DE102014001872B4 - Method and device for influencing the deformation behavior, in particular the springback when forming workpieces in clocked forming and processing stations, in particular during bending in progressive dies - Google Patents

Abstract

Method for influencing the deformation behavior, in particular the springback when forming workpieces (1) in clocked forming and processing stations, in particular during bending in progressive tools, in which a workpiece (1) is processed successively in a sequence of cyclically linked processing stations and subjected to at least one forming is characterized in that the workpiece (1) made of metallic material during passage through the clocked concatenated processing stations before and / or after at least one Umformungsstation (13) of an adaptively guided and at least one region of the workpiece (1) temperature control (6) is subjected, in the previously formed in the forming station (13) formed workpieces the springback behavior of the formed workpieces or the geometric shape of the formed workpieces continuously monitored metrologically and for adaptive change of the temp the adaptive temperature control influences the deformation behavior of at least this area (9) of each individual workpiece (1) in this forming station (13) such that the stress state, in particular the springback and / or the residual stresses of the material of the workpiece (1) after the conversion (13) reaches a desired value for achieving the desired finished part geometry or an intermediate geometry to be achieved of the workpiece (1) to be formed.

Description

The invention relates to a method for influencing the deformation behavior, in particular the springback when forming workpieces in clocked forming and processing stations, in particular during bending in progressive dies according to the preamble of claim 1 and a corresponding device according to the preamble of claim 27.

Forming operations and in particular punching and bending processing are used for the production of a large variety of components and workpieces, which have great economic importance for consumer and capital goods, especially by the possible mass production and mass production. Here, in addition to individual punching and bending operations on the workpiece often clocked forming and processing stations such as progressive dies or transfer tools are used, a variety of punching and forming processes that are necessary for the production of the complete component or workpiece in clocked and timed perform bound sequence. For example, in a follow-on composite tool, a coil called sheet metal strip from a flat initial state by cutting operations, bending operations, deep drawing operations or the like. Step by step transformed into the desired workpiece. Here, a trend is to be found that more and more components produced in this way should be ready to be used dropping without post-processing following the punching and forming machining. For this purpose, the workpieces must be dimensionally and dimensionally stable from the punching and forming, z. B. Bending angle etc. must be made as accurate as possible even with different quality starting materials due to batch differences between individual coils.

Not only during forming and in particular during bending of specially formable technically workable sheets of steel materials, but also when bending high and ultra high strength materials occur strong deviations in form, which can be controlled only with great effort. Such high- and ultra-high-strength materials are often used for particularly stressed components and lightweight, but the potential use of such lightweight materials can not be exhausted. The reasons for this are the lack of suitable process-safe processing methods and the necessary know-how. The many years of experience accumulated with the previously industrially used sheet metal materials can often not be transferred to the transformation of such new materials. Due to their different chemical composition and the resulting microstructure, the new high to ultra high strength materials have different mechanical properties and behave differently during the forming process than conventional sheet metal materials. In particular, the high elastic elongation during bending forming is a major problem leading to springback upon relieving after forming. High dimensional and dimensional accuracy can be achieved only with great effort when bending in progressive tools, especially when using high-strength lightweight materials.

Components produced by stamping and bending machining are used in many areas, but especially frequently in the automotive industry. Especially there, however, is to be noted as a general trend that ever smaller tolerances in bending accuracy and ever increasing complexity of the bent parts are required, which makes ensuring the required quality increasingly difficult. An example of this are the multiple bent handlebar components on flaps, doors and hoods, which have complicated bending forms and still have to have only small tolerances.

In addition to the increased technological requirements for vehicles in terms of safety, comfort and lightweight construction properties, the background is also the generally prevalent enormous cost pressure. This is often achieved by integral components with extremely short process chains. The stamped and formed part should, after production, in the best case represent a ready-to-install part with all secondary features. The often required reworking or straightening work makes the component already unprofitable for the supplier. Machining of mounting surfaces and drill holes is only allowed in rare cases for cost reasons. Through the use of fully automated assembly systems and modern joining technologies such. As the laser welding, this trend is still supported, as this principle requires only the smallest tolerances.

These partially contradictory requirements can hardly reproduce the currently used methods and tools in the stamping and forming technology. Smallest batch fluctuations in the material properties, wear of the tools or the pressing machine or slightly changed tribological parameters often cause scrap production and inadmissible fluctuations in manufacturing accuracy. The narrow required tolerances can no longer be met and it may even be rectified manually if necessary.

The central point in the situation described in the currently used methods and tools in the stamping and forming technology is the Mastery of the unavoidable springback of the formed workpieces after forming, which contribute significantly to the described inaccuracies.

During the plastic shaping of a metallic workpiece and in particular a sheet by means of forming processes such. B. bending elastic energy is stored in the workpiece. If the workpiece is taken out of the forming tools, the release of the introduced during bending elastic expansions causes a spring back of the component. This resilience causes a reduction in the energetic level, but at the same time a deviation from the desired form. If the component is cut to the desired size and shape after shaping, the springback behavior and thus the shape deviation can change again.

The springback depends essentially on the modulus of elasticity, the yield stress and the sheet thickness of the material, based on the bending radius. In the increasingly used high-strength steels, such as. B. DP and TRIP steels, which have a very high yield stress, the springback is very high because of the greater proportion of elastic strains. For lightweight construction, the sheet thickness is also reduced, so that due to two mechanisms of action, the springback when using high-strength materials is uncontrollable. Compared to typical deep drawing steels DC04, DC06, the springback or the so-called popping up of DP and TRIP steels is therefore more clearly visible and causes greater problems. When bending the springback is usually compensated by overbending. However, this possibility is associated with a good prediction of the tool geometry, which must have exactly the over-arched geometry, which leads to the required workpiece geometry after the unloading. In particular, batch differences between coils of the materials used lead to the problems described above, which can not be solved safely by a simple overbending.

Sheet metal parts with forming geometries for large-scale production are, as already briefly described, generally produced by a cold forming process in a complex follow-on composite tool. For this purpose, in a complex sequence of a sheet metal strip, which is unwound from a coil, directed and introduced into the press, first punched out the desired geometry from the sheet and then by a sequence of bending operations, the spatial forming and in particular the bending geometry of the sheet Workpiece applied. These transformations are realized by integrated stamps. In the last stages of the tool, the forming part is released by further punching steps of the sheet metal strip and ejected as a finished part of the tool.

