WO2010018188A1

WO2010018188A1 - Method and device for machining parts with a shape check

Info

Publication number: WO2010018188A1
Application number: PCT/EP2009/060418
Authority: WO
Inventors: Nicolas Colin; Didier Simonet
Original assignee: European Aeronautic Defence And Space Company Eads France
Priority date: 2008-08-14
Filing date: 2009-08-12
Publication date: 2010-02-18
Also published as: FR2935044B1; FR2935044A1

Abstract

The invention relates to a part machining device (2) that comprises at least one machine tool for machining said parts, and at least one substrate (10) including i) a bearing surface (100) on which each part (2) to be machined is immobilised during the machining operations, said bearing surface being defined by a theoretical boundary surface (101) having a shape geometrically matched to an at least local theoretical shape of the parts (2) to be machined, said theoretical boundary surface defining a substrate side (101b) and a part side (101a), and ii) a plurality of sensors (102) arranged in the vicinity of the theoretical boundary surface (101) of the substrate side (101b). Said sensors are suitable for measuring, at a plurality of points of the substrate (10), values that are representative of the local distances between said substrate and each immobilised part (2) in order to determine if said part is compliant and must be machined. The invention also relates to a method for machining parts (2) that comprises the step of checking each part (2) in order to determine if the latter must be machined.

Description

Method and device for machining workpieces with form verification

The present invention belongs to the field of machining parts, and more particularly relates to a device and a machining process with verification of the parts to be machined, to detect deviations of shape of the parts from a theoretical form wanted for said rooms. Machining operations, especially operations requiring a high accuracy generally less than one millimeter or even one tenth of a millimeter, use machining devices comprising a machining support, whose shape is at least locally geometrically adapted to a theoretical form of workpieces, on which each part is immobilized during machining.

For example, it is known, in the field of aeronautical construction, for machining sheet metal, or composite material or other, to use plate-shaped supports on which the sheets are immobilized by compression, for example aspirated and / or flanged. Plating such sheets on a geometrically shaped support adapted to the desired theoretical shape of the sheet makes it possible in particular to reduce the deformations of said sheets introduced for example by the gravitational force in the case of large sheets.

When the sheets have deformations due to a manufacturing defect, the sheets are not, at least locally, in contact with the support at the time of machining, which generally results in the presence of under-thickness machining . If the deformations are too important, such sheets are not usable as they are and must be discarded.

A detection after machining of non-compliant sheets, that is to say having deformations larger than the tolerated dimensions, reduces the machining rates of the compliant sheets since said non-compliant sheets are machined unnecessarily.

It is not known device and method to check before machining, little or no penalty for machining rates, if a sheet has deformations and if these deformations are acceptable from a precision point of view sought or if on the contrary the sheet in question must be put off.

The present invention proposes to solve the aforementioned problems by means of a part machining device comprising at least one machine tool for machining said parts, and comprising at least one support comprising:

a bearing face on which each workpiece is immobilized during the machining operations, which said bearing face being delimited by a limiting theoretical shape geometrically adapted to a theoretical shape at least local parts to be machined, which said theoretical limit surface defining a support side and a workpiece side,

a plurality of sensors arranged in the vicinity of the theoretical limiting surface of the support side, the sensors being adapted to measure, at a plurality of points of the support, values representative of local distances between the support and each immobilized part in order to determine whether the part complies with and must be machined. According to other features of the machining device:

the support is of dimensions close to the dimensions of the part and the sensors are arranged in a substantially regular manner on the bearing face, and preferably the sensors are of inductive type,

the sensors form on the support face a substantially periodic mesh in two non-parallel directions,

it comprises means for storing at least one threshold value representative of a maximum local distance between the support and the part, and preferably means for comparing the at least one threshold value with the measured values representative of the distances between the support and the room,

it comprises second means for storing at least one corrective value representative of a local distance between a sensor and the limiting theoretical surface,

it comprises a module for selecting a sensor or a group of sensors at a time. According to the invention, a method for machining workpieces using the machining device, in which each workpiece is immobilized on the support face of the support, comprises a step of verifying the workpiece to determine whether a workpiece is conform. A machining step of a piece immobilized on the support is not performed if said part is deemed non-compliant. During the verification step:

at various points of the support, values representative of local distances between the support and each immobilized part are measured; the measured values are compared with at least one threshold value representative of a maximum local tolerated distance between the support and each immobilized part,

