Jetting medium and method for surface treatment using such jetting medium

Abstract

The invention relates to an injection medium (10) comprising first ice particles (11) and second particles (12) having a hardness between 2000 and 2500 HV, said second particles being embedded in the surface and the volume of the first particles.

Description

Technical Field

[0001] The present invention relates to the cleaning and treatment of the external surface of parts using a medium (media) for sandblasting (which can also be in the singular form "medium"), the parts usefully being, for example, aerospace parts.

[0002] Thus, it relates to a cleaning and / or surface treatment method which proposes to project this pressure jet medium onto the surface to be treated. The present invention is particularly suitable for cleaning and treating parts obtained by an additive manufacturing method. Background Art

[0003] Parts obtained by an additive manufacturing method have a high level of roughness, where the arithmetic roughness of the profile (Ra) is in the range of 5 μm to 50 μm. The first factor contributing to this roughness is associated with the layering technique of the additive manufacturing method, which produces a staircase effect similar to that of the parts shown in Figure 1 The presence of this roughness can cause functional and mechanical problems in the mechanical assembly. Another factor contributing to the roughness is the presence of powder grains coalesced on the surface of the part. These powder grains coalesced on the surface can escape during the operation of the part and damage the mechanical system associated with the part, such as an oil circuit. These grains can also escape during handling by the operator, presenting health and environmental risks. Finally, for parts obtained by additive manufacturing, it is necessary to remove the residual powder that has melted during manufacturing. This is done by brushes and vacuum cleaners, but this is not sufficient. Additionally, in some cases, as long as this step has been omitted and the part has been heat-treated, it is no longer possible to remove the powder sintered to the part due to the thermal effect.

[0004] In order to fully exploit the performance of additive manufacturing parts, it is therefore essential to remove the surface roughness and the residual powder grains present on the surface. For this purpose, it is known to use a jetting technique based on corundum grains to reduce the roughness. This technique consists of projecting corundum grains onto the surface of the part to be treated under pressure. This technique reduces the roughness, but there is a significant risk of contaminating the part. This is because when the corundum grains collide with the surface of the part, the corundum grains can become embedded in the surface of the part. The encrustation rate is approximately 5% of the volume of the corundum grains projected. The presence of these corundum grains on the surface of the part has the same adverse effects as the powder grains and can have an impact on the mechanical properties of the part.

[0005] Alternatively, dry ice particles can be projected onto the surface of the part under pressure to remove powder grains from the surface of the part before heat treatment. The term "dry ice" refers to carbon dioxide CO2 in solid form. It has the property of evaporating directly without melting, transitioning from solid to gas without passing through the liquid state. This technique is similar to sandblasting and, due to the hardness of the dry ice particles, allows for a reduction in roughness or the removal of powder grains. The advantage of dry ice compared to conventional spraying techniques is that it sublimes after the impact caused by the thermal energy generated during the impact. The dry ice particles immediately turn into gas and evaporate into the atmosphere. Thus, unlike conventional sandblasting where the projected corundum particles can become embedded in the surface of the part, there is no risk of contamination with dry ice particles and the part remains clean. The hardness of the dry ice allows the powder grains on the surface of the part to be loosened and the residual powder to be removed without leaving any residue on the surface of the part.

[0006] Technical problem:

[0007] Jetting using dry ice particles is not effective enough for removing residual powder when the part has been heat-treated. This is because the residual powder coalesces on the surface of the part under the thermal effect of the sintering phenomenon. It will then not be possible to remove it using only dry ice jetting.

[0008] Therefore, the present invention relates to a new jetting medium that allows for the removal of roughness and the removal of powder grains and residual powder present on the surface of parts obtained by additive manufacturing or any other technique. Specifically, the proposed new jetting medium is effective in removing residual powder, even when the part has previously been heat-treated. Compared to the jetting media of the prior art, the new jetting medium thus increases the cleaning efficiency while maintaining the integrity of the part. Summary of the invention

[0009] A method for cleaning and treating the outer surface of a part by using a jetting medium is proposed, the jetting medium comprising first ice particles and second particles having a hardness between 2000 and 2500 HV, the second particles being embedded in the surface and the volume of the first particles, the method comprising the steps of generating a jetting medium flow and projecting it towards a region on the surface of the part to be treated, adjusting the projection speed of the particles so as to avoid separation between the second particles and the first particles when the first particles impact the surface of the part.

