Method for controlling chemical polishing

Abstract

The present invention relates to a method for monitoring polishing, the method comprising: positioning a workpiece in a chemical polishing solution, the workpiece being attached to a dynamometer suspended from a support positioned above the chemical polishing solution, the workpiece being in an initial state referred to as "to be polished"; measuring the change in the workpiece's weight using the dynamometer; comparing the measurement to a predetermined threshold, the threshold corresponding to a measurement of the workpiece's weight when the workpiece is in a final state referred to as "polished"; and removing the workpiece from the chemical polishing solution when the measurement reaches the threshold, the workpiece being in the final state referred to as "polished". Figure for the abstract: Fig. 1

Description

Title of the invention: Method for controlling chemical polishing FIELD OF INVENTION

[0001] The present presentation relates to the field of manufacturing metal parts and more specifically to the field of polishing metal parts, in particular for a turbomachine.

[0002] More particularly, the present exposition relates to a method for controlling the chemical polishing of metal parts. STATE OF THE ART

[0003] To treat a metal part produced by additive manufacturing, it is possible to subject it to chemical polishing. Chemical polishing can modify characteristics of the part such as its thickness, roughness, etc.

[0004] Chemical polishing consists of placing the part to be treated in a chemical solution for a certain time. In order to obtain the desired characteristics for the part, it is necessary to determine the time during which the part is placed in the chemical solution.

[0005] To determine the time after which the part should be removed from the chemical solution, a representative specimen of the part can be placed in the chemical solution at the same time. The specimen is periodically removed from the chemical solution, and its characteristics are measured. This allows the part's characteristics to be monitored indirectly, and the part can be removed from the chemical solution when the specimen's characteristics meet the desired specifications.

[0006] Such a process therefore induces a loss of time related to the removal and positioning of the test specimen.

[0007] Furthermore, such a process requires the production of a test specimen similar to the part to be treated. It therefore requires the production of a test specimen for each type of part.

[0008] Furthermore, removing the test specimen introduces significant differences between the measurements of the characteristics performed on the specimen and the characteristics of the part itself, as the part remains in the chemical solution during the specimen's removal. Moreover, the evolution of the specimen's and the part's characteristics differs before the specimen's removal from the measurement and after the specimen is repositioned in the chemical solution. This further complicates the accuracy and repeatability of the polishing process. Description of the invention

[0009] One aim of the present presentation is therefore to improve the process of polishing a metal part by eliminating the need for the use of a follow-up test piece.

[0010] To this end, according to one aspect of this description, a method for controlling polishing is proposed, the method comprising: - a positioning of a part in a chemical polishing solution, the part being attached to a dynamometer suspended from a support positioned above the chemical polishing solution, the part being in an initial state called "to be polished"; - a measurement of the change in the weight of the part using a dynamometer; - a comparison of the measurement to a predetermined threshold, the threshold corresponding to a measurement of the weight of the part when the part is in a final, so-called "polished" state; and - removal of the part from the chemical polishing solution when the measurement reaches the threshold, the part being in the final state known as "polished".

[0011] This method eliminates the need for a tracking test piece and improves polishing accuracy. Furthermore, this method simplifies and automates the polishing steps.

[0012] Advantageously, but optionally:

[0013] - the process includes, prior to the positioning of the part, a step of Determination of the threshold, including: - A first measurement of the characteristics of a test piece, the test piece being a copy of the part; - Positioning the test piece in the chemical polishing solution, the test piece being attached to a dynamometer suspended from a support positioned above the chemical polishing solution; - A measurement of the change in weight of the test piece using the dynamometer; - Removal of the test piece from the chemical polishing solution; - A second measurement of the characteristics of the test piece; and - A calculation of a correlation of the characteristics of a test piece by the first measurement and the second measurement with the measurement of the weight;

[0014] - if the characteristics of the test piece in the second measurement are less than the desired characteristics, positioning, measurement, withdrawal, second measurement and calculation are implemented again;

[0015] - the correlation calculation is configured to determine the threshold at which the withdrawal should to be carried out, depending on the characteristics of the part in question;

[0016] - the method includes measuring the initial weight of the part using a dynamometer just after the part is positioned and before measuring the change in the part's weight, to select the threshold to consider for the withdrawal;

[0017] - the measured characteristics of the test piece are the weight and / or the thickness and / or roughness.

