DE102016211782A1 - Method for monitoring a thermal processing of a workpiece and monitoring device - Google Patents

Abstract

The invention relates to a method for monitoring and / or analyzing a thermal processing, in particular by laser beam welding, of a processing area (108a) of a workpiece (101) with a processing beam (102a), in particular a laser beam, comprising the method steps: a) detecting a two-dimensionally spatially resolved Surface temperature distribution TO in a predetermined area (103a) of the surface of the workpiece (101), b) Determining a predefined number n comprising set of location-independent coefficient values Cj, preferably with j = 1 .. n, from the two-dimensionally spatially resolved surface temperature distribution TO by means of a function f, which relates the spatially resolved surface temperature distribution TO according to To (XO) = f (XO; C1, .., Cj,..., Cn) at predefinable surface support points XO to the location-independent coefficient values Cj, c) determining a three-dimensional temperature distribution T at support point X within the workpiece (101) on the basis of the coefficient values Cj and the function f according to T (X) = f (X; C1, .., Cj, ..., Cn), The invention further relates to a monitoring device (10) for carrying out the method.

Description

The invention relates to a method for monitoring and / or analyzing a thermal processing, in particular by laser beam welding, a processing region of a workpiece.

So far, a machining quality of a thermally, in particular by laser beam welding, machined workpiece and in particular form and / or course of a weld produced usually destructive tested. For this purpose, cuts of the workpiece, for example, as a cross section of a weld made. This can therefore be done only by a time-consuming and costly destruction of the workpiece and also only random samples. In particular in order to examine the quality of the thermal processing, for example with regard to seam shapes and / or welding depths or to draw conclusions about possible seam defects, it is particularly desirable to be able to non-destructively check the quality of the thermal processing of each workpiece as possible.

From the DE 692 04 488 T2 is a method for controlling a surface treatment using a scan with a radiation beam, in particular a laser beam, known. In this method, temperatures inside a thermally treated workpiece are determined from knowledge of surface temperatures of the workpiece. However, the determination of the temperatures in depth is made on the basis of a one-dimensional approximation and detecting a temporal temperature history at a surface point of the workpiece. Three-dimensional volume effects are largely ignored. The validity and applicability of the statements obtained by this method is therefore limited.

However, in order to be able to determine or monitor welding depths, shapes of welding baths or of welds or the like, as accurate a knowledge as possible of the three-dimensional temperature distribution in the interior of a workpiece during and / or after a welding operation is desirable.

The invention is therefore based on the object to offer an improved method for monitoring or analysis of a thermal processing of a workpiece.

• a) Erfassen einer zweidimensional ortsaufgelösten Oberflächentemperaturverteilung T_O in einem vorgegebenen Bereich der Oberfläche des Werkstücks,
• b) Bestimmen eines eine vordefinierte Anzahl n umfassenden Satzes von ortsunabhängigen Koeffizientenwerten C_j, vorzugsweise mit j = 1 .. n, aus der zweidimensional ortsaufgelösten Oberflächentemperaturverteilung T_O mittels einer Funktion f, die die ortsaufgelöste Oberflächentemperaturverteilung T_O gemäß T_O(X_O) = f(X_O; C₁, .., C_j, ..., C_n) an vorgebbaren Oberflächenstützpunkten X_O in Beziehung setzt zu den ortsunabhängigen Koeffizientenwerten C_j,
• c) Ermitteln einer dreidimensionalen Temperaturverteilung T an Stützpunkten X innerhalb des Werkstücks anhand der Koeffizientenwerte C_j und der Funktion f gemäß T(X) = f(X; C₁, .., C_j, ..., C_n)

The object is achieved by a method for monitoring and / or analyzing a thermal processing, in particular by laser beam welding, of a processing area of a workpiece comprising the method steps:

• a) detecting a two-dimensionally spatially resolved surface temperature distribution T _O in a predetermined area of the surface of the workpiece,
• b) Determining a set of n-independent coefficient values C _j , preferably with j = 1... n, from the two-dimensionally spatially resolved surface temperature distribution T _O by means of a function f that satisfies the spatially resolved surface temperature distribution T _O according to T _O (X _O ) = f (X _O ; C ₁ , .., C _j , ..., C _n ) at predefinable surface support points X _O relates to the location-independent coefficient values C _j ,
• c) determining a three-dimensional temperature distribution T at interpolation points X within the workpiece on the basis of the coefficient values C _j and the function f according to T (X) = f (X; C ₁ , .., C _j , ..., C _n )

The method according to the invention thus provides that a two-dimensionally spatially resolved surface temperature distribution T _{o is} detected and from this a set of location-independent coefficient values C _{j is} determined. Based on the coefficient values C _j , a three-dimensional temperature distribution T within the workpiece is then determined.

