Parts verification process

Abstract

A method comprising: estimating (106) a first quantity indicative of a porosity rate of a sample from a tomogram representing the sample; polishing (108) a surface of the sample using initial polishing parameters; estimating (114) a second quantity indicative of the porosity rate of the sample from a micrograph showing the surface of the sample after polishing; from the initial polishing parameters, determining (116) adjusted polishing parameters making it possible to reduce a difference between the porosity rate indicated by the first quantity and the porosity rate indicated by the second quantity; polishing (208) a surface of another sample in the same material using the adjusted polishing parameters; estimating (214) a quantity indicative of the porosity rate of the other sample from a micrograph showing the surface of the other sample after its polishing.Figure for abstract: Fig. 2.

Description

Title of the invention: Method for verifying parts FIELD OF THE INVENTION

[0001] The present invention relates to a method for verifying parts. This method can in particular be applied to parts used in the design of a turbomachine. STATE OF THE ART

[0002] As is known, the porosity rate of a part is a physical quantity defined as a ratio between the volume of voids and the total volume of the part (sum of the volume of solid and the volume of pores). The value of the porosity rate is between 0 and 1 (or, as a percentage, between 0 and 100%). We thus have:

[0003] Porosity rate = pore volume / total volume

[0004] For example, a porosity of 0% is indicative of a non-porous part, i.e. one without pores.

[0005] In the present disclosure, the density of a part is the physical quantity such that porosity rate of the part + density of the part = 1. Thus, a part having a porosity rate of 2% also has a density of 98%.

[0006] Controlling the porosity rate of a part for use in the aeronautical field is important in controlling the quality of the products because this quantity has an influence on certain of the properties of the materials.

[0007] A known method for estimating the porosity rate of a part consists of making a cut of the part, so as to reveal a section of the part. The surface of this section is subjected to a metallographic preparation, this preparation comprising a polishing of the surface of the revealed section. Then, a metallographic analysis of the prepared surface is carried out, this analysis producing an estimate of the porosity rate of the part examined.

[0008] However, the porosity rate is a quantity very sensitive to the metallographic preparation. Consequently, different metallographic preparations can result in very significant differences in estimated porosity.

[0009] Another known method for estimating the porosity rate of a part is X-ray tomography. Tomography is a technique that produces radiographic images representing sections of an object, these images being called "tomograms" in the literature. Tomography is a non-destructive process, in the sense that the images show the interior of the object considered, without it being necessary to make a cut of this object beforehand. The tomogram of a metal part constitutes an input data which makes it possible to quantify the rate of porosity with much more precision thanks to the results analysis tools available, in particular by obtaining: • Directly the porosity of the entire volume of the room • The porosity of the part in any analytically chosen cutting plane • And, consequently, the porosity of the part in a particular cutting plane of interest

[0010] Tomography, however, requires implementation constraints which prevent it from being used in an industrial environment and on an industrial scale to check the porosity rate of a large number of metal parts. Indeed, tomography must be implemented in laboratory conditions, and takes time. Statement of the invention

[0011] An aim of the invention is to control the porosity of parts in an industrial environment and on an industrial scale while providing precise and consistent results.

[0012] This aim is achieved by a method comprising the following steps: • estimation of a first quantity indicative of a porosity rate of a sample from a tomogram representing the sample, • polishing a sample surface using initial polishing parameters, • estimation of a second quantity indicative of the porosity rate of the sample from a micrograph showing the surface of the sample after polishing, • from the initial polishing parameters, determination of adjusted polishing parameters making it possible to reduce a difference between the porosity rate indicated by the first quantity and the porosity rate indicated by the second quantity, • polishing a surface of another sample using the adjusted polishing parameters, the sample and the other sample being made of the same material, • estimation of a quantity indicative of the porosity rate of the other sample from a micrograph showing the surface of the other sample after polishing the surface of the other sample.

[0013] The inventors have found that the measurement of the porosity rate is very sensitive to polishing. In the proposed method, tomography is used to determine the polishing conditions. These polishing conditions can thus be reused on other parts / samples in order to obtain a measurement of satisfactory accuracy. The accuracy of the estimation results provided by this technique is thus affects the porosity estimate of the other part, without it being necessary to implement a tomography for this other part.

[0014] The above method constitutes a first object of the present disclosure, and may also comprise the following optional features, taken alone or in combination whenever technically possible.

[0015] Optionally, the material is metallic.

[0016] Optionally, the surface of the sample is revealed by cutting a piece, and in which the tomography represents the surface of the sample.

[0017] Optionally, the adjusted polishing parameters include a grain size of an abrasive medium to be applied to a surface to be polished.

[0018] Optionally, the adjusted polishing parameters include pressure exerted by an abrasive medium on a surface to be polished.