- a part is considered non-compliant if it is determined that at least one local distance is greater than a maximum local tolerated distance.

Preferably, the machining method also comprises a characterization step in which:

at least one reference block of characteristics close to those of the part and comprising at least one defect of dimensions corresponding to the maximum tolerated dimensions, is plated on the support surface,

the at least one threshold value is determined by measuring at the level of the at least one defect a value representative of a local distance between the support and the at least one reference block. Advantageously, the machining method also comprises a calibration step in which:

at least one reference block of characteristics close to those of the part and comprising at least one defect-free surface is stamped on the bearing face, at least one corrective value is determined by measuring at the level of the at least one surface without defect a value representative of a local distance between the support and the at least one reference block. The at least one corrective value is used to compensate for measurement bias on the measured values in the characterization step and the verification step, the compensation being performed either in the calibration step or in the step of characterization and verification step. The following description of modes of the invention is made with reference to the figures, in which identical references designate identical or similar elements, which represent in a non-limiting way:

FIG. 1: a schematic representation of a workpiece verification device according to the invention, FIG. 2: a partial schematic sectional view of a support of the verification device according to the invention, in a zone comprising sensors,

3: a partial diagrammatic sectional view of the support of FIG. 2, used to check a part, FIG. 4: a schematic sectional view of a reference block used in a process for verifying workpieces according to FIG. 'invention.

The present invention relates first of all to a workpiece verification device 1 used to check that a shape of a workpiece 2 conforms to a predefined template before machining said workpiece.

Such a verification device 1, shown schematically in FIG. 1, mainly comprises a support 10.

The support 10 comprises a bearing face 100, on which a face 21 to verify the workpiece 2 bears, said workpiece being immobilized during the verification for example by clamping and / or suction.

The bearing face 100 is delimited in space by a limiting theoretical surface 101 of shape geometrically adapted to a theoretical at least local shape of the face 21 to be verified of the part 2.

By delimited in space by the limiting theoretical surface 101, it is meant that the bearing face 100 comprises one or more bearing surfaces which are included in said limit theoretical surface.

By geometrically adapted means that the shape of the limiting theoretical surface 101 and the theoretical shape at least local of the part 2 are substantially the same, any differences between said shapes being of dimensions smaller than the maximum tolerated dimensions for the defects of the part 2, preferably of dimensions significantly smaller than said maximum tolerated dimensions. In the nonlimiting example shown in FIG. 2, the theoretical limiting surface 101 is of substantially flat shape to check parts with faces to be verified substantially plane.

The theoretical limiting surface 101 defines locally to the support 10 a first half-space on the side of the part, said part-side 101a, and a second half-space, said support side 101b.

Preferably to verify all the face 21 to be checked of the part 2, the support 10 and the theoretical limit surface 101 are of dimensions close to those of the part 2.

The support 10 also comprises a plurality of sensors 102 which are arranged in said support in the vicinity of the theoretical limit surface 101, the support side 101b. Said sensors are adapted to evaluate at a plurality of points of the support 10 local distances between said support and the part 2 to be verified.

In a preferred embodiment, particularly suitable for the verification of electrically conductive parts 2 such as metal sheets, each sensor 102 is an inductive type sensor, for example a flat coil, which when it is supplied with alternating current by a Generator 110 creates a magnetic field which in turn creates induced currents on the surface of said metal sheet, called eddy currents. The eddy currents in turn create a magnetic field that changes the impedance across said inductive sensor. The impedance modification, in particular the inductance, makes it possible to evaluate the distance between the inductive sensor 102 and the metal sheet.