The disadvantage of this approach is yet that z. B. when bending the bending accuracy can vary greatly. By usual batch fluctuations and fluctuations in a coil, such as the mechanical characteristics and the thickness, the springback and thus the geometry of the bent part varies greatly. Dimensionally stable parts without rejects can therefore generally not be produced. The geometry can only be influenced to a limited extent on the built-in progressive compound tool, since the geometry is defined in terms of shape by the punches and the die. The bending geometry can be difficult in the process to be corrected, for example, by additional straightening, which leads to a high design cost and high tooling costs.

By adjusting the bending and straightening punches, it is possible to influence the bending result. For this purpose, the individual punch tools are to be replaced or adjusted by fitting plates. In general, the steps of the progressive dies influence each other, so that complex setups often require multiple setup passes to find a matching configuration of all dies. Nevertheless, if the bending parts can not be formed in compliance with the tolerances, manual straightening of the workpieces is unavoidable. This work takes a long time and leads to rejects, so that productivity is significantly reduced. In addition, the setting of the bending tools requires empirical empirical knowledge, so that for new tools and sheet materials is initially expected from long training phases.

In addition to setting the stamp can be influenced by the pressing force on the bending result. If a shape tolerance can not be maintained, the pressing force is increased to repress the bending part by a pressure overlay in the stamp and thereby minimize the elastic distortion after discharge. However, the measure leads to premature wear of the punch and increased machine stress. The wear of the bending tools also leads to alternating tribological contact conditions, resulting in a further influence on the product geometry. Furthermore, the number of punching and bending stages is reduced due to the maximum pressing force by this measure, so that only less complex components can be manufactured.

In order to meet the required dimensional and positional tolerances must therefore in the In many cases, special precautions are taken when using high strength, high resilience materials. The springbacks can make up a few degrees depending on the geometry. In order to limit the tolerance of bent parts, only small bending radii and minimum sheet thicknesses based on the bending angle are used in particular for materials with high yield strength. This limits the creative freedom of the bending products and it requires many iterations between suppliers and customers to find an acceptable geometry. Nevertheless, the bending radius is limited due to cracking or Gestaltforderungen downwards, leaving only the possibility to use larger sheet thicknesses. This condition leads to larger product weights, since the lower strength is compensated by a higher material use. Also, the use of lightweight materials such as aluminum alloys in progressive tools is difficult, since this high elastic distortions occur because of the low modulus of elasticity. The market demand for high-strength bending products with low weights, which harmonize with environmental aspects, can therefore not be met with conventional progressive tools.

Furthermore, it is known that z. B. in bending of large pipes and in individual applications the so-called. Hot bending is used. The objective here is often to reduce high bending forces or bending moments, which no longer allow a cold bending process due to large component dimensions and wall thicknesses. By heating the entire component, the yield strength of the material is reduced and the plastic flow begins at lower voltages. This allows for a reduction of the bending moment or the bending force and thus also a very good reduction of the springback and the residual stresses. In the field of sheet metal bending, especially in larger quantities, a hot bending is unusual.

A kind of three-point bending with heated bending zone is in the DE 691 13 237 T2 described. First, a workpiece is heated by means of a heating source and then bent with a punch in a die while the heating source is removed. The process was developed for forming plastic material. The heating serves to improve the formability of the material, which is not necessarily given at room temperature. The main advantage of this arrangement is seen in the fact that even after initiation of forming the workpiece can still be heated, so that the temperature is kept high throughout the process. If the method were to be used in the bending of metallic materials, however, due to the one-sided arrangement of the heating source, no homogeneous heating of the workpiece in the forming area can be achieved. Due to the priority heating of the tensile zone, the arch would be thinned out and thereby weakened. In addition, it would first come when heating the sheet metal part for greater expansion of the tensile region, so that after bending the bending angle would be increased due to the cooling. This would result in addition to the springback and the inhomogeneous temperature field during bending to an increase in the bending angle after the discharge and cooling.

In laser-assisted three-point bending, the forming zone is heated by means of lasers before and during forming [Bammer 2010]. The aim here is to enable the transformation of brittle materials such as magnesium, titanium and high-strength aluminum and steel materials. Heating with the laser technology has the advantage that the bending part is only locally heated and the material properties are not changed in the complete bending part. The integration of the heating in the lower bending tool further allows that even during the forming process, the workpiece can be heated. As a result, any temperature curves over time and the transformation are conceivable. Depending on the sheet material and thickness, 1 ... 10 s is required for heating with the laser. Complex with this technology is the integration of the laser technology in the lower bending tool. The bending tool is accordingly expensive. A disadvantage arises from the arrangement that the heating passes over the train area. With thick sheet materials with low thermal conductivity, significant temperature gradients over the thickness are to be expected. If higher temperatures are present in the tensile zone, an increased stretching of the tensile zone is to be expected. The pressure zone, which is also cooled by the upper bending tool, is therefore likely to experience only reduced compression. To ensure that even thicker sheet metal materials bend well, low heating rates are necessary, so that no significant temperature gradients over the thickness occur. Due to the heating principle, the use of this technology is not suitable for use in rapidly clocked progressive processes. Typical cycle frequencies in the follow-on composite process are around 1 Hz, so that warming principles of highest performance are needed for hot bending of bent parts with larger sheet thicknesses.

The DE 10 2012 021 031 A1 describes a whole series of different processes for press hardening of sheet metal components, which have in common that the heating of the starting material should take place immediately before the forming and then the actual press hardening by austenitization and a subsequent targeted Cooling of the deformed component in the pressed state and should be done by cooling by means of the ram. At no point, however, is it mentioned that the result of the machining of the workpiece is pulled in or used in any way to influence subsequent processing of other sheet metal workpieces.

The DE 691 13 237 T2 describes a hot working of a piece of plastic material by means of bending, in which the deformation pressure is controlled.