[0019] Optionally, the adjusted polishing parameters include a rotational speed of an abrasive medium relative to a surface to be polished.

[0020] Optionally, the adjusted polishing parameters include a polishing duration.

[0021] Optionally, the sample and the other sample are derived from parts obtained by additive manufacturing.

[0022] Optionally, the polishing step using the adjusted parameters is applied to several other samples that are distinct from the sample.

[0023] A second object of the present disclosure is a system comprising: • a polishing device capable of: polishing a surface of a sample using initial polishing parameters, polishing a surface of another sample using adjusted polishing parameters, the sample and the other sample being made of the same material, • a processing unit configured to: estimate a first quantity indicative of a porosity rate of the sample from a tomogram representing the sample; estimate a second quantity indicative of a porosity rate of the sample from a photograph showing the surface of the part after polishing the part; from the initial polishing parameters, determine the adjusted polishing parameters, the adjusted polishing parameters making it possible to reduce a difference between the porosity rate indicated by the first quantity and the porosity rate indicated by the second quantity; estimate a quantity indicative of the porosity rate of the other part from a micrograph showing the surface of the other sample after polishing the surface of the other sample. DESCRIPTION OF FIGURES

[0024] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0025] [Fig.l] schematically illustrates a system according to a first embodiment of the invention.

[0026] [Fig.2] is a flowchart of steps of a method according to one embodiment of the invention.

[0027] [Fig.3] shows two photographs of a polished surface of a metal part.

[0028] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION OF THE INVENTION

[0029] 1) System for manufacturing and verifying metal parts

[0030] With reference to [Fig.l], a system 1 for manufacturing and controlling metal parts comprises an additive manufacturing machine 2, a tomography device 4, a cutting device 6, a polishing device 8, a microscope 10, and a processing unit 12.

[0031] The additive manufacturing machine 2, known in itself, has the function of manufacturing a metal part by an additive manufacturing process. Additive manufacturing is for example a laser fusion on a powder bed (in English designated by the acronym PBF, for Powder Bed Fusion or SLM, for Selective Laser Melting). For this purpose, the machine 2 comprises a support, a metal powder injector to form a powder bed on the support, and a laser to locally irradiate the powder applied to the support, so as to cause fusion of the grains of the powder.

[0032] The tomography device 4, also known from the prior art, is configured to produce tomograms. The tomography device 4 is for example an X-ray device.

[0033] The cutting device 6 is adapted to cut a part manufactured by the machine 21. For this purpose, the cutting device 6 may comprise a blade, a saw or a laser.

[0034] The polishing device 8 is suitable for polishing a sample from a part manufactured by the machine 2, for example a coated sample. For this purpose, the polishing device 8 may comprise an abrasive support intended to be applied to a surface of the sample to be polished. The abrasive support may be in the form of an abrasive sheet (of the “sandpaper” type), a sheet on which grains are formed. The grains give the sheet its abrasive character. Alternatively, the abrasive support may be in the form of a felt soaked with a solution containing abrasive particles (for example diamond particles).

[0035] The polishing device 8 may comprise different abrasive supports, having different abrasive properties. For example, the polishing device 8 may comprise different abrasive sheets having different grain sizes and / or felts soaked in more or less abrasive solutions. The grain size constitutes an adjustable polishing parameter of the polishing device 8 (by selecting one of the available abrasive supports).

[0036] The polishing device 8 may also comprise a press configured to press any of the abrasive media described above onto the surface of a workpiece to be polished. The pressure exerted by this press on the surface to be polished is another adjustable polishing parameter of the polishing device 8.

[0037] The polishing device 8 is configured so that the abrasive media are rotatable relative to the surface to be polished. The rotational speed of the abrasive media is yet another adjustable polishing parameter of the polishing device 8.

[0038] The duration of a polishing, i.e. the duration of application of the pressure by the press, is yet another adjustable polishing parameter of the polishing device 8.

[0039] The microscope 10 comprises a photographic apparatus adapted to acquire photographic images of a metallurgical sample with a high magnification rate. In the following, the images acquired by the microscope are referred to as “micrographs”. In this document, the term “photographic apparatus” designates any apparatus capable of imaging an object in a purely optical manner using an objective and a photodetector, without requiring sensors of other types. Thus, in this document, the microscope 10 is a non-tomographic imager.

[0040] The processing unit 12 is configured to apply processing operations to images provided by the tomography device 4 and by the microscope 10. These processing operations will be described later. The processing unit 12 comprises a processor configured to execute the code instructions of a program; during such execution, the aforementioned processing operations are implemented. The processing unit 12 may also comprise a memory accessible by the processor, and in which the program is stored. The processor is of any type (CPU, GPU, SoC, ASIC, FPGA, etc.).

