Method for determining minimum width and connection position of micro-connections and method for machining a workpiece

Abstract

The invention relates to a method for determining a minimum width (B MJ,min ) of a micro-connection (17) by means of which a workpiece part (14) is kept connected to a remaining workpiece (15) of a workpiece (8), in particular a sheet-like workpiece (8), during machining. In the method, the minimum width (B MJ,min ) of the micro-connection (17) is determined as a function of at least one machining parameter (p) which influences the relative orientation of the workpiece part (14) with respect to the remaining workpiece (15) during machining of the workpiece (8). The invention also relates to a method for determining a connection location (m) of such a micro-connection (17) and to a method for machining a workpiece (8), in particular a sheet-like workpiece (8).

Description

TECHNICAL FIELD

[0001] The invention relates to a method for determining a minimum width of a micro-connection, by which a workpiece part is kept connected to a remaining workpiece when machining a workpiece, in particular a sheet-like workpiece. The invention also relates to a method for determining a connection position of such a micro-connection and to a method for machining a workpiece, in particular a sheet-like workpiece, which comprises machining the workpiece with the formation of at least one micro-connection, by which a workpiece part is kept connected to a remaining workpiece. The micro-connection is a holding tab between the workpiece part and the remaining workpiece, which is sometimes also referred to as remaining grid in the following. The micro-connection is used, for example, mainly when laser cutting or punching a workpiece, in particular a sheet-like workpiece, in order to keep the workpiece part, which would otherwise separate, in the remaining grid without tilting and to prevent, for example, a collision between the machining head and the workpiece part during the workpiece machining in this way. Furthermore, the micro-connection also simplifies the automatic unloading of the workpiece part together with the remaining grid. BACKGROUND

[0002] The holding tab or micro-connection is produced by cutting or punching the outer contour of the workpiece part incompletely. The small holding tab, the so-called micro-connection, with a width of a few tenths of a millimeter to one millimeter is set manually by the programmer of the control program of the machining machine, for example a laser cutting machine, or by rules contained in the programming software. Along the outer contour of the workpiece, the size and position of the micro-connection must usually be determined by the programmer. In most cases, all micro-connections provided on the sheet-like workpiece have the same width, regardless of the process conditions, the workpiece part properties (weight, geometry), the material, etc.

[0003] This leads to the micro-connections on small workpiece parts often being too wide and thus making the removal of the small workpiece part from the remaining grid very difficult. Furthermore, the additional effort required to remove the micro-connections that are too wide is also very laborious. Generally speaking, the wider the micro-connection, the greater the additional effort required to remove the connection mark at the cutting or punching edge. Conversely, on large workpiece parts, the micro-connections set by the programmer can not be wide enough, so that the workpiece part cannot be reliably held in the remaining grid and thus can lead to a collision between the tilted workpiece part and the machining head.

[0004] It is disclosed by JPH0663659A that the optimum width of the micro-connection is calculated from the workpiece thickness, the length and physical properties of the workpiece material and the area of the severed workpiece part. It is disclosed by JPH0439706A that the optimum micro-connection width, which is related to the material and thickness of the workpiece, is automatically read from a parameter database. SUMMARY

[0005] It is the object of the present invention to provide a method for determining the minimum width of a micro-connection, the connection position or the starting position of a micro-connection, wherein the micro-connection has an optimum width, and a method for machining a workpiece.

[0006] According to the first aspect, this object is solved by a method of the type mentioned at the outset, in which the minimum width of the micro-connection is determined from at least one machining parameter, which influences the relative position of the workpiece portion with respect to the remaining workpiece during machining of the workpiece.

[0007] The inventors have realized that, in order to determine the optimum micro-connection width, not only the parameters or workpiece portion information of the workpiece portion, as in JPH 0663659 A, must be taken into account, but also the machining parameters of the process or machining method, with which the workpiece portion is formed, usually cut or punched, or manipulated, for example moved. The at least one machining parameter usually influences the relative position or the relative orientation of the workpiece portion with respect to the remaining workpiece during machining of the workpiece. If the width of the micro-connection is below the minimum permissible width, it is no longer possible to machine the workpiece in a process-reliable manner, because the workpiece portion, which is connected to the remaining workpiece portion by the micro-connection, can collide with components of the machining machine, for example the machining nozzle, or can jam with the remaining workpiece.

[0008] The machining parameters can be, for example, the cutting gas pressure acting on the workpiece portion during laser cutting, the acceleration and / or the static friction during the movement of the workpiece portion together with the remaining workpiece along the workpiece support, the vibrations during a combined punching / laser machining of the workpiece, etc.