The object of the present invention is therefore to provide a method and a device for influencing the springback when forming workpieces in clocked forming and processing stations, especially when bending in progressive tools, with which avoided the disadvantages and form and true to size workpieces with such forming processes can also be produced in clocked forming and processing stations.

The solution of the object of the invention results in terms of the method of the characterizing features of claim 1 and in terms of the device from the characterizing features of claim 27 in conjunction with the features of the associated preamble. Further advantageous embodiments of the invention will become apparent from the dependent claims.

The invention is based on a method for influencing the springback when forming workpieces in clocked forming and processing stations, in particular during bending in progressive dies, in which a workpiece is processed one after the other in a succession of cyclically linked processing stations and subjected to at least one forming. Such a generic method is further developed in accordance with the invention, that the workpiece is subjected during passing through the clocked concatenated processing stations before and / or during and / or after at least one Umformungsstation an adaptively guided and at least a portion of the workpiece temperature control, the Forming behavior of at least this area of each individual workpiece in this forming station influenced such that the stress state, in particular the springback and / or the residual stresses of the material of the workpiece after forming reaches a target value to achieve the desired finished part geometry or to be achieved intermediate geometry of the workpiece to be formed. The basic idea here is to gain influence on the deformation and the resulting stress state, in particular the resilience and / or the residual stresses of the material, by the at least local tempering of the workpiece in the region of the deformation zone such that the unavoidable springback occurs only in this way in that the shaped workpiece then corresponds as closely as possible to the desired finished part geometry or to an intermediate geometry of the workpiece to be formed. The temperature changed by their influence on the material of the workpiece to be reshaped specifically the forming behavior in the forming, so that the geometrically predetermined by the forming tools deformed workpiece subsequently changed by the springback so that exactly the desired finished part geometry or to be achieved intermediate geometry of reshaping Workpiece setting. This will not make adjustments to the tools z. As the formed deformation or bending, which otherwise have to be adjusted consuming and thus no change in the actual deformation necessary. So z. For example, the forming of the workpiece by the forming tool is carried out a little too strong, after which the adaptively influenced springback leads to a transition of the workpiece into the desired desired geometry.

The geometric shape of the workpiece after forming is influenced by the state of stress of the material in the forming zone and in particular by the springback or the residual stresses of the material. In this case, the various stresses introduced mechanically and thermally into the material of the workpiece in connection with the forming process and remaining in the material possibly from preceding processing steps overlap to form a complex stress state which has a direct influence on the geometric shape of the workpiece after the forming. A significant influence is given by the springback, another by the residual stresses in the material of the workpiece. In addition to the compensation of the springback, the inventive method also enables the setting of such residual stresses. The residual stresses in the formed workpiece can, depending on the stress and strain state in the forming, z. B. turn out a different strength. High yield stresses lead to high residual stresses after relieving, so that the residual stress pattern can also be influenced by an adapted temperature and yield stress. If forming at high temperatures with low yield stress, in addition to the springback and the residual stress image is weaker. In addition, z. B. the bending with a temperature gradient in the metal strip the option to change the characteristic residual stress curve completely. Becomes bent with a heated pressure zone (inner arc) and a relatively cold tensile zone (outer arc) occur after the discharge significant compressive stress in the outer arc and in the inner arc of the workpiece, which are not observed in conventional bending at room temperature. This makes it possible to positively influence the corrosion behavior and other product properties (for example, tensile stresses on the surface lead to greater corrosion).

In addition to the state of stress, the moldability of, in particular, high-strength materials such as high-strength steels can be specifically favorably influenced by the method according to the invention, which can not be shaped accurately and dimensionally accurately without heating due to their strength properties. For example, hardened steels could be reshaped in the austenite region without cracking in the room temperature hard structure. In a controlled cooling then similar strengths could be achieved. The heated forming such as bending offers, in addition to adapted product properties, the possibility of expanding the forming limits in comparison with cold forming. The forming of high-strength materials is often possible only in limited dimensions because of the low elongation at break. In order to still allow high changes in shape, dislocation movements can be thermally activated and thereby the forming capacity can be increased.

If, in the following, simplification is used to influence the springback in connection with the method according to the invention, this always means influencing the complex stress state in the workpiece after the deformation or the formability of the workpiece during the forming, which also has a specific effect on the May contain residual stresses.

Using the example of a bending process as forming, for example, the workpiece is bent over a little more than necessary and returns to the desired value of the bend due to the tempered springback. If now the springback behavior of the formed workpiece or the manufactured geometric shape of the formed workpiece continuously monitored metrologically, then adjusting deviations can be detected and influenced by a change in temperature specifically in the sense that after the changed spring back exactly the desired finished part geometry or a to be reached intermediate geometry of the workpiece to be formed is present. By an integrated temperature, in particular in the form of at least local inductive or conductive heating of the workpiece, which is carried out before, during and / or after the forming, the shape deviations of the workpiece to the desired contour can be significantly reduced by the inevitable spring backs or even eliminated completely. Conventional variations in the forming behavior and the springback resulting from batch fluctuations of the material used, the currently present tribological conditions in the forming, the tool and the press conditions, have no effect on the deviation from the desired geometry in the present method. Deviations of the forming geometry from the desired geometry are recorded adaptively and eliminated in an active control depending on the product requirements. The production process is significantly more robust and the downtime is minimized by the regulation of the forming with feedback of the measurement result.

The example of a bending deformation in a progressive tool, the advantages of the invention can be well explained, but are not limited to this forming process. Due to the complex relationships of bending deformation z. B. in progressive tools, an adjustment of the forming tools is necessary depending on the material used. The otherwise necessary and lengthy adjustments of the bending tools are saved by the method according to the invention. As a result, not only the output of a production plant is significantly increased, it also labor costs for manual adjustment of the tools can be saved. The manual adjustment requires many years of experience and is therefore difficult to automate. The reason for this is the interaction of form deviations of the bending deformation with subsequent tool stages for straightening and further processing. To counter this problem, precise and controllable shapes in a bending stage without an otherwise additional leveling step are desirable. In addition, the rejects are reduced by an inventively automatically controlled forming process. At the beginning or end of a material coil, a manual adjustment is often necessary because of different thicknesses, but can not be performed partly for economic reasons. With the forming process according to the invention, a proper transformation is still possible in this area of the coil and thus the material used used in the best possible way, so that despite the energy expenditure for temperature control, the energy balance of the process can be positively influenced. In addition, with standardized tempering concepts, the development effort and production costs for follow-on composite tools are minimized. Follow-on composite tools are conventionally designed taking into account form deviations of the product geometry, which requires the designer much experience. With a forming process according to the invention would thereby also productivity increased because, for example, fewer stages would be necessary for a progressive tool.

