DE102018114653A1 - Process for manufacturing load-optimized sheet metal components - Google Patents

Abstract

The invention relates to a method for producing sheet metal components from a material, in particular for an automobile body, comprising the method steps: preforming a workpiece into a preformed component, excess material being introduced into the preformed component at least in regions; and calibrating the preformed component to form an at least partially finished component using the excess material, the preformed component being compressed at least in sections, characterized in that the material has a ratio of yield strength R to tensile strength R of R / R≥0.53.

Description

The invention relates to a method for producing sheet metal components from a material, in particular for an automobile body, comprising the method steps: preforming a workpiece to a preformed component, excess material being introduced into the preformed component at least in regions and calibrating the preformed component to an at least partially final molded component using the excess material, in particular wherein the preformed component is compressed at least in sections. In addition, the invention relates to the use of a sheet metal component.

Molded sheet metal components, in particular half shells, are usually produced on an industrial scale from sheet metal blanks by a deep-drawing process (with and without hold-down devices). H. essentially flat sheets. In conventional deep drawing, a sheet metal blank is formed into a half-shell by tensile pressure forming in accordance with DIN 8584. A hold-down device is used to prevent the board material from buckling and wrinkling when it flows into the die under the effect of the tangential compressive stress. The hold-down presses on the edge of the sheet and this against the edge of the die, causing frictional tension between the edge of the sheet and the hold-down. However, this has the disadvantage that the sheet-metal blank is subjected to a strong deformation during deep drawing and the frictional stresses cannot always be carried out reliably due to batch-dependent material deviations. Deep-drawn components, whether with or without the use of a hold-down device, generally require a final edge trimming in which excess areas of the deep-drawn component are cut off. In the case of parts with flanges, this can be done, for example, by one or more trimming tools which partially or wholly trim the flange from above or obliquely in the desired manner. In the case of flangeless parts, on the other hand, the trimming is already much more complex because it has to be passed, for example, via a wedge slide, and cut off from the side. However, the trimming operations are disadvantageous in that the trimming usually requires one or even several separate operations, which often also require their own tool technology and their own logistics system. In addition, trimming operations often reduce material utilization, which means additional costs due to the high operating weight per sheet metal component.

In order to avoid, in particular, the batch-dependent dimensional accuracy and the high proportion of trimmings in the manufacture of sheet metal components, the generic methods described at the beginning with preforms and calibrations (the so-called reduced or free trimming calibrated deep drawing) were developed. In these, the inhomogeneous stress state of the preform induced by the preforming is realigned by calibration. This largely prevents undesired, batch-dependent springback of the component, which occurs in particular in the case of high-strength materials in combination with small sheet thicknesses.

However, this approach itself has some restrictions. For example, various boundary conditions must be observed when manufacturing the preform. Here, too, the batch-dependent mechanical material properties, friction and tool wear influence and change the lengths of the local cross-sectional developments, since the board is then stretched more or less. Such an uncontrolled stretching of the material leads to the fact that the material addition for the subsequent calibration step may leave the range of values that can be reliably controlled.

This could be counteracted by dispensing with active, external sheet metal holding compared to conventional production by deep drawing. When producing the preform, however, less plastic stretching occurs in particular in the component frames. The disadvantage here is that due to the reduced elongation, the material used, particularly in the frames, does not solidify as much as in the case of deep-drawn components. Solidification is understood to mean an increase in the yield or yield point of a steel material as plastic deformation progresses. Another disadvantage is the lower plastic elongation which leads to a reduced decrease in sheet thickness. In addition, the sheet thickness of the component is increased when calibrating the preform. Because here the distributed material addition of the preform is compressed in the direction of the sheet plane, which leads to a further increase in the sheet thickness in the component. This leads to higher required forces and tool loads. Overall, this leads to an increased sheet thickness of the formed component compared to the conventional method.