To localize the surface support points X _O and / or the support points X in the workpiece, a Cartesian coordinate system with x, y, z can be used as coordinates, in which the x-axis points against a machining direction, the z-axis is perpendicular to the workpiece surface and the y-axis is perpendicular to the x and z axes. The origin of the coordinate system can be selected in the region of a point of impact of the machining beam on the workpiece surface. In particular, the origin of the coordinate system can be selected such that surface support points X _O correspond to coordinates with z = 0.

The surface support points X _O and / or the support points X can also be described by means of different coordinate systems, in particular in polar coordinate form.

According to the invention, it has been recognized that, under suitable circumstances, ie assuming a suitable model and with the validity of suitable process conditions (eg constant material parameters of the workpiece), the temperatures T _o determined spatially resolved at the surface of the workpiece two times with the aid of a Model resulting function f with sufficient accuracy close to a temperature distribution T within the workpiece.

The value range of the index j or the predefined number n can be selected, for example, as a function of a desired accuracy of the monitoring or the analysis and / or depending on a processing mode, for example through-welding or welding. It is understood that instead of an index j, it is also possible to provide a plurality of index levels, for example two index levels m, l or an index pair m, l formed therefrom. For this purpose, it can preferably be provided that indices of several index levels are each uniquely assignable to an index j, so that representations of parameters with multiple index levels can be converted to an equivalent representation of the parameters with an index level j.

The predefined number n can be selected in a process variant in which a through-welding is analyzed in the range of 6,000 to 6,500. For example, an n of about 6200 can be chosen.

In an alternative method variant, in which a weld is analyzed, the predefined number n in the range of 3000 to 3600, can be selected. For example, an n of about 3600 can be selected.

In the method according to the invention, the entire temperature field T forming in the workpiece is governed by a mathematical function dependent on the location X and the coefficient values C _j T (X) = f (X; C ₁ , ..., C _j , ..., C _n ) (1) represents approximately.

Preferably, the function f can still depend on further parameters, in particular an ambient temperature T _U.

Preferably, the function f is chosen so that equation (1) on the workpiece surface (ie in Cartesian coordinates at z = 0) is uniquely solvable after the coefficient values C _j , ie that either an analytically unique solution exists or there are numerical methods, leading to a unique set of coefficient values C _j .

The coefficient values C _j are defined location-independently or across locations. The surface temperature distribution T _O can thus be described by a combination of location-dependent and location-independent components. This allows a determination of the coefficient values C _j . The coefficient values C _j can then be set in a renewed relationship with the location-dependent components, and now points of intersection within the volume of the workpiece can be selected as locations X for determining the three-dimensional temperature distribution T within the volume of the workpiece. This makes it possible to determine, in particular calculate, a three-dimensional temperature distribution T for these interpolation points X within the workpiece, which in turn is dependent on location.

It is particularly preferred if the location-independent coefficient values C _{j are} determined such that the surface temperature distribution T _{O is} a linear combination of predefined location-dependent basic temperature fields T _j , preferably with j = 1... N, weighted with the coefficient values C _j and a calibration constant K according to FIG T _O (X _O ) = K + C ₁ T ₁ (X _O ) + ... + C _j T _j (X _O ) + ... + C _n T _n (X _o ) (2) can be determined.

Preferably, the calibration constant K can be selected as a function of, particularly preferably in accordance with, the ambient temperature T _U. For this purpose, advantageously, the ambient temperature T _U before, during and / or after the measurement of the spatially resolved temperature distribution T _{O are} measured and the calibration constants are assigned.

In alternative process variants, the calibration constant K can also be defined on the basis of a typical fixed value, for example in the range of 270-330 K.

