EP4217130A1

EP4217130A1 - Method for modelling the behaviour of a circular rolling mill

Info

Publication number: EP4217130A1
Application number: EP21790945.6A
Authority: EP
Inventors: Edouard Frédéric Christian Claude MARCHAL; Julien Jean Edmond SCHWARTZ; Patrice André Modeste LASNE
Original assignee: Safran Aircraft Engines SAS
Current assignee: Safran Aircraft Engines SAS
Priority date: 2020-09-25
Filing date: 2021-09-20
Publication date: 2023-08-02
Also published as: US20230372988A1; FR3114524B1; CN116209531A; FR3114524A1; WO2022064127A1

Abstract

The invention relates to a method for modelling the behaviour of a circular rolling mill (1) intended for rolling a cylindrical component on the basis of a setpoint, the circular rolling mill comprising at least one tapered roller (3) configured to effect a translational movement in a first direction (Y), and a mandrel (2), configured to effect a translational movement in a second direction (X), the setpoint comprising a setpoint for the rate of increase of an outside diameter of said cylindrical component as a function of said external diameter, and a setpoint for the height of the cylindrical component in the first direction as a function of a thickness of the cylindrical component in the second direction.

Description

DESCRIPTION

TITLE: Process for modeling the behavior of a circular rolling mill

FIELD OF THE INVENTION

The present invention relates to the field of modeling forging processes, and in particular the modeling of circular rolling processes.

STATE OF THE ART

The modeling of forging processes today represents a major industrial challenge because it makes it possible to design new ranges of forging or to optimize existing ranges. A range of forging is the set of shaping operations allowing, using specific tools, to evolve a piece until obtaining, without defect, a raw part of the desired shape. A reliable and realistic modeling of all of these operations, and in particular of the behavior of the tools and the billet, makes it possible to reduce the design time of a new range of forges, since this also makes it possible to reduce the number of parts. tests to be produced to validate the new range.

Forging processes with a hydraulic press or more generally vertical forging machines are generally easy to model because the principle of controlling the press is simple. Indeed, there is only a translational movement of the press during forging. However, these forging processes are not very suitable for producing crowns or rings without welding, for example. In order to allow optimal use of the material, a circular rolling process is therefore used to produce such parts.

In the case of circular rolling, the modeling of the behavior of the tools is complicated to implement, because it is necessary to take into account in a synchronized way the simultaneous movements of translation and rotation of different tools. Similarly, the movements of the different tools lead to several simultaneous changes in the parameters of the workpiece, which must be mastered. As a reminder, the principle of a circular rolling process is generally to reduce the section and the height of the billet to increase its diameter, in a controlled manner.

To model this type of process, it is necessary to control the movement of all the tools making up the circular rolling mill. In general, the commands for the tools are given as input to a rolling mill control system by an operator, and depend on the part to be rolled. When the operator wishes to roll a new part, he must first determine the input data, which are not only the final dimensions of the part to be obtained, but the joint evolution of these dimensions.

The rolling process can be modeled numerically by finite element calculations that do not take into account the adaptive operation of the rolling mill tools managed by the control system. In this case, it is generally necessary to machine at least one part to control the quality of the forging range and to recover acquisition data, in particular the tool displacement data and the force data exerted by the tools. during the rolling of the part, to integrate them into the modeling of the rolling process.

However, this practice has several limitations. On the one hand, it is necessary to produce a part to carry out a modelling, which leads to a loss of time and a significant cost. On the other hand, each modeling carried out is relevant only with respect to a particular shape of part and a particular tool, and it is therefore impossible to predict the behavior of the different tools if the roughing of the cylindrical part to be made is different. Finally, such models are complicated to put into data, because there is a need to rework the acquisitions.

There are finite element calculation models taking into account the adaptive operation of the rolling mill tools managed by the control system.

To date, there are machine control models integrated into calculation codes such as Simufact. However, the models used do not take into account the mechanical aspects of the circular rolling mill 1 . Modeling predictions are therefore not very precise, and it is necessary to forge real parts to validate new forging ranges. Typically, existing models can greatly underestimate the duration of the rolling process, for example by 10%. Existing models can also simulate radial and axial forces F _CO not representative of reality.

PRESENTATION OF THE INVENTION

An object of the invention is to remedy at least in part the aforementioned drawbacks by proposing a modeling method taking into account the behavior of all the mobile tools of a circular rolling mill, and their interactions, making it possible to determine ranges of forges reliably and quickly.