[0009] The minimum width of the micro-connection is determined before machining of the workpiece. The at least one machining parameter influencing the relative position is stored, for example, in the programming system for creating the control program for machining the workpiece portion and is therefore known in advance, so that the minimum width of the micro-connection can be determined before machining of the workpiece.

[0010] In addition to the at least one machining parameter, the width of the micro-connection is also determined from workpiece information. The workpiece information can be the workpiece material, the workpiece physical properties, such as the modulus of elasticity and the yield limit of the material, the nesting of the plate-shaped workpiece by the workpiece portions to be formed during the separation machining, the workpiece portion information, etc. Examples of workpiece portion information are: the geometry of the workpiece portion, the weight of the workpiece portion, the orientation of the workpiece portion on the workpiece and with respect to the support sheet of the workpiece support (lying polygon), the acting gravitational force, etc.

[0011] It is possible that, by means of the workpiece information, the width of the micro- joint is calculated in a programming system for creating a control program for cutting the workpiece in dependence on the distance of the micro-joint from the center of gravity of the workpiece part, such that the micro-joint prevents the workpiece part from tilting with respect to the remaining workpiece due to the force of gravity. For this purpose, the moment of force of the workpiece part on the micro-joint cannot be so large as to exceed the yield limit of the micro-joint.

[0012] It can be taken into account in the calculation that, due to the force of the workpiece part, the micro-joint can be elastically and plastically deformed. The greater the width of the micro-joint, the smaller the tilting of the workpiece part will generally be. In the course of the tilting, the maximum allowed height of the workpiece part must be less than the distance between the machining nozzle of the laser cutting head and the workpiece in a machining machine in the form of a laser cutting machine, for example. In practice, this distance is generally in the range of values from 0.4 mm to 1 mm. From this maximum allowed height of the workpiece part and the geometry of the workpiece, the maximum allowed tilting angle a max of the workpiece part can be calculated. max From this maximum tilting angle a MJ the width B

[0013]

[0014] If the cut end of the outer contour of the workpiece part is at the micro-joint, i.e. the micro-joint is formed by cutting the (outer) contour incompletely to the end, then the above calculation is sufficient. In this case, the force of the cutting gas acting on the workpiece part at the site of the micro-joint by the gas pressure of the cutting gas coming out of the machining nozzle plays only a minor role at the cut end, since the workpiece part is held at this site by the micro-joint.

[0015] In a variant of the above method, the machining of the workpiece comprises a thermal cutting of the workpiece with a machining beam, in particular with a laser beam, wherein the minimum width of the at least one micro-joint is determined in dependence on a machining parameter in the form of a gas pressure of a cutting gas ejected from a machining nozzle acting on the workpiece part when the workpiece part is cut out of the remaining workpiece.

[0016] In this variant, the gas flow generally acts on the workpiece part along the outer contour at a cut-open position which is spaced apart from the micro-joint. The cut-open position is understood to be a position along the outer contour of the workpiece part at which the cut end is located. Upon reaching the cut-open position, further cutting along the outer contour of the workpiece part generally no longer takes place.

[0017] If the micro-connection is arranged on the outer contour at a location which does not coincide with the cut position / cutting end, the gas pressure of the cutting gas acts on the workpiece portion at the cut position at the moment when the outer contour closes at the end of the cutting. Depending on how the workpiece portion is arranged relative to the supporting workpiece carrier elements (carrier sheet, carrier slide,...), there can be regions on the outer contour on which the gas pressure of the cutting gas causes the workpiece portion to tilt at the cut position.

[0018] In addition to the cutting gas pressure acting on the workpiece portion in the cut position spaced apart from the micro-connection, it can also be necessary to take into account the cutting gas pressure acting on the cut workpiece portion in the positioning movement of the cutting head or in the cutting of a (near) adjacent contour, in particular in the case of a close nesting of the workpiece portions. Thus, the minimum width of the micro-connection can be determined in addition to or instead of the above-mentioned variants from the cutting gas pressure acting on the workpiece portion as a result of the positioning travel of the cutting head across the workpiece and / or from the cutting gas pressure acting on the workpiece portion as a result of the cutting of an adjacent contour, regardless of the positioning of the micro-connection (at the cutting end or at a location away from the cutting end).

[0019] In an extended embodiment, the minimum width of the micro-connection is determined at which the maximum height of the workpiece portion standing up from the remaining workpiece is not exceeded when the workpiece portion tilts relative to the remaining workpiece as a result of the effect of the gas pressure on the workpiece. In this case, the (minimum) width of the micro-connection is so great that the height of the tilted workpiece portion does not exceed a predetermined maximum height.

