DE102018214436B4 - Method for determining a stress state in a component - Google Patents

Abstract

Method for determining a stress state in a component (110), comprising the steps: a) providing a component (110); b) making a cut (112) through the component (110), whereby the component (110) along a cutting contour (114 ) is separated into two component halves (116, 118) such that each of the two component halves (116, 118) has a cutting surface (120) along the cutting contour (114); c) measuring the cutting surface (120) of each of the two component halves (116 , 118); d) performing a simulation during which the two component halves (116, 118) are joined together at the cut surfaces (120), as a result of which the stress state in the component (110) is determined, with step b) or during step b ) a plurality of markings (140) are introduced into the cut surface (120) of each of the two component halves (116, 118), a position of the plurality of markings (140) in the component half (116, 118) being determined during step c) , and w o during step d) the two component halves (116, 118) are joined together at the plurality of markings (140) in the cut surfaces (120).

Description

The present invention relates to a method for determining a voltage state in a component and a computer program which is set up to carry out steps of the method.

State of the art

So-called "internal stresses" can occur in solids and components, which are mechanical stresses that stress the component and / or the associated material without external load. Since the residual stresses occur in a component without external load, they compensate in every cross-section, i.e. an integral of the residual stresses over a cutting surface is zero. In addition, the inner moments of a component that is only subjected to internal stresses are in balance.

Residual stresses can arise due to thermal gradients, plastic deformation, structural changes and their interaction, for example as a result of plasticization due to a thermal gradient. They can be unwanted (e.g. in the case of residual welding stresses) as well as wanted (e.g. auto frettage in the case of high-pressure lines), since they overlap with the operating loads during operation of the component and can thus locally increase or reduce the stress. In particular, when a component is subjected to vibrating stresses, residual stresses can significantly increase the service life (usually by means of residual compressive stresses at a point subject to the highest stress) or decrease (by means of residual stresses at the point subject to the highest stress) without this being visually apparent on the component.

Non-destructive or destructive methods can be used to determine the residual stresses. Here, however, it applies that the non-destructive methods (X-ray diffraction or neutron diffraction in a corresponding diffractometer) can only be used to measure the internal stresses on the surface or near the surface of a component. Residual stresses over a larger cross section can only be determined in a destructive manner at the present time. Only the residual stress measurement by means of neutron diffraction, which allows a three-dimensional analysis in depth, is an exception. However, due to high costs and extensive testing, this method is not widely used.

A commonly used method for determining the internal stresses along a cutting plane through a component is the so-called “contour method”. A very fine cut is made through the component, usually by eroding, usually by wire EDM. Due to the cut, residual stresses are released, which lead to deformation of the component. The deformation perpendicular to the cutting plane is subsequently determined by measuring the two cutting surfaces. The residual stresses perpendicular to the cutting plane are determined by means of a subsequent numerical simulation, in which the two component halves are put together again in the form of the simulation.

The disadvantage of this is that the residual stresses can only be determined perpendicular to the cutting plane. Only the deformations in this direction can currently be measured directly. However, there is no information about deformations in the cutting plane itself. It is therefore currently not possible to determine the shear stresses acting in the cutting plane. The deformed cutting surfaces can also only be meaningfully joined together perpendicular to the cutting plane. This means that the original shape of the component cannot be fully recalculated. The residual stresses determined in this way therefore have an unknown error. The reason for this is that reference points are determined in the recalculated form of the component, which generally do not match the position of the original state.

The stress state is indicated by the stress tensor, i.e. by six components, in particular by three normal stresses and three shear stresses. With a cutting plane, there is therefore always a normal stress and two shear stresses. Therefore, the stress state cannot be approximated by a single normal stress value. The actual voltage state cannot therefore be determined using known methods. The level of the normal stress value determined also depends on the cutting angle used.

In a further method known from the prior art for determining normal stresses perpendicular to a first cutting plane, a second cut is carried out. Due to the second cut, which is carried out perpendicular to the first cutting plane, only the residual stresses remaining after the first cut can be determined. information about
Residual stresses in the first cutting plane are lost. In addition, information in the second section level also remains incomplete. There is still the problem that information about the deformation in the cutting plane is lost.

In another method known from the prior art, no cut is made performed, rather the component is broken open, preferably at low temperatures. In general, the component is at least locally plastically deformed when it is broken open, so that no more statements can be made about the residual stress state of the original component state.

For more details regarding the contour method and many of its known designs, see the review article by F. Hosseinzadeh, J. Kowal, PJ Bouchard, Towards good practice guidelines for the contour method of residual stress measurement, J. Eng. 2014, doi: 0.1049 / joe.2014.0134, the publication by J. Araujo de Oliveira, J. Kowal, S. Gungor, ME Fitzpatrick , Determination of normal and shear residual stresses from fracture surface mismatch, Materials & Design 83, 2015, pp. 176-184, and the dissertation by P. Pagliaro, Mapping multiple residual stress components using the contour method and superposition, Ph.D. Thesis, Università degli Studi di Palermo, 2008.

US 6 470 756 B1 discloses a method for determining a stress state in a component into which a cut is made along a cutting contour with a known configuration, whereby each component half has a cutting surface along the cutting contour. To determine the stress state, a computer-aided simulation is carried out with an empirical data set, which is defined by points along the cutting contour.