[0018] According to another aspect of this presentation, a turbomachine part for aircraft is proposed, obtained by additive manufacturing or configured to be subjected to fatigue, and subjected to a polishing process as previously described.

[0019] According to another aspect of this presentation, an implementation set for a control method as previously described is proposed, the set comprising: - A bath to receive a chemical polishing solution; - A support positioned above the bath; and - A dynamometer attached to the support and configured to support a part immersed in the chemical polishing bath solution.

[0020] Advantageously, but optionally:

[0021] - the dynamometer is chosen according to the part to be polished and is configured for to support a part whose weight is between 1 and 30kg and to indicate a weight variation between 10g and 500g;

[0022] - the assembly may include an automatic control device comprising: - A device for acquiring weight measurements using a dynamometer; - A processing device to compare the weight measurement to a predetermined threshold; and - An actuation device to remove the part from the chemical polishing solution. DESCRIPTION OF THE FIGURES

[0023] Other features, purposes and advantages will become apparent from the following description, which is purely illustrative and not limiting, and which should be read in conjunction with the accompanying drawings on which:

[0024] Fig. 1 illustrates a schematic view of an implementation assembly for a polishing control method.

[0025] Figure 2 illustrates a flowchart of the steps in a process for controlling a polishing.

[0026] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION OF THE INVENTION

[0027] Polishing allows modification of an external surface of a part 1, such as the roughness of the external surface. A suitable type of polishing for polishing parts 1 in series is chemical polishing.

[0028] Chemical polishing consists of using a chemical polishing solution 2 to treat the surface of the workpiece 1 to be polished. For this purpose, a bath 3 is filled with the chemical polishing solution 2, as illustrated in [Fig. 1]. A support 4 for the workpiece 1 is positioned above the bath 3. The workpiece 1 to be polished is then configured for polishing by being fixed to the support 4, positioned in the bath 3, and immersed in the chemical polishing solution 2 from the bath 3.

[0029] The part 1 to be polished can be any type of part, for example, serial parts 1 for an aircraft engine. The part 1 to be polished can also be a part 1 obtained by additive manufacturing and which may require low roughness or a part 1 which may be subject to fatigue.

[0030] To follow precisely, in real time and simply the polishing of the part, a dynamometer 5 is hung on the support 4 and configured to support the part 1 positioned in the chemical polishing solution 2 of the bath 3.

[0031] The dynamometer 5 is chosen according to the part 1 to be polished and is configured to support a part 1 whose weight can be between 0.1 kg and 100 kg and preferably between 3 kg and 30 kg. The variation in weight of the part between before and after polishing can be from 0.8 kg to 1.5 kg.

[0032] The dynamometer 5 must have a tolerance of + / -20% and can indicate a variation in the weight of the part 1 of between 1g and 1kg and preferably the dynamometer may have a sensitivity of less than 0.16kg. The dynamometer may for example be a Pesola digital dynamometer 30kg / 10g, 50kg / 20g or 100kg / 50g — Raig.

[0033] The dynamometer 5 measures the weight of the part, or the force exerted by the test part 10 on the dynamometer 5. The force can be easily related to the weight because the part 1 is suspended from the support 4 in the direction of gravity. Thus, for simplicity, we will refer to the measurement of the weight of the dynamometer 5.

[0034] The polishing of part 1 must be controlled in order to obtain a part 1 which has desired characteristics such as a particular roughness of the external surface, a desired thickness etc... For this, a control process whose steps are illustrated by [Fig.2] is implemented.

[0035] The control process includes calibration of the dynamometer 5 and control steps for the polishing of the part.

[0036] Calibration

[0037] Calibration allows a measurement of the weight of part 1 by the dynamometer 5 to be correlated to the polishing of the external surface of part 1 positioned in the chemical polishing solution 2 of the bath 3.

[0038] The calibration is carried out with a part 1 called test part 10. The test part 10 is a copy of the part 1 to be polished considered.

[0039] The calibration comprises a series of steps detailed below.