[0041] 2) Manufacturing process and verification of metal parts

[0042] With reference to [Fig.2], a method using the system 1 described previously includes two phases: a calibration phase 100 and a subsequent phase 200.

[0043] The calibration phase 100 comprises the following steps.

[0044] In a manufacturing step 102, a part, referred to below as a reference part, is manufactured by the additive manufacturing machine 2, using a method known from the state of the art.

[0045] The reference part may be made of a metallic material. This metallic material may be copper, aluminum, nickel or an alloy comprising at least one of these metals. Alternatively, the reference part is made of a composite material or a ceramic material.

[0046] In a cutting step 103, the cutting device 6 cuts the part, in order to remove a portion of the part which is hereinafter referred to as a “sample”. The sample has an external surface corresponding to an internal section of the part before it is cut.

[0047] In a tomography step 104, a tomogram representing the surface of the sample is generated by the tomography device 4, using a tomography method known from the state of the art. Thus, the section represented in the tomogram coincides with the section plane of the initial part.

[0048] In a processing step 106, the processing unit 12 applies a processing to the tomogram, this processing estimating a first quantity indicative of the porosity rate of the part. This processing is known from the state of the art. The first quantity can be directly the porosity rate of the part. Alternatively, the first quantity is the density of the part (it is recalled that density + porosity rate = 1). The first quantity is then stored.

[0049] In a polishing step 110, the polishing device 8 polishes the surface of the sample revealed by the cutting, using initial polishing parameters. These initial polishing parameters include: • An initial polishing time, • An initial grain size of abrasive support used during polishing, • An initial pressure of application of the abrasive support on the surface, • A rotation speed of the abrasive support relative to the surface.

[0050] In other words, during the polishing step 110, an abrasive support having the initial grain size is pressed according to the initial pressure onto the surface of the sample taken from the reference part during the initial polishing time.

[0051] In an acquisition step 112 carried out after the polishing 110, the microscope 10 acquires a micrograph showing the polished surface.

[0052] In a metallographic analysis step 114, the processing unit 12 applies a metallographic processing to the micrograph, this processing estimating a second quantity indicative of the porosity of the sample, and therefore of the part from which the sample originates. This processing is also known from the state of the art. The second quantity in question can be directly the porosity rate of the sample. Alternatively, the second quantity is the density of the sample (remember that density + porosity rate = 1). The second quantity is then stored.

[0053] As an example, [Fig. 3] shows two micrographs obtained on the basis of a metal sample polished using different polishing parameters. Analysis of the left micrograph led to a porosity rate of 5%, while analysis of the right micrograph led to a porosity rate of 0.25%. This illustrates that the porosity rate estimated during step 114 is very sensitive to the polishing parameters used upstream to polish the sample examined.

[0054] At this stage, the processing unit 12 has two quantities indicative of the porosity rate of the sample: the first quantity, obtained by tomography, and the second quantity, obtained by metallographic analysis.

[0055] In a determination step 116, adjusted polishing parameters are determined from the initial polishing parameters. The adjusted polishing parameters include: • A polishing time that may be the same or different from the initial polishing time, • A grain size of abrasive support, which may be identical or different from the initial grain size, • A pressure of application of an abrasive support on a surface to be polished, likely to be identical or different from the initial pressure, • A rotation speed of the abrasive support relative to a surface to be polished, which may be identical to or different from the initial rotation speed.

[0056] To determine polishing parameters adjusted during this step, the processing unit 12 can calculate a difference between the porosity indicated by the first quantity and the porosity indicated by the second quantity, and then compare this difference with a predefined threshold.

[0057] If the deviation is greater than the threshold, then it is considered that the initial polishing parameters used were not correct. It is indeed considered that the first quantity, obtained by tomography, constitutes precise and reliable reference information (and which, in any case, is independent of the polishing since this quantity is obtained before the polishing). In this situation, adjusted polishing parameters are determined which make it possible to reduce the deviation between the porosity indicated by the first quantity and the porosity indicated by the second quantity. By "making it possible to reduce the deviation", it is meant that the use of the adjusted polishing parameters instead of the initial polishing parameters during step 110 would have led to a smaller deviation. Thus, if the deviation is greater than the threshold, the adjusted polishing parameters differ from the adjusted polishing parameters by at least one polishing parameter.

[0058] If, on the contrary, the deviation is not greater than the threshold, then it is considered that the initial polishing parameters were suitable. In this case, the adjusted polishing parameters are equal to the initial polishing parameters.

[0059] In practice, one can choose a threshold extremely close to zero, or even equal to zero. In this case, there will always be an adjustment of the parameters, even slight, when the two quantities differ beyond this threshold (which should normally happen).

[0060] The closer the threshold tends towards zero, the more precise the calibration result will be.

[0061] The calibration phase 100 is then completed.

[0062] The subsequent phase 200 comprises the following steps.