US 10 018 522 B2 discloses a further method for determining a stress state in a component, for which purpose a shank is used in order to successively make a cut in the component along a cutting contour and to detect the internal stresses thereby released. The cutting contour is a conical or cylindrical surface that is arranged concentrically to an axis of the shaft.

US 8 997 577 B2 discloses a further method for determining a stress state in a component, into which cuts are progressively made, wherein in each case a deflection of the component is measured at the point of intersection.

WO 2006/008554 A1 discloses another method for determining a stress state in a component, wherein input variables are generated with respect to a cut made in the component, which flow into a model for calculating the stress state of the component, the inelastic stress distribution in the component using a set of parameters is minimized.

Against this background, the object of the present invention is to provide a method for determining a stress state in a component and a computer program which is set up to carry out steps of the method which at least partially overcome the disadvantages and shortcomings of the prior art. In particular, the method and the computer program should make it possible to examine a component in such a way that information about a deformation in a cutting contour can be obtained, preferably in order to determine a normal stress more precisely on the basis of the information obtained about the deformation in the cutting contour, and moreover also To be able to determine shear stresses.

Disclosure of the invention

This object is achieved by a method for determining a stress state in a component and a computer program with the features of the independent claims. Advantageous refinements can be found in the dependent claims.

In a first aspect, the present invention relates to a method for determining a stress state in a component. Here, the term “component” denotes a solid that is expanded in three dimensions and that comprises one or more materials. For example, the component can have a metal, a ceramic or a composite material. However, other materials are possible. In particular, due to thermal gradients within the component, a plastic deformation of the component, structural changes in parts of the component and / or their interaction, for example as a result of plasticization due to a thermal gradient, stress states, which are referred to as "internal stresses", can occur in the Component occur. The term "internal stresses" refers to mechanical stresses that stress the component and / or the associated material without external load. Since the residual stresses occur in a component without external load, they compensate in every cross-section, i.e. an integral of the residual stresses over a cutting surface is zero. In addition, the inner moments of a component that is only subjected to internal stresses are in balance. However, since it is not clear a priori that an observable stress state in the component can only be traced back to an internal stress, the proposed method is generally aimed at determining a stress state in the component.

1. a) Bereitstellen eines Bauteils;
2. b) Einbringen eines Schnittes durch das Bauteil, wodurch das Bauteil entlang einer Schnittkontur derart in zwei Bauteilhälften aufgetrennt wird, dass jede der beiden Bauteilhälften entlang der Schnittkontur eine Schnittfläche aufweist;
3. c) Vermessen der Schnittfläche jedes der beiden Bauteilhälften;
4. d) Durchführen einer Simulation, während welcher die beiden Bauteilhälften an den Schnittflächen zusammengefügt werden, wodurch der Spannungszustand in dem Bauteil bestimmt wird,

wobei vor Schritt b) oder während Schritt b) eine Mehrzahl von Markierungen in die Schnittfläche jeder der beiden Bauteilhälften eingebracht wird, wobei während Schritt c) eine Position der Mehrzahl der Markierungen in der Bauteilhälfte bestimmt wird, und wobei während Schritt d) die beiden Bauteilhälften an der Mehrzahl der Markierungen in den Schnittflächen zusammengefügt werden. Hierbei erfolgt somit ein Zusammenfügen der beiden Bauteilhälften in Form einer Simulation, insbesondere in Form einer numerischen, kontinuumsmechanischen Simulation. Vorzugsweise kann die kontinuumsmechanische Simulation hierbei insbesondere eine Finite Elemente-Simulation darstellen oder umfassen.The method proposed for determining the stress state in the component includes steps a) to d) described below:

1. a) providing a component;
2. b) making a cut through the component, as a result of which the component is cut along a cutting contour into two component halves in such a way that each of the two component halves has a cutting surface along the cutting contour;
3. c) measuring the cut area of each of the two component halves;
4. d) performing a simulation during which the two component halves are joined together at the cut surfaces, as a result of which the stress state in the component is determined,

wherein before step b) or during step b) a plurality of markings are introduced into the cut surface of each of the two component halves, a position of the plurality of markings in the component half being determined during step c), and wherein during step d) the two component halves at the majority of the markings in the cut surfaces. The two component halves are thus combined in the form of a simulation, in particular in the form of a numerical, continuum mechanical simulation. Preferably, the continuum mechanical simulation can in particular represent or include a finite element simulation.

Here, successive steps can sometimes also be carried out simultaneously. In addition, steps b) to d) can be carried out repeatedly at different points in the component in order in this way to be able to determine the stress state in the component in different directions.

According to step a), a component that corresponds to the above definition is provided.