With regard to the material used is given by the z. B. inductively heated bending the advantage to be able to produce different sheet materials in the same progressive tool. In general, the progressive dies are now tailored to a specific sheet metal material to meet the elastic distortions after bending. This would significantly increase the flexibility in the use of progressive tools. In addition, higher-strength materials with a greater tendency to spring back can be processed. Today fine-grain structural steel is often used in composite materials with a tensile strength R _m ≈ 400 MPa, so that the lightweight construction potential is far from exhausted. Further, since materials with greater strength tend to have lower ductility, temperability prior to bending can increase moldability. In addition to increased formability, the material could be heat-treated using a set temperature curve during the process and the material properties for graded components could be variably adjusted. If the springback during unloading is minimized by warming according to this method, the residual stresses in the bent product, in particular the tensile stresses of the pressure zone, are lower. This can improve the performance in terms of corrosion and fatigue fractures. The use of high-strength lightweight materials with a specific low density saves material, weight and, ultimately, costs. In addition, the adjusted material properties within a component increase the product value.

The forming process according to the invention offers further advantages with regard to the tool press. In addition to the springback behavior, the moldability of the materials can be improved by the inductive heating. If the bending force is lowered as a result of the heating, on the one hand, the load on the press can be lowered, thereby increasing their durability. If the available press force is fully utilized, on the other hand, the machine benefit can be increased by the product complexity with further force-demanding bending steps in the tool or larger product dimensions. In addition, because of the resulting reduction in press force, heating serves to allow more single stages to be molded in a press and progressive tooling.

It is particularly advantageous if the tempering is carried out as heating, preferably as a local inductive or conductive heating of the workpiece. For this purpose, in a further embodiment, the heating in the direction of passage in front of the forming station by an inductive or conductive heating station, in particular a controlled by means of integrated temperature measurement inductive or conductive heating station can be performed. Inductive and conductive heating methods are widely known for controlling the temperature of metallic materials and are easy to control or the material to be heated can thus be influenced well. For example, in the inductive heating of metallic materials by the upper and / or lower coupling distance of the induction coil to the workpiece or at a fixed distance via a regulation of the generator current for charging the induction coils, a targeted and highly effective coupling of heat energy into a metallic strip, by the metallic strip can be brought to high temperatures in a very short time. Of course, it is also conceivable that the temperature control may have a heating with a gas flame or with a laser or the like.

In another embodiment, it is also conceivable that the temperature control as cooling, preferably as a measuring unit for temperature sensing controlled cooling of the workpiece z. B. is performed with cooling fluids or cooling contact components. Thus, for example, during or after the successful forming specifically the workpiece cooled at least in sections and thus the springback can be influenced. The combination of heating and cooling in connection with the forming allows a substantial influence on the springback.

In a further embodiment of the temperature, it is conceivable that the temperature control is homogeneous or generates a predetermined temperature gradient in the cross section of the workpiece, preferably by non-uniform temperature of the workpiece based on its tempered surfaces.

In the inductive heating, the height of the temperature of the workpiece in the temperature control range can be adjusted specifically in a homogeneous two-sided heating. By lowering the yield stress, the proportion of the superimposed elastic strains is reduced and the sheet springs back less when relieving. The inductive heating of a sheet-like workpiece can be carried out homogeneously on both sides by induction coils arranged above and below the passage path of the sheet-like workpiece.

Alternatively, the sheet-like workpiece during inductive heating can not be heated symmetrically to the neutral fiber of the sheet and thereby be varied in addition to the temperature itself, the temperature profile over the sheet thickness. The Realization of a non-symmetrical heating (hereinafter referred to as one-sided heating) can be achieved with various inductor designs. If a total low heating of the metal strip can be achieved, a one-sided design is used. Thus, the electrical energy consumption is low and the material structure is affected as little as possible. However, if a forming at relatively high temperatures is provided because the sheet material is sufficiently ductile only at higher temperatures, a two-sided Induktorbauform is used. In order to achieve a temperature gradient across the thickness with two induction coils arranged on the top side and underside of the metal strip, the coupling distance of the strip conductors must be adapted to the top and bottom side of the metal sheet. The regulation of the temperature gradient for controlling the bending contour is carried out here either via the upper and lower coupling distance of the induction coil to the sheet or at fixed conductor track positions on the generator current. In a single-sided induction coil, the regulation of the temperature gradient in the sheet runs only via the generator current. It may be of particular advantage here that the asymmetrical heating of the workpiece takes place over its cross section in such a way that primarily the pressure zone of the deformation region is heated so that the pressure zone of the workpiece is subject to a greater thermal expansion than the tensile zone.

As a particularly advantageous forming process, a bending deformation in particular sheet-metal materials and / or a deep-drawing in particular sheet-metal materials and / or a massive forming in particular solid metal materials, individually or in combination can be performed. Of course, all the other work processes that can be carried out in clocked processing stations are also fundamentally covered by the invention, even if they are not described further here. The method according to the invention is particularly preferably always applicable when it is carried out on workpieces produced in strip-like semifinished products in progressive dies or of occasionally present semi-finished products in transfer tools.

In particular, all metallic materials, but preferably also high to ultra-high-strength metal materials can be processed as the material of the workpieces.

It is particularly advantageous that the shape produced by means of forming and / or the resulting springback of the workpiece after the forming in a measuring station, preferably a particular non-contact contour measuring station detected and used to influence the springback of subsequent reshaping workpieces. Through the use of a particular optical measuring system for detecting the bending contour online directly after the forming or cooling can be done for the subsequent workpiece in the next impact the springback by the temperature, so that occurring deviations on the measured workpiece can be virtually corrected immediately and thereby almost no rejects are produced.