[0010] The presence of the first particles forming a protective barrier means that the second abrasive particles can no longer become directly embedded in the surface of the part. The abrasive particles are then released after the sublimation of the dry ice or the melting of the ordinary ice, thus keeping the part clean.

[0011] Thus, unlike conventional jetting media where abrasive particles can contaminate the part surface by embedding in it after jetting, the new media keeps the surface clean, without any solid elements inherent in the jetting media, so that the cleaned and treated surface leaves no residue.

[0012] The invention can be advantageously supplemented by the following features obtained individually or in any technically possible combination thereof:

[0013] - The first particles are water ice particles with a temperature between -10°C and -20°C,

[0014] - The first particles are dry ice particles with a temperature between -60°C and -80°C,

[0015] - The proportion of the second particles by volume relative to the first ice particles is between 20% and 40%, preferably between 20% and 30%,

[0016] - The second particles are corundum particles,

[0017] - The diameter of the first particles is between 1 mm and 50 mm, preferably between 20 mm and 30 mm, and the diameter of the second particles is between 0.01 mm and 0.5 mm, preferably between 0.1 mm and 0.2 mm.

[0018] According to an embodiment of the invention, the projection speed is between 10 m / s and 290 m / s, preferably between 100 m / s and 150 m / s.

[0019] Another aspect of the invention relates to a method for manufacturing a jetting media as defined above, which comprises the following steps:

[0020] - Supplying liquid carbon dioxide;

[0021] - Expanding the liquid carbon dioxide to atmospheric pressure to form dry ice snow;

[0022] - Sprinkling the second particles on the dry ice snow;

[0023] - Mixing the whole to obtain a first mixture;

[0024] - Compressing the first mixture to form a dry ice solid, where the corundum particles are embedded in the surface and volume of the solid;

[0025] - Extruding the solid through a plate to obtain a cylinder;

[0026] - Cutting the cylinder to obtain first dry ice particles with the desired size.

[0027] The invention can be advantageously supplemented by the following features obtained individually or in any technically possible combination thereof:

[0028] - The amount of the second particles introduced into the dry ice snow is between 20% and 40% by volume relative to the first ice particles, preferably between 20% and 30%.

[0029] - The second particles are corundum particles. Description of the Drawings

[0030] Other features, details, and advantages will emerge upon reading the following detailed description and upon analysis of the drawings, in which:

[0031] Figure 1 schematically shows a jetting medium according to an embodiment of the invention used in a method for surface treatment of a part obtained by additive manufacturing;

[0032] Figure 2 shows the state of the treated surface of the part after treatment, in which first dry ice particles are embedded;

[0033] Figure 3 shows the state of the treated surface of the part after the first dry ice particles have melted. Detailed Description

[0034] The following diagrams and description mainly contain elements of a definite nature. Therefore, they can be used not only to improve the understanding of the invention, but also, where appropriate, to contribute to its definition.

[0035] Figure 1 A new jetting medium 10 according to an embodiment of the invention is schematically illustrated. The medium is projected, by means of a suitable device 2 (such as a gun), in a compressed air stream towards the surface to be treated of a rough part 1 obtained, for example, by additive manufacturing.

[0036] The rough part 1 consists of a succession of layers 4 forming steps. Additionally, powder 3 coalesces on the surface of the steps.

[0037] The medium 10 comprises a plurality of first ice particles 11 and second abrasive particles 12 embedded in the surface and the volume of the first particles.

[0038] In an embodiment of the invention, the first ice particles are dry ice particles obtained from liquid CO2. The dry ice particles sublime and evaporate into a gas upon contact with the surface of the part, thus leaving no residue.