According to step b), a separation process takes place by making a cut through the component provided during step a). The term “cut” here means a spatial separation of the component into two component halves by means of a so-called “separating device”, which is set up to disassemble the component along a cutting contour into the two component halves. A wire erosion machine, which has a continuous wire, which is also referred to as “eroding wire”, can preferably serve as the separating device, which wire can cut the component along the cutting contour by means of so-called “wire erosion” into the two two component halves. As a result of electrical voltage pulses, sparks can be generated, which transfer material from the component, which is usually connected as an anode, to the continuous wire, which is usually connected as a cathode, and into a separating dielectric medium. The wire can be provided, preferably wound on a spool, from there, preferably via at least one deflection roller, to an upper wire guide and by means of a feed speed through a cutting gap in the component created by the material removal and then through a lower wire guide and then to be disposed of. The upper and lower wire guides and the deflection rollers are designed to guide and support the wire and, according to the prior art, to suppress vibrations. The cut through the component is preferably carried out in such a way that a liquid dielectric, which in particular can have an aqueous solution and / or an eroding oil, flows through the cutting gap. Permanent rinsing with the dielectric means that erosion waste accumulating during the cut can be disposed of from the cutting gap and / or the current-carrying wire can be cooled. However, other types of separating devices are also possible, in particular the use of diamond saws, which can preferably be operated with a liquid flowing through the cutting gap and receiving or transporting away the chips that occur.

By making the cut, the component provided during step a) is cut into two component halves along the cutting contour in such a way that each of the two component halves has a cutting surface along the cutting contour. While a cut made according to the prior art in a method for determining the stress state in the component always represents a uniform, straight cut through the component, which cuts the component along a cutting plane into two component halves, it is particularly advantageous if the component is cut according to the proposed method in the component introduced cut does not represent, or at least not exclusively, a uniform, straight cut through the component. Rather, the term "cut contour" differs from the term "cut plane" in that the cut contour generally does not represent a flat surface, since the step into the component that generates it is not carried out, or at least not exclusively, evenly and straight. In this way, a cut surface is simultaneously created in each of the two component halves along the cutting contour, which therefore cannot represent a flat surface either, but rather can be formed based on the cutting contour and the local residual stresses, which can change the cutting contour locally.

In order to be able to obtain the desired information about a deformation in the cutting contour, it is proposed to make a plurality of markings in the cutting surface of each of the two component halves before step b) or during step b). If the majority of the markings are simultaneously applied to originally adjacent positions of the cut surfaces of the two component halves, additional conclusions about deformations of the component occurring in the cut contour due to residual stresses are possible in this way, as explained in more detail below. The term “marking” here denotes a change in a surface property of the cut surface within the cut surface on each of the two component halves, which is designed in such a way that a position that can be found in each case is determined at positions of the cut surfaces that were originally arranged adjacent to one another. The change in the surface property of the cut surface can preferably take place at regular intervals from one another with respect to a cutting direction. In this way, the retrievable positions of each marking on the cutting surface can be related to one another without the need to actually determine the position or the distance between two positions, in particular two adjacent positions. As an alternative to this, the change in the surface property of the cut surface can also take place at stochastic distances from one another. In the event that it cannot be possible to insert markings at regular intervals, in particular transversely to the cutting direction, stochastic distances can additionally have the advantage that an assignment of the two halves is unambiguous even if an edge area is not completely preserved. As a result, absolute information can be provided due to an uneven spacing of the markings.

A particularly preferred embodiment provides for the majority of the markings to be introduced directly into the cutting contour and thus simultaneously into the cutting surface of each of the two component halves during step b). For this purpose, it is proposed to generate the majority of the markings by locally changing the material removal, in particular by changing at least one process parameter over time, when the cut is introduced into the component. For this purpose, as explained above, the wire erosion method can preferably be used, which has a large number of process parameters that can be varied individually or in cooperation. Preferred process parameters for the method of wire erosion include in particular a current intensity with which the wire is applied, a thickness of the wire, a direction of movement of the wire or a local configuration of a surface of the wire. A variation of other process parameters is also possible. In this way, the majority of the markings can be applied simultaneously to the two cut surfaces of the two component halves by changing the geometry or, alternatively or additionally, by changing the color or the surface texture of the cut surface.

In this embodiment, a distinction can be made in particular between the markings which can be produced in the direction of movement of the wire when the wire erosion is varied and markings which can be produced in the direction of advance of the wire when the wire erosion is varied. The wire erosion can be varied in the direction of movement of the wire by at least one of the first measures described in more detail below. A rate of erosion of the wire erosion at the cut surface of each of the two component halves can preferably be set by means of the process parameter current intensity with which the wire is applied, and can therefore be varied regularly or stochastically, since a change in the current flow can lead to more or less material being removed from the Component removed at the cutting edge and thus the cutting width is varied. For example, the current flow can be increased by a fixed value at regular time intervals during a defined time interval and returned to the original value after the time interval has elapsed, in order to increase one at regular intervals during a uniform execution of the cutting process in one direction along the cutting contour (cutting direction) To achieve material removal, which can in each case serve as the desired marking, the distance between two adjacent markings being able to be set by the variation of the current intensity over time.

A comparable effect can be achieved by alternatively or additionally a lateral movement of the component with respect to the cutting direction during the defined time interval during wire erosion, which can also cause the material removal to be increased at regular intervals, which in this case is also the desired one Marking can serve. Consequently, a relative movement between the component and the eroding wire can be carried out in particular along the component during the wire erosion. In particular, the eroding wire can be moved while the component can be mounted in a stationary manner. Alternatively, the component can be moved, in particular moved, while the eroding wire can be fixed in place. Alternatively, both the eroding wire and the component can be moved, in particular at the same time. For example, the eroding wire in an x-direction and the component in a y direction perpendicular to the x direction. However, other types of directions are possible. Instead of or in addition to a purely lateral relative movement of the component to the wire, further movement patterns can also be used, in particular a movement in the form of a sine wave, rectangular steps, trapezoid steps, a triangular shape or a combination thereof. In addition, other movement patterns are possible. The distance between two adjacent markings can be set by a speed of the movement pattern of the component.

