Method for determination of part machining stage conditions at controlled cutting speed

FIELD: machine building.

SUBSTANCE: proposed method is used in adjustment of cutting speed between part and machine. It comprises the stages that follow. Simulation of said stage by presetting parameters of speed adjustment function. Part surface conditions are derived by computation after completion of cutting process. It comprises iteration modification of said parameters of adjustment function with simulation of cutting stage at every iteration to derive appropriate surface conditions therefrom unless said conditions reach tolerable magnitude. Also, it includes execution of cutting stages at cutting speed variation in applying adjustment function corresponding to tolerable magnitude of surface conditions.

EFFECT: higher accuracy of cutting speed determination.

4 cl, 1 dwg

The invention in General relates to the determination of the conditions for machining parts that can start to vibrate during machining. The task of the invention consists in the determination of cutting conditions and, in particular, the cutting speed to avoid the appearance of vibrations.

Some large parts, such as rotor disks of the turbine, have a bell-shaped form with the wall, which is quite thin, and they are prone to vibration during machining.

There are already machines to simulate vibration during machining, and in some circumstances they can prevent problems with vibration when turning or milling. However, such machines simulation, in General, are based on the frequency approach, which is suitable for study only those systems in which the rotation speed constant. However, in order to prevent this detail was included in the resonance, it is preferable to periodically change the rotation speed (the speed of turning or milling) to prevent occurrence of a system in resonance and thus prevent occurrence of vibration. This function is to regulate the speed of cutting is characterized by two parameters - the amplitude of the rate and period changes.

However, for each stage of the mechanism, the standard treatment remains the need to determine the appropriate regulatory functions. Still this was done empirically. This means that when preparing the plan procedures for machining each part is necessary to perform a variety of tests, thereby causing significant losses in time and wypracowanie many parts made of expensive alloy.

The invention provides a solution to this problem, offering a consistent simulation of the stages of machining to allow optimization of the parameters of the regulatory functions.

In particular, the invention provides a method of determining conditions stage of machining parts when adjusting the cutting speed between the part and the machine, and the method is characterized by the following stages: simulation of the machining stage by pre-setting of options for regulating said speed; obtaining from the appropriate state of the workpiece surface by calculating the after stage machining is completed; the iterative modification of the parameters specified regulatory functions with simulation of the machining stage at each iteration to obtain from it the appropriate surface condition, while the condition of the surface does not reach the allowable value; and executing the machining stage, causing changed the e speed cutting in the application of regulatory functions, the corresponding allowable surface condition.

The invention may be better understood, and other characteristics will become clearer in the light of the following description of an example of a method of determining conditions stage of machining parts with a speed control cutting between the part and the machine is provided solely as an example and made with reference to the accompanying drawing, which shows a structural diagram of a flowchart for the iterative process of determining the parameters that control the mechanical processing.

The drawing shows a simulation of machining. It is assumed that the passage of the machining must be performed within the specified time T. Let ΔT is the time interval in a predetermined time T. the smaller the value chosen for ΔT, the greater the number of calculations that must be performed, but the more accurately you can describe the characteristics and form of the parts, including the state of its surface at the end of the passage machining. This passage of mechanical processing is the stage of mechanical treatment, during which the machine continues to interact with the material details.

In addition, various models are available to represent parts and components that make up the system, in computer form and the La describe the interactions between the various parts and sub-assemblies. Most models describing the mechanical behavior of parts and assemblies that are created by the so-called technique of "end item". Item or node is represented as a set of elements forming a grid. Each node of the grid is associated with a value that represents the described characteristic. For example, for a simple representation of items, which is assumed as rigid coordinates of the nodes enough to build the model. If a part described by the model, may vary (deform, move), the additional degrees of freedom needed to model transformations. As an example, three degrees of freedom are added to rotation and three degrees of freedom to move.

A model describing the interaction between the various parts and elements can be of several types: conversion function, a descriptive model equation.

According to the invention a distinction is drawn between the following models:

- Gw is the source geometric model of the area of the part that is machined.

