contour of a board according to the preamble of patent claim 1. The inventive method is characterized in comparison to known methods for producing a component, in particular by increased freedom of design during the forming particularly sheared Edge areas 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 sheet metal blanks may be uncoated or provided with a metallic and / or organic 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 highly competitive automotive market is forcing manufacturers to constantly seek solutions to reduce their fleet consumption while maintaining maximum comfort and occupant safety. 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 material suppliers are trying to meet the material requirements by reducing the wall thicknesses by providing high-strength and ultra-high-strength steels, while at the same time improving component behavior during production and operation.

These steels must therefore meet comparatively high requirements in terms of strength, deformability, toughness, energy absorption capacity and corrosion resistance and their processability, for example in cold forming with respect to fatigue behavior and during welding.

Among the above aspects, the production of components of higher and high strength steels with yield strengths above 400 MPa, advantageously above 600 or above 800 MPa to about 1800 MPa or even more important.

It is known to first cut a sheet metal blank of hot or cold strip at room temperature to produce a component. The cutting process is usually mechanical separation processes, such. shearing or punching, but more rarely also thermal separation methods, such as e.g. 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 deformation to material separation. On the other hand, a notch effect can occur, which arises due to the topography of the cut surface.

In the case of the steels considered here, therefore, an increased crack probability occurs in the edge regions of these cut edges in the subsequent forming.

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 edge crack sensitivity described above in the cold forming of sheared or punched sheet edges, for example, approaches to changing the alloy composition and material processing (eg targeted setting of an optimized microstructure) or the process technology in Kaltbeschnitt the board (eg via modifications of cutting gap, speed, Mehrfachbeschnitt etc.).

These measures are either expensive and expensive (e.g., multi-stage cutting operations, maintenance of 3-D cutting tools, etc.), or they do not yet provide optimal results.

Furthermore, it is from the published patent application DE 10 2009 049 155 A1 It is known to heat at least the region of the cut edge to a defined temperature and to perform cutting at this temperature in order to improve the formability of the cut edges and thus to reduce or avoid strain hardening in the region of the cut 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 the DE 10 2011 121 904 A1 It is also known to cold form a sheared sheet and to heat the cold worked areas locally by means of a laser before further forming operations with the aim of partial softening. The disadvantage here is in particular the local softening, which represents a discontinuity in terms of the often used highly and extremely strong material, especially in stress situations and under oscillatory stress. 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. Furthermore, it is unclear how and to what extent by partial softening the forming capacity of the already cold-formed sheet can be improved.

The DE 10 2014 016 614 A1 describes a method of manufacturing a component by forming a steel blank by subjecting a blanked blank to a short temperature treatment (at most 10 seconds) at a minimum of 600 ° C after optional blanking and / or cutting operations in the areas of the sheared edges. 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, which preferably increased in the edge portions of the board severely stressed by cutting or punching operations during the subsequent cold forming by a conventional method Formability and reduced crack sensitivity distinguishes.

The invention achieves this object with the features of the claims and in particular by a method for producing a component by further shaping an already preformed contour of a board, wherein the previously cut at ambient 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 breakthroughs, in selected, by the punching or cutting operations work hardened edge portions to obtain a preformed contour of a first deformation at ambient temperature is subjected, which is characterized in that optional already provided for forming edge portions at least the edge regions already subjected to the first deformation are heated to a temperature of at least 600 ° C. for a maximum of 10 seconds, and the edge regions are subjected to a respective subsequent heat treatment at any time after the heat treatment of a second transformation or further transformations at ambient temperature ,

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.

Experiments have shown that the unwanted but inevitable work hardening of mechanically cut edges, which becomes even more pronounced in the subsequent shaping of the edge regions, can be significantly reduced or even eliminated by at least 600 ° C. temperature treatment of only the claimed edge regions. 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 can be reshaped or reshaped at room temperature at least 600 ° C after the brief heat treatment, without any risk of crack formation in the edge areas. Because by the temperature treatment of the edge portions of the preformed contour not only the unwanted work hardening is eliminated, but it is also Gefügeschädigungen in the material and adverse contour changes such as microcracks removed, so that the previously almost deformed in its formability material after temperature treatment can be re-formed without hesitation , The sequence according to the invention of a first transformation, the temperature treatment and the second transformation therefore permits a substantially greater deformation potential of materials than conventional processes can offer.

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 undesirable material properties resulting from strain hardening, in particular the increased susceptibility to cracking, are initially set in the material in each forming step, but are eliminated or at least significantly reduced by the subsequent temperature treatment become.

Therefore, according to this embodiment of the method according to the invention, any number of alternating forming and heat treatment steps can follow the second forming, as a result of which the desired component is finally 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 formability, 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 in indefinite to be treated edge portions, the inductive method, radiation heating or laser processing with longer exposure times in question.

Thus, the heat input is very concentrated in the shear-influenced cutting edge areas and is therefore associated with a comparatively low energy consumption, in particular with regard to methods in which the entire board is supplied to a heating or by orders of magnitude temporally more expensive stress relief is applied.

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 Ac1, conversion into so-called metastable phases takes place after treatment in the course of a 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.

Surprisingly, a microstructure transformation with as a rule associated increase in hardness has no negative influence on the Lochaufweitvermögen, regardless of whether a harder compared to the initial structure and thus less tough structure is set, so that treatment temperatures of the cut edges to the solidus limit are possible.