In addition to carrying out the temperature control of the workpiece in separate temperature control stations, it is also conceivable that the material of the workpiece is heated and / or cooled at least in the region of the forming zone during the forming by tempering at least individual parts of the forming tools themselves. For this purpose, at least parts of participating in the actual forming tools, ie z. B. stamp and counterholder / die in a bending, z. B. different temperatures by heating or cooling, so that a temperature gradient can be generated within the reshaping cross section of the sheet-like workpiece by different heating and / or cooling. In a further embodiment, it is conceivable for the workpiece to remain in the region of the tempering by at least individual parts of the forming tools in the area of the forming zone after the forming during an at least temporary holding time, and the workpiece is thereby further heated and / or cooled. As a result, the effect of the temperature control by the forming tools can be set more targeted, since the temperature due to the heat conduction within the material of the workpiece takes a moment.

In another embodiment, it is also conceivable that the material of the workpiece is cooled at least in the region of the deformed zone after forming in a cooling station. This also makes it possible to influence the resilience, as the residual stress behavior in the previously heated region of the workpiece can be influenced in a targeted manner by the cooling after the deformation.

Furthermore, it is also conceivable in another embodiment that influencing the springback of the workpiece has an influence on the forming speed during the forming and thus the yield stress of the material, wherein influencing the forming speed in the forming by controlling the tool drives a servo press or the like . can be achieved. For example, with the aid of the servo press technology, it is possible to control the elastic stress superposition and finally the springback of the workpiece after forming by adjusting the forming speed. Only in the heated state are the yield stress of typical metallic materials depending on the forming speed, so that it can be influenced. For example, by integrating a two-sided heating with the aim of a homogeneous temperature in the metal strip depending on the material behavior in addition to the resilience by adjusting the punch speed and the formability can be increased.

If z. B. operated a follow-on composite tool on a servo press, the punch speed can be varied during forming at a constant rate and output, so that the yield stress can be influenced. The servo press technology with variable ram speed can be used to set the yield stress over the forming speed during heated bending in the progressive tool so that the nominal contour results after overbending and springback. Here, the springback is controlled precisely by the set yield stress in the process.

Of course, it is also conceivable that influencing the springback of the workpiece by influencing the forming speed and by influencing the springback by tempering at least the forming zone in the form of superimposed control loops and thereby another influencing factor for influencing the springback can be used in addition to the temperature.

It is also conceivable that the workpiece is locally cooled differently in the cooling station and / or the tool, for. B. on one side more or less than on the other side. This can be realized, for example, by differently tempered fluid media streams which act separately from one another on the upper side and the lower side of the workpiece. This also allows a targeted generation of a temperature gradient in the cross section of the workpiece is achieved during cooling and thereby the springback can be influenced.

The invention further relates to a device for influencing the springback when forming workpieces in clocked forming and processing stations, in particular during bending in progressive dies, in which a workpiece in a succession of cyclically linked processing stations processed one after another and subjected to at least one forming. Such a generic device is thereby further formed in accordance with the invention by a Temperierungsstation is arranged before and / or after and / or after at least one Umformungsstation, which by an adaptively guided and at least a portion of the workpiece temperature control affects the workpiece so adaptively that the workpiece achieved by the springback of the material after the forming a desired finished part geometry or an intermediate geometry to be achieved.

The essential properties and advantages of devices constructed and manufactured in this way have already been explained in detail in relation to the method according to the invention. It is therefore only referred to device specific features extra, otherwise reference is made to the description of the process in its entirety for the explanation of the device according to the invention itself.

It is conceivable, in particular, that the tempering station has an inductive or conductive heating station, in particular an inductive or conductive heating station regulated by means of integrated temperature measurement. Alternatively or additionally, the tempering station but also a cooling station, preferably as controlled by a measuring unit for temperature sensing cooling station with z. B. cooling fluids or cooling contact components.

For the controlled influencing of the deformation and the springback, it is particularly advantageous if, after the forming, a measuring station, preferably a non-contact contour measuring station is arranged, which detects the shape of the formed workpiece and further influences the springback of workpieces to be reshaped.

A particularly preferred embodiment of the method according to the invention or of the device according to the invention is shown in the drawing.

Show it:

1 A first embodiment of the device according to the invention exemplified in a simple bending operation of an angled workpiece, which is formed in a progressive tool from a strip-shaped starting material, in a cutout in the environment of the forming station of the progressive tool,

2 - An alternative embodiment of the device according to 1 with inductive heating of the starting material arranged on both sides of the strip-shaped starting material,

3 Curvatures of the deformed portions of the sheet metal strip after heating, after bending under load, after unloading and after cooling,

4 Lowering the yield strength, the tensile strength and the modulus of elasticity depending on the temperature in the forming zone for a micro-alloyed fine-grained strip steel,

5 - yield stress of a steel alloy (steel C15 - 1.0401, left partial diagram) and an aluminum alloy (AlMgMn - 3.3527, right partial diagram) above the deformation rate for different temperatures according to [Doege 1986],

6 - schematic temperature of the parts of the bending tool,

7 - Exemplary structure of superimposed control circuits in influencing the springback according to the inventive method.

In the 1 a first embodiment of the device according to the invention is exemplified in a simple bending operation of an angled workpiece 1 , which in a progressive tool from a strip-shaped starting material 2 is formed in a cutout in the environment of the forming station 13 of the progressive tool. The follow-on composite tool only partially shown here consists of a known sequence of individual punching and forming stations 13 , which are designed to be workpiece-dependent. As a starting material 2 Here comes a strip-shaped starting material for example from a coil, not shown, used in the illustration according to 1 in a non-illustrated portion of the progressive tool in individual sections 8th is cut to size and in the forming station shown in the cutout 13 here to a simple curved rag 5 to be angled, the then, but not shown to the workpiece 1 from the strip 2 is cut out. This transformation 13 is very simplified and shown schematically in order to describe the basic principle of the present invention easily understandable. This in no way means that the invention is based on such simple transformations 13 and especially not limited to Biegeumformungen, but is only as an example of the different conceivable transformations 13 to watch.