This object is achieved by the present invention thanks to a method for modeling the behavior of a circular rolling mill intended to roll a cylindrical part from a set point, the circular rolling mill comprising at least one conical roller, configured to have a movement of translation in a first direction, and a mandrel, configured to have a movement of translation in a second direction, the setpoint comprising a setpoint for the speed of increase of an outer diameter of said cylindrical part as a function of said outer diameter, and a setpoint for the height of the cylindrical part in the first direction as a function of a thickness of the cylindrical part in the second direction, said method comprising the steps of: E1- obtaining a first set of parameters characteristic of the behavior of the circular rolling mill by means of a control formula linking a translational speed of the mandrel in the second direction direction of translation at the rate of increase of the external diameter and function of the setpoint; E2- Calculation by finite elements of a force value exerted on the conical roller from the first set of parameters; E3- Comparison of the value of force exerted on the calculated conical roller with at least one threshold value of force admissible by the circular rolling mill, and if the value of force exerted on the conical roller is greater than the threshold value of allowable force, obtaining a second set of parameters, such that the increase speed setpoint is not respected, correction of the second set of parameters in order to obtain a third set of parameters; if the force value exerted on the calculated conical roller is less than the admissible force threshold value, correction of the first set of parameters by taking into account a stiffness of the mandrel in order to obtain a third set of parameters; said third set of parameters being characteristic of the behavior of the circular rolling mill for the given set point.

Other characteristics, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and not limiting, and which must be read in conjunction with the appended drawings in which:

- the first set of parameters obtained by the control formula comprises a speed of movement of the conical roller h and a speed of translation of the mandrel s;

- the control formula is given by: with s the position of the mandrel, s the speed of translation of the mandrel, D the speed of increase of the external diameter D of the piece to be rolled;

- during the comparison step E3, the at least one admissible force threshold value depends on the outer diameter of the cylindrical part;

- during the correction step, a deformation of a cage of the mandrel, modeled as a spring of stiffness constant k is taken into account, so that the third set of parameters is obtained by a shift of at least one characteristic parameter of the behavior of the mandrel of the circular rolling mill. DESCRIPTION OF FIGURES

Figure 1 schematically illustrates a circular rolling mill for rolling a cylindrical part.

Figures 2a and 2b schematically illustrate steps of a method for modeling the behavior of a circular rolling mill according to the invention.

Figure 3 schematically illustrates a cylindrical part that can be obtained by a circular rolling process.

Figure 4 illustrates examples of input setpoints for a circular rolling mill.

Figure 5 schematically illustrates a system for controlling the movements of mobile tools of the circular rolling mill of Figure 1.

Figure 6 illustrates different stages defined by threshold force values admissible by a conical roll of the rolling mill.

FIG. 7 is a graph representing the evolution of the axial force at the level of a conical roller, calculated by a modeling obtained by a method according to the invention, by a modeling of the prior art, and measured experimentally.

FIG. 8 is a graph representing the evolution of the radial force at the level of a mandrel, calculated by a modeling obtained by a method according to the invention, by a modeling of the prior art, and measured experimentally.

FIG. 9 is a graph representing the evolution of the external diameter of a part during rolling, calculated by a modeling obtained by a method according to the invention, by a modeling of the prior art, and measured experimentally.

FIG. 10 is a graph representing the evolution of the rate of increase in the external diameter of a part during rolling, calculated by a modeling obtained by a method according to the invention, by a modeling of the art earlier, and measured experimentally.

Only the elements necessary for understanding the invention have been represented. To facilitate reading of the drawings, similar elements bear identical references in all the figures. DETAILED DESCRIPTION OF THE INVENTION

Figure 1 schematically illustrates moving tools of a system allowing the production of a cylindrical part called crown 5 during a circular rolling process illustrated in Figures 2a and 2b. The circular rolling mill 1 comprises at least one conical roller 3, in translation along a first direction Y, and in rotation along a roller direction X'. In the illustrated embodiment, the circular rolling mill 1 comprises an upper conical roller 3 and a lower conical roller 3'.

The circular rolling mill comprises a motor cylinder 4 in rotation around an axis tangent to the first direction Y, substantially vertical. The engine cylinder 4 is driven in rotation speed by a control unit 10, illustrated schematically in Figure 5.

The rolling mill 1 comprises another cylindrical tool called mandrel 2, also in rotation around an axis in the first direction Y. The mandrel 2 can be translated in a second direction X, substantially orthogonal to the first direction Y. The translation movement and the rotational movement of the mandrel 2 are controlled by the control unit 10.