As already mentioned, markings that are generated alternatively or additionally when the wire erosion is varied in the feed direction of the wire can be distinguished. Here, the wire erosion can be varied in the feed direction of the wire by at least one of the second measures described in more detail below, which can be carried out during the wire erosion. In contrast to the prior art described above, the eroding wire itself can be excited to vibrate by impressing vibrations. The marks can be introduced into the cutting plane in a regular manner, in particular by standing waves. The eroding wire can be excited, for example, via the deflection rollers of the wire described above, in particular permanently or periodically or stochastically, in order in this way to be able to achieve a material and / or time-wise uneven removal of material at the cutting surface. In addition, there are other methods with which such uneven material removal can be obtained at the cut surface. Partial painting of the wire can influence the formation of sparks and thus material removal, since the cutting width along the partially painted wire is uneven, and a distance between two adjacent markings can be set via the feed speed of the wire. Alternatively or additionally, the wire can be deformed in sections in this way, for example by squeezing and / or by bending, as a result of which a level of material removal can also be influenced here. Furthermore, the liquid dielectric in which the wire erosion is carried out can also influence the spark formation and thus the material removal rate. Thus, alternatively or additionally, the cutting width can be varied by changing a water level or by providing different layers of oil in water or different layers of water in oil. Here, the water and the oil can be introduced sequentially into the cutting gap, in particular at a slow flow rate.

In an alternative embodiment, the majority of the markings can be made in the component before step b). This can preferably take place in the form of a plurality of parallel bores, each of the bores being introduced into the component in such a way that it penetrates the component essentially perpendicular to the intended cutting contour. The term “essentially vertical” here includes not only a vertical arrangement, but also a deviation of at most ± 15 °, preferably of at most ± 5 °, particularly preferably of ± at most 1 ° from the vertical arrangement. In this way, the bores can be used to make the deformations in the cut contour visible as markings, with the cut being able to be made uniformly and straightly in this embodiment, so that the cut contour can also be designed as a cutting plane. The term “drilling” describes a conical or cylindrical removal of a material from the component by means of a drilling process, whereby a regular or stochastic drilling pattern can be present. A distance from two adjacent bores is preferably a factor 5 up to a factor 25th larger than a diameter of the holes. In particular, a drilling tool and / or a drill can be used for the drilling method. The drill can be a mechanical drill, in particular a twist drill. However, other configurations are also conceivable in principle. In this way, a sufficient number of markings can be achieved without mutual interference. In particular, however, care should be taken to ensure that mechanical machining of the component by drilling the holes has as little influence as possible on the residual stress state of the cutting contour to be examined.

Deep hole drilling, hole eroding or laser drilling are particularly suitable as drilling methods. To shorten the process time, a tool is conceivable that can drill several holes at the same time. An electrode that can be used for hole eroding can preferably be insulated at the side; this allows the material removal to be adjusted during hole erosion and prevents the bore from expanding. The electrode can be designed as a tube in order to ensure that an electrolyte is transported to the site to be processed. The surfaces of the component on which the bore begins can preferably be machined flat, for example by milling, which can facilitate an essentially vertical course of the bore. Such a processing can avoid influencing the residual stresses in the cutting contour to be examined. In addition, the planar surface provided in this way can preferably be configured parallel to the cutting plane.

According to step c), the cutting area of each of the two component halves is measured, a position of the majority of the markings in the component half being determined at the same time. Here, in particular, a high-resolution image of the cut surfaces of each of the two component halves can take place, preferably with a resolution (pixel spacing) of at most 5 μm, preferably of at most 2 μm, in the lateral direction within the image. The image itself can include information on the height of each pixel in relation to an arbitrarily defined reference height on the one hand and the position of the majority of the markings in the respective cut surface on the other hand. For this purpose, one or more imaging methods known from the prior art can be used, preferably photogrammetry; Interferometry, in particular white light interferometry; Computed tomography or a scanning technique. However, it is possible to use further imaging methods, in particular digital image correlation or triangulation, preferably with a stripe projection.

In the embodiment comprising a plurality of bores, the spatial position of each of the bores made in the component can preferably be measured not only after step b) but also before step b). The same imaging method can preferably be used for this. With the help of a numerical evaluation algorithm, edges of the holes can be measured and reference points belonging to the holes can be formed. A bore angle can be determined on the basis of the determined data of the initial state. For this purpose, a comparison of a bore opening in an elliptical shape with a bore opening in an ideal circular shape can be used to determine an oblique position of the bore. As an alternative or in addition, the bore angle can be determined by offsetting the reference points of bore inlets and bore outlets with a known thickness of the component.

With the help of the known reference points of the bore entrances and the bore exits, the theoretical reference points can be determined in the later cutting plane. After the separation process in step b), the newly established reference points can be determined for this purpose. By comparing the reference points before and after the cutting process, the displacements in the cutting plane can be measured. If the bore angle deviates from 90 °, the cutting width used during the cutting process can preferably be taken into account, since the reference points can otherwise be shifted from one another. This can be done, for example, by applying half the cutting width on both sides, and the reference points can then be shifted accordingly.