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

To protect the heated cut edge regions from oxidation, an advantageous development of the invention provides for flushing these regions with inert gases, for example argon or nitrogen. The Inertgasspülung takes place during the duration of the heat treatment, but can also, if necessary, in addition to take place shortly before the start and / or in a limited period of time after performing 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 a particularly high flexibility in the production process is made possible in the industrial application of the method. If it appears advantageous from a production engineering 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, high-strength steels 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, including impurities caused by melting.

Compared with the known measures for reducing edge crack sensitivity, the method according to the invention has the advantage that only the shard-influenced edge regions are microstructured by the heat treatment and the strength is generally 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 reduced due to the significantly increased formability of the critical shear-influenced edge regions of boards on the one hand, the Committee of deformed components and on the other hand, previously necessary Joining operations can be saved, for example, by now practicable collar operations in the training of eg bearing points.

The inventive method also allows more complex component geometries and thus greater freedom in design when using the same materials due to the improved formability of the cut edge regions. In addition, the fatigue strength of the cold-formed component is expected not to be reduced due to the self-adjusting, but possibly harder but more homogeneous compared to the initial state, but in particular in the case of pronounced biphasic structures, such as e.g. Dual phase structures increased.

Due to the short temperature treatment period of a maximum of 10 seconds, the method according to the invention can be integrated as an intermediate production step in a series production which specifies a cycle in the range of 0.1 to 10 seconds. 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 also relates to the use of a steel circuit board for the manufacture of a component, wherein the board previously cut to size from a strip or sheet at room temperature is subjected to optional further production steps carried out at room temperature, e.g. Punching or cutting operations to provide recesses or apertures 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 reshaped edge portions are 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 and the edge portions are subjected to a second transformation at room temperature at any time after the heat treatment

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 blank is cut by shearing, the term shear cutting including both open and closed cuts, i. both cutting and punching operations.

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

The left picture of the 1 shows the optional preforming of a board already cut by shear cutting. The second picture from the left in the 1 shows the punching of a hole in the board (step 1 ). The cut edges of the hole are then optionally subjected to heating according to the invention (step 1a The inventive method further includes the subsequent forming of the board in its edge regions to a preformed contour, for example, to an incomplete collar (step 2 ).

Since the preformed contour obtained in this way has a high work hardening in its shear-damaged edge regions, which would possibly lead to defects in the material during further forming, the edge regions are subsequently eliminated or reduced by at least 600 ° C. for at least 600 ° C. for a duration of for a maximum of 10 seconds (step 3 ).

As a result of the temperature treatment, the component is also given a considerable degree of deformability in the stressed edge regions, so that a further, further transformation can take place in the next step (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 in the above description, in the 1 As well as in the claims disclosed features of the invention, both individually and in any combination for the realization be essential to the invention in its various embodiments.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• DE 102009049155 A1 [0019]
• DE 102011121904 A1 [0020]
• DE 102014016614 A1 [0021]

Claims (17)

A method for producing a component by further forming 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 performed at ambient temperature manufacturing steps, such as punching or cutting operations to achieve recesses or openings in selected is subjected to a first deformation at ambient temperature by the punching or cutting operations to obtain a preformed contour, 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 on a Temperature of at least 600 ° C are heated and the edge portions at any time after this heat treatment of a second transformation or other transformations at ambient temperature, each with vorges be subjected to heat treatments. Method according to Claim 1 , characterized in that the strip or sheet from which the blank used to produce the component is preformed in a pretreatment step prior to the first forming. Method according to Claim 1 and 2 , characterized in that the component is obtained by the second deformation. Method according to one of the preceding claims, characterized in that after the second deformation nor any 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 , Method according to at least one of the preceding claims, 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. Method according to at least one of the preceding claims, characterized in that the edge portions subjected to the first deformation are heated for a period of 0.1 to 2 seconds to a temperature of at least 600 ° C. Method according to at least one of the preceding claims, characterized in that the edge portions subjected to the first deformation are heated to a temperature of 600 ° C to solidus temperature. Method according to at least one of the preceding claims, characterized in that the edge portions subjected to the first deformation are heated to a temperature from the transformation temperature Ac1 to the solidus temperature. Method according to at least one of the preceding claims, characterized in that the heating to a temperature of at least 600 ° C is effected inductively, conductively, by means of radiation heating or by means of laser radiation. Method according to at least one of the preceding claims, characterized in that the board has an organic and / or metallic coating. Method according to Claim 10 , characterized in that the metallic coating Zn, Mg, Al and / or Si contains. 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. Method according to at least one of the preceding claims, characterized in that the area is purged around the point of heat treatment for protection against oxidation during, and optionally before and / or after the heat treatment by means of an inert gas. 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 previously at room temperature from a tape or a sheet cut sheet after optional further carried out at room temperature manufacturing steps, such as punching or cutting operations to achieve recesses or openings, in selected by the punching or cutting operations work hardened edge portions to obtain a preformed contour of a first transformation at room temperature, and wherein the first reshaped edge portions for a maximum of 10 seconds to a temperature of at least 600 ° C are heated and the edge portions are subjected at any time after the heat treatment of a second transformation at room temperature. Use after Claim 15 , characterized in that the edge portions subjected to the first forming are heated to a temperature of at least 600 ° C for a period of 0.02 to 10 seconds. Use after Claim 15 or 16 , characterized in that the edge portions subjected to the first deformation are heated for a period of 0.1 to 2 seconds to a temperature of at least 600 ° C.

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