FIG. 3 illustrates an example of a cylindrical ring 5 that can be obtained by rolling a billet with the circular rolling mill 1. In order to form a ring 5 having a height a along the first direction Y and a thickness e and an external diameter D along the second direction X, an operator can place the crown 5 under the at least one conical roller 3 and between the mandrel 2 and the motor cylinder 4.

A rotational movement of the conical roller 3 simultaneous with a translational movement of the conical roller 3 makes it possible to change the height a of the crown 5. In a related manner, rotational movements of the motor cylinder 4 and of the mandrel 2, simultaneous d a translational movement of the mandrel 2 makes it possible to change the thickness e of the crown.

All the movements of the tools modify at the same time the external or external diameter D of the crown 5.

In order to achieve the desired dimensions of the crown 5, it is necessary to give input instructions to the control unit 10 (also called control system 10) of the circular rolling mill 1. The input instructions include at least the desired dimensions of the cylindrical crown 5 to be rolled. Preferably, the input instructions also include the laws of evolution of the dimensions of the crown 5.

In an exemplary embodiment, the setpoint includes a setpoint for the rate of increase Ô(D) of the external diameter of the cylindrical crown 5 as a function of the external diameter D. The setpoint may include a height setpoint a(e) of the cylindrical crown 5 along the first direction Y as a function of the thickness e of the crown 5 along the second direction X. An example of such input setpoints is illustrated on Figure 4.

From the instructions given at the input of the control unit 10, the control unit 10 can control the translational and rotational movements of the tools 2, 3, 4 in motion of the rolling mill 1, as illustrated schematically in FIG. 5 Each forge range is associated with a specific instruction. In particular, the circular rolling process stops once the desired external diameter Dtarget is reached.

A first step E1 of the process for modeling the behavior of the circular rolling mill 1 is to determine a control formula, making it possible to link the input setpoint to at least one movement of a mobile tool 2.3 of the rolling mill 1. The control formula piloting makes it possible to obtain a first set of parameters characteristic of the behavior of the circular rolling mill 1 .

Preferably, it is a question of determining a control formula making it possible to link the input setpoint to all the movements of the mobile tools 2,3 of the rolling mill 1.

In an exemplary embodiment, it is a question of linking the rate of increase D of the external diameter D of the crown 5 to be rolled, associated with a particular range of forging, to the rate of increase é of the thickness s of the crown 5 in the second direction X. The speed of increase é of the thickness e is directly linked to the translational movement of the mandrel 2 in the second direction X and therefore to the translational speed of the mandrel s

Preferably, the relationship between the rate of increase D of the external diameter D and the rate of increase é of the thickness e also depends on the other parameters of the crown 5, that is to say its height a, its external diameter D and its thickness e.

In order to determine the control formula describing the different movements of the rolling mill 1, it is possible to study the principle of the servo loop of the rolling mill 1 which makes it possible to manage all the movements of the mobile tools 2,3,4 to from the instructions entered by the operator.

In an exemplary embodiment, the control formula which has been identified to reproduce part of the behavior of the rolling mill 1 as well as the main instructions entered by the operator in the control unit 10 of the rolling mill 1 is given by: with s the position of the mandrel directly linked to the thickness e of the ring, s the speed of translation of the mandrel directly linked to the speed of increase é of the thickness e of the ring, h the position of the conical roller, h travel speed of the conical roller h.

This nonlinear control formula makes it possible to obtain a first translation speed of the mandrel s of the theoretical thickness s, respecting the input instructions, as illustrated in figure 4.

It is also possible to link the rate of increase D of the external diameter D of the crown 5 to be rolled, to the rate of increase a of the height a of the crown 5 in the first direction Y.

Preferably, the relationship between the rate of increase D of the external diameter D and the rate of increase h of the position h also depends on the other parameters of the crown 5, that is to say on its height a, on its external diameter D and its thickness e.

The control formula making it possible to obtain the first set of parameters characteristic of the behavior of the circular rolling mill 1 can be integrated into a computer code by finite elements. In an exemplary embodiment, it can be integrated into the Forge calculation code by the Transvalor calculation code editor.

The finite element calculation code makes it possible to model the rolling process and in particular to calculate a force F _CO ne exerted by the conical roller 3 on the crown 5 during a rolling process as a function of the first set of parameters.

In order to improve the control model obtained previously, the mechanical characteristics of the circular rolling mill 1 can be taken into account. In particular, it is possible to integrate into the modeling a first mechanical model reflecting a limitation in force on the conical roller 3 , and a second mechanical model reflecting the elasticity of the mandrel 2.