By a linear combination of these basic temperature T _j fields by the coefficients values C _j thus an approximation of the real temperature field that is of Cartesian coordinates, for example, using y T may everywhere, x, z, in the workpiece in accordance with T (x, y, z) = T _U + C ₁ T ₁ (x, y, z) + ... + C _j T _j (x, y, z) + ... + C _n T _n (x , y, z) (3) and on the workpiece surface according to T _O (x, y) = T (x, y, 0) = T _U + C ₁ T ₁ (x, y, 0) + ... C _j T _j (x, y, 0) + ... + C _n T _n (x, y, 0) (3 ') respectively.

From the two-dimensional spatially resolved surface temperature distribution T _O measured at the ambient temperature T _U, the coefficient values C ₁ ,..., C _n can be determined with the aid of equation (3 '), with which subsequently the temperature distribution T within the workpiece can be calculated.

In particular, the basic temperature fields T _j can be predefined in a parameterized manner by properties of the workpiece, for example density, specific heat capacity, thermal conductivity, thickness, and / or by movement data of the workpiece and / or the machining beam or a machining head, in particular a heat source of the machine tool. Movement data can be, for example, the speed and / or direction of a relative movement of the workpiece to a heat source of a processing machine (or vice versa).

mit k = ρcν / 2λ (5) und den modifizierten Bessel-Funktionen

wobei r, φ, z den Koordinaten eines Stützpunktes X im Werkstück in Polarkoordinatenform (mit x = rcosφ und y = rsinφ), h der Dicke des Werkstücks, ρ seiner Dichte, λ seiner Wärmeleitfähigkeit und c seiner Wärmekapazität entsprechen. v kennzeichnet die Geschwindigkeit einer Relativbewegung zwischen Werkstück und Bearbeitungsmaschine (bzw. Bearbeitungsstrahl). s stellt die Integrationsvariable und ds das Differential von s im Integral dar. Es versteht sich, dass ohne den Rahmen der Erfindung zu verlassen in analoger Weise die Basistemperaturfelder B_m,l auch mittels in anderen Koordinatensystemen, insbesondere kartesischen Koordinatensystemen, dargestellten Stützpunkten bzw. Orten X formuliert sein können.The base temperature fields T _j can be defined in particular as base temperature fields B _{m, l} with the indices j, an unambiguously assignable index pairs m, l. Preferably, the base temperature fields B _{m, l may form} an orthogonal basis. The indices m can be chosen to be integers and the indices 1 to be non-negative integers. In particular, base temperature fields B _{m, l} can be defined according to the following equations:

With k = ρcν / 2λ (5) and the modified Bessel functions

where r, φ, z correspond to the coordinates of a support point X in the workpiece in polar coordinate form (with x = rcosφ and y = rsinφ), h the thickness of the workpiece, ρ its density, λ its thermal conductivity and c its heat capacity. v denotes the speed of a relative movement between the workpiece and the processing machine (or processing beam). s represents the integration variable and ds the differential of s in the integral. It is understood that without departing from the scope of the invention in an analogous manner, the base temperature fields B _{m, l} also by means of in other coordinate systems, in particular Cartesian coordinate systems, represented bases or locations X can be formulated.

Thus, for a set of vertices X _{O of} the surface of the workpiece at which a surface temperature T _O (X _O ) is detected and thus known, the equation: T _O (X _O ) = T _U + Σ _{m, 1} C _{m, 1} B _{m, 1} (X _O ) for all X _O (7) Preferably, the coefficient values C _{m, l} can be uniquely assigned to the coefficient values C _j via the one-to-one assignment of the indices j to index pairs m, l. It then only requires a technically feasible solution of a linear equation system for determining the coefficient values C _{m, l} or C _j .

In an alternative method variant, a number n ₂ of values of the indices m, l can be predefined and the resulting coefficients C _{m, l} based on Eq. (7). For this purpose, the number n _{2 can be selected} smaller than the number n in this process variant. Thus, as a rule, an overdetermined equation system results from Eq. (7), which can be approximately solved in this process variant by means of an approximation method, for example by means of the method of least squares.

For the analysis of a penetration weld the following 7 index values for m
m ε {-3; -2; -1; 0; 1; 2; 3}
and the following 5 index values for l
l ∈ {0; 1; 2; 3; 4}
to get voted. This results in a number n ₂ = 35 in this process variant.