- Gt is a geometric model of the active parts of the machine. Gt can be permanent, although it is possible to foresee and describe the slow change in this model to take into account, for example, wear of the machine. More specifically, this geometric model is actually the two the is the set of models, describe various individual tools (teeth, insert, blade). The geometric model is a surface model. She is an active part of the machine, in particular its cutting surface.

If the active part of the machine can be deformed, the geometric model may include deformation of the active parts over time as a function of the interaction between the machine and workpiece.

- Fc is a model of cutting forces (local cutting relationship, derived from the interaction of the machine and parts. As an example, you can use cutting relationship type Circle, which is known to specialists in the field of technology and which serves for the local determination of the instantaneous cutting forces as a function of the area of the removed material (fineness and thickness of the slice, i.e. the size of the chip) and as a function of the dynamics of the machine-part". Instantaneous cutting forces are the forces applied by the machine to the workpiece, and opposition to the points selected for a precise description of the interaction between the machine and workpiece.

- Dwmt is a dynamic model of the system "part-machine". This model Dwmt is usually a model of finite element used to describe the dynamic behavior of the system during machining. The dynamic model of the Dwmt uses the parameters M, C and K in the form of matrices and od is stolbovoy matrix q, as is described below.

What follows is a description of the simulation of machining, and the description is given with reference to the drawing, which is a different model, defined above as participating in the process shown in the circuit block diagram that illustrates the algorithm 10 to define a function to model the cutting speed.

Time t=0 is the beginning stage of the simulation the proposed mechanical treatment. For each t=t+Δt can determine the feed speed of the machine relative to the workpiece (block 12). This feed rate varies over time because it depends on the function of regulating the cutting speed. For example, the cutting speed can be expressed as follows:

Ω(t)=Ω_N+ΔΩ×Fω(t)

where -1<Fω(t)<1,

and Fω(t) is a periodic function with period 2π/ω, Ω_N- rated speed, and ΔΩ is the amplitude of the deviations from the nominal speed.

Preferably, Fω(t) was a sine wave.

Search parameters this regulatory functions, which allow to achieve a satisfactory surface condition, i.e. when the "roughness" or "waviness" is less than the specified values.

Based on that description 12 feed speed "machine-part" and model Gw and Gt can be described (block 13) interaction (intersection) between the part and the machine. The result entries batch is I and model Fc serve to describe the local forces Fcut(t) (block 14).

Using a dynamic model Dwmt and local forces Fcut(t), we can write and solve a system of differential equations (block 15):

where- single-column matrix of the set of parameters qi(t);

-the first derivative of q(t);

-the second derivative of q(t);

- Q_c(t) represents the generalized forces obtained from the interaction between the machine and workpiece. They arise from the local forces Fcut(t), obtained by using the model of cutting;

- Q_b(t) represents the generalized forces in addition to the Q_c. It refers, in particular, to the power clamp;

- M(t,Ω) is the mass matrix;

- C(t,Ω) is the damping matrix; and

- K(t,Ω) is the stiffness matrix.

Matrices M, C and K can vary (slowly) during mechanical processing to account for losses in mass and stiffness resulting from the removal of material. These matrices also include a gyroscopic effect, which is a function of Ω.

For each given increment of time Δ(t) solves the system of differential equations. Thus, knowing q(t) for t lying in the interval [0,T], we can obtain q(t+Δt) provided that accrued time intervals ΔT less than T, i.e. provided that the estimated stage of mechanical treatment is not interrupted. Each increment d is occurs algorithm 16 material removal. The objective of this algorithm is the removal of the material consists in the simulation of material removal at each time interval, i.e. clarification of the Gw model.

Because the full stage of mechanical treatment was simulated for time (T), the state of Gw is compared with the sample Gwr (test 17), in particular, to estimate the state of the workpiece surface at the end of the machining stage, as a rule, one pass of the machine.

If the state of the surface Gw satisfactorily, i.e. at least equal to the state of the surface of the Gwr, the parameters of the regulatory function that achieves this result is stored (block 18). These parameters ΔΩ and ω are then used to change the speed of rotation of the rod when turning in the application of regulatory functions during actual machining duration T.

If the surface condition is not satisfactory, the parameters of the regulatory function change (block 19) to modify flow characteristics "machine-part", and the simulation of the machining stage starts again, what happens as often as it is necessary to obtain more refined models of Gw, which represents a satisfactory surface condition.