With the conventional deep drawing described at the beginning, an increase in the yield or yield point can be achieved. For conventional forming, however, this has the consequence that the forming capacity of the high-strength material used is already largely consumed during the forming process, and the finished component can therefore hardly bear any plastic deformation. For the load on the component, for example in the case of body components in the event of a crash, this can mean that the material is folded or Buckling due to tearing fails and the component cannot withstand the required level of energy and force. Such failure thus has a negative impact on the deformation behavior of the components in the event of a crash and thus on vehicle safety. But even for post-molding operations that may be necessary, such as the so-called putting through of a collar (e.g. for RPS holes), after the main shaping, there may no longer be sufficient plastic forming capacity available.

Based on this prior art, the present invention has for its object to provide a method for producing sheet metal components, with which the advantages of deep drawing and trimming-free calibrating deep drawing can be combined with little equipment, that is, in particular high-dimensional sheet metal components can be produced that have at least similar advantageous mechanical properties (for example with regard to strengthening) as appropriately dimensioned deep-drawn sheet metal components and thereby require the lowest possible operating weight. In addition, the present invention is based on the object of specifying the use of a corresponding sheet metal component.

This object is achieved according to a first teaching of the present invention in a method for producing sheet metal components from a material, in particular for an automobile body, comprising preforming a workpiece into a preformed component, excess material being introduced into the preformed component at least in regions, and calibrating the Preformed component to an at least partially finished component using the excess material, in particular wherein the preformed component is compressed at least in sections, in that the material has a ratio of yield strength R _p0.2 to tensile strength R _m of R _p0.2 / Rm ≥ 0.53.

The preformed component can be produced in one or more steps using various shaping processes that can also be combined with one another. The preforming may include, for example, a deep-drawing step. The sheet metal component can in particular be a flanged or flangeless half-shell. In the case of half-shells in particular, the preforming can also involve multi-stage shaping, for example embossing the base to be created and raising the frames to be created or optionally placing the flanges to be created. Special forms of deep drawing are also conceivable, such as combinations of folding and / or (stamping) embossing. The preformed component obtained by the preforming can in particular be regarded as a component close to the final shape, which corresponds as closely as possible to the intended finished part geometry, taking into account given boundary conditions such as springback and deformability of the material used.

Calibration can be understood in particular to mean final shaping of the preformed component, which can be achieved, for example, by a pressing process. In this respect, the final molded component can be understood as an essentially finished molded component. However, it is possible that the final molded component can be subjected to further processing steps that modify the component, such as, for example, the introduction of connection holes. However, the aim is to design the calibration form in such a way that, if possible, no further shaping steps are necessary.

The workpiece is, for example, an essentially flat sheet metal blank. The material from which the workpiece is produced is in principle any material which has the ratio of yield strength to tensile strength according to the invention. However, the material is preferably a malleable metal, in particular a steel material, preferably a multi-phase steel.

Excess material means at least additions in the local cross-sectional lengths of the preformed sheet metal component, which means that at least locally more material is available than would actually be necessary for the wall thickness or sheet thickness or the actually developed cross-sectional length of the final molded sheet metal component. This excess material is squeezed out during calibration. The excess material can be provided, for example, as a material reserve in the floor area, in the frame area, in the flange area and / or in a transition area between the flange and frame area or frame and floor area.

The yield strength R _p0.2 and the tensile strength R _m as well as other parameters described here, such as the elongation at break, are determined in the sense of the invention in particular in a tensile test according to DIN EN ISO 6892-1: 2017-02 , e.g. B. Method A determined.

