DE102010022133A1 - Method for simulative representation of draw tool in automobile industry to manufacture body components, involves repeating displacement determination and displacement steps until parameter characterizing uniformity exceeds preset value - Google Patents

Abstract

The method involves describing geometry of an upper part (3) and a lower part (2) by a network of nodes. Pressure distribution is simulated on tool surfaces (9, 10) of the parts. Displacement of the nodes of the parts is determined based on a displacement function when the simulated pressure exceeds a preset value. The nodes are displaced around a determined value for obtaining a new network of nodes for the parts. A displacement determination step and a displacement step are repeated until a parameter characterizing uniformity of the pressure distribution exceeds another preset value. The upper part comprises a metal sheet holder (5) and a stamper (6). An independent claim is also included for a computer program product comprising a set of instructions for executing a method for simulative representation of a draw tool.

Description

The invention relates to a method for the simulative imaging of a drawing tool with a tool upper part and a lower tool part. It further relates to the use of such a method in the manufacture of a drawing tool.

Such a drawing tool is used for example in the automotive industry for the production of body parts. Typically, the tool upper part comprises a blank holder and a punch, while the lower die part has a die.

In the production of such drawing tools, a raw form is first milled in an NC (Numerical Control) process and subsequently reworked. Such a method is for example from the DE 10 2006 001 712 A1 known.

For post-inking processes are known in which a coated with Tuschierfarbe sheet metal part is inserted into the drawing tool and subjected to a pressing operation. Subsequently, the upper tool part and / or the lower tool part is reworked at the points at which a lack of spiked ink on the sheet indicates a high pressure. In this case, a temporally and locally as even as possible pressure distribution on the tool surfaces is sought, to which usually several Tuschierdurchgänge are necessary. In addition, the Tuschieren is performed for different strokes of the punch.

Increasingly, simulations in the production of drawing tools also play a role, with post-processing by means of inking or other finishing methods hardly being able to be dispensed with so far. One of the problems with simulations is that elastic properties of the materials used are not taken into account in a realistic manner.

The object of the invention is to provide a method for the simulative imaging of a drawing tool, which allows the most realistic possible description of the tool.

Next, a method for producing a drawing tool is to be specified, which is particularly economical and requires no or no costly reworking and at the same time provides a uniform pressure distribution on the tool surfaces.

According to the invention, this object is achieved with the subject matter of the independent patent claim. Advantageous developments of the invention are the subject of the dependent claims.

• a) elektronische Beschreibung der Geometrie des Oberteils und des Unterteils durch jeweils ein Netz aus Knoten;
• b) Simulation einer Druckverteilung auf der Werkzeugfläche des Oberteils und/oder des Unterteils;
• c) Ermittlung einer Verschiebung von Knoten des Oberteils und/oder des Unterteils, für die der simulierte Druck einen vorgegebenen ersten Wert übersteigt, anhand einer Verschiebungsfunktion;
• d) Verschiebung dieser Knoten um den ermittelten Wert, um ein neues Netz von Knoten für das Oberteil und/oder das Unterteil zu erhalten.

A method according to the invention for the simulative imaging of a drawing tool with a top part and a bottom part comprises the following steps:

• a) electronic description of the geometry of the upper part and the lower part by a respective network of nodes;
• b) simulation of a pressure distribution on the tool surface of the upper part and / or of the lower part;
• c) determining a shift of nodes of the upper part and / or the lower part, for which the simulated pressure exceeds a predetermined first value, by means of a shift function;
• d) shifting these nodes by the determined value in order to obtain a new network of nodes for the upper part and / or the lower part.

The steps b) to d) are repeated in a loop until a magnitude characterizing the uniformity of the pressure distribution on the tool surface of the upper part and / or the lower part exceeds a predetermined second value.

A variable characterizing the uniformity of the pressure distribution on the tool surface of the upper part and / or of the lower part is here and hereinafter understood to be a variable whose value is a measure of the uniformity of the pressure distribution. The concrete choice of this size depends on practical considerations, but also on the intended use of the tool. For example, the magnitude may be a sum of the weighted deviations from an average pressure. However, if extreme pressure spikes are to be prevented in particular, the size can, for example, also be the sum of those nodes with a pressure which exceeds a minimum value. In doing so, smaller deviations from the average value would be neglected.