In the alternative method variant, in which a weld-in is analyzed, the following 11 index values for m
m ε {-5; -4; -3; -2; -1; 0; 1; 2; 3; 4; 5}
and the following 4 index values for l
l ∈ {0; 1; 2; 3}
to get voted. This results in a number n ₂ = 44 in this alternative method variant.

Likewise, the three-dimensional temperature distribution T from the coefficient values C _{m, l} and the base temperature fields B _{m, l} at interpolation points X within the workpiece can then be determined directly as follows: T (X) = T _U + Σ _{m, 1} C _{m, 1} B _{m, 1} (X) (8)

Thus, information about a state inside the workpiece in the form of the three-dimensional temperature distribution T can be obtained and used for monitoring and / or analysis of the thermal processing.

• • Wärmetransport im Werkstück erfolgt nur durch Wärmeleitung.
• • Das Werkstück weist eine unendliche Länge und Breite aber eine endliche Dicke auf.
• • Die Materialparameter des Werkstücks sind nicht temperaturabhängig.
• • Die Werkstückober- und -unterseite ist gegenüber der Umgebung isoliert.
• • In weiter Entfernung zu der Wärmequelle stellt sich Umgebungstemperatur ein.

To determine the basis functions B _{m, l} , the following assumptions can preferably be made:

• • Heat transport in the workpiece only occurs through heat conduction.
• • The workpiece has an infinite length and width but a finite thickness.
• • The material parameters of the workpiece are not temperature dependent.
• • The upper and lower sides of the workpiece are insulated from the environment.
• • Ambient temperature is set far from the heat source.

It is advantageous that the accuracy achievable with these assumptions is typically sufficient for monitoring or analyzing a process with regard to the desired information, for example about the depth and shape of a weld seam or a formed seam.

A particularly accurate monitoring or analysis can be achieved by the according to Eq. (4) predefined basis temperature fields B _{m, l are} obtained when the surface temperature distribution T _O outside a predefined radius R around a center of an exposure zone and / or outside the weld pool is detected and / or evaluated. The action zone is understood to be an area on the surface of the workpiece or within a volume of the workpiece within which thermal power is introduced into the workpiece as a result of the machining. If only the area of the workpiece surface outside the molten bath is analyzed, the accuracy of the temperature field calculation can be improved since the convection occurring in the molten bath has no influence on the temperature field determination. If the analyzed area includes the molten bath (outside of the exposure zone), the accuracy of the evaluation may be reduced, however, conclusions can be drawn about the molten bath, eg. As the Schmelzbadgeometrie be enabled.

For this purpose, a radius R of a cylinder penetrating the workpiece in its thickness direction can be selected, which completely or at least largely encloses the zone of action.

In order to be able to determine the extent of a molten bath, the radius R can preferably be selected to be so small that it is expected that the molten bath extends to outside the cylinder.

Preferably, in this case analogous to the surface temperature distribution T _O lying outside the cylinder points X of the three-dimensional temperature distribution T are considered and their temperature can be monitored or analyzed with high precision. In terms of the polar coordinate form, r> R applies to these interpolation points if the cylinder center line runs through the origin of the polar coordinate system.

Advantageously, the surface temperature distribution T _{O can be} detected by first detecting an intensity distribution I _O of the heat radiation emanating from the surface of the workpiece and from this determining the surface temperature distribution T _O. For example, an intensity distribution I _O of the emitted infrared radiation from the workpiece or radiation of a defined wavelength band can be detected using an InGaAs camera. From the intensity distribution I _O obtained in this way, the surface temperature distribution T _O can then be determined on the basis of a suitable radiation model, for example of the Wien radiation model.

und geeignet kalibrierten Konstanten a und b eine zur Intensität I_n korrespondierende Oberflächentemperatur T_n ermittelt werden.For example, by means of the relationship

and suitably calibrated constants a and b, a surface temperature T _n corresponding to the intensity I _n are determined.

It is particularly preferred if the intensity distribution I _{O is} detected by first a plurality of temporally successive individual intensity distributions I _EO are detected and then an average image is determined from these. As a result, it is possible to determine an intensity distribution I _O or surface temperature distribution T _O that can be considered approximately as stationary.