According to step d), a simulation, in particular a numerical, continuum-mechanical simulation is carried out, during which the two component halves are joined together at the cut surfaces, in order to determine the state of stress in the component, whereby during step d) the two component halves on the majority of the Markings in the cut surfaces are put together. The joining of the two component halves on the cutting surfaces can preferably be carried out in such a way that the two component halves can be made to coincide with one another taking into account the cutting thickness on the cutting contour. Each individual cut surface can preferably be evaluated point by point, in particular in the case of discrete markings in the form of lines, lines, depressions, paragraphs or points. A two-dimensional compensation function can be adapted to the cut surface based on the positions of the markings recorded by measurement, preferably using a method known from the prior art, preferably using the method of least squares. An FE model can now be developed on the basis of a cut surface determined in this way. In a particularly preferred alternative embodiment, the nodes of the FE network can be placed, as precisely as possible, on the positions of the discrete markings recorded by measurement, which can have a particularly positive effect in a simpler implementation of the simulation. In particular, the nodes of the FE network in the simulation can preferably match discrete reference points of the holes, the hole pattern preferably being adapted to the FE network.

In a special embodiment in which a geometric marking such as e.g. if there is a sinusoidal variation of the cutting gap, the variation of the cutting gap can be taken into account by applying half a cutting width on both sides.

In a further embodiment, the recorded voltage curve can be optimized such that it is assumed to be as constant as possible across the cutting contour, for example by allowing small deviations when contracting, in particular by means of a suitable numerical algorithm. Preferably, a uniform course across the cutting contour can be assumed for all tension components, for which purpose the relevant values should be almost identical on both sides of the cutting contour.

In a further embodiment, a combination with another method for stress analysis can be carried out. For this purpose, one or more strain gauges can preferably be applied to an outer surface of the component, which can be used to determine the stress curve during cutting, in order to obtain an additional adjustment variable. By measuring the entire geometry of the component before and / or during and / or after the cutting process in step b), the deformation caused by the cutting process can be recorded. The imaging methods mentioned above can also be used for this purpose, preferably photogrammetry, interferometry or computer tomography etc. The consideration of the separation process in the simulation should compensate for its influences. To do this, the component can be brought back to its original state in the reverse order of the cutting direction.

In a further aspect, the present invention relates to a computer program which is set up to carry out individual, several or all steps of the proposed method. In this case, the computer program can include the algorithms already mentioned or further algorithms, which are specially designed to carry out a method step or a part thereof. For further details with regard to the computer program, reference is also made to the rest of the description and the exemplary embodiments.

Advantages of the invention

The present method for determining a stress state in a component makes it possible to determine the shear stresses that occur in this way on the basis of the information obtained about the deformation in the cutting contour. In addition, the normal stress can be determined more precisely. By stacking FE nodes of the numerical model on the discrete markings on the component, joining the two component halves in the form of the simulation can be significantly simplified in the numerical simulation.

Figure list

• 1: eine schematische Darstellung des vorliegenden Verfahrens zur Bestimmung eines Spannungszustands in einem Bauteil;
• 2A und 2B: ein bevorzugtes Ausführungsbeispiel für eine Erzeugung einer Mehrzahl von Markierungen in den Schnittflächen der Bauteilhälften in Bewegungsrichtung eines Drahtes mittels Variation der Schnittbreite (2A), erzeugt durch eine zeitliche Variation der Stromstärke (2B);
• 3A bis 3E: weitere, bevorzugte Ausführungsbeispiele für eine Erzeugung einer Mehrzahl von Markierungen in den Schnittflächen der Bauteilhälften in Bewegungsrichtung des Drahtes durch Querbewegung (3A) oder ein zweidimensionales Bewegungsmuster (3B bis 3E) des Bauteils;
• 4A bis 4D: weitere, bevorzugte Ausführungsbeispiele für eine Erzeugung einer Mehrzahl von Markierungen in den Schnittflächen der Bauteilhälften in Vorschubrichtung des Drahtes;
• 5: ein weiteres bevorzugtes Ausführungsbeispiel für eine Erzeugung einer Mehrzahl von Markierungen in den Schnittflächen der Bauteilhälften durch Einbringen eines Bohrungsmusters; und
• 6A bis 6C: Auswertung von Abbildungen des Bohrungsmusters: Optische Auswertung (6A); Winkelbestimmung durch Vergleich von referenzpunkten (6B); und Berücksichtigung eines Einflusses der Schnittbreite bei nicht senkrechtem Bohrungswinkel.

Preferred exemplary embodiments of the present invention are shown in the figures and are explained in more detail in the following description without restricting the generality. Here show:

• 1 : a schematic representation of the present method for determining a stress state in a component;
• 2A and 2 B : A preferred embodiment for generating a plurality of markings in the cut surfaces of the component halves in the direction of movement of a wire by varying the cutting width ( 2A) , generated by a temporal variation of the current strength ( 2 B) ;
• 3A to 3E : Further, preferred exemplary embodiments for producing a plurality of markings in the cut surfaces of the component halves in the direction of movement of the wire by transverse movement ( 3A) or a two-dimensional movement pattern ( 3B to 3E) of the component;
• 4A to 4D : further, preferred exemplary embodiments for producing a plurality of markings in the cut surfaces of the component halves in the direction of advance of the wire;
• 5 : Another preferred exemplary embodiment for producing a plurality of markings in the cut surfaces of the component halves by introducing a bore pattern; and
• 6A to 6C : Evaluation of images of the hole pattern: Optical evaluation ( 6A) ; Determining the angle by comparing reference points ( 6B) ; and taking into account an influence of the cutting width with a non-perpendicular bore angle.

