EP0542748A1

EP0542748A1 - Control method for numerically controlled machines for automatic machining of mechanical components

Info

Publication number: EP0542748A1
Application number: EP19910906300
Authority: EP
Inventors: Pierre Leulier
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-08-31
Filing date: 1991-02-27
Publication date: 1993-05-26
Also published as: FR2651340A1; WO1992015927A1; FR2651340B1

Abstract

Procédé de commande de machines à commande numérique pour l'usinage automatique de pièces mécaniques, caractérisé par: l'automatisation de l'usinage sans intervention de l'opérateur d'où, dissociation de l'homme et de la machime; prise en compte dans l'usinage de la cote et de la tolérance de chaque cote décrite au maximum de matière; prise en compte pour le calcul de la valeur de la cote à usiner d'un positionnement automatique dans l'intervalle de tolérance et du comportement et/ou de l'usure de l'outil coupant; usinage en simultané de pièces différentes du fait que le programme commande numérique contient des macros instructions pouvant appartenir à des pièces différentes.Process for controlling numerically controlled machines for the automatic machining of mechanical parts, characterized by: automation of the machining without operator intervention, hence, dissociation of man and machime; taking into account in machining the dimension and the tolerance of each dimension described to the maximum of material; taking into account for the calculation of the value of the dimension to be machined, an automatic positioning within the tolerance range and of the behavior and / or wear of the cutting tool; simultaneous machining of different parts due to the fact that the numerical control program contains macro instructions which may belong to different parts.

Description

Process for controlling numerically controlled machines for the automatic machining of mechanical parts.

The present invention relates to a method for controlling numerically controlled machines for the automatic machining of mechanical parts.

The most common machining programs take into account only average dimensions with tolerances distributed on either side of the value of the average dimension. Thus, during the execution of a program, it is the value of the average rating which is taken into account. However, this leads to restricting in practice the tolerance interval. Indeed, the bending and the wear of the tools always go in the same direction. To find a tolerance interval equivalent to that of the product definition, it is therefore necessary to modify a "tool corrector" on the machine. Correcting involves manual intervention by an experienced operator, which prevents proper automated machining.

In addition, the choice of average machining dimensions leads to machining dimensions with the same value around the average dimension, while it is desirable that the machining is carried out towards the minimum material of each dimension in order to facilitate mounting. and product quality.

The present invention aims to remedy the aforementioned drawbacks and to allow fully automatic machining of a mechanical part, without operator intervention, so as to lead to a dissociation of man and machine.

The invention further aims to allow direct taking into account for machining the dimension and tolerance of each dimension provided by the product definition.

Another object of the invention is to allow different parts to be machined simultaneously.

These goals are achieved through a control process, numerically controlled machines for the automatic machining of mechanical parts, characterized in that for each dimensional value of the definition of the part to be machined, one specifies on the one hand, a dimensionless parameter b_ of value + 1 or - 1 depending on whether the element to be machined is of the bore type or of the type shaft, and, on the other hand, a maximum nominal dimension of material Cn and a tolerance interval IT. In addition, a machining position towards the minimum material is chosen in the tolerance interval defined by a fraction ke the tolerance interval

IT, one determines a parameter a_ of auto-correction of the dimension to be machined taking into account the behavior and the wear of the cutting tool and one determines the dimension to be machined Cu from the formula

Cu = Cn + b. (IT. K) + a

The parameter a_ of the o-correction of the dimension to be machined can be determined from analysis curves of the cutting tools used for machining.

This self-correction parameter a_ can however also be determined using an integrated measurement of the workpiece mounted on a numerically controlled machine tool.

More particularly, according to the present invention, the values of the definition for the parameter b_, for the nominal dimension Cn, for the tolerance interval IT, for the fraction k of the tolerance interval IT, the value determined for the self-correction parameter a_ as well as the formula for calculating the value of each dimension to be machined Cu are included either in volume and parameterized macro-instructions or in the parameterized programming of the part. This programming thus takes into account the tolerated dimensions of the product definition.

With the machining control method according to the invention, for the various volume operations for machining a part, a series of resident macro-parameterized volume instructions on the numerically controlled machine tool is determined, or parametric programming of the part, and the tools assigned to these different volume operations are directly associated with macro or subroutines.

