METHOD FOR WINDING A FILAMENT FOR AN ADDITIVE MANUFACTURING DEVICE

Abstract

The present invention relates to an assembly for a turbomachine turbine extending along an axis (X), comprising: —an ejection cone (100) comprising a radially outer annular wall (102) defining a flow duct for a flow of hot gases and a sound box radially arranged inside the outer annular wall (102), the sound box comprising a radially inner annular wall (104), —a connecting member (106) intended to be axially inserted between the exhaust housing and the ejection cone (100), the connecting member (106) comprising an upstream annular flange (108) intended to be attached to the exhaust housing and a plurality of downstream securing tabs (110) connected to the inner annular wall (104), —an annular sealing shroud (112) comprising an upstream portion surrounding the securing tabs (110) of the connecting member (106) so as to cover the spaces circumferentially located between the securing tabs (110) and axially located between the upstream annular flange (108) of the connecting member (106) and the radially inner annular wall (104).

Claims

1. A method for winding a filament for an additive manufacturing device comprising the steps of: providing a filament filled with at least 80% metal powder by mass; heating said filament up to a temperature of at least 70° C. and keeping said filament at said temperature; winding said filament around the axis of a coil, preferably metallic, the diameter of the coil being in the empty state larger than or equal to a diameter of 100 mm.

2. The method for winding a filament according to claim 1, wherein said diameter of the coil is comprised between 100 and 140 mm, preferably between 120 and 140 mm.

3. The method for winding a filament according to claim 1, wherein said filament is heated to a temperature comprised between 70 and 140° C., preferably between 70 and 90° C.

4. An installation for winding a filament onto a coil for an additive manufacturing device comprising: a filament extruder; stretching means; means for heating and keeping said filament at a temperature of at least 70° C.; drive means; means for winding said filament around the coil, preferably metallic, the diameter of the coil of which in the empty state is larger than or equal to a diameter of 100 mm.

5. The installation for winding a filament onto a coil according to claim 4, wherein the means for heating and keeping said filament at a temperature of at least 70° C. intervene between the stretching means and the winding means.

6. The installation for winding a filament onto a coil according to claim 4, wherein the stretching means comprise a drawing belt.

7. The installation for winding a filament onto a coil according to claim 4, wherein the means for heating said filament comprise means for blowing air at said temperature.

8. The installation for winding a filament onto a coil according to claim 4, wherein the means for heating said filament include an infrared heating means.

9. The installation for winding a filament onto a coil according to claim 4, wherein the drive means include at least one drive roller.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0034] FIG. 1 represents a metal powder injection molding process, also called “Metal Injection Molding” (MIM);

[0035] FIG. 2 represents a fused filament fabrication process, also called “Fused Filament Fabrication” (FFF);

[0036] FIG. 3 represents a volume variation between a green part in FIG. 3A and a sintered part in FIG. 3B.

[0037] FIG. 4 represents a three-point bending test on a filament at room temperature and more specifically the evolution of the bending stress a of said filament in Mega Pascal (MPa) as a function of the strain rate e;

[0038] FIG. 5 represents an example of a damaged filament comprising cracks;

[0039] FIG. 6 represents a filament surrounded by a polymer skin;

[0040] FIG. 7 represents an extrusion device or industrial extrusion line for a filament according to the invention;

[0041] FIG. 8 represents in FIG. 12A a coil according to the invention and in FIG. 12B a conventional coil.

[0042] FIG. 9 represents the evolution of the elastic modulus G′ as a function of the temperature T for a filament during dynamic thermomechanical analysis tests (DMTA) according to the invention;

[0043] FIG. 10 represents three-point bending tests on a filament at a temperature T of 80° C. and more specifically the evolution of the bending stress a of said filament in Mega Pascal (MPa) as a function of the strain rate ε according to the invention;

[0044] FIG. 11 represents in FIG. 11A the evolution of the bending stress σ of said filament in Mega Pascal (MPa) as a function of the strain rate ε and in FIG. 11B, the evolution of the minimum radius of curvature R in millimeters (mm) of the central roll of the coil such that the filament is not damaged as a function of the strain rate ε according to the invention;

[0045] FIG. 12 represents a diagram illustrating the obtainment of a radius of curvature as a function of a strain during a three-point bending test.

DETAILED DESCRIPTION OF THE INVENTION

[0046] The present document falls in the context of an additive manufacturing device allowing building a part layer-by-layer, by depositing a molten filament which solidifies while cooling. FIG. 7 illustrates an installation 108 for extruding a filament 104 and winding it onto a coil 110 for subsequent use in an additive manufacturing device.

[0047] In such an installation, the filament 104 is produced by means of an extruder 112. This filament 104 has a diameter comprised between 1.5 and 5 mm. It comprises between one and three polymers and is filled with at least 80% metal powder by mass.