Embodiments of the invention

1 shows a schematic representation of the present method for determining a stress state in a component 110 .

According to step a), a solid which is expanded in three dimensions and which comprises one or more materials is used as the component 110 provided. For example, the component 110 have a metal, a ceramic or a composite material as the material. However, other materials are possible. In particular due to thermal gradients within the component 110 , a plastic deformation of the component 110 , structural changes in parts of the component 110 and / or their interaction, for example as a result of plasticization due to a thermal gradient, stress states in the form of residual stresses in the component 110 occur with mechanical stresses affecting the component 110 and / or claim the associated material without external load as the residual stresses are called. Because the residual stresses are therefore without external load in the component 110 occur, they equalize in every cross-section, ie an integral of the residual stresses across a cutting surface is zero. There are also internal moments of a component that is only subjected to internal stresses 110 in balance.

According to step b), a cut is made 112 thus through the component provided during step a) 110 introduced that the component along a cutting contour 114 like this in two component halves 116 , 118 is separated that each of the two component halves 116 , 118 along the cutting contour 114 an intersection 120 having. This results in a spatial separation of the component 110 in two component halves 116 , 118 by means of a separating device 122 , which is set up to the component 110 along the cutting contour 114 into the two component halves 116 , 118 disassemble.

As in 1 shown schematically, a wire erosion machine 124 preferably as the separator 122 serve. The wire EDM machine 124 has a continuous eroding wire 126 which is the component 110 along the cutting contour 114 by means of wire erosion in the two two component halves 116 , 118 can separate. As a result of electrical voltage pulses, sparks can be generated, the material from the component 110 , which is usually connected as an anode, on the continuous eroding wire 126 , which is usually connected as a cathode, and can be transferred into a separating dielectric medium (not shown).

The EDM wire 126 can, as from 1 emerges, preferably on a spool 128 be wound up, provided, from there, preferably via at least one deflection roller (not shown), to an upper wire guide 130 and by means of a feed speed in the direction of movement 132 through a cutting gap 134 in the component 110 and then through a lower wire guide 136 pulled and then onto another spool 138 be wound up for disposal. Here are the top wire guides 130 and the lower wire guide 136 as well as the at least one deflection roller (not shown) set up around the eroding wire 126 to guide and support.

The cut 112 through the component 110 is preferably carried out such that a liquid dielectric (not shown), which can in particular comprise an aqueous solution and / or an eroding oil, the cutting gap 134 flows through. A permanent flush with the dielectric can help with the cut 112 eroding waste (not shown) from the cutting gap 134 disposed of and / or cooling the current-carrying erosion wire 126 be made. Other types of separators 122 are however also possible, in particular the use of diamond saws, which preferably have a cutting gap 134 flowing and receiving the erosion waste in particular in the form of chips.

While a state of the art in a method for determining the state of tension always a uniform, straight cut 112 into the component 110 is introduced, it is particularly advantageous if the according to the proposed method in the component 110 introduced cut 112 not, or at least not exclusively, evenly and straight through the component 110 runs, but the cutting contour 114 assumes which generally deviates from a flat cutting surface. In this way it is now possible to have a plurality of markings before step b) or during step b) 140 into the cut surface 120 each of the two component halves 116 , 118 to attach.

2A shows a preferred embodiment for introducing the markings 140 into the cut surfaces 120 the component halves 116 , 118 in the direction of movement 132 of the EDM wire 126 which is based on influencing a removal rate of the wire erosion at the cutting surface 120 each of the two component halves 116 , 118 based. In the exemplary embodiment according to 2A each of the markers 140 generated by varying the cutting width, for example by a in 2 B schematically illustrated variation of the eroding wire 126 current I applied over time t. At a constant feed rate of the erosion wire 126 through the cutting gap 134 can according to the in 2 B shown temporal variation of the current intensity I at regular intervals the markings 140 also at regular intervals into the cut surface 120 each of the two component halves 116 , 118 be attached. Alternatively, the markings 140 also be generated at irregular, especially at stochastic intervals.

In the 3A to 3E are further preferred exemplary embodiments for the generation of the majority of the markings 140 in the cut surfaces 120 the component halves 116 , 118 in the direction of movement 132 of the EDM wire 126 schematically represented by a movement of the component 110 can be generated during wire erosion. 3A shows an example of how the majority of the markings 140 through a transverse movement 142 of the component 110 at regular intervals into the cutting surface 120 each of the two component halves 116 , 118 can be attached. The in the 3B to 3E schematically represented markings 140 are determined by a fixed two-dimensional movement pattern of the component 110 generated. For example, there is a sinusoidal movement 144 ( 3B) , a step-like movement 146 ( 3C ), a trapezoidal movement 148 ( 3D ) or a triangular movement 150 ( 3E) of the component 110 conceivable, which is used to generate the majority of the markings 140 let insert. More types of movements of the Component 110 and / or the eroding wire 126 are conceivable, including irregular, especially stochastic, movements.