The from the strip 2 punched out sections 8th cycled through a likewise only schematically indicated, the underside of the metal strip 2 arranged induction coil 6 for heating the area to be subsequently formed 9 the sections 8th , be in a bending stage 13 from a bending stamp 3 and a counterpart 4 to a simple angle 5 bent, then go through a cooling unit 12 and are in the reshaped area 9 with an optical contour knife 10 captured in their reshaped contour before the sections 8th reach the next no longer shown punching or bending operation in the progressive tool. In the direction of passage 21 from right to left after the one-sided warming the sections 8th of the metal strip 2 conventionally bent. When unloading the thus formed sheet of the section springs 8th analogous to cold bending, with cooling during and after bending 13 compensates the elastic distortion.

In this case, the bending tool 13 consisting of the punch 3 , Backstop 4 and hold down 14 , and the cooling unit 12 be tempered at will. To regulate the bending angle to a desired dimension, various parameters can be set flexibly in the process, so that the bending angle is ensured with a minimum tolerance depending on the applicable requirements from product geometry and material properties. An otherwise normal level after bending 13 for ensuring a shape tolerance of the finished bent workpiece 1 deleted by this procedure. The follow-on composite tool is operated in a servo press, not shown, with different speeds of the bending tool with the same cycle time 13 can be realized during forming. The heating of the sections 8th of the metal strip 2 in the area of the later forming zone 9 before bending 13 done by induction coils 6 with highest heating rates, so that the original cycle time can be maintained. The heating of the later forming zone 9 can, for example, optically operating temperature measuring devices 7 recorded and adjusted accordingly, the temperature of the sections 8th in the area of the later forming zone 9 continuously record.

At least one setting parameter can be influenced by means of a regulation for a given setpoint bending angle, which can be influenced by the forming process 13 the generated arc of the section 8th after bending 13 affected. The return of the bending angle by an optical or otherwise working angle measuring system 10 allows adjustment of the adjustment parameter such that only minimal tolerances of the bending angle relative to the nominal contour of the bending angle arise. Depending on the product and material requirements, various elements can be used as setting parameters for setting the bending angle. These include the inductive heating parameters 6 the later forming zone 9 , the speed of the punch 3 during forming 13 and the parameters of the setting of the cooling unit 12 and the temperature of the parts 3 . 4 . 14 of the tool 13 ,

In the 2 is an alternative embodiment of the device according to 1 with both sides of the strip-shaped starting material 2 arranged inductive heating 6 the sections 8th to recognize that through top and bottom of the sections 8th in the direction of passage 21 of the strip 2 are arranged from right to left. In this case, the respective top side and bottom side surface of the later forming zone 9 by their own optically operating temperature measuring devices 7 recorded and readjusted separately from each other.

With such one-sided or two-sided Temperierungsstationen by means of inductive heating 6 can the temperature distribution in the later forming zone 9 be specifically influenced so that the springback after bending in the bending station 13 is maintained at the setpoint and therefore the finished part geometry of the sections 8th closely tolerated.

For bilateral homogeneous heating according to 2 before reshaping 13 becomes a geometry of the formed bending tool 3 . 4 used, which is initially the desired contour of the sections 8th overbends, ie bends more, than the desired finished part geometry (here the bending angle) of the sections 8th actually necessary. The setpoint contour is only reached during spring-up by a controlled springback, which exceeds the forming temperature of the sections 8th in the area of the forming zone 9 is set. For this purpose, the induction coils 6 used the sheet metal strip 2 in the area of the forming zone 9 the sections 8th warms up equally strong on both sides.

In the 3 are the curvatures of the reshaped section 8th of the metal strip 2 after heating (configuration according to item no 15 ), after bending under load still between stamp 3 and counterholds 4 (Configuration according to item number 17 ), after unloading (configuration according to item no 18 ) and after cooling (configuration according to item no 16 ). The contour 16 After cooling, the nominal contour ideally corresponds to and is determined by the measuring system 10 optical 11 detected.

But it is also conceivable, both with the embodiment of the device according to 1 as well as according to 2 , the forming zone 9 the sections 8th To heat up different degrees and thus a temperature gradient in the cross section of the sections 8th in the area of the forming zone 9 to create. Depending on how strong the temperature gradient is over the material thickness of the sections 8th is set by the heating, you get a different bias of the sections 8th of the metal strip 2 in the bending tool 13 ,

When using a one-sided and deliberately inhomogeneous heating 6 the springback is compensated by graded thermal expansions. For this, the pressure zone before bending 13 with a single-acting induction coil 6 according to 1 heated, so that the pressure zone experiences a greater thermal expansion than the tensile zone. This will make the bow in the bending tool 13 biased and undergoes a major plastic deformation. Here, the temperature gradient is regulated in relation to the sheet thickness with the help of inductive heating 6 , This is what the induction coil calls for 6 by adjusting the coupling distances at the top and bottom of the sheet metal strip 2 a temperature gradient in the metal strip 2 out. Alternatively, both sides of the sheet metal strip 2 arranged induction coils 6 be used with the same coupling distances on both sides, wherein the coupling on the side of the tension zone by a between induction coil 6 and section 8th lying shield is reduced.

In inductive heating can in a homogeneous two-sided heating according to 2 specifically the height of the temperature of the section 8th in the forming zone 9 be set in the Temperierungsbereich. By lowering the yield stress, the proportion of the superimposed elastic strains is reduced and the section 8th springs less when relieving. In 4 This is illustrated graphically above the temperature for the steel S420MC. In an analytical model often used for the calculation of the description of the springback, a constant yield stress k _{f is} assumed. As a substitute, the yield strength R _e and the tensile strength R _m for the yield stress k _f are used in this example. It can be seen from the ratio of the yield strength R _e or tensile strength R _m to the modulus of elasticity E that for high temperatures around 700 ° C. the springback level drops markedly. Is thus by a z. B. inductive heating 6 before bending the section 8th of the metal strip 2 heated on both sides, the springback level can be lowered or controlled depending on the temperature. For complete compensation of the shape deviation is in addition to the two-sided heating a slight overbending in the bending tool 13 necessary. The amount of springback after bending in the bending tool 13 is controlled by the heating temperature, so that the target contour is reached.