It is also necessary to manage the interaction of these two mechanical models with the model of the circular rolling servo loop. Finally, it was necessary to make consistent hypotheses for the circular rolling process to make the models interact with each other. This makes it possible to obtain a final piloting model representative of reality.

Force limitation integrated in the conical roller 3

In order not to damage the rolling mill 1, it is necessary that the force F _CO ne exerted on the conical roller 3 does not exceed a threshold value F _seU ii. In an exemplary embodiment, the threshold value F _seU ii depends on the outer diameter D of the crown 5 during rolling. For example, the threshold value F _se uii(D) can depend on the position in the second direction X of a point of the outer edge of diameter D of the crown 5, in contact with a surface of the conical roller 3.

FIG. 6 illustrates an exemplary embodiment in which four force threshold values Fseuii(D)={N1,N2,N3,N4} are defined, defining four force limitation levels associated with three different thresholds of external diameter D. The force threshold values depend on the type of rolling mill 1. For example, we can have N 1 =50 tons, N2=100 tons, N3=150 tons and N4=200 tons. Dmax is the maximum outer diameter that can be rolled. Dmax is preferably less than the axial dimension of the conical roller 3 along the second direction X.

In order to manage the interaction of this first mechanical model with the model of the control loop of the control formula of the circular rolling mill 1 , two different situations can be defined.

Preferably, the first mechanical model intervenes when the radial force F _CO ne of the conical roller 3 exceeds the threshold value F _seU ii.

The modeling method comprises a step E3 of comparing the value of force F _CO ne exerted on the conical roller 3 calculated with the threshold value of force F _seU ii admissible by the rolling mill 1.

If the force value F _CO ne exerted on the conical roller is greater than the admissible force threshold value Fseuii, a second set of parameters is obtained, corresponding to the first set of corrected parameters.

During force limitation, the control formula, for example one of the control formulas presented previously, is no longer applied. A constant force is applied by the conical roller 3 on the crown 5. The first mechanical model will thus modify the displacement of the conical roller 3, in order to ensure the maximum admissible force. The applied force of the first mechanical model being reduced compared to the theoretical force calculated by the finite element calculation code, this will imply a slowing down of the rate of increase D of the external diameter D.

In an exemplary embodiment, the second set of parameters is calculated by a control formula following only the entry setpoint in height h(s) of the crown 5 in the first direction Y as a function of the thickness s of the crown 5 in the second direction X, so that the increase speed setpoint D is not respected.

The modeling presented makes it possible to account more reliably for the behavior of the rolling mill 1, in the transition zones where the force applied F _CO not by the conical roller 3 of the model would be too high to be tolerable by the tool. FIG. 7 illustrates a comparison between the axial force F _CO ne calculated by the proposed modeling method, in comparison with a modeling of the prior art not taking this mechanical model into account, and with experimental force measurements. It can be seen that the proposed modeling method makes it possible to account more reliably for the axial force on the conical roller 3.

During the rolling process, the diameter D of the crown 5 calculated will increase to a diameter value causing the force level to change. If the force value exerted on the calculated conical roller 3 is less than the new admissible force threshold value, the set of parameters is calculated according to the control formula in normal operation.

During step E3 of the proposed modeling method, the first set of parameters or the possible second set of parameters are corrected in order to obtain a third set of corrected parameters, making it possible to translate the kinematics of all the mobile tools of the circular rolling mill 1, and in particular of the mandrel 2. The third set of parameters is thus characteristic of the behavior of the circular rolling mill 1 for the given instruction.

Take into account the stiffness of the mandrel 2

In order to improve the modeling process, it is possible to calculate the third set of parameters to take into account the stiffness of the mandrel 2. The control formula as determined during the first step E1 uses a theoretical position of the mandrel 2.

In an exemplary embodiment, the mandrel 2 may be contained in a cage which deforms elastically during the rolling process, which has the effect of disturbing the position of the mandrel 2. It has in fact been observed empirically that the thickness e actual crown 5 was generally greater than the theoretical thickness e. It was identified that the control unit 10 of the circular rolling mill 1 did not take into account the deformation of the cage of the mandrel 2 in the control during the rolling process.

The elastic deformation of the cage of the mandrel 2 can be modeled simply as the deformation of a spring fixed between the mandrel 2 and the cylinder 21 allowing the translation movement according to the second direction X of the mandrel 2.