It should be noted that the algorithms described above steps, were published. Links to these publications is presented below:

Dissertation

Kaled Dekelbab, 1995, "Modelisation et simulation du comportement dynamique de l ensemble Piece-tool-Machine en usinage par'outil coupant" [Modeling and simulating the dynamic behavior of a workpiece and machinetool assembly during machining by a cutter tool], Ecole Nationale Superieure d ' Arts et Metiers - CER, Paris.

Erwan Beahchesne, 1999, "Modelisation et simulation dynamique de l usinage: prise en compte d'une piece deformable" [Dynamic simulation and modeling of machining: taking account of a workpiece that is deformable], Ecole Nationale Superieure d ' Arts et Metiers - CER, Paris.

Audry Marty, 2003, "Simulation numerique de l usinage par'outil coupant and l echelle macroscopique: contribution a la definition geometrique de la surface usinee", [Numerical simulation of machining by a cutting tool at a macroscopic scale: contribution to a geometrical definition of the machined surface], Ecole Nationale Superieure d ' Arts et Metiers - CER, Paris.

Stephanie Cohen-Assouline, 2005, "Simulation numerique de l usinage à l echelle macroscopique: prise en compte d'une piece deformable" [Numerical simulation of machining at macroscopic scale: taking account of a workpiece that is deformable], Ecole Nationale Superieure d ' Arts et Metiers - CER, Paris.

Articles published in journals

S. Assouline, E. Beauchesne, G. Coffignal, Lorong P. and A. Marty, 2002, "Simulation numerique de l usinage à l echelle macroscopique: modeles dynamiques de la piece" [Numerical simulation of machining at macroscopic scale: dynamic models of the workpiece], Mecanique et Industrie, Vol. 3, pp. 389-402.

P. Lorong, J. Yvonnet, G. Coffignal and S. Cohen, 2006, "Contribution of Computational Mechanics in Numerical Simulation of Machining and Blanking", Archives of Computational Method in Engineering, Vol. 13, pp. 45-90.

Currently, the preferred algorithm used in the software tool, known as Nessy. Nessy was described in more detail in the following articles:

P. Lorong, F. Ali and G. Coffignal, 2000, "Research oriented software development platform for structural mechanics: a solution for distributed coputing", Second International Conference on Engineering Computational Technology, Developments in engineering computational technology, ed. B.H.V. Topping Louvain, Belgium, pp. 93-100.

G. Coffignal and Lorong P., 2003, "Un Logiciel elements finis pour developper et capitaliser des travaux de recherche" [Finite element software for developing and capitalizing research work], 6eme Colloque National en Calculation des Structures, Giens.

The method according to the invention particularly suitable for surfacing of parts of large diameter, such as rotor disks turbines or compressors for turbojet aircraft. Such details can start to vibrate during machining under the action of forces. Preliminary determination of the optimal regulatory functions for the relative speed between the workpiece and the machine tool during the machining stage is used to prevent the occurrence of such vibrational States and thus to achieve the desired surface condition.

1. The method of determining conditions stage of machining parts when adjusting the cutting speed between the part and the machine, characterized by the following stages: simulation (10) specified the machining stage by pre-setting function parameters for speed control; obtaining from the appropriate state of the workpiece surface by calculating the after stage machining is completed; iterative modification (19) of these parameters is aguiruya functions with simulation of the machining stage at each iteration to obtain from it the appropriate surface condition, while the state of the surface does not reach the allowable value; and executing the machining stage, causing the cutting speed (Q(t)) in the application of regulatory functions, the corresponding allowable surface condition.

2. The method according to claim 1, characterized in that the modular function has the following form:
Ω(t)=Ω_N+ΔΩ×Fω(t),
where
-1<Fω(t)<1,
and Fω(t) is a periodic function with period 2P/ω, Ω_N- rated speed, and ΔΩ is the amplitude of the deviations from the nominal speed.

3. The method according to claim 2, characterized in that the periodic function is a sine wave.

4. The method according to any one of claims 1 to 3, characterized in that the above-mentioned machining is a machining.