Other characteristics and advantages of the invention will emerge from the following description of particular embodiments, given by way of examples, with reference to the appended drawings, in which:

- Figure 1A shows an example of the definition plot of a volume macro-instruction established in accordance with the invention, the definition plot applying to the production of a groove seen in section, - Figure 1B is a view in section along the plane 1B-1B of FIG. 1A, to complete the definition plot of FIG. 1A,

- Figure 2 shows a diagram showing the positioning of a tool relative to a dimension to be machined according to a conventional process control process, Figure 3 shows a diagram showing the modification of the positioning of a tool relative to a dimension to be machined, according to a conventional method of controlling the machining in which a manual correction of the "tool corrector" is carried out in order to machine in the unexplored part of the tolerance interval,

FIG. 4 represents a diagram showing the positioning of a tool with respect to a dimension to be machined towards the minimum material, in the case of a shaft, in accordance with the method according to the invention,

- Figure 5 shows a diagram showing, 1st position of a tool with respect to a dimension to be machined towards the minimum material, in the case of a bore, in accordance with the method according to the invention, and - Figure 6 shows on a diagram similar to those of Figures 4 and 5, taking into account an automatic correction of the behavior or wear of a tool, in the context of the implementation of the method according to the invention.

We will first briefly recall with reference to Figures 2 and 3 a machining process as it is implemented so classic.

From a definition of dimension to be machined (for example 20.0 mm) and a tolerance interval (for example 0.2 mm in addition to the dimension to be machined), according to conventional machining methods which use using medium dimension programming, the dimension to be machined is transformed into a dimension with distributed tolerance.

Thus, in the example considered, the value of the average dimension is fixed at 20.1 mm and the tolerance of 0.2 mm is distributed on either side of the average dimension, in the form of a value of _ + 0.1 mm.

Programming using average dimensions amounts to giving only half the tolerance to the machinist. Indeed, the bending and the wear of the tools always go in the same direction so that if we take into account the average dimension (for example 20.1 mm) the tool 11 of diameter FI will be positioned as shown in Figure 2, and the only area explored by ZE machining will extend between the average dimension and the average dimension minus the half-value of the tolerance given in the initial definition, while the ZNE zone is extending between the average dimension and this average dimension increased by the half-value of the tolerance given in the initial definition will remain unexplored by the machining.

To overcome this drawback, and allow exploration by machining of at least part of the ZNE zone normally not explored by machining, it is necessary to use a tool corrector which simulates for the machine tool a fictitious tool with a diameter smaller than the actual diameter F.

There is shown in Figure 2, in dotted lines, a real tool 13 of real diameter F, and, in solid lines, a dummy tool 12 whose diameter is less than the diameter F, and corresponds for example to the diameter F reduced in half -value of the tolerance given in the initial definition (for example 0.1 mm). In this case, if the positioning system of the real tool 13 positions it as if it were the dummy tool 12, it is this dummy tool 12 which will be positioned at the mean dimension (for example 10.1 mm) only known by the program. As the real tool 13 has a diameter F greater than that of the dummy tool 12, the real tool 13 is therefore positioned at a dimension (for example 10.15 mm) which is located in the ZNE zone which without the above device would not be explored by the tool. It will be noted that the ZNE zone remains only partially explored, however, and that the bending and wear of the tool still tend to reduce the part actually explored.

The use of a tool offset requires the intervention of the operator responsible for monitoring the machining process, since the value assigned to the tool offset is that which will be calculated from the smallest tolerance dimensions which will be machined during the course of the tool in the material. In the case of conventional machining control methods taking into account average dimensions with distributed tolerances, the tolerances do not constitute data recognized by the machine. It follows that the tool offset must be implemented by a knowledgeable operator.

Operator intervention prevents the machining operation from being fully and correctly automated.

Furthermore, in such known machining methods, all the dimensions are machined with the same value around the average dimension, while it is desirable that the machining is carried out towards the minimum material of each dimension in order to facilitate the product quality.

To overcome the various drawbacks mentioned above, according to the present invention, the nominal dimension Cn at the maximum of material as well as the tolerance interval IT is taken into account for the machining process and a dimensionless parameter b is assigned the value + 1 or - 1 depending on whether the element to be machined is of the bore type or of the shaft type.

According to the invention, the dimensions of the definition are thus used directly and it is not necessary to calculate an average dimension, distribute the tolerance on either side of this average dimension, or to manually determine a tool offset for the path to be carried out by the tool on the workpiece.

According to the invention, a better quality of the product can be obtained by machining the dimensions to the minimum material in order to facilitate the assemblies and ensure the operating clearances. For this, the value of a coefficient k is determined which makes it possible to position the machining within the tolerance interval so as to be at the minimum material as illustrated with reference to FIGS. 4 and 5. The value of the coefficient k depends on the choice of the position of the tool in the tolerance interval and defines a confidence interval. This value can thus be determined from a Gauss curve and be chosen to define a position corresponding to a predetermined number of standard deviations on the Gauss curve.