In the 4A to 4D are further preferred exemplary embodiments for generating the plurality of markings 140 in the cut surfaces 120 the component halves 116 , 118 in the feed direction 152 of the EDM wire 126 shown, which is due to an impression of vibrations on the eroding wire 126 , by deforming the erosion wire 126 and / or by applying at least one layer to the erosion wire 126 Have them generated at regular intervals or at irregular, in particular at stochastic, intervals, in particular in combination with a cyclic variation of the process parameters.

4A shows an example of how the majority of the markings 140 through one on the EDM wire 126 imprinted vibration 154 , preferably in the form of a standing wave, can be generated. Alternatively or additionally, the eroding wire can be used 126 , as in 4B shown, for example be deformed by squeezing or bending and for example by a periodic change or non-periodic, in particular stochastic, change 156 of its wire cross section. Alternatively or additionally, the eroding wire can be used 126 , how 4C shows, over at regular intervals or in irregular, especially in stochastic, layers of lacquer applied 158 which spark and thus the rate of removal of wire erosion at the cutting surface 120 each of the two component halves 116 , 118 can reduce. A combination with cyclically varying process parameters (eg current strength, wire speed, feed speed) can be used in particular to generate the structures. It is particularly advantageous if the frequency of the markings on the wire coincides at least approximately with the frequency of the variation of the process parameters or a multiple.

Alternatively or additionally, the eroding wire can be used 126 according to 4D at regular intervals or at irregular, especially at stochastic, intervals due to an alternating liquid dielectric 160 in which the wire erosion is carried out, which can also influence the spark formation and thus the material removal rate. For example, by changing a water level or by providing different layers of oil in the water or different layers of water in the oil, the cutting width of the erosion wire can be changed 126 can thus be varied over the height.

5 shows a further preferred embodiment for generating the plurality of markings 140 in the cut surfaces 120 the component halves 116 , 118 , with a variety of parallel holes 162 in the form of a hole pattern 164 such in the component 110 be attached to each of the holes 162 the component 110 essentially perpendicular to the intended cutting contour 114 penetrates, meaning that each of the holes 162 perpendicular or with a deviation of at most ± 15 °, preferably of at most ± 5 °, particularly preferably of at most ± 1 ° from the vertical arrangement with respect to the cutting contour 114 is arranged. The holes created in this way 162 are suitable as the markings 140 to avoid deformations in the cutting contour 114 make visible. In this preferred embodiment, the cut can thus 112 preferably done evenly and straight, so that the cutting contour 114 can be designed as a sectional plane. The hole pattern 164 can be present as a regular hole pattern or as an irregular, in particular stochastic, hole pattern, each of the holes 162 a conical or cylindrical removal of a material from the component 110 by means of a drill. There is preferably a distance 166 from two adjacent holes 162 by a factor 5 up to a factor 25th larger than a diameter 168 of the holes 162 . In this way, a sufficient number of markings can be made 140 achieve without drilling adjacent holes 162 could influence each other.

Deep hole drilling, hole eroding or laser drilling are particularly suitable as drilling methods. To shorten the process time, a tool is conceivable that can drill several holes at the same time. An electrode that can be used for hole eroding can preferably be insulated at the side; this allows the material removal to be adjusted during hole erosion and an expansion of the bore 162 be prevented. The electrode can be designed as a tube in order to ensure that an electrolyte is transported to the site to be processed. A surface 170 of the component 110 on which the bore 162 starts, can preferably be machined flat, for example by milling, which results in an essentially vertical course of the bore 162 can be facilitated. In addition, the planar surface thus provided 170 of the component 110 preferably parallel to the cutting contour present as the cutting plane 114 be designed.

According to step c), the cut surface is measured in this way 120 each of the two component halves 116 , 118 that during step c) a position of the majority of the markings 140 is determined in the component half, in particular in the form of a high-resolution image of the cut surfaces 120 each of the two component halves 116 , 118 , preferably with a resolution (pixel spacing) of at most 5 µm, preferably of at most 2 µm, in the lateral direction within the image. The image itself can, on the one hand, in particular provide information on the height of each pixel in relation to an arbitrarily defined reference height and, on the other hand, the position of the majority of the markings 140 in the respective cut surface 114 include. Photogrammetry can preferably be used as the imaging method; Interferometry, in particular white light interferometry; Computed tomography or a scanning technique. However, it is possible to use further imaging methods.

In the execution according to 5 can also be a spatial location of each of the holes drilled in the component 162 not only after step b), but preferably also before step b). The same imaging method can preferably be used for this. With the help of a numerical evaluation algorithm, edges of the holes can be identified 162 metrologically recorded and to the holes 162 belonging reference points 172 be formed. Based on the determined data of the initial state, how 6A schematically shows a bore angle α can be determined. This can be compared to a hole opening 174 in ellipse shape with a hole opening 176 ideally used in a circular shape to incline the hole 162 ascertain.

Alternatively or additionally, according to 6B the bore angle α over an offset of the reference points 172 of entrances to the holes 162 and from exits of the holes 162 with known component thickness 110 be determined. With the help of the known reference points 172 the entrances to the holes 162 and the outputs of the holes 162 theoretical reference points can be determined in the later section plane. After the separation process according to step b), the newly established reference points 172 determined. By comparing the reference points 172 Before and after the cutting process, the displacements in the cutting plane can be measured.