[0020] In an advantageous extended embodiment, the maximum height of standing up is not greater than the distance between the machining nozzle and the remaining workpiece, wherein this distance is preferably less than 2 mm, particularly preferably less than 1 mm. In this case, the minimum width of the micro-connection is determined so that a collision of the standing workpiece portion with the machining nozzle of the laser cutting head is prevented. The distance is usually determined between the end side of the machining nozzle and the remaining workpiece.

[0021] In another variant, the machining of the workpiece comprises a movement of the remaining workpiece together with the workpiece portion along a workpiece carrier, wherein the minimum width of the at least one micro-connection is determined in accordance with at least one machining parameter in the form of an acceleration of the remaining workpiece when moving in at least one movement direction. The acceleration along the respective movement direction usually corresponds to an axis parameter of a drive device of the machining machine which is configured for moving the remaining workpiece together with the workpiece portion in the respective axis direction or movement direction.

[0022] The workpiece support can have workpiece support elements, for example in the form of balls, brushes or the like, in order to reduce friction when the remaining workpiece and the workpiece portion connected by at least one micro-connection are moved along the workpiece support. Generally speaking, there are some areas along the workpiece support between the workpiece support elements in which the workpiece or the workpiece portion held by the micro-connection is not supported. When the workpiece held by the micro-connection is moved on the workpiece support, as in a sheet metal machine (such as a punch head or a punch-laser combination machine), gravity acts on the workpiece in the Z direction when the workpiece passes through the unsupported area of ​​the workpiece support. In addition, the workpiece portion bends around the micro-connection in the XY plane. Therefore, the minimum width of the micro-connection is also subject to the following condition, that is, the bending of the micro-connection cannot become so strong that the workpiece portion slides under or over the remaining part of the workpiece.

[0023] In another embodiment, a minimum width of the microjoint is determined at which the bending stress at the microjoint does not exceed a maximum bending stress when the workpiece portion moves together with the remaining workpiece. The value of the maximum bending stress is typically determined in such a way that the workpiece portion does not slide under or over the remaining workpiece when moving along the workpiece support.

[0024] Preferably, the maximum bending stress at the micro-joint is not greater than the yield strength of the workpiece material. In this application, the yield strength is understood to be the elongation limit R of 0.2%. p0.2 (elastic limit), since it (in contrast to the yield limit) can always be determined unambiguously from the nominal stress-total strain diagram. If the yield limit of the workpiece material is exceeded, the microjoint deforms plastically during bending, so that the workpiece portion is usually permanently held in an inclined orientation relative to the rest of the workpiece.

[0025] In a development of this variant, the minimum width of the microjoint consists of the minimum width of the microjoint without exceeding the maximum bending stress and a safety factor, wherein the safety factor preferably depends on the minimum width of the microjoint without exceeding the maximum bending stress. In this development, an empirically determined safety factor is added to the calculated minimum width of the microjoint, which takes into account the influence of external disturbance variables, such as vibrations during the stamping process, sagging of the workpiece part, and deflection of the workpiece part when passing through a support element (e.g., a ball or brush). In addition, the safety factor can take into account the notch effect that occurs at the connection point of the microjoint due to the sudden reduction in diameter, which reduces the maximum permissible bending stress. The safety factor preferably depends on the calculated microjoint width, that is, it is not an absolute value. In this way, the minimum microjoint width calculated for different workpiece parts varies relatively rather than absolutely, which prevents small workpieces from being connected by microjoints that are too large.

[0026] Another aspect of the present application relates to a method for determining a connection position of a micro-connection by which a workpiece part remains connected to a remaining workpiece, in particular a sheet-like workpiece, comprising determining a minimum width of the micro-connection at a plurality of different connection positions along an outer contour of the workpiece part, wherein the minimum width is determined according to the above described method, and selecting a connection position along the outer contour for machining the workpiece at which the minimum width of the micro-connection has been determined. In this case, the determination of the minimum width of the micro-connection is carried out for different connection positions along the outer contour in order to find out at which point or at which connection position the micro-connection will have the smallest width. This position can then be automatically selected as the connection position of the micro-connection in a programming system for creating a control program of a machining machine.

[0027] Another aspect of the present application relates to a method for machining a workpiece, in particular a sheet-like workpiece, in which at least one micro-connection is formed at a connection position along an outer contour of a workpiece part, which connection position has been determined according to the above described method for determining a connection position. As described above, one connection position is selected along the outer contour line at which the micro-connection has the smallest width.