According to the invention, it was recognized that a method of the generic type, that is to say a calibrated deep drawing which is reduced or free of trimmings (hereinafter also referred to as the “BKT method”), can be used in such a way that sheet metal components, in particular half-shells, which have a high dimensional accuracy and can produce similar partially identical or even improved mechanical properties as appropriately dimensioned have conventionally deep-drawn sheet metal components, but require a lower operating weight and can also be manufactured true to size and reliably. It has been shown that the skilful selection of materials described ensures that the finally formed component has at least similar or essentially identical mechanical properties (in particular with regard to hardening) and wall thicknesses or sheet thicknesses like a correspondingly dimensioned deep-drawn sheet metal component. This means that the selection of materials according to the invention means that sheet metal components can be provided, which on the one hand have dimensional accuracy familiar from the BKT process on the one hand, and on the other hand the usual low wall thicknesses and mechanical properties, such as residual forming capacity, that are familiar from conventional deep drawing (with or without the use of a hold-down device) ( _That is, the possibility of a plastic change in shape that a material can bear without cracking, such as the elongation at break and the yield strength R _p0.2 and / or tensile strength R _m ). In some cases, these mechanical properties known from conventional deep drawing, such as the residual formability, can also be exceeded with the same starting material. The properties of the material described relate to the unformed state.

Embodiments of the BKT method that goes back to the applicant are, for example, in the German published documents DE 10 2007 059 251 A1 . DE 10 2008 037 612 A1 . DE 10 2009 059 197 A1 . DE 10 2013 103 612 A1 . DE 10 2013 103 751 A1 . DE 10 2016 118 418 A1 and DE 10 2016 118 419 A1 described, the content of which is incorporated by reference. The features of the BKT process have in common that in a first process step a modified deep-drawing process is used to produce a preform that comes as close as possible to the final shape or finished shape of the component, but with the difference that in the component sections such as flange, frame and / or Bottom-defined material excesses are introduced, which are shaped out again in a second method step by a special upsetting of the at least sectionally, in particular entire, preformed component during calibration.

So the present can in particular as in the DE 10 2007 059 251 A1 Described in further details, it can be provided that the entire cross section of the preformed component has excess board material due to its geometrical shape, by which the excess material is compressed during the shaping of the preformed component into its final shape by at least one further pressing process, and that final molded component has an increased wall thickness essentially over the entire cross section.

Also like in the DE 10 2008 037 612 A1 described in further details, it can be provided that the preformed component has excess board material due to its geometric shape, the component being compressed into the final molded component by the excess material during the shaping of the preformed component into its final shape by at least one further pressing operation, the preformed component has the excess board material in the transition area between the frame area and the flange area.

Furthermore, as in the DE 10 2016 118 418 A1 described in further details, it can be provided that a material quantity adjustment is set in the preformed component, the material quantity adjustment being set with a floor-specific, frame-specific, radius-specific and / or flange-specific material quantity adjustment.

After all, like in the DE 10 2016 118 419 A1 In further details, it can be provided that the bottom area of the preformed component essentially has the geometry and / or the local cross sections of the bottom area of the at least partially finished component.

Compared to conventional deep drawing, in which active, external holding-down can take place, less plastic expansion occurs in the manufacture of the preformed component, which has a positive effect on the residual formability. During the subsequent calibration, the introduced excess material is compressed in the direction of the sheet metal plane, which leads to the fact that the springback of the sheet metal components is essentially eliminated, since the introduced compressions overlap the springback forces or transform stresses in the sheet metal component that trigger a springback.

It has been shown that the reduction in plastic elongation and thus the lower increase in the yield strength of the material compared to conventional deep drawing can advantageously be compensated for by using a material with a higher yield point than the material used in conventional deep drawing. The final molded component can then have similar or essentially identical mechanical characteristics than if it had been thermoformed. The increased wall thickness or sheet thickness of the in the method described final formed sheet metal component compared to sheet metal components produced by conventional deep drawing can also be advantageously used in such a way that a sheet metal blank of reduced thickness is now used. In particular with regard to a possible elimination of the edge trim, the operating weight can thus be reduced even further.

As a result, it was recognized that, through a skilful selection of materials, the described method can be used to provide components which, with less operating weight and less equipment, have the high dimensional accuracy of a BKT method and still have a similar or essentially identical geometry as well as similar ones or have essentially identical mechanical properties to conventionally deep-drawn sheet metal components. At the same time, the outlay on equipment is reduced compared to classic deep drawing, and the lower degrees of forming also reduce the load on the tools and increase tool life.