In 5 are yield stresses of a steel and an aluminum alloy over the forming rate for different temperatures. Only when heated, the yield stresses of the two metallic materials are dependent on the forming speed, so that it can be influenced. If, for example, a variable forming speed of φ = 1.6 ... 6.4 results from the permissible operating range of the press and the tool, the yield stress for steel C15 at a bending temperature of 700 ° C can be anywhere in the range k _f = 266 ... 315 MPa vary. For the aluminum alloy AlMgMn, the yield stress at a temperature of 480 ° C could be set correspondingly in the range k _f = 80 ... 90.

In addition to the temperature of the sections 8th in the forming zone 9 through the upstream temperature control station in the form of induction coils 6 can also be a tempering of the sections 8th in the bending tool 13 according to 6 yourself. So according to 6 the punch 3 or the counterpart 4 with self-contained channels 19 . 20 be penetrated, through which a coolant or a heating medium can be pumped and thus bending punch 3 or the counterpart 4 can also be tempered differently to each other. So z. B. the backstop 4 by means of heated oil through the holes arranged in it 20 warmed up, the hold-down 14 and the stamp 3 by means of coolant in the holes 19 on z. B. room temperature to be cooled. When bent, the section cools 8th the just formed sheet metal strip 2 over the contact with the cooled stamp 3 out if a full contact between section 8th and stamp 3 is present. Such a caused temperature gradient in the section 8th of the metal strip 2 causes thermal tensile stresses in the outer arch of the reshaped area 9 and the section 8th is further plastically deformed by the thermal tensile stresses. After relieving the section springs 8th initially as usual back, but the section curves 8th due to uneven thermal expansion during cooling of the section 8th stronger after unloading, as the inside is warm and the outside cold.

In the 7 is in several sub-diagrams and largely self-explanatory the structure of a superimposed control loop ( 7a ), which can be used in influencing the springback according to the method according to the invention. Here are the two control parameters tempering the sections 8th in the area of the forming zone 9 and speed of the punch 3 used in the forming, according to the subordinate control loops according to the 7b and 7c can be constructed. In both subordinate control loops, the angle measurement of the achieved bending of the sections is central 8th through the optical contour detection 10 , which leads to the feedback and, if necessary, the change of the manipulated variables.

By integrating a two-sided heating with the aim of a homogeneous temperature in the section 8th of the metal strip 2 according to 1 can thus be increased depending on the material behavior in addition to the springback by adjusting the punch speed and the formability. If the follow-on composite tool is operated on a servo press, the punch speed during forming can be varied while maintaining the same cycle rate and output so that the yield stress can be influenced.

bibliography

• [Bammer 2010] Bammer, F., Holzinger, B., Humenberg, G., Schuöcker, D., Schumi, T., 2010. Integration of high power lasers into bending tools. Phys. Procedia 5, 205-209.
• [Doege 1986] Doege, E., Meyer-Nolkemper, H., Saeed, I., 1986. Flow curve atlas of metallic materials with flow curves for 73 materials and a basic introduction. Carl Hanser Verlag, Munich.

LIST OF REFERENCE NUMBERS

1

workpiece

2

metal strip

3

Stamp bending tool

4

Counterholder bending tool

5

curved section

6

inductive heating coil

7

temperature measurement

8th

section

9

forming zone

10

Contouring

11

optical beam path

12

cooling station

13

bending tool

14

Downholder bending tool

15

deformed configuration section after heating

16

Precast part section after complete forming and cooling

17

over-arched contour section under load

18

after bending relieved contour section

19

drilling

20

drilling

21

Throughput direction

Claims (34)

