Intermediate assembly for additive manufacturing

Abstract

The invention relates to an intermediate manufacturing assembly (34) comprising a workpiece (21), the workpiece (21) comprising an overhanging part (30), the intermediate assembly (34) further comprising a support structure (36) for supporting the overhanging part (30), the support structure (36) comprising: - a fusible, porous connecting part (38) extending from the overhanging part (30), - a base plate (40) extending from the connecting part (38) and defining a plurality of channels (48), and - at least one column (42) carrying the base plate (40).

Description

[0001] DESCRIPTION

[0002] TITLE: Intermediate assembly for additive manufacturing

[0003] Technical field of the invention

[0004] The invention relates to an intermediate assembly for manufacturing a mechanical part using an additive manufacturing method. The invention also relates to a method for manufacturing a part using such an intermediate assembly.

[0005] State of the prior art

[0006] A method is known in the art which consists of manufacturing at least one part, in particular one or more metal part(s), by melting successive layers of powder using a laser beam controlled by an information processing system in which the three-dimensional coordinates of the points of the successive layers to be produced to form said parts have been recorded.

[0007] Figure 1 illustrates a manufacturing device 1 intended to implement such a method. The manufacturing device 1 comprises a reservoir 3 containing a metal powder 5 and whose bottom 7 is movable, movable in translation vertically by a rod 9 of a jack, and a neighboring tank 11, substantially parallelepiped, whose bottom is constituted by a movable plate 13, movable in translation vertically by a rod 15 of a second jack.

[0008] The manufacturing device 1 further comprises a scraper 17 for bringing powder from the reservoir 3 to the tank 11, the scraper 17 being movable in translation along a horizontal plane A substantially parallel to the plate 13. The manufacturing device 1 further comprises means 18 for generating a laser beam 19, coupled to a device 20 for moving said laser beam 19, making it possible to orient it and / or move it to reach any point of the tank 11.

[0009] To manufacture one or more parts 21, a first layer of powder is placed in the tank 11, substantially in the horizontal plane A, using the scraper 17.

[0010] The layer then has a lower surface corresponding to the surface of the plate 13 and an upper surface on which the laser beam 19 is directed and moved. The energy provided by this beam causes the local melting of the powder which, by solidifying, forms a first layer of the or each part 21.

[0011] After forming this first layer, the plate 13 is lowered by a distance corresponding to the thickness of a layer of powder, while the bottom 7 of the reservoir 3 is raised by a corresponding height, so that a certain quantity of powder 22 is located above the horizontal plane A. Then, this quantity of powder 22 is brought by a blade 23 of the scraper 17, from the reservoir 3 into the tank 11, to form a second layer over the previous layer. In the same way as previously, a second layer of each part 21 is formed using the laser beam 19. The quantity of powder and the positions of the bottom 7 and the plate 13 are determined so as to form layers of powder of a chosen and constant thickness.

[0012] These operations are repeated so as to stack the layers of powder in a vertical direction Z, perpendicular to the horizontal plane A, and to melt targeted parts of these layers by means of the laser beam 19, until the parts 21 are completely manufactured.

[0013] This method allows complex parts to be manufactured quickly and fully automatically, resulting in significant savings in time and resources.

[0014] However, it presents constraints that limit the possibilities when designing parts.

[0015] In particular, the overhanging lower surfaces of the parts 21 cannot form angles greater than approximately 45° with the vertical direction Z to be manufacturable according to such a method.

[0016] More inclined bottom surfaces are not sufficiently supported during powder layer stacking, and their fabrication requires the addition of support parts to the part design model 21. These support parts must be manually removed after the additive manufacturing step, which requires time-consuming and specific machining work.

[0017] Presentation of the invention

[0018] The invention aims to overcome these drawbacks by providing a method for additively manufacturing a metal part comprising overhanging surfaces, without requiring machining steps subsequent to additive manufacturing.

[0019] To this end, the invention relates to an intermediate manufacturing assembly comprising a part, the part comprising an overhanging part, the intermediate assembly further comprising a support structure for the overhanging part, the support structure comprising:

[0020] - a fusible porous connecting part, extending from the overhanging part,

[0021] - a sole extending from the connecting portion and defining a plurality of channels, and

[0022] - at least one column supporting the sole. Such an intermediate assembly allows the manufacture of a part comprising overhanging parts thanks to the support structure, this support part being easily removable afterwards by taking advantage of the surface treatment step by chemical dissolution.

[0023] The intermediate assembly and the part are made of a metallic material.

[0024] The overhanging part comprises at least one lower surface forming with a vertical direction an angle strictly greater than 45°.

[0025] The bonding part may have a porosity greater than or equal to 50%.