According to a preferred embodiment of the method according to the invention, the preforming of the workpiece into the preformed component takes place essentially without holding. This is understood in particular to mean that the method is carried out with a distanced, with a non-force-loaded or even without hold-down or sheet holder. The workpiece is therefore preferably not clamped during preforming. This can be achieved by preforming, for example, using a special form of deep drawing, so-called "crash forming" or "embossing with folding".

According to a preferred embodiment of the method according to the invention, the material (in the non-deformed state) has a ratio of yield strength R _p0.2 to strength R _m of ≥ 0.56, preferably ≥ 0.6, preferably ≥ 0.62, particularly preferably ≥ 0 , 64, more preferably from ≥ 0.66, more preferably ≥ 0.7. With materials that have a ratio of yield strength R _p0.2 to strength R _m of particularly preferably ≥ 0.64, it is possible to adjust the material properties on the finally formed sheet metal component in such a way that they differ from those of a conventionally deep-drawn sheet metal component of similar or essentially identical dimensions not significantly differentiate or exceed them. However, these sheet metal components can be manufactured more dimensionally than with conventional deep drawing. A further improvement in matching the properties of the finally formed sheet metal component to a similarly or identically dimensioned conventionally deep-drawn sheet metal component results in particular with a ratio of yield strength R _p0.2 to strength R _m of ≥ 0.66, preferably ≥ 0.7.

According to a further embodiment of the method according to the invention, essentially the entire cross section of the preformed sheet metal component has excess material. As a result, the finally formed sheet metal components can be produced in a dimensionally stable form without provoking excessive local loads, in particular on the tools.

In a further preferred embodiment of the method according to the invention, the sheet metal component is a half-shell-shaped sheet metal component, in particular a sheet metal component which is U-shaped or hat-shaped in cross section. It has been shown that half-shell-shaped sheet metal components, and in particular U-shaped or hat-shaped sheet metal components in cross section, can be produced particularly dimensionally and with advantageous mechanical properties by means of the method according to the invention.

According to a preferred embodiment of the method according to the invention, the workpiece is a sheet metal blank. In particular, the sheet metal plate has a thickness of less than 3.5 mm, preferably less than 3 mm, particularly preferably less than 2.4 mm. For example, the sheet metal plate can have a thickness between 0.7 mm and 1.8 mm. The method according to the invention can be used particularly advantageously directly on sheet metal blanks, further preforming steps can thus be avoided.

According to a further embodiment of the method according to the invention, the material (in the non-deformed state) has a tensile strength R _m of at least 500 MPa, preferably at least 600 MPa, particularly preferably at least 700 MPa along and / or transversely to the rolling direction. For example, the material has a tensile strength R _m of at least 800 and / or at most 1250 MPa along and / or across the rolling direction. It has been shown that, in particular by using materials with a tensile strength in the specified range, it is possible to produce sheet metal components with shaped properties that are similar or identical to conventionally dimensioned, deep-drawn sheet metal components.

The material preferably has a tensile strength R _m of 900 to 1200 MPa along and / or across the rolling direction. With such a material, a further improved adjustment of the properties of the finally formed sheet metal component to a similarly or essentially identically dimensioned conventionally deep-drawn sheet metal component can be achieved.

According to a further embodiment of the method according to the invention, the material has a yield strength R _p0.2 of at least 400 MPa, preferably at least 500 MPa, more preferably at least 600 MPa along and / or across the rolling direction. For example, the material has a yield strength R _p0.2 of at least 700 and / or at most 950 MPa along and / or across the rolling direction. It has been shown that, in particular, by using such a material, a further improved matching of the properties of the finally formed sheet metal component to a similarly or essentially identically dimensioned conventionally deep-drawn sheet metal component can be achieved. At the same time, however, it has been shown that, despite the reshaping with a comparatively high yield strength compared to conventional deep drawing, a high degree of dimensional accuracy can be achieved, in particular due to the lower equipment expenditure and the reduced operating weight.