[0040] A first measurement E00 of the characteristics of the test piece 10. The characteristics measured are the weight and / or the thickness and / or the roughness of the external surface of the test piece 10.

[0041] The first measurement E00 is followed by positioning E01 of the test piece 10 in the polishing chemical solution 2. For this purpose, the test piece 10 is attached to the dynamometer 5, which is suspended from the support 4 positioned above the bath 3. The weight measurement taken by the dynamometer 5 immediately after the test piece 10 is positioned in the polishing chemical solution 2 is recorded. This measurement corresponds to the weight of the piece 1 before polishing, referred to as the initial weight for simplicity.

[0042] Once the test piece 10 is in the bath 3, the calibration includes a measurement E02 of the evolution of the weight of the test piece 10 by the dynamometer 5.

[0043] After a certain time in the chemical polishing solution 2, the test piece 10 is removed (step E03) from the chemical polishing solution 2. The measurement of the dynamometer 5 just before the removal E03 of the test piece 10 is recorded. This measurement corresponds to the weight of the piece 1 after polishing, referred to as the final weight for simplicity.

[0044] A second measurement E04 of the characteristics of the test piece 10 is then carried out. The removal E03 makes it possible to measure more precisely the characteristics of the test piece 10, which would be more difficult to achieve if the piece 1 remained in bath 3.

[0045] The second measurement E04 is followed by a calculation E05 correlating the characteristics of the first and second measurements with the weight measurement E02 obtained from the dynamometer 5. The correlation can be performed between the first and second measurements, and between the initial and final weights, respectively. In other words, the correlation associates the first measurement E00 of the characteristics of part 1 with the initial weight measurement and the second measurement E04 with the final weight measurement.

[0046] The correlation calculation E05 is configured to indicate at what value of the weight measurement by the dynamometer 5 the removal of part 1 should be carried out according to the desired characteristics of the part 1 in question. The value in question is called the threshold.

[0047] If the characteristics of the test piece 10 at the second measurement are less than the desired characteristics, the positioning E01, the weight measurement E02, the retraction E03, the second measurement E04, and the calculation E05 are repeated. This increases the accuracy of the correlation between the weight measurement and the polishing of the test piece 10.

[0048] Once the calibration has been carried out, the polishing control steps of the control process can be implemented. The calibration may only need to be performed once per step, thus allowing the independent implementation of the steps. control. Calibration thus allows the implementation of simplified and repeatable control steps.

[0049] Furthermore, calibration can be performed only once for each part 1 with its own characteristics in order to create a calibration chart. For this purpose, a test piece 10 specific to each type of part 1 (i.e., each part 1 having different characteristics measured by an initial measurement) is subjected to calibration. The calibration chart thus includes a weight threshold corresponding to each characteristic of parts 1 to be polished. Once the calibration has been carried out, the inspection steps can be implemented directly and for one or more parts 1 simultaneously in the same bath 3. In this case, each part 1 is attached to a dynamometer 5.

[0050] Control steps

[0051] The process of controlling a polishing comprises several successive steps.

[0052] First, the part 1 to be polished is attached to the dynamometer 5 suspended from the support 4 positioned (step El) above the bath 3 comprising the chemical polishing solution 2 and is positioned in the chemical polishing solution 2. The part 1 is then in an initial state said to be "to be polished".

[0053] The characteristics of part 1 can be measured (steps E0) to select the threshold to be considered. The E0 measurement of the characteristics of part 1 before its placement in the bath 3 allows the threshold to be selected from the nomogram to be taken into account for subsequently removing part 1 from the chemical polishing solution 2. Furthermore, it is also possible to directly record the weight measurement by the dynamometer 5 immediately after the part is placed in the bath, in other words, its initial weight. This allows the threshold corresponding to such an initial weight of part 1 to be selected from the nomogram (in other words, the threshold corresponding to a test piece 10 whose initial weight is equal to the initial weight of the part).

[0054] The positioning El is followed by a measurement E2 of the evolution of the weight of the part 1 by the dynamometer 5.

[0055] The E2 weight measurement is compared to the threshold determined previously during calibration, and selected as explained above.