A self-correction parameter _a_ of the dimension to be machined is also determined, taking account of the behavior and wear of the tool.

In the case where the actual position of the workpiece is continuously measured with respect to the dimension to be machined, which corresponds to an integrated measurement system of the workpiece mounted on the machine tool, the value of the parameter a_ d self-correction can be determined directly from said integrated measurement of the workpiece, which integrated measurement takes into account both the wear of the tool and all the hazards linked to the behavior of the tool such as bending for example. As a variant, the parameter a_ of auto-correction of the dimension to be machined can however also be determined from analysis curves of the cutting tools used for machining, which analysis curves can be established by the manufacturers. of tools. For each dimensional value of the definition of a part, the Cu dimension to be machined by the machine tool is automatically determined from the following formula:

Cu = Cn + b (IT. K) + a (1) where Cn represents the maximum nominal dimension of material, b has the value - 1 if the element to be machined is consisting of a shaft and the value + 1 if the element to be machined consists of a bore,

IT represents the tolerance interval within which the machining must be carried out, represents a fraction of the tolerance interval defining a position of the machining in the tolerance interval which aims to locate the machining towards the minimum material, and a represents a self-correction parameter of the dimension to be machined taking into account the behavior and wear of the cutting tool.

By way of example, FIG. 4 illustrates the case of machining a shaft for which machining must be carried out at a nominal dimension Cn of 20.2 mm with an IT tolerance of 0.2 mm. For the application of the above-mentioned formula (1), the parameter b is assigned the value - 1 since it is an element of the tree type. The value of the coefficient k depends on the confidence interval C that one wishes to reserve within the tolerance interval IT. For example, the coefficient k can be chosen equal to 0.8. In this case, if one does not take into account the per_ameter of auto-correction of the dimension to be machined, the application of formula (1) leads to a dimension to be machined Cmin situated towards the minimum material at 20, 2 - 0.2 x 0.8 = 20.04 mm.

FIG. 5 illustrates by way of another example the case of machining a bore for which machining must be carried out at a nominal dimension Cn of 20.0 mm with an IT tolerance of 0.2 mm. In this case, the parameter b takes the value + 1 since the element to be machined is of the bore type. As in the previous case, the value of the coefficient k depends on the confidence interval C that one wishes to reserve. For example, if the coefficient k is 0.8 and not taking into account the self-correction coefficient a, the application of formula (1) leads to a dimension to machine Cmin located towards the minimum material at 20.0 + 0.2 x 0.8 ≈ 20.16 mm.

Figure 6 illustrates the same example as Figure 5, ma ⁱ s dan * i _θ case where we take into account the perameter of auto- correction of tool behavior and wear.

As indicated previously, the value of the corrector parameter a is either calculated by a measurement macro-instruction during the integrated measurement of the part mounted on a numerically controlled machine tool, or provided by a data item in the parameters of each tool ( machining with dynamic correction).

In the case of FIG. 6, the actual machined dimension Cr is, by way of example, equal to 20.06 mm, this value being taken by measurement of the part. This corresponds to a value of the self-correction parameter a_ equal to 0.1 mm. The taking into account of this parameter a_ in the formula (1) leads to bring back the dimension machined in the vicinity of the theoretical value which was discussed during the discussion of Figure 5. The machining program is carried out at using macro instructions which take into account e) the morphology of the machining, and in particular the geometry, the technical specifications, the notion of shaft or bore; b) the nominal Cn, the sign of the tolerance (parameter b linked to the notion of shaft or bore) and the tolerance of each of the dimensions to be achieved by situating the machining towards the minimum material with a linked confidence interval to the value of the coefficient k, c) the formula (1) which makes it possible to calculate the value of each dimension to be machined by taking into account the behavior and the usu¬ re of the tool via the parameter a_ d ' auto correction. A complete automation of the machining process can thus be carried out. The program itself is made up of a series of parameterized macro-instructions resident on numerically controlled machines and subroutines indicated in the machining program as conventional macro-instructions.

The tools assigned to the different volume operations are not linked to parts but to macro-instructions. It follows that the machining program takes into account, for a spindle tool, the machining of macro-instructions distributed over a set of different pieces. The method according to the invention is thus quite suitable for carrying out machining operations simultaneously on different parts.