[0028] The present application also relates to a computer program product which is configured to carry out all steps of the above described method when the computer program is run on a data processing device. The data processing device can in particular be a programming system, i.e. a computer for programming a control program for a digital control device of a machining machine, for example for cutting machining and / or for transporting a workpiece or a machine assembly with such a machining machine. If the computer program is run in a programming system, a machining program is generated which has in particular a sequence of (control) commands for machining a workpiece. The machining program generated in this way can then be executed by a digital control device of a machining machine or a machine assembly comprising the machining machine. BRIEF DESCRIPTION OF DRAWINGS

[0029] Further advantages of the present application can be derived from the description and the drawings. Likewise, the above mentioned features and further features to be listed can be used individually or in any combination. The shown and described embodiments are not to be understood as exhaustive, but rather have exemplary character for illustrating the present application.

[0030] In the drawings:

[0031] Figure 1 Schematic illustration of a machining machine in the form of a laser cutting machine for separating machining of a sheet-like workpiece;

[0032] Figure 2a,b shows a schematic diagram of a workpiece portion, which is connected to the remaining workpiece via a micro-joint, when tilting occurs due to the pressure of the cutting gas;

[0033] Figure 3 a schematic diagram showing a processing machine in the form of a combined laser and punch machine; and

[0034] Figure 4a ,b shows a diagram of a workpiece part as it moves along a workpiece support, the workpiece part being connected to the remaining workpiece via a micro-joint.

[0035] In the following description of the figures, the same reference numerals are used for identical or functionally identical components. DETAILED DESCRIPTION

[0036] Figure 1 A CO2 laser cutting machine 1 for laser cutting is shown, which comprises a CO2 laser resonator 2, a laser processing head 4, and a workpiece support 5. The laser beam 6 generated by the laser resonator 2 is guided by a beam guiding device 3 via a deflection mirror (not shown) to the laser processing head 4, where it is focused and oriented perpendicularly to a surface 8a of a workpiece 8 by means of a mirror (also not shown in the figure), i.e., the beam axis (optical axis) of the laser beam 6 extends perpendicularly to the workpiece 8.

[0037] To laser cut a workpiece 8, the laser beam 6 is first penetrated, that is, the workpiece 8 is melted or oxidized at one point, and the melt formed therein is blown out. The laser beam 6 is then moved over the workpiece 8, thereby creating a continuous cutting gap 9, along which the laser beam 6 cuts the workpiece 8.

[0038] Both the penetration and the laser cutting can be supported by the addition of gas. Oxygen, nitrogen, compressed air, and / or application-specific gases can be used as cutting gas 10. The gas ultimately used depends on the material to be cut and the quality requirements for the workpiece 8. The particles and gases produced can be sucked out of the suction chamber 12 with the help of a suction device 11. The schematically shown programmable numerical control device 13 controls all basic functions of the laser cutting machine 1, such as the movement of the laser processing head 4 when the processing program is executed on it.

[0039] Figure 2a ,b shows the separation process of the workpiece 8, more precisely the separation process of the rectangular workpiece part 14, which is separated from the remaining workpiece 15 (remaining grid) along the cutting contour 9. During the separation process, the workpiece part 14 remains connected to the remaining workpiece 15 at its outer contour P via the micro-connection 17. Figure 2aIn the example shown in FIG. 1 , the micro-joint 17 is located at the micro-joint position m along the outer contour P in the XY plane (the workpiece plane). This micro-joint position does not correspond to the cutting position f along the outer contour P, which forms the cutting end when the separation process is performed along the cutting contour 9. When the cutting contour 9 is closed at the cutting position f, the gas pressure p of the cutting gas 10 from the processing nozzle 18 of the laser cutting machine 1 acts on the workpiece portion 14 (see FIG. 1 ). Figure 2b ).

[0040] If the active, pressurized surface of the laser cutting head 4 or the cutting gas nozzle 18 (cf. Figure 2b ) is moved again to the region of the workpiece part 14 connected by the micro-connection 17, the micro-connection 17 should connect the workpiece part 14 exactly in this region. In this way, the force introduced by the gas pressure p has a minimal leverage effect on the micro-connection 17, and thus the generated stress is also minimal.

[0041] Depending on the arrangement of the workpiece part 14 relative to the supporting workpiece support element 5, there may be areas along the cutting contour 9 or along the outer contour P of the workpiece part 14 in which the gas pressure p of the cutting gas 10 causes the workpiece part 14 to tilt relative to the remaining workpiece 15 at the cutting position f.