If the bore angle α deviates from 90 °, how 6C schematically shows the cutting width used in the cutting process 178 should preferably be taken into account as the reference points 172 otherwise can be shifted to each other. This can be done, for example, by applying half the cutting width 178 on both component halves 116 , 118 of the component 110 done, the reference points 172 then can be moved accordingly.

According to step d), a simulation is carried out during which the two component halves 116 , 118 on the cut surfaces 120 be put together. In this way the stress state in the component 110 determined, the two component halves 116 , 118 during step d) - in contrast to the prior art - on the majority of the markings 140 in the cut surfaces 120 be put together. Here, the evaluation of each individual cut surface 120 preferably point by point, especially in the case of discrete markings in the form of lines, lines, indentations, paragraphs or points. An adaptation of a two-dimensional compensation function to the cut surface 120 can, based on the measured positions of the markings 140 , preferably using a method known from the prior art, preferably using the least squares method. An FE model can now be developed on the basis of a cut surface determined in this way.

Alternatively, in a particularly preferred embodiment, the nodes of the FE network can be as precise as possible on the positions of the discrete markings recorded by measurement 140 which can have a positive effect in a simpler implementation of the simulation. There is a sinusoidal variation in the cutting gap 134 , the variation of the cutting gap 134 be taken into account by half a cutting width 178 can be applied on both sides. Alternatively, the nodes of the FE mesh can preferably be used with the discrete reference points in the simulation 172 of the holes 162 should match, with the hole pattern 164 can preferably be adapted to the FE mesh.

Furthermore, the recorded voltage curve can be optimized so that it over the cutting contour 114 is assumed to be as constant as possible, for example by allowing small deviations when contracting, in particular by means of a suitable numerical algorithm. A uniform course over the cutting contour can preferably be used for all tension components 114 are assumed, for which the relevant values on both sides of the cutting contour 114 should be almost identical.

Reference list

110

Component

112

cut

114

Cutting contour

116

Component half

118

Component half

120

Cutting surface

122

Separating device

124

Wire EDM machine

126

EDM wire

128

Kitchen sink

130

upper wire guide

132

Direction of movement

134

Cutting gap

136

lower wire guide

138

another coil

140

Markings

142

Lateral movement

144

sinusoidal movement

146

step-like movement

148

trapezoidal movement

150

triangular movement

152

Feed direction

154

vibration

156

Change in wire cross section

158

Paint layer

160

liquid dielectric

162

drilling

164

Hole pattern

166

distance

168

diameter

170

surface

172

Reference point

174

Hole opening in the shape of an ellipse

176

Hole opening in a circular shape

178

Cutting width

Claims (10)

Method for determining a stress state in a component (110) with the steps: a) providing a component (110); b) making a cut (112) through the component (110), whereby the component (110) is cut along a cutting contour (114) into two component halves (116, 118) such that each of the two component halves (116, 118) along the cutting contour (114) has a cutting surface (120); c) measuring the cut surface (120) of each of the two component halves (116, 118); d) performing a simulation during which the two component halves (116, 118) are joined together at the cut surfaces (120), as a result of which the stress state in the component (110) is determined, a plurality of prior to step b) or during step b) Markings (140) are introduced into the cut surface (120) of each of the two component halves (116, 118), a position of the plurality of markings (140) in the component half (116, 118) being determined during step c), and during Step d) the two component halves (116, 118) are joined together at the plurality of markings (140) in the cut surfaces (120). The method according to the preceding claim, wherein the plurality of markings (140) are introduced by changing a surface property of the cut surface (120) in the cut surface (120) of each of the two component halves (116, 118) during step b). Method according to one of the preceding claims, wherein the change in a surface property of the cut surface (120) takes place at regular intervals or at stochastic intervals. Method according to one of the preceding claims, wherein the cut (112) is made through the component during step b) by means of wire erosion, whereby the component (110) along the cut contour (114) by means of an erosion wire (126) into the two component halves (116 , 118), and the plurality of markings (140) are made in the cut surface (120) by varying the wire erosion. Method according to the preceding claim, wherein the wire erosion is varied in the direction of movement (132) of the erosion wire (126) and / or in the feed direction (152) of the erosion wire (126). Method according to the preceding claim, wherein the wire erosion is varied in the direction of movement (132) of the erosion wire (126) by at least one of the following first measures: Influencing a removal rate of the wire erosion at the cutting surface (120) of each of the two component halves (116, 118); - Executing a relative movement between the component (110) and the eroding wire (126) during the wire erosion. Method according to one of the two preceding claims, wherein the variation of the wire erosion in the feed direction (152) of the erosion wire (126) is carried out by at least one of the following second measures during the wire erosion: - applying vibrations (154) to the erosion wire (126); - deforming the erosion wire (126); - Applying at least one layer (158) to the erosion wire (126). Method according to one of the preceding claims, wherein the majority of the markings (140) are introduced into the component (110) in the form of a plurality of parallel bores (162) before step b), each of the bores (162) in this way in the component ( 110) is introduced in such a way that it penetrates the component (110) essentially perpendicular to the intended cutting contour (114). Method according to the preceding claim, wherein a spatial position of each of the bores (162) made in the component (110) is determined before step b) and after step b). Computer program which is set up to carry out steps of the method according to one of the preceding claims.

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