FIGS. 1A and 1B show an example of a part with definition data for the production of a non-emerging groove, the definition data being able to be introduced into a parameterized volume macro-instruction, called RAINFD2.

FIG. 1A represents a sectional view along a plane XOY and FIG. 1B is a section along a plane 1B-18 perpendicular to the plane XOY and containing an axis Z perpendicular to the plane XOY.

A series of definition data is introduced into a parameterized macro-instruction to define the conditions for machining the groove 21 in the part 20, using a tool 22.

In FIG. 1A, A and B represent the offsets of the origin of the model (point 6) along the X and Y axes of a coordinate system

XOY, compared to the origin 0 of the program. C represents the actual radius of the tool 22 increased by a value e for example equal to 2 mm.

The different data taken into account in the example of FIGS. 1A and 1B are the following:

000 parameter provided to automatically receive the value of the actual radius of the tool 22. 001 nominal dimension of the length of the groove 21.

002 tolerance attached to the nominal dimension 001 of the length of the groove 21.

003 nominal dimension of the width of the groove 21.

004 tolerance attached to the dimension, nominal 003 of the width of the groove 21.

005 distance defining a safety plane above the part 20 along the Z axis.

006 parameter which can take the value 1 or - 1.

The value 1 corresponds to machining "downstream" (arrival at point 1 then course of points 2, 3, 4, 5 then mounted according to the Z axis of the distance 005 then positioning at point 6).

The value - 1 corresponds to a machining in opposition (arrival at point 1 then course of points 5, 4, 3, 2 then mounted along the Z axis of the distance 005 for positioning at point 6.

007 nominal dimension of the thickness of material between the bottom of the part 20 and the bottom of the groove 21.

008 tolerance on dimension 007.

009 value of the radius of the rounded part 23 of the non-opening groove.

010 tolerance on the value of radius 009.

011 advance work.

012 fast approach along the Z axis to then reach the nominal dimension 007. 013 angle between the axis of the groove in the XOY plane, and the X axis.

014 tolerance coefficient 002.

015 tolerance coefficient 004.

016 tolerance coefficient 008.

017 coefficient relating to tolerance 010. 018 theoretical radius of the tool.

019 coefficient relating to the machining time.

020 increment along the Z axis (for values 007 and 012)

021 lateral increment of dimension 001.

022 lateral increment of dimension 003. P01 speed of rotation.

P02 feed speed.

Claims

1. A method of controlling numerically controlled machines for the automatic machining of mechanical parts, characterized in that for each dimensional value of the definition of the part to be machined, one specifies, on the one hand, a dimensionless parameter b _^ of value + 1 or - 1 depending on whether the element to be machined is of the bore type or of the shaft type, and, on the other hand, a nominal dimension at the maximum of material Cn, a tolerance interval IT, a position of machining towards the minimum material in the tolerance interval defined by a fraction k of the IT tolerance interval, a self-correction parameter a_ of the dimension to be machined is determined, taking behavior and wear into account of the cutting tool and the dimension to be machined Cu is determined from the formula Cu = Cn + b. (IT. K) + a

2. Method according to claim 1, characterized in that the parameter a_ of auto-correction of the dimension to be machined is determined from analysis curves of the cutting tools used for machining.

3. Method according to claim 1, characterized in that the parameter a_ of self-correction of the dimension to be machined is determined using an integrated measurement of the workpiece mounted on a machine tool with digital control.

4. Method according to any one of claims l to 3, characterized in that the values for the parameter b ^ for the nominal dimension Cn, for the IT tolerance interval, for the fraction k of the IT tolerance interval , the value determined for the self-correction parameter a_ as well as the formula for calculating the value of each dimension to be machined CU are included in volume macro-parameters and parameterized.

5. Method according to any one of claims l to 3, characterized in that the values for the parameter b_, for the nominal dimension Cn, for the IT tolerance interval, for the fraction k of the IT tolerance interval , the value determined for the self-correction parameter a_ as well as the formula for calculation of the value of each dimension to be machined CU are included in the parameterized programming of the part.

6. Method according to any one of claims 5, characterized in that one determines for the different volume operations of machining a part, a series of macro-instructions configured volume resident on the machine tool è command digital, and in that the tools assigned to these different volume operations are directly associated with macro-instructions, or with subroutines.

7. Method according to any one of claims l to 5, characterized in that ^" it is determined for the different volume operations of machining a part, a programmed programming of the part and in that the tools assigned to these different volume operations are directly associated with macro-instructions, or with subroutines.