In another nonlimiting example, each sensor 102 is an ultrasonic type sensor, for example air-coupled. In response to an electrical pulse provided by a generator 110, each ultrasonic sensor 102 emits ultrasonic waves towards the workpiece 2 and receives waves reflected by said workpiece. The time of flight of ultrasonic waves, corresponding to the time elapsed between the emission of the ultrasonic waves and the reception of the waves reflected by the face 21 to be checked, makes it possible to evaluate the distance between the ultrasonic sensor 102 and the part 2.

Preferably, the sensors 102 are positioned in a substantially regular manner in the vicinity of the theoretical limiting surface 101. In the nonlimiting example shown in FIG. 1, the sensors 102 form on the support surface 100 a substantially periodic mesh following two non-parallel x and y directions. The spacings between the sensors 102 of the support 10 are for example between 10 cm and 30 cm. In a variant, the sensors 102 are not positioned in a substantially regular manner and are for example concentrated in a zone, known a priori, in which the parts 2 are likely to present deformations.

In the example shown in FIG. 2, the sensors 102 are located in recesses 103 of the bearing face 100. In another non-limiting example, not shown, the support 10 has openings between a face of the support, called a face machining 104, on the opposite side to the bearing face 100, through which the sensors 102 are arranged in the vicinity of the theoretical limit surface 101.

Preferably, a space between the sensors 102 and the theoretical limiting surface 101 is free, that is to say that the sensors 102 are in line-of-sight with the part 2 pressed against the support 10. Advantageously, each sensor 102 comprises a outer surface 1020, on the side of the theoretical limiting surface 101, which is tangential at least locally to said limit theoretical surface, or even locally confused with said limiting theoretical surface, so that the local distance between the sensor 102 and the theoretical limitary surface 101 is substantially zero, the sensor 102 being theoretically in contact with the part 2 pressed onto the support 10.

The sensors 102 are connected to at least one measuring device 120, which measures values representative of the local distances between the support 10 and the part 2 at the level of each sensor 102. For example, the measured values correspond to the values of the physical quantities enabling evaluate local distances (impedance, flight time, etc.) or correspond directly to homogeneous values at distances, which are for example determined by calculation as a function of the values of the physical quantities or by means of abacuses associating homogeneous values at distances with values of physical quantities.

Connecting cables connecting the sensors 102 to the measuring device 120 are for example arranged in grooves 105 arranged on the support face 100. Advantageously in the case where the part 2 is immobilized on the support 10 at least by suction grooves 105 are also used to create low pressure zones between the bearing face 100 and the face to be checked of said part. According to another nonlimiting example, the connection cables pass through openings made between the sensors 102 and the machining face 104 of the support 10.

In a particular embodiment, the verification device 1 also comprises means 130 for storing a threshold value representative of a maximum local tolerated distance between the support 10 and the part 2. Preferably, a plurality of threshold values are stored in the storage means 130, for example a sensor threshold value 102.

The storage means 130 are preferably non-volatile (magnetic hard disk, ROM memories, optical disk, etc.), volatile memory means 130 (RAM memories, etc.) are usable if the threshold value (s) to be determined is determined. each start of the verification device 1.

The verification device 1 also comprises in the preceding embodiment a control unit 140 comprising comparison means 141 (microcontroller, computer equipped with a microprocessor executing the instructions of a comparison software, etc.) values measured by the measuring apparatus 120, representative of the local distances between the support 10 and the part 2, with the threshold value or values stored in the storage means 130, representative of the maximum local tolerated distances. Advantageously, the control unit 140 also comprises a screen making it possible to display the results of the comparison, for example in the form of a mapping of the face 21 to be checked of the part 2 indicating the zones in which the threshold values have been exceeded.