In particularly advantageous embodiments of the invention can be provided that a shape, such as depth, width, area, and / or a course of a molten bath and / or a shape, such as depth, width and / or surface, and / or a course of a seam , in particular a weld, are determined from the three-dimensional temperature distribution T. For example, a shape and a course of a molten bath can be determined by determining the molten bath boundary from the three-dimensional temperature distribution T.

Thus, a shape and / or a course of a molten bath and / or a shape and / or a course of a seam on or within the workpiece can be determined and investigated without destruction.

It can also be provided that machining settings, in particular pulse energy, pulse duration, pulse frequency, power, focal point position and / or surface and / or machining speed of a thermal processing device, preferably a laser beam welding device, are selected and / or changed on the basis of the determined three-dimensional temperature distribution T. Thus, the information obtained can be used to further optimize the thermal processing of the workpiece during workpiece machining. Thus, the quality of the thermal processing can be improved easily. For example, this can ensure that a desired weld depth or a desired weld shape is achieved.

A monitoring of the thermal processing can be done in real time or simultaneously to the workpiece machining.

An analysis of the thermal processing, for example with regard to the achieved manufacturing quality, can be carried out by first carrying out the thermal processing at least in a section or area of the workpiece, during which surface temperature distributions T _{O are} determined and intermediately stored. After completion of the processing, the further steps of the method according to the invention can then be carried out. From the determined three-dimensional temperature distribution can then be determined, for example, the shape of the molten bath. A quality measure for evaluating the completed thermal processing can then be obtained, for example, from the comparison of this molten bath mold with a desired shape.

The scope of the invention also includes a monitoring device for carrying out the method according to the invention with a sensor, a movement device and an evaluation unit. The monitoring device is preferably set up by means of the sensor first to detect a two-dimensionally spatially resolved surface temperature distribution T _O in a predetermined region of the surface of the workpiece. It is further set up, by means of the evaluation unit, subsequently to determine a predefined number n of coefficient values C _j , preferably with j = 1 .. n, from the surface temperature distribution T _o and a three-dimensional temperature distribution T within the workpiece based on the coefficient values C _j to investigate. The sensor can be designed as an infrared camera, in particular as an InGaAs camera.

The evaluation unit may have at least one arithmetic unit which is set up to solve a non-linear and / or a linear system of equations and / or to determine an approximate solution for an over-determined system of equations and / or to determine a product sum. For this purpose, the evaluation unit can preferably have a computer unit. The arithmetic unit can preferably be designed as a computer program component. Then, in a particularly preferred manner, the arithmetic unit can be installed in the computer unit of the evaluation unit and, if necessary, be executed on the computer unit.

In a further preferred embodiment, the computer unit can also have a coefficient determination device with a computing unit which is set up to solve a linear or non-linear system of equations or to determine approximate solutions. The computer unit can also have a further computing unit which is set up to calculate a product sum.

The evaluation unit can also have a display unit for displaying monitoring and / or analysis results.

The method for monitoring a thermal processing and the monitoring device are suitable for a variety of types of thermal processing methods, in particular laser beam welding, electron beam welding, gas fusion welding, manual arc welding, inert gas welding, plasma welding, brazing, hardening and the like. In other words, the method can be used in a particularly advantageous manner for monitoring and / or analyzing thermal processes which introduce thermal power into the workpiece in a region on the surface of a workpiece or within a volume of the workpiece.

Also, the method and the monitoring device can be advantageously used for a variety of different materials or workpieces. Material-specific properties can be taken into account in the method by calibrating the coefficient values C _j and / or the base temperature fields T _j on the basis of a sample of the workpiece and / or by material-specific characteristics, in particular density, heat capacity and thermal conductivity of the material, and / or or workpiece-specific characteristics, in particular thickness of the workpiece, and / or machining-specific characteristics, in particular movement speed of the workpiece or welding speed, are taken into account. It is advantageous if the workpiece is approximately cuboid-shaped, band-shaped and / or sheet-shaped, ie has a small thickness in relation to its width and its length.

It is further understood that the term workpiece in the sense of the invention means any kind of part or combination of parts to be thermally processed. For example, two or more individual parts, which are laser-welded together, are to be understood as a workpiece to be thermally processed.