[0042] In this case, the width B of the micro-connection 17 is MJ Cannot be less than the minimum width B MJ,min At this minimum width, the standing height of the inclined workpiece portion 14 reaches Figure 2b The predetermined maximum standing height h shown in max .exist Figure 2a In the example shown in b, the maximum standing height h max This corresponds to the distance A between the machining nozzle 18 and the remaining workpiece 15 or the workpiece 8. By determining the maximum rising height hmax in this way, it is possible to prevent the raised workpiece part 14 from colliding with the machining nozzle 18 of the laser cutting head 4. In the example shown, the distance A between the end side of the machining nozzle 18 and the upper side 8a of the workpiece 8 is less than approximately 2 mm, typically 1 mm or less.

[0043] exist Figure 2a In the example shown in b, the minimum micro-connection width B MJ,min The calculation or determination of the height (which should not be lowered in order to prevent the raised workpiece part 14 from colliding with the machining nozzle 18) is carried out as follows:

[0044] Calculate the set of all points given by the top of the bracket piece 5 in the XY plane as the bracket piece configuration S. These points are Figure 2aIn the figure, the outer contour P to be cut, the position m of the micro-connection and the cutting position f along the outer contour P to be cut of the workpiece 14 are also shown.

[0045] Figure 2a The shaded area I in the figure represents the set of intersections of the interior of the outer contour P and the bracket sheet configuration S, including the micro-joint locations m. The bracket polygon A, represented by the dashed line, represents the convex envelope of I. D represents the side of the bracket polygon A closest to the cutting location f. The distance between side D and the cutting location f is denoted by d. The distance between the position q located on the other side of D relative to the cutting location f and at the greatest distance from D is denoted by e. The force acting on the inner side of the outer contour P at the cutting location f is generated by the gas pressure p of the cutting gas 10 exiting the processing nozzle 18, and this force is denoted by F below.

[0046] The minimum width B of the micro-connection 17 can be determined based on the above variables. BJ,min If the above-mentioned force F caused by the gas pressure p acts on the cut workpiece part 14, the latter will tilt about the axis D.

[0047] In a first approximation, the inclination angle α of the workpiece part 14 about the axis D is proportional to F*d, so that, under the material-dependent constant c0, the maximum inclination angle α max W(P,S,f,m)=max(90;c0*F*d) degrees.

[0048] In addition, it was found in the experiment that 1 / α is related to the width B of the micro-connection 17 at the micro-connection position m. MJ Therefore, for the material-related constant c, the following applies:

[0049] W(P,S,f,m)=max(90;c*F*d / B MJ 3 ).

[0050] Among them B MJ represents the width of the micro-connection 17 at point m.

[0051] For a given inclination angle α, according to the present invention, it should be ensured that the standing height

[0052] H(P,α)=sin(α)e

[0053] Less than the predetermined value h allowed as the maximum tilt height max , that is, the following applies

[0054] H(P,α) <h max .

[0055] This condition is met if

[0056] sin(a)e<h max i.e.

[0057] (sin(W(P,S,p,m))e<h max i.e.

[0058] (sin(max(90;c*F*d / B MJ 3 ))e<h max .

[0059] i.e. if e<h max , the workpiece portion 14 can in principle be made too high, so that the resulting condition is:

[0060] sin(c*F*d / B MJ 3 )<h Max / e, which applies exactly if

[0061] c*F*d / B MJ 3 <arcsin(h Max / e), which applies exactly if

[0062]

[0063] The width B MJ of the micro-connections 17 is determined by this inequality MJ,min .

[0064] The minimum width B MJ,min of the micro-connections 17 determined in the above-described manner is used in a programming system for creating a control program for machining the workpiece 8 to generate a machining program which is run on the numerical control device 13 when machining the workpiece 8.

[0065] The minimum width B MJ,min of the micro-connections 17 can not only be determined as a function of the cutting gas pressure p as a machining parameter, but also as a function of other machining parameters which influence the relative orientation of the workpiece portion 14 and the remaining workpiece 15 when machining the workpiece 8. This is the case, for example, during the manipulation, or rather during the movement of the workpiece 8, which will be described below with reference to the combined laser and punching machine 20 shown in Figure 3 .