[0056] Once the weight measurement by the dynamometer 5 has reached the threshold considered, the part 1 is removed (step E3) from the chemical polishing solution 2. The part 1, once removed, is in the final state known as "polished".

[0057] The process can be implemented by a human or by an automatic control device 6. The automatic control device 6 may include: - a device for acquiring the E2 measurement of the weight by the dynamometer 5; - a processing device to compare the weight measurement to a threshold predetermined; and / or - an actuation device to carry out the removal E3 of part 1 from the chemical polishing solution 2 when the weight measurement is equal to the predetermined threshold.

[0058] Thus, the polishing is more precise because it is controlled directly by the weight measurement indicated by the dynamometer 5 and faster because it no longer requires the use of a follow-up test piece.

[0059] Moreover, the polishing is thus more easily repeatable and reliable over time.

Claims

Demands

1. Method for checking a polishing process comprising: - Positioning (E1) a part (1) in a chemical polishing solution (2), the part (1) being attached to a dynamometer (5) suspended from a support (4) positioned above the chemical polishing solution (2), the part (1) being in an initial state referred to as "to be polished"; - A measurement (E2) of the evolution of the weight of the part (1) by the dynamometer (5); - A comparison (E3) of the measurement to a previously predetermined threshold, the threshold corresponding to a measurement of the weight of the part (1) when the part (1) is in a final state referred to as "polished"; and - A withdrawal (E4) of the part (1) from the chemical polishing solution (2) when the measurement reaches the threshold, the part (1) being in the final state referred to as "polished".

2. A method according to claim 1, comprising, prior to the positioning (E1) of the part (1), a threshold determination step comprising: - A first measurement (E00) of the characteristics of a test part (10), the test part (10) being a copy of the part (1); - A positioning (E01) of the test part (10) in the chemical polishing solution (2), the test part (10) being attached to a dynamometer (5) suspended from a support (4) positioned above the chemical polishing solution (2); - A measurement (E02) of the evolution of the weight of the test part (10) by the dynamometer (5); - A withdrawal (E03) of the test part (10) from the chemical polishing solution (2); - A second measurement (E04) of the characteristics of the test part (10); and - A calculation (E05) of a correlation of the characteristics of a test piece (10) by the first measurement (E00) and the second measurement (E04) with the measurement (E02) of the weight.

3. A method according to claim 2, wherein, if the characteristics of the test piece (10) of the second measurement (E04) are lower than desired characteristics, the positioning (E01), the measurement (E02), the withdrawal (E04), the second measure (E04) and the calculation (E05) are implemented again.

4. A method according to any one of claims 2 and 3, wherein the correlation calculation (E05) is configured to determine the threshold at which the withdrawal (E3) must be carried out, depending on the characteristics of the part (1) considered.

5. A method according to any one of claims 2 to 4, wherein the measured characteristics of the test piece (10) are the weight and / or the thickness and / or the roughness.

6. A method according to any one of claims 1 to 5, comprising a measurement (E0) of the initial weight of the part (1) by the dynamometer (5) just after the positioning (El) of the part (1) and before the measurement (E2) of the evolution of the weight of the part (1), to select the threshold to be considered for the withdrawal (E4).

7. Aircraft turbomachine part (1) obtained by additive manufacturing or configured to be subjected to fatigue, and subjected to a polishing process according to any one of claims 1 QA

8. of U. Assembly for implementing a control method according to any one of claims 1 to 6, the assembly comprising: - A bath (3) for receiving a chemical polishing solution (2); - A support (4) positioned above the bath (3); and - A dynamometer (5) attached to the support (4) and configured to support a part (1) immersed in the chemical polishing solution (2) of the bath (3).

9. Assembly according to claim 8, wherein the dynamometer (5) is chosen according to the part (1) to be polished and is configured to support a part (1) whose weight is between 1 and 30kg and to indicate a weight variation between 10g and 500g.

10. Assembly according to any one of claims 8 and 9, comprising an automatic control device (6) including: - A device for acquiring the weight measurement by the dynamometer (5); - A processing device for comparing the weight measurement to a predetermined threshold; and - An actuation device for removing the part (1) from the chemical polishing solution (3).