Further features and advantages of the invention will become apparent from the following description of an embodiment of the invention, with reference to the figures of the drawing showing essential to the invention details, and from the claims. The features shown there are not necessarily to scale and presented in such a way that the features of the invention can be made clearly visible. The various features may be implemented individually for themselves or for a plurality of combinations in variants of the invention.

In the schematic drawing embodiments of the invention are illustrated and explained in more detail in the following description.

Show it:

1 a processing arrangement with a monitoring device, by means of which the method according to the invention can be carried out;

2 a schematic representation of the steps of the method;

3 a schematic representation of a cross section of a thermally machined workpiece with determined shape of a molten bath.

The 1 shows an embodiment of a monitoring device 10 according to the invention. Of the 1 to be seen is a processing arrangement 100 , Using the editing arrangement 100 should a workpiece 101 in a editing area 108a thermally processed, in this case laser-welded.

In the embodiment shown, the height h of the workpiece 101 less than its width and length. The height h is preferably 0.1 to 10 mm, z. B. 2 mm. In particular, the workpiece 101 designed as a sheet.

The workpiece 101 is on a motor device 104 arranged. The movement device 104 moves or moves the workpiece 101 relative to a heat source, in the exemplary embodiment a laser beam 102 a laser 102 , opposite to a direction designated x at a speed v, in this case in the range of 0.5 to 10 m / min, z. B. 6 m / min.

The workpiece 101 is through the laser beam 102 processed with a laser power in the range of about 0.5 to 20 kW. The laser beam 102 in the area of an exposure zone 107 on the workpiece 101 ,

The point of impact of the laser beam 102 is as a center 107a the exposure zone 107 characterized. Furthermore, in the 1 a radius R of a circular cylinder extending in the z-direction 107b with one of the height h of the workpiece 101 corresponding height marks the impact zone 107 encloses.

Thus, the workpiece becomes 101 laser-welded in x-direction. It can be seen that already a part of a weld 108 of the workpiece 101 is made.

Of the 1 Furthermore, a direction indicated by y, which is perpendicular to the x-direction parallel to the plane of a surface of the workpiece 101 runs. Perpendicular to the x- and y-direction and in the beam direction of the laser beam 102 extending a direction marked z is further marked. The x, y, and z directions thus span a Cartesian coordinate system whose origin coincides with the center 107a coincides. The same is the case 1 to take a polar coordinate system r, φ, z with a pole corresponding to the origin and a polar axis corresponding to the x-direction.

A sensor 103 optically captures a given area 103a the laser 102 facing surface of the workpiece 101 , This is the sensor 103 formed as an InGaAs camera, the workpiece surface at an angle to the laser beam 102 detected. In alternative embodiments, it is provided that the sensor 103 as a camera, for example as an InGaAs camera, is formed, the workpiece surface coaxial with the laser beam 102 detected.

The camera or the sensor 103 detects in particular intensity distributions of the surface of the workpiece 101 radiated near infrared radiation. The default range 103a is selected in this embodiment so that infrared radiation or temperatures are absorbed, which also from the sensor 103 detectable, in this embodiment according to temperatures of at least about 1000 K, and yet below the melting point of the material of the workpiece 101 lie. In other words, the default range 103a chosen so that within the given range 103a the material of the workpiece 101 at least largely in a solid state and the local temperatures through the sensor 103 can be safely detected.

The sensor 103 provides a spatially resolved, in the x- and y-direction expanded mapping of these intensity distributions within the range 103a ,

The from the sensor 103 The information obtained reaches an evaluation unit 105 to which a display device 106 connected. In this embodiment, the evaluation unit 105 when Computer unit with a first and a second processing unit 105a . 105b formed, which in turn are each formed as computer program components.

The first arithmetic unit 105a is in particular designed to solve a multi-dimensional, linear system of equations. The second arithmetic unit 105b is specifically designed to form product totals.

The evaluation unit 105 is with an ambient temperature sensor 109 connected. The ambient temperature sensor 109 detects the ambient temperature T _U.

The evaluation unit 105 is also on the movement device 104 connected and receives from this information to the movement or displacement speed v. The evaluation unit 105 is set up, if necessary, to control the displacement speed v.

Furthermore, the evaluation unit 105 with the laser 102 connected. About this connection is the evaluation unit 105 capable of the laser 102 to control or work settings of the laser 102 to set up.