[0066] The machine tool 20 shown is designed as a laser and punching machine 220 and has as machining tools a conventional punching head 21 with a punching head 21a and a laser machining head 4, which machining tools perform separating machining on a plate-shaped workpiece 8 in the form of a sheet. During workpiece machining, the workpiece 8 to be machined is supported on a workpiece support 5 in the form of a machining table. By means of a conventional holding device 22 with a clamp 23 for fixedly holding the workpiece 8, the workpiece 8 can be moved in the X direction of the workpiece plane (XY plane of the XYZ coordinate system) relative to the punching head 21a and the laser machining head 4 by means of a conventional linear drive 23a, which is indicated by an arrow. The workpiece 8 can be moved in the Y direction of the workpiece plane in such a way that the workpiece support 5, which is supported on a base 24, is moved relative to the base 24 by means of a conventional linear drive device 23b, which is indicated by an arrow.

[0067] In this way, the workpiece 8 can be moved in the X and Y directions relative to the punching head 21a and the laser machining head 4, so that a respective region of the workpiece 8 to be machined can be positioned in the positionally fixed machining zone 25 of the punching head 21a or in the positionally fixed machining zone 26 of the laser machining head 4. In the machining zone 25 of the punching head 21, a (replaceable) die 27 is positioned, which has an opening 27a for engaging the (also replaceable) punching head 21a. Correspondingly, in the positionally fixed machining zone 26 of the laser machining head 4, a laser die 28 is provided, which serves as an opening boundary for a substantially circular suction opening 26a in the workpiece support 5. Here, a partial region of the workpiece support 5 in the X direction is positionally fixed and does not move in the Y direction relative to the base 24, on which partial region the machining zones 25, 26 are formed. Here, the laser machining head 4 can be moved in the X and Y directions, which is limited by the suction opening 26a. Figure 3 The machine tool 20 shown also has a control device 13 for controlling the linear drives 23a, 23b in the X and Y directions of the machine tool 20.

[0068] Figure 4a Fig. b shows a workpiece portion 14, which is held on the remaining workpiece 15 by a micro joint 17. When the workpiece portion 14 held by the micro joint 17 is moved on the workpiece support 5 or along the workpiece support in the X direction, the gravitational force F G acts on the workpiece portion 14 in the Z direction. In addition, the workpiece portion 14 is bent in the XY plane around the micro joint 17. The minimum width B BJ,min of the micro joint 17 is therefore also influenced by the condition that the bending does not become so strong that the workpiece portion 14 slips under or over the remaining workpiece 15.

[0069] Minimum micro joint width BBJ,min The calculation of is related to the position m of the micro-joint on the workpiece part 14:

[0070] Advantageously, the micro-joint 17 is arranged on the workpiece part 14 at a location (micro-joint location or joining location m) where the main inertia axis of the workpiece part 14 intersects the outer contour P (e.g. on the axis of symmetry of the workpiece part 14 - with the outer contour P). Figure 4a In this way, the micro-connection 17 is not affected by the gravity F G Additionally, if the micro-connection 17 is located at a position m along the outer contour P, which is obtained by projecting the center of gravity S of the workpiece part 14 into the direction of relative movement between the workpiece part 14 and the workpiece support 5, further bending loads due to acceleration forces and frictional forces in the second axial direction are eliminated.

[0071] Furthermore, the micro-connection 17 should be located at the intersection of the main inertia axis and the outer contour P (which is at the shortest distance from the center of gravity S of the workpiece 14 ) or in the axial direction (X or Y) where the maximum acceleration acts on the workpiece 14 .

[0072] The following assumptions apply to the minimum necessary micro-joint width B described below: BJ,min Design:

[0073] - the weight F of the workpiece part 14 G Acting in the Z direction, this gravity force acts on the center of mass (center of gravity S);

[0074] -In the X and Y directions, (axial) acceleration a X 、a Y and static friction acting on the micro-connection 17;

[0075] These forces act on the center of gravity S, whereby a smaller leverage (=center of gravity S-distance of connection position m of micro-joint 17) is advantageous. This determines the preferred connection position m of micro-joint 17 on workpiece 14.

[0076] - the micro-connection 17 is located on one of the main axes of inertia;

[0077] During laser cutting, the microjoints 17 are provided on the cut ends, so that the gas pressure plays a minor role and can be neglected.

[0078] In order to calculate the minimum necessary micro-joint width B under the above assumptions BJ,min , the following variables are required:

[0079] - Geometrical properties of the workpiece portion 14:

[0080] o center of gravity S of the workpiece part 14

[0081] o connection point m of the micro connection 17: preferably on one of the principal axes of inertia of the workpiece part 14, which corresponds to the respective axis of symmetry of the workpiece part 14, if any;

[0082] - material properties:

[0083] o sheet thickness d

[0084] o permissible stress B ges

[0085] o E* modulus

[0086] o density (weight or mass m)

[0087] o friction value or friction coefficient μ with the workpiece holder 5;

[0088] - spindle parameters of the machine tool 20:

[0089] o acceleration a in the X and Y directions X , a Y .