In a particular embodiment, the verification device 1 also comprises second storage means 131, volatile or non-volatile, in which a corrective value is stored, which can be used to compensate for measurement biases corresponding to non-zero local distances. between sensors 102 and the theoretical limiting surface 101. Preferably, a plurality of corrective values are stored in the second storage means 131, for example a corrective value per sensor 102 of the support 10. Advantageously, the storage means 130 and the second storage means 131 are the same, and the threshold values on the one hand and the corrective values on the other hand are stored in different storage areas.

In an even more specific embodiment, the verification device 1 comprises a selection module 150 of the sensors 102 to be used, for example controlled by the control unit 140. The selection module 150 activates a sensor 102 or a group of sensors. sensors 102 at a time, for example by changing sensor 102 or sensor group 102 substantially periodically. The invention also relates to a device for machining parts 2 of the same theoretical form, not shown, comprising the verification device 1 according to the invention for checking each part 2 before machining. The machining device further comprises at least one machine tool, for example a milling machine, a boring machine or the like, for machining the workpieces 2. The machining operations are performed by immobilizing each workpiece 2 on the support 10 of the operating device. check 1, implemented as seen to determine if the part is compliant and needs to be machined. If the part 2 is compliant, it is machined on the support 10.The support 10 comprises for example openings arranged to allow the passage at least partially of the at least one machine tool through said support at the locations where the parts 2 must be machined, in the case where the machining operations must be performed on the face 21 of the part 2 from the machining face 104. The invention also relates to a process for verifying workpieces, which is described below in the nonlimiting case of an implementation by the verification device 1 according to the invention.

The verification method comprises a step in which a piece 2 to be checked and immobilized on the support 10 of the verification device 1 is placed and immobilized.

The verification method then comprises a step of checking the part 2 in which:

at various points of the support 10, values representative of the local distances between the support and the part 2 are measured,

the measured values are compared with a previously established threshold value, representative of a maximum local tolerated distance, and it is determined whether at least one local distance is greater than the maximum local tolerated distance. In the case where a plurality of threshold values, for example a threshold value per sensor 102, is available, each measured value at a sensor 102 is compared with the associated threshold value, and it is determined whether the local distance corresponding is greater than the maximum local distance associated. When at least one local distance is greater than a maximum local distance, indicating the presence of a defect larger than the tolerated dimensions, the part 2 is considered non-compliant.

An exemplary implementation of the verification method is illustrated in FIG. 3 in the case of a verification of a curved part 2. In FIG. 3, the maximum local tolerated distance between the support 10 and the part 2 is represented under the reference D _M.

At a sensor designated by the reference 102a, a local distance between the support 10 and the part 2 is less than the maximum local distance D _M. At a sensor designated by the reference 102b, a local distance between the support 10 and the part 2 greater than the maximum local distance D _M is detected, and the part 2 is deemed non-compliant.

In a preferred mode of implementation, the verification method also comprises a characterization step, carried out prior to the steps already described, in which the threshold value (s) are determined. Since the threshold value (s) do not depend on said pieces but essentially on the support (10) and the maximum tolerated dimensions for the defects, the characterization step is advantageously performed once only for the verification of a plurality of pieces (2).

To determine the threshold value or values, using a reference shim 3, as represented in the nonlimiting example of FIG. 4, comprising a groove 30 whose depth D _M corresponds to the maximum tolerated dimensions for the defects that the we try to identify. Such a reference shim 3 also has characteristics similar to those of the parts 2 to be checked.

In particular, the reference shim 3 is, apart from the groove 30, of a shape that is geometrically adapted at least locally to the shape of the theoretical limit surface 101, and therefore to the theoretical local shape of the faces 21 to inspect parts 2.