According to an idea on which the invention is based, a simulation of the drawing tool can be improved by simulating the known spotting method with several iterative passes in the simulation, wherein elastic properties of the materials can be taken into account during the deformation of the material.

In the simulation, unlike the conventional spotting, it is not necessary to perform spotting at different strokes, since in the simulation it is possible to obtain the maximum values of, for example, the pressure for each node over the entire stroke.

The method has the advantage that a simulation of the drawing tool can be carried out very accurately and realistically, so that the new network of nodes obtained at the end of the loop can serve as the basis for an NC process for producing or reworking the tool. If the simulation considers the press and tool deflection, the quality of the simulation can be improved.

The invention relates in particular, but not exclusively, to drawing tools whose upper part comprises a blank holder and a punch and the lower part of which comprises a die.

The method of simulatively imaging a pull tool can be used in the manufacture of a pull tool.

In one embodiment, the new network of nodes for the top and / or bottom is used to create an NC program, and the tool is made by an NC process. In this case, it may be advantageous or necessary to specify a correction factor that takes into account the properties of the contact on the tool surfaces. Namely, in the simulation, such contacts are described with various contact types that do not correspond to all aspects of physical reality. If necessary, this must be taken into account when machining or manufacturing the tool in an NC procedure.

Alternatively, the method can also be used only for post-processing, so that the new network of nodes for the upper part and / or the lower part is used to create an NC program and the tool is reworked by means of an NC method.

In one embodiment, the predetermined first value of the pressure occurring in the simulation on average at the nodes of the upper part and / or the lower part. In this embodiment, therefore, only those nodes are shifted, where there is an above-average contact pressure. In this way, a more even pressure distribution is achieved by repeating the process.

Advantageously, in the simulation of the pressure distribution, a pressure variable is determined for each node, wherein as the pressure variable, for example, the maximum pressure occurring over a predetermined time interval can be used.

In this procedure, for example, the maximum pressure occurring at a node over the entire stroke is used as the pressure variable.

In one embodiment of the method, a shift is determined only for those nodes of the upper part and / or the lower part for which a difference between the upper-level pressure variable and the lower-level pressure variable is not more than a predetermined third value, the predetermined third For example, the value may be 60% of the minimum of the print variable for the top and the print variable for the bottom.

In this embodiment, it is considered that a high pressure occurring only on one side of the sheet is an indication of an entangling fold or shaft. Namely, in such a case, a high pressure occurs locally on one side of the sheet, while a low pressure is observed on the other side. In the method according to the embodiment of the invention, therefore, it is first checked whether there is a strongly deviating pressure on the other side of the sheet, that is to say for the corresponding knot on the other tool part. Only if this is not the case, this node is moved. Otherwise it gets the value zero.

In one embodiment of the method, to determine the displacement of nodes of the upper part and / or of the lower part, at least for those nodes for which the pressure variable exceeds the predetermined third value, a new pressure variable is determined, the new pressure variable being the maximum from the pressure variable for the Upper part and the pressure variable for the lower part is used. However, it would also be conceivable, for example, to choose the average of the two pressure variables for upper part and lower part as the new pressure variable.

Advantageously, the displacement function takes into account an elasticity of the material used. The shift function can be derived from the elasticity theory as follows:
Out E = σ / ε. with ε = Δt / t and p = σ, where E is the modulus of elasticity, σ is the
Stress, ε the strain, t a distance, Δt the displacement and p mean the contact pressure prevailing at the node, is given by Δt = p · t / E a shift proportional to the pressure. With a sheet thickness of 1 mm, there is an increase in the displacement function of 4.76 10 ^-6 mm ³ / N.