[0090] In the following, the micro connection 17 is assumed to be a flexural beam, on which the following moments act:

[0091] Moment in the direction of gravity (about the X axis):

[0092] M X = F G *h y , with F G = m*g

[0093] Moments in the X and Y directions (about the Z axis):

[0094] M z = (F ax +F R )*h y +(F ay +F R )*h x , with

[0095] F ax = m*a x and F ay = m*a y and F R = F G *μ,

[0096] with m = mass of the workpiece, g = acceleration due to gravity, h x= the distance from the center of gravity S to the connection point m of the micro-connection component 17 in the X direction, h y = the distance from the center of gravity S to the connection point m of the micro-connection component in the Y direction, a x = acceleration in the X direction, a y = acceleration in the Y direction, μ = coefficient of friction between the material of the workpiece part 14 and the material of the workpiece support 5 .

[0097] exist Figure 4a In the example shown in FIG. 2 (in which the workpiece portion 14 moves only in the X direction), the friction force FR in the Y direction is omitted. Since the micro-connection 17 is simplified to be located on one of the main inertia axes, the moment about the Y axis is omitted.

[0098] Determine the resistance torque W of the micro-connection 17 X 、W Y :

[0099] W x =I x / (d / 2), where Ix=(B MJ *d 3 ) / 12

[0100] W z =I z / (B MJ / 2), where I z =(d*B MJ 3 ) / 12

[0101] (d=workpiece thickness, B MJ = micro-connection width).

[0102] From this, the bending stress B at the micro-connection 17 can be calculated. ges :

[0103] B x =M x / W X

[0104] B z =M z / W z

[0105] B ges =B x +B z (Vector addition).

[0106] That is, the micro-connection width B BJ must be chosen so that the bending stress B ges The yield strength R of the material of the workpiece 8 that is currently being movedp0.2 is as large as:

[0107] B ges，max ≤ R p0，2

[0108] Then, for this predefined limit value R ges，max of the stress B p0，2 , the minimum micro joint width B MJ，minB is calculated as follows:

[0109]

[0110] where a = -R p，02 ;

[0111] and finally:

[0112] B BJ，min B = max{B MJ1 , B MJ2}.

[0113] The minimum micro joint width B BJ，min B is the maximum of the two values B MJ1 , B MJ2 , since the smaller of the two values is always negative due to the root used in the calculation.

[0114] An empirically determined safety factor c1, which takes into account the influence of external interference variables, such as, for example, a wobble during the punching process, a sag of the workpiece portion 14, a deflection of the workpiece portion 14 when passing over a support element, for example a ball or a brush, i.e. B BJ，min = B BJ，minB + c1, can be added to the calculated minimum micro joint width B BJ，minB .

[0115] In addition, by means of the safety factor c1, a notching effect, which leads to a reduction of the maximum permissible bending stress B ges，max , can be taken into account, which occurs at the joint location m of the micro joint 17 due to a sudden diameter reduction. Here, the safety factor c1 depends on the calculated micro joint width (c1(B BJ，minB )) in the ideal case, i.e. it is not an absolute value. In this way, the calculated minimum micro joint width BBJ, min for different workpiece portions 14 of the workpiece 4 is changed relatively and not absolutely, which prevents small workpiece portions 14 from being connected by micro joints 17 of too large a size.

[0116] Typically, the described determination of the minimum width B Figure 2a , b of the micro joint 17 is carried out not only in combination with the stress B Figure 4a , b but also in combination with the strain EBJ，min The method is carried out for a plurality of different connection positions m along the outer contour P of the workpiece portion 14. For the machining of the workpiece 8, the following connection positions m along the outer contour P are selected for which the minimum width B BJ，min of the micro-connection 17 has been determined. In the subsequent machining of the workpiece 8, the at least one micro-connection 17 by which the workpiece portion 14 remains connected to the remaining workpiece 15 is formed at the connection position m selected in the manner described above and has the minimum width B BJ,min .