According to a further embodiment of the method according to the invention, the material has an elongation at break Aso of less than 30%, in particular less than 25%, preferably less than 20%, preferably less than 15%, particularly preferably less than 10%.

In a further embodiment of the method according to the invention, the material is a steel, in particular a multi-phase steel, preferably a dual-phase steel. It was recognized that the method according to the invention can advantageously be used for the production of sheet metal components made of steel, in particular of multi-phase steel, preferably of dual-phase steel.

In a further preferred embodiment of the method according to the invention, the material is a steel which has one or more (in particular all) of the following alloy components in percent by weight (% by weight): 0 < C ≤ 0.115, 0 < Si ≤ 0,650, 0 < Mn ≤ 2,350, 0 < P ≤ 0,040, 0 < S ≤ 0.0050, 0,015 < al ≤ 0,060, 0 < Cr + Mo ≤ 1,000%, 0 < Nb + Ti ≤ 0.120%, 0 < V ≤ 0.060%, 0 < B ≤ 0.0030%, 0 < Cu ≤ 0.350%, with rest of Fe and unavoidable impurities. It has been shown that such steels are particularly suitable for the substitution of steels which are used in a conventional deep-drawing process for the production of similarly or identically dimensioned sheet metal components, and nevertheless can achieve essentially the same mechanical properties as in the deep-drawn sheet metal components. By combining the material according to the invention with the method steps according to the invention, sheet metal components with essentially identical properties as in conventional deep drawing can be provided inexpensively.

According to a second teaching, the invention also relates to the use of a sheet metal component produced using a method according to the invention as an automobile body component, in particular as a component of a frame, a longitudinal or cross member, a column or a crash structure. In particular, it is a component that is relevant for crash safety. It has been shown that the sheet metal components produced according to the invention are optimally suited for use as an automotive body component. The car body components previously used by conventional deep drawing can thus be replaced by appropriate alternatives.

Furthermore, the invention will be explained in more detail using an exemplary embodiment.

The advantages of the method according to the invention can be seen in particular in comparison to a corresponding conventional method which is to be described first. Conventional deep-drawing initially produces a sheet metal component from a flat sheet metal sheet of 1.5 mm thickness consisting of a dual-phase steel of the type CR330Y590T-DP with a yield strength of 330 MPa and an elongation at break A ₈₀ of 18%. By using, for example, pressurized hold-down devices in combination with drawing beads during deep drawing to form a sheet metal component with an average wall thickness or sheet thickness of 1.35 mm, an average elongation of 10% results on the sheet metal component during molding. Due to the expansion of the material and the simultaneous hardening, the sheet metal component still has a possible residual expansion of 8% before cracks occur, so that the formability is limited accordingly. In addition, there is an increased yield strength of 700 MPa for this conventionally deep-drawn sheet metal component.

In order to use the method proposed _according to the _invention to produce a sheet metal component with similar or improved properties to the previous deep drawing, a material is first selected which has a ratio of yield strength R _p0.2 to strength R _m of ≥ 0.53, particularly preferably ≥ 0 , 64 or even ≥ 0.7. The material is supposed to look after After forming, it has essentially the same mechanical properties as the conventionally deep-drawn sheet metal component, a yield strength of 700 MPa and a minimum elongation at break of 8%. For this, so that the final formed component after forming has essentially the same wall thickness or sheet thickness as the deep-drawn sheet metal component, a flat sheet metal plate with a reduced thickness of 1.35 mm to 1.4 mm compared to the deep drawing shown above is selected. In particular, a dual-phase steel of the type CR700Y980T-DP with a thickness of 1.4 mm is used, which has a ratio of yield strength R _p0.2 to strength R _m of particularly preferably ≥ 0.64. The sheet metal blank made of this material is first preformed into a preformed component, excess material being introduced into the preformed component at least in some areas, and then the preformed component is calibrated to an at least partially finished component using the excess material. The final molded component produced in this way has a geometry that is essentially identical to that of the conventionally deep-drawn component, in particular an essentially identical wall thickness, and also has mechanical properties and crash properties similar to this, but could be produced reliably with high dimensional accuracy.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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