However, typically in the simulation, the contact stiffness of the sheet does not match the modulus of elasticity. It depends on the software and the contact algorithm. The shift function is therefore advantageously calibrated, for which an invoice is performed on a simple model. In the model, a load is applied via a ramp function to a simple sheet metal on the upper tool part in each case. Subsequently, the displacement of the nodes of the tool shell is applied above the pressure or a contact force. The calibration for the shift function then results from the slope of the calibration curve.

Since a thickness of 1 mm was assumed for the calibration, the gradients for other sheet thicknesses t must be determined using the following formula:

Since not all nodes are to be displaced by means of the shift function, but only those whose pressure variable is above the average value, the calibration curve is shifted along the pressure axis by the average value p _average . For the calibration curve thus results y = m _t * p + b, assuming from the condition x = p _average for y = 0 b = -m _t · P _average receives.

This results in the shift function s = f (p) = MIN [0; m _t · (p - p _average )] ·

According to one aspect of the invention, a computer program product for carrying out the method is provided when the computer program is executed on a computer unit or a control unit.

Embodiments of the invention are explained below with reference to the accompanying figures.

1 schematically shows a sectional view of a drawing tool;

2 schematically shows a flow of the method according to an embodiment of the invention;

3 shows a diagram for the distribution of the pressure after different numbers of iterations;

4 shows a simulation of the pressure distribution on the blank holder before the first iteration;

5 shows a simulation of the pressure distribution on the blank holder after the first iteration and

6 shows a simulation of the pressure distribution on the blank holder after the fourth iteration.

The same parts are provided in all figures with the same reference numerals.

1 schematically shows a sectional view of a drawing tool 1 with a lower part 2 and a top 3 , The drawing tool 1 is designed for example for the production of body parts.

The lower part 2 includes a die 4 while the top part 3 a sheet holder 5 and a stamp 6 includes. For deep drawing is a sheet 8th in a recording 7 held and the stamp 6 pressed down, leaving the sheet 8th is deformed.

During this process, the blank holder fulfills 5 the function of a hold-down and exerts as uniform as possible pressure on the top of the sheet 8th on. With the sheet 8th comes the tool area 9 the sheet holder and the tool surface 10 the die in contact.

In order to ensure a high quality of the drawing result, a uniform as possible pressure distribution on the tool surfaces 9 and 10 sought, by the most accurate shape of the tool surfaces 9 and 10 must be ensured.

2 schematically shows a sequence of the method according to an embodiment of the invention. As an input into the simulation, in the first illustrated step, an electronic description of the tool geometry is provided by a respective network of nodes. Based on this description, a forming process in the drawing tool 1 simulated.

The result of this simulation is the pressure distribution on the tool surfaces 9 and 10 of the drawing tool 1 in which the maximum pressure measured at the respective node and measured during the entire deformation is used as the pressure variable for this pressure distribution.

It is checked whether there is already a sufficiently uniform pressure distribution. If so, the process is ended.

If not, then in a next step for all nodes, where between the pressure on the matrix 4 and the pressure on the blank holder 5 There is a maximum difference of 60%, a new pressure variable is generated, whereby the new pressure variable is the larger of the two pressure variables on the tool surfaces 9 and 10 is used. All other nodes receive the value zero.

In a next step is a shift of nodes of the shell 3 and / or the lower part 2 determined by a shift function. However, only those nodes are moved where the simulation has produced an above-average pressure.

The shift function takes into account peculiarities of the simulation software used by a calibration.

Finally, the respective nodes are shifted by the determined value to a new network of nodes for the top 3 and / or the lower part 2 to obtain.

At the new network of nodes, the simulation of the pressure distribution is carried out again.

3 shows by way of example a diagram for distributing the pressure after different numbers of iterations in the method according to 2 in the manner of a histogram.

The curve A indicates the number of elements or nodes in each pressure class before the first iteration, that is, on the still unchanged drawing tool 1 ,

Curve B shows the number of elements or nodes in each pressure class after the first iteration, curve C after the fourth iteration and curve D after the seventh iteration.

From the diagram in 3 It can be seen that as the number of iterations increases, the number of high pressure nodes decreases. After four or seven iterations, almost all nodes have a relatively low pressure below 5 N / mm ² . The pressure distribution has become more uniform.