[0026] It is recalled that the porosity of a medium comprising a solid part and an interstitial part is defined as the ratio of the volume of the interstitial part to the total volume.

[0027] The bonding part may have a porosity greater than or equal to 70%.

[0028] The porosity of the connecting part can for example be approximately equal to 75%.

[0029] Such porosity values ​​allow significant weakening of the bonding part during a surface treatment step by chemical dissolution.

[0030] The sole comprises a plurality of pillars defining the channels between them, the channels opening opposite the connecting part.

[0031] Each pillar may comprise an upper surface carrying the connecting portion, a gap separating the upper surfaces of the pillars from each other being less than 1 millimeter. The upper surfaces of the pillars may have, for example, a hexagonal shape, or a square shape.

[0032] The invention also relates to a method of manufacturing a metal part, the method comprising the following steps:

[0033] - manufacturing of an intermediate assembly as above using an additive manufacturing method by selective melting or selective sintering on a bed of metal powder,

[0034] - immersion of the intermediate assembly in a dissolving solution and dissolution of an external surface of the intermediate assembly, and

[0035] - removal of the support structure by mechanical rupture of the connecting part.

[0036] Mechanical rupture of the connecting portion may be implemented by applying a transverse force to a distal end of the column.

[0037] The transverse force is oriented approximately perpendicular to the main direction of extension of the column.

[0038] Such a removal method is made possible by the geometry of the support structure and allows for easy removal of the support structure, particularly manually.

[0039] Dissolution of the external surface can take place over a thickness of between 0.05 millimeters and 0.2 millimeters.

[0040] Dissolution of the external surface can reduce the mechanical strength of the bonding part by at least 90%. Such a feature allows easy removal of the support structure, especially manually.

[0041] Mechanical strength is defined here as the value of mechanical stress that must be exerted on the connecting part to achieve complete rupture.

[0042] The chemical dissolution solution is notably an acid solution, capable of “eating away” metallic materials.

[0043] Such a solution allows surface dissolution over a small thickness, which improves the surface condition of the part and weakens the bonding part, without removing too much material from the part.

[0044] Brief description of the figures

[0045] [Fig. 1] Figure 1 is a schematic view of an additive manufacturing device,

[0046] [Fig. 2] Figure 2 is a front view of a part including an overhanging portion,

[0047] [Fig. 3] Figure 3 is a front view of an intermediate assembly according to the invention, intended for the manufacture of the part of Figure 2, and

[0048] [Fig. 4] Figure 4 is a detail view of a support structure of the intermediate assembly of Figure 3.

[0049] Detailed description of the invention

[0050] Figure 2 represents a part 21 that it is desired to manufacture by an additive manufacturing process according to the invention.

[0051] The part 21 comprises an overhanging portion 30, which has a lower surface 32 extending in a plane P forming an angle greater than 45° with a vertical direction Z.

[0052] In the example shown, the lower surface 32 of the overhanging part 30 extends in a substantially horizontal plane P, i.e. forming an angle of 90° with the vertical direction Z.

[0053] The vertical direction Z considered here is relative to the previous additive manufacturing device 1, during an additive manufacturing step, and does not necessarily correspond to the vertical direction in the environment in which the part 21 is intended to be implemented.

[0054] The method of manufacturing the part 21 comprises a step of manufacturing an intermediate assembly 34, shown in FIG. 3, according to a method by additive manufacturing by selective laser melting or selective sintering, as described above.

[0055] The intermediate assembly 34 is a manufacturing intermediate which comprises the part 21 as well as a support structure 36 shaped to support the overhanging portion 30. The support structure 36 comprises a connecting portion 38 extending from the overhanging portion 30, a sole 40 carrying the connecting portion 38 and a column 42 carrying the sole 40 and extending so as to rest on the plate 13 by its distal end 44.

[0056] The connecting part 38 is manufactured at the same time as the rest of the intermediate assembly 34 by additive manufacturing.

[0057] The connecting part 38 is fusible, that is to say it is intended to be destroyed to separate the support structure 36 from the part 21.

[0058] The connecting portion 38 extends below the entirety of the lower surface 32, so as to support it during the additive manufacturing step.

[0059] It has a high porosity, preferably greater than 50%, in particular greater than or equal to 70%. The porosity of the connecting part 38 is for example substantially equal to 75%. The sole 40 extends between the connecting part 38 and the column 42, relative to the vertical direction Z, so as to support the connecting part 38.

[0060] The sole 40 comprises a plurality of pillars 46 having flared shapes, defining between them fluid circulation channels 48.

[0061] The column 42 is dense and extends substantially in the vertical direction Z, from the sole 40 to its distal end 44 intended to be in contact with the plate 13 during manufacturing.