[0048] Afterwards, the filament 104 is stretched by stretching means 114. These stretching means 114 comprise a drawing belt 116. The filament 104 is then heated by heating means 118 to a temperature of at least 80° C. These heating means 118 comprise means for heating air to said temperature 120 and/or an infrared heating means 122. Thus, the filament 104 is heated and kept at said temperature: one of the compounds of the binder is kept in the molten state to soften the filament. Afterwards, the filament is driven by drive means 124 towards a coil 110. These drive means comprise at least one drive roller 126.

[0049] The filament 104 is then wound by winding means 127 around a coil 110. This coil includes a central roll 128 or cylindrical portion with a circular base around which the filament is wound.

[0050] The central roll 128 includes an external perimeter of its base which is inscribed within a circle so that this central roll 128 could be a cylindrical portion with a polygonal base. This central roll 28 has a diameter larger than or equal to 100 mm, preferably comprised between 100 and 140 mm, still more preferably between 120 and 140 mm.

[0051] FIG. 8 illustrates a comparison between a conventional coil 140 in FIG. 12B and a coil 142 used to wind the filament filled with metal powder according to the invention in FIG. 12A. The diameter of the central roll 128 is 120 mm on the coil 142 according to the invention which is preferably made of metal and which is illustrated in FIG. 12A while the diameter of the central roll 128 is smaller for the conventional coil 140 in FIG. 12B. The coil 142 according to the invention includes a first cylindrical flange 144 and a second cylindrical flange 146 each having a diameter larger than that of the central roll 128.

[0052] In operation, thanks to these elastic properties, the filament can be wound without breaking or cracking starting from a temperature of at least 70° C., preferably between 70 and 90° C. Once wound hot, as it cools down, the filament keeps the shape of the winding. To unwind it without breaking or cracking it, it is necessary to heat the filament again up to a temperature of at least 70° C., preferably comprised between 70 and 140° C., still more preferably between 70 and 90° C.

[0053] FIG. 9 illustrates the evolution of the elastic modulus G′ in Mega Pascal (MPa) of said filament as a function of the temperature T during a dynamic thermomechanical analysis test, also called DMTA. This elastic modulus G′ teaches about the rigidity and the elastic component of the material. The elastic modulus G′ has a value of 9.5×10.sup.3 MPa for a temperature of about 50° C. and decreases as the temperature increases. Softening occurs at temperatures comprised between 80 and 140° C. conferring on said filament the properties necessary for winding without breaking or cracking around the coil. At a temperature T of 80° C., the elastic modulus G′ drops to 4.4×10.sup.3 MPa and to less than 10.sup.3 MPa at a temperature T of 140° C.

[0054] FIG. 10 illustrates the three-point bending tests carried out on said filament at a temperature of 80° C. and more specifically this FIG. 10 shows the evolution of the bending stress a in Mega Pascal (MPa) as a function of the strain rate e. Four curves are presented corresponding to the same tests carried out four times. In contrast with the results of three-point bending tests carried out at room temperature in FIG. 4, the bending stress a is herein lower. A plateau is reached starting from about 1% of strain rate for which the bending stress a is comprised between 7 and 9 MPa. Thus, even at strain rates of 5%, there is no rupture, break-up of the filament in response to these stresses.

[0055] Based on the results of the three-point bending tests illustrated in FIG. 9, it is possible to determine a minimum radius of curvature R that the filament could accept before rupture for a given temperature and in this case for a temperature of 80° C. This is illustrated in FIG. 11.

[0056] FIG. 11B illustrates the radius of curvature R of the central roll of the coil in millimeters (mm) as a function of the strain rate e. FIG. 11B is obtained knowing the position of three red dots as illustrated in FIG. 12 during the three-point bending test. A machine records a displacement of the central point 160 and two other support points 162, 164 remain at a fixed position. Thus, it is possible to determine the radius of curvature R of a part illustrated by a curve 166 during the three-point bending test via a small geometric calculation thanks to the positions of the three points 160, 162, 164 and that being so according to the displacement of the central point.

[0057] To the extent that these displacements and stresses are recorded throughout the three-point bending test, it is therefore possible to express the radius of curvature R thanks to the displacement of the central point as a function of the stress in the part. Finally, it is possible to plot for each position of the central point which therefore corresponds to a radius of curvature R a curve expressing the radius of curvature R as a function of the strain rate e and thus determine the maximum radius of curvature R acceptable by the filament, as illustrated in FIG. 10B.

[0058] Thus, based on the performed calculations, a critical strain rate e that should not be exceeded in order not to damage the filament has been deduced. This critical strain is comprised between 2 and 4% and is preferably lower than 4%. FIG. 11A corresponds to FIG. 6 and allows making the link with FIG. 11B. As illustrated in FIG. 11B, a rupture of the filament occurs between 5.5 and 6.5% as indicated by the two dotted straight lines 150, 152.

[0059] The graph in FIG. 11B shows that the greater the strain rate e, the smaller will be the minimum radius of curvature R that should not be exceeded in order not to damage said filament. Under the aforementioned conditions, i.e. with a strain rate lower than 4% as indicated by the limit line 154, the minimum diameter of the central roll of the coil is comprised between 100 and 140 mm and preferably larger than or equal to equal to 120 mm.