Of the 2 now the process of the invention can be seen in detail.

In a first step 201 becomes a two-dimensional spatially resolved surface temperature distribution T _{O of} the workpiece 101 ( 1 ) within the given range 103a at a predefined number n outside the circular cylinder 107b situated surface points X _o is determined.

For this purpose, first by means of the sensor 103 ( 1 ) each individual intensity distributions I _EO of the workpiece 101 emitted radiant infrared or thermal radiation while the workpiece 101 by means of the movement device 104 ( 1 ) is moved at the speed v against the x direction. Thus, the predetermined range 103a relative to the workpiece 101 displaced in the x direction and detect the individual intensity distributions I _EO each relative to the workpiece 101 shifted surface areas.

Each of the recorded individual intensity distributions I _EO represents a two-dimensionally spatially resolved image of the workpiece 101 outgoing thermal radiation. From the individual individual intensity distributions I _EO a mean value image of an intensity distribution I _{O is} obtained by averaging. Using Eqs. (9) then determines the evaluation unit 105 ( 1 ) from the intensity distribution I _O a two-dimensionally spatially resolved surface temperature distribution T _O for a predefined number n of surface support points X _O.

Due to the averaging, the surface temperature distribution T _O approximately corresponds to a temperature distribution of a stationary state of the workpiece 101 ,

In a second step 202 Now, a set of n total coefficient values C _j from the two-dimensionally spatially resolved surface temperature distribution T _o and the by means of the ambient temperature sensor 109 determined ambient temperature T _U determined.

By means of the first arithmetic unit 105a Now, employing the known surface temperature distribution T _O , the coordinates of the surface support points X _O expressed in polar coordinates become the parameters of the workpiece 101 , in particular its thickness h, thermal conductivity λ, heat capacity c and its speed of movement with magnitude v, and the ambient temperature T _U in the Eq. (7) formed and solved an n-dimensional system of linear equations. For this purpose, n values for m and l are predefined (for example based on test welds), where all m are chosen to be integers and all l to be nonnegative integers.

In one step 202 subsequent process step 203 is through the evaluation unit 105 using equation (8), a three-dimensional temperature distribution T within the volume of the workpiece 101 ( 1 ).

To determine the three-dimensional temperature distribution T forms the arithmetic unit 105b Product sums of the coefficient values C _{m, l} with the base temperature fields B _{m, l} corresponding to Eq. (8th).

In a further alternative method variant according to the invention, the evaluation unit subsequently provides 105 the determined temperature distribution T in perspective view or as a sectional image on the display device 106 ( 1 ).

In a further alternative method variant, a further step is also provided, in which the evaluation unit 105 from the temperature distribution T as a function of the melting temperature of the material of the workpiece 101 the boundary of the molten bath, in other words the shape of a molten bath determined.

In a further alternative method variant, an additional method step is provided in which the evaluation unit 105 based on the determined three-dimensional temperature distribution T a processing device, in this case the laser 102 , controls. For example, the evaluation unit 105 in this embodiment set up that when the workpiece 101 is to be welded through, but it is recognized on the basis of the determined shape of the molten bath that the molten bath is not the entire thickness h of the workpiece 101 engages, in other words, that the welding depth is less than the thickness h, the evaluation unit 105 the laser 102 so controls that its pulse energy increases. Alternatively, the evaluation unit can reduce the movement or displacement speed v.

The 3 now shows a section of a picture 300 of the display device 106 of the 1 , Evident is a schematic representation of a cross section of a workpiece 301 with thickness h '. In the picture 300 registered is an exposure zone 307 with her center 307a , A the action zone 307 enveloping cylinder 308 with radius R 'is in the picture 300 marked. Outside of this cylinder 308 a determined three-dimensional temperature distribution T is shown. In particular, border areas 303a . 303b a molten bath 302 marked. Thus, from such an illustration 300 non-destructive example, depth, width and surface of the molten bath or the weld formed and the expected quality of the weld in a simple and cost-effective monitoring.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 69204488 T2 [0003]

Claims (11)