[0117] The minimum width B BJ,min of the micro-connection 17 and the connection position m are used in a programming system to create a control program or to create control commands for machining the workpiece 8. The control program created in this way is processed by the control device 13 when machining the workpiece 8. The workpiece information and machining parameters for machining the workpiece 8, which are required to determine the minimum width B BJ,min of the micro-connection 17, are stored in the programming system, for example the cutting gas pressure p when cutting the workpiece 8 or the axis acceleration a X ,a Y It is understood that, in addition to or instead of the machining parameters mentioned above, other machining parameters can also be used to determine the minimum width B BJ,min of the micro-connection 17, which influence the relative position of the workpiece portion 14 connected to the remaining workpiece 15 by the micro-connection 17 with respect to the remaining workpiece 15 or with respect to the workpiece holder 5.

Claims

1. A method for determining the minimum width B of a micro-connection (17) MJ,min The method is characterized in that, when machining a workpiece (8), the workpiece portion (14) is connected to the remaining workpiece (15) of the workpiece (8) through the micro-connection portion. The minimum width B of the micro-connection (17) MJ,min The method is determined based on at least one machining parameter different from the workpiece information, which affects the relative orientation of the workpiece part (14) relative to the remaining workpiece (15) when machining the workpiece (8).

2. The method according to claim 1, wherein The machining of the workpiece (8) comprises thermally cutting the workpiece (8) with a machining beam, wherein the minimum width B of the micro-joint (17) is MJ,min The process is determined based on the following process parameters in the form of the gas pressure of the cutting gas (10) acting on the workpiece part (14) from the process nozzle (18) at the moment when the workpiece part (14) is cut out from the remaining workpiece (15).

3. The method according to claim 2, wherein: Determine the minimum width B of the micro-connection (17) MJ,min , at this minimum width, when the action of the gas pressure on the workpiece portion (14) causes the workpiece portion (14) to tilt relative to the remaining workpiece (15), the maximum standing height is not exceeded, and the workpiece portion (14) protrudes from the remaining workpiece (15) at this maximum standing height.

4. The method according to claim 3, wherein The maximum stand-up height is no greater than the distance between the machining nozzle (18) and the remaining workpiece (15), wherein the distance is less than 2 mm.

5. The method according to claim 1, wherein The machining of the workpiece (8) comprises the movement of the remaining workpiece (15) together with the workpiece portion (14) along the workpiece support (5), wherein the minimum width B of the micro-joint (17) is MJ,min The method is determined based on at least one machining parameter in the form of an acceleration of a workpiece part (14) while it is moved along at least one direction of movement.

6. The method according to claim 5, wherein: Determine the following minimum width B of the micro-connection (17) MJ,minB , at the minimum width B MJ,minB Under the present invention, when the workpiece portion (14) moves together with the remaining workpiece (15), the bending stress at the micro-connection (17) does not exceed the maximum bending stress.

7. The method according to claim 6, wherein: The maximum bending stress at the micro-connection portion (17) is not greater than the yield limit of the material of the workpiece (8).

8. The method according to claim 6 or 7, wherein: The minimum width B of the micro-connection (17) MJ,min The minimum width B of the micro-connection (17) without exceeding the maximum bending stress MJ,minB And it is composed of a safety factor, wherein the safety factor is related to the minimum width B of the micro-connection (17) without exceeding the maximum bending stress. MJ,min,B Related.

9. The method according to any one of claims 1 to 4, wherein: The workpiece (8) is plate-shaped; and / or, The minimum width B MJ,min The connection with the processing parameters is that if the width of the microconnection is below a minimum width, process-reliable processing of the workpiece with the processing parameters is no longer possible, because the workpiece part connected to the remaining workpiece part via the microconnection may collide with components of the processing machine or may get stuck with the remaining workpiece.

10. The method according to claim 2, wherein: The machining beam is a laser beam.

11. The method according to claim 4, wherein This distance is less than 1 mm.

12. A method for determining a connection position of a micro-connection (17), wherein a workpiece portion (14) is connected to a remaining workpiece (15) via the micro-connection during machining of a workpiece (8), the method comprising: The minimum width B of the micro-joint (17) is determined at a plurality of different joint positions along the outer contour of the workpiece part (14). MJ,min , wherein the minimum width is determined according to the method according to one of claims 1 to 11; and The following connection position is selected along the outer contour for processing the workpiece (8), for which the smallest minimum width B of the micro-connection (17) is determined. MJ,min .

13. A method for machining a workpiece (8), comprising: machining a workpiece (8) while forming at least one microjoint (17), by which the workpiece part (14) remains connected to the remaining workpiece (15), It is characterized in that The at least one micro-connection (17) is formed at a connection location along the outer contour of the workpiece part (14), the connection location being determined according to the method according to claim 12.

14. A computer program product configured to perform all the steps of the method according to any one of the preceding claims when the computer program is run on a data processing device.

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