Method for influencing the deformation behavior, in particular the springback when forming workpieces ( 1 ) in clocked forming and processing stations, in particular during bending in progressive dies, in which a workpiece ( 1 ) is processed one after the other in a succession of cyclically linked machining stations and subjected to at least one deformation, characterized in that the workpiece ( 1 ) of metallic material as it passes through the clocked linked processing stations before and / or during and / or after at least one forming station ( 13 ) an adaptively guided and at least a portion of the workpiece ( 1 ) tempering ( 6 ), in which by means of previously in the forming station ( 13 ) formed workpieces that Springback behavior of the formed workpieces or the produced geometric shape of the formed workpieces is continuously monitored metrologically and used for the adaptive change of the temperature control, the adaptive temperature control the deformation behavior of at least this range ( 9 ) of each individual workpiece ( 1 ) in this forming station ( 13 ) such that the state of stress, in particular the springback and / or the residual stresses of the material of the workpiece ( 1 ) after forming ( 13 ) a target value for achieving the desired finished part geometry or an intermediate geometry to be achieved of the workpiece to be formed ( 1 ) reached. Method according to claim 1, characterized in that the deformation of the workpiece ( 1 ) by the forming tool ( 13 ) excessive deformation of the workpiece ( 1 ), whereby the adaptively influenced springback causes the workpiece ( 1 ) takes place in the desired desired geometry. Method according to one of the preceding claims, characterized in that the temperature control ( 6 ) as heating, preferably as local inductive or conductive heating ( 6 ) of the workpiece ( 1 ) is carried out. Method according to claim 3, characterized in that the heating ( 6 ) in the direction of passage ( 21 ) in front of the forming station ( 13 ) by an inductive or conductive heating station ( 6 ), in particular one by means of integrated temperature measurement ( 7 ) controlled inductive or conductive heating station ( 6 ) is carried out. Method according to one of the preceding claims, characterized in that the temperature control as cooling ( 12 ), preferably as cooled by a measuring unit for temperature sensing cooling ( 12 ) of the workpiece ( 1 ) is performed with cooling fluids or cooling contact components. Method according to one of the preceding claims, characterized in that the temperature control ( 6 ) a predeterminable temperature gradient in the cross section of the workpiece ( 1 ), preferably by uneven temperature control of the workpiece ( 1 ) Based on its tempered surfaces. Method according to one of the preceding claims, characterized in that as deformation ( 13 ) a bending deformation in particular sheet-metal materials is performed. Method according to one of the preceding claims, characterized in that as deformation ( 13 ) a deep drawing in particular sheet-metal materials is performed. Method according to one of the preceding claims, characterized in that as deformation ( 113 ) a massive forming in particular solid metal materials is performed. Method according to one of the preceding claims, characterized in that the material of the workpieces ( 1 ) high to ultra-high-strength metal materials are processed. Method according to one of the preceding claims, characterized in that, as clocked processing, processing of strip-like semi-finished products ( 2 ) producible workpieces ( 1 ) is carried out in follow-on composite tools or of occasionally present semi-finished products in transfer tools. Method according to one of the preceding claims, characterized in that the shape produced by means of forming and / or the resulting springback of the workpiece ( 1 ) after forming ( 13 ) in a measuring station ( 10 ), preferably a non-contact working contour measuring station ( 10 ) and for influencing the springback of subsequently to be reshaped workpieces ( 1 ) is being used. Method according to one of the preceding claims, characterized in that the influencing of the springback of the workpiece ( 1 ) a temperature control ( 6 ), in particular targeted heating of at least the area to be reshaped ( 9 ) of the workpiece ( 1 ) before and / or during forming ( 13 ) having. Method according to claim 13, characterized in that the material of the workpiece ( 1 ) at least in the region of the forming zone ( 9 ) before forming ( 13 ) in a separate tempering station ( 6 ) is heated. Method according to one of claims 13 or 14, characterized in that the material of the workpiece ( 1 ) at least in the region of the forming zone ( 9 ) during forming ( 13 ) by a tempering of at least individual parts ( 3 . 4 . 14 ) of the forming tools ( 13 ) is heated and / or cooled. A method according to claim 15, characterized in that by different heating and / or cooling of Umformgegenhalters ( 4 ) and the forming stamp ( 3 ) a temperature gradient within the cross-section to be formed ( 9 ) of the sheet-like workpiece ( 1 ) is produced. Method according to one of claims 15 or 16, characterized in that the workpiece ( 1 ) in the region of the forming zone ( 9 ) after forming ( 13 ) during at least a short holding time in the region of the temperature control by at least individual parts of the forming tools ( 13 ) and the workpiece ( 13 ) is thereby further heated and / or cooled. Method according to one of the preceding claims, characterized in that the material of the workpiece ( 1 ) at least in the area of the transformed zone ( 9 ) after forming ( 13 ) in a cooling station ( 12 ) is cooled. Method according to one of the preceding claims, characterized in that the influencing of the springback of the workpiece ( 1 ) an influence on the forming speed during forming ( 13 ) and thus the yield stress of the material. A method according to claim 19, characterized in that the influencing of the deformation rate in the forming ( 13 ) by controlling the tool drives a servo press or the like. Is achieved. Method according to one of the preceding claims, characterized in that the influencing of the springback of the workpiece ( 1 ) by influencing the forming speed and by influencing the springback by tempering ( 6 ) at least the forming zone ( 9 ) takes place in the form of superimposed control circuits. Method according to one of the preceding claims, characterized in that the inductive heating ( 6 ) of a sheet-like workpiece ( 1 ) on both sides homogeneous by above and below the passage path of the sheet-like workpiece ( 1 ) arranged induction coils ( 6 ) he follows. Method according to one of the preceding claims, characterized in that an asymmetrical heating of the workpiece ( 1 ) is carried out over its cross section so that primarily the pressure zone of the transformation region ( 9 ) is heated, so that the pressure zone of the workpiece ( 1 ) is subject to greater thermal expansion than the tensile zone. A method according to claim 23, characterized in that the regulation of the temperature gradient of the sheet-like workpiece ( 1 ) asymmetrically over its cross section through the upper and / or lower coupling distance of the induction coils ( 6 ) to the workpiece ( 1 ) or at a fixed distance via a regulation of the generator current for charging the induction coils ( 6 ) he follows. Method according to one of the preceding claims, characterized in that the tempering station ( 6 ), the tool ( 13 ) and the cooling station ( 12 ) for generating controlled temperature profiles at least in the area acted on ( 9 ) of the workpiece ( 1 ) is used, a local heat treatment, in particular a local hardening or tempering of the applied area ( 9 ) of the workpiece ( 1 ). Method according to one of the preceding claims, characterized in that the workpiece ( 1 ) in the cooling station ( 12 ) and / or the tool ( 13 ) is locally cooled differently. Device for influencing the deformation behavior, in particular the springback when forming workpieces ( 1 ) in clocked forming and processing stations, in particular during bending ( 13 ) in progressive tools, in which a workpiece ( 1 ) are processed in succession in a sequence of clocked, linked machining stations and at least one transformation ( 13 ), for carrying out the method according to claim 1, characterized in that before and / or during and / or after at least one forming station ( 13 ) a tempering station ( 6 ), which is guided by a guided and at least a portion of the workpiece ( 1 ) tempering ( 6 ) the workpiece ( 1 ) of metallic material is adaptively influenced such that the workpiece ( 1 ) by the springback of the material after forming ( 13 ) reaches a desired finished part geometry or an intermediate geometry to be achieved. Apparatus according to claim 27, characterized in that the tempering station an inductive or conductive heating station ( 6 ), in particular one by means of integrated temperature measurement ( 7 ) controlled inductive or conductive heating station ( 6 ) having. Device according to one of claims 27 or 28, characterized in that the tempering station is a cooling station ( 12 ), preferably as via a measuring unit for temperature sensing controlled cooling station ( 12 ) with cooling fluids or cooling contact components. Device according to one of claims 27 to 29, characterized in that the deformation ( 13 ) has a bending deformation. Device according to one of claims 27 to 30, characterized in that the deformation ( 13 ) has a deep drawing in particular sheet-metal materials. Device according to one of claims 27 to 31, characterized in that the deformation ( 13 ) has a massive forming in particular solid metal materials. Device according to one of claims 27 to 32, characterized in that after the forming ( 13 ) a measuring station ( 10 ), preferably one in particular non-contact ( 11 ) working contour measuring station ( 10 ) is arranged, which the shape of the formed workpiece ( 1 ) and for influencing the springback of subsequently to be reshaped workpieces ( 1 ). Device according to one of claims 27 to 33, characterized in that at least individual parts ( 3 . 4 . 14 ) of the forming tools ( 13 ) are heatable and / or coolable.

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