[0063] In a manufacturing step 202, a second part is manufactured by the additive manufacturing machine 2. The second metal part is made of the same material as the reference part.

[0064] In a cutting step 208, the cutting device 6 performs a cut of the second part, so as to take a second sample from the second part. This step is similar to the cutting step 108.

[0065] In a polishing step 210, the polishing device 8 polishes a surface of the second sample, using the adjusted polishing parameters having been determined during step 116.

[0066] In an acquisition step 212 carried out after the polishing 210, the microscope 10 acquires a micrograph showing the polished surface of the second sample.

[0067] In a metallographic analysis step 214, the image processing unit applies a processing to the micrograph, this processing estimating a quantity indicative of the porosity rate of the second sample, and therefore of the second part from which the second sample originates. This step is identical to the metallographic analysis step 114.

[0068] In a verification step 216, the magnitude indicative of the porosity rate is compared to a threshold magnitude. If the result of this comparison indicates that the porosity rate of the second sample is excessive, then it is considered that the additive manufacturing carried out by the machine 2 is not satisfactory. Certain parameters of the machine 2 can then be updated in order to obtain other less porous parts. These parameters can for example concern the laser and / or the geometry of the deposited powder layers. If, on the contrary, the result indicates that the porosity rate of the second sample is excessive, then it is considered that the additive manufacturing carried out is satisfactory.

[0069] Phase 200 is repeated over time. In other words, manufacturing step 202 is repeated to manufacture separate parts, and steps 208-216 are applied to several of these metal parts. At each implementation of the polishing step 210, the same adjusted polishing parameters are used by the polishing device 8.

[0070] Unlike the reference part, no tomography step is applied to these parts. The tomography applied only to the reference part was used to calibrate the polishing, that is to say to determine the polishing parameters which make it possible to obtain results of similar precision by passing through a metallographic analysis, without however undergoing the implementation constraints required by tomography (in particular laboratory conditions).

[0071] In this case, we say that the polishing range is validated and can thus be frozen.

[0072] The method described above is advantageously implemented in a production line for parts intended for use in the aeronautical field, for example parts intended to be included in an aircraft engine. Machine 2 is used to manufacture such parts. The method is not directly applied to these parts due to the cutting step which is destructive, but is applied to test parts (also called specimens) specifically intended for this purpose, and which are manufactured at regular intervals by machine 2.

Claims

Claims

1. A method comprising: - estimating (106) a first quantity indicative of a porosity rate of a sample from a tomogram representing the sample, - polishing (108) a surface of the sample using initial polishing parameters, - estimating (114) a second quantity indicative of the porosity rate of the sample from a micrograph showing the surface of the sample after polishing, - from the initial polishing parameters, determining (116) adjusted polishing parameters making it possible to reduce a difference between the porosity rate indicated by the first quantity and the porosity rate indicated by the second quantity, - polishing (208) a surface of another sample using the adjusted polishing parameters, the sample and the other sample being made of the same material,- estimation (214) of a quantity indicative of the porosity rate of the other sample from a micrograph showing the surface of the other sample after polishing the surface of the other sample.,

2. Method according to the preceding claim, in which the material is metallic.

3. A method according to any preceding claim, wherein the surface of the sample is revealed by cutting out a piece, and wherein the tomography represents the surface of the sample.

4. A method according to any preceding claim, wherein the adjusted polishing parameters comprise a grain size of an abrasive media to be applied to a surface to be polished.

5. A method according to any preceding claim, wherein the adjusted polishing parameters comprise pressure exerted by an abrasive media on a surface to be polished.

6. A method according to any preceding claim, wherein the adjusted polishing parameters include a rotational speed of an abrasive media relative to a surface to be polished.

7. A method according to any preceding claim, wherein the adjusted polishing parameters include a polishing duration.

8. A method according to any preceding claim, wherein the sample and the other sample are derived from parts obtained by additive manufacturing.

9. A method according to any preceding claim, wherein the step of polishing using the adjusted parameters is applied to several other samples which are distinct from the sample.

10. System (1) comprising: a polishing device (8) capable of: - polishing a surface of a sample using initial polishing parameters, - polishing a surface of another sample using adjusted polishing parameters, the sample and the other sample being made of the same material, a processing unit (12) configured to: - estimate a first quantity indicative of a porosity rate of the sample from a tomogram representing the sample, - estimate a second quantity indicative of a porosity rate of the sample from a photograph showing the surface of the part after polishing the part, - from the initial polishing parameters, determine the adjusted polishing parameters, the adjusted polishing parameters making it possible to reduce a difference between the porosity rate indicated by the first quantity and the porosity rate indicated by the second quantity,- estimate a quantity indicative of the porosity rate of the other part from a micrograph showing the surface of the other sample after polishing the surface of the other sample.,

Images