4 shows an example of a simulation of the pressure distribution on the blank holder 5 before the first iteration.

In the simulation, two areas occur in which particularly high pressures occur, namely the elongated area F ₁ and the less extensive area F ₂ .

5 shows the simulation of the pressure distribution on the blank holder after the first iteration. After the first iteration, the pressure conditions have changed, especially in the region F ₁ . The high pressures in this area have almost completely disappeared and are still present only in the narrower subarea F ₁ '.

6 shows the simulation of the pressure distribution on the blank holder after the fourth iteration. After the fourth iteration, the pressure distribution is significantly more uniform both in the region F ₁ and in the region F ₂ . Large areas with particularly high pressures are no longer available.

LIST OF REFERENCE NUMBERS

1

drawing tool

2

lower part

3

top

4

die

5

blankholder

6

stamp

7

Workpiece holder

8th

sheet

9

tool face

10

tool face

A

Curve

B

Curve

C

Curve

D

Curve

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102006001712 A1 [0003]

Claims (13)

Method for Simulatively Depicting a Drawing Tool ( 1 ) with a top ( 3 ) and a lower part ( 2 ), the method comprising the following steps: a) electronic description of the geometry of the upper part ( 3 ) and / or the lower part ( 2 ) each through a network of nodes; b) Simulation of a pressure distribution on the tool surface ( 9 . 10 ) of the upper part ( 3 ) and / or the lower part ( 2 ); c) determination of a displacement of nodes of the upper part ( 3 ) and / or the lower part ( 2 ) for which the simulated pressure exceeds a predetermined first value, based on a shift function; d) shifting these nodes by the determined value to a new network of nodes for the upper part ( 3 ) and / or the lower part ( 2 ) to obtain; wherein steps b) to d) are carried out repeatedly until the uniformity of the pressure distribution on the tool surface ( 9 . 10 ) of the upper part ( 3 ) and / or the lower part ( 2 ) characterizing size exceeds a predetermined second value. The method according to claim 1, wherein the predetermined first value of the one in the simulation averages to the node of the upper part ( 3 ) and / or the lower part ( 2 ) is occurring pressure. The method of claim 1 or 2, wherein in the simulation of the pressure distribution for each node, a pressure variable is determined. Method according to Claim 3, wherein the maximum pressure which occurs over a predefined time interval is used as the pressure variable. Method according to claim 3 or 4, wherein only for those nodes of the upper part ( 3 ) and / or the lower part ( 2 ) a shift is determined for which a difference between the pressure variable for the upper part ( 3 ) and the pressure variable for the lower part ( 2 ) is not more than a predetermined third value. Method according to claim 5, wherein for determining the displacement of nodes of the upper part ( 3 ) and / or the lower part ( 2 ) is determined at least for those nodes for which the pressure variable exceeds the predetermined third value, a new pressure variable, wherein as a new pressure variable, the maximum from the pressure variable for the upper part ( 3 ) and the pressure variable for the lower part ( 2 ) is used. The method of claim 5 or 6, wherein the predetermined third value is 60% of the minimum of the print variable for the top ( 3 ) and the pressure variable for the lower part ( 2 ) is. Method according to one of claims 1 to 7, wherein the displacement function takes into account an elasticity of the material used. Method according to one of claims 1 to 8, wherein the upper part ( 3 ) a blank holder ( 5 ) and a stamp ( 6 ) and the lower part ( 2 ) a die ( 4 ). Use of the method according to one of claims 1 to 9 in a method for producing a drawing tool ( 1 ) with a top ( 3 ) and a lower part ( 2 ). Use according to claim 10, wherein the new network of nodes for the top ( 3 ) and / or the lower part ( 2 ) used to create an NC program and the drawing tool ( 1 ) is produced by means of an NC process. Use according to claim 10, wherein the new network of nodes for the top ( 3 ) and / or the lower part ( 2 ) used to create an NC program and the drawing tool ( 1 ) is reworked by means of an NC method. Computer program product for carrying out the method according to one of claims 1 to 9, when the computer program is executed on a computer unit or a control unit.

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