[0039] In an embodiment of the invention, the dry ice particles are in the form of rods (so-called pellets), having a length between 1 mm and 60 mm and a diameter between 1 mm and 50 mm, preferably between 20 mm and 30 mm. They can also be of an oval shape, as in the example shown in Figure 1 .

[0040] ​​​Advantageously, the temperature of the first dry ice particles is between -60°C and -80°C.

[0041] In one embodiment, the first ice particles may also be water ice particles obtained from chilled water. The ice particles are projected onto the surface of the part and melt under the thermal effect upon contact with the surface, and the resulting liquid evaporates, leaving no residue. The first particles are water ice particles having a temperature between -10°C and -20°C.

[0042] It is known to project dry ice particles onto the surface to be treated in a part to perform dry ice cleaning. The effectiveness of the surface treatment and cleaning is based on a combination of three effects:

[0043] - The mechanical effect caused by the kinetic energy of the dry ice particles at the instant of impact on the part;

[0044] - The thermal effect due to the temperature of the particles, where the residue becomes brittle and shrinks;

[0045] - The explosive effect produced by the sublimation of dry ice, causing the residue to fall off.

[0046] However, the treatment using only dry ice particles is not effective in reducing roughness and / or removing the powder that has coalesced on the surface of a previously heat-treated part. The authors of the present invention have found a way to solve this problem by means of a new jetting medium that combines dry ice particles with abrasive particles having a hardness between 2000 HV and 2500 HV embedded in the surface and volume of the dry ice particles.

[0047] This new medium combines the effects of the dry ice particles mentioned above with the abrasive ability of the second particles to reduce roughness and remove the coalesced powder.

[0048] In addition, the presence of the dry ice particles forming a protective barrier means that the abrasive particles are no longer likely to be directly embedded in the surface of the part. It is carried by the dry ice particles embedded in the surface of the treated part after spraying, as Figure 2 shown. The abrasive particles are then released after the sublimation of dry ice or the melting of ordinary ice, thus keeping the part clean.

[0049] Therefore, unlike conventional jetting media where the abrasive particles are embedded in the part surface after spraying and thus contaminate the part surface, the new medium keeps the surface clean, as Figure 3 illustrated, and it has no solid elements inherent in the jetting medium, so that the cleaned and treated surface leaves no residue.

[0050] According to the present invention, the hardness of the second abrasive particles is preferably between 2000 HV and 2500 HV.

[0051] Its diameter is between 0.01 mm and 0.5 mm, preferably between 0.1 mm and 0.2 mm.

[0052] Preferably, the second particles comprise corundum particles.

[0053] Advantageously, the proportion of the second particles of the second particles is between 20% and 40% by volume relative to the first ice particles, preferably between 20% and 30%.

[0054] A method for manufacturing a new medium comprising first dry ice particles and second abrasive particles embedded in the surface and volume of the first particles will now be described.

[0055] The first step of the method consists in obtaining CO2 snow by expanding the liquid carbon dioxide contained in the housing. Pressurized liquid CO2 is introduced into the housing. The pressure inside the housing is at or near atmospheric pressure. The pressurized liquid CO2 stream expands inside the housing with a temperature drop to form solid CO2 snow.

[0056] In a second step, corundum particles or other abrasive particles with a hardness between 2000 HV and 2500 HV are sprinkled on the dry ice snow and mixed with the CO2 snow to obtain a first mixture.

[0057] In a third step, this first mixture is then injected into a compaction and extrusion member to form a compacted solid mixture of CO2, in which the corundum particles are embedded in the solid CO2.

[0058] In a fourth step, the compacted solid is then pressed through an extrusion plate to form a cylinder, which is subdivided into dry ice rods or pellets, in which the corundum particles are embedded in the surface and volume of the dry ice pellets.

[0059] An example of a method for surface treating a part using the injection medium of the present invention will now be described, assuming that the first particles are dry ice particles.