In addition, the reference shim 3 is made of the same material as the parts 2 to be checked. For example, in the case of a piece 2 of metal alloy, the reference shim 3 is made of the same alloy, that is to say using metals of the same kind taken in the same proportions. Preferably, the reference shim 3 is of a thickness close to that of the parts 2 to be checked.

In the characterization step, the reference wedge 3 is slid onto the support 10 with the groove on the side of said support opposite a sensor 102 and a value representative of the local distance at the level of the sensor is measured. groove 30 between the support 10 and the reference block 3.

The value thus measured corresponds to the threshold value at least for the sensor 102 considered. The threshold value corresponds directly to the value of the evaluated physical quantity (impedance, flight time, etc.) or corresponds to a homogeneous value at a distance, etc. Where appropriate, a plurality of threshold values are determined by repeating the preceding operation for each sensor 102 of the support 10. For example, a plurality of reference shims 3 are used, or advantageously a reference shim 3 comprising a plurality of grooves which are arranged so that, in a suitable position of the reference block 3, grooves are opposite all the sensors 102.

In a particular embodiment, the verification method also comprises a calibration step, preferably carried out prior to the characterization step or after said characterization step but before the other steps of said method, in which the one or more corrective values, used to correct measured values in the verification step and threshold values.

By correction, it should be understood that a value measured at a sensor 102 is, without correction, representative of a local distance between said sensor and the part 2, which said local distance being equal to the sum of the two following distances :

a local distance between the sensor 102 and the theoretical limiting surface 101, which corresponds to a constant measurement bias, a local distance between said theoretical limit surface and the part

2, which actually characterizes a possible defect of said piece. The correction therefore consists in compensating for the measurement bias, that is to say reducing it to the case in which the local distance between the sensor 102 and the theoretical limiting surface 101 is substantially zero. The correction is carried out either in the calibration step (which is in this case performed before the characterization step) or in the characterization and verification steps, using the corrective value or values representative of the measurement bias. .

In the case where the correction is performed in the calibration step, a single correction value is preferably considered which is used to determine the same setting of the different devices of the verification device 1 for all the sensors 102. the case for example when evaluating impedances: a correction value is determined for a sensor 102, and the different devices are adjusted so as to measure with the sensor considered a predefined target impedance in the absence of defects.

In the case where flight times, distances, etc. are evaluated, the correction is preferably performed in the characterization step and the verification step, subtracting the corrective value from the values respectively. thresholds and values measured in the verification step.

It should be noted that it is possible to identify the defects of parts 2 without making this correction, because the measurement biases are the same in the values measured in the verification step and in the threshold values, which are compared in said verification step.

In the calibration step, a reference block is used to determine the corrective value (s). Since the corrective value or values essentially depend on the support 10, the calibration step is advantageously performed once for the verification of a plurality of parts 2.

The reference block used for the calibration step is also of characteristics close to those of the parts 2 to be verified, and comprises at least one surface 31 having no groove.

Preferably, and this is the case considered in the remainder of the description, the same reference wedge 3 is used for the calibration step and for the characterization step, and the reference wedge 3 comprises at least two surfaces 31 having no groove, on either side of the groove 30.

In the calibration step, the reference wedge 3 is slid onto the support 10 with a surface 31 not having a groove on the side of said support opposite the sensor 102 in question. Because the reference wedge

3 is geometrically adapted to the limiting theoretical surface 101, the surface 31 having no groove is, at said sensor, substantially coincidental with the limiting theoretical surface 101. The measured value is representative of the local distance between said sensor and the theoretical limit area 101, and is used as a corrective value.

Where appropriate, a plurality of corrective values are determined by repeating the preceding operation for each sensor 102 of the support 10. For example in the case of a reference block 3 comprising a plurality of grooves for determining the threshold values without moving said hold in the characterization step, the reference shim 3 also has a plurality of non-groove surfaces which are arranged such that, in a suitable position of the reference shim 3, surfaces having no grooves are vis-à-vis all the sensors 102. The invention also relates to a method of machining parts 2 implementing the verification method according to the invention. According to the invention, each piece (2) to be machined is immobilized on the bearing face (100) of the support (10). If at the end of the verification process, a part 2 is deemed compliant, a machining step of said part, immobilized on the support 10, is performed. Otherwise, the part (2) is not machined and is rejected.