[0062] The column 42 has, in the example shown, a shape which tapers progressively from the sole 40 to the distal end 44, while retaining lateral flanks forming angles of less than 45°, and preferably less than 30°, with the vertical direction Z. This shape makes it possible to reduce the quantity of material required for manufacturing the column 42 and makes it easier to grip, without restricting the manufacturability of the intermediate assembly 32.

[0063] Figure 4 is a detail view showing the sole 40 and the upper part of the column 42.

[0064] As shown, each pillar 46 comprises an upper end 50, opposite the column 42 with respect to the vertical direction Z. Said upper end 50 forms a flat surface carrying the connecting portion 38.

[0065] Each upper end 50 has a substantially square shape, in a horizontal plane.

[0066] Alternatively, the upper ends may have rectangular or hexagonal shapes.

[0067] A spacing E separating the upper ends 50 of each pillar 46 is less than or equal to 1 mm, in order to allow the manufacturing of the connecting part 38 over the sole. The channels 48 defined between the pillars 46 open between the upper ends 50, over an entire lower surface of the connecting part 38, which allows the entire connecting part to be brought into contact with the liquid circulating in the channels 48.

[0068] The method for manufacturing the part 21 comprises, after the additive manufacturing step, a step of immersing the intermediate assembly 34 in a dissolution solution.

[0069] The chemical dissolution solution is, for example, an acid solution, capable of “eating away” metallic materials.

[0070] The intermediate assembly 34 is immersed in the dissolution solution bath for an immersion time of between 15 minutes and 1 hour, preferably between 15 and 45 minutes.

[0071] The dissolving solution flows into the channels 48 and permeates the entire connecting portion 38.

[0072] During the immersion step, an external surface of the intermediate assembly 32 is dissolved by the dissolution solution, over a small thickness. The dissolution thickness is notably between 0.05 millimeters and 0.2 millimeters.

[0073] Such a step of immersion and surface dissolution is classic in additive manufacturing processes by selective powder bed fusion, and makes it possible to improve the surface condition of the manufactured parts.

[0074] This step also makes it possible, here, to significantly weaken the connecting part 38, since its high porosity makes the dissolution thickness non-negligible relative to its structure.

[0075] The connecting part 38 loses for example at least 90% of its mechanical strength during the immersion and surface dissolution step.

[0076] The method then comprises a step of removing the support structure 36, during which a transverse force, i.e. oriented in a direction in a horizontal plane, is applied to the distal end 44 of the column 42.

[0077] This transverse force, applied manually or by means of a tool depending on the dimensions involved, allows the mechanical rupture of the connecting part 38 and the removal of the support structure 36.

[0078] The invention can be generalized to any part having an overhanging portion 30 whose lower surface 32 forms an angle greater than 45° with the vertical direction Z, by changing the shape of the column 42 and / or the orientation of the sole 40, to have suitable support during the additive manufacturing step.

Claims

DEMANDS 1. Intermediate assembly (34) for additive manufacturing comprising a metallic part (21), the part (21) comprising an overhanging portion (30), the intermediate assembly (34) further comprising a support structure (36) for the overhanging portion (30), the support structure (36) comprising: - a fusible porous connecting section (38), extending from the overhanging section (30), - a sole (40) extending from the connecting part (38) and defining a plurality of channels (48), and - at least one column (42) supporting the footing (40), the column being dense, in which the footing (40) comprises a plurality of pillars (46) defining between them the channels (48), the channels (48) opening opposite the connecting part (38).

2. Intermediate assembly (34) according to the preceding claim, in which the connecting part (38) has a porosity greater than or equal to 50%.

3. Intermediate assembly (34) according to the preceding claim, in which the connecting part (38) has a porosity greater than or equal to 70%.

4. Intermediate assembly (34) according to the preceding claim, in which each pillar (46) comprises an upper end (50) carrying the connecting part (38), a gap (E) separating the upper ends (50) of the pillars (46) from each other being less than 1 millimeter.

5. A process for manufacturing a metallic part (21), the process comprising the following steps: - manufacturing an intermediate assembly (34) according to any one of the preceding claims, by an additive manufacturing method using selective melting or selective sintering on a metal powder bed, - immersion of the intermediate assembly (34) in a dissolving solution and dissolution of an external surface of the intermediate assembly (34), and - removal of the support structure (36) by mechanical breakage of the connecting part (38).

6. Method according to the preceding claim, wherein the mechanical rupture of the connecting part (38) is implemented by applying a transverse force to a distal end (44) of the column (42). A method according to claim 5 or 6, wherein the dissolution of the external surface takes place over a thickness of between 0.05 mm and 0.2 mm. A method according to any one of claims 5 to 7, wherein the dissolution of the external surface reduces the mechanical strength of the connecting portion (38) by at least 90%.

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