• DE 102007059251 A1 [0015, 0016]
• DE 102008037612 A1 [0015, 0017]
• DE 102009059197 A1 [0015]
• DE 102013103612 A1 [0015]
• DE 102013103751 A1 [0015]
• DE 102016118418 A1 [0015, 0018]
• DE 102016118419 A1 [0015, 0019]

Non-patent literature cited

• DIN EN ISO 6892-1: 2017-02 [0013]

Claims (12)

A method for producing sheet metal components from a material, in particular for an automobile body, comprising the method steps: - preforming a workpiece to a preformed component, excess material being introduced into the preformed component at least in some areas, and - calibrating the preformed component to an at least partially finished component Component using the excess material, in particular wherein the preformed component is compressed at least in sections, characterized in that the material has a ratio of yield strength R _p0.2 to tensile strength R _m of $${\text{R}}_{\text{p0}\text{2}}{\text{/ R}}_{\text{m}}\ge 0.53$$

having. Procedure according to Claim 1 , characterized in that the preforming of the workpiece into the preformed component takes place essentially without holding. Procedure according to Claim 1 or 2 , characterized in that the material has a ratio of yield strength R _p0.2 to strength R _m of ≥ 0.56, preferably ≥ 0.6, preferably ≥ 0.62, particularly preferably ≥ 0.64, further preferably ≥ 0, 66, more preferably ≥ 0.7. Procedure according to one of the Claims 1 to 3 , characterized in that substantially the entire cross section of the preformed sheet metal component has excess material. Procedure according to one of the Claims 1 to 4 , characterized in that the component is a half-shell-shaped sheet metal component, in particular a sheet metal component which is U-shaped or hat-shaped in cross section. Procedure according to one of the Claims 1 to 5 , characterized in that the workpiece is a sheet metal plate and that the sheet metal plate has in particular a thickness of less than 3.5 mm, preferably less than 3 mm, particularly preferably less than 2.4 mm. Procedure according to one of the Claims 1 to 6 , characterized in that the material has a tensile strength R _m of at least 500 MPa, preferably at least 600 MPa, particularly preferably at least 700 MPa along and / or transversely to the rolling direction Procedure according to one of the Claims 1 to 7 , characterized in that the material has a yield strength R _p0.2 of at least 400 MPa, preferably at least 500 MPa, more preferably at least 600 MPa along and / or transverse to the rolling direction. Procedure according to one of the Claims 1 to 8th , characterized in that the material has an elongation at break Aso of less than 30%, in particular less than 25%, preferably less than 20%, preferably less than 15%, particularly preferably less than 10%. Procedure according to one of the Claims 1 to 9 , characterized in that the material is a steel, in particular a multi-phase steel, preferably a dual-phase steel. Procedure according to one of the Claims 1 to 10 , characterized in that the material is a steel which has one or more of the following alloy components in percent by weight (% by weight): 0 < C ≤ 0.115, 0 < Si ≤ 0.650, 0 < Mn ≤ 2,350, 0 < P ≤ 0.040, 0 < S ≤ 0.0050, 0,015 < al ≤ 0.060, 0 < Cr + Mo ≤ 1,000%, 0 < Nb + Ti ≤ 0.120%, 0 < V ≤ 0.060%, 0 < B ≤ 0.0030%, 0 < Cu ≤ 0.350%, with rest of Fe and unavoidable impurities. Use of a sheet metal component produced using a method according to one of the Claims 1 to 11 as an automobile body component, in particular as a component of a frame, a longitudinal or cross member, a column or a crash structure.