By making it possible to measure at a plurality of points of a support, of a shape geometrically adapted to a desired theoretical shape of a part, values representative of local distances between the support and the part which are compared with predetermined threshold values, the device and the verification method according to the invention make it possible to quickly determine whether the workpiece is to be machined or rejected.

Claims

- A part machining device (2) comprising at least one machine tool for machining said parts, characterized in that it comprises at least one support (10) comprising:

a bearing face (100) on which each piece (2) to be machined is immobilized during the machining operations, which said bearing face being delimited by a theoretical limit surface (101) of shape geometrically adapted to a shape theoretical at least local of the workpieces (2) to be machined, which said theoretical limiting surface defining a support side (101b) and a workpiece side (101a), - a plurality of sensors (102) arranged in the vicinity of the limiting theoretical surface (101) on the support side (101b), said sensors being adapted to measure at a plurality of points of the support (10) representative values of local distances between said support and each piece (2) immobilized to determine if said part is compliant and must be machined. - Machining device according to claim 1, wherein the support (10) is of dimensions close to the dimensions of the workpieces (2) to be machined. - Machining device according to claim 1 or 2, wherein the sensors

(102) form on the bearing face (100) a substantially periodic mesh in two non-parallel directions. - Machining device according to one of the preceding claims, wherein the sensors (102) are sensors of the inductive type. - Machining device according to one of the preceding claims, comprising means (130) for storing at least one threshold value representative of a maximum local tolerated distance between the support (10) and each workpiece (2) to be machined . - Machining device according to claim 5, comprising means for comparing (141) the at least one threshold value with the measured values representative of the local distances between the support (10) and each workpiece (2) to be machined. - Machining device according to claim 6, comprising seconds means for storing (131) at least one corrective value representative of a local distance between a sensor (102) and the limiting theoretical surface (101). - Machining device according to one of the preceding claims, comprising a selection module (150) of a sensor (102) or a group of sensors (102) at a time. - Machining process parts (2) wherein each workpiece (2) to be machined is immobilized on a bearing face (100) of a support (10), said support face is delimited by a theoretical surface limit (101) geometrically adapted to a theoretical shape at least local workpieces, said method being characterized in that it comprises a step of checking each piece (2) during which:

at various points of the support (10), values representing local distances between said support and each immobilized workpiece (2) are measured,

comparing the measured values with at least one threshold value representative of a maximum local tolerated distance between the support (10) and each immobilized part (2),

- a part (2) is considered non-compliant if at least one local distance is greater than a maximum local tolerated distance. and in that a step of machining a workpiece (2) immobilized on the support (10) is not performed if said workpiece is judged non-compliant. - Machining method according to claim 9, including a characterization step in which: - one plate on the support face (100) at least one reference block

(3) characteristics similar to those of the workpieces (2) to be machined and comprising at least one defect (30) of dimensions corresponding to the maximum tolerated dimensions,

the at least one threshold value is determined by measuring at the level of the at least one defect (30) a value representative of a local distance between the support (10) and the at least one reference wedge (3) . Machining method according to claim 10, comprising a calibration step in which: at least one reference shim (3) of characteristics similar to those of the workpieces (2) to be machined and comprising at least one defectless surface (31), is plated on the bearing face (100),

at least one corrective value is determined by measuring at the level of the at least one defectless surface a value representative of a local distance between the support (10) and the at least one reference wedge (3) . - Machining method according to claim 11, wherein the at least one corrective value is used to compensate for measurement bias on the values measured in the characterization step and the verification step, the compensation being performed either in the calibration step is in the characterization step and the verification step.