Method for monitoring and / or analyzing thermal processing, in particular by laser beam welding, of a processing area ( 108a ) of a workpiece ( 101 ) with a processing beam ( 102 ), in particular a laser beam, comprising the method steps: a) detecting a two-dimensionally spatially resolved surface temperature distribution T _O within a predetermined range ( 103a ) of the surface of the workpiece ( 101 b) determining a set of n-independent coefficient values C _j , preferably with j = 1... n, from the two-dimensionally spatially resolved surface temperature distribution T _o by means of a function f which satisfies the spatially resolved surface temperature distribution T _o T _O (X _O ) = f (X _O ; C ₁ , .., C _j , ..., C _n ) at predeterminable surface support points X _O relates to the location-independent coefficient values C _j , c) determining a three-dimensional temperature distribution T at support points X within the workpiece ( 101 ) based on the coefficient values C _j and the function f according to T (X) = f (X; C ₁ , .., C _j , ..., C _n ). Method according to Claim 1, characterized in that the location-independent coefficient values C _{j are} determined such that the surface temperature distribution T _{O is} a linear combination of predefined, location-dependent base temperature fields T _j , preferably j = 1 .. n, weighted with the coefficient values C _j and a calibration constant K according to T _O (X _O ) = K + C ₁ T ₁ (X _O ) + ... + C _j T _j (X _O ) + ... + C _n T _n (X _O ) can be determined. A method according to claim 2, characterized in that the base temperature fields T _j by properties of the workpiece ( 101 ) and / or by movement data of the workpiece ( 101 ) and / or the processing beam ( 102 ) parameterized predefined. Method according to one of claims 2 or 3, characterized in that the base temperature fields T _{j are defined} as basic temperature fields B _{m, l} with the indices j a uniquely assignable index pairs m, l according to the following equation:

where r, φ, z are the coordinates of a support point X in the workpiece ( 101 ) in polar coordinate form, h the thickness of the workpiece ( 101 ), ρ the density of the workpiece ( 101 ), λ the thermal conductivity of the workpiece ( 101 ) and c the heat capacity of the workpiece ( 101 ) and v the speed of a relative movement between the workpiece ( 101 ) and the processing beam ( 102 ). Method according to one of the preceding claims, characterized in that the surface temperature distribution T _O outside a predefined radius R about a center of an action zone ( 107 ) of the processing beam ( 102 ) around and / or outside a molten pool is detected and / or evaluated. Method according to one of the preceding claims, characterized in that the surface temperature distribution T _{O is} detected by first an intensity distribution I _O of the surface of the workpiece ( 101 ) outgoing heat radiation is detected and from this the surface temperature distribution T _{O is} determined. Method according to one of the preceding claims, characterized in that the intensity distribution I _{O is} detected by first a plurality of temporally successive individual intensity distributions I _EO are detected and then an average image is determined from these. Method according to one of the preceding claims, characterized in that a shape and / or a course of a molten bath ( 302 ) and / or a shape and / or a course of a seam, in particular a weld, are determined from the three-dimensional temperature distribution T. Method according to one of the preceding claims, characterized in that processing settings, in particular pulse energy, pulse duration, pulse frequency, power, focus position and / or surface and / or processing speed of a thermal processing device, preferably a laser beam welding device, selected on the basis of the determined three-dimensional temperature distribution T and / or be changed. Monitoring device for carrying out the method according to one of the preceding claims for monitoring and / or analyzing a thermal processing of a workpiece ( 101 ) with a sensor ( 103 ), a movement device ( 104 ) and an evaluation unit ( 105 ), the monitoring device ( 10 ) is set up by means of the sensor ( 103 ) First, a two-dimensional spatially resolved surface temperature distribution T _O in a predetermined range ( 103a ) of the surface of the workpiece ( 101 ), and wherein the monitoring device ( 10 ) is set up, by means of the evaluation unit ( 105 ) then to determine a predefined number n comprising set of location-independent coefficient values C _j , preferably with j = 1... n, from the surface temperature distribution T _O and a three-dimensional temperature distribution T within the workpiece ( 101 ) based on the coefficient values C _j . Monitoring device according to claim 10, characterized in that the evaluation unit ( 105 ) at least one arithmetic unit ( 105a . 105b ), which is set up to solve a non-linear and / or a linear equation system and / or to determine an approximate solution for an over-determined system of equations and / or to determine a product sum.

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