[0060] It comprises (irrespective of the type of the first particles) the step of generating a stream of the injection medium and projecting it towards the area of the surface of the part to be treated. Under the action of compressed air, the first particles or pellets of dry ice are accelerated to a predetermined speed. This speed is adjusted so as to avoid separation between the second particles and the first particles during the projection phase and when the first particles collide with the surface of the part. The projection speed is between 10 m / s and 290 m / s, preferably between 100 m / s and 150 m / s. Tests are carried out to determine the optimal speed.

[0061] Before starting to treat and clean the surface of the part, parameters must be predetermined: the sizes of the first and second dry ice particles, the projection speed, the projection pressure and the projection rate at the outlet of the nozzle of the injection device.

[0062] The projection rate is between 10 kg / h and 100 kg / h.

[0063] Thus, if the first particles are dry ice particles, then due to the high speed and the low temperature between -60 °C and -80 °C, impurities will freeze and cracks will appear. The pellets penetrate these cracks, burst and thus loosen the deposits. This dry ice cleaning effect is combined with the abrasive action of the abrasive particles embedded in the dry ice pellets to remove sintered powder from the surface of the heat-treated parts.

[0064] The combined action of the dry ice pellets and the abrasive particles removes the agglomerated and sintered powder from the surface of the heat-treated parts, thus keeping the parts clean after said operation.

[0065] Industrial applications

[0066] The invention can be applied in particular to the field of cleaning and treating parts, more precisely parts obtained by additive manufacturing, to remove the roughness and powder residues specific to additive manufacturing.

Claims

1. A method for cleaning and treating the outer surface of a part (1) by using a jetting medium (10), the jetting medium comprising first ice particles (11) and second particles (12) having a hardness between 2000 and 2500 HV, with a plurality of the second particles embedded in the surface and volume of each first ice particle, the method comprising the steps of generating a jetting medium flow and projecting it towards a region of the surface of the part to be treated, and adjusting the projection speed of the particles so as to avoid separation between the second particles and the first ice particles when the first ice particles collide with the surface of the part.

2. The method according to claim 1, wherein The first ice particles are water ice particles having a temperature between -10 °C and -20 °C.

3. The method according to claim 1, wherein The first ice particles are dry ice particles having a temperature between -60 °C and -80 °C.

4. The method according to any one of claims 1 to 3, characterized in that, The proportion of the second particles in the volume of the first ice particles is between 20% and 40%.

5. The method according to claim 4, wherein The proportion of the second particles in the volume of the first ice particles is between 20% and 30%.

6. The method according to any one of claims 1 to 3, characterized in that, The second particles are corundum particles.

7. The method according to any one of claims 1 to 3, characterized in that, The diameter of the first ice particles is between 1 mm and 50 mm.

8. The method according to claim 7, wherein The diameter of the first ice particles is between 20 mm and 30 mm.

9. The method according to any one of claims 1 to 3, characterized in that, The diameter of the first ice particles is between 0.01 mm and 0.5 mm.

10. The method according to claim 9, wherein The diameter of the first ice particles is between 0.1 mm and 0.2 mm.

11. The method according to any one of claims 1 to 3, characterized in that, The projection speed is between 10 m / s and 290 m / s.

12. The method according to claim 11, wherein The projection speed is between 100 m / s and 150 m / s.

13. A method for manufacturing the jetting medium used in the method according to claim 3, comprising the following steps: - Supplying liquid carbon dioxide; - Expanding the liquid carbon dioxide to atmospheric pressure to form dry ice snow; - Sprinkling the second particles on the dry ice snow, wherein the amount of the second particles introduced into the dry ice snow is between 20% and 40% by volume relative to the first ice particles; - Mixing the whole to obtain a first mixture; - Compressing the first mixture to form a dry ice solid, wherein the second particles are embedded in the surface and volume of the solid; - Extruding the solid through a plate to obtain a cylinder; - Cutting the cylinder to obtain first dry ice particles having the desired dimensions.

14. The method according to claim 13, wherein The amount of the second particles introduced into the dry ice snow is between 20% and 30% by volume relative to the first ice particles.

15. The method according to claim 13 or 14, characterized in that, The second particles are corundum particles.

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