It can be considered that the cage of the mandrel 2 behaves like a spring of stiffness k, radially exerting a force on the crown 5 depending on the position of the mandrel 2 according to the axis of second direction X. In this embodiment, one obtains the values of the third set of parameters by adding an offset, positive or negative (in English “offset”).

The offset applied in correction may depend on the radial force calculated by the finite element calculation code. In particular, in the example where the set of parameters includes the rate of increase s of the thickness s of the crown 5, which directly depends on the translational movement of the mandrel 2, the addition of this second mechanical modeling is relevant. because the fact of taking into account the stiffness of the mandrel 2 makes it possible to change the theoretical stroke of the latter, which is notably influenced by the virtual deformation of the cage.

Preferably, this second mechanical model can be fully integrated by Transvalor into the Forge calculation code.

Figure 8 illustrates a comparison between the radial force calculated by the proposed modeling method, in comparison with prior art modeling that does not take this second mechanical model into account, and with experimental force measurements. It can be seen that the proposed modeling process makes it possible to account more reliably for the radial force on the mandrel 2.

Thus, the method of modeling the behavior of the circular rolling mill 1 as presented makes it possible to obtain a complete model predicting the behavior of the circular rolling installation.

To better explain the contribution of what has been developed, we can compare the results of the modeling using a rolling mill servo-control model from the prior art and using the new model presented taking into account the two mechanical models. translating the mechanical characteristics of the mandrel 2 and the conical roller 3.

Figures 9 and 10 illustrate the comparison between the evolution of the external diameter D of the crown 5 and the rate of increase D of the external diameter of the crown 5, calculated by a model of the prior art, by the model presented and obtained by experimental measurements.

It can be seen that the modeling process described makes it possible to obtain a new model that more realistically follows the real evolutions of the parameters. Thus, for a setpoint corresponding to a new range of forging, it is possible to predict all the parameters characterizing the evolution of the piece to be rolled and the behavior of the rolling mill 1.

In particular, this allows the optimization of the rolling operation without producing real parts. It is thus possible to reduce the design blows of forging ranges.

Finally, it is possible thanks to the proposed modeling process to predict the duration of the rolling process, which is not a priori known and depends on the part to be rolled. In particular, this allows you to know if there is a risk of forging the part cold. This control model also makes it possible to limit the risks of rejecting parts in production.

Claims

1 . Method for modeling the behavior of a circular rolling mill (1), intended to roll a cylindrical workpiece from a setpoint, the circular rolling mill comprising at least one conical roller (3), configured to have a translation movement according to a first direction (Y), and a mandrel (2), configured to have a translation movement in a second direction (X), the setpoint comprising a setpoint for the rate of increase of an external diameter of the said cylindrical part as a function of the said diameter external, and a set height of the cylindrical part in the first direction as a function of a thickness of the cylindrical part in the second direction, comprising the steps of:

E1- obtaining a first set of parameters characteristic of the behavior of the circular rolling mill (1) by means of a control formula linking a translation speed of the mandrel (2) according to the second direction of translation to the speed of increase of the outer diameter and setpoint function;

E2- Calculation by finite elements of a force value exerted on the conical roller (3) from the first set of parameters;

E3- Comparison of the value of the force exerted on the conical roller (3) calculated with at least one threshold value of force admissible by the circular rolling mill (1), and if the value of the force exerted on the conical roller is greater at the allowable force threshold value, obtaining a second set of parameters, such that the increase speed setpoint is not respected, correction of the second set of parameters in order to obtain a third set of parameters; if the force value exerted on the calculated conical roller is less than the admissible force threshold value, correction of the first set of parameters by taking into account a stiffness of the mandrel in order to obtain a third set of parameters; said third set of parameters being characteristic of the behavior of the circular rolling mill for the given setpoint.

2. Modeling method according to claim 1, in which the first set of parameters obtained by the control formula comprises a speed of movement of the conical roller h and a speed of translation of the mandrel s.

3. Modeling method according to any one of the preceding claims, in which the control formula is given by: with s the position of the mandrel, s the speed of translation of the mandrel, D the speed of increase of the external diameter D of the piece to be rolled (5).

4. Modeling method according to any one of the preceding claims, in which, during the comparison step E3, the at least one admissible force threshold value depends on the outer diameter of the cylindrical part.

5. Modeling method according to any one of the preceding claims, in which, during the correction step, a deformation of a cage of the mandrel, modeled as a spring of constant stiffness k is taken into account, so that the third set of parameters is obtained by a shift of at least one parameter characteristic of the behavior of